Method and apparatus for controlling spatial temperature distribution across surface of workpiece support

The present invention relates to a substrate support, and more particularly to methods and devices for achieving a uniform temperature distribution within the substrate during plasma processing.

A general plasma etching apparatus has a reactor, and a chamber through which a reactive gas (single or more) flows is provided in the reactor. The gas is generally ionized into plasma by high frequency energy in this chamber. The highly reactive plasma gas ions can react with materials such as polymer masks on the surface of semiconductor wafers processed into integrated circuits (ICs). Prior to etching, the wafer is placed in the chamber and held in place by a chuck or holder, exposing the top surface of the wafer to plasma gas. There are several types of chucks (sometimes also called susceptors) known in the art. The chuck forms an isothermal surface and functions as a heat sink for the wafer. In one form, the semiconductor wafer is held in place for etching by mechanical clamping means. In other types of chucks, the semiconductor wafer is held in place by the electrostatic force generated by the electric field between the chuck and the wafer. The present invention is applicable to both types of chucks.

In a general plasma etching operation, reactive ions of plasma gas chemically react with a portion of material on the surface of a semiconductor wafer. Some heating of the wafer is done by several methods, but most of the heating is done by plasma. On the other hand, the chemical reaction between the gas (ions and radicals) and the wafer material is accelerated to some extent by the temperature rise of the wafer. The local wafer temperature and the chemical reaction at each microscopic location on the wafer are related to the degree to which harmful heterogeneity of etching of the material on the wafer surface is likely to occur when the temperature across the wafer surface changes significantly. doing. In most cases, it is desired that the etching be uniform to a near perfection. Otherwise, the manufactured integrated circuit devices will have electronic properties that deviate from the desired standards. Also, as the wafer diameter increases, the problem of ensuring the uniformity of each batch of ICs becomes increasingly difficult. In other cases, it is desired to be able to control the surface temperature of the wafer in order to obtain a custom profile.

The problem of wafer temperature rise during reactive ion etching (RIE) is well known, and various attempts have been made to control the temperature of wafers during etching. FIG. 1 shows a method of controlling the wafer temperature in the RIE. Coolant gas (eg, helium) is introduced at a single pressure into a single narrow space between the bottom surface of the wafer 104 and the top of the chuck 106 that holds the wafer.

There are generally no O-rings or other edge seals around the chuck, except for smooth sealing lands that extend 1-5 mm in length at the outer edge of the chuck 106 to reduce coolant leakage. Inevitably, without the elastomer seal, there is an increasing pressure loss across the sealing land, resulting in inadequate cooling of the edges of the wafer 104. Therefore, a large amount of heat colliding near the edge of the wafer 104 must flow inward in the radial direction before the heat is effectively conducted to the chuck. The arrow 108 above the wafer 104 indicates the ingress heat flux that heats the wafer 104. The heat flow in the wafer 104 is indicated by arrow 110. This is the reason why the edge region of the chuck tends to be hotter than the rest of the surface. FIG. 2 shows a typical temperature distribution on the wafer 104. Due to the pressure loss at the peripheral portion of the wafer 104, the peripheral portion of the wafer 104 becomes very hot.

One way to address the need for zone cooling is to change the surface roughness or cut the relief pattern to effectively change the local contact area. Such a scheme is carried out without the use of any backside coolant gas, in which case the contact area, surface roughness and clamping force determine the heat transfer. However, the local contact area cannot be adjusted without remachining the chuck. Another way to deal with zone cooling is to use coolant gas with variable pressure to increase and fine-tune heat transfer. However, the relief pattern remains substantially fixed. A high degree of independent space control can be achieved by dividing the surface of the chuck into different zones with (or without) small sealing lands as dividers and supplying separate cooling gases to each zone. .. The gas supply to each zone can be configured differently or set to different pressures to alter heat conduction. The operation control of each zone is set by compounding adjustment or dynamically stabilized during each machining stage. Such a scheme is based on redistributing the heat flux entering from the plasma and extracting it into different regions. This is relatively effective for high power heat flux, but can only give a small temperature difference to low power heat flux. For example, about 1 W / cm²With a uniform heat flux and a ceiling land of about 3 mm, the central part can be provided with an edge heat gradient that results in a temperature rise of 10-30 ° C near the periphery of the wafer. A thermal gradient of this magnitude is very effective as a process control parameter. However, other processing, such as low power polygate processing, is only 0.2W / cm.²Has a heat flux of. Unless the average conduction is made very small (which is extremely difficult to control and results in inadequate overall cooling), it will generally result in very small temperature differences of 5 ° C or less.

