Thin film deposition system with automatic cleaning function for cleaning inside

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical field to which the invention belongs]

The present invention relates to a thin film forming apparatus used in a process for manufacturing a semiconductor device circuit, and more particularly to a thin film forming apparatus having an automatic cleaning function and an automatic cleaning method for the thin film forming apparatus.

【0002】

[Problems to be Solved by Conventional Techniques and Inventions]

In the process of forming a thin film on a semiconductor substrate, the semiconductor substrate, that is, the object to be processed, is placed on a resistance type heater that functions as a susceptor provided in an exhausted reaction chamber. After a shower head with a hole for discharging the reaction gas is opposed to the heater, 13.56 MHz radio frequency energy is applied to the shower head so that the plasma discharge region supports the semiconductor substrate between the heater and the shower head. Formed between. The reaction gas supplied by the shower head is excited and activated in the plasma discharge region, and a thin film is formed on the semiconductor substrate according to the type of the reaction gas. At this time, the thin film and the reaction by-product adhere to the inner surface of the reaction chamber in addition to the semiconductor substrate.

【0003】

With the repetition of the thin film forming process, undesired precipitates adhering to parts other than the semiconductor substrate accumulate. After being separated from the adhesion surface, the undesired precipitates become particles and adhere to the surface of the semiconductor substrate, causing impurity contamination and stopping the function of the semiconductor element. Many thin film forming devices have an automatic cleaning function to remove unwanted precipitates from the reaction chamber.

【0004】

After separating the thin film-formed semiconductor substrate from the heater and transporting it out of the reaction chamber, the automatic cleaning function uses fluorine-containing active species to clean the reaction chamber. Specifically, when forming a silicon nitride film on a semiconductor substrate, SiH₄, NH₃And N₂The mixed gas is supplied to the reaction chamber as a reaction gas to generate a plasma discharge region in the reaction chamber using radio frequency energy.

【0005】

Unwanted precipitates made of the same material as the thin film, which are mainly deposited on the semiconductor substrate, also adhere to the inner surface of the reaction chamber. After the completed semiconductor substrate is transported out of the reaction chamber, C₂F₆And oxygen or C₃F₈And a mixture of oxygen is supplied from the shower head into the reaction chamber. Then, by applying radio frequency energy of 13.56 MHz, fluorine-active species are generated in the reaction chamber. Unwanted precipitates inside the reaction chamber are vaporized by the fluorine-active species and exhausted from the reaction chamber. An automatic cleaning sequence keeps the inside of the reaction chamber clean at all times after performing one or more thin film formations on the semiconductor substrate.

【0006】

Conventionally, the requirement for forming a thin film of a silicon nitride film and a silicon oxide film (silicon nitride type thin film) by a capacitively coupled plasma CVD method is SiH.₄: N₂: NH₃The gas flow rate ratio of the system is almost SiH₄: N₂: NH₃= 1: 1-50: 1-10, and the temperature of the object to be treated is approximately 400 ° C or less. Both requirements are used industrially for insulating films of semiconductor devices. Some examples of thin film formation requirements are disclosed in US Pat. No. 5,336,640. Since the thin film takes in hydrogen, if the step of having a temperature higher than the thin film forming temperature continues, the hydrogen taken in the thin film is released, which greatly deteriorates the electrical characteristics of the semiconductor element. Therefore, the main application is final passivation thin films for semiconductor devices that do not have higher temperature treatment steps (the example disclosed in US Pat. No. 5,336,640 is used as the final protective film).

【0007】

In order to solve the problem of the increase in RC delay (proportional to the product of metal wire resistance and capacitance between wirings) due to the increase in the density of semiconductor elements, the resistance is lowered by introducing Cu wiring to reduce the wiring capacitance. A proposal was made that it should be reduced. In a semiconductor element having Cu wiring, since Cu wiring has high heat resistance, a SiOF film formed by plasma CVD at a relatively high temperature can be used as an insulating film arranged between metal wirings.

【0008】

When applying Cu wiring, a damascene process is generally introduced in which a groove pattern of metal wires is formed in the insulating film between layers and the Cu wiring is embedded in the grooves. Heteroetching by reactive ion etching (RIE) is used to form grooves in the insulating film between the layers. The silicon nitride type thin film formed by plasma CVD may be used as the RIE etching stop layer. The silicon nitride type thin film formed by plasma CVD may be used as an antireflection film for preventing the reflection of exposure in the lower portion of the resist in the lithography process in order to accurately perform the microstructure processing.

【0009】

In the above situation, the processing temperature of about 400 ° C increased until it exceeded 500 ° C. When the substrate is heated to above 500 ° C. and thin film formation is performed on the semiconductor substrate, unwanted precipitates adhere to the inside of the reaction chamber. Since the attached unwanted precipitates are a source of particles and contamination, they are removed by performing an automatic cleaning sequence as described above. In the process of forming the silicon nitride film, a gas containing fluorine is used for automatic cleaning. In the plasma discharge region within the reaction chamber or in the excitation chamber isolated from the reaction chamber, the fluorine-active species used to remove unwanted precipitates in the reaction chamber are produced. In order to form a thin film on the semiconductor substrate, the surface of the ceramic heater supporting the substrate is set to a predetermined temperature range for forming the thin film. The automatic cleaning sequence immediately follows as the thin film-formed semiconductor substrate is carried out of the reaction chamber. That is, the ceramic heater portion, which directly holds and heats the semiconductor substrate in the reaction chamber, is in a so-called "thin film formation temperature" state, and at its high temperature, it is exposed to an automatic cleaning environment. However, the above-mentioned conventional cleaning treatment causes the following problems.

