Controlling the flow of vapors sublimated from solids

Control the flow of vapor from solid sublimation

The present invention relates to controlling the sublimation of solid materials under vacuum conditions and precisely controlling the flow of generated vapor into a vacuum chamber with a small pressure drop. An important application is to control the supply of vapor into the evacuated ionization chamber of the ion source used to generate the ion beam. Ion beams can be used to implant ions into semiconductor substrates. Another important application is to control the flow of vapor into the vacuum processing chamber used to interact with the workpiece.

The ionization chamber of the ion source can function under vacuum conditions, and the material that needs to be ionized is supplied in gaseous form with greater accuracy and reproducibility.

Many manufacturing procedures can also be carried out in vacuum. The process incorporating the chemical reaction with the workpiece usually requires the introduction of reagents in gaseous form, which react with each other and/or with the workpiece through specific processing chemicals. Such procedures may result in changes in the composition of the workpiece, the deposition of thin films on the workpiece, or the etching or removal of material from the workpiece. For example, in semiconductor manufacturing, such procedures must be executed with greater accuracy and reproducibility.

Therefore, for the ion source and the workpiece processing chamber, it is necessary to introduce an accurate and stable gas flow into the vacuum chamber. Although many supply materials can be used in gaseous form from a pressurized gas cartridge, other supply materials can only be used in solid form. Solid materials require special processing steps that are different from those used for gaseous sources. Among the important solid materials, include decaborane, octaborane, indium trichloride, trimethyl indium and triethyl antimony.

Important solids usually have a lower vapor pressure and must first be heated and sublimated in a reduced pressure environment to generate a certain volume of vapor. This vapor must then be introduced into the vacuum chamber at the flow rate or number of molecules per second required for the operation to conduct flow in the vacuum chamber. Because this flow requirement is similar to the requirement for the introduction of normal gas, standard gas processing equipment has been used to deliver vapor obtained from solids but with mixed results. In typical gas processing, the gas source is maintained at pressure P₀, Which is substantially higher than the inlet delivery pressure P for the vacuum chamber_D. In order to precisely control the flow of gas entering the vacuum chamber, P must be precisely controlled_D. This is usually accomplished by a commercially available mass flow controller (MFC) positioned between the gas source and the inlet of the vacuum chamber. MFC is a digital control device that changes its conductance to match the delivered mass flow rate (grams per second) with the requested mass flow rate in a closed loop. Because the MFC system is generally used for relatively high pressure gas sources, the MFC is generally configured to operate within a range that establishes a relatively large pressure drop and a correspondingly small conductance. For evaporative solid materials, such as borohydride decarboborane (B₁₀H₁₄) Or octadecaborane (B₁₈H₂₂), this method has encountered several serious problems.

The vapor pressure of this type of solid borohydride is relatively low, so the material must be heated to close to its melting point (100°C for decaborane) to establish a sufficiently high vapor pressure to allow the use of MFC. This has the risk of decomposition of the heat-sensitive borohydride molecules.

Because the borohydride vapor can easily condense on the surface (especially the surface below the temperature at which the material evaporates), the blockage of the relatively small MFC conductance (smaller channel) can lead to unstable operation and early component failure .

These problems have largely appeared in the commercially viable implementation of a vapor flow control system for controlling the delivery of such borohydride vapors supplied to ions, in which the generated ion beam is used for ion implantation In the device, it is used for the doping of semiconductors.

When steam is obtained from a fixed solid filler, further complications ensue. Generally speaking, in order to provide a larger surface area, the filler material is placed in the evaporator in powder form. As the filler is consumed, the evaporation area of the fixed filler will decrease over time, especially when the temperature becomes too high, the solid material is prone to molecular dissociation. Especially when the operation in which steam is to be used requires precise maintenance of the steam flow rate (this is a common situation), serious problems will occur.

The control of vapor from solid materials has not yet reached the required accuracy, and has involved frequent maintenance of equipment, such as disassembling flow control equipment to remove deposits of condensed materials that affect its operation. When seeking to use the desired dopant materials decaborane, octaborane and other thermally unstable or other thermally sensitive compounds, all such harmful conditions will face ion implantation of the semiconductor substrate.

A vapor delivery system for the steady flow of sublimation vapor to the vacuum chamber includes a solid material evaporator, a mechanical throttle valve, and a pressure gauge, followed by a vapor conduit to the vacuum chamber. The steam flow rate is determined by the setting of the temperature of the evaporator and the conductance of the mechanical throttle valve. Preferred embodiments have one or more of the following features. The temperature of the evaporator is controlled to the set point temperature by the closed loop control device. The mechanical throttle valve is electrically controlled. For example, the valve position is controlled by the output of a pressure gauge under a closed loop control device. Using this method, the steam flow rate can generally be proportional to the pressure gauge output. Heat all surfaces exposed to the vapor from the evaporator to the vacuum chamber to prevent condensation. The gate valve acts as an upstream throttle valve. The rotary butterfly valve acts as an upstream throttle valve. The use of solid material fixed packing can keep the temperature of the evaporator stable for an extended period. During this period, as the packing sublimates, the throttle valve is gradually opened with a lower conductance in the operating range of the throttle valve. When a larger valve displacement is reached, the temperature will be increased so that the valve can be readjusted to its lower conductance setting. With this setting, the valve can gradually open again.

A specific feature is a vapor delivery system that controls the flow of vapor sublimated from solid materials to a vacuum chamber. It includes a heated evaporator for solid materials that can be operated at sub-atmospheric pressure, and from the evaporator to the The combination of the vapor delivery channel of the vacuum chamber, the vapor delivery channel includes: a throttle valve followed by the steam conduit; a pressure gauge responding to sub-atmospheric pressure, which is positioned between the throttle valve and the steam conduit; exposed to sublimated steam The surface of the steam conveying passage of the, which includes the throttle valve, pressure gauge, and steam conduit, is adapted to maintain a temperature above the condensation temperature of the solid material; and a closed loop control system incorporating the pressure gauge, which is It is configured to change the flow conductance of the throttle valve to control the sub-atmospheric pressure downstream of the throttle valve, thereby responding to the output of the pressure gauge. The flow of steam entering the vacuum chamber is determined by the area between the throttle valve and the steam conduit Determined by the pressure of the steam.