<p> Therefore, there is a need for methods and devices that control the temperature of semiconductor wafers during reactive ion etching and similar processing methods without the need for large plasma heat flux. A primary object of the present invention is to solve these demands and provide other related advantages.</p>

<p> The chuck of the plasma processing machine according to the present invention has a temperature control type base, a heat insulating material, a flat support, and a heater. The temperature controlled base has a temperature equal to or lower than the desired temperature of the work. Insulation is placed on the temperature controlled base. A flat support is placed on the heat insulating material, and the flat support holds the work. The heater is embedded in the flat support and / or placed on the underside of the flat support. The heater has a plurality of heating elements that heat a plurality of corresponding heating zones. The power supplied to each heating element and / or the temperature of each heating element is controlled independently.</p>

<figref num="1">It is a schematic side view which shows the support which holds a wafer during processing by a prior art.</figref><figref num="2">It is a plot which shows the temperature of the wafer and the pressure of coolant in the apparatus of FIG. 1 by the prior art.</figref><figref num="3A">It is a schematic side view which shows the work temperature control apparatus by one Embodiment of this invention.</figref><figref num="3B">It is a schematic side view which shows the work temperature control apparatus by another embodiment of this invention.</figref><figref num="3C">It is a simplified schematic diagram of the heat flow dynamics in the device of FIG. 3A.</figref><figref num="4A">It is a schematic side view which shows the apparatus provided with the integrated single flat layer electrode / heater for the work temperature control by another embodiment of this invention.</figref><figref num="4B">FIG. 6 is a schematic plan view showing an apparatus including an integrated single flat layer electrode / heater for controlling the work temperature according to another embodiment of the present invention.</figref><figref num="5">It is a schematic side view which shows the work temperature control apparatus using the side insulation layer approach by another embodiment of this invention.</figref><figref num="6">It is a flowchart which shows the temperature control method of the chuck by one Embodiment of this invention.</figref><figref num="7">It is the schematic which shows the temperature control system of the chuck by one Embodiment of this invention.</figref>

The accompanying drawings incorporated in the specification of the present application and forming a part thereof have a function of showing one or more embodiments of the present invention and explaining the principles and practices of the present invention in combination with a detailed description. There is. Embodiments of the present invention will be described in relation to methods and devices for controlling the spatial temperature distribution across the surface of a work support. Those skilled in the art will appreciate that the following detailed description of the present invention is merely exemplary and does not imply any limitation. Other embodiments of the invention are readily suggested to those skilled in the art who would benefit from the disclosure of the present application. For the practice of the present invention, refer to those shown in the accompanying drawings in detail. The same reference numbers are used for the same or similar parts throughout the drawings and the detailed description below.

From the point of view of clarification, not all practical features are illustrated and described. In carrying out any such practical implementation, it is necessary to make a number of specific decisions in the implementation in order to achieve the developer's specific objectives such as follow-up to the application and commercial restraints. It will of course be understood that these specific objectives change from one implementation to another, and from one developer to another. Moreover, although such development efforts are complicated and time-consuming, those skilled in the art who have the benefit of the disclosure of the present application will be able to commercialize them engineeringly.

The device of the present invention seeks to achieve an accurate large temperature difference, for example greater than 5 ° C, but for example 2 W / cm.²As shown below, it does not require a large plasma heat flux. FIG. 3A is a schematic side view showing a work temperature control device according to an embodiment of the present invention. The base 302, the heat exchanger, supports the insulation 304. A flat support 306 is preferably mounted on the heat insulating material 304. A heater 308 is embedded in the support 306. A work 310 such as a wafer is arranged on the support 306. The thermal conductor 312 forms a thermal close contact between the support 306 and the work 310. The thermal conductor 312 is preferably a gas such as helium. The helium pressure controls the heat conduction between the work 310 and the support 306.

According to one embodiment, the base 302 is composed of a metal material (preferably an aluminum-based cooling plate) that is maintained at a relatively constant temperature through a conventional heat exchange system such as a cooling / heating fluid loop. According to other embodiments, the base 302 can also be constructed of a non-metallic material such as aluminum nitride. However, the base 302 must be cooled more than during standard operation without the heater 308. For example, the temperature of the base 302 can be 10 to 50 ° C lower than the desired temperature of the work 310. The base 302 also forms a heat sink in the case of plasma heating. An external coolant cooler (not shown) can also be used to maintain the temperature of the base plate 302. The amount of heat removed by the external coolant cooler and the temperature of the coolant can be limited to 2000 W and -20 ° C or less, respectively. The base 302 may be provided with several holes and cavities (not shown) for arranging heater feeders 312 or other service lines. Such service lines include feeders, sensors, and feeders for high voltage electrostatic clamps. Those skilled in the art will understand that service lines are not limited to those listed above.