【0010】

[Means for solving problems]

In order to form a thin film on a semiconductor substrate, the surface of the ceramic heater supporting the substrate is set in a predetermined temperature range of 470-600 ° C. In a temperature environment above 470 ° C, aluminum nitride reacts with fluorine-active species to produce aluminum fluoride, and the produced aluminum fluoride is sequentially released into the reaction chamber. When the surface temperature of the heater exceeds 500 ° C, the formation and release of aluminum fluoride causes great damage to the reaction chamber. The surface temperature of the shower head opposed to the ceramic heater supporting the semiconductor substrate is 100 to 250 ° C, which is lower than that of the ceramic heater. Aluminum fluoride released from the ceramic heater adheres to the shower head at a relatively low temperature and accumulates by reaction with the fluorine-active species during the automatic cleaning sequence. Once attached to the shower head, aluminum fluoride cannot be removed except by opening the reaction chamber and wiping it off.

【0011】

An object of the present invention is to provide an automatic cleaning method that does not generate aluminum fluoride on the shower head.

【0012】

Another object of the present invention is to achieve the formation of a contamination-free thin film by an automatic cleaning sequence with good reproducibility.

【0013】

Yet another object of the present invention is to provide a thin film forming apparatus that reduces downtime for cleaning and improves productivity by using an automatic cleaning sequence.

【0014】

That is, the thin film forming apparatus according to the embodiment of the present invention is (a) a reaction chamber for forming a thin film on an object to be treated placed on a susceptor provided in the reaction chamber, and the susceptor is the object to be processed. It is equipped with a heater for heating, the reaction chamber is equipped with a conveyor for loading and unloading the object to be processed into and out of the reaction chamber, and (b) does not adhere to the inside of the reaction chamber at predetermined time intervals. The cleaning device consists of a cleaning device for cleaning the desired precipitate, which is (i) a cleaning gas controller for introducing a cleaning gas into the reaction chamber and exhausting the reaction chamber after the cleaning procedure, (. ii) Clean gas activator that activates clean gas in radical form, (iii) Lowers the temperature of the susceptor at a predetermined rate for cleaning after the completion of thin film formation, and then activates the clean gas controller and clean gas activator. It consists of a temperature and timing controller programmed to allow.

【0015】

In the above, the temperature of the susceptor for cleaning is preferably 500 ° C or lower, more preferably 470 ° C or lower, while the temperature of the susceptor for thin film formation is 500 ° C or higher. May be good. In the examples, the clean gas contains fluorine and the activated clean gas contains fluorine radicals. In particular, the clean gas is activated using the plasma discharge region generated in the reaction chamber or using a remote plasma discharge chamber before introducing the clean gas into the reaction chamber. In addition, the clean gas controller introduces clean gas through a shower head located above the susceptor in the reaction chamber.

【0016】

Unwanted precipitates in the examples include silicon nitride, SiO, SiON, SiOF, SiC and hydrocarbons. The equipment includes a plasma CVD equipment and a thermal CVD equipment.

【0017】

The present invention is also a method for cleaning unwanted precipitates adhering to the inside of a reaction chamber for forming a thin film on an object to be treated placed on a susceptor given in the reaction chamber. The susceptor is applicable to a method in which the susceptor is provided with a heater for heating the object to be processed, and the reaction chamber is provided with a conveyor for loading and unloading into and out of the reaction chamber. Is (a) a step of reducing the temperature of the susceptor at a predetermined rate for cleaning after the thin film formation is completed, (b) a step of contacting the inside of the reaction chamber with the activating clean gas, and (c) the activating clean gas. Consists of a step of cleaning unwanted precipitates.

【0018】

BEST MODE FOR CARRYING OUT THE INVENTION

Applicable Thin Film Forming Equipment Problems arise when conventional silicon nitride films formed by plasma CVD within semiconductor devices are used. That is, when a silicon nitride type film having a high hydrogen concentration originally used as a final protective film is formed, and then a SiOF film formed by plasma CVD at a relatively high temperature is formed on the silicon nitride type film. Hydrogen in the SiOF membrane dissociates during formation and the binding force of the membrane decreases, resulting in membrane separation. The reason is that the film formation temperature is relatively high at 470 ° C. When the film is separated, the semiconductor element having the separated portion causes a short circuit in the wiring and deteriorates the conduction, so that the productivity of the object to be processed is lowered as a whole.

【0019】

Silicon nitride type films formed by thermal CVD above 700 ° C without plasma are not used as interlayer insulating films because the temperature of film formation after Al or Cu formation is too high. Since most of the films do not contain hydrogen, silicon nitride type films have been used as an etching stop layer for the first interlayer insulating film on semiconductor devices to which a thermal process is later applied.

