JP2013038109A - Removing method of oxide film and batch type semiconductor device manufacturing apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an oxide film removing method capable of increasing the etching amount without reducing the uniformity of etching amount on the wafer surface, and to provide a batch type semiconductor device manufacturing apparatus for use in this method.SOLUTION: A dry etching step including a first step for making hydrogen fluoride and ammonium fluoride react with an oxide film on a silicon wafer surface, and a second step for removing the reaction products produced by this reaction by heating and evaporating at 200-530°C is performed while setting the interval of adjoining silicon wafers to 2-5 mm. The batch type semiconductor device manufacturing apparatus has: a wafer boat comprising an etching chamber, a microwave excitation mechanism, a load lock chamber, and a clean booth and capable of mounting the processed silicon wafers at an interval of 2-5 mm.

Description

  The present invention relates to an oxide film removal method and a batch type semiconductor device manufacturing apparatus, and more particularly to convert a wafer oxide film on a wafer into a volatile substance and remove it in a short time to obtain a wafer with excellent in-plane uniformity. The present invention relates to a method for removing an oxide film and a batch type semiconductor device manufacturing apparatus used for the removal method.

In recent years, with the progress of miniaturization of semiconductor devices, there has been an increasing demand for higher device operation speed, higher integration, and thinner films. At that time, various thin films are formed on a silicon wafer (Si substrate). In such various film forming steps, an oxide film (SiO ₂ film) such as a natural oxide film is formed on the substrate surface as a base. Since the device characteristics deteriorate when the film exists, it is necessary to remove a natural oxide film or the like before the film formation to obtain an active wafer surface and deposit a desired thin film thereon.

  Conventionally, a wet process using hydrofluoric acid or a hydrogen annealing process at a high temperature of about 1000 ° C. has been used to remove the natural oxide film. However, there are problems such as difficulty in penetrating the liquid to the bottom of fine holes and undesired fluorine remaining on the wafer surface. Also, as the processing temperature is lowered and semiconductor devices are miniaturized, dry processing is performed. There is a demand for removal of natural oxide film.

As one of the methods for removing a natural oxide film in such a low-temperature and dry process, a radical containing at least hydrogen and nitrogen trifluoride gas (NF) produced by generating a plasma by high-frequency discharge of a gas containing at least hydrogen atoms. An etching method using ammonium fluoride (NH _x F _y ) generated from a mixture with ₃ gas) as an etching gas is known (see, for example, Patent Documents 1 and 2). In this etching method, a reaction product such as ammonium silicofluoride ((NH ₄ ) ₂ SiF ₆ ) is generated on the substrate surface by reacting the etching gas with a natural oxide film on the substrate surface. A clean substrate surface without an oxide film is obtained by heating to a predetermined temperature for decomposition, evaporation and removal.

  In the case of Patent Document 1, the temperature required for removing the native oxide is 120 to 150 ° C., and the time required for the removal process of the native oxide is just over 30 minutes. However, in order to take out the wafer from which the natural oxide film has been removed, it is necessary to cool to room temperature, and if the waiting time is included, there is a problem that it takes too much time (30 minutes).

  Conventionally, a first step in which an etching gas reacts with an oxide film on the substrate surface, and a second step in which volatile reaction products (volatile substances) generated on the substrate surface by the first step are removed by heating. And a third step of cooling the substrate that has become high temperature in the second step, a fourth step of transferring the substrate to the film forming apparatus, and a fifth step of raising the temperature in the film forming apparatus to the film forming temperature. The oxide film removing process and the film forming process were performed in the above process and the sixth process for forming a film on the substrate in the film forming apparatus. However, when the volatile reaction product in the second step is removed by heating in the fifth step, the second to fourth steps can be omitted. At that time, secondary etching is caused by a gas such as hydrogen fluoride (HF) or ammonium fluoride generated by thermal decomposition of the reaction product at the film formation temperature in the fifth step. There is a possibility that the etching amount of the oxide film can be increased as compared with the conventional method. However, since the uniformity of the etching amount in the substrate surface due to the secondary etching is poor, there is a problem that the yield is deteriorated as compared with the case where the secondary etching does not occur.