Specific embodiments of this feature have one or more of the following features.

The vapor delivery system includes a temperature control system that is adapted to maintain the temperature of the surface of the delivery channel above the temperature of the evaporator.

The vapor delivery system has multiple stages of vapor delivery passages, which are adapted to maintain a gradually higher temperature as the stages move away from the evaporator.

The system has a vapor flow rate, which is adapted to be determined by the control system for the temperature of the evaporator and the control system for the conductance of the throttle valve.

The temperature of the evaporator is controlled to the set point temperature by the closed loop control device.

Throttle valve maximum N₂The conductance is at least 1 liter per second.

When the throttle valve is fully open, the pressure drop across the throttle valve is less than 100 millitorr.

The maximum conductance of the throttle valve is at least 5 or 10 times the conductance of the steam duct.

The throttle valve is a variable position gate valve or a butterfly valve.

The evaporator is configured to operate with a refillable fixed packing of solid material. The solid material is gradually consumed in a way to reduce the vapor emission area of the solid material, and the control system is configured to respond to the flow or pressure behind the valve Reduce, to reset the position of the throttle valve to restore the required flow, and sometimes as the throttle valve is close to its maximum useful conductance, to increase the temperature of the evaporator to increase the pressure in the evaporator and make throttling The valve can be operated within its optimal flow conductance dynamic range.

In a preferred form, the evaporator delivery system includes a throttle-based sensing and control system that can provide the evaporator set point temperature to the regulator of the evaporator heater, which can keep the evaporator temperature at the set point Point, the sensing measurement and control system stores at least one predetermined valve displacement value representing the upper limit of the required conductance for the throttle valve. The sensing and control system is configured to increase the set point temperature value to the regulator heater to cause the throttle The throttle valve increases steam production and steam pressure upstream, so that the closed loop control device of the throttle valve can cause the throttle valve to return to a substantially lower conductance position. In a preferred embodiment of this feature, the evaporator delivers a reference table containing a predetermined increment of temperature rise suitable for operation, and after detecting that the valve approaches or reaches a displacement value, the sensing and control system can be effective Ground causes the evaporator temperature set point to increase to the next step in the reference table.

The vapor delivery system is constructed and configured to deliver ionizable vapor to the ion source.

The vapor delivery system is constructed and configured to deliver ionizable vapor to the ion source of the ion implanter.

The vapor delivery system is constructed and configured to deliver ionizable vapor to a workpiece processing vacuum chamber, or a processing chamber used to provide a dose for semiconductors.

The vapor delivery system is configured to deliver its vapor to a high vacuum. The system is configured to respond to a decrease in the downstream atmospheric pressure of the throttle valve, thereby increasing the temperature of the evaporator.

The control system of the vapor delivery system includes a servo loop, which adjusts the position of the throttle valve in response to the output signal of the pressure gauge, so as to maintain the vapor pressure in the pressure gauge at the set point value.

The vapor delivery system is configured to contain and vaporize decaborane B₁₀H₁₄Or octaborane B₁₈H₂₂。

The vapor delivery system is constructed to contain and vaporize indium trichloride (InCl₃), trimethyl indium [In(CH₃)₃], or other solid low-temperature dopant supply materials.

Another feature is a method of generating an ion beam in a vacuum chamber. The generation is performed by using the described vapor delivery system. At this time, the vapor delivery system is adapted to deliver the sublimated vapor from the solid material to control the ionization flow to Ionization chamber.

Another feature is the method of conveying the sublimated vapor from the solid material to the vacuum chamber. The conveying is performed by using a vapor delivery system having one or more of the features described above.

The details of one or more specific embodiments of the present invention are presented below in the drawings and description. The other features, purposes and advantages of the present invention will be understood from the description and drawings and the scope of the patent application.

FIG. 1A is a diagram of the ion source 10. The details of the structure and the preferred mode of ionization action are disclosed in detail by Horsky et al. International Application No. PCT/US03/20197, dated June 26, 2003: "By the borohydride cluster ion Ion implantation device and method for implanting semiconductors", and US Patent Application No. 10/183,768, "Electron Impact Ion Source" filed by Horsky, application dated June 26, 2002; US Patent No. 6,686,595 No., which are respectively incorporated into this article by reference. The ion source 10 is connected to the evacuated vacuum chamber of the ion implanter via the mounting flange 36. Therefore, as shown in Fig. 1A, the part of the ion source 10 on the right side of the flange 36 is in a high vacuum (pressure<1x10^-4Trust). The ion source is maintained at a high voltage by a high-voltage power supply, and is electrically isolated from the rest of the high-vacuum housing. The gaseous material is introduced into the ionization chamber 44, where the gas molecules are ionized by the impact of electrons from the electron beam 70A or 70B. The electron beam exits the ionization chamber 44 through the opposite aperture 71B or 71A, or may be absorbed by the beam collector or the wall of the ionization chamber as the beam collector. In a specific embodiment incorporating a single electron gun and beam collector, as shown in FIG. 1B, the electron beam originates from the cathode in the electron gun 112 and is bent by the magnetic field 135 generated by the magnet 130 and the pole piece 125, and The electron entrance aperture 71A or 71B enters the ionization chamber 44 so that the electron beam 70A or 70B moves parallel to the elongated ion extraction aperture 81. After leaving the ionization chamber 44, the electron beam 70 is blocked by the beam collector 72 positioned outside the ionization chamber 44. Therefore, the ion beam is established adjacent to the ion extraction aperture 81, which appears as a groove in the ion extraction aperture plate 80. Then the ions are captured by the extraction electrode (not shown in the figure) positioned in front of the ion extraction aperture plate 80 and formed into a high-energy ion beam, and maintained at a substantially lower voltage.

