JP6348430B2 - Manufacturing method of semiconductor device - Google Patents

Description

  The technology disclosed in this specification relates to a method for manufacturing a semiconductor device.

  Patent Document 1 discloses a technique in which a protective film is formed on the front and back surfaces of a SiC substrate, and then the SiC substrate is heat-treated. According to this method, the sublimation of Si from the SiC substrate is suppressed by the protective film during the heat treatment.

JP 2011-35257 A

  In recent years, a thin SiC substrate has been used to reduce the loss of a semiconductor device. When a SiC substrate having a small thickness is used, the stress balance in the SiC substrate may be lost during the manufacturing process, and the SiC substrate may be warped. In order to alleviate such warpage of the SiC substrate, a warpage adjustment film may be formed on the back surface of the SiC substrate. By forming the warp adjusting film, it is possible to reduce the warp of the SiC substrate as compared to before the warp adjusting film is formed. For this reason, it can process with respect to a SiC substrate with high flatness.

  When a protective film is formed on the back surface as in the technique of Patent Document 1 and the protective film is removed after the heat treatment, the warpage adjusting film can be formed on the back surface after removing the protective film. However, in this case, the warp adjusting film is formed on the back surface of the SiC substrate through four steps of forming a protective film on the back surface, heat treatment, removing the protective film from the back surface, and forming a warp adjusting film on the back surface. It is formed. There is a problem that the number of processes is large and the production efficiency is poor.

  On the other hand, if a protective film is not formed on the back surface, Si is sublimated from the back surface of the SiC substrate during heat treatment, and a carbon-rich layer is formed on the back surface. When the warp adjusting film is formed on the carbon rich layer, the warp adjusting film is easily peeled off from the SiC substrate together with the carbon rich layer. For this reason, in a subsequent process, the warpage adjusting film is peeled off from the SiC substrate together with the carbon-rich layer. Since the film peeled off becomes particles, this method cannot manufacture a high-quality semiconductor device. Therefore, the present specification provides a manufacturing method capable of efficiently manufacturing a high-quality semiconductor device.

  The method for manufacturing a semiconductor device disclosed in this specification includes a step of forming a protective film on a surface of a SiC substrate, a step of heat-treating the SiC substrate on which the protective film is formed, and a back surface of the SiC substrate in the heat treatment. A step of removing the carbon-rich layer formed on the surface, and a step of forming a warpage adjusting film on the back surface from which the carbon-rich layer has been removed. The SiC substrate has a warp before the warp adjustment film is formed, and the warp of the SiC substrate is reduced after the warp adjustment film is formed.

  In this manufacturing method, a warpage adjusting film is formed on the back surface of the SiC substrate from which the carbon-rich layer has been removed. Therefore, the warpage adjusting film is strongly bonded to the SiC substrate, and the warpage adjusting film can be prevented from peeling off from the SiC substrate. Therefore, generation of particles can be suppressed, and a high-quality semiconductor device can be manufactured. Further, in this manufacturing method, the warp adjustment film can be formed in three steps, that is, a heat treatment step, a step of removing the carbon rich layer, and a step of forming a warp adjustment film on the back surface of the SiC substrate. That is, the warp adjusting film can be formed with a small number of steps. Thus, according to the manufacturing method of this specification, a high quality semiconductor device can be manufactured efficiently.

The longitudinal cross-sectional view of the SiC substrate 12. FIG. 6 is a flowchart showing a manufacturing process of a semiconductor device. The longitudinal cross-sectional view of the SiC substrate 12 in which the protective film 14 was formed. The longitudinal cross-sectional view of the SiC substrate 12 after a heat treatment process. The longitudinal cross-sectional view of the SiC substrate 12 from which the protective film 14 was removed. FIG. 3 is an explanatory diagram of a plasma etching apparatus 60. The longitudinal cross-sectional view of the SiC substrate 12 which warped so that the surface 12a might become convex after the carbon rich layer 16 was removed. The longitudinal cross-sectional view of the SiC substrate 12 in which the curvature adjustment film | membrane 18 was formed. Explanatory drawing of the plasma etching apparatus 80. FIG. The longitudinal cross-sectional view of the SiC substrate 12 which warped so that the surface 12a might become concave after the carbon rich layer 16 was removed.