JP 2003-133284 A JP 2006-229085 A

An object of the present invention is to solve the above-described problems of the prior art, and it is possible to increase the etching amount without deteriorating the uniformity of the etching amount in the Si substrate (silicon wafer) surface. An object of the present invention is to provide a method for removing an oxide film (SiO ₂ film) including an oxide and a batch type semiconductor device manufacturing apparatus for carrying out this removal method.

  The method for removing an oxide film according to the present invention includes a first step of reacting hydrogen fluoride or ammonium fluoride with an oxide film on a silicon wafer surface, and heating a reaction product generated by the reaction at 200 ° C. to 530 ° C. A method of removing an oxide film by performing a dry etching step having a second step of evaporating and removing the oxide film, and setting the interval between adjacent silicon wafers to 2 mm to 5 mm; It is characterized by carrying out.

  If the heating / evaporation temperature of the product in the second step is less than 200 ° C., there is a problem that the effect of secondary etching cannot be obtained, and if it exceeds 530 ° C., it is difficult to control the etching amount and distribution. There is. Further, if the distance between adjacent silicon wafers is less than 2 mm, the operation is difficult, and if it exceeds 5 mm, the distribution of the etching amount in the wafer surface tends to deteriorate.

  The dry etching step is performed by setting the pressure in the second step to about atmospheric pressure, preferably 0.05 MPa to 0.1 MPa.

  The dry etching step is performed in a film forming apparatus that performs a step of further forming a film on the surface of the silicon wafer from which the oxide film has been removed from the surface. Thereby, there exists an advantage that an apparatus structure can be reduced.

  The batch type semiconductor device manufacturing apparatus of the present invention includes an etching chamber capable of being evacuated, a microwave excitation mechanism for generating reactive species by exciting a reaction gas introduced into the etching chamber, and the etching chamber. The load lock chamber capable of being evacuated and a clean booth connected to the load lock chamber, and as a wafer boat, adjacent silicon wafers to be processed are 2 mm to 5 mm in length. It has an etching apparatus for removing an oxide film on the surface of a silicon wafer, having a wafer boat that can be placed at intervals.

  The batch type semiconductor device manufacturing apparatus of the present invention is also constituted by a chamber that can be evacuated, and as a wafer boat, a wafer boat that can place adjacent wafers of silicon wafers to be processed at intervals of 2 mm to 5 mm. And a high temperature furnace for removing an oxide film on the surface of the silicon wafer.

  The batch type semiconductor device manufacturing apparatus of the present invention further includes an etching chamber that can be evacuated, a microwave excitation mechanism for generating reactive species by exciting a reaction gas introduced into the etching chamber, and the etching chamber. It is composed of a load lock chamber that can be evacuated and a clean booth that is connected to the load lock chamber. As a wafer boat, adjacent wafers of silicon wafers to be processed are 2 mm to 2 mm. It has a wafer boat that can be placed at intervals of 5 mm, and a step of reacting hydrogen fluoride or ammonium fluoride with an oxide film on the surface of the silicon wafer is performed by placing the wafer to be processed on the wafer boat. It has an etching apparatus for removing an oxide film on a silicon wafer surface configured to be able to That.

  The batch type semiconductor device manufacturing apparatus according to the present invention further includes a chamber that can be evacuated, and as a wafer boat, wafers on which adjacent wafers of silicon wafers to be processed can be placed at intervals of 2 mm to 5 mm. A step of removing a reaction product produced by reacting hydrogen fluoride or ammonium fluoride with an oxide film on the surface of a silicon wafer by heating and evaporating at 200 ° C. to 530 ° C. It is characterized by having a high-temperature furnace for removing an oxide film on the surface of a silicon wafer which is configured so that a wafer to be processed can be mounted on a wafer boat.

  The batch type semiconductor device manufacturing apparatus according to the present invention is further configured to perform the first step and the second step of the oxide film removing method.

  According to the present invention, by setting the interval between adjacent wafers to 2 mm to 5 mm, a gas such as hydrogen fluoride gas or ammonium fluoride generated between the wafers by thermal decomposition is caused between the adjacent wafers to the outside of the wafer. Therefore, secondary etching by this gas can be used, and the effect of increasing the etching amount with respect to the oxide film and achieving uniformity within the wafer surface can be achieved.