【0020】

However, semiconductor devices have recently become so fine that gate lengths have become smaller and are now less than 0.18 μm. Therefore, it is difficult to prevent the formation and diffusion of the impurity layer due to the heat load during the high temperature heating process exceeding 700 ° C. In the case of insufficient control of the diffusion layer, the reliability of the semiconductor element is reduced because the operating voltage varies. Therefore, what is desired is to require a low thermal load on the semiconductor device, to form a thin film at a temperature lower than that of high temperature thermal CVD, and the thin film is a silicon nitride type film having a low concentration of hydrogen. The method.

【0021】

To this end, the inventors have invented a method of forming a silicon nitride film using plasma CVD at a relatively higher temperature, which is described in Patent Application No. 1999, No. 243914. By raising the temperature of the semiconductor substrate at about 400 ° C to the range of 430 to 600 ° C, a silicon nitride film having a low concentration of hydrogen is formed. The semiconductor substrate temperature is preferably 470 ° C. or higher, and more preferably 550 to 600 ° C.

【0022】

In order to set the semiconductor substrate temperature to 470-600 ° C, the surface of the heater (supporting the semiconductor substrate) for heating the substrate needs to be raised to 500-650 ° C, which is the conventional sheath heater. It exceeds the heat resistance of the metal heater buried in the aluminum alloy. Therefore, ceramic heaters are used to achieve high temperatures. As the ceramic material, aluminum nitride having a high thermal conductivity is generally used. A ceramic heater consisting of an aluminum nitride disk or plate has a resistance heater and a metal for the plasma discharge ground electrode embedded by integral sintering, whereby the semiconductor substrate can be heated up to approximately 650 ° C.

【0023】

Unwanted precipitates adhere to the inside of the reaction chamber when the analytical substrate of a conventional cleaning device is heated above 470 ° C using a ceramic heater and when thin film formation is performed on the semiconductor substrate. The attached unwanted precipitates are a source of particles and contamination, which are removed by performing an automatic cleaning sequence as described above. In the process of forming the silicon nitride film, a gas containing fluorine is used for automatic cleaning. In the plasma discharge region within the reaction chamber or in the excitation chamber away from the reaction chamber, a fluorine-active species is produced, which is used to remove unwanted precipitates in the reaction chamber.

【0024】

In order to form a thin film on the semiconductor substrate, the surface of the ceramic heater supporting the substrate is set to 470 to 600 ° C in a predetermined temperature range. The automatic cleaning sequence immediately follows as the thin film-formed semiconductor substrate is transported out of the reaction chamber. That is, a portion of the reaction chamber, especially the ceramic heater that directly holds and heats the semiconductor substrate, is in the so-called "film formation temperature" state, at which high temperature it is exposed to an automatic cleaning environment. In a temperature environment above 470 ° C, aluminum nitride reacts with fluorine-active species to produce aluminum fluoride, and the produced aluminum fluoride is sequentially released into the reaction chamber.

【0025】

When the surface temperature of the heater exceeds 500 ° C, the formation and release of aluminum fluoride causes great damage to the reaction chamber. The surface temperature of the shower head opposed to the ceramic heater supporting the semiconductor substrate is 100 to 250 ° C, which is lower than that of the ceramic heater. Aluminum fluoride released from the ceramic heater adheres to the relatively cold shower head and accumulates by reacting with the fluorine-active species during the automatic cleaning sequence. Aluminum fluoride once fixed to the shower head cannot be removed unless the reaction chamber is opened and wiped off.

【0026】

Adhesion of aluminum fluoride to the surface of the shower head effectively causes two problems. The first problem is that the growth rate of the film formed on the semiconductor substrate changes. When the non-conductor aluminum fluoride adheres to the surface of the shower head, the non-conductor aluminum fluoride functions as a newly formed electrical insulator formed on the surface of the shower head, thereby reducing the film formation rate. The difference in the adhesion (thickness) of aluminum fluoride on the surface of a single shower head creates an unusual distribution of film thickness formed on the surface of the semiconductor substrate. Volatility of only ± 3% is required for film thickness (defined as the maximum thickness minus the minimum thickness divided by twice the average).

【0027】

The difference in film thickness formed on the semiconductor substrate leads to non-uniformity of the semiconductor element function of the semiconductor substrate. If the film thickness is not achieved as designed, the semiconductor element does not function properly and is judged to be an inferior product. Aluminum fluoride adhering to the entire surface of the shower head causes an insufficient thickness of the entire film on the semiconductor substrate. Repeated film formation on the semiconductor substrate gradually reduces the film thickness, which must be increased in other ways. According to current technical standards, the reproducibility of film thickness on semiconductor substrates should be approximately ± 3% or less. When the film thickness grown on the semiconductor substrate changes beyond this value, all the semiconductor elements on the semiconductor substrate are inferior products.