  In the manufacturing method of the present embodiment, a semiconductor device is manufactured from the SiC substrate 12 shown in FIG. The manufactured semiconductor device is, for example, a MOSFET or a diode. In addition, the SiC substrate 12 is subjected to thinning processing in advance. For this reason, the thickness of the SiC substrate 12 is thin. In this manufacturing method, each process is implemented according to the flowchart shown in FIG.

(Ion implantation process)
First, in step S2, ion implantation is performed. In the ion implantation step S2, n-type impurities and p-type impurities are implanted into the surface 12a of the SiC substrate 12. Ion implantation is repeatedly performed while selecting an implantation range and implantation depth.

(Protective film formation process)
Next, in step S4, protective film 14 is formed on surface 12a of SiC substrate 12, as shown in FIG. Here, the protective film 14 is formed by carbon sputtering. Protective film 14 is formed over the entire surface 12 a of SiC substrate 12.

(Heat treatment process)
Next, in step S6, the SiC substrate 12 with the protective film 14 is placed in the furnace, and the SiC substrate 12 is heat-treated. Here, SiC substrate 12 is heated to a temperature of 1700 ° C. or higher. The n-type impurity and the p-type impurity implanted into the SiC substrate 12 in the ion implantation step S2 are activated by the heat treatment. For this reason, an n-type semiconductor region and a p-type semiconductor region are formed in the SiC substrate 12. Further, Si is sublimated from the back surface 12b of the SiC substrate 12 by the heat treatment. Therefore, as shown in FIG. 4, the carbon rich layer 16 having a higher C concentration than Si is formed on the back surface 12b. On the other hand, the surface 12 a of the SiC substrate 12 is covered with a protective film 14. For this reason, sublimation of Si from surface 12 a of SiC substrate 12 is suppressed by protective film 14. Therefore, a carbon rich layer is not formed on surface 12a of SiC substrate 12.

(Protective film removal process)
Next, in step S8, the protective film 14 is removed. More specifically, first, ashing is performed on the protective film 14 to peel the protective film 14 from the SiC substrate 12. Next, the surface 12a of the SiC substrate 12 is subjected to SPM cleaning, and the residue of the protective film 14 is removed from the surface 12a. Thereby, as shown in FIG. 5, surface 12a of SiC substrate 12 is exposed.

(Carbon rich layer removal process)
Next, in step S10, the carbon rich layer 16 is removed. Here, the carbon rich layer 16 is removed by dry etching.

  FIG. 6 shows the plasma etching apparatus 60 used in the carbon rich layer removing step S10. The plasma etching apparatus 60 includes a gas supply pipe 62, a plasma generation chamber 64, a microwave generator 66, a chamber 68, a shower plate 70, a stage 72, and an exhaust pipe 74. The gas supply pipe 62 extends from the outside of the chamber 68 to the inside of the chamber 68. An etching gas is supplied to the upstream end of the gas supply pipe 62. The plasma generation chamber 64 is interposed in the middle of the gas supply pipe 62. The microwave generator 66 is disposed around the plasma generation chamber 64 and irradiates the plasma generation chamber 64 with microwaves. The shower plate 70 is installed in the chamber 68 and connected to the downstream end of the gas supply pipe 62. The stage 72 is installed at a position below the shower plate 70 in the chamber 68. The stage 72 is not connected to other wirings, and no external potential is applied to the stage 72. That is, the stage 72 is floating in potential. The exhaust pipe 74 is connected to the chamber 68 below the stage 72.