The typical sectional view of the dry etching apparatus used for the removal method of the oxide film of the present invention. FIG. 2 is a schematic cross-sectional view of a vertical furnace (high temperature furnace) in which a wafer after being etched by the dry etching apparatus 1 shown in FIG. 1 is heated to evaporate a reaction product. It is typical sectional drawing of the wafer boat which mounts a wafer, (a) is typical sectional drawing of the conventional wafer boat, (b) is typical sectional drawing of the wafer boat used by this invention. It is a flowchart for demonstrating the process which performs the removal of the oxide film of this invention using the dry etching apparatus shown in FIG. 1, and the vertical furnace shown in FIG. 2, (a) is a process with a dry etching apparatus, ( b) Processing in a vertical furnace.

According to the embodiment of the method for removing an oxide film according to the present invention, hydrogen fluoride or ammonium fluoride is reacted with an oxide film (SiO ₂ film) such as a natural oxide film on the silicon wafer surface (for example, 20 ° C. To 30 ° C.) A dry etching step having a first step and a second step of removing the reaction product generated by the reaction by heating and evaporation at 200 ° C. or higher, preferably 200 ° C. to 530 ° C. is performed. And the distance between adjacent silicon wafers is set to 2 mm to 5 mm, and / or the pressure in the second step is about atmospheric pressure, preferably 0.05 MPa to 0.1 MPa. And the dry etching process is performed to remove the oxide film.

  The dry etching step can be performed in a film forming apparatus that performs a step of further forming a film on the surface of the silicon wafer from which the natural oxide film has been removed.

As described above, the volatile reaction product is evaporated and removed at 200 ° C. or higher. When various film forming steps after removing an oxide film (SiO ₂ film) such as a natural oxide film are performed at a temperature of 200 ° C. or higher, according to the present invention, volatilization is purposely performed using a high temperature furnace or the like. Even if the step of evaporating the volatile reaction product is not provided, the volatile reaction product can be evaporated in this film forming step. The film deposition apparatus raises the temperature inside the apparatus to the film deposition temperature in advance before film formation and starts film formation in a stable state inside the apparatus. Therefore, volatile reaction products are evaporated in the process of stabilizing the film formation temperature. Can be made. For this reason, after the volatile reaction product is generated, the heat removal step of the product and the film formation step performed at 200 ° C. or higher are continuously performed in the film formation apparatus. It can be shortened as a whole.

  According to the embodiment of the present invention, the process of removing the natural oxide film on the wafer includes (1) hydrogen radicals and / or ammonia obtained by exciting hydrogen gas and / or ammonia gas with microwaves, ICP or heat. Reacting nitrogen fluoride gas to produce ammonium fluoride gas, reacting an etching gas comprising this ammonium fluoride gas with a silicon oxide film to produce ammonium silicofluoride, and (2) ammonium silicofluoride Heating the wafer on which is produced to a predetermined temperature to evaporate ammonium silicofluoride. By using such a process, it is possible to shorten the processing time for removing the oxide film and to improve the in-plane uniformity.

  In the step (1), when using remote plasma, the reaction temperature on the wafer may generally be about 20 ° C. to 30 ° C., preferably about 25 ° C., and if the temperature is higher than 40 ° C., The reaction to produce ammonium silicofluoride is difficult to proceed. When remote plasma is not used, the reaction temperature can be appropriately set according to the plasma to be used. In the step (2), the wafer temperature needs to be 200 ° C. or higher, preferably 200 ° C. to 530 ° C. is sufficient.

FIG. 1 is a schematic cross-sectional view of a dry etching apparatus used in the method for removing an oxide film of the present invention. The apparatus 1 performs, for example, a process of removing a natural oxide film of the silicon wafer 10 in batch units of about 50 sheets, and includes an etching chamber 11 and a reaction gas (N ₂ , NH ₃ ) introduced into the etching chamber. Is composed of a microwave excitation mechanism 12 for generating active species (radicals), a load lock chamber 13 connected to the etching chamber, and a clean booth 14 connected to the load lock chamber. Yes. In the etching chamber 11, a quartz wafer boat 15 (see FIG. 3B) on which silicon wafers 10 to be processed are placed at a predetermined interval is conveyed from the load lock chamber 13 in the drawing, The state of arrangement is shown. A heating means 16 such as a heater is provided on the outer periphery of the etching chamber 11, and a vacuum pump 17 is attached to the etching chamber so that the etching chamber can be evacuated. A vacuum pump 18 for evacuating the room is attached to the load lock chamber 13. A wafer cassette 19 is placed in the clean booth 14, and the wafer cassette is configured to be transported between the clean booth and the load lock chamber by a robot 20.

