JP2017055098A - Manufacturing method for semiconductor device and semiconductor manufacturing device for use therein - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method for semiconductor device capable of reducing the interface state density of silicon carbide and silicon dioxide, when forming a silicon oxide film by thermal oxidation of the surface of a semiconductor substrate using silicon oxide as a material or the surface of a semiconductor layer using silicon carbide as a material.SOLUTION: A manufacturing method for semiconductor device includes a step (S11) of forming a silicon oxide film by supplying gas, containing an oxidizer, to the surface of a processed substrate using silicon carbide as a material, thereby thermally oxidizing the surface of the processed substrate, a step (S12) of replacing the atmosphere by lowering the partial pressure of oxidizer in the gas to 10 Pa or less, after the step for forming a silicon oxide film, and a step (S13) of lowering the temperature of the processed substrate, after the step of replacing the atmosphere.SELECTED DRAWING: Figure 2

Description

The present invention relates to a method of manufacturing a semiconductor device including a step of thermally oxidizing the surface of a semiconductor substrate made of silicon carbide (SiC) or a semiconductor layer made of SiC to form a silicon oxide film (SiO ₂ film). The present invention relates to a semiconductor manufacturing apparatus used for this.

As conventional SiC semiconductor devices, MOSFETs, MOS capacitors, and the like using a semiconductor substrate made of SiC (hereinafter referred to as “SiC substrate”) or a semiconductor layer made of SiC (hereinafter referred to as “SiC layer”) are known. It has been. A SiO ₂ film is used as a gate insulating film of a MOSFET or a capacitor insulating film of a MOS capacitor. The SiO ₂ film has a high insulating property due to a wide band gap and a high energy barrier at the interface with a semiconductor or metal. For this reason, it is widely studied to use the SiO ₂ film also in the SiC semiconductor device.

As a method for forming the SiO ₂ film on the surface of the SiC substrate or the SiC layer, a thermal oxidation method by exposing the surface of the SiC substrate or the SiC layer brought to a high temperature to an oxidizing atmosphere, or a source gas such as an organosilane is heated. Examples include chemical vapor deposition (CVD) by decomposition and physical vapor deposition (PVD) such as sputtering. Of these methods of forming the SiO ₂ film, the thermal oxidation method is advantageous from the viewpoint of insulation characteristics such as leakage current and interface state.

However, it has been reported that when an SiO ₂ film is formed on the surface of a SiC substrate or SiC layer by a thermal oxidation method, an interface defect peculiar to the interface between SiO ₂ and SiC is formed. Due to this interface defect, the characteristics of the interface between SiO ₂ and SiC become poor. For this reason, the channel mobility of the SiC-MOSFET having the gate insulating film made of the SiO ₂ film formed by the thermal oxidation method on the surface of the SiC substrate or the SiC layer is a value predicted from the electron mobility of the SiC bulk. However, it is not practical as a transistor. Thus, since the channel mobility of the SiC-MOSFET is extremely small, its on-resistance value (R _on ) is extremely higher than a value theoretically predicted from its physical property values.

In particular, in the case of four-layered periodic hexagonal silicon carbide (4H—SiC), a gate oxide film was formed by a normal thermal oxidation method such as dry oxidation even though the bulk electron mobility was about 900 cm ² / Vs. The channel mobility of the MOSFET is as extremely low as about 0 to 5 cm ² / Vs. This is considered to be caused by a high interface state density in the vicinity of the conduction band of the channel portion.

As a general method for improving the interface characteristics of SiO ₂ and SiC, after oxidizing the surface of the SiC substrate or the SiC layer in an atmosphere containing oxygen (O ₂ ), dinitrogen monoxide (POA (Post Oxidation Annealing)) A method of supplying a gas containing N ₂ O) or nitric oxide (NO) is known (see Patent Document 1). In this case, nitridation occurs simultaneously with oxidation, and nitrogen contributes to the termination of dangling bonds in the oxide film or at the interface, and is said to have an effect of reducing the interface state density.

Moreover, a thermal oxide film is formed on the surface of the SiC substrate or SiC layer at a temperature in the range of 1100 ° C. to 1200 ° C. in an O ₂ or water vapor atmosphere, and the interface state density is reduced by lowering the temperature in an inert gas. Has been proposed (see Patent Document 2).

However, in the method using a gas containing N ₂ O or NO described in Patent Document 1, nitrogen-derived charge trapping centers are formed in the oxide film, which deteriorates the long-term reliability of the oxide film against electrical stress. There are concerns. In the method of reducing the interface state density by lowering the temperature in an inert gas described in Patent Document 2, the effect of reducing the interface state density is insufficient.

JP 2004-511101 A JP 2003-31571 A

In view of the above problems, the present invention provides a method of manufacturing a semiconductor device capable of reducing the interface state density of SiO ₂ and SiC when thermally oxidizing the surface of a SiC substrate or a SiC layer to form an SiO ₂ film, and to this An object is to provide a semiconductor manufacturing apparatus to be used.

  According to one aspect of the present invention, (a) supplying a gas containing an oxidant to the surface of a substrate to be processed using SiC as a material to thermally oxidize the surface of the substrate to be processed to form a silicon oxide film; (B) After the step of forming the silicon oxide film, the step of replacing the atmosphere by reducing the partial pressure of the oxidant in the gas to 10 Pa or less; and (c) The temperature of the substrate to be processed after the step of replacing the atmosphere And a step of lowering the temperature of the semiconductor device.

  In another aspect of the present invention, (a) a step of forming a silicon oxide film by thermally oxidizing the surface of the substrate to be processed by supplying a gas containing an oxidant to the surface of the substrate to be processed made of SiC. And (b) after the step of forming the silicon oxide film, lowering the temperature of the substrate to be processed within 2 seconds from the completion of the formation of the silicon oxide film to a temperature at which the oxidation of the surface of the substrate to be processed is stopped. The manufacturing method of the semiconductor device containing this is provided.

  Still another embodiment of the present invention includes (a) a reaction tube that houses a substrate to be processed made of SiC, and (b) a gas supply tube that supplies a gas containing an oxidant into the reaction tube. The surface of the substrate to be processed is thermally oxidized to form a silicon oxide film. After the silicon oxide film is formed, the partial pressure of the oxidant in the reaction tube is reduced to 10 Pa or less, and then the temperature in the reaction tube is lowered. A semiconductor manufacturing apparatus is provided.

  Still another embodiment of the present invention includes (a) a reaction tube that houses a substrate to be processed made of SiC, and (b) a gas supply tube that supplies a gas containing an oxidant into the reaction tube. By supplying, the surface of the substrate to be processed is thermally oxidized to form a silicon oxide film, and after forming the silicon oxide film, the temperature of the substrate to be processed is changed to a temperature at which the oxidation of the surface of the substrate to be processed is stopped. Provided is a semiconductor manufacturing apparatus capable of lowering the temperature within 2 seconds from the end of formation of an oxide film.

According to the present invention, when a SiO ₂ film is formed by thermally oxidizing the surface of a SiC substrate or a SiC layer, a method for manufacturing a semiconductor device capable of reducing the interface state density of SiO ₂ and SiC, and a semiconductor manufacturing used for the same An apparatus can be provided.

It is the schematic which shows an example of the semiconductor manufacturing apparatus (oxidation furnace) which concerns on the 1st Embodiment of this invention. It is a flowchart of the oxide film formation process which concerns on the 1st Embodiment of this invention. FIG. 3A to FIG. 3C are timing charts respectively showing temperature changes in the oxide film forming process according to the first embodiment of the present invention. It is sectional drawing which shows an example of a structure of the MOS capacitor which concerns on the 1st Embodiment of this invention. FIG. 5A to FIG. 5D are process cross-sectional views of the MOS capacitor manufacturing method according to the first embodiment of the present invention. It is a graph which shows the measured value of the interface state density of the 1st example in comparison with comparative examples A and B. It is a graph which shows the measured value of the interface state density of 2nd Example AF. It is a flowchart of the oxide film formation process which concerns on the 1st modification of the 1st Embodiment of this invention. FIG. 9A to FIG. 9C are timing charts respectively showing temperature changes in the oxide film forming process according to the first modification of the first embodiment of the present invention. It is sectional drawing which shows an example of a structure of MOSFET which concerns on the 2nd modification of embodiment of this invention. FIG. 11A to FIG. 11C are process cross-sectional views of a MOSFET manufacturing method according to a second modification of the first embodiment of the present invention. FIG. 12A to FIG. 12C are process cross-sectional views subsequent to FIG. 11C of the MOSFET manufacturing method according to the second modification of the first embodiment of the present invention. FIG. 13A to FIG. 13C are process cross-sectional views subsequent to FIG. 12C of the MOSFET manufacturing method according to the second modification of the first embodiment of the present invention. 14A and 14B are process cross-sectional views subsequent to FIG. 13C of the MOSFET manufacturing method according to the second modification of the first embodiment of the present invention. It is sectional drawing which shows an example of a structure of MOSFET which concerns on the 3rd modification of the 1st Embodiment of this invention. FIG. 16A to FIG. 16D are process cross-sectional views of a method for manufacturing a MOSFET according to a third modification of the first embodiment of the present invention. 17A to 17B are process cross-sectional views subsequent to FIG. 16D of the MOSFET manufacturing method according to the third modification example of the first embodiment of the present invention. 18A and 18B are process cross-sectional views subsequent to FIG. 17B of the MOSFET manufacturing method according to the third modification of the first embodiment of the present invention. It is the schematic which shows an example of the semiconductor manufacturing apparatus (oxidation furnace) which concerns on the 2nd Embodiment of this invention. It is the schematic which shows an example of the semiconductor manufacturing apparatus (oxidation furnace) which concerns on the 2nd Embodiment of this invention. It is a flowchart of the oxide film production | generation process which concerns on the 2nd Embodiment of this invention. It is a timing chart showing the temperature change of the oxide film production | generation process which concerns on the 2nd Embodiment of this invention. It is sectional drawing which shows the structure of a MOS capacitor provided with an oxide film. It is a graph which shows the measured value of the interface state density of the oxide film of an Example, and the oxide film of a comparative example. It is a graph which shows the measured value of the interface state density in various oxide film formation temperature. It is the schematic which shows an example of the semiconductor manufacturing apparatus (oxidation furnace) which concerns on the 1st modification of the 2nd Embodiment of this invention. It is the schematic which shows another example of the semiconductor manufacturing apparatus (oxidation furnace) which concerns on the 1st modification of the 2nd Embodiment of this invention. It is the schematic which shows an example of the semiconductor manufacturing apparatus (oxidation furnace) which concerns on the 2nd modification of the 2nd Embodiment of this invention.