Referring again to FIG. 1A, gas can be supplied into the ionization chamber 44 via the gas conduit 33. It is possible to evaporate, for example, decaborane or octaborane in the evaporator 28, and supply the vapor into the ionization chamber 44 through the vapor conduit 32 in the ion source block 35. Generally speaking, the ionization chamber 44, the ion extraction aperture 80, the ion source block 35 (including the vapor supply conduit 32), and the evaporator housing 30 are all made of aluminum. The solid supply material 29 positioned under the perforated separation barrier 34A is maintained at a uniform temperature by the closed loop temperature control of the evaporator housing 30. The sublimation vapor 50 accumulated in the ballast volume 31 is supplied through the duct 39 and the throttle valve 100 and the closing valve 110. The capacitance pressure gauge 60 monitors the nominal pressure of the steam 50 between the throttle valve 100 and the shut-off valve 110. The vapor 50 is supplied into the ionization chamber 44 through the vapor conduit 32 positioned in the ion source block 35. Therefore, both the gaseous material and the evaporation material can be ionized by the ion source.

The flow rate of the vapor entering the ionization chamber 44 is determined by the vapor pressure in the area just in front of the vapor supply conduit 32 (ie, in the shut-off valve 110). This is measured by the capacitance pressure gauge 60 positioned between the throttle valve 100 and the closing valve 110. Generally speaking, the flow rate is directly proportional to the vapor pressure. This allows the pressure signal to represent the flow rate and can be used as a set point for selecting the flow rate. In order to generate the required vapor flow rate into the ion source, the evaporator housing 30 is brought to a certain temperature so that when the throttle valve 100 is in its fully open position, the required flow rate will be exceeded. The throttle valve 100 is then adjusted to achieve the desired pressure output. In order to establish a stable flow over time, a dual PID controller (such as Omron E5CK digital controller) is used to implement an independent closed loop control device for the evaporator temperature and vapor pressure. The control (feedback) variables are thermocouple output for temperature and pressure gauge output for pressure.

The specific ion source shown is an electron impact ion source, which is fully controlled by temperature. Rather than striking an arc discharge plasma to create ions, this ion source uses high-energy electrons injected in the form of one or more focused electron beams to ionize by impacting "soft" electrons from the process gas. The "soft" ionization process preserves larger molecules in order to form ionized clusters. As shown in Figures 1A and 1B, the solid borohydride material is heated in an evaporator and flows through the vapor conduit to the metal chamber, that is, the ionization chamber. The electron gun located outside the ionization chamber delivers high-current turbulence of high-energy electrons to the ionization chamber, and guides the electron turbulence to be roughly parallel and adjacent to the elongated slot in front of the ionization chamber. The ion extraction electrode extracts ions from the tank, thereby forming a high-energy ion beam. During the delivery of the sublimated borohydride vapor to the ionization chamber, all surfaces are maintained at a temperature higher than the temperature of the evaporator (but suitably lower than the temperature of dissociation) to prevent condensation of the vapor. Based on several hours of testing, it has been confirmed that the steam supply and the surface of the valve are in fact kept clean.

The throttle valve presents a vapor path with a changed conductance. Figures 7E, F, and G respectively illustrate that the gate valve is closed, the first number is opened, and the second number, which is a larger number, is opened, thereby serving as a high maximum conductance throttle valve.

As shown generally in FIG. 1, the vapor delivery system provides a stable flow of sublimation vapor to the vacuum chamber 130. The vacuum chamber may be an ionization chamber having an ionization action different from the ionization action described above, or may be a vacuum processing chamber in which vapor interacts with other materials. The vapor delivery system is composed of an evaporator 28, a mechanical throttle valve 100 and a pressure gauge 60. The vapor flow rate is determined by the temperature of the evaporator 28 and the conductance of the mechanical throttle valve 100 positioned between the evaporator and the inlet duct 32 of the vacuum chamber. The closed loop control device 35 determines the temperature of the evaporator 28 as the set point temperature. The mechanical throttle valve 100 is electrically controlled, that is, the valve position is controlled by the output of the pressure gauge under the closed loop control device 120. The steam flow rate can be maintained in direct proportion to the pressure gauge output.

The described vapor delivery system satisfies the inherent challenge of delivering controlled vapor flow to a vacuum system within a few hours, such as to an ionization chamber of an ion source, or more generally as far as operations performed in a vacuum chamber. This system allows certain criteria to be observed that provide important advantages over the prior art, especially when using low-temperature materials such as decaborane or octaborane:. Minimize the temperature, therefore minimize the vapor pressure in the evaporator;. Maximize the vapor conductance of the conveyor chain; Adopt high conductance, heatable valve; Keep the maximum component temperature low, for example below 150°C for borohydrides;. Temperature control of all surfaces that expose the contact surface to steam to prevent condensation;. Close the loop downstream of the pressure of the throttle valve instead of trying to directly measure the mass flow rate, thereby eliminating the need for traditional MFC; As the supply material is exhausted, the evaporator temperature is allowed to be adjusted upwards over time to allow the evaporator material to be completely consumed, and the pressure servo loop is stabilized by allowing the throttle valve to operate at the "most effective point" of its flow conductance dynamic range .

Of course, these criteria are not completely independent, and the variables are related to each other. However, the criteria can solve or improve completely different problems found in the prior art system, and therefore should be clearly stated.

