JP6221592B2 - Manufacturing method of semiconductor device - Google Patents

Description

  The present invention relates to a method for manufacturing a semiconductor device.

Conventionally, as a method for forming a silicon oxide film on the surface of a semiconductor made of silicon carbide (SiC), a thermal oxidation method generally used in a semiconductor made of silicon (Si) has been applied. When silicon carbide is thermally oxidized, an interface state is generated at the interface between the silicon oxide film and the silicon carbide due to the influence of carbon contained in the silicon carbide, and there is a problem that the carrier mobility in the silicon carbide is lowered. is there.
As a technique for solving this problem, oxidation is performed by supplying an oxidizing gas while maintaining the temperature at a desired temperature, while the inside of the oxidation furnace is maintained at the time of temperature increase until reaching the desired temperature and at the time of temperature decrease after oxidation. A method of making an inert gas atmosphere is known (for example, see Patent Document 1). According to the method described in Patent Document 1, since oxidation is performed only at a desired temperature, dangling bonds and residual carbon in the oxide film can be reduced. Thereby, the interface state density (Dit) between the semiconductor made of silicon carbide and the oxide film can be reduced.

JP 2003-031571 A

  When a thermal oxide film is formed on a silicon carbide material, a heat history due to temperature and time is applied to the silicon carbide material because heat treatment at a high temperature is required. Here, in the method described in Patent Document 1, the time during which the oxidation reaction is actually performed is the time during which the oxidizing gas is supplied after reaching the desired temperature, but until the desired temperature is reached. There is also a time zone in which the silicon carbide material is at a high temperature even when the temperature is raised and when the temperature is lowered after the oxidation reaction. As a result, the time of the high temperature state becomes longer than the time of the oxidation reaction.

For this reason, there are problems that the surface of the silicon carbide material becomes rough and crystal defects of the silicon carbide material progress. This leads to deterioration in the interface state density between the silicon carbide semiconductor and the gate insulating film and an increase in leakage current between the source and drain of a MOSFET such as a voltage controlled transistor. In a semiconductor device in which a transistor and a diode are integrated into one device, a thermal history is also generated at the interface with the silicon carbide material that forms the electrode of the diode due to the high-temperature treatment process for the transistor that forms the gate insulating film. Therefore, the leakage current increases more remarkably.
In view of the above problems, the present invention can reduce the time during which a silicon carbide material is exposed to a high temperature when forming an insulating film on the surface of the silicon carbide material. An object of the present invention is to provide a method of manufacturing a semiconductor device that can prevent the progress of the above.

  According to one aspect of the present invention, when forming an insulating film on the surface of a silicon carbide material, the gist is to raise the temperature while supplying an active gas to the surface of the silicon carbide material during a temperature rising period.

  According to the present invention, when the insulating film is formed on the surface of the silicon carbide material, the time during which the silicon carbide material is exposed to a high temperature can be shortened, and the surface roughness of the silicon carbide material and the progress of crystal defects are prevented. It is possible to provide a method for manufacturing a semiconductor device that can be used.