  FIG. 2 is a schematic cross-sectional view of a vertical furnace in which a wafer after being etched by the dry etching apparatus 1 shown in FIG. 1 is heated to evaporate volatile reaction products. The vertical furnace 2 includes, for example, a chamber 21 (high temperature furnace), a load lock chamber 22 connected to the chamber, and a clean booth 23 connected to the load lock chamber. In the chamber 21, in the drawing, a quartz wafer boat 25 (FIG. 3B) on which silicon wafers 24 to be processed are placed at a predetermined interval is transported from the load lock chamber 22 and arranged. The state is shown. A heating means 26 such as a heater is provided on the outer periphery of the chamber 21, and a vacuum pump 27 is attached to the chamber 21 so that the inside of the chamber can be evacuated. A vacuum pump 28 for evacuating the chamber is attached to the load lock chamber 22. A wafer cassette 29 is placed in the clean booth 23, and the wafer cassette is configured to be transported between the clean booth and the load lock chamber by a robot 30.

  Although the dry etching apparatus and the vertical furnace used in the present invention have been shown and described separately, it is needless to say that these may be combined into one oxide film removing apparatus.

  3A and 3B are schematic cross-sectional views of a quartz wafer boat on which wafers are placed, FIG. 3A shows a conventional wafer boat, and FIG. 3B shows a wafer boat used in the present invention. In FIG. 3A, 31 is a wafer, 32 is a wafer boat, and the interval between adjacent wafers is set to 9 mm. In FIG. 3B, 33 is a wafer and 34 is a wafer boat, and the interval between adjacent wafers is set at an equal interval in the range of 2 mm to 5 mm.

  FIG. 4 shows a process for removing the oxide film of the present invention using the quartz wafer boat shown in FIG. 3B and the dry etching apparatus shown in FIG. 1 and the vertical furnace shown in FIG. This will be described with reference to a flowchart.

  For example, as shown in the flowchart of FIG. 4A, first, the wafer cassette 19 placed in the clean booth 14 of FIG. 1 is transferred to the load lock chamber 13 by the robot 20, and the wafer is transferred to FIG. The quartz wafer boat 15 shown in FIG. 1 is moved to evacuate the load lock chamber to a predetermined pressure (for example, 0.01 to 0.1 Pa). Next, after transferring the wafer boat 15 into the etching chamber 11, when introducing a reaction gas (for example, nitrogen gas, ammonia gas, etc.), a microwave is applied by the microwave excitation mechanism 12 (for 5 to 10 minutes, 1 to 3 kW, preferably 2.8 kW), the excited radical H is introduced into the etching chamber, and the reaction (etching) is performed at a pressure of 200 to 800 Pa and a temperature of 20 to 30 ° C. The amount of reaction gas introduced may generally be 1000-15000 sccm. Further, nitrogen trifluoride as a reaction gas is directly introduced into the etching chamber 11 without passing through the microwave excitation mechanism 12 (generally 2000 to 4000 sccm). The mixing ratio of ammonia gas: nitrogen gas: nitrogen trifluoride gas as a reaction gas is generally 1-2: 1 to 10: 1 to 4, preferably 1 to 2: 4 to 6: 2 to 4. More preferably, the ratio is 2: 6: 3, and the total flow rate is 5 to 10 liters / minute, preferably 7.2 liters / minute. Etching is performed for a predetermined time (5 to 20 minutes) under such conditions.

  In the above etching process, ammonium fluoride is produced in the etching chamber by the reaction of hydrogen radicals obtained by exciting a mixed gas of ammonia gas and nitrogen gas and nitrogen trifluoride gas. By reaction with the upper oxide film, ammonium silicofluoride is formed. This is shown by the following reaction formula.

  After the etching is completed, the introduction of the reaction gas and the microwave application are stopped, and the etching chamber is exhausted. The wafer boat 15 in the etching chamber is transferred into the load lock chamber 13, and the wafer is transferred from this boat to the wafer cassette 19.