It is expected that the form of a closed-loop control pressure-based system for conveying the sublimated gas-phase material in the vacuum chamber by means of continuous suction follows a properly defined law. Referring again to FIG. 1, the solid material 29 is evaporated into a vapor 50 contained in the reservoir 31. The vapor exits the reservoir 31 through the evaporator outlet 39, thereby establishing vapor pressure in front of the throttle (or "choke") valve 100. The pressure gauge (or sensor) 60 behind the throttle valve 100 is followed by a relative flow restricting steam conduit 32, which represents the flow restriction into the vacuum chamber. The throttle valve 100 and the pressure sensor 60 combined with the closed loop controller 120 provide components to control the pressure behind the throttle valve 100 (in front of the duct 32) through the closed loop control of the throttle valve conduction. Therefore, the opening degree (valve position) of the throttle valve 100 is actively set in real time by closing the circuit on the output of the pressure sensor, thereby servoing the valve position to the downstream pressure set point. As a result, the downstream pressure and the conductance of the vapor outlet duct 32 determine the flow rate of vapor entering the vacuum chamber 130. The term for the conduit 32 is the "metering section" of the flow control system. The pipe 32 introduces the vapor into the vacuum chamber 130, and the vacuum pump 135 maintains a desired value of vacuum in the vacuum chamber 130.

The basic gas dynamic requirement for the flow rate in this type of system is that the gas phase pressure of the substance to be controlled is higher in the vapor storage 31 than in the vacuum chamber 130. By considering the basic equation that controls the flow in a vacuum system, pressure-based mass flow control is implemented in this type of system. The simplest case of the type is the case of molecular flow, where the mean free path of gas molecules is larger for the physical size of the vacuum system. The molecular flow range can be adapted to describe the vapor flow entering the ion implantation system, for example, with the system of the present invention, where the pressure anywhere in the vapor path is <<1 Torr. For any such system, if the pressure P at each of the two important points and the conductance C between the two points are known, the mass flow between the two points can be calculated.

The mass flow equation system for the metering section 32: (1) Q_{Meteringsection}=(P_{PressureSensor}-P_{VacuumChamber})(C_{MeteringSection})。

(For example, Q means mass flow or quantity, and the unit is grams per second).

It should be noted that if P_{VacuumChamber}<<P_{PressureSensor}(It is the situation even at very low mass flow rate, if C_{MeteringSection}<<S_{VacuumChamber}[Ie the suction speed S in the vacuum chamber 130]), the equation (1) can be simplified to (2) Q_{Meteringsection}~(P_{PressureSensor})(C_{MeteringSection})。

According to the continuous requirements of gas dynamics for steady-state flow and defined flow paths, the Q at any point in the downstream of the conveying chain of the vapor store 31 must be equal to Q at any other point in the conveying chain. Therefore, (3) Q_{AcrossThrottleValve}=Q_{MeteringSection}。

Should pay attention to C_{MeteringSection}In comparison, the conductance from the steam storage 31 to the throttle valve 100 is relatively large. If P_upstreamDefined as the pressure in the evaporator outlet 39 from the evaporator, then: (4) Q_{AcrossThrottlingVa}l_ve=(P_Upstream-P_{PressureSensor})(C_{ThrottlingValve})。

The following situation is also relatively clear, because Q is stored across the conveyor chain, (5) Q_{AcrossThrottlingValve}=Q_{MeteringSection}=(P_Upstream-P_{VacuumChamber})(C_{Upstream-VacuumChamber})。

For the simple case of molecular flow, the series conductance has no bunching effect, and there is no scattering and vent loss, and the overall conductance is: (6)1/C_overall=1/C₁+1/C₂+1/C₃...1/C_n

For this situation, the effective conductance between the vapor outlet of the evaporator and the vacuum chamber 130 can be calculated: (7)1/C_{Upstream-VacuumChamber}=1/C_{ThrottlingValve}+1/C_{MeteringSection}

Reconfiguration item: (8)C_{Upstream-VacuumChamber}=((C_{ThrottlingValve})(C_{MeteringSection}))/(C_{ThrottlingValve}+C_{MeteringSection})

The equation drawn in Figure 2 can be used to estimate the appropriate maximum conductance of the throttle valve to achieve the required dynamic range for the delivery system. For example, Figure 2 shows: if C_{ThrottlingValveMaximum}=C_{MeteringSection}, The maximum obtainable overall conductance is only 1/2 of the metered-length conductance (that is, the conductance of the steam duct 32). When it is beneficial to reduce the working vapor pressure (and the evaporator temperature in the present invention is therefore reduced) when the evaporative material is used for operation, a C of at least about 5:1 or even 10:1 or higher_{ThrottlingValveMax}With C_{MeteringLength}The ratio will help to maximize the dynamic range of vapor flow for a given metering length conductance.

Figure 3 shows a cross-sectional view of an ion source suitable for establishing decaborane or octaborane in an ion implanter. It is different from FIGS. 1A and 1B in that the butterfly-type mechanical throttle valve 100' is described, instead of using the gate valve 100 as the throttle valve, as shown in FIG. 1A.

In the example of the butterfly throttle valve 100' shown in the figure, the movable element is a circular flow obstructing disc, the size of which is close to suitable for a cylindrical channel, and is installed to surround the disc diameter perpendicular to the axis of the channel While rotating. It presents a steam path that controls the conductance, see Figures 7A, 7B and 7C.

The vapor path from the evaporator to the ionization chamber is clearly shown. The steam duct 150 of FIG. 3 performs the same function as the steam duct (metering section) 32 of FIGS. 1, 1A and 1B. In this ion source, the solid borohydride material 140 (such as decaborane or octaborane) is heated by the evaporator 145 into a sublimation vapor 165, which passes through the evaporator outlet port 155 and the butterfly throttle valve 100' , Isolate the valve 160, the conduit 150, and enter the ionization chamber 170, where the vapor is ionized by the electron beam 175. The extraction electrode (not shown in the figure) at a potential that is largely different from that of the electrode of the ion source captures and forms the ion beam 180 through the vertical slot 185 in the end plate 190 of the ionization chamber 170.