It is sectional drawing which shows an example of a structure of the furnace which concerns on embodiment of this invention. It is a timing chart which shows the procedure of the formation method of the insulating film which concerns on embodiment of this invention. FIGS. 3A and 3B are timing charts showing the procedure of the insulating film forming method according to the comparative example. FIG. 4A to FIG. 4C are timing charts showing the procedure of the insulating film forming method according to the embodiment of the present invention. FIG. 5A to FIG. 5C are timing charts showing the procedure of the insulating film forming method according to the embodiment of the present invention. It is process sectional drawing which shows an example of the manufacturing method of the semiconductor device which concerns on embodiment of this invention. FIG. 7 is a process cross-sectional view subsequent to FIG. 6, illustrating an example of a method for manufacturing a semiconductor device according to an embodiment of the present invention. FIG. 8 is a process cross-sectional view subsequent to FIG. 7, illustrating an example of a method for manufacturing a semiconductor device according to an embodiment of the present invention. FIG. 9 is a process cross-sectional view subsequent to FIG. 8 illustrating an example of the method for manufacturing the semiconductor device according to the embodiment of the present invention. FIG. 10 is a process cross-sectional view subsequent to FIG. 9 illustrating an example of the method for manufacturing the semiconductor device according to the embodiment of the present invention. FIG. 11 is a process cross-sectional view subsequent to FIG. 10 illustrating an example of the method for manufacturing the semiconductor device according to the embodiment of the present invention. FIG. 12 is a process cross-sectional view subsequent to FIG. 11 illustrating an example of the method for manufacturing the semiconductor device according to the embodiment of the present invention. FIG. 13 is a process cross-sectional view subsequent to FIG. 12 illustrating an example of the method for manufacturing the semiconductor device according to the embodiment of the present invention. FIG. 14 is a process cross-sectional view subsequent to FIG. 13 illustrating an example of the method for manufacturing the semiconductor device according to the embodiment of the present invention. FIG. 15 is a process cross-sectional view subsequent to FIG. 14 illustrating an example of the method for manufacturing the semiconductor device according to the embodiment of the present invention. It is sectional drawing which shows an example of a structure of the semiconductor device which concerns on the 1st modification of embodiment of this invention. It is process sectional drawing which shows an example of the manufacturing method of the semiconductor device which concerns on the 1st modification of embodiment of this invention. FIG. 18 is a process cross-sectional view subsequent to FIG. 17 illustrating an example of the method for manufacturing the semiconductor device according to the first modification example of the embodiment of the present invention; FIG. 19 is a process cross-sectional view subsequent to FIG. 18 illustrating an example of the method for manufacturing the semiconductor device according to the first modification example of the embodiment of the present invention. FIG. 20 is a process cross-sectional view subsequent to FIG. 19 illustrating an example of the semiconductor device manufacturing method according to the first modification example of the embodiment of the present invention; FIG. 21 is a process cross-sectional view subsequent to FIG. 20 illustrating an example of the method for manufacturing the semiconductor device according to the first modification example of the embodiment of the present invention. FIG. 22 is a process cross-sectional view subsequent to FIG. 21, illustrating an example of a method for manufacturing a semiconductor device according to a first modification example of the embodiment of the present invention. FIG. 23 is a process cross-sectional view subsequent to FIG. 22 illustrating an example of the method for manufacturing the semiconductor device according to the first modification example of the embodiment of the present invention. FIG. 24 is a process cross-sectional view subsequent to FIG. 23 illustrating an example of the method for manufacturing the semiconductor device according to the first modification example of the embodiment of the present invention. FIG. 25 is a process cross-sectional view subsequent to FIG. 24 illustrating an example of the method for manufacturing the semiconductor device according to the first modification example of the embodiment of the present invention. It is sectional drawing which shows an example of a structure of the semiconductor device which concerns on the 2nd modification of embodiment of this invention. It is process sectional drawing which shows an example of the manufacturing method of the semiconductor device which concerns on the 2nd modification of embodiment of this invention. FIG. 28 is a process cross-sectional view subsequent to FIG. 27, illustrating an example of a method for manufacturing a semiconductor device according to a second modification example of the embodiment of the present invention. FIG. 29 is a process cross-sectional view subsequent to FIG. 28 illustrating an example of the method for manufacturing the semiconductor device according to the second modification example of the embodiment of the present invention; FIG. 30 is a process cross-sectional view subsequent to FIG. 29 illustrating an example of the method for manufacturing the semiconductor device according to the second modification example of the embodiment of the present invention; FIG. 31 is a process cross-sectional view subsequent to FIG. 30 illustrating an example of the method for manufacturing the semiconductor device according to the second modification example of the embodiment of the present invention. It is sectional drawing which shows an example of a structure of the semiconductor device which concerns on the 3rd modification of embodiment of this invention. It is sectional drawing which shows another example of a structure of the semiconductor device which concerns on the 3rd modification of embodiment of this invention. 34 (a) and 34 (b) are timing charts showing a procedure of an insulating film forming method according to another embodiment of the present invention.

  Next, embodiments of the present invention will be described with reference to the drawings. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. In the embodiment of the present invention, the “first conductivity type” and the “second conductivity type” are opposite conductivity types. That is, if the first conductivity type is n-type, the second conductivity type is p-type. If the first conductivity type is p-type, the second conductivity type is n-type. In the following description, the first conductivity type is n-type and the second conductivity type is p-type. However, the first conductivity type may be p-type and the second conductivity type may be n-type. When the n-type and the p-type are switched, the polarity of the applied voltage is also reversed. In the embodiment of the present invention, the symbols “+” and “−” indicate the relative high density and low density of the introduced impurities.

[Configuration of furnace]
First, an example of a furnace (oxidation furnace) used in the method for forming an insulating film of a silicon carbide semiconductor according to an embodiment of the present invention will be described.

  As shown in FIG. 1, an oxidation furnace according to an embodiment of the present invention includes a reaction tube 101 having a substantially cylindrical shape and a door 110 that can be opened and closed at one end, and a heater 102 provided around the reaction tube 101. A boat 103 that holds a plurality of SiC substrates 104 and is introduced into the reaction tube 101, gas supply tubes 105 a to 105 c provided at the other end of the reaction tube 101, and gas supply tubes 105 a to 105 c Gas valves 106 a to 106 c provided respectively, and an exhaust pipe 107 provided in the vicinity of one end of the reaction tube 101 are provided. The exhaust pipe 107 is connected to the exhaust pump 108.

The gas supply pipe 105 a appropriately supplies an inert gas such as nitrogen (N ₂ ) gas or argon (Ar) to the reaction pipe 101. The gas supply pipe 105 b appropriately supplies an active gas such as oxygen (O ₂ ) gas, water vapor, or a mixed gas thereof to the reaction pipe 101. The gas supply pipe 105 c appropriately supplies an active gas containing nitrogen such as nitric oxide (NO) gas, nitrous oxide (N ₂ O) gas, or ammonia (NH ₃ ) gas to the reaction pipe 101.

  The gas supplied from the gas supply pipes 105a to 105c is pushed out of the system through the exhaust pipe 107 by the gas supplied from the gas supply pipes 105a, and the gas replacement is sequentially performed. Therefore, the exhaust pump 108 is not necessarily required. Although not shown, temperature measurement sensors such as thermocouples are provided at several locations inside the reaction tube 101 so that the temperature inside the reaction tube 101 can be measured.