According to one embodiment, the insulation 304 is a large thermal impedance between the support 306 and the base 302. Function as break). The insulation 304 can consist of a thick RTV adhesive layer made of polymer, plastic or ceramic. However, the thermal impedance insulation layer of the insulation 304 must not be excessive enough to cool the wafer 310 sufficiently. For example, the heat insulating material preferably has a thermal conductivity in the range of about 0.05 to 0.20 W / mK. In this case, the heat insulating material 304 has both functions as a heat resistant element and as a bonding material between the support 306 and the base 302. Also, the insulation 304 must maintain sufficient RF coupling between the plasma and the base 304. Insulation 304 must also be able to tolerate large thermal-mechanical shear due to the different materials and temperatures present above and below the layer. According to one embodiment, the thickness of the insulation 304 should be 2 mm or less. The insulation 304 may be provided with several cavities or vias (not shown) adjacent to the cavities of the base 304 to accommodate the feeder feeder 312 and other service lines.

According to one embodiment, the support 306 is made of a ceramic material. The ceramic can be formed of a non-conductive material such as alumina. The shape of the support 306 is preferably a conventional disc commonly used in plasma etching systems. The work 306 can be constructed of a conventional electrostatic chuck or a ceramic with a mechanical clamp that holds the wafer 310. According to one embodiment, the thickness of the support 306 is about 2 mm. However, those skilled in the art will appreciate that other thicknesses are also suitable. According to another embodiment, the structure of the support 306 is a "thin disc bonded to the base", otherwise the lateral heat conduction will be very high and the heater input will be expanded laterally. Zone separation becomes inefficient. The support can dissipate heat locally.

The heater 308 has at least one resistance element. According to one embodiment, the heater 308 can be embedded within the support 306 under the clamp electrode plane and can be shaped, for example, symmetrically or in any desired pattern. The heater 308 may also be composed of one or more flat heating elements. Each heating element forms an independently controlled heating zone or region. The multi-zone pattern has one or more flat heating elements that act in opposition to conduction cooling to the support 306. Sensor 309 associated with each heating zone measures the temperature of each heating zone and sends a signal to a controller or computer (see Figure 7) to monitor and control individual flat heating elements. For example, a sensor such as an infrared radiation sensor or a thermocouple sensor can be attached through a port so that it can be read directly from the workpiece 310. The sensor 309 can also be mounted inside or on the back of the support 306. The heater 308 can be fed by a feeder arranged through the openings of the insulation 304 and the base 302.

According to one embodiment, the heater 308 is composed of an induction heater. According to another embodiment, the heater 308 comprises a heating lamp such as a krypton lamp or a quartz lamp. According to yet another embodiment, the heater 308 can consist of a thermoelectric module capable of cooling or heating. When using a thermoelectric module, the base or insulation layer can be optionally configured. Those skilled in the art will appreciate that there are many other ways to heat the support 306.

FIG. 3B shows another embodiment of the present invention. In the embodiment of FIG. 3B, the heater 308 is formed by an etching foil technique such as a thin film heater. The heater 308 can be embedded in the work support 306 or mounted on the back of the work support 306 (not shown). A polymer-like bonding layer (not shown; the thickness of each layer is, for example, 0.003 inch) is placed between the insulation 304 and the support 306 and between the insulation 304 and the base 302.

FIG. 3C is a simplified schematic showing the heat flow dynamics in the device of FIG. 3A. The entering plasma heat flux Q1 contributes to the temperature T1 on the surface of the wafer 310. The heater 308 supplies heat Q3 to the wafer 310. The out-of-system heat flux Q2 entering the cooled base 302 through the work support 306 is approximately equal to the sum of the ingress heat flux Q1 and Q3, and is therefore expressed as: Q1 + Q3 = Q2 By definition, the sum of the temperature T1 of the wafer 310 and the temperature ΔT through the insulation 304 is equal to the temperature T1 of the cooled base 302. T1 = T2 + ΔT Note that ΔT is determined by the thermal conductivity of the insulation 304. Thus, the ingress heat flux Q3 generated by the heater 308 controls ΔT. Therefore, the output of the heater 308 is adjusted so that the desired temperature T1 is obtained on the surface of the wafer in the range of Q1.