FIG. 4 illustrates a specific embodiment of the present invention in more detail, which is designed to provide a stream of vapor entering the vacuum chamber 260 to a utilization point 270. Vacuum processing may be performed, such as chemical vapor deposition (CVD) processing or low pressure CVD (LPCVD) processing, or other processing in which a thin film is deposited on a workpiece (such as a boron-containing thin film (such as boron nitride)). By heating the evaporator housing 210 to a temperature T above room temperature, the solid supply material 200 residing in the evaporator 205 is maintained at a suitably defined temperature. The evaporator heater controller 215 in the digital steam supply controller 220 actively controls the resistance heater in the evaporator housing 210. The evaporator heater controller 215 is incorporated into a closed loop PID controller (for example, Omron type E5CK-AA1-500), which receives the set point temperature from the digital steam supply controller 220, and shuts down the temperature set by the evaporator outside 210. The thermocouple (TC) output 225 provides a loop on the temperature readback, and, for example, provides a variable power 248 to the resistance heater in the form of a pulse width modulated heater voltage. The vapor generated from the supply material 200 passes upstream of the evaporator outlet 230 of the throttle valve 235. The purpose of the throttle valve 235 is to reduce the vapor flow downstream of the valve so that the pressure gauge 240 reaches a specific set point pressure value. The set point pressure value is provided by the digital steam supply controller 220 to the closed loop throttle valve position controller 245, and its servo throttle valve 235 is moved to the mechanical position (by transmitting the position signal 247 to the throttle valve assembly) In the motor), where the pressure gauge output 250 is equal to the set point value, that is, the throttle position controller 245 closes the loop on the pressure gauge output 250. The two set point values, the heater set point value and the pressure set point value, are provided to the digital steam supply controller 220, which is provided manually through the user interface, or by providing an additional automatic function code Decoding. In the case where the throttle valve includes a butterfly valve (for example, Nor-Cal type 040411-4), a throttle valve position controller such as Nor-Cal type APC-200-A can be used. Heat all surfaces in contact with the vapor to at least the evaporator temperature, or slightly higher. Therefore, the throttle valve 235, the pressure gauge 240, and the channel wall (the wall including the metering section 232) are heated. The temperature between 100°C and 150°C is sufficient to prevent condensation of the feed material normally used for the evaporator 205. When decaborane is run in the configuration shown in Figure 4, the typical evaporator temperature is 25 In the range of °C to 40 °C, for octaborane, the temperature is, for example, between 80 °C and 120 °C. Therefore, a heated capacitive pressure gauge (for example, MKS Baratron model 628B-22597 or 631A-25845) can be used as the pressure gauge 240. This type of pressure gauge can read pressures in the range of a few millitorr to a few torr, and is suitable for this application. Under certain circumstances, the pressure gauge configured by the manufacturer can be used to read the maximum pressure of 100 mTorr or 500 mTorr (full scale reading). This type of pressure limit is selected to provide an excellent signal-to-noise ratio for controlling manometer readings between 20 mTorr and about 100 mTorr (signals near the lower part of the range tend to be noisy, which may cause the servo loop to fail stability).

The appropriate set point pressure value is determined by the required partial pressure of the vapor in the vacuum chamber 260 and the vapor conductance between the throttle valve 235 and the vacuum chamber 260.

FIG. 5 shows a procedure in a vacuum environment, in which a vapor stream 227 impinges on a semiconductor workpiece 280. Such a process can be a thin film deposition process, such as the production of a polysilicon film or a silicon germanium film, in which the vapor containing the dopant allows P-type or N-type doping of the semiconductor film during film growth. Another important application is plasma doping (PLAD). In PLAD, the substrate is held on a platen electrically isolated from the vacuum chamber, dopant vapor is introduced and the plasma is formed adjacent to the platen. One or more high-voltage platens are applied to the platen and therefore to the substrate, causing high-energy ions of the plasma to be attached to dope the substrate.

Fig. 6 shows a system in which vapor is supplied to an ion source to form an ionized beam, thereby performing ion implantation. The vapor passes through the throttle valve 235, the vapor conduit 228 of the ion source 285, and enters the ionization chamber 287 of the ion source 285. The ionization chamber 287 is maintained at a high voltage. The vapor is ionized in the ionization chamber 287 by an appropriate energizing member. Once the ions are established, the ions are extracted in the evacuated chamber by the extraction optics 290, accelerated, and formed into a high-energy ion beam 295, which is essentially A voltage different from the voltage of the ionization chamber. The ion beam is guided into the implantation chamber to implant the semiconductor substrate 298 for doping. The procedure can be to implant ions into a polysilicon coating on a larger glass panel to manufacture, for example, a flat panel display (FPD doping). Mass analysis can be performed on the ion beams produced by such systems, but there is usually no mass analysis. The ion source is usually quite large, and its ionization chamber has a dimension slightly larger than the shorter dimension of the implanted panel, which can be 1 meter long or longer. In a typical system, a fixed "ribbon" ion beam is captured from an ionization chamber and focused on a flat panel, and the panel is mechanically scanned across the ion beam along the longer dimension of the panel. This procedure is more important in the following aspects: manufacturing FPDs with CMOS driver circuits along the periphery of the display panel, such as manufacturing TVs or computer monitors based on thin film transistors.

Figure 7 shows the following system: it is adapted to a traditional beamline ion implanter with mass analysis. After the ion beam 295 is extracted from the ion source 285 by the extraction optics 290, the ion beam passes through the dispersive bipolar electromagnet, which separates the undecomposed ion beam 295 into small ion beams, which depend on the mass-filler ratio of the ions. Separation in space, as understood by those familiar with this technique. The electromagnet current can be adjusted, and therefore the bending and dispersion of the bipolar field can be adjusted, so that by decomposing the pore 297, only a specific mass-filler ratio (or a certain range of mass-filler ratio, depending on the width of the decomposition pore 297) can be reduced. The ions are transferred to the semiconductor substrate.