[Method of forming insulating film]
Next, an example of a method for forming an insulating film on the surface of the silicon carbide material according to the embodiment of the present invention will be described. As shown in FIG. 2, the method for forming an insulating film according to the embodiment of the present invention includes a temperature raising step (first step) at times t1 to t2, and a temperature holding step (second step) at times t2 to t3. ), And three steps of a temperature lowering step (third step) at times t3 to t4.

  In the temperature raising process at times t1 to t2, an insulating film is formed on the surface of the silicon carbide material while raising the silicon carbide material to a desired temperature. In the temperature holding process at times t2 to t3, nitriding treatment is performed on the interface between the silicon carbide material and the insulating film while holding the silicon carbide material at a desired temperature. In the temperature lowering process at times t3 to t4, nitriding is performed in the same manner as the temperature holding process while lowering the temperature from a desired temperature.

  Here, an insulating film forming method according to a comparative example will be described first with reference to FIGS. 3A and 3B. In FIG. 3A, there are three steps: a temperature raising step at times t101 to t102, a temperature holding step at times t102 to t103, and a temperature lowering step at times t103 to t104.

In the temperature raising process at times t101 to t102, the temperature is raised while supplying N ₂ gas into the furnace. When the desired temperature is reached at time t102, the supply of N ₂ gas is stopped. In the temperature holding process at times t102 to t103, O ₂ gas is supplied into the furnace to form an insulating film (oxide film) on the surface of the silicon carbide material. After the formation of the insulating film having a desired thickness, the supply of O ₂ gas is stopped at time t103. In the temperature lowering process from time t103 to t104, the temperature is lowered while supplying N ₂ gas into the furnace. FIG. 3B is different from FIG. 3A in that N ₂ O gas is supplied instead of O ₂ gas in the temperature holding process at times t102 to t103. In this case as well, an insulating film is formed by supplying N ₂ O gas.

  In the comparative example shown in FIG. 3A and FIG. 3B, oxidation is performed only in the temperature holding process from time t102 to t103 after reaching a desired temperature. For this reason, in addition to the time in the high temperature state in the temperature holding process at times t102 to t103, the time in the high temperature state in the temperature raising process at times t101 to t102 and the temperature lowering process at times t103 to t104 becomes longer.

  Next, regarding the method for forming an insulating film according to the embodiment of the present invention, details of the temperature raising step (first step), the temperature holding step (second step), and the temperature lowering step (third step) are described. Each will be explained. Hereinafter, an oxide film will be described as an example of the insulating film, but the type of the insulating film is not particularly limited thereto.

[Temperature raising process]
First, the temperature raising process at times T11 to T13 will be described with reference to FIG. A silicon carbide material is charged into the furnace at a temperature Ta in the range of room temperature to several hundred degrees. At time t11, temperature rise and introduction of inert gas are started. As the inert gas, N ₂ gas or Ar gas can be used. At times t11 to t12, the silicon carbide material is raised to a temperature Tb (about 1000 ° C.) in an inert gas atmosphere. Unlike silicon materials, silicon carbide materials are hardly oxidized up to about 1000 ° C. Therefore, it is preferable that the temperature of the silicon carbide material is increased only in an inert gas atmosphere up to about 1000 ° C. in that unnecessary traps are not formed at the interface.

  In addition, although the temperature increase rate of a furnace is based on the performance of a furnace, in order to reduce a thermal history as much as possible, it is preferable to raise temperature in a short time. In addition, regarding the rate of temperature rise and fall of the furnace, it is necessary to consider thermal distortion due to rapid temperature changes.

At time t12, the introduction of the O ₂ gas that is the active gas is started while continuing the introduction of the inert gas. As the active gas, in addition to O ₂ gas, water vapor, a mixture of water vapor and O ₂ gas, NO gas, N ₂ O gas, or the like can be used. The temperature Tb is equal to or higher than the temperature at which the silicon carbide material can be oxidized, for example, and can be set as appropriate. Incidentally, may initiate the introduction of the O ₂ gas at the timing when reaching the time t12 to a predetermined without the predetermined temperature Tb, the O ₂ gas when a predetermined time t12 without set temperature Tb in advance Introduction may begin.

  From time t12 to t13, the temperature is raised to about 1200 ° C., which is a desired temperature Tc, in a mixed gas atmosphere of active gas and inert gas. At time t12 to t13, an insulating film (oxide film) is formed on the surface of the silicon carbide material by using an active gas atmosphere. The insulating film can be formed with a thickness of about 1 nm to 1 μm, for example. In addition, an insulating film can be formed in the furnace at normal pressure or reduced pressure.

  By forming the insulating film at the time of temperature rise from time t12 to time t13, the oxidation time required after time t13 can be completely omitted or reduced. Therefore, the heat history by the high temperature area | region of the temperature holding process of the time t13-t14 can be reduced. In addition, if an insulating film having a desired film thickness is formed at the time of temperature increase from time t12 to t13, only the nitriding treatment may be performed after time t13, and the time for the insulating film forming process can be shortened.

Further, the oxidation rate of the active gas is higher for O ₂ gas or water vapor than for N ₂ O gas or NO gas. By using a gas having a higher oxidation rate than the gas used after time t13 at the time of temperature increase from time t12 to t13, the insulating film formed at the time of temperature increase from time t12 to t13 can be thickened in a short time. Thus, an insulating film having a desired film thickness can be formed before the temperature holding process at times t13 to t14. For example, among the three steps, the thickness of the insulating film formed in the temperature raising step at times t12 to t13 can be maximized.

