JP5539302B2 - Carbon film removal method - Google Patents

Description

  The present invention relates to a carbon film removal method, and more particularly to the formation and removal of a carbon film as a cap protection film used for activation annealing after ion implantation used in a SiC wafer process.

  In the SiC wafer process, when ion implantation is performed on the surface layer, a method of activating the implanted ion species by performing an annealing process thereafter is disclosed (for example, Patent Document 1). This annealing treatment requires a heat treatment at 1500 ° C. or higher because it is difficult to diffuse the dopant species in the SiC wafer.

  In the heat treatment at 1500 ° C. or higher, if the annealing process is performed in a state where the surface layer of the SiC wafer is exposed, the electrical characteristics deteriorate due to out-diffusion (outward diffusion) of the dopant species.

  Therefore, before the treatment, a carbon film 4 as a protective film that can withstand heat treatment at 1500 ° C. or higher is formed on the surface of the SiC wafer.

JP 2009-260115 A

  Since the carbon film deposition apparatus for forming a carbon film as described above vaporizes ethanol in a decompressed chamber to form a carbon film, the carbon film is also formed at a location other than the SiC wafer in the apparatus. .

  For this reason, the carbon film adheres to the inner wall of the apparatus. For example, if the film is deposited to a thickness of 1 μm or more, the carbon film on the inner wall is peeled off, and becomes a foreign substance to the carbon film formed on the SiC wafer surface. There was a problem that mixing with the carbon film on the surface of the SiC wafer causes deterioration of the quality of the carbon film. In order to prevent this, it was necessary to periodically remove the carbon film adhered in the apparatus.

  The present invention has been made to solve the above-described problems. In a carbon film deposition apparatus for forming a carbon film on a SiC wafer surface, in order to prevent quality deterioration of the carbon film on the SiC wafer surface, An object of the present invention is to provide a carbon film removing method for properly removing a carbon film adhering to the film.

The carbon film removing method according to the present invention includes: (a) introducing O ₂ gas at 840 to 860 ° C. into the apparatus under reduced pressure in a carbon film deposition apparatus for forming a carbon film on a SiC wafer surface; and b) removing the carbon film adhering to the inside of the apparatus by the introduced O ₂ gas.

According to the carbon film removal method of the present invention, in the carbon film deposition apparatus for forming a carbon film on the surface of the SiC wafer, (a) introducing O ₂ gas at 840 to 860 ° C. into the apparatus under reduced pressure; And (b) removing the carbon film adhering to the inside of the apparatus by the introduced O ₂ gas, thereby appropriately removing the carbon film adhering to the inside of the apparatus, Quality degradation can be prevented.

It is sectional drawing of a SiC wafer. It is a figure which shows the whole structure of a carbon film deposition apparatus. It is a figure which shows the structure of the boat turntable of a carbon film deposition apparatus.

  As a prerequisite technique for the carbon film removal method according to the present invention, carbon film formation, annealing treatment, and the like in the SiC wafer process will be described below.

  First, a SiC wafer as shown in FIG. 1 is prepared. That is, the epitaxial layer 5 is formed on the SiC substrate 1, and the first implanted layer 2 and the second implanted layer 3 in which ions of different conductivity types (for example, P-type) are implanted are formed in the surface layer of the epitaxial layer 5.

  Next, a heat treatment step (annealing step) for activating ions implanted into the first implantation layer 2 and the second implantation layer 3 is entered, but before that, the exposed epitaxial layer 5, the first implantation layer 2, A carbon film 4 for protecting each of the second injection layers 3 is formed.

  The heat treatment step for activating the first implantation layer 2 and the second implantation layer 3 is performed in a temperature region of 1500 ° C. or higher in consideration of difficulty in diffusing dopant species in the SiC wafer. If the heat treatment step is performed with each of the first implantation layer 2 and the second implantation layer 3 being exposed, the electrical characteristics of the SiC wafer are deteriorated due to out-diffusion (outward diffusion) of the dopant species. .

  Therefore, before this treatment, a carbon film 4 as a protective film is formed on the SiC wafer surface. The carbon film can withstand heat treatment at 1500 ° C. or higher.

  For the formation of the carbon film 4, methods such as film formation by plasma CVD and film formation by low pressure CVD are conceivable. However, considering the annealing process at 1500 ° C. or higher in the subsequent process, it is desirable that the film stress of the carbon film 4 is not applied as much as possible.

  When the carbon film is formed by single-wafer plasma CVD, the carbon film is formed only on the upper surface side of the wafer surface. Therefore, the film stress becomes relatively large.

  On the other hand, when the carbon film is formed by batch-type low pressure CVD, the carbon film is uniformly formed on both surfaces of the wafer. Therefore, the film stress becomes relatively small.

  From the above, it can be seen that it is desirable to form a carbon film by batch-type low pressure CVD.