  In the following, first and second embodiments of the present invention will be described with reference to the drawings. In the description of the drawings referred to in the following description, the same or similar parts are denoted by the same or similar reference numerals. However, it should be noted that the drawings are schematic, and the relationship between the thickness and the planar dimensions, the ratio of the thickness of each layer, and the like are different from the actual ones. Therefore, specific thicknesses and dimensions should be determined in consideration of the following description. Moreover, it is a matter of course that portions having different dimensional relationships and ratios are included between the drawings.

  Further, the first and second embodiments described below exemplify a semiconductor manufacturing apparatus and a semiconductor device for embodying the technical idea of the present invention, and the technical idea of the present invention is configured as follows. The material of the parts, their shape, structure, arrangement, etc. are not specified below. The technical idea of the present invention can be variously modified within the technical scope defined by the claims described in the claims.

  Further, the conductivity type of the semiconductor device described in this specification is an example, and it is not necessary to be limited to the selection of the conductivity type used in the following description. Further, in the present specification and the accompanying drawings, it means that electrons or holes are majority carriers in the layers and regions with n or p, respectively. Further, + and − attached to n and p by superscript means that the semiconductor region has a relatively high or low impurity density as compared with a semiconductor region where + and − are not added. When n and p including + and − are the same, it indicates a close concentration, but the concentration is not necessarily equal. Further, in this specification, in the Miller index notation, “−” means a bar attached to the index immediately after that, and “−” is added before the index to indicate a negative index.

  In this specification, the definitions of “upper” and “lower” such as “upper” and “lower” are merely representational problems on the illustrated cross-sectional view. For example, the orientation of the semiconductor device is 90 °. If the observation is changed, the designations of “upper” and “lower” become “left” and “right”, and if the observation is changed by 180 °, the relations of the designations “upper” and “lower” are of course reversed. .

<Semiconductor manufacturing equipment>
As shown in FIG. 1, the semiconductor manufacturing apparatus according to the first embodiment of the present invention includes a reaction tube 101 made of substantially cylindrical quartz containing a substrate 100 to be processed made of SiC, and a reaction tube 101 around the reaction tube 101. It is an oxidation furnace provided with a heating means 102 provided and a susceptor 103 which is disposed in the reaction tube 101 and can hold a plurality of substrates 100 to be processed. The to-be-processed substrate 100 made of SiC has a single-layer structure of a SiC substrate or a multilayer structure in which the uppermost surface is a SiC layer. The susceptor 103 is preferably made of a material containing SiC. As the heating means 102, for example, an infrared lamp can be used.

One end of a plurality of gas supply pipes 105, 106 is connected to the upstream side of the reaction tube 101, and an inert gas supply source 113 and an oxidant supply source 114 are connected to the other ends of the plurality of gas supply pipes 105, 106, respectively. It is connected. Gas valves 107 and 108 capable of adjusting the gas flow rate are provided in the middle of the paths of the gas supply pipes 105 and 106. The inert gas supply source 113 supplies an inert gas such as argon (Ar), helium (He), nitrogen (N ₂ ), or a mixed gas thereof to the reaction tube 101 through the gas supply tube 105. The oxidizing agent supply source 114 supplies a gas (oxidizing gas) containing an oxidizing agent such as O ₂ , water vapor, NO, N ₂ O, or a mixed gas thereof to the reaction tube 101 via the gas supply tube 106. In the POA process described later, the oxidant supply source 114 supplies a gas such as O ₂ , water vapor, NO, NO ₂ , ammonia (NH ₃ ) gas, or a mixed gas thereof to the reaction tube 101 via the gas supply tube 106. To supply.

  A vacuum pump 110 is connected to the downstream side of the reaction tube 101 through an exhaust pipe 109. As the vacuum pump 110, a turbo molecular pump, a cryopump, a rotary pump, or the like can be used. Inside the reaction tube 101, temperature measuring means 112 for measuring the temperature of the inside of the reaction tube 101 and the substrate to be processed 100 is provided. As the temperature measuring means 112, a B-type thermocouple (rhodium 30% platinum rhodium alloy-rhodium 6% platinum rhodium alloy) or the like can be used. An oxidant concentration meter 111 capable of measuring the partial pressure of the oxidant concentration in the gas in the reaction tube 101 is provided inside the reaction tube 101.

  A controller 120 is electrically connected to the temperature measuring unit 112, the oxidant concentration meter 111, the heating unit 102, the gas valves 107 and 108, and the vacuum pump 110. Based on the temperature in the reaction tube 101 and the substrate 100 to be processed measured by the temperature measuring means 112 and the concentration of the oxidant measured by the oxidant concentration meter 111, the control unit 120 heats the heating means 102, The flow rate of the inert gas, the flow rate of the oxidizing agent, the exhaust amount by the vacuum pump 110, and the like are controlled. The control unit 120 includes a microprocessor having a central processing unit (CPU) function, a memory, and the like.

<Method for forming oxide film>
Next, an example of an oxide film forming process using the semiconductor manufacturing apparatus according to the first embodiment of the present invention shown in FIG. 1 will be described with reference to FIGS. As shown in the flowchart of FIG. 2, the oxide film forming step includes a temperature raising process in step S10, an oxidation process in step S11, an atmosphere replacement process in step S12, and a temperature lowering process in step S13.

  As shown in FIG. 1, a substrate to be processed 100 made of SiC is fixed in advance to a susceptor 103 in a reaction tube 101. Although this example is a batch type in which a plurality of substrates to be processed 100 are provided with respect to the susceptor 103, a single wafer type in which one substrate to be processed 100 is placed on the susceptor 103 may be used. In the case of the single wafer type, the volume of the reaction tube 101 can be reduced, and the atmosphere replacement can be performed more efficiently.

  First, the temperature raising process in step S10 in FIG. 2 is performed. In the temperature raising process, as shown in FIG. 3A, at time t10 to t11, the substrate to be processed 100 is heated by the heating means 102, and the reaction tube 101 and the substrate to be processed 100 can be thermally oxidized by SiC. The temperature is raised to a predetermined temperature T1.

Next, the oxidation process of step S11 in FIG. 2 is performed. In the oxidation process, as shown in FIG. 3A, at time t11 to t12, heating is continued by the heating means 102, and the temperature T1 of the substrate to be processed 100 measured by the temperature measuring means 112 is changed to thermal oxidation of SiC. Is maintained in a temperature range of about 1250 ° C. or higher and 1600 ° C. or lower. The oxidant supply source 114 supplies a gas containing an oxidant such as O ₂ , water vapor, NO, N ₂ O, or a mixed gas thereof into the reaction tube 101 to make the inside of the reaction tube 101 a dry oxygen atmosphere. As a result, the surface of the substrate to be processed 100 is thermally oxidized in a dry oxygen atmosphere at atmospheric pressure, and a SiO ₂ film having a thickness of, for example, about 30 nm is formed.

  Next, the atmosphere replacement process in step S12 of FIG. 2 is performed. In the atmosphere replacement process, as shown in FIG. 3A, at time t12 to t13, the reaction tube 101 is evacuated by using the vacuum pump 110 at a temperature T1 of 1250 ° C. or higher, for example. The gas containing the remaining oxidizing agent is removed, and the partial pressure of the oxidizing agent measured by the oxidizing agent concentration meter 111 is reduced to 10 Pa or less.

Subsequently, at times t13 to t14, the inert gas supply source 113 supplies an inert gas such as Ar, He, N ₂ or a mixed gas thereof into the reaction tube 101 at a temperature T1 of 1250 ° C. or higher. Then, the pressure in the reaction tube 101 is increased to atmospheric pressure to replace the inside of the reaction tube 101 with an inert gas atmosphere. The atmosphere replacement process may be performed at the same temperature as the temperature of the oxidation process, or may be performed at a temperature different from the temperature of the oxidation process (higher or lower temperature than the temperature of the oxidation process).