  Further, in consideration of the performance of the furnace and a desired temperature, the insulating film is formed with a desired thickness by adjusting the temperature at which the active gas is introduced and the flow rate ratio (mixing ratio) of the active gas and the inert gas. be able to. The flow rate ratio can be adjusted by increasing or decreasing the active gas. As for the flow rate ratio, if the flow rate of the active gas is increased, the oxidation rate increases, and if it is decreased, the oxidation rate decreases. Also, the higher the furnace temperature, the higher the oxidation rate.

Incidentally, as shown in FIG. 4 (b), as the active gas at time t12 to t13, or by using _{N 2} O gas instead of using an _{O 2} gas.

Further, as shown in FIG. 4C, the insulating film is not formed unless the temperature rises to around 1000 ° C., but O ₂ gas is introduced from the start of the temperature raising process at time t11, and the temperature at time t12 is reached. The introduction of O ₂ gas may be continued after the holding step.

Further, as shown in FIG. 5A, after forming an insulating film using O ₂ gas as the active gas at times t12 to t13, the active gas is switched to N ₂ O gas or water vapor at times t13 to t14. Also good. As described above, the section in which the oxidation is performed in the temperature raising step may be a plurality of sections in which different active gases are sequentially introduced.

[Temperature holding process]
Next, an example of the temperature holding process at times t13 to t14 will be described with reference to FIG. In the temperature holding process at time t13 to t14, nitriding treatment is performed by introducing an active gas containing nitrogen mainly for the purpose of removing dangling bonds existing at the interface between the silicon carbide material and the insulating film and residual carbon. I do. As the active gas containing nitrogen, NO gas, N ₂ O gas, NH ₃ gas, or the like can be used. In addition, the progress of the nitriding treatment can be adjusted by using a mixed atmosphere of an active gas containing nitrogen and an inert gas. As the inert gas, N ₂ gas or Ar gas can be used.

  In FIG. 4A, the temperature Tc at the end of the temperature raising process at time t13 is increased to 1200 ° C., and the temperature Tc is held for a predetermined time in the temperature holding process from time t13 to t14. The temperature Tc is set to a temperature at which nitriding can be performed, and is preferably about 1000 ° C. to 1400 ° C., for example. When the temperature is less than 1000 ° C., the silicon carbide material and the reactive species hardly react. On the other hand, when the temperature is raised to 1200 ° C. to 1300 ° C., the reaction rate is improved and nitriding can be performed in a short time. However, when the temperature exceeds 1400 ° C., the oxide film is sublimated.

  What is necessary is just to adjust the time of the temperature holding process of time t13-t14 with the desired thickness of an insulating film. If the flow rate ratio of the active gas containing nitrogen to the inert gas is increased, the reaction increases, so that the nitriding time can be shortened.

If a gas containing oxygen such as NO or N ₂ O gas is used as the active gas containing nitrogen, the insulating film can be formed following the temperature raising step in parallel with the nitriding treatment. For this reason, it is necessary to consider the film thickness of the insulating film formed after time t13 in addition to the film thickness of the insulating film formed in the temperature raising process from time t12 to t13. The temperature of the oxidation reaction is preferably about 1000 ° C to 1400 ° C. When the temperature is less than 1000 ° C., the silicon carbide material and the reactive species hardly react. When the temperature exceeds 1400 ° C., the oxide film is sublimated.

In the temperature holding process, a plurality of nitriding treatments using different active gases may be sequentially performed. For example, as shown in FIG. 5B, after introducing N ₂ O gas at times t13 to t14, it may be switched to NO gas and introduced at times t14 to t15.

[Cooling process]
Next, the temperature lowering process from time t14 to t16 will be described with reference to FIG. Following the temperature holding process at times t13 to t14 in FIG. 4A, nitriding treatment can be performed also in the temperature lowering process at times t14 to t16.

Since the holding temperature Tc in the temperature holding process at times t13 to t14 is set to 1200 ° C., sufficient nitriding treatment is possible even during the temperature drop from 1200 ° C. From time t14 to t15, nitriding is performed in a mixed atmosphere of an active gas containing nitrogen and an inert gas. As the active gas containing nitrogen, NO gas, N ₂ O gas, NH ₃ gas, or the like can be used. As the inert gas, N ₂ gas or Ar gas can be used. As described above, since the nitriding treatment can be performed in the temperature lowering process from time t14 to t15 together with the temperature holding process from time t13 to t14, the heat history is reduced by shortening the time of the nitriding treatment from time t13 to t14. can do.

  At time t14, for example, when the temperature Tb reaches about 1000 ° C., the introduction of the active gas is stopped. And in time t14-t15, temperature is dropped only by an inert gas atmosphere. The temperature Tb when the introduction of the active gas is stopped at the time t14 is the same temperature as the temperature Tb when the introduction of the active gas at the time t12 is started, but is different from the temperature Tb at the time t12 (time). The temperature may be higher or lower than the temperature Tb at t12. Further, the introduction of the active gas may be stopped at a timing when the predetermined temperature Tb is reached without setting the time t14 in advance, or the temperature Tb is not set in advance, and the active gas is discharged at a certain time t14. The introduction may be stopped.