<Embodiment 1>
<Configuration>
A carbon film deposition apparatus for forming a carbon film by batch type low pressure CVD will be described below. The pressure is, for example, 1.2 kPa.

  FIG. 2 shows a specific configuration diagram of a carbon film deposition apparatus. The apparatus is a vertical reduced pressure CVD apparatus in order to suppress the formation of a natural oxide film due to air entrainment. The arrows in the figure schematically show the gas flow.

The SiC substrate 1 is transported into the loading area 11, and the SiC substrate 1 is transferred to the boat in the loading area 11. A side filter 20 (rectifier plate) is installed in the loading area 11 to circulate the atmosphere in the area. Further, in the loading area 11, an N ₂ shower introduction port 21 and an N ₂ introduction port 17 are respectively installed as shown in FIG.

  On the other hand, the back door 18 in the loading area 11 is provided with an intake port 26 and an intake port 27.

  Thereafter, the boat on which the SiC substrate 1 is mounted is inserted into the chamber 12. A manifold 25 having a plurality of valves mounted in parallel is disposed at the bottom of the chamber 12.

Then, after decompression, various processes are performed on the SiC substrate 1 by introducing a gas such as N ₂ , ethanol, or Ar from the gas introduction line 22 connected to the lower portion of the chamber 12.

  As an exhaust side configuration, a sensor mechanism 23, a valve mechanism 14, a dust trap 24, and a pump 15 are provided on an exhaust line 16 from the chamber 12.

  The sensor mechanism 23 includes a pressure sensor, an atmospheric pressure return sensor, and the like, and measures the pressure and the like in the exhaust line 16.

  The valve mechanism 14 includes a plurality of valves of SSV (sub-sub valve), SV (sub-valve), and MV (main valve). When reducing the pressure from the atmospheric pressure, it is desirable to perform evacuation slowly in order to prevent generation of foreign matter. However, by changing and controlling the valve of the valve mechanism 14 as appropriate, evacuation with a gradual change is performed. Realize.

  The dust trap 24 cools the exhaust gas (water-cooled trap). Then, unreacted by-products are removed.

  The pump 15 is directly connected to the loading area 11 in addition to the exhaust line 16, and exhausts the chamber 12 and the loading area 11.

<Operation>
The carbon film deposition apparatus described above vaporizes ethanol in a decompressed chamber to form a carbon film. Therefore, a carbon film is also formed in a portion other than the SiC wafer in the chamber 12.

  For this reason, the carbon film adheres to the inner wall of the chamber 12, and for example, when deposited to 1 μm or more, the carbon film on the inner wall peels off and becomes a foreign substance to the carbon film formed on the surface of the SiC wafer. Is mixed into the carbon film on the surface of the SiC wafer. Therefore, the quality of the carbon film is deteriorated.

In order to suppress the occurrence of such a phenomenon, it is necessary to periodically remove the carbon film attached to the inner wall of the chamber 12. As a removal method, there is a method of burning and removing the carbon film adhering to the inner wall of the chamber 12 by flowing O ₂ gas into the decompressed chamber 12.

  By adopting this method, it is not necessary to physically remove the carbon film by removing the chamber 12, etc., and the film can be removed without lowering the temperature in the chamber 12, so that a significant maintenance time is required. It can be shortened.

However, applying dry cleaning with O ₂ gas (hereinafter referred to as O ₂ cleaning) causes other problems.

In the O ₂ cleaning, O ₂ is generated by thermal decomposition of ethanol introduced into the chamber 12, but aldehyde and the like are also generated in this process.

This aldehyde or the like adheres to SUS (stainless steel) material, Cu material, etc. constituting the equipment provided in the chamber 12, and further reacts with O ₂ to generate carboxylic acids such as formic acid and acetic acid. End up.

  As the carboxylic acid is generated, the attached SUS material, Cu material and the like are corroded. Rust generated by this corrosion accumulates in the chamber 12 and is mixed into the carbon film when the carbon film is formed on the surface of the SiC wafer. This mixing causes deterioration of the quality of the carbon film.

Here, the O ₂ cleaning is performed by introducing a high-temperature O ₂ gas into the chamber 12, and the corrosion rate of the SUS material, the Cu material, etc. is accelerated as the temperature of the O ₂ gas is higher. .

On the other hand, the rate at which the carbon film adhering to the inner wall of the chamber 12 is removed by combustion increases as the O ₂ gas temperature increases.

When O ₂ gas was introduced at a temperature of 900 to 1000 ° C., corrosion of the SUS material in the exhaust line 16 was accelerated. The acceleration decreased to a certain level when the temperature of the O ₂ gas was decreased to 840 to 860 ° C.