【0028】

The second problem is contamination of the semiconductor substrate by particles. When aluminum fluoride adheres to and accumulates on the surface of the shower head, the aluminum fluoride particles fall off the surface and adhere to the surface of the semiconductor substrate. Aluminum fluoride deposited on the semiconductor substrate causes contamination or defects at the bottom, middle or surface of the film to be formed on the semiconductor substrate, which causes malfunction of the semiconductor element. Generally speaking, the number of particles adhering to the semiconductor substrate should not exceed 20 within the range of 0.2 μm or more in diameter.

【0029】

Furthermore, in order to eliminate the problems caused by aluminum fluoride, as mentioned above, there is no other way but to physically remove the aluminum fluoride adhering to the surface of the shower head, the film formation and processing are interrupted, and the reaction chamber Must be opened and wiped clean by hand. Since the wiping and cleaning is performed in a state where the film formation and processing by the thin film forming apparatus are stopped, the operating efficiency and productivity of the apparatus are extremely lowered.

【0030】

Membrane formation and treatment before cleaning In the embodiment, a first semiconductor substrate is provided as an object to be processed for film formation and treatment on a heater having a surface temperature of 500 ° C. or higher, which is arranged in a reaction chamber of a thin film forming apparatus. The reaction gas is supplied from a shower head to which a radio frequency of 13.56 MHz is applied. In the plasma discharge region generated between the shower head and the heater supporting the semiconductor substrate, the reaction gas is decomposed and a thin film is formed on the semiconductor substrate. The first semiconductor substrate on which the film formation is completed is removed from the heater and carried out of the reaction chamber. A second semiconductor substrate for film formation and processing is carried into the reaction chamber and placed on the heater. The same film formation and processing as in the first semiconductor substrate is performed. The second semiconductor substrate is removed from the reaction chamber after film formation and processing is complete.

【0031】

Unwanted adhesion to the inside of the reaction chamber after removing the nth semiconductor substrate from the reaction chamber during a series of film forming and processing steps (membrane sequence) of the 1st to nth semiconductor substrates. A cleaning sequence to clean the precipitate follows.

【0032】

Subsequent cleaning sequence The cleaning sequence involves a cooling step that lowers the temperature of the heater that supports and heats the semiconductor substrate. When the nth semiconductor substrate is removed from the reaction chamber and ready for automatic cleaning for the reaction chamber, nitrogen gas is introduced into the reaction chamber to obtain any pressure and the temperature of the ceramic heater is 20 per minute. It descends at a speed not exceeding ° C.

【0033】

When the surface temperature of the ceramic heater drops below 500 ° C, clean gas is sprayed into the reaction chamber to perform automatic cleaning in the reaction chamber, and unwanted precipitates adhering to the inside of the reaction chamber are vaporized. And it is exhausted. The cleaning step of removing the product from the reaction chamber is substantially, but not limited to, performed in the following manner.

【0034】

On-site plasma cleaning In the embodiment, C controlled at a predetermined flow rate as a clean gas.₃F₈A mixed gas of gas and oxygen gas is introduced into the reaction chamber from the shower head. While maintaining the inside of the reaction chamber at a predetermined pressure, radio frequency energy of, for example, 13.56 MHz is applied to the shower head to form a plasma discharge region between the shower head and the ceramic heater. The clean gas introduced from the shower head is activated by plasma discharge to become a fluorine-containing active species, which reacts with unwanted deposits adhering to the inside of the reaction chamber and should be exhausted from the reaction chamber by an exhaust pump. Convert to gas material. During the cleaning process, the surface temperature of the ceramic heater is maintained below 500 ° C.

【0035】

Radio frequency energy applied to the shower head and C₃F₈When the gas is finished, the cleaning process is finished. The oxygen gas supplied to the reaction chamber as part of the cleaning gas is injected into the reaction chamber after the cleaning process is completed. The reaction products from the reaction of the fluorinated species and the fluorinated active species produced during the cleaning step with the unwanted precipitates in the reaction chamber are purged from the reaction chamber. After evacuating the reaction chamber, a heating step of raising the temperature of the ceramic heater to the temperature for film formation and processing of the semiconductor substrate continues. When the temperature of the ceramic heater reaches a predetermined temperature, the automatic cleaning sequence is completed. When the automatic cleaning sequence is completed, the (n + 1) th semiconductor substrate is brought into the reaction chamber so as to be placed on the ceramic heater. After that, the thin film formation and processing (film formation sequence) of the semiconductor substrate described above are executed.

【0036】

Remote Plasma Cleaning The cleaning step can be performed by another method such as: The clean gas is activated in a remote plasma discharge chamber away from the reaction chamber where the thin film formation is performed on the semiconductor substrate. The activated clean gas is introduced through a duct into the reaction chamber where the thin film formation and treatment on the semiconductor substrate is performed. The activated clean gas introduced into the reaction chamber converts unwanted precipitates adhering to the inside of the reaction chamber into a gaseous material, which is expelled from the reaction chamber.