  Note that in the case where an insulating film having a desired thickness can be formed in the temperature raising process at time t12 to t13, the nitriding treatment can be already performed from the temperature raising process at time t12 to t13, and the processing time is further shortened. be able to.

Further, as shown in FIG. 4 (c), it may be introduced active gas containing nitrogen, such as N _{2 O} gas in the entire period of the cooling step time t13 to t14.

Further, as shown in FIG. 5 (b), at time t14 to t15, as an inert gas including nitrogen, may be used NH ₃ gas in place of _{N 2} O gas.

For example, as shown in FIG. 5C, nitriding treatment with NH ₃ gas may be performed at times t15 to t16 after nitriding treatment with NO gas at times t14 to t15. In this way, a plurality of nitriding treatments may be combined.

[Semiconductor device]
Next, a voltage-controlled transistor having a gate insulating film (gate oxide film) will be described below as an example of a semiconductor device having an insulating film formed by the method for forming an insulating film according to an embodiment of the present invention.

As shown in FIG. 6, the semiconductor device according to the embodiment of the present invention includes a base 1 made of n ⁺ type silicon carbide, and a drift region 2 made of n ⁻ type silicon carbide formed on base 1. , P-type well region 3 formed on drift region 2, n ⁺ -type source region 4 formed on well region 3, and provided in part of source region 4, well region 3 and drift region 2. A gate insulating film 6 formed on the surface of the groove 5 and a gate electrode 7 embedded in the groove 5 via the gate insulating film 6 are provided. An interlayer insulating film 8 is formed on the gate electrode 7. A source electrode 10 is formed on the source region 4. A drain electrode 9 is formed on the back surface of the substrate 1.

  The semiconductor device according to the embodiment of the present invention functions as a transistor by controlling the potential of the gate electrode 7 with a positive potential applied to the drain electrode 9 with the potential of the source electrode 10 as a reference. That is, when the voltage between the gate electrode 7 and the source electrode 10 is set to a predetermined threshold voltage or higher (forward voltage), an inversion layer serving as a channel is formed in the well region 3 located on the side surface of the gate electrode 7 and is turned on. A current flows between the drain electrode 9 and the source electrode 10.

  On the other hand, when the voltage between the gate electrode 7 and the source electrode 10 is set to a predetermined threshold voltage or less (reverse voltage), the inversion layer of the well region 3 disappears and is turned off, and the current between the drain electrode 9 and the source electrode 10 is reduced. Is cut off.

  Next, an example of a method for manufacturing a semiconductor device including the method for forming an insulating film according to the embodiment of the present invention will be described with reference to FIGS.

(A) First, as shown in FIG. 7, a drift region 2 that is an epitaxial growth layer made of n ⁻ type silicon carbide is formed on a substrate 1 made of n ⁺ type silicon carbide.

(B) Next, a resist is applied on the drift region 2, and the resist is patterned using a photolithography technique. A p-type impurity and an n-type impurity are sequentially ion-implanted into the drift region 2 using the patterned resist as a mask. After removing the resist with hydrofluoric acid or the like, the impurities are activated by heat treatment. As a result, as shown in FIG. 8, a p-type well region 3 and an n ⁺ -type source region 4 are formed.

  (C) Next, a resist is applied on the source region 4, and the resist is patterned by using a photolithography technique. Etching such as reactive ion etching (RIE) is performed using the patterned resist as a mask, and the source region 4, the well region 3, and a part of the drift region 2 are selectively removed. Thereafter, the resist is removed with hydrofluoric acid or the like. As a result, a groove 5 is formed as shown in FIG.

  (D) Next, as shown in FIG. 10, a gate insulating film 6 is formed on the surface of the trench 5 and the source region 4 by using the insulating film forming method according to the embodiment of the present invention. As a method for forming the insulating film according to the embodiment of the present invention, any of the methods shown in FIGS. 4A to 5C may be used.

  (E) Next, as shown in FIG. 11, a polycrystalline silicon film 7 is deposited on the gate insulating film 6 by chemical vapor deposition (CVD) or the like. Thereafter, the polycrystalline silicon film 7 is etched back and impurities are ion-implanted to form the gate electrode 7 as shown in FIG.

  (F) Next, as shown in FIG. 13, an interlayer insulating film 8 is deposited by CVD or the like. A resist is applied on the interlayer insulating film 8, and the resist is patterned using a photolithography technique. Using the patterned resist as a mask, a part of the interlayer insulating film 8 is selectively removed by the RIE method or the like. Thereafter, the resist is removed using hydrofluoric acid or the like. As a result, the upper surface of the gate electrode 7 is covered with the interlayer insulating film 8 as shown in FIG.

  (G) As shown in FIG. 15, the source electrode 10 is formed on the source region 4 and the interlayer insulating film 8 by vapor deposition, sputtering, or the like. Further, the drain electrode 9 is formed on the back surface of the substrate 1 by vapor deposition or sputtering, thereby completing the semiconductor device shown in FIG.