In the carbon rich layer removing step S10, first, the SiC substrate 12 is placed on the stage 72 as shown in FIG. Here, the surface 12 a of the SiC substrate 12 is brought into contact with the stage 72, and the surface of the carbon rich layer 16 is opposed to the shower plate 70. Further, the inside of the chamber 68 is heated to a temperature of 200 ° C. or higher. Next, the etching gas is supplied to the upstream end of the gas supply pipe 62 and the microwave generator 66 irradiates the plasma generation chamber 64 with microwaves. Here, a mixed gas of oxygen gas (O ₂ ) and fluorine compound gas (eg, CF ₄ or SF ₆ ) is used as the etching gas. In particular, in the present embodiment, a mixed gas in which the ratio of the fluorine compound gas in the mixed gas is 3 to 10% and the remainder is oxygen gas is used. The etching gas supplied to the upstream end of the gas supply pipe 62 flows into the plasma generation chamber 64. The etching gas is irradiated with microwaves in the plasma generation chamber 64. Thereby, the etching gas is turned into plasma. The plasma-ized etching gas flows downstream in the gas supply pipe 62 and flows into the chamber 68 from the shower plate 70. The etching gas that has flowed into the chamber 68 from the shower plate 70 flows along the surface of the carbon rich layer 16, and is then discharged from the exhaust pipe 74 to the outside of the chamber 68. The etching gas flowing along the surface of the carbon rich layer 16 reacts with the carbon rich layer 16 and chemically decomposes the carbon rich layer 16. As a result, the carbon rich layer 16 is etched. In the carbon rich layer removal step S10, the entire carbon rich layer 16 is removed.

  By using a mixed gas of oxygen gas and fluorine compound gas as an etching gas, the carbon rich layer 16 can be etched at a high etching rate. For this reason, carbon rich layer removal process S10 can be completed in a comparatively short time.

  If a low potential is applied to the stage 72, a potential difference occurs in the space on the stage 72. Then, the charged etching gas is accelerated toward the stage 72 and the etching gas collides with the carbon rich layer 16 at a high speed. When the etching gas collides with the carbon rich layer 16 at a high speed, the back surface 12b of the SiC substrate 12 after the carbon rich layer 16 is removed becomes rough. On the other hand, in this embodiment, since the potential of the stage 72 is floating, the acceleration of the etching gas due to the potential difference does not occur. For this reason, after the removal of the carbon rich layer 16, the back surface 12b of the SiC substrate 12 becomes smooth.

  When the processes from the ion implantation step S2 to the carbon rich layer removal step S10 are executed, the stress distribution inside the SiC substrate 12 changes. More specifically, the stress on the front surface 12a side and the stress on the back surface 12b side are imbalanced. For this reason, although not shown in FIGS. 3 to 5, the SiC substrate 12 is warped in the process of performing steps S <b> 2 to S <b> 10. Therefore, after the carbon rich layer removing step S10, the SiC substrate 12 is warped as shown in FIG. In the present embodiment, the SiC substrate 12 warps so that the surface 12a is convex.

(Warpage adjustment film forming process)
Next, in step S12, as shown in FIG. 8, a warpage adjusting film 18 is formed on the back surface 12b of the SiC substrate 12. More specifically, a silicon oxide film (that is, an insulating film) is grown (deposited) on the back surface 12b of the SiC substrate 12 by atmospheric pressure plasma CVD using TEOS (Tetraethyl orthosilicate) as a raw material. A silicon oxide film formed by this method is called a P-TEOS film. When the warpage adjusting film 18 (that is, the P-TEOS film) is grown on the back surface 12 b of the SiC substrate 12, compressive stress is generated in the warpage adjusting film 18. For this reason, when the warpage adjusting film 18 is formed, the warpage of the SiC substrate 12 is reduced as shown in FIG. In the present embodiment, the warp of the SiC substrate 12 is substantially eliminated, and the SiC substrate 12 becomes substantially flat.

(Surface-side machining process)
Next, in step S <b> 14, processing is performed on the surface 12 a side of the SiC substrate 12. In the surface side processing step S14, a structure necessary for a semiconductor device such as an electrode and an insulating film is formed on the surface 12a of the SiC substrate 12.