【0037】

When the thin film formation and processing of a predetermined number of semiconductor substrates are completed and the automatic cleaning sequence in the reaction chamber is completed, a cooling step of lowering the temperature of the heater supporting the semiconductor substrates to 500 ° C. or less is executed. .. When the cooling step is completed, argon gas controlled to a predetermined flow rate is supplied into the remote plasma discharge chamber. NF controlled to a given flow rate after a 400kHz radio frequency discharge is generated in the remote plasma discharge chamber₃Fluorine-containing clean gases such as are introduced to produce fluorine-active species. Fluoroactive species are introduced into the reaction chamber through a remote plasma discharge chamber and a duct that couples with the reaction chamber for membrane formation. The inside of the reaction chamber is cleaned with fluorine-active species, and the heating step in which the heater temperature in the reaction chamber rises to the thin film formation temperature is carried out as described above.

【0038】

The first automatic cleaning sequence described above is called in-situ plasma cleaning, where the discharge electrodes and radio frequency energy supply in the reaction chamber used during film formation are employed to activate the cleaning gas. The second automatic cleaning sequence described above is called remote plasma cleaning, where a remote plasma discharge chamber isolated from the reaction chamber is used to activate the cleaning gas, but at the radio frequency for membrane formation. No energy supply is used.

【0039】

Example 1 Equipment structure (on-site plasma cleaning) FIG. 1 shows one embodiment of the thin film forming and processing apparatus 1 according to the present invention, in which a parallel plate plasma CVD apparatus and an on-site plasma purifying apparatus for automatic cleaning are used.

【0040】

The object to be processed 9 such as a semiconductor substrate is placed on a ceramic heater 3 for holding the object to be processed in the reaction chamber 2. A shower head 4 is arranged so as to face the heater 3 and supply a uniform reaction gas onto the object 9 to be processed. The reaction gas for forming a film on the surface of the object 9 is controlled by a mass flow controller (not shown) at a predetermined flow rate and enters the duct 5 from the duct 5 through the valve 6. After passing through the hole 7 of the reaction chamber 2, gas is supplied into the reaction chamber 2 through thousands of small holes with a diameter of 1 mm or less of the shower head 4.

【0041】

To exhaust the reaction chamber 2, an exhaust pump (not shown) is coupled into the hole 20 of the reaction chamber 2 through a duct 17 and a conductance control valve 21. The heater 3 for holding the object 9 includes an aluminum nitride plate 13 in which a resistance heating element 26 is embedded and is coupled to the reaction chamber 2 by a shaft 29.

【0042】

Membrane formation treatment A method of forming a film on the object 9 is described below. When a silicon nitride film is formed on the object 9 to be treated, SiH₄, NH₃And N₂Or SiH₄And NH₃Or SiH₄And N₂Gas is used as the reaction gas, and a radio frequency energy of 13.56 MHz or a mixed power of 13.56 MHz and 430 kHz is applied to the shower head 4. The object 9 receives heat from a heater at 600 ° C so that the temperature ranges from approximately 530 ° C to 550 ° C. SiH₄And N₂The reaction gas such as, etc. is introduced from the duct 5 through the valve 6 into the duct 11, and is uniformly supplied to the inside of the reaction chamber 2 through the hole 7 of the duct 11 through the shower head 4. While introducing the reaction gas into the reaction chamber 2 at a predetermined flow rate, the pressure in the reaction chamber 2 is from 1 Torr in response to the signal on the pressure meter 28a through the opening of the conductance control valve 21 controlled by the pressure controller 28. Adjusted to the range of 8 Torr.

【0043】

As described above, while maintaining the temperature, gas flow rate and pressure controlled to predetermined values, predetermined radio frequency energy is applied between the electrodes to generate plasma, which in turn is nitrided onto the object 9 to be processed. Form a silicon film. By controlling the time interval in which the radio frequency energy is applied, a silicon nitride film having a required thickness can be obtained. When the gate valve of the reaction chamber opening 19 is opened after the thin film is formed on the object 9 to be processed, the object 9 to be processed is carried out of the reaction chamber 2 by an automatic conveyor (not shown).

【0044】

On-site plasma cleaning sequence Unwanted precipitates adhering to the inside of the reaction chamber 2 when forming a thin film on the object to be treated are removed by an automatic cleaning sequence. The automatic cleaning sequence includes a cooling process that lowers the temperature of the heater 3 that supports the object 9 to 500 ° C or less, a cleaning process that cleans the inside of the reaction chamber 2, and a temperature of the heater 3 that is 600 for thin film formation. It consists of a heating process that raises the temperature to ° C.

【0045】

In the cooling process, the pressure is in the range of 0.5-9 Torr and the temperature of the heater 3 does not exceed 20 ° C / min, while introducing nitrogen gas into the reaction chamber 2 at 2 liters / min (2slm). Can be lowered. The flow rate of nitrogen gas is not limited to 2 liters per minute. The gas to be introduced is not limited to nitrogen, and instead, an inert gas such as helium or argon that does not damage the ceramic heater 3, the reaction chamber 2, and the internal substances may be used. The temperature drop rate of the heater 3 is not limited to 20 ° C. per minute or less, and any rate that does not cause damage to the heater 3 may be used. The cooling process is completed when the temperature of the heater 3 drops below 500 ° C. Preferably, it should be 450 ° C or less. The temperature of the heater 3 is defined by the temperature on the surface of the ceramic heater that contacts the back side of the semiconductor substrate 9.