Next, the temperature lowering process in step S13 of FIG. 2 is performed. In the temperature lowering process, as shown in FIG. 3A, at time t14 to t15, heating by the heating means 102 is stopped, and the inside of the reaction tube 101 and the substrate to be processed 100 are cooled to 800 ° C. or less in an Ar atmosphere. Let the temperature drop. Thereafter, the substrate 100 on which the SiO ₂ film is formed is taken out from the reaction tube 101, and the oxide film forming step is completed.

  In the atmosphere replacement process in step S12, without evacuation using the vacuum pump 110 as shown in FIG. 3A, as shown in FIG. By introducing an inert gas into the reaction tube 101 and diluting the oxidant remaining in the reaction tube 101, the partial pressure of the oxidant in the reaction tube 101 is reduced to 10 Pa or less and the atmosphere is replaced. May be.

  Further, in the atmosphere replacement process in step S12, as shown in FIG. 3C, only the exhaust using the vacuum pump 110 is performed at time t12 to t14, and the oxidant measured by the oxidant concentration meter 111 is performed. It is not necessary to perform the subsequent process of introducing the inert gas as shown in FIG. However, since the cooling effect by the inert gas is lost, the time required for the subsequent temperature lowering process becomes longer.

<Method for Manufacturing Semiconductor Device>
Next, the case of manufacturing the MOS capacitor shown in FIG. 4 will be described as an example of the method of manufacturing the SiC semiconductor device according to the first embodiment of the present invention. 4 includes an n ⁺ -type SiC substrate 1, an n-type SiC layer 2 disposed on the SiC substrate 1, and a capacitor insulating film (SiO ₂ film) 3 disposed on the SiC layer 2. And an electrode 4 disposed on the capacitor insulating film 3 and an electrode 5 disposed on the back surface of the SiC substrate 1. The SiC substrate 1 and the SiC layer 2 constitute a substrate to be processed (1, 2) according to the first embodiment of the present invention. The SiC layer 2, the capacitor insulating film (SiO ₂ film) 3 and the electrode 4 constitute a capacitor.

  Next, an example of a method of manufacturing the MOS capacitor shown in FIG. 4 including the oxide film forming step according to the first embodiment of the present invention will be described with reference to FIGS. 5 (a) to 5 (d). To do.

First, an n ⁺ -type SiC substrate 1 having an impurity density of about 7 × 10 ^{17 to} 5 × 10 ¹⁸ cm ⁻³ is prepared. As the SiC substrate 1, for example, a 4H-SiC (0001) substrate (0 to 8 degrees off substrate from the (0001) plane) can be used. As shown in FIG. 5A, an n-type SiC layer (epitaxial layer) 2 having an impurity density of about 5 × 10 ¹⁶ cm ^{−3 is} grown on the SiC substrate 1 by about 5 μm, and the SiC substrate 1 and the SiC layer 2 are To be processed (1) and (2) are prepared. The substrate to be processed (1, 2) according to the first embodiment of the present invention preferably has a flat surface that defines a specific orientation plane. Of course, the substrate (1, 2) to be processed after the epitaxial growth also has a flat surface that is off by 0 to 8 degrees from the (0001) plane which is a specific orientation plane.

Next, after cleaning the substrate to be processed (1, 2), the substrate to be processed (1, 2) is accommodated in the oxidation furnace shown in FIG. 1, and the oxidation according to the first embodiment of the present invention described above. A film forming step is performed. As a result, as shown in FIG. 5B, a capacitor insulating film 3 made of a SiO ₂ film having a thickness of about 30 nm is formed on the entire surface of the SiC layer 2, and also on the entire back surface of the SiC substrate 1. A SiO ₂ film 3x is formed.

  Next, as shown in FIG. 5C, a metal film 4 such as aluminum (Al) is deposited on the entire surface of the capacitor insulating film 3 by vapor deposition or sputtering at room temperature. Thereafter, a photoresist film is applied on the metal film 4, and the photoresist film is patterned using a photolithography technique. Using the patterned photoresist film as a mask, a part of the metal film 4 is selectively removed by dry etching or the like, thereby forming a dot-like electrode 4 as shown in FIG.

Next, the SiO ₂ film 3x on the back surface of the SiC substrate 1 is removed by grinding or wet etching. Thereafter, as shown in FIG. 4, an electrode 5 made of Al or the like is formed on the entire back surface of the SiC substrate 1 by vapor deposition or sputtering, thereby completing the MOS capacitor.

According to the first embodiment of the present invention, when forming the capacitor insulating film 3 made of the SiO ₂ film of the MOS capacitor, the partial pressure of the oxidizing agent in the reaction tube 101 is reduced to 10 Pa or less in the atmosphere replacement process. Thus, the interface state density of SiC and SiO ₂ can be reduced by setting the partial pressure of the oxidant at the start of the temperature lowering process to 10 Pa or less. Therefore, good quality oxide film 3 can be formed on SiC layer 2.

<First embodiment>
As a first example, the MOS capacitor shown in FIG. 4 was produced. In the step of forming the capacitor insulating film of the MOS capacitor, the oxide film forming step shown in FIGS. 2 and 3A was performed. In the oxidation process of step S11, the substrate to be processed (1, 2) composed of the SiC substrate 1 and the SiC layer 2 similar to FIG. 5A is oxidized at 1400 ° C. in a dry oxygen atmosphere at atmospheric pressure. A capacitor oxide film 3 having a thickness of 30 nm was formed on the surface of the SiC layer 2. In the atmosphere replacement process in step S12, the oxidizing agent in the reaction tube 101 was removed using the vacuum pump 110 at 1400 ° C., and the partial pressure of the oxidizing agent (oxygen) was set to 10 Pa or less. Thereafter, Ar was introduced into the reaction tube 101, and the pressure in the reaction tube 101 was set to atmospheric pressure. In the temperature lowering process in step S13, the substrate to be processed (1, 2) on which the capacitor oxide film 3 is formed is cooled to 800 ° C. or lower in an Ar atmosphere, and then the substrate to be processed (1 on which the capacitor oxide film 3 is formed). , 2) was taken out of the reaction tube 101.

  As a comparative example A to be compared with the first embodiment, the MOS capacitor is replaced by the same method except that the temperature lowering process is immediately started in the atmospheric pressure oxygen atmosphere without performing the atmosphere replacement process after the oxidation process. Was made. As a comparative example B, in the atmosphere replacement process, the vacuum pump 110 is used to lower the partial pressure of the oxidant to 100 Pa, and then the temperature lowering process is started to introduce Ar (that is, the partial pressure of the oxidant is different). Other than that, a MOS capacitor was fabricated in the same manner.

The MOS capacitors according to the first embodiment and the comparative examples A and B were measured with a CV meter, and the high-low (High-) due to the CV characteristics of 1 MHz and the quasi-static CV characteristics. The difference in interface state density _Dit was investigated by the Low method. Figure 6 shows the interface state density D _it obtained from the measurement results of the MOS capacitor according to the first embodiment Comparative Example A, with B. The horizontal axis in FIG. 6 represents the interface state energy (Ec is the conduction band energy edge) in the band gap, and the vertical axis represents the interface state density _Dit .

As shown in FIG. 6, when compared with the atmosphere during the temperature decrease process, in Comparative Example B compared with Comparative Example A, a deep (Ec-E is large) energy although the effect of reducing the interface state density D _it is seen shallow interface state reduction of the density D _it energy is small. On the other hand, in the first embodiment, the effect of reducing the interface state density _Dit is recognized for both the deep interface state and the shallow interface state.

Thus, according to the first example, by reducing the partial pressure of the oxidant in the reaction tube 101 during the temperature lowering process to 10 Pa or less, it is derived from carbon segregated at the interface between SiC and SiO ₂ . can be reduced defect surface density 2 × ¹⁰ 12 ^{cm -2} or less, it could reduce the interface state density _{D it.}

<Second embodiment>
Next, as a second example, a plurality of MOS capacitors similar to those in the first example were manufactured at different temperatures during the oxidation process. In the oxidation process, oxidation was performed at 1150 ° C., 1200 ° C., 1250 ° C., 1300 ° C., 1450 ° C., and 1600 ° C. in a dry oxygen atmosphere at atmospheric pressure, and a capacitor oxide film having a thickness of 30 nm was formed on the SiC layer. It was set as 2nd Example AF.

The MOS capacitor according to the second embodiment A~F measured by C-V meter, by the high-low method using C-V characteristics and擬静manner C-V characteristics of 1MHz the difference in interface state density _{D it} investigated. Figure 7 shows the interface state density D _it obtained from the measurement result of the second embodiment to F. As shown in FIG. 7, in Examples A, B, and C having an oxidation temperature of 1250 ° C. or lower, the interface state density _Dit decreased as the oxidation temperature increased. On the other hand, in Examples D, E, and F having an oxidation temperature of 1300 ° C. or higher, no significant difference was observed in the interface state density.

According to the second example, when the oxidation process was performed at 1250 ° C. or lower, the interface state density D _it increased. Therefore, when the oxidation process is performed at 1250 ° C. or lower, it is particularly effective to perform the temperature lowering process at a partial pressure of the oxidizing agent of 10 Pa or lower to reduce the interface state density _Dit .