  For example, in the surface side processing step S14, the surface 12a of the SiC substrate 12 may be partially etched to form a trench. If the SiC substrate 12 is warped, a trench shape abnormality may occur during etching. On the other hand, in this embodiment, since the SiC substrate 12 is planarized, a trench can be formed with high accuracy during etching. As described above, since the SiC substrate 12 is flattened in the warpage adjusting film forming step S12, the SiC substrate 12 can be processed with high accuracy in the surface side processing step S14.

  Further, when the SiC substrate 12 is etched in the front surface side processing step S14 (for example, when a trench is formed), if the back surface 12b of the SiC substrate 12 is rough, the back surface 12b of the SiC substrate 12 becomes a stage during etching. Does not stick. For this reason, the in-plane temperature distribution of SiC substrate 12 becomes non-uniform at the time of etching, and etching accuracy may deteriorate. However, in this embodiment, since the back surface 12b becomes smooth after the removal of the carbon rich layer 16, such a problem does not occur. Therefore, etching can be performed with high accuracy.

  Thus, the SiC substrate 12 can be processed with high accuracy in the front surface side processing step.

  In addition, since warpage adjusting film 18 is directly bonded to back surface 12b of SiC substrate 12, warping adjusting film 18 is firmly bonded to back surface 12b. For this reason, it is possible to prevent the warp adjusting film 18 from being peeled off from the SiC substrate 12 in the surface side processing step S14. That is, if the warp adjusting film 18 is formed on the carbon rich layer 16 without removing the carbon rich layer 16, the carbon rich layer 16 is fragile, so that the warp adjusting film 18 together with the carbon rich layer 16 can be easily removed from the SiC substrate 12. Peel off. When these peel in the surface side processing step S14, the peeled warp adjusting film 18 and the carbon rich layer 16 become particles, which causes a problem in the surface side processing step S14. On the other hand, in the manufacturing method of the present embodiment, the warp adjustment film 18 is formed after the carbon rich layer 16 is removed, so that the warp adjustment film 18 is firmly bonded to the back surface 12b. Therefore, according to the method of the present embodiment, it is possible to prevent the warp adjusting film 18 from being peeled off from the SiC substrate 12 in the surface side processing step S14. For this reason, a semiconductor device can be manufactured with high quality.

(Back side processing process)
Next, in step S16, the back surface 12b of the SiC substrate 12 is processed. In the back surface side processing step S16, the warp adjusting film 18 is removed, and then the back surface 12b is processed. Thereafter, SiC substrate 12 is diced. The semiconductor device is completed through the above steps.

  As described above, according to the manufacturing method of the present embodiment, it is possible to prevent the warp adjustment film 18 from being peeled off from the SiC substrate 12. For this reason, a high-quality semiconductor device can be manufactured.

  In the manufacturing method of the present embodiment, the carbon rich layer 16 is allowed to be formed on the back surface 12b of the SiC substrate 12 in the heat treatment step S6. And the carbon rich layer 16 is removed in carbon rich layer removal process S10, and the curvature adjustment film | membrane 18 firmly connected to the SiC substrate 12 is formed by performing curvature adjustment film formation process S12 after that. In this method, the steps necessary for forming the warp adjusting film 18 are three steps, that is, a heat treatment step S6, a carbon rich layer removing step S10, and a warp adjusting film forming step S12. That is, according to this method, it is possible to form the warpage adjusting film 18 that is difficult to peel off in three steps. Similarly, as a method of forming the warp adjustment film 18 that is difficult to peel off, a method of preventing the formation of a carbon-rich layer on the back surface 12b in the heat treatment step is conceivable. In this method, a protective film is formed on the back surface 12b before the heat treatment step. Therefore, formation of carbon rich layer 16 on back surface 12b of SiC substrate 12 in the subsequent heat treatment is prevented. Next, the protective film on the back surface 12b is removed. Thereafter, the warpage adjusting film 18 is formed on the back surface 12b from which the protective film has been removed. Even with this method, it is possible to form the warp adjusting film 18 that is difficult to peel off. However, in this method, four steps are necessary to form the warp adjusting film 18: a back surface 12b protective film forming step, a heat treatment step, a back surface 12b protective film removing step, and a warp adjusting film forming step. In contrast, in the manufacturing method of the present embodiment, the warp adjustment film 18 that is difficult to peel off in three steps can be formed as described above. That is, according to the manufacturing method of this embodiment, a semiconductor device can be manufactured efficiently.