Preferably, the temperature of the base 302 produces an outgoing heat flux Q2 that is about half of the maximum heat flux Q3 when the ingress heat flux Q1 is absent and the maximum heat flux Q3 is approximately equal to the maximum heat flux Q1. Is set to. That is, Q1 = 0 and Q3_max Q1_maxWhen Q2 1/2 Q3_max

In this preferred scheme, the range in which T1 can change is maximized. That is, the local temperature of the wafer can be adjusted by controlling the heating output of the zone of the heater 308. According to one embodiment, the temperature of the base 302, or coolant temperature, is set about 20 ° C lower than a conventional device in which the sum of the maximum value Q1 and the maximum value Q3 is equal to the maximum value Q2. Now referring to the schematic side view of FIG. 4A, there is shown a device with an integrated single flat layer electrode / heater that controls the temperature of the workpiece according to another embodiment of the invention. The base 402 supports the insulation 404. A flat support 406 is mounted on the heat insulating material 404. According to one embodiment, the flat support 406 has an inner spiral 408 and an outer spiral 410, both of which spirals 408 and 410 are used as heaters to heat the workpiece and the electrodes that clamp the workpiece. Both heaters and electrodes are integrated to form a single flat layer structure represented by the flat support 406. FIG. 4B is a plan view of the flat support 406. A differential high voltage HV412 is applied between the inner spiral 408 and the outer spiral 410 to generate the electrostatic clamping function of the flat support 406. When a differential high voltage HV412 is applied to both the inner spiral 408 and the outer spiral 410 with respect to ground, the flat support 406 acts as a unipolar electrostatic chuck. When a differential high voltage HV is applied between the inner spiral 408 and the outer spiral 410, the plano support 406 acts as a bipolar chuck. A first control power supply 414 is connected to the inner coil 408 to generate a first heating zone. A second control power supply 414 is connected to the outer coil 410 to generate a second heating zone.

FIG. 5 is a schematic side view showing a workpiece temperature control device using the lateral thermal break approach according to another embodiment of the present invention. A double or multiple manifold heat sink can be used to circulate the temperature controlled fluid instead of using direct electrical heating or coolant at different temperatures. A temperature controlled base 502 supports an insulating material (eg, ceramic) 504. The flat support 506 forms the support of the work 508. The base 502 is azimuthally separated into two or more zones by a heat insulating material 510, each zone representing a heat sink. The arrows represent different heatsink zones. More specifically, the lateral insulation layer 510 separates the heat sink into two or more thermal zones, such as zones T1 and T2. The temperature of each thermal zone can be controlled independently by controlling the fluid temperature in each fluid loop. By using such a heat insulating layer 510, any spatial zone can be taken into account.

FIG. 6 is a flowchart showing a method of controlling the temperature of the chuck according to the embodiment of the present invention. More specifically, FIG. 6 shows how to control the temperature of a chuck with two separate thermal zones. Those skilled in the art will appreciate that the methods of the invention are applicable to chucks with one or more thermal zones. In the first block 602, the temperature of the first zone is measured using the first set of sensors. Based on these measurements, block 604 controls the output of the heating element, which affects the temperature of the first zone, to adjust the temperature of the first zone to the temperature set by the user and / or computer. .. In the second block 606, the temperature of the second zone is measured using the second set of sensors. Based on these measurements, block 608 controls the output of the heating element, which affects the temperature of the second zone, to adjust the temperature of the second zone to the temperature set by the user and / or computer. ..

FIG. 7 is a schematic view showing a chuck temperature control system according to an embodiment of the present invention. User 702 inputs a set of parameters to computer 704. As a set of such parameters, for example, there is a desired temperature in the first zone of the chuck and a desired temperature in the second zone of the chuck. Those skilled in the art will appreciate that the chuck can have one or more zones. The computer 704 communicates with a storage element 706 that stores the algorithm of FIG. 6, the inputs and outputs of the computer 704. The first set of sensors 708 measures the first zone of the chuck, and the second set of sensors 710 measures the second zone of the chuck. Based on the temperature readings of the first set of sensors 708, the computer 704 controls the first set of heating elements 712 to regulate the temperature in the first zone of the chuck. Based on the temperature readings of the second set of sensors 710, the computer 704 controls the second set of heating elements 714 to regulate the temperature in the second zone of the chuck.

The above method of controlling the temperature distribution of the wafer on the electrostatic chuck is not only suitable for application in Inductive Coupled Plasma (ICP) machines, but also particularly low plasma output heat flux to the wafer. It is also suitable for use in any other system that requires it. This technique can be applied to any other application in which the technique of the present invention has a need to form a thermal gradient.

Although the embodiments and uses of the present invention have been illustrated and described above, those skilled in the art who have the benefit of the present disclosure can conceive many modifications other than the above without departing from the concept of the present invention. Is obvious. Therefore, the present invention is not subject to any limitation except for the spirit described in the claims.

302 base 304 insulation 306 support 308 heater 310 Work (wafer) 412 differential high voltage 414 First heater power supply 416 Second heater power supply