【0046】

The cleaning process is carried out by the following method. 300sccm C₃F₈A mixed gas of 700 sccm of oxygen is introduced from the shower head into the reaction chamber 2 as a clean gas. The pressure in the reaction chamber 2 is in the range of 2 to 5 Torr, and 500 W to 2000 W of 13.56 MHz radio frequency energy is applied to the shower head to create a plasma discharge region between the shower head 4 and the ceramic heater 3. Will be done. The clean gas is activated by plasma, which produces fluorine-containing active species. The fluorinated species react with the unwanted precipitates attached to the inside of the reaction chamber 2 and eventually convert them into a gas. Gas is exhausted from the reaction chamber 2 through hole 20 by an exhaust pump (not shown). The temperature of the ceramic heater 3 during the cleaning process is maintained below 500 ° C.

【0047】

Upon completion of cleaning of the reaction chamber 2, the supply of radio frequency energy to the shower head 4 was stopped, and C to the reaction chamber 2 was stopped.₃F₈Supply is stopped. The inside of the reaction chamber 2 is purged with oxygen gas. The reaction chamber 2 may be purged by stopping the supply of oxygen gas and supplying nitrogen gas instead.

【0048】

The subsequent heating step raises the temperature of the heater 3 to the film formation temperature. Nitrogen gas is supplied through the shower head 4 to the reaction chamber 2 at a flow rate of 2 liters (2 slm) per minute, which keeps the pressure in the reaction chamber 2 in the range of 0.5-9 Torr and the temperature of the heater 3 at 20 ° C. Raise at a speed that does not exceed C. The gas supplied to the reaction chamber 2 is not limited to nitrogen gas, and any gas can be used as long as the parts including the heater 3 in the reaction chamber 2 are not damaged. The flow rate of the gas, including nitrogen gas, is not limited to 2 liters per minute (2 slm) and can be any flow rate that can maintain the pressure in the reaction chamber 2.

【0049】

In addition, the rate of temperature increase of the heater 3 is not limited to 20 ° C. per minute or less, and the temperature of the heater 3 can be increased at a rate that does not damage the heater 3. When the temperature of the heater 3 reaches the film forming temperature, the heating step is completed. Upon completion of the heating process, the automatic cleaning sequence is completed. The next object to be processed is carried in and the thin film forming process is executed.

【0050】

In the cooling and heating steps that change the temperature of the heater 3, the rate of change is not limited to 20 ° C. per minute or less. As long as the heater 3 is not damaged by the temperature change, the faster the temperature change, the shorter the automatic cleaning sequence, which enhances the productivity of the thin film forming apparatus.

【0051】

Example 2 Device structure (remote plasma cleaning) FIG. 2 shows an example of a film forming and processing apparatus 30 having a remote plasma discharge chamber, except for a structure in which unwanted precipitates adhering to the inside of the reaction chamber 2 are automatically removed. Similar to the forming and processing equipment.

【0052】

The upper part of the reaction chamber 2 is provided with a duct 5 and a valve 6 for supplying the reaction gas to the reaction chamber 2 for thin film formation and processing. The reaction gas is uniformly supplied to the surface of the object 9 to be processed through the shower head 4 having thousands of small holes having a diameter of 1 mm or less through the opening 32 of the duct 14 and the reaction chamber 2. While performing the thin film formation and treatment of the object 9 to be processed, the valve 15 is closed and the valve is provided on the duct 16 connecting the remote plasma discharge chamber 16 to the reaction chamber 2.

【0053】

Remote plasma cleaning sequence After at least one thin film formation and treatment step has been completed for the object 9 in the reaction chamber 2, an automatic cleaning sequence is performed which cleans the unwanted precipitates deposited inside the reaction chamber 2. As mentioned above, the automatic cleaning sequence consists of three steps: cooling, cleaning and heating. In the cooling process, nitrogen gas is supplied from the duct 5 to the reaction chamber 2 through the valve 6, the branch 31, the duct 14, the opening 32 and the shower head 4 at a rate of 2 liters per minute, and the pressure of the reaction chamber 2 is 0.5 to 9 Torr. The temperature of the heater 3 is lowered at a speed not exceeding 20 ° C. per minute while maintaining the range.

【0054】

Subsequent is a cleaning step, which removes unwanted deposits deposited inside the reaction chamber 2. The step is carried out in the following way. After the supply of nitrogen gas completed during the cooling process is discontinued and the reaction chamber is exhausted, argon gas is injected from duct 22 into the remote plasma discharge chamber 16 at a flow rate of 3 liters (3 slm) per minute. At that time, the valve 15 is opened and the valve 6 is closed, and the argon gas introduced from the duct 22 is carried to the reaction chamber 2 through the remote plasma discharge chamber 16.