  The method for manufacturing the semiconductor device according to the present embodiment has been described above. In the above embodiment, the plasma etching apparatus 60 of FIG. 6 is used in the carbon rich layer removing step S10. However, the plasma etching apparatus 80 shown in FIG. 9 can also be used in the carbon rich layer removing step S10. The plasma etching apparatus 80 includes a gas supply pipe 82, a chamber 84, a shower plate 86, a stage 88, an exhaust pipe 90, and a high frequency power source 92. The gas supply pipe 82 extends from the outside of the chamber 84 to the inside of the chamber 84. An etching gas is supplied to the upstream end of the gas supply pipe 82. The shower plate 86 is installed in the chamber 84 and connected to the downstream end of the gas supply pipe 82. The shower plate 86 is made of metal and also serves as an electrode for generating plasma. The high frequency power source 92 is connected to the shower plate 86 and applies a high frequency voltage to the shower plate 86. The stage 88 is installed below the shower plate 86. The stage 88 is not connected to other wirings, and no external potential is applied to the stage 88. That is, the stage 88 is floating in terms of potential. The exhaust pipe 90 is connected to the chamber 84 below the stage 88.

  When plasma etching apparatus 80 of FIG. 9 is used, SiC substrate 12 is placed on stage 88 so that the surface of carbon rich layer 16 faces shower plate 70. Further, the inside of the chamber 68 is heated to a temperature of 200 ° C. or higher. Next, an etching gas is supplied to the upstream end of the gas supply pipe 82, and a high frequency voltage is applied to the shower plate 70 by the high frequency power source 92. Here, the same etching gas as that of the plasma etching apparatus 60 of FIG. 6 can be used. The etching gas supplied to the upstream end of the gas supply pipe 82 flows into the chamber 84 from the shower plate 86. Further, when a high frequency voltage is applied to the shower plate 70, microwaves are generated in the chamber 84. Therefore, the etching gas that has flowed into the chamber 84 is irradiated with microwaves and turned into plasma. The plasma-ized etching gas flows along the surface of the carbon rich layer 16, and is then discharged from the exhaust pipe 90 to the outside of the chamber 68. The etching gas flowing along the surface of the carbon rich layer 16 reacts with the carbon rich layer 16 and chemically decomposes the carbon rich layer 16. As a result, the carbon rich layer 16 is etched. Thereby, the carbon rich layer 16 is removed.

  Even when the plasma etching apparatus 80 is used, since the mixed gas of oxygen gas and fluorine compound gas is used as the etching gas, the carbon rich layer 16 can be etched at a high etching rate. Even when the plasma etching apparatus 80 is used, since the stage 88 is floating, the back surface 12b of the SiC substrate 12 becomes smooth after the carbon rich layer 16 is removed.

  In the plasma etching apparatus 80 of FIG. 9, since plasma is generated in the chamber 84, the SiC substrate 12 may be damaged by the plasma. When such damage becomes a problem, the plasma etching apparatus 80 in FIG. 6 (that is, an apparatus that generates plasma upstream of the chamber) is preferable.