<First Modification>
As a first modification of the first embodiment of the present invention, a modification of the oxide film forming step will be described. As shown in FIG. 8, the oxide film forming process according to the first modification of the first embodiment of the present invention includes a temperature rising process at step S20, an oxidation process at step S21, a POA process at step S22, and a step S23. Atmosphere replacement process, and the temperature lowering process of step S24. That is, the POA process of step S22 is added between the oxidation process of step S21 and the atmosphere replacement process of step S23. The oxide film formation according to the first embodiment of the present invention shown in FIG. Different from the process procedure.

In step S20 of FIG. 8, a temperature raising process is performed. In the temperature raising process, as shown in FIG. 9A, at time t20 to t21, the heating means 102 heats and raises the temperature to a predetermined temperature T1. Next, in step S21 of FIG. 8, an oxidation process is performed. In the oxidation process, as shown in FIG. 9A, at time t21 to t22, as in the oxidation process of step S11, a gas containing an oxidant while being heated to a predetermined temperature T1 (about 1250 ° C. to 1600 ° C.). And the surface of the substrate to be processed 100 is thermally oxidized to form a SiO ₂ film.

Next, in step S22 of FIG. 8, a POA process is performed. If the temperature is lowered in an oxygen atmosphere before the POA process, the interface characteristics deteriorate. Therefore, in the POA process, as shown in FIG. 9A, the POA process is performed at the same temperature T1 without lowering the temperature from the oxidation process. From time t23 to t24, the oxidant supply source 114 performs heat treatment (annealing) while supplying a gas containing O ₂ , water vapor, NO, NO ₂ , NH _3, or a mixed gas thereof into the reaction tube 101.

Note that the supply of the gas containing O ₂ , water vapor, NO, NO ₂ , NH _3, or a mixed gas thereof into the reaction tube 101 is started immediately from time t22 without leaving an interval between times t22 and t23. May be. That is, heat treatment (annealing) may be performed while supplying gas into the reaction tube 101 at times t22 to t24. When the temperature is lowered to a temperature lower than the temperature of the oxidation process (for example, about 1000 ° C. to 1100 ° C.) when the oxidation process of step S21 is changed to the POA process of step S22 at time t22 to t23, In addition, an atmosphere replacement process is preferably added.

  Next, the atmosphere replacement process in step S23 of FIG. 8 is performed. In the atmosphere replacement process, as shown in FIG. 9A, the POA remaining in the reaction tube 101 is exhausted by evacuating the reaction tube 101 using the vacuum pump 110 at a predetermined temperature T1 at times t24 to t25. The gas used in the process is removed, and the partial pressure of the oxidant in the reaction tube 101 is reduced to 10 Pa or less.

  Subsequently, at times t25 to t26, an inert gas is introduced from the inert gas supply source 113 into the reaction tube 101 and replaced with an inert gas atmosphere. Note that the temperature of the atmosphere replacement process may be the same as that of the POA process, or may be different from the temperature of the oxidation process (higher or lower temperature than the temperature of the oxidation process).

  Next, in step S24 of FIG. 8, a temperature lowering process is performed. In the temperature lowering process, as shown in FIG. 9A, at time t26 to t27, the heating means 102 is stopped and the temperature is lowered to a predetermined temperature (for example, 800 ° C.) or lower in an inert gas atmosphere.

According to the first modification, even when the POA process is performed after the oxidation process, the partial pressure of the oxidant in the reaction tube 101 is reduced to 10 Pa or less in the atmosphere replacement process after the POA process, and the temperature lowering process is started. By setting the partial pressure of the oxidizing agent at 10 Pa or less, the interface state density of SiC and SiO ₂ can be reduced. Therefore, a high-quality SiO ₂ film can be formed on the surface of the substrate to be processed 100.

  In the atmosphere replacement process in step S23 in FIG. 8, without exhausting using the vacuum pump 110 as shown in FIG. 9A, as shown in FIG. 9B, at times t24 to t26. By introducing an inert gas such as Ar into the reaction tube 101 to dilute the oxidant, the partial pressure of the oxidant in the reaction tube 101 may be reduced to 10 Pa or less to replace the atmosphere.

  Further, in the atmosphere replacement process in step S23 of FIG. 8, as shown in FIG. 9C, the evacuation using the vacuum pump 110 is performed from time t24 to t26, and measurement is performed by the oxidant concentration meter 111. Only the treatment for reducing the partial pressure of the oxidant to 10 Pa or less may be performed, and the subsequent inert gas as shown in FIG. 9A may not be introduced. However, since the cooling effect by the inert gas is lost, the time required for the subsequent temperature lowering process becomes longer.

<Second Modification>
A method of manufacturing the lateral MOSFET shown in FIG. 10 will be described as a method of manufacturing the semiconductor device according to the second modification of the first embodiment of the present invention. A semiconductor device according to a second modification of the first embodiment of the present invention includes a p ⁺ type SiC substrate 6 and a p type epitaxial layer 7 disposed on the SiC substrate 6 as shown in FIG. With. A drain region 12, a source region 13, and a ground region (contact region) 14 are formed on the epitaxial layer 7. Reaction layers 20a and 20b of SiC and metal are formed on the drain region 12, the source region 13, and the ground region 14, and electrodes 21a and 21b are formed on the reaction layers 20a and 20b. An electrode 22 is arranged on the back surface of the SiC substrate 6. A gate electrode 18 is disposed on the epitaxial layer 7 via a gate insulating film 17 made of a SiO ₂ film, and an electrode 21 c is disposed on the gate electrode 18.

  Next, an example of a method of manufacturing a semiconductor device according to the second modification example according to the first embodiment of the present invention will be described with reference to FIGS. 11 (a) to 13 (c).

First, as the p ⁺ -type SiC substrate 6, a 4H—SiC substrate ((000-1) plane 0 to 8 degrees off substrate, preferably 0 to 4 having an impurity density of about 5 × 10 ^{17 to} 3 × 10 ¹⁸ cm ^−3. Prepare an off-substrate). Then, as shown in FIG. 11A, a p-type epitaxial layer 7 having an impurity density of about 1 × 10 ¹⁶ cm ⁻³ is grown on the SiC substrate 6 to have the SiC substrate 6 and the epitaxial layer 7. A substrate to be processed (6, 7) is prepared.

Next, a 1 μm thick SiO ₂ film is deposited on the surface of the epitaxial layer 7 by low pressure (LP) CVD or the like. Then, a part of the SiO ₂ film is selectively removed using a photolithography technique, and a pattern of the mask 8 made of the SiO ₂ film is formed as shown in FIG. Thereafter, by using the mask 8, for example, phosphorus ions 9 are set at a substrate temperature of 500 ° C., a multistage acceleration energy of 40 keV to 250 keV, and a dose amount of 2 × 10 ¹⁵ to 1 × 10 ¹⁶ cm ^{−2 at} each stage. Is selectively ion-implanted so as to be 1 × 10 ²⁰ to 1 × 10 ²¹ cm ⁻³ . Thereafter, the mask 8 is removed by dry etching or the like.

Next, a SiO ₂ film having a thickness of 1 μm is deposited on the surface of the epitaxial layer 7 by LPCVD, and a part of the SiO ₂ film is selectively removed by using a photolithography technique. As shown in FIG. 3, a pattern of a mask 10 made of a SiO ₂ film is formed. Thereafter, by using the mask 10, for example, the final implantation amount of aluminum ions 11 is set at a substrate temperature of 500 ° C., a multistage acceleration energy of 40 keV to 200 keV, and a dose amount of 5 × 10 ¹⁵ to 2 × 10 ¹⁶ cm ⁻² in each step. Is selectively ion-implanted so as to be 1 × 10 ²⁰ to 1 × 10 ²¹ cm ⁻³ . Thereafter, the mask 10 is removed by dry etching or the like. Next, by performing activation annealing at 1600 ° C. for 5 minutes in an Ar atmosphere, the drain region 12, the source region 13, and the ground region 14 are formed on the epitaxial layer 7 as shown in FIG. Selectively form.

  Next, a field oxide film 15 having a thickness of 0.5 μm is deposited by LPCVD. A photoresist film is applied onto the field oxide film 15, and the photoresist film is patterned using a photolithography technique. A portion of the field oxide film 15 is removed by wet etching using the patterned photoresist film as a mask to form a rectangular window portion that defines the active region 16 as shown in FIG. .

Next, after cleaning the substrate to be processed (6, 7) having the epitaxial layer 7 defining the active region 16, the above-described oxide film forming step according to the first embodiment of the present invention is performed. For example, it is installed on the susceptor 103 made of a material containing SiC. Then, the substrate to be processed (6, 7) is heated using the heating unit 102 while monitoring the temperature using the temperature measuring unit 112, and the oxidation process is performed in a dry oxygen atmosphere at 1300 ° C. As a result, as shown in FIG. 12C, a gate insulating film 17 made of a SiO ₂ film having a thickness of 50 nm is formed on the surface of the epitaxial layer 7 in the active region 16. Thereafter, the vacuum pump 110 is used to evacuate the partial pressure of the oxidant to a pressure of 10 Pa or less, and then Ar gas is introduced to replace the inert gas atmosphere. Thereafter, the temperature of the semiconductor substrate is lowered to 800 ° C. or lower by a temperature lowering process.