In order to implant ions in the semiconductor wafer, the ionization chamber 287 has a volume less than about 100 ml, and the maximum flow rate of sublimation vapor entering the ionization chamber is about 1 sccm.

7A to 7C illustrate the relative position of the butterfly valve roughly corresponding to the following situations in a qualitative manner: in Fig. 7A: closed position; in Fig. 7B: 7.5 degree rotation; Fig. 7C: 15 degree rotation. The rotating position is electrically controlled by a rotary stepping motor. The clearance between the periphery of the rotatable circular plate B of the butterfly valve and its cylindrical housing H is indicated by C<C'<C", where C is the smallest clearance in the "closed" position, which is a few thousandths of an inch . Figure 7D shows the calculation of N₂Flow conductance, which is a function of the rotation angle for a 1.4 inch diameter circular butterfly valve. The points corresponding to Figs. 7A to 7C are marked on the curve of Fig. 7D and are approximately equal to ~0l/s, 2l/s and 8l/s, respectively.

Figures 7E to 7G illustrate the relative position of the sliding gate valve implemented as a throttle valve in a qualitative manner, see Figures 1A and 1B. The system shown: Figure 7E: Gate valve G is in the closed position; Figure 7F: Gate valve G is 10% opening; Figure 7G: 30% opening. Gate valves available in diameters ranging from about 0.5 inches to about 2.5 inches can be used as shut-off valves (which seal when closed) and throttle valves (with a stepper motor that operates the valve driver). The butterfly valve is not a sealed valve, that is, it has a small and limited flow conductance when closed.

8 and 8A show the second embodiment of the vapor delivery system for supplying vapor to the ion source of the ion implanter (for example, the ion source of FIG. 3). The overall length of the valve chain has been minimized and designed to be tightly coupled with the ion source. Shown are evaporator 400, evaporator isolation valve V1 410, valve driver 415, evacuation port 420 (connected to V3, not shown), throttle valve TV1 430, throttle valve electric driver 435, ion source isolation valve V2 440, V2 driver 445, heated capacitance meter G1 450, N₂Exhaust valve V4 460.

Figure 9 shows a schematic diagram of the vapor delivery system of Figure 8, indicating significant control points. The vapor delivery system is described as being controlled through the operator interface 700, through which the operator can provide input to open or close the valves V1 410 (evaporator isolation valve), V2 440 (ion source isolation valve), V3 441 (roughly Vacuum valve), V4 460 (drain valve) and TV1 430 (throttle valve), all these valves provide a read-back interface to the operator to confirm the valve status. Position V3 between the two isolation valves V1 and V2, and open the valve when needed to evacuate the static volume between the two valves, for example, when the evaporator 400 has been removed for service (using V1) Or after refilling and replacing. In the same way, V4 is used to discharge this static volume to prepare component removal, such as removing the evaporator 400. Other user-accessible inputs include three temperature set points: PID 1 for the evaporator 400, PID 3 for valves V1 to V4 and TV1, and one temperature set point for the ion source including the vapor conduit 150 of FIG. 3 Block. Generally speaking, all surfaces in contact with the vapor are maintained at a temperature at least as high as the temperature of the evaporator. It is better to maintain the set point temperature of the ion source>PID 3>PID 1. Therefore, it is preferable to maintain the surface of the conduit 150 at a temperature greater than the set point of PID 3 through the ion source block. PID 2 is a closed loop controller, which adjusts the throttle valve TV1 430 so that the pressure gauge G1 450 The pressure read reaches its set point value. This pressure set point for the heated pressure gauge G1 450 is read back to the operator interface. This pressure readback signal indicates the vapor pressure between the throttle valve TV2 and the vapor conduit entering the ion source (vapor conduit 150 in FIG. 3), thereby providing a control signal for the closed loop control device of the TV1 position. Because the flow rate of the vapor entering the ionization chamber 170 of the ion source through the vapor conduit 150 is close to proportional to the inlet pressure, PID 2 provides a stable and repeatable inlet pressure to actuate a stable and appropriately defined pressure in the ionization chamber 170. This in turn enables a very stable ion current to be extracted from the ion source.

Fig. 10 is an exploded view of the vapor stream of decaborane entering the ion source of Fig. 3 using the vapor delivery system of Fig. 9; The position of the butterfly throttle valve outlined in FIGS. 7A, 7B, and 7C is shown on the curve in FIG. 9. The useful dynamic range of the vapor delivery system covers a factor of about 10. For a vapor temperature of 30°C, from about 0.1 sccm (standard cc per minute) to 1.0 sccm or more, the fixed vapor pressure upstream of the delivery throttle valve. In order to obtain a higher flow rate, a higher evaporator temperature can be used. The typical gas flow rate consumed by the ion source used in the ion implanter is about 2 sccm or less. Therefore, the vapor delivery conductance and pressure are tuned to the required vapor flow rate to use the conductance at the ion source inlet, as shown in FIG. 2 and the accompanying background, and will be further expanded in the description of FIG. 12.

Figure 11 shows the response of the control pressure gauge 450 to the rotation of the throttle valve in the system exemplified by Figures 3 and 8-10. In the case of 40 mtorr manometer pressure (that is, the pressure at the inlet of the ion source), the vapor pressure in the ionization chamber 170 is about 1 mtorr, and the pressure upstream of the throttle valve (the outlet of the evaporator) is about 65 millitorr. Therefore, the greatest pressure drop is across the vapor conduit 150 of the ion source of FIG. 3, which for example has a N of about 0.5 l/s₂Flow conduction.