  As described above, according to the method of manufacturing a semiconductor device including the method of forming an insulating film according to the embodiment of the present invention, when the silicon carbide material is thermally oxidized, FIGS. ), An insulating film can be formed on the surface of the silicon carbide material in an active gas atmosphere containing oxygen in the temperature raising step. Therefore, the time can be shortened compared to the case where the insulating film is formed only by the time of the temperature holding process as shown in FIGS. 3A and 3B. The applied heat history can be reduced. Therefore, the reduction of the thermal history given to the silicon carbide material can suppress the roughening of the interface and the progress of crystal defects, so that the interface state density (Dit) can be reduced, the source-drain and the transistor between The leakage current on the diode side of the semiconductor device integrated with the diode can be reduced.

  Further, at least one of the temperature holding step and the temperature lowering step, nitriding is performed in an active gas atmosphere containing nitrogen to terminate dangling bonds generated at the interface between the silicon carbide material and the insulating film, Can be removed. With this effect, an insulating film with a low heat history, a low interface order density (Dit), and a high density can be formed.

  For example, in a gate insulating film of a MOSFET such as a voltage-controlled transistor described as a semiconductor device according to an embodiment of the present invention, a semiconductor device having high carrier mobility when a channel is formed and operating at high speed is provided. This reduces the leakage current during reverse application due to the roughening of the interface between the source and drain, the progress of crystal defects, and the deterioration of the interface order density, improving the trade-off between MOSFET on and off operations. can do.

Further, as the active gas used in the temperature raising step, O ₂ gas or water vapor or both of them is used, or an active gas containing nitrogen such as NO gas or N ₂ O gas is included in the atmosphere in the furnace body, thereby carbonizing. The surface of the silicon material is oxidized and an insulating film can be formed.

Moreover, dangling bonds existing at the interface between the silicon carbide material and the insulating film are terminated by including NO gas, N ₂ O gas, or NH ₃ gas as the gas used in the temperature holding process in the atmosphere in the furnace body. Or residual carbon can be removed.

Moreover, dangling bonds existing at the interface between the silicon carbide material and the insulating film are terminated by including NO gas, N ₂ O gas, or NH ₃ gas as the gas used in the temperature lowering process in the atmosphere in the furnace body. Or residual carbon can be removed.

  Further, in each of the temperature raising step, the temperature holding step, and the temperature lowering step, the mixed gas atmosphere of the active gas and the inert gas can be used to control the oxidation rate and the nitriding reaction rate.

In addition, since N ₂ or Ar is used as the inert gas in each of the temperature raising step, the temperature holding step, and the temperature lowering step, the inert gas that is normally used in the semiconductor manufacturing process can be used.

(First modification)
Next, a first modification of the semiconductor device according to the embodiment of the present invention will be described. As shown in FIG. 16, the semiconductor device according to the first modification is different from the structure shown in FIG. 6 in that a transistor and a diode are integrated in one device.

  As shown in FIG. 16, in the semiconductor device according to the first modification, grooves 5 a and 5 b penetrating a part of the source region 4, the well region 3 and the drift region 2 are formed. A gate electrode 7 is buried in one trench 5 a via a gate insulating film 6. A heterojunction region 11 is embedded in the other groove 5b. The heterojunction region 11 and the drift region 2 form a heterojunction diode (unipolar diode).

  Next, an example of a method for manufacturing a semiconductor device according to the first modification will be described.

  (A) The procedures of FIGS. 7 and 8 are substantially the same as the method of manufacturing a semiconductor device according to the embodiment of the present invention. Next, a resist is applied onto the source region 4, and the resist is patterned using a photolithography technique. Using the patterned resist as a mask, a part of the source region 4, well region 3 and drift region 2 is selectively removed by RIE or the like. Thereafter, the resist is removed using hydrofluoric acid or the like. As a result, grooves 5a and 5b are formed as shown in FIG.

  (B) Next, using the thermal oxidation method according to the embodiment of the present invention, a gate insulating film 6 is formed on the surfaces of the trenches 5a and 5b and the source region 4 as shown in FIG. Thereafter, a resist is applied on the gate insulating film 6, and the resist is patterned using a photolithography technique. Using the patterned resist as a mask, a part of the gate insulating film 6 is selectively removed by the RIE method or the like. As a result, a gate insulating film 6 is formed in the trench 5a as shown in FIG.

  (C) Next, as shown in FIG. 20, a polycrystalline silicon film 12 is deposited on the trenches 5a and 5b and the source region 4 by the CVD method or the like and etched back to obtain the trenches as shown in FIG. A polycrystalline silicon film 12 is embedded in 5a and 5b.

  (D) Next, a resist is applied on the polycrystalline silicon film 12 and the source region 4, and the resist is patterned using a photolithography technique. Using the patterned resist as a mask, p-type impurities and the like are ion-implanted into the polycrystalline silicon film 12 embedded in the grooves 5a and 5b. Thereafter, the resist is removed with hydrofluoric acid or the like, and heat treatment is performed. As a result, as shown in FIG. 22, the gate electrode 7 and the heterojunction region 11 are formed.

  (E) Next, as shown in FIG. 23, an interlayer insulating film 8 is deposited on the source region 4, the gate electrode 7 and the heterojunction region 11 by CVD or the like. A resist is applied on the interlayer insulating film 8, and the resist is patterned using a photolithography technique. Using the patterned resist as a mask, a part of the interlayer insulating film 8 is selectively removed by the RIE method or the like. Thereafter, the resist is removed using hydrofluoric acid or the like. As a result, the upper surface of the gate electrode 7 is covered with the interlayer insulating film 8 as shown in FIG.