  Next, as shown in the flowchart of FIG. 4 (b), the vertical cassette shown in FIG. 2 is used for the wafer cassette 29 on which the wafer with the ammonium silicofluoride obtained on the surface is placed. The wafer 30 is transferred from the clean booth 23 into the load lock chamber 22 by the robot 30, and the wafer is transferred to a quartz wafer boat 25 shown in FIG. 3B. The wafer boat is moved to a predetermined temperature (for example, 200 to 530 ° C.). ) Held in the chamber (high temperature furnace) 21, and then flowing the purge gas such as nitrogen gas into the chamber, the above-mentioned predetermined pressure, predetermined time (5 to 30 minutes), Evaporate. Thereafter, the inside of the chamber 21 is vented, the wafer boat 25 in the chamber is transferred into the load lock chamber 22, the wafer is transferred from this boat to the wafer cassette 29, and this cassette is transferred into the clean booth 23 to form the oxide film. End the removal process. The processing time for all the steps is about 40 to 60 minutes.

  In this embodiment, using the apparatus shown in FIGS. 1 and 2 and the quartz wafer boat shown in FIG. 3B, the natural oxide film on the surface of the silicon wafer is removed according to the flowchart shown in FIGS. 4A and 4B. did. As this wafer boat, a plurality of silicon wafers (for example, 50 wafers), which are configured so that adjacent wafers can be placed at equal intervals of 2 mm, 3 mm, 4 mm and 5 mm, respectively, For comparison, those configured to be placed at equal intervals of 1.5 mm, 5.5 mm, and 10 mm were used.

  First, in a vacuum, for example, at room temperature (20 to 30 ° C.), excitation was performed by applying a microwave to a mixed gas of ammonia gas and nitrogen gas to obtain hydrogen radicals. The hydrogen radical thus obtained is reacted with nitrogen trifluoride gas to generate ammonium fluoride gas. The ammonium fluoride gas as an etching gas and the natural oxide film on the silicon wafer are allowed to react at room temperature (20-30). )) To produce ammonium silicofluoride. At this time, the silicon wafer is exposed to an atmosphere where the mixing ratio of ammonia gas, nitrogen gas, and nitrogen trifluoride gas is 2: 6: 3, the total flow rate is 14.4 liters / minute, and the pressure is 266 Pa, and excited for 8 minutes. The microwave was processed with 2.8 kW input.

  Next, a silicon wafer with ammonium silicofluoride formed on the surface is placed in a chamber of a high-temperature furnace maintained at 200 ° C., the inside of the chamber is set to about atmospheric pressure (0.1 MPa), and treated for 30 minutes. After the ammonium was evaporated, the wafer was taken out.

  The processing time for all the steps was 70 minutes.

  The etching amount of the etched wafer obtained as described above was evaluated by reflection spectroscopy. As a result, when using each wafer boat configured so that adjacent wafers can be placed at intervals of 2 mm, 3 mm, 4 mm, and 5 mm, the etching gas generated between the wafers is transferred from between the wafers to the outside of the wafers. Diffusion to the surface and outflow were suppressed, and an increase in etching amount and in-plane uniformity by secondary etching were realized. On the other hand, when each wafer boat configured so that adjacent wafers can be placed at intervals of 1.5 mm, 5.5 mm, and 6 mm, it is difficult to transfer the wafer to the wafer boat at 1.5 mm. At 5.5 mm and 10 mm, the etching gas generated between the wafers diffuses from between the wafers to the outside of the wafers and flows out as the distance increases, so that the action of secondary etching can be used. Therefore, the increase in etching amount and in-plane uniformity could not be achieved. Therefore, as described above, it has been found that when the interval between adjacent silicon wafers is set to 2 mm to 5 mm, an increase in the etching amount with respect to the oxide film and exceptional uniformity in the wafer surface can be achieved.

(Comparative Example 1)
When the process of Example 1 was repeated except that the secondary etching (second process) was performed in a chamber of a high temperature furnace maintained at 180 ° C., the effect of the secondary etching was not obtained, and 550 When the same process was performed in a chamber of a high-temperature furnace maintained at ℃, it was difficult to control the etching amount and distribution. Thus, the secondary etching is preferably performed at 200 ° C. to 530 ° C.