Figure 12 plots the effective N of the entire conveyor chain of Figures 3 and 8 to 10₂The flow conductance is a function of the rotation angle of the butterfly throttle. When the throttle valve is opened, the overall conductance of the system is almost equal to the conductance of the vapor conduit 150 of the ion source. The dynamic range of the flow conductance of the throttle valve should match the minimum conductance of the system, in this case the conductance of the conduit 150 entering the ion source. The steam pipe 150 of FIG. 3 is (for example) a cylindrical bore with a diameter of 1 cm and a length of 25 cm. For larger or smaller conductance ion source inlet conduits, larger or smaller throttle valves should be used respectively (a throttle valve has larger or smaller conductance in its dynamic range). The vapor delivery system disclosed herein is used to actuate an "open" valve and structure (high conductance), which is not easily blocked by condensed vapor. In addition, all valves and connecting elements can be maintained at a temperature greater than the temperature of the evaporator. For example, referring to Figure 9, for an operation using decaborane, keep the evaporator at 30°C, V1 to V4 and TV1 at 50°C, pressure gauge G1 at 100°C, and keep the ion source at >50°C . This "grading" of the temperature of the continuous elements along the conveyor chain prevents any important condensation of the sublimation vapor. Importantly, the use of high-conductivity elements following the evaporator can minimize the vapor pressure and therefore minimize the evaporator temperature required to achieve and maintain the required flow rate. This can increase the useful life of the borohydride or other solid materials stored in the evaporator, because it is known that it can dissociate or polymerize under high temperature conditions using a reaction that is a strong function of temperature.

Within the scope of the implementation plan, the maximum throttle valve N₂The gas flow conductance is at least 1 liter per second or more, and the pressure drop across the throttle valve when the valve system is fully opened is less than 100 mTorr, and is usually less than 25 mTorr in the preferred case.

For illustrative purposes, all previous figures 10 to 12 show the so-called "open circuit" operation of the throttle valve, in which the valve position is set as an independent variable. Figure 13 shows the time signal of the vapor delivery system when operating in its normal "closed loop" mode. In this mode, referring now to FIG. 7, the pressure set point is provided to the throttle position controller 245 by the digital steam supply controller 220. The position controller can adjust the valve position to minimize the "error" between the control pressure gauge output 250 and the pressure set point value. This is accomplished by a so-called PID (Proportional Integrated Differential) control loop, which can be scheduled to have appropriately defined response characteristics, such as rate and settling time, and the degree of overshoot. The Nor-Cal type APC-200-A incorporates this type of PID controller, which is coupled with a stepping motor, which rotates the shaft to the position where the circular plate of the butterfly throttle valve is installed. (It should be pointed out at this junction: the butterfly throttle valve used in this example is designed by its manufacturer for a basically different application, namely downstream pressure control applications, so as to throttle the suction speed in the vacuum chamber, and the present invention This hardware is used for "upstream" control to introduce gas into the vacuum chamber. Similarly, it is believed that the sealed gate valve is used to complete the upstream throttle control system under electric control conditions, which is novel.) In order to generate the timing of Figure 13 The signal, through the graphical user interface, randomly inputs three different pressure setting points (20 mTorr, 30 mTorr, and 40 mTorr) into the digital steam supply controller 220 at an interval of about 10 seconds to generate data. Figure 13 shows that when octaborane (B₁₈H₂₂) When supplying materials, this system has fast settling time and excellent reproducibility. Referring to Fig. 13 in detail, the control pressure is read as 20 mTorr in the case of time=0 seconds, and the set point (SP1) of 30 mTorr is input to the controller 220 by the operator in the case of T=10 seconds. Enter the set point (SP2) of 20 mtorr under the condition of T=25 seconds, and so on, until SP7. The characteristic indication of the "step response" recorded in Figure 13: The settling time of the pressure is typically only a few seconds, the stability is very good, and the overshoot is minimal.

Figure 14 illustrates the remote implementation of the vapor delivery system of Figures 4 to 7, such as positioning the evaporator, throttling valve and other flow control elements in the gas distribution box of the ion implanter, which requires a connection pipe up to 1 meter long Connect to the inlet of the ion source. By using a larger diameter (at least 1 inch diameter) pipeline, the overall conductance of the vapor transport chain will not be substantially reduced, and it will remain controlled by the vapor inlet conductance of the ion source according to FIG. 2.

Figure 15 illustrates further important features of the vapor delivery system. It should be understood that the rate at which the feed material evaporates is a function of its open surface area (especially the available surface area on the solid vacuum interface). The supply material in the form of powder in the evaporator is consumed over time, and the available surface area will steadily decrease, resulting in a decrease in the vapor pressure in front of the throttle valve until the vapor exhaust rate cannot support the required vapor flow rate. This system is understood as the "draining rate limit" operation. Therefore, in the case of a new filler of a given supply material in the evaporator, for example, an evaporator temperature of 25°C may support the required steam flow at the nominal throttle position at the low end of its dynamic range. For example, the flow rate represented by the point 7B indicated on the curve of FIG. 10. After the time passage (for example, after 20% of the supplied material has been consumed), then a valve position commensurate with the point 7C indicated on the curve of FIG. 10 may be required to maintain the same required flow rate. The state of the system is now such that the throttle valve is close to the high displacement limit of its dynamic range. With proper provision, the steam supply controller 220 senses this displacement. It transmits the new higher heater set point temperature to the evaporator heater controller (regulator) 215 through the signal 246 of FIG. 14, for example. The steam supply controller has resident look-up table information that determines the next increase in temperature change that will produce the required increase in steam generation, and the pressure increase in front of the throttle. For example, for a nominal 30°C operation, the next increment can be 2°C, which becomes 32°C. The increment is selected so that once the evaporator temperature sinks to its new value, the nominal throttle operating point is restored to 7B of Figure 10, which is close to the low displacement end of its dynamic range. Therefore, the ability of the digital controller 220 to adapt to the short-time range change in the set point vapor pressure and the long-time range change in the evaporator temperature makes the control of the vapor flow rate within the life of the supplied material filler very effective.