  (F) Next, as shown in FIG. 25, the source electrode 10 is formed on the source region 4 and the interlayer insulating film 8 by vapor deposition or sputtering. Further, the drain electrode 9 is formed on the back surface of the substrate 1 by vapor deposition or sputtering, thereby completing the semiconductor device shown in FIG.

  According to the first modification, in the semiconductor device in which the transistor and the heterojunction diode are integrated into one device, the thermal history to the diode side added in the gate insulating film forming process can also be reduced. Reduction of thermal history can reduce deterioration of interface state density at the interface between the diode and the silicon carbide material due to the heterojunction, or prevent roughening of the junction surface and progression of crystal defects. It is also possible to reduce the leakage current when a reverse voltage is applied to the heterojunction diode caused by the thermal history.

(Second modification)
Next, a second modification of the semiconductor device according to the embodiment of the present invention will be described. As shown in FIG. 26, the semiconductor device according to the second modification has a structure in which a transistor and a diode are integrated into one device, and includes a Schottky barrier diode (unipolar diode). The configuration of the semiconductor device according to the first modification is different.

  As shown in FIG. 26, the metal electrode 13 connected to the source electrode 10 is embedded in the groove 5b of the semiconductor device according to the second modification. As a material of the metal electrode 13, for example, nickel (Ni), aluminum (Al), or the like can be used. The metal electrode 13 and the drift region 2 form a Schottky barrier diode.

  Next, an example of a method for manufacturing a semiconductor device according to a second modification will be described.

  (A) The procedure of FIGS. 7 to 12 is substantially the same as the manufacturing method of the semiconductor device according to the embodiment of the present invention. Next, a resist is applied onto the source region 4, and the resist is patterned using a photolithography technique. Using the patterned resist as a mask, a part of the source region 4, the well region 3 and the drift region 2 is removed by the RIE method or the like. Thereafter, the resist is removed using hydrofluoric acid or the like. As a result, a groove 5b is formed as shown in FIG.

  (B) Next, as shown in FIG. 28, an interlayer insulating film 8 is deposited on the trench 5b and the source region 4 by the CVD method or the like. A resist is applied on the interlayer insulating film 8, and the resist is patterned using a photolithography technique. Using the patterned resist as a mask, a part of the interlayer insulating film 8 is selectively removed by the RIE method or the like. As a result, the upper surface of the gate electrode 7 is covered with the interlayer insulating film 8 as shown in FIG.

  (C) Next, a metal film is deposited on the groove 5b and the source region 4 by sputtering or vapor deposition. A resist is applied on the metal film, and the resist is patterned using a photolithography technique. Etching is performed by RIE or the like using the patterned resist as a mask, so that a part of the metal film is selectively removed. As a result, as shown in FIG. 30, the metal electrode 13 is embedded in the groove 5b.

  (D) Next, as shown in FIG. 31, the source electrode 10 is formed on the source region 4 and the interlayer insulating film 8 by vapor deposition, sputtering, or the like. Further, the drain electrode 9 is formed on the back surface of the substrate 1 by vapor deposition or sputtering, thereby completing the semiconductor device shown in FIG.

  According to the second modification, in the semiconductor device in which the transistor and the diode are integrated into one device, the thermal history to the diode side added in the gate insulating film forming step can also be reduced. That is, by reducing the thermal history, deterioration of the interface state density at the interface between the diode and the silicon carbide material due to the Schottky junction can be reduced, and the roughness of the junction surface and the progress of crystal defects can be prevented. It is also possible to reduce the leakage current when applying the reverse voltage of the Schottky diode, which is generated by the thermal history of the forming process.

(Third Modification)
Next, a third modification of the semiconductor device according to the embodiment of the present invention will be described. As shown in FIG. 32, the semiconductor device according to the third modification includes a base body 1 made of n ⁺ type silicon carbide, a drift region 2 made of silicon carbide formed on the base body 1, and a drift region 2 N ⁺ -type source region 4 formed on the drain region 2, a p-type well region 3 formed on the drift region 2 so as to surround the source region 4, a source electrode 10 connected to the source region 4, and a drift region 2 and a gate insulating film 6 formed on the well region 3, a gate electrode 7 disposed on the gate insulating film 6, and an interlayer insulating film 8 formed so as to cover the gate electrode 7. A drain electrode 9 is formed on the back surface of the substrate 1.

  The gate insulating film 6 includes an oxide film 6a formed on the drift region 2 and the well region 3, and a deposited insulating film 6b deposited on the oxide film 6a. As the deposited insulating film 6b, a nitride film or an oxide film can be used.

  When manufacturing the semiconductor device according to the third modification, first, the deposited insulating film 6 b is deposited on the surface of the drift region 2. As the deposition method, a chemical vapor deposition (CVD) method under normal pressure or reduced pressure is suitable. Thereafter, the drift region 2 is oxidized by using the insulating film forming method according to the embodiment of the present invention, and the oxide film 6a is formed between the deposited insulating film 6b and the drift region 2 as shown in FIG. It is formed.