  Further, when removing the carbon film adhering to the inner wall of the chamber 12 in a processing time of about 1 hour, the highest possible temperature must be maintained. If an attempt is made to remove the carbon film at a temperature below 840 ° C., the possibility that a carbon film that cannot be completely removed will increase.

Therefore, by setting the temperature of the O ₂ gas to be introduced to 840 to 860 ° C., the carbon film adhering to the inner wall of the chamber 12 can be removed in a short time while suppressing the corrosion of the SUS material, the Cu material and the like. . The etching rate is, for example, 15 to 20 nm / min.

<Measures against corrosion>
It is desirable to remove the carbon film by the above O ₂ cleaning and to take measures against corrosion in the apparatus configuration.

FIG. 3A shows a state in which red rust (shaded portion) is generated after the O ₂ cleaning is performed on the boat turntable 100 made of SUS material that has been installed at the bottom of the boat of the carbon film deposition apparatus.

In the rust, 5 × 10 ¹¹ atms / cm ² of Cu was detected by heavy metal contamination evaluation using total reflection fluorescent X-ray.

  For this reason, it is desirable that the boat turntable 100 be quartzized.

  Further, in the configuration around the boat turntable as shown in FIG. 3B, the magnetic seal 101 and the magnetic seal coupling 102 are arranged at the lower part of the boat turntable 100.

  Among these, it is desirable to remove also the shaft part of the magnetic seal 101 which is a member using Cu.

  Here, the magnetic seal 101 is a boat rotation mechanism that improves the film thickness uniformity of the carbon film formed on the surface of the SiC wafer.

In addition, the sensor mechanism 23 disposed in the exhaust line 16 of the carbon film deposition apparatus is specifically connected to the port from the exhaust line 16, and O ₂ cleaning is performed when a sealing material (sealing material) to be connected is made of metal. There is a risk of corrosion later.

  Therefore, it is desirable that these sealing materials are made of a synthetic rubber material (for example, Viton (registered trademark) or Kalrez material (registered trademark)).

Furthermore, when the dust trap 24 (water-cooled trap) installed in the exhaust line 16 is installed downstream of the exhaust port of the chamber 12, the metal surface inside the trap (particularly where the cooling water flows) is obtained by performing O ₂ cleaning. Will corrode and rust. This is probably because water contained in ethanol dewed in the water-cooled trap and was oxidized by O ₂ cleaning to become rust.

  The rust is reversely diffused when the chamber 12 is returned to the atmospheric pressure, adheres to the surface of the SiC wafer installed in the chamber 12, and is mixed into the carbon film.

  For this reason, it is desirable that the water-cooled trap be installed after the main valve (MV) that is closed when the chamber 12 returns to the atmospheric pressure, that is, downstream, so that rust generated in the trap does not reversely diffuse into the chamber 12.

Moreover, even if the structure in the exhaust line 16 of the apparatus and the manifold 25 arranged at the lower part of the chamber 12 are made of carbon, corrosion during O ₂ cleaning can be prevented even if it is made of SUS material. This is because the exhaust line 16 and the manifold 25 are kept at a lower temperature than the inside of the chamber 12 even during O ₂ cleaning, so that the carbon coating is not removed.

<Effect>
According to the embodiment of the present invention, in the carbon film removal method, in the carbon film deposition apparatus for forming the carbon film 4 on the surface of the SiC wafer, (a) O ₂ gas at 840 to 860 ° C. is applied under reduced pressure. And (b) removing the carbon film 4 adhered to the inside of the apparatus by the introduced O ₂ gas, so that the carbon film deposited and deposited in the apparatus is deposited on the surface of the SiC wafer. It can suppress mixing as a foreign material in the carbon film to form. That is, the carbon film adhering to the inside of the apparatus can be appropriately removed by the removal method, and the quality deterioration of the carbon film on the surface of the SiC wafer can be prevented.

  Further, according to the removal method, it is not necessary to physically remove the carbon film attached to the apparatus by removing the chamber 12, and the film can be removed without lowering the temperature in the chamber 12. Therefore, the maintenance time can be greatly shortened.

Further, according to the embodiment of the present invention, in the carbon film removing method, the configuration (boat turntable 100 or the like) in the carbon film deposition apparatus is formed of quartz, so that the apparatus can be used for O ₂ cleaning. It is possible to prevent corrosion of the structure in the apparatus by adhering aldehyde and the like produced therein and further producing carboxylic acid. Therefore, it is possible to suppress the rust formed by the corrosion from being mixed into the carbon film on the surface of the SiC wafer and to form a high quality carbon film.

  In addition, according to the embodiment of the present invention, in the carbon film removal method, the carbon film deposition apparatus has a rotating mechanism (magnetic seal) for placing an SiC wafer for improving the in-plane uniformity of the carbon film 4. 101) is not provided, metal portions used for the rotating mechanism are eliminated, and rust caused by corrosion of the portions can be prevented from deteriorating the quality of the carbon film on the surface of the SiC wafer.