  Next, a polycrystalline silicon film is deposited on the gate insulating film 17 to a thickness of 0.3 μm by LPCVD. The polycrystalline silicon film is patterned using photolithography technology to form a gate electrode 18 on the gate insulating film 17 as shown in FIG. An etching mask for the photoresist film 71 is formed by a photolithography technique, and the gate insulating film 17 is etched with hydrofluoric acid or the like using this etching mask, so that the drain region 12 and the source are formed as shown in FIG. A contact hole is selectively opened in a part of the gate insulating film 17 on the region 13 and the ground region 14. A multilayer metal layer is deposited by vapor-depositing 10 nm thick Al and further 60 nm nickel (Ni) on the photoresist film 71 used as an etching mask. After vapor deposition, the photoresist film 71 is removed by wet processing or the like. The multilayer metal film is patterned by the lift-off process, and the contact metals 19a and 19b are selectively left inside the contact holes as shown in FIG.

Heat treatment is performed as ohmic contact annealing by holding at 950 ° C. for 2 minutes in an inert gas atmosphere such as N ₂ , He or Ar, and contact metals 19a and 19b react with SiC as shown in FIG. The reaction layers 20a and 20b are formed. A metal film made of Al is deposited to a thickness of 300 nm on the surface, and pad electrodes 21a to 21c are formed on the gate electrode 18 and the reaction layers 20a and 20b as shown in FIG. 14B by photolithography and etching using phosphoric acid. Form. Further, the electrode 22 made of Al having a thickness of about 100 nm is formed on the back surface by vapor deposition or the like, thereby completing the semiconductor device shown in FIG.

According to the second modified example, when forming the gate insulating film 17 of the MOSFET, in the atmosphere replacement process, the partial pressure of the oxidant in the reaction tube 101 is reduced to 10 Pa or less to oxidize at the start of the temperature lowering process. By setting the partial pressure of the agent to 10 Pa or less, the interface state density of SiC and SiO ₂ can be reduced. Therefore, the gate insulating film 17 made of a high-quality SiO ₂ film can be formed on the epitaxial layer 7. In the second modification, the case where the oxide film forming step not including the POA process shown in FIG. 2 is performed has been described. However, the oxide film forming step including the POA process shown in FIG. Good.

<Third Modification>
As a semiconductor device according to a third modification of the first embodiment of the present invention, a vertical MOSFET that forms a channel in the vicinity of the surface of the SiC epitaxial substrate in the on state will be described. The semiconductor device according to the third modification of the first embodiment of the present invention is lower than the n ⁺ -type SiC substrate 23 and the SiC substrate 23 disposed on the SiC substrate 23 as shown in FIG. And an n-type epitaxial layer 24 having an impurity density.

  A plurality of p-type regions 25 a and 25 b are selectively formed on the epitaxial layer 24. The p-type regions 25 a and 25 b are exposed on the surface of the epitaxial layer 24. A p-type SiC layer 26 having a lower impurity density than p-type regions 25a and 25b is formed on the surfaces of p-type regions 25a and 25b. In the SiC layer 26 on the epitaxial layer 24 in which the p-type regions 25 a and 25 b are not formed, the n-type region 27 is formed with the same thickness as the SiC layer 26. That is, n-type region 27 is sandwiched between two SiC layers 26 so as to penetrate SiC layer 26 in the depth direction and reach epitaxial layer 24. The n-type epitaxial layer 24 and the n-type region 27 are n-type drift regions. The impurity density of the n-type region 27 is preferably higher than that of the n-type epitaxial layer 24.

On the SiC layer 26, n ⁺ type source regions 28a and 28b and p ⁺ type contact regions 29a and 29b are formed so as to be in contact with each other. Source regions 28a and 28b are formed to face each other with SiC layer 26 sandwiching n-type region 27 therebetween. Contact regions 29a and 29b are located on the opposite side of source regions 28a and 28b to n-type region 27 side. The impurity density of contact regions 29 a and 29 b is higher than the impurity density of SiC layer 26. The portions of SiC layer 26 excluding source regions 28a and 28b, contact regions 29a and 29b, and n-type region 27 become p-type base regions together with p-type regions 25a and 25b.

  Source electrodes 30a and 30b are formed on the surfaces of the source regions 28a and 28b and the contact regions 29a and 29b. A gate electrode 32 is formed on the surface of the p-type SiC layer 26 and the n-type region 27 between the adjacent source regions 28 a and 28 b via a gate insulating film 31. The gate electrode 32 is electrically insulated from the source electrodes 30a and 30b by an interlayer insulating film (not shown) (see reference numeral 72 in FIG. 18B). A drain electrode 33 is formed on the back surface of the SiC substrate 23 in contact with the SiC substrate 23.

  Next, with reference to FIGS. 16A to 17B, according to a third modification of the first embodiment of the present invention, including the oxide film forming step of the first embodiment of the present invention. An example of a method for manufacturing a semiconductor device will be described.

First, as shown in FIG. 16A, an n-type epitaxial layer 24 is grown on an n ⁺ -type SiC substrate 23, and a preparation substrate (23, 24) having the SiC substrate 23 and the n-type epitaxial layer 24 is obtained. ). Next, as shown in FIG. 16B, a plurality of p-type regions 25a and 25b are selectively formed on the epitaxial layer 24 by photolithography, ion implantation, heat treatment, or the like. Thereafter, as shown in FIG. 16C, a p-type SiC layer 26 having a lower impurity density than the p-type regions 25a and 25b is grown on the surfaces of the epitaxial layer 24 and the p-type regions 25a and 25b. By growing the SiC layer 26, the preparation substrate (23, 24) becomes the substrate to be processed (23, 24, 26).

  Next, an n-type region 27 is formed in part of the SiC layer 26 by photolithography, ion implantation, heat treatment, or the like. The n-type region 27 is formed on the epitaxial layer 24 on which the p-type regions 25a and 25b are not formed on the planar pattern. The p-type regions 25 a and 25 b penetrate the SiC layer 26 in the depth direction and reach the epitaxial layer 24. The epitaxial layer 24 and the n-type region 27 are drift regions. The impurity density of the n-type region 27 is desirably higher than that of the epitaxial layer 24.

Further, as shown in FIG. 16D, p ⁺ -type contact regions 29a and 29b are formed in the SiC layer 26 by photolithography, ion implantation, heat treatment, and the like. The impurity density of contact regions 29a and 29b is higher than the impurity density of SiC layer 26. Further, n ⁺ -type source regions 28 a and 28 b are formed in SiC layer 26 by impurity ions exhibiting n ⁺ -type such as phosphorus ions by photolithography technology, ion implantation, heat treatment, and the like.

  Next, the substrate to be processed (23, 24, 26) having the SiC substrate 23 and the n-type epitaxial layer 24 is introduced into the semiconductor manufacturing apparatus shown in FIG. 1, and according to the first embodiment of the present invention. Using the oxide film formation step, as shown in FIG. 17A, the surface of the SiC layer 26 is thermally oxidized to form the gate insulating film 31 on the entire surface. Further, a polysilicon layer 32 is deposited on the entire surface of the gate insulating film 31. A part of the gate insulating film 31 and the polysilicon layer 32 is selectively removed by using a photolithography technique or the like, and the SiC layer between the contact regions 29a and 29b facing each other as shown in FIG. A gate electrode 32 is formed through a gate insulating film 31 so that a part of the SiC layer 26 is exposed on the surfaces of the n-type region 27 and the n-type region 27.

  As shown in FIG. 18A, an interlayer insulating film 72 is deposited on the entire surface by LPCVD or the like. Thereafter, the interlayer insulating film 72 is selectively etched by photolithography as shown in FIG. 18B to cover the gate electrode 32 with the interlayer insulating film 72. Although not shown, a gate contact hole is also opened during this selective etching.

  As shown in FIG. 18B, source electrodes 30a and 30b are formed on the surfaces of the source regions 28a and 28b and the contact regions 29a and 29b by vapor deposition or sputtering, and the gate contact holes are interposed. A gate wiring is formed in contact with the gate electrode 32. Further, as shown in FIG. 15, by forming the drain electrode 33 on the back surface of the SiC substrate 23 by vapor deposition or sputtering, the semiconductor device according to the third modification of the first embodiment of the present invention. Is completed.

(Second Embodiment)
As shown in FIG. 19, the semiconductor manufacturing apparatus according to the second embodiment of the present invention is arranged around a reaction tube 201 containing a substrate to be processed (semiconductor substrate) 200 made of SiC, and around the reaction tube 201. It is an oxidation furnace provided with the heated means 202 and the susceptor 203 arranged in the reaction tube 201. In FIG. 19, the z-axis is the direction of gravitational acceleration, the lower side is the positive direction of the z-axis, and the upper side is the negative direction of the z-axis.

The to-be-processed base body 200 made of SiC has a single layer structure of a SiC substrate or a multilayer structure in which the uppermost surface is a SiC layer. The reaction tube 201 is made of, for example, substantially cylindrical quartz. The heating means 202 heats the substrate to be processed 200. As the heating means 202, for example, an infrared lamp, a high frequency induction heating device, or the like can be used. The susceptor 203 is preferably made of a material containing SiC or alumina (Al ₂ O ₃ ).

  In the reaction tube 201, a wire 204 bonded to the substrate to be processed 200 is disposed so as to hold the substrate to be processed 200. A holder 205 is disposed in the vicinity of the bonding portion between the wire 204 and the substrate to be processed 200. A liquid tank 212 into which the liquid L is injected is disposed below the reaction tube 201.