(Comparative Example 2)
When the pressure in secondary etching: 0.1 MPa was set to 0.1 Pa and the process of Example 1 was repeated, the effect of secondary etching was not observed. This is because evaporated hydrogen fluoride and ammonium silicofluoride are exhausted. Moreover, when it set in 0.2 MPa and it carried out similarly, the target etching was not able to be performed.

  According to the present invention, when an oxide film such as a natural oxide film, which is formed on the wafer surface and causes deterioration of semiconductor device characteristics, is removed, the amount of etching by secondary etching is increased and the in-plane uniformity is achieved. Can be realized. Therefore, since a desired thin film can be deposited on the surface of the active wafer from which the oxide film has been removed, it can be used for various film formations in the semiconductor device field.

1 Dry etching equipment 2 Vertical furnace (chamber)
DESCRIPTION OF SYMBOLS 10 Silicon wafer 11 Etching chamber 12 Microwave excitation mechanism 13 Load lock chamber 14 Clean booth 15 Wafer boat 16 Heating means 17, 18 Vacuum pump 19 Wafer cassette 20 Robot 21 Chamber 22 Load lock chamber 23 Clean booth 24 Silicon wafer 25 Wafer boat 26 Heating means 27, 28 Vacuum pump 29 Wafer cassette 30 Robot 31, 33 Wafer 32, 34 Wafer boat

Claims (8)

A first step of reacting hydrogen fluoride or ammonium fluoride with an oxide film on the silicon wafer surface, and a second step of removing the reaction product generated by the reaction by heating and evaporating at 200 ° C. to 530 ° C. A method of removing an oxide film by performing a dry etching process including: an interval between adjacent silicon wafers is set to 2 mm to 5 mm, and the dry etching process is performed. Removal method. 2. The method for removing an oxide film according to claim 1, wherein the pressure in the second step is set to 0.05 MPa to 0.1 MPa. 3. A method of removing an oxide film, wherein the dry etching process according to claim 1 or 2 is performed in a film forming apparatus for performing a process of further forming a film on a silicon wafer surface from which an oxide film has been removed from the surface. An etching chamber capable of being evacuated; a microwave excitation mechanism for exciting reactive gas introduced into the etching chamber to generate active species; and a load-lock chamber capable of being evacuated and connected to the etching chamber. And a clean booth connected to the load lock chamber, and as a wafer boat, a wafer boat capable of mounting adjacent wafers of silicon wafers to be processed at intervals of 2 mm to 5 mm. A batch type semiconductor device manufacturing apparatus comprising an etching apparatus for removing an oxide film on a surface of a silicon wafer. Oxidation on the silicon wafer surface, which is composed of a chamber that can be evacuated and has a wafer boat that can place adjacent wafers of silicon wafers to be processed at intervals of 2 mm to 5 mm. A batch type semiconductor device manufacturing apparatus comprising a high temperature furnace for removing a film. An etching chamber capable of being evacuated; a microwave excitation mechanism for exciting reactive gas introduced into the etching chamber to generate active species; and a load-lock chamber capable of being evacuated and connected to the etching chamber. A clean booth connected to the load lock chamber, and a wafer boat capable of mounting adjacent wafers of silicon wafers to be processed at intervals of 2 mm to 5 mm. The silicon wafer is configured so that the step of reacting hydrogen fluoride or ammonium fluoride with the oxide film on the surface of the silicon wafer can be performed by placing the wafer to be processed on the wafer boat. A batch type semiconductor device manufacturing apparatus comprising an etching apparatus for removing an oxide film on a surface. It is composed of a chamber that can be evacuated, and has a wafer boat that can place adjacent wafers of silicon wafers to be processed at intervals of 2 mm to 5 mm. The step of removing the reaction product generated by reacting ammonium with the oxide film on the silicon wafer surface by heating and evaporation at 200 ° C. to 530 ° C. is performed by placing the wafer to be processed on the wafer boat. A batch type semiconductor device manufacturing apparatus comprising a high-temperature furnace for removing an oxide film on a silicon wafer surface configured to be capable of performing the same. 3. A batch type semiconductor device manufacturing apparatus configured to perform the first step and the second step of the oxide film removing method according to claim 1.

Images