  In the embodiment described above, after the carbon rich layer removing step S10, the SiC substrate 12 is warped so that the surface 12a is convex as shown in FIG. However, when the characteristics of the SiC substrate 12 and the processing on the SiC substrate 12 are different, the SiC substrate 12 may warp so that the surface 12a is concave as shown in FIG. In this case, in the warp adjustment film forming step S12, the warp adjustment film 18 that causes a tensile stress can be formed on the back surface 12b of the SiC substrate 12. By forming the warp adjustment film 18 that generates tensile stress, the warp of the SiC substrate 12 can be reduced. Examples of the warp adjusting film 18 that generates tensile stress include an LP-TEOS film, NSG, and BPSG. The LP-TEOS film is a silicon oxide film formed by low pressure CVD using TEOS as a raw material. The NSG (None-doped Silicate Glass) film is a silicon oxide film that does not contain impurities such as phosphorus and boron. A BPSG (Boro-phospho silicate glass) film is a silicon oxide film doped with phosphorus and boron.

  In the above-described embodiment, the protective film removal step S8 is performed immediately after the heat treatment step S6. However, the protective film 14 may be removed at any time after the heat treatment step S6.

  In the above-described embodiment, the carbon rich layer 16 is etched by performing dry etching with the stage in a floating state. According to this method, the back surface 12b of the SiC substrate 12 after etching becomes smooth as described above. As a method for smoothing the back surface after etching the carbon-rich layer, the back surface of the SiC substrate is oxidized to form a sacrificial oxide film, and then the carbon-rich layer and the sacrificial oxide film are removed by wet etching using hydrofluoric acid. There is a way. However, this method requires two steps, a sacrificial oxidation step and a wet etching step, in order to remove the carbon-rich layer. On the other hand, in the method of this embodiment, the carbon rich layer 16 can be removed only by dry etching.

  The technical elements disclosed in this specification are listed below. The following technical elements are each independently useful.

  In the configuration of an example disclosed in this specification, an insulating film is deposited on the back surface of the SiC substrate in the step of forming the warp adjustment film. The insulating film may be a TEOS film.

  In an example configuration disclosed in the present specification, in the step of removing the carbon rich layer, a SiC substrate is placed on the stage, and dry etching using plasma is performed on the carbon rich layer without applying a voltage to the stage. .

  According to this method, after removing the carbon rich layer, the surface of the SiC substrate becomes smooth.

  In an example configuration disclosed in this specification, a mixed gas of oxygen gas and fluorine compound gas is used in dry etching.

  According to this method, the carbon rich layer can be efficiently etched.

  The configuration of an example disclosed in this specification further includes a step of implanting impurities into the SiC substrate before forming the protective film.

  According to this method, the impurities implanted into the SiC substrate can be activated during the heat treatment.

The embodiments have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.
The technical elements described in this specification or the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology exemplified in this specification or the drawings achieves a plurality of objects at the same time, and has technical usefulness by achieving one of them.

12: SiC substrate 14: Protective film 16: Carbon rich layer 18: Warpage adjusting film 60: Plasma etching apparatus 80: Plasma etching apparatus

Claims (6)

A method for manufacturing a semiconductor device, comprising:
Forming a protective film on the surface of the SiC substrate;
Heat treating the SiC substrate on which the protective film is formed;
Removing the carbon rich layer formed on the back surface of the SiC substrate in the heat treatment;
Forming a warpage adjusting film on the back surface from which the carbon-rich layer has been removed,
Have
A manufacturing method in which the SiC substrate has a warp before the warp adjustment film is formed, and the warp of the SiC substrate is reduced after the warp adjustment film is formed.   The manufacturing method according to claim 1, wherein in the step of forming the warp adjusting film, an insulating film is deposited on the back surface.   The manufacturing method according to claim 2, wherein the insulating film is a TEOS film.   The said process of removing the said carbon rich layer places the said SiC substrate in a stage, and performs dry etching using plasma with respect to the said carbon rich layer, without applying a voltage to the said stage. Any one manufacturing method.   5. The method according to claim 4, wherein a gas mixture of oxygen gas and fluorine compound gas is used in the dry etching.   The manufacturing method according to claim 1, further comprising a step of injecting impurities into the SiC substrate before forming the protective film.

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