  The holder 205 has a function of holding or separating the substrate to be processed 200 in accordance with a control signal from the control unit 211. When the holder 205 separates the substrate to be processed 200, the substrate to be processed 200 falls downward and is poured into the liquid L in the liquid tank 212 as shown in FIG. 20. The arrangement position of the holder 205 is not particularly limited as long as the substrate to be processed 200 can be held in the reaction tube 201. 20 illustrates the case where the holder 205 stays in the reaction tube 201 after being separated from the substrate 200 to be processed. However, the holder 205 may be detached from the reaction tube 201 and dropped together with the substrate 200. I do not care.

  The wire 204 is, for example, a sheath thermocouple, and can measure the temperature in the reaction tube 201 and the substrate 200 to be processed. For example, the sheath thermocouple constituting the wire 204 preferably has a length that can reach at least the liquid tank 212. When the holder 205 is separated from the substrate to be processed 200 and the substrate to be processed 200 is dropped and put into the liquid tank 212, the state where the sheath thermocouple constituting the wire 204 is connected to the substrate to be processed 200 is maintained. it can. For this reason, it is possible to measure the temperature of the substrate to be processed 200 even after the liquid tank 212 is charged, and it is possible to detect that the temperature of the substrate to be processed 200 has dropped to a temperature at which oxidation stops. Note that the wire 204 may be separated from the substrate 200 when the holder 205 is separated from the substrate 200.

  An open lid 210 is provided below the reaction tube 201. As a method of opening the opening lid 210, it may be a single opening or a sliding type. The opening lid 210 opens and closes in response to a control signal from the control unit 211. When the opening lid 210 is closed, the reaction tube 201 is sealed, and the oxidizing gas is not released to the outside of the reaction tube 201. On the other hand, as shown in FIG. 20, the substrate to be processed 200 can be taken out of the reaction tube 201 by opening the opening lid 210.

  A liquid L that can rapidly cool the substrate 200 to be processed that has dropped from the inside of the reaction tube 201 is injected into the liquid tank 212. The temperature of the liquid L is set to be lower than a predetermined temperature for cooling the substrate to be processed 200. Here, “rapidly cool” means to cool to a predetermined temperature within 2 seconds from the end of the formation of the oxide film. The “predetermined temperature” is, for example, 800 ° C., which is a temperature at which the oxidation of the surface of the substrate to be processed 200 stops in a dry oxygen atmosphere. Further, when the temperature is cooled to a predetermined temperature within 2 seconds from the end of the formation of the oxide film, the growth of the oxide film during the cooling becomes 0.1 nm or less.

  For example, water can be used as the liquid L injected into the liquid tank 212, but is not limited thereto, and any liquid can be used as long as it can rapidly cool the substrate to be processed 200 that has dropped from the inside of the reaction tube 201. . For example, other liquids having the same thermal conductivity as water may be used. Since water evaporates at 100 ° C. to become a gas, when it is desired to cool in the range of 100 ° C. to 800 ° C., mercury (Hg), gallium (Ga), indium (In ), A liquid metal such as tin (Sn), or the like may be used. However, since Hg has an evaporation temperature of 480 ° C., the temperature that can be used for cooling as a liquid is lower than 800 ° C.

As shown in FIG. 19, one end of a gas supply pipe 206 is connected to the upper side (upstream side) of the reaction pipe 201. An oxidant supply source 208 is connected to the other end of the gas supply pipe 206. A gas valve 207 capable of adjusting the gas flow rate is provided in the middle of the path of the gas supply pipe 206. The oxidant supply source 208 supplies a gas (oxidizing gas) containing O ₂ , water vapor (H ₂ O), NO, N ₂ O, or a mixed gas thereof to the reaction tube 201 via the gas supply tube 206. Note that a vacuum pump (not shown) may be connected to the downstream side of the reaction tube 201.

  The control unit 211 is electrically connected to the heating means 202, the holder 205, the gas valve 207, the oxidant supply source 208, the wire 204, and the opening lid 210. Based on the temperature of the reaction tube 201 and the substrate 200 to be processed measured by the wire 204 and the time indicated by the clock (not shown) of the control unit 211, the control unit 211 is heated by the heating means 202, and the oxidizing agent. Flow rate, joining and separation between the holder 205 and the substrate 200, opening and closing of the opening lid 210, and the like are controlled. The control unit 211 is configured by, for example, a microprocessor or a memory having a CPU function.

<Method for forming oxide film>
Next, an example of an oxide film forming process using the semiconductor manufacturing apparatus according to the second embodiment of the present invention shown in FIG. 19 will be described with reference to FIGS. FIG. 21 is a flowchart of an oxide film generation process according to the second embodiment of the present invention, and FIG. 22 is a timing chart showing a temperature change in the oxide film generation process according to the second embodiment of the present invention. . As shown in the flowchart of FIG. 21, the oxide film forming step includes a temperature raising process in step S31, an oxidation process in step S32, and a cooling process in step S33.

  As shown in FIG. 19, a substrate to be processed 200 made of SiC is mounted on a susceptor 203 of a reaction tube 201. The substrate to be processed 200 is bonded to one end of the wire 204. The to-be-processed base body 200 is held by a holder 205 so that it can fall freely when separated from the holder 205. In addition, the to-be-processed base | substrate 200 may be in the state hung with the wire 204, or the state hold | maintained only by the holder 205, without mounting in the susceptor 203. FIG.

First, the temperature raising process in step S31 of FIG. 21 is performed. In the temperature raising process, as shown in FIG. 22, the substrate to be processed 200 is heated by the heating means 202 from time t30 to t31, and the temperature of the reaction tube 201 and the substrate to be processed 200 is increased to a predetermined temperature T2. The predetermined temperature T2 is equal to or higher than a temperature at which SiC can be thermally oxidized. The predetermined temperature T2 is preferably 1250 ° C. or higher and 1600 ° C. or lower. As will be described later, the temperature lower than 1250 ° C. is a state in which interface defects are easily formed in the oxide film, and when the oxide film is formed at this temperature, the interface state density _Dit increases. The time from time t30 to t31 is, for example, about 10 minutes.

Next, the oxidation process of step S32 in FIG. 21 is performed. In the oxidation process, as shown in FIG. 22, at time t31 to t32, heating is continued by the heating means 202, and the temperature of the substrate to be processed 200 measured by the wire 204 is maintained in a temperature range of about a predetermined temperature T2. . An oxidant supply source 208 supplies a gas (oxidizing gas) containing O ₂ , water vapor (H ₂ O), NO, N ₂ O, or a mixed gas thereof to the reaction tube 201 via the gas supply tube 206, The inside of the reaction tube 201 is a dry oxygen atmosphere. As a result, the surface of the substrate to be processed 200 is thermally oxidized in a dry oxygen atmosphere at atmospheric pressure, and, for example, a SiO ₂ film having a thickness of about 40 nm is formed. The time from time t31 to t32 is, for example, about 5 minutes.

  Next, the cooling process of step S33 in FIG. 21 is performed. In the cooling process, as shown in FIG. 22, at time t <b> 32, heating by the heating unit 202 is stopped, the target substrate 200 is separated from the holder 205, and the opening lid 210 is opened. The timing of separating the holder 205 and the substrate to be processed 200 is preferably before the opening lid 210 is opened. However, when the substrate to be processed 200 does not contact the closed opening lid 210, it may be immediately after the opening lid 210 is opened. Absent.

  The timing of stopping the heating by the heating means 202 is before separating the holder 205 and the substrate 200, after separating the holder 205 and the substrate 200, or separating the holder 205 and the substrate 200. It can be done at the same time. The timing of stopping the heating by the heating means 202 may be any of before opening the opening lid 210, after opening the opening lid 210, or simultaneously with opening the opening lid 210.

  As shown in FIG. 20, when the holder 205 and the substrate to be processed 200 are separated, the substrate to be processed 200 falls. Since the opening lid 210 is open, the substrate to be processed 200 is discharged from the reaction tube 201 and is put into the liquid tank 212. A liquid L having a temperature of 800 ° C. or lower is injected into the liquid tank 212 in order to rapidly cool the substrate 200 to be processed. Since the liquid L has a higher thermal conductivity than the gas, the substrate to be processed 200 is rapidly cooled.

  As shown in FIG. 22, the substrate to be processed 200 finishes cooling by time t33. The time from time t32 to t33 is, for example, within 2 seconds.

  Thereby, a series of processes in the oxide film forming process according to the second embodiment of the present invention is completed. By performing the oxide film forming step according to the second embodiment of the present invention, an oxide film is formed on the substrate to be processed 200. The characteristics of the oxide film formed in the oxide film forming process according to the second embodiment of the present invention will be described below.

FIG. 23 is a cross-sectional view showing a configuration of a MOS capacitor including an oxide film. As shown in FIG. 23, the MOS capacitor has an epitaxial layer 42 made of n-type SiC on a first main surface (front surface) of an n ⁺ -type SiC substrate 41, for example, a (0001) plane (Si surface). Is deposited. The base (41, 42) in which the SiC substrate 41 and the epitaxial layer 42 are combined corresponds to the target base 200 shown in FIGS.

  A capacitor insulating film 43 is provided on the surface of SiC epitaxial layer 42 opposite to SiC substrate 41. The capacitor insulating film 43 corresponds to the oxide film described above. An electrode 44 is provided on a part of the surface of the capacitor insulating film 43 opposite to the SiC substrate 41. An electrode 45 is provided on the second main surface (back surface) of SiC substrate 41.