  Alternatively, after the oxide film 6a is first formed on the surface of the drift region 2 by using the insulating film forming method according to the embodiment of the present invention, the deposited insulating film 6b is deposited on the oxide film 6a as shown in FIG. A structure can be formed. Other steps for manufacturing the semiconductor device according to the third modification are substantially the same as those for manufacturing the semiconductor device according to the embodiment of the present invention.

  According to the third modified example, the time for forming the gate insulating film 6 can be reduced by the thickness of the deposited insulating film 6b. For this reason, the time reduction can be spent on the nitriding treatment, the time required for the process of the gate insulating film 6 can be shortened, and the thermal history can be reduced.

  Further, by combining the deposited insulating film 6b and the oxide film 6a formed using a furnace, the oxide film 6a formed by the furnace can be made thinner than the desired film thickness of the gate insulating film 6. For this reason, the process time in a furnace can reduce and a heat history can be reduced.

  Note that the semiconductor device shown in FIG. 33 has a structure obtained by further modifying the semiconductor device shown in FIG. 32, and has a structure in which a transistor and a diode (unipolar diode) are integrated into one device. Different from the structure shown in FIG. A heterojunction region 11 is formed on the drift region 2, and the heterojunction region 11 and the drift region 2 form a heterojunction diode. Also in the structure shown in FIG. 32, the gate insulating film 6 is composed of an oxide film 6a formed by the insulating film forming method according to the embodiment of the present invention and a deposited insulating film 6b formed on the oxide film 6a. It can be a layer.

(Other embodiments)
As described above, the present invention has been described according to the embodiment. However, it should not be understood that the description and drawings constituting a part of this disclosure limit the present invention. From this disclosure, various alternative embodiments, examples and operational techniques will be apparent to those skilled in the art.

For example, as shown in FIG. 34 (a), in the temperature holding process at times t13 to t14, the nitriding process is performed with a gas containing nitrogen such as N ₂ O and the nitriding process is performed sufficiently. In the temperature lowering process from t14 to t15, only an inert gas such as N ₂ gas may be supplied. Thus, the nitriding treatment may be performed in at least one of the temperature holding step and the temperature lowering step.

Further, as shown in FIG. 34B, in the temperature holding process at times t13 to t14, an oxide film is formed without supplying nitriding treatment by supplying an active gas not containing nitrogen such as O ₂ gas. May be. Thereafter, in the temperature lowering process from time t14 to t15, nitriding treatment may be performed by supplying an active gas containing nitrogen.

  In addition, a plurality of insulating films may be stacked by combining a plurality of series of procedures of the temperature raising step, the temperature holding step, and the temperature lowering step in the method for forming an insulating film according to the embodiment of the present invention.

  As described above, the present invention naturally includes various embodiments not described herein. Therefore, the technical scope of the present invention is defined only by the invention specifying matters according to the scope of claims reasonable from the above description.

DESCRIPTION OF SYMBOLS 1 ... Base | substrate 2 ... Drift area | region 3 ... Well area | region 4 ... Source area | region 5, 5a, 5b ... Groove 6 ... Gate insulating film 6a ... Oxide film 6b ... Depositioned insulating film 7 ... Gate electrode 8 ... Interlayer insulating film 9 ... Drain electrode 10 ... Source electrode 11 ... Heterojunction region 13 ... Metal electrode 101 ... Reaction tube 102 ... Heater 103 ... Boat 104 ... SiC substrate 105a-105c ... Gas supply pipe 106a-106c ... Gas valve 107 ... Exhaust pipe 108 ... Exhaust pump 110 ... Door

Claims (7)

A method for manufacturing a semiconductor device for forming an insulating film on a surface of a silicon carbide material,
A temperature raising step for raising the silicon carbide material to a predetermined temperature in an active gas atmosphere;
Holding the silicon carbide material at a predetermined temperature, and a temperature holding step of forming an insulating film on the surface of the silicon carbide material ;
A temperature lowering step for lowering the temperature of the silicon carbide material,
At least one of the temperature holding step and the temperature lowering step is performed in an active gas atmosphere containing nitrogen.   2. The semiconductor device manufacturing according to claim 1, wherein the active gas atmosphere in the temperature raising step includes at least one of oxygen gas, water vapor, or a mixture thereof, or nitrogen monoxide gas or nitrous oxide gas. Method.   2. The temperature holding step is performed in an active gas atmosphere containing nitrogen, and the active gas atmosphere containing nitrogen contains at least one of nitrogen monoxide gas, nitrous oxide gas, and ammonia gas. Or the manufacturing method of the semiconductor device of 2.   The temperature lowering step is performed in an active gas atmosphere containing nitrogen, and the active gas atmosphere containing nitrogen contains at least one of nitrogen monoxide gas, nitrous oxide gas, and ammonia gas. 4. A method for manufacturing a semiconductor device according to any one of 3 above.   The method for manufacturing a semiconductor device according to claim 1, wherein an active gas and an inert gas are mixed in each of the temperature raising step, the temperature holding step, and the temperature lowering step. 6. The method of manufacturing a semiconductor device according to claim 5, wherein the inert gas is nitrogen gas or argon gas .
The semiconductor device is a voltage-controlled transistor;
The method for manufacturing a semiconductor device according to claim 1, wherein the insulating film is a gate oxide film.

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