Many specific embodiments of the present invention have been described. However, it should be understood that various modifications can be made without departing from the spirit and scope of the present invention. Therefore, other specific embodiments are within the scope of the following patent applications.

<p>10Ion source</p><p>28Evaporator</p><p>29Solid supply material</p><p>30Evaporator shell</p><p>31Storage/ballast volume</p><p>32Steam pipe</p><p>33Gas pipe</p><p>34APerforated separation barrier</p><p>35Ion source block</p><p>36Flange</p><p>37Vapor delivery channel</p><p>39Conduit</p><p>44Ionization Chamber</p><p>50Sublimation steam</p><p>60Capacitance pressure gauge</p><p>70Electron beam</p><p>70AElectron beam</p><p>70BElectron beam</p><p>71AElectron inlet aperture</p><p>71BElectron inlet aperture</p><p>72Beam Collector</p><p>80Porous Plate</p><p>81Porosity</p><p>100Throttle valve</p><p>100'Butterfly Mechanical Throttle Valve</p><p>110Close valve</p><p>120Closed loop controller/control system</p><p>125Magnetic pole piece</p><p>130Magnet/Vacuum Chamber</p><p>135Magnetic field</p><p>140Solid borohydride material</p><p>145evaporator</p><p>150Conduit</p><p>155Exit port</p><p>160Isolation valve</p><p>165Steam</p><p>170Ionization Chamber</p><p>175Electron beam</p><p>180Ion beam</p><p>185Vertical slot</p><p>190end plate</p><p>200Solid supply material</p><p>205evaporator</p><p>210Evaporator shell</p><p>215Evaporator heater controller</p><p>220Digital Steam Supply Controller</p><p>225Thermocouple output</p><p>227Vapour flow</p><p>228Steam pipe</p><p>230Evaporator outlet</p><p>232Measurement section</p><p>235Throttling valve</p><p>240Pressure gauge</p><p>245Throttle valve position controller</p><p>246Signal</p><p>247Position signal</p><p>248variable power</p><p>250Pressure gauge output</p><p>260Vacuum Chamber</p><p>270Use point</p><p>280Semiconductor workpiece</p><p>285Ion source</p><p>287Ionization Chamber</p><p>290Acquisition optics</p><p>295High-energy ion beam</p><p>297Decomposition of pores</p><p>298Semiconductor substrate</p><p>400evaporator</p><p>410Evaporator isolation valve</p><p>415Valve Driver</p><p>420Evacuation port</p><p>430Throttling valve</p><p>435Throttle valve electric actuator</p><p>440Ion source isolation valve</p><p>445Drive</p><p>450Heated Capacitance Meter/Pressure Gauge</p><p>460Drain valve</p><p>700Operator interface</p><p>BRotating round plate</p><p>GGate Valve</p><p>HCylinder shell</p><p>MFCMass Flow Controller</p><p>P₀pressure</p><p>P_DInlet delivery pressure</p><p>TTemperature</p>

Figure 1 shows a simplified schematic diagram of the vapor delivery system of the present invention.

FIG. 1A shows an ion source with a vapor delivery system, and FIG. 1B shows details of a specific embodiment of the ion source.

Figure 2 plots the calculated effective conductance from the evaporator outlet to the vacuum chamber as a function of the maximum throttle conductance.

Figure 3 shows an ion source with another vapor delivery system.

Figure 4 shows in the form of a block diagram a system using a controlled set point to generate a precisely controlled flow of vapor sublimated from a solid feed material into the vacuum chamber.

Figures 5, 6, and 7, which are similar to Figure 4, respectively, show a system for accurately controlling the flow of sublimation vapor to be generated. Figure 5 shows the flow of semiconductor dopants entering the vacuum doping process; Figure 6 shows the flow of entering the ion source that generates ion beams to implant high vacuum ions into the surface of the semiconductor substrate; and Figure 7 shows the flow of entering high The ion source of the vacuum ion implantation chamber is a process in which the mass decomposition implantation dopant ions are implanted into the surface of the semiconductor substrate.

Figures 7A, 7B, and 7C illustrate in schematic form the clearance of the butterfly throttle valve when closed and in the lower and upper areas of the useful range.

Figure 7D shows the calculated N used to generate the 1.4-inch throttle valve of Figures 10, 11 and 12₂Flow conduction.

Figures 7E, 7F and 7G illustrate the gap of gate-type throttle when closed, 10% opening and 30% opening.

8 and 8A are a top view and a side view of a preferred embodiment of the vapor delivery system of the present invention for delivering vapor to the ion source of the ion implanter.

Figure 9 shows a schematic diagram of the vapor delivery system of Figure 8 indicating significant control points for embodiments of the present invention.

Figure 10 is a graph illustrating that under open loop conditions and at a fixed evaporator temperature, decaborane is used as a solid supply material for semiconductor dopants, and ions are entered from the evaporator through the throttle valves of Figures 8 and 9 The steam flow rate of the source.

Figure 11 shows the control pressure gauge pressure just downstream of the throttle valve as a function of the butterfly rotation angle used in the configurations of Figures 8 and 9.

Figure 12 shows the effective N of the vapor delivery system of Figures 8 and 9₂Conductance (liters per second).

Figure 13 shows the step response of the vapor delivery system of Figures 8 to 12 as the set point pressure is changed.

Figure 14 illustrates a remote embodiment of the vapor delivery system.

Figure 15 illustrates the valve position over time as the solid supply material is consumed, in which case the evaporator temperature is periodically updated to adapt to the dynamic range of the throttle valve.

The same reference symbols in the various drawings indicate the same elements.