<Example>
In order to measure the interface state density of the oxide film according to the second embodiment of the present invention, as an example, the capacitor insulating film 43 of the MOS capacitor shown in FIG. It was formed as an oxide film on the substrate 200 to be processed.

  Further, as a comparative example for comparison with the embodiment, the MOS capacitor is cooled to 800 ° C. or less in about 5 minutes after the temperature rising process in step S31 and the oxidation process in step S32 in the flowchart shown in FIG. Comparative Example A was prepared. Further, Comparative Example B was prepared in which the MOS capacitor was cooled to 800 ° C. or less in about 30 seconds after the temperature raising process in Step S31 and the oxidation process in Step S32 of the flowchart shown in FIG. For example, Comparative Example A was cooled by installing a MOS capacitor on a susceptor made of alumina, and Comparative Example B was cooled by installing a MOS capacitor on a susceptor made of SiC.

The MOS capacitors of the example, comparative example A and comparative example B were measured with a CV meter, and high-low due to the 1 MHz CV characteristic and the quasi-static (Quasi-Static) CV characteristic. The difference in interface state density _Dit was investigated by the method. FIG. 24 is a graph showing measured values of the interface state density _Dit of the oxide films of the examples and the oxide films of Comparative Examples A and B. The vertical axis in FIG. 24 indicates the interface state energy (Ec is the conduction band energy edge) in the band gap, and the vertical axis indicates the interface state density _Dit .

As shown in FIG. 24, in the example, it is recognized that the interface state density _Dit is lower than that of Comparative Example A and Comparative Example B in all energies. In particular, deep energy (Ec-E is large) is observed that the effect of reducing the interface state density D _it is large. Further, Comparative Example B is less effective than Comparative Example A, although the reduction effect is recognized at the interface state density _Dit having a deep energy. For this reason, when it cools to 800 degrees C or less in about 30 second time, it turns out that the reduction effect of interface state density _Dit is small. This is because, in the time when the MOS capacitor is at a temperature from 1250 ° C. to 800 ° C., an interface defect is easily formed, and an oxide film is further generated, and the interface state density D _it is increased by this oxide film. is there.

  Next, as described above, when the temperature T2 to be raised in the temperature raising process in step S31 in FIG. 21 is lower than 1250 ° C., it is explained that interface defects are easily formed in the oxide film. . In order to investigate the relationship between the oxide film formation temperature and the interface state density, Comparative Examples a to f were prepared. In Comparative Example a, the oxide film formation temperature is set to 1150 ° C., and after performing the temperature rising process in step S31 and the oxidation process in step S32 in the flowchart shown in FIG. Created by cooling. Comparative examples b to f are examples in which the oxide film formation temperatures are 1200 ° C., 1250 ° C., 1300 ° C., 1450 ° C., and 1600 ° C., respectively.

FIG. 25 is a graph showing measured values of interface state density at various oxide film formation temperatures. As shown in FIG. 25, it is recognized that the comparative example b has a lower interface state density D _it than the comparative example a, and the comparative example c has a lower interface state density D _it than the comparative example b. It is recognized that On the other hand, Comparative Example c~f is no significant difference in the reduction of interface state density _{D it.} Accordingly, the oxide film formation temperature of 1250 ° C. to 1600 ° C. is a state in which interface defects are hardly formed, and by setting the oxide film formation temperature to 1250 ° C. to 1600 ° C., the interface state density _Dit can be reduced. I understand that I can do it. On the contrary, a temperature lower than the oxide film formation temperature of 1250 ° C. is a state in which interface defects are easily formed in the oxide film. By setting the oxide film formation temperature lower than 1250 ° C., the interface state density D _it is increased. I understand that

  As described above, according to the second embodiment of the present invention, the interface defect is formed by lowering the temperature of the SiC substrate within 2 seconds from the end of the formation of the oxide film to the temperature at which the surface oxidation stops. The time during which it is easy to be done can be shortened. As a result, the time during which an oxide film is formed on the surface of the SiC substrate is shortened in a state where interface defects are easily formed, and the interface defects formed on the surface of the SiC substrate are reduced. For this reason, the interface state density on the surface of the SiC substrate can be reduced.

<First Modification>
As shown in FIG. 26, the oxidation furnace according to the first modification of the second embodiment of the present invention has a plurality of holders 205a and 205b below the wire 204, and a plurality of substrates 200a to be processed. , 200b is different from the structure of the oxidation furnace according to the second embodiment of the present invention shown in FIG. FIG. 26 illustrates the case where there are two each of the plurality of holders 205a and 205b and the plurality of substrates to be processed 200a and 200b, but the number of holders and substrates to be processed is not particularly limited.

  The plurality of substrates to be processed 200a and 200b are mounted on the plurality of susceptors 203a and 203b, respectively. When the plurality of holders 205a and 205b and the plurality of substrates to be processed 200a and 200b are separated in the cooling process after the formation of the oxide films on the plurality of substrates to be processed 200a and 200b, the plurality of substrates to be processed 200a and 200b are dropped. Then, it is put into the liquid tank 212 and rapidly cooled. Thereby, a good quality oxide film can be collectively formed with respect to the plurality of substrates to be processed 200a and 200b.

  Further, as shown in FIG. 27, a structure having a plurality of wires 204a and 204b and accommodating a plurality of substrates 200a and 200b connected to the plurality of wires 204a and 204b, respectively, may be used. By having the plurality of wires 204a and 204b, the temperatures of the plurality of substrates to be processed 200a and 200b can be individually detected.

<Second Modification>
In the second embodiment of the present invention, as a method for rapidly cooling the substrate to be processed 200, a method for putting the substrate to be processed 200 into the liquid tank 212 is exemplified, but the substrate to be processed 200 is rapidly cooled. The method to do is not limited to this. That is, any method can be used as long as the process substrate 100 can be rapidly cooled so that the oxide film is grown to a thickness of 0.1 nm or less while the temperature is lowered from the end of the formation of the oxide film to a temperature at which the surface oxidation stops.

  For example, as shown in FIG. 28, an oxidation furnace according to a second modification of the second embodiment of the present invention includes a quartz tube or the like in which one end is disposed in the vicinity of the substrate to be processed 200 in the reaction tube 201. The point which further comprises the cooling gas supply pipe 213 which consists of differs from the structure of the oxidation furnace which concerns on the 2nd Embodiment of this invention shown in FIG. A cooling gas supply source 214 is connected to the other end of the cooling gas supply pipe 213.

  In the oxide film forming process using the oxidation furnace according to the second modification of the second embodiment of the present invention, the cooling gas supply from the cooling gas supply source 214 is performed after the formation of the oxide film of the substrate 200 to be processed. By spraying a large amount of low-temperature gas onto the substrate to be processed 200 through the pipe 213, the substrate to be processed 200 can be rapidly cooled. If a non-oxidizing gas is used as the low temperature gas, an oxide film can be expected to grow to 0.1 nm or less even if the temperature drop takes 2 seconds or more.

(Other embodiments)
As described above, the present invention has been described according to the first and second embodiments. However, it should not be understood that the descriptions 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, in the first embodiment of the present invention, the method for manufacturing a lateral MOSFET using an SiC substrate as a semiconductor device has been described as an example. However, the present invention is not limited to this, and the vertical MOSFET using an SiC substrate is used. It can also be applied to semiconductor devices having various high voltage structures such as MOS static induction transistors (SIT), IGBTs, electrostatic induction thyristors having MOS gate structures, etc. There is an effect. The MOS gate structure is not limited to the planar gate structure, and may be a trench gate or a more complicated MOS gate structure.

  In the second embodiment of the present invention, the MOS capacitor using SiC is exemplified as the semiconductor device. However, the present invention is not limited to this, and the SiC substrate illustrated in the first embodiment of the present invention is used. The present invention can also be applied to a lateral MOSFET. Furthermore, the present invention can be applied to a semiconductor device having a high withstand voltage structure such as an electrostatic induction thyristor having a MOSFET, MOSSIT, IGBT, or MOS gate structure, and similar effects can be obtained. The MOS gate structure is not limited to the planar gate structure, and may be a trench gate or a more complicated MOS gate structure.

  In the first embodiment of the present invention, the horizontal semiconductor manufacturing apparatus has been described as shown in FIG. 1, but a vertical semiconductor manufacturing apparatus may be used. In addition, the first and second semiconductor manufacturing apparatuses of the present invention do not have to be single oxidation furnaces, and may be multipurpose furnaces having a function as a diffusion furnace or an annealing furnace.

  In the first and second embodiments of the present invention, the substrate to be processed (1, 2) having the SiC substrate 1 and the SiC layer 2, and the substrate to be processed (6, 6) having the SiC substrate 6 and the epitaxial layer 7 are provided. 7) The substrate to be processed (23, 24, 26) having the SiC substrate 23, the epitaxial layer 24 and the SiC layer 26, and the substrate to be processed (41, 42) having the SiC substrate 41 and the epitaxial layer 42 are described as an example. did. However, the “substrate to be processed” of the present invention is not limited to the multilayer structure as illustrated, and may be a single semiconductor substrate. Alternatively, for example, in FIG. 15, the portion of the epitaxial layer 24 may be an SiC substrate, and the portion of the SiC substrate 23 may be an epitaxial growth layer or an impurity introduction layer.