【0055】

A 400 kHz radio frequency discharge is generated within the remote plasma discharge chamber 16 while maintaining the pressure in the reaction chamber 2 in the range 0.05-8 Torr. The flow rate of argon gas gradually changes to 2 liters per minute, NH₃Gas is ejected from duct 22, which is gradually increased from zero to 1 slm by a mass flow controller (not shown). The gas supplied to the remote plasma discharge chamber 16 is NF₃It simply changes by gradually increasing the amount of. The gas (clean gas) supplied to the remote plasma discharge chamber 16 in a stable state is 2 liters of argon per minute and 1 liter of NF per minute.₃Consists of. The radio frequency discharge plasma generated in the remote plasma discharge chamber 16 produces fluorine-active species. The clean gas containing the fluorine-active species is injected from the upper opening 32 of the reaction chamber 2 to the shower head 4 through the valve 15 and the duct 14. The clean gas introduced into the reaction chamber 2 through thousands of small holes provided in the shower head 4 converts unwanted precipitates deposited inside the reaction chamber 2 into gas and exhausts them from the reaction chamber 2. To do. During the cleaning process, the temperature of heater 3 must be maintained at least 500 ° C.

【0056】

The flow rate of the cleaning gas injected into the remote plasma discharge chamber 16 during the cleaning process is not limited to the above-mentioned flow rate, and is NH.₃It may be selected from the range of 100 sccm to 5 slm with respect to and from the range of 100 sccm to 5 slm with respect to argon. A rare gas such as helium may be used as a clean gas instead of the argon gas. NF₃, C instead of CF gas₃F₈Gas such as may be used. At that time, oxygen gas may be mixed in addition to or instead of argon gas.

【0057】

During the cleaning process, the temperature of the heater is maintained below 500 ° C, preferably below 470 ° C. The power frequency supplied to the remote plasma discharge chamber 16 is not limited to 400 kHz and may be selected from 300 to 500 kHz. The power value must be one, which gives the given fluorine-active species. In an embodiment of the invention, 2000-5000 W of power is used at 400 kHz to generate radio frequency discharge plasma in the remote plasma discharge chamber 16.

【0058】

The NF injected from the duct 22 after the unwanted precipitates adhering to the inside of the reaction chamber 2 were completely removed from the inside of the reaction chamber 2 by a clean gas having a fluorine-active species.₃The gas supply is stopped and the radio frequency discharge in the remote plasma discharge chamber 16 is stopped. NF₃Argon gas is supplied from the duct 22 into the reaction chamber 2 through the remote plasma discharge chamber 16 even after the gas supply and the radio frequency discharge are stopped, and it is a clean gas having fluorine-active species remaining in the reaction chamber 2. Purge. The heating process is started, the purging in the reaction chamber 2 with argon gas is started, and the temperature of the heater 3 rises to the film formation temperature. The heating step is performed in the same manner as the cooling step described above, except that the temperature of the heater 3 is raised at a rate of 20 ° C. or less per minute. The heating step is completed when the temperature of the heater 3 reaches the temperature at which the thin film formation and treatment of the object 9 to be processed are executed (film formation temperature).

【0059】

While the cooling and heating steps are being carried out, the introduction of nitrogen gas into the reaction chamber 2 may be carried out in another way: A predetermined flow rate of nitrogen gas is supplied through duct 22 and injected into reaction chamber 2 through remote plasma discharge chamber 16, valve 15 and duct 14. At this time, the valve 6 is closed and no plasma discharge is performed in the remote plasma discharge chamber 16. Argon gas injection and cooling and heating steps are also performed from the duct 22 through the remote plasma discharge chamber 16 into the reaction chamber 2.

【0060】

[Example]

Cleaning result Examples according to the present invention will be described. The results when a silicon nitride film is formed on a semiconductor substrate at a film formation temperature of 600 ° C. will be described below. The equipment used was the thin film forming and processing equipment shown in FIG. The first semiconductor substrate 9, which is an object to be processed made of an aluminum nitride substrate, was placed on the ceramic heater 3. The ceramic heater 3 was held at 600 ° C by an embedded resistor heater 26, which heated the first semiconductor substrate 9 supported on the ceramic heater 3 from about 540 ° C to 550 ° C. SiH₄Gas and nitrogen gas were mixed and introduced from duct 5. The mixed gas was uniformly distributed by the shower head 4 on the surface of the first semiconductor substrate 9 placed on the heater 3 in the reaction chamber 2.

【0061】

At 13.56 MHz, 400 W of radio frequency energy was applied to the shower head 4, and a plasma region was formed between the shower head 4 and the heater supporting the first semiconductor substrate 9. After that, a 100 nm silicon nitride film was formed on the surface of the first semiconductor substrate 9. After opening the gate 18 and removing the first semiconductor substrate 9 on which the silicon nitride film is formed, the second semiconductor substrate 9 is introduced into the reaction chamber 2 through the holes 19 of the reaction chamber 2 by the same route as above, and the silicon nitride film is formed. Was placed on the heater 3 to form.

【0062】

Similar to the film formation and treatment of the silicon nitride film, the silicon nitride film is formed on the second semiconductor substrate 9. In this way, film formation and processing of the silicon nitride film was carried out continuously on 25 substrates. After the 25th substrate, which had completed film formation and treatment, was removed from the reaction chamber 2, an automatic cleaning sequence was performed to clean the unwanted precipitates adhering to the inside of the reaction chamber 2.