  Further, according to the embodiment of the present invention, in the carbon film removal method, the carbon film deposition apparatus further includes the sensor mechanism 23 as a measuring instrument in the exhaust line 16, and the sensor mechanism 23 is a synthetic rubber material (Viton). (Registered trademark), Kalrez material (registered trademark), etc.) are connected to the exhaust line 16 as a sealing material, so that no metal is used at the connection location. It is possible to suppress the reverse diffusion during the return to the atmospheric pressure and the deterioration of the quality of the carbon film on the surface of the SiC wafer.

  Further, according to the embodiment of the present invention, in the carbon film removal method, the carbon film deposition apparatus further includes a water-cooled trap and an MV in the exhaust line 16, and the water-cooled trap that takes in a reaction byproduct in the exhaust line 16 is provided. The MV that is closed when the pressure in the carbon film deposition apparatus is returned to the atmospheric pressure is arranged downstream of the exhaust line, so that when the chamber 12 is returned to the atmospheric pressure, the MV installed upstream of the water-cooled trap is By closing, it is possible to prevent the rust generated in the water-cooled trap from back-diffusing into the chamber 12. Therefore, it is possible to suppress the diffusion of rust in the chamber 12 and to suppress the quality deterioration of the carbon film on the surface of the SiC wafer.

Further, according to the embodiment of the present invention, in the carbon film removal method, the structure in the exhaust line 16 of the carbon film deposition apparatus is coated with carbon, so that the piping in the exhaust line 16 is made of SUS material. Even in this case, corrosion and rust are suppressed during O ₂ cleaning, and deterioration of the quality of the carbon film on the surface of the SiC wafer due to back diffusion from the exhaust line 16 is suppressed.

The piping in the exhaust line 16 is kept at a lower temperature than in the chamber 12, so that the carbon film is not removed even during O ₂ cleaning. That is, the coated carbon film is not peeled off, and the quality of the carbon film on the SiC wafer surface is not deteriorated.

Moreover, according to the embodiment of the present invention, in the carbon film removal method, the carbon film deposition apparatus further includes the manifold 25 at the lower portion of the chamber 12 for introducing the O ₂ gas, and the manifold 25 is coated with carbon. Therefore, even when the manifold 25 is made of SUS material, corrosion during O ₂ cleaning and rusting are suppressed, and deterioration of the quality of the carbon film on the surface of the SiC wafer is suppressed. The

Since the manifold 25 is kept at a lower temperature than in the chamber 12, the carbon film is not removed even during O ₂ cleaning. That is, the coated carbon film is not peeled off, and the quality of the carbon film on the SiC wafer surface is not deteriorated.

  It should be noted that the present invention can be modified or omitted in any constituent elements in the present embodiment within the scope of the invention.

  DESCRIPTION OF SYMBOLS 1 SiC substrate, 2 1st injection layer, 2nd injection layer, 4 Carbon film, 5 Epitaxial layer, 11 Loading area, 12 Chamber, 14 Valve mechanism, 15 Pump, 16 Exhaust line, 17 Inlet, 18 Back door, 20 side filter, 21 inlet, 22 gas inlet line, 23 sensor mechanism, 24 dust trap, 25 manifold, 26 air inlet, 27 intake, 100 boat turntable, 101 magnetic seal, 102 magnetic seal coupling.

Claims (7)

In a carbon film deposition apparatus that forms a carbon film on the SiC wafer surface,
(A) introducing O ₂ gas at 840 to 860 ° C. into the apparatus under reduced pressure;
(B) a step of removing the carbon film adhered in the apparatus by the introduced O ₂ gas,
Carbon film removal method. The structure in the carbon film deposition apparatus is formed of quartz,
The carbon film removal method according to claim 1. The carbon film deposition apparatus does not include a rotation mechanism for placing the SiC wafer for improving in-plane uniformity of the carbon film,
The carbon film removal method according to claim 1 or 2. The carbon film deposition apparatus further comprises a measuring instrument in the exhaust line;
The measuring instrument is connected to the exhaust line by a synthetic rubber material,
The carbon film removal method according to claim 1 or 2. The carbon film deposition apparatus further comprises a water-cooled trap and a main valve in the exhaust line,
The water-cooled trap is disposed downstream of the exhaust line of the main valve that closes when returning the pressure in the carbon film deposition apparatus to atmospheric pressure,
The carbon film removal method according to claim 1 or 2. The structure in the exhaust line of the carbon film deposition apparatus is coated with carbon,
The carbon film removal method according to claim 1 or 2. The carbon film deposition apparatus further includes a manifold at a lower portion of the chamber for introducing the O ₂ gas,
The manifold is coated with carbon,
The carbon film removal method according to claim 1 or 2.

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