  Further, the semiconductor manufacturing apparatus and the semiconductor device manufacturing method according to the first and second embodiments of the present invention may be appropriately combined. For example, the semiconductor manufacturing apparatus according to the first embodiment of the present invention shown in FIG. 1 is a vertical type, and the wire 204 and the holder 205 included in the semiconductor manufacturing apparatus according to the second embodiment of the present invention shown in FIG. Further, an opening lid 210, a liquid tank 212, and the like may be further provided.

  Then, in the method of manufacturing a semiconductor device according to the first embodiment of the present invention, when the temperature lowering process in step S13 of FIG. 100 may be rapidly cooled. That is, the cooling time of the substrate 100 to be processed at times t14 to t15 shown in FIGS. 3A to 3C is set to 2 seconds or less, and the oxide film is grown to 0.1 nm or less at the times t14 to t15. You may let them. Similarly, when the temperature lowering process in step S24 in FIG. 8 is performed, the time from time t26 to t27 shown in FIGS. 9A to 9C is set to 2 seconds or less, and the time from time t26 to t27 is set. The oxide film may be grown to 0.1 nm or less.

  As described above, the present invention can be applied to various semiconductor device manufacturing methods and semiconductor manufacturing apparatuses used therefor without departing from the scope of the invention described in the claims.

  A semiconductor device manufacturing method according to the present invention and a semiconductor manufacturing apparatus used therefor are high withstand voltage semiconductor devices used for power transmission, in addition to high withstand voltage semiconductor devices used in power supply devices and power conversion devices for various industrial machines. It is also useful for semiconductor devices and the like.

DESCRIPTION OF SYMBOLS 1, 6, 23, 41 ... SiC substrate 2, 7, 24, 42 ... Epitaxial layer 3, 43 ... Capacitor insulating film 4, 5, 22, 44, 45 ... Electrode 8, 10 ... Mask 9 ... Phosphorus ion 11 ... Aluminum Ion 12 ... Drain region 13, 28a, 28b ... Source region 14 ... Ground region 15 ... Field oxide film 16 ... Active regions 17, 31 ... Gate insulating films 18, 32 ... Gate electrodes 19a, 19b ... Contact metals 20a, 20b ... Reaction Layers 21a to 21c ... Pad electrodes 25a, 25b ... p-type region 26 ... SiC layer 27 ... n-type regions 29a, 29b ... Contact regions 30a, 30b ... Source electrode 33 ... Drain electrode 71 ... Photoresist film 72 ... Interlayer insulating film 100 , 200, 200a, 200b... Substrate 101, 201... Reaction tube 102, 202. 103, 203, 203a, 203b ... susceptors 105, 106,206 ... gas supply pipes 107,108,207 ... gas valve 109 ... exhaust pipe 110 ... vacuum pump 111 ... oxidizer concentration meter 112 ... temperature measuring means 113 ... inert gas supply Sources 114, 208 ... Oxidant supply sources 120, 211 ... Control units 204, 204a, 204b ... Wires 205, 205a, 205b ... Holders 210 ... Opening lid 212 ... Liquid tank 213 ... Cooling gas supply pipe 214 ... Cooling gas supply source

Claims (25)

Forming a silicon oxide film by thermally oxidizing the surface of the substrate to be processed by supplying a gas containing an oxidant to the surface of the substrate to be processed using silicon carbide as a material;
After the step of forming the silicon oxide film, reducing the partial pressure of the oxidant in the gas to 10 Pa or less to replace the atmosphere;
After the step of replacing the atmosphere, lowering the temperature of the substrate to be processed;
A method for manufacturing a semiconductor device, comprising:   The step of replacing the atmosphere includes reducing the partial pressure of the oxidant to 10 Pa or less by exhausting the gas remaining in the reaction tube in which the substrate to be processed is accommodated using a vacuum pump. The method of manufacturing a semiconductor device according to claim 1. Replacing the atmosphere comprises:
By exhausting the gas remaining in the reaction tube containing the substrate to be processed using a vacuum pump, the partial pressure of the oxidant is reduced to 10 Pa or less,
2. The method according to claim 1, further comprising: replacing the inside of the reaction tube with an inert gas atmosphere by supplying an inert gas into the reaction tube after reducing the partial pressure of the oxidizing agent to 10 Pa or less. The manufacturing method of the semiconductor device of description.   In the step of replacing the atmosphere, the partial pressure of the oxidizing agent in the reaction tube is reduced to 10 Pa or less by supplying an inert gas into the reaction tube in which the substrate to be processed is housed to dilute the oxidizing agent. The method of manufacturing a semiconductor device according to claim 1, further comprising:   5. The method of manufacturing a semiconductor device according to claim 1, wherein the step of forming the silicon oxide film is performed in a temperature range of 1250 ° C. or more and 1600 ° C. or less.   The method for manufacturing a semiconductor device according to claim 1, wherein the step of replacing the atmosphere is performed at a temperature of 1250 ° C. or higher.   The method for manufacturing a semiconductor device according to claim 1, further comprising a POA process between the step of forming the silicon oxide film and the step of replacing the atmosphere.   8. The oxidant used in the step of forming the silicon oxide film includes at least one of oxygen, water vapor, nitrogen monoxide, and dinitrogen monoxide. A method for manufacturing the semiconductor device according to the item.   5. The method for manufacturing a semiconductor device according to claim 3, wherein the inert gas used in the step of replacing the atmosphere includes at least one of argon, helium, and nitrogen.   8. The POA process according to claim 7, wherein a gas containing at least one of hydrogen, water vapor, nitric oxide, dinitrogen monoxide, and ammonia is supplied to a surface of the substrate to be processed. A method for manufacturing a semiconductor device.   8. The method of manufacturing a semiconductor device according to claim 7, wherein the step of replacing the atmosphere is performed at the same temperature as the POA process.   12. The substrate to be processed, on which the silicon oxide film is formed after the temperature of the substrate to be processed becomes 800 ° C. or lower after the step of lowering the temperature, is taken out to the atmosphere. A method for manufacturing the semiconductor device according to the item. Forming a silicon oxide film by thermally oxidizing the surface of the substrate to be processed by supplying a gas containing an oxidant to the surface of the substrate to be processed using silicon carbide as a material;
After the step of forming the silicon oxide film, lowering the temperature of the substrate to be processed to a temperature at which oxidation of the surface of the substrate to be processed stops within 2 seconds from the end of the formation of the silicon oxide film; A method for manufacturing a semiconductor device, comprising:   14. The method of manufacturing a semiconductor device according to claim 13, wherein the silicon oxide film is grown to a thickness of 0.1 nm or less while the temperature of the substrate to be processed is lowered.   15. The method of manufacturing a semiconductor device according to claim 13, wherein in the step of lowering the temperature, the temperature of the substrate to be processed is lowered by putting the substrate to be processed into a liquid tank into which a liquid has been injected. Method. A reaction tube containing a substrate to be processed made of silicon carbide;
A gas supply pipe for supplying a gas containing an oxidant into the reaction pipe;
With
By supplying the gas, the surface of the substrate to be processed is thermally oxidized to form a silicon oxide film, and after forming the silicon oxide film, the partial pressure of the oxidizing agent in the reaction tube is reduced to 10 Pa or less. Then, the semiconductor manufacturing apparatus is characterized in that the temperature in the reaction tube is lowered.   The semiconductor manufacturing apparatus according to claim 16, further comprising an oxidant concentration meter that measures a partial pressure of the oxidant.   18. The semiconductor manufacturing apparatus according to claim 16, further comprising a susceptor made of a material containing silicon carbide for holding the substrate to be processed in the reaction tube.   The semiconductor manufacturing apparatus according to claim 16, further comprising a temperature measuring unit that measures a temperature of the substrate to be processed.   The semiconductor manufacturing apparatus according to any one of claims 16 to 19, further comprising heating means for heating the substrate to be processed. A reaction tube containing a substrate to be processed made of silicon carbide;
A gas supply pipe for supplying a gas containing an oxidant into the reaction pipe;
With
By supplying the gas, the surface of the substrate to be processed is thermally oxidized to form a silicon oxide film, and after forming the silicon oxide film, the temperature of the substrate to be processed is changed to the oxidation of the surface of the substrate to be processed. The semiconductor manufacturing apparatus is characterized in that the temperature is lowered within 2 seconds from the end of the formation of the silicon oxide film until the temperature stops.   The semiconductor manufacturing apparatus according to claim 21, wherein the silicon oxide film is grown to a thickness of 0.1 nm or less while the temperature of the substrate to be processed is lowered. A liquid tank disposed outside the reaction tube and filled with a liquid;
23. The semiconductor manufacturing apparatus according to claim 21, wherein the temperature of the substrate to be processed is lowered by putting the substrate to be processed into the liquid tank. A wire disposed in the reaction tube, bonded to the substrate to be processed, and capable of measuring the temperature of the substrate to be processed;
And a holder that is disposed in the reaction tube and holds the substrate to be processed when thermally oxidized to form a silicon oxide film and separates from the substrate to be processed when the temperature is lowered. The semiconductor manufacturing apparatus according to claim 23.   23. The semiconductor manufacturing apparatus according to claim 22, further comprising a cooling gas supply pipe that is disposed in the reaction tube and blows a cooling gas onto a surface of the substrate to be processed when the temperature is lowered.

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