【0063】

In the cooling process, the temperature of heater 3 was lowered to 470 ° C. Argon gas was supplied from the duct 22 to the remote plasma discharge chamber 16 by 3 slm, and the pressure in the reaction chamber 2 was set to 1 to 1.5 Torr by opening the valve 15. After a 400kHz radio frequency discharge is generated in the remote plasma discharge chamber 16, the flow rate of argon gas is gradually reduced to 2slm and the NF ejected from duct 22.₃The gas flow rate was gradually increased until it reached 1 slm. NF introduced from duct 22₃When the gas reached the remote plasma discharge chamber 16, fluorine-active species were produced. The fluorinated species produced in the remote plasma discharge chamber 16 was introduced into the reaction chamber 2 from the shower head 4 through the valve 15, the duct 14 and the hole 32 together with other gases. Unwanted precipitates adhering to the inside of the reaction chamber 2 were cleaned with a fluorine-active species.

【0064】

The cleaning process with fluorine-active species corresponded to the cleaning process described above, which lasted approximately 70 seconds. After the reaction chamber 2 has been cleaned, the radio frequency discharge and NF in the remote plasma discharge chamber 16₃Both of the supplies have been discontinued. After that, the supply of argon gas from the duct 22 was stopped, the valve 15 was closed, and nitrogen gas was supplied from the duct 5. At the same time as this step, a heating step was carried out to raise the temperature to 600 ° C.

【0065】

The silicon nitride film formation and treatment of 2000 semiconductor substrates was performed by performing the silicon nitride film formation and processing on a set of 25 continuous semiconductor substrates and then executing the automatic cleaning sequence once.

【0066】

FIG. 3 shows the measurement result (reproducibility of film thickness) of the thickness of the formed silicon nitride film. The thickness dispersion (film thickness reproducibility) of the grown silicon nitride film is ± 2.1% (1σ = 0.92%), which is a good result.

【0067】

FIG. 4 shows the thickness distribution (uniformity of film thickness) of the silicon nitride film formed on one semiconductor substrate. The thickness distribution averages ± 2.0% for 2000 continuously formed films, which is good and stable.

【0068】

FIG. 5 shows the measurement results of particles on the surface of the semiconductor substrate after forming the silicon nitride film. The maximum number of particles detected is 9, and the average value per semiconductor substrate is 3.3, which indicates that the surface of the semiconductor substrate is very clean.

【0069】

[effect]

Other features and effects The present invention relates to an automatic cleaning method and an apparatus for purifying undesired precipitates adhering to the inside of a semiconductor substrate processing apparatus, but is not limited to a film forming method for forming a film on a semiconductor substrate. The explanation is based on the formation of a silicon nitride film according to the plasma CVD method. However, the invention is not limited to the formation of silicon nitride films, including inorganic films of SiO, SiON and SiOF, organic films of fluorinated hydrocarbon polymers, and CVD films such as methylsilane, tetramitylsilane, SiO or SiC films. It may be used for formation.

【0070】

Further, the automatic cleaning method according to the present invention may be applied to a thermal CVD method for forming a W type metal thin film or a high dielectric constant film such as Ta205, and is effective for forming a thin film and cleaning the inside of a processing apparatus. Used for.

【0071】

When cleaning the unwanted precipitates adhering to the inside of the reaction chamber, the surface temperature of the heater supporting the semiconductor substrate in the examples is lowered to 500 ° C. or less, so that aluminum fluoride adheres to the surface of the shower head. Be prevented. Since there is no adhesion of aluminum fluoride to the surface of the shower head, the thin film formation and treatment of the semiconductor substrate is carried out in a state where the quality of the formed film is constant.

【0072】

In the embodiment, since aluminum fluoride does not adhere to the shower head, particles are not generated from the adhered aluminum fluoride, and the semiconductor substrate is not contaminated. Particle contamination is not generated on the semiconductor because the unwanted precipitates adhering to the inside of the reaction chamber are removed by the automatic cleaning sequence. In addition, since aluminum fluoride is not produced, the operating time of the cleaning device is reduced, which makes the thin film forming device highly productive.

【0073】

It will be appreciated that various modifications can be made by those skilled in the art without departing from the idea of the present invention. Therefore, it should be clearly understood that the form of the invention is exemplary only and does not limit aspects of the invention.

[Simple explanation of drawings]

[Figure 1]

FIG. 1 is an example of a thin film forming and processing apparatus according to the present invention.

[Figure 2]

FIG. 2 shows a thin film forming and processing apparatus having a remote plasma discharge chamber.

[Fig. 3]

FIG. 3 shows the measurement result of the thickness of the formed silicon nitride film.

[Fig. 4]

FIG. 4 shows the distribution of the thickness of the silicon nitride film formed on one semiconductor substrate.

[Fig. 5]

FIG. 5 shows the measurement results of particles on the surface of the semiconductor substrate after the formation of the silicon nitride film.

[Explanation of symbols]

1 Thin film forming device 2 Reaction chamber 3 heater 4 shower head 5 duct 6 valve 7 holes 9 Processed object 11 Duct 13 Aluminum nitride plate 17 Duct 18 Gate valve 19 openings 20 holes 21 Conductance control valve 26 Resistive heating element 28 Pressure controller 28a pressure meter 29 axes