JP7259527B2 - Semiconductor substrate manufacturing method and semiconductor device manufacturing method - Google Patents

Description

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

Conventionally, when fabricating (manufacturing) a semiconductor device made of silicon carbide (SiC), a silicon carbide epitaxial film is formed on a starting substrate made of silicon carbide with a predetermined impurity concentration and a predetermined thickness according to the design conditions of the semiconductor device. An epitaxial substrate (semiconductor substrate) on which is epitaxially grown is required. This epitaxial substrate is usually a starting substrate placed on a tray in a CVD (Chemical Vapor Deposition) apparatus with the back side facing the tray. made in

As a method for manufacturing a semiconductor device using a semiconductor substrate obtained by forming a silicon carbide epitaxial film on a starting substrate made of silicon carbide, a silicon carbide epitaxial film is formed on the front surface of the starting substrate, and then the starting substrate is: A method of forming a carbonized film as a deformation control layer on the back surface of the substrate has been proposed (see, for example, Patent Document 1 below). In Patent Document 1 below, after a silicon carbide epitaxial film is formed on the front surface of a starting substrate, a deformation control layer is formed on the back surface of the starting substrate, so that the front surface side and the back surface side of the semiconductor substrate are separated. It adjusts the stress balance.

Further, as a method for manufacturing a semiconductor device using a semiconductor substrate formed by forming a silicon carbide epitaxial film on a starting substrate made of silicon carbide, the back surface of the starting substrate and the front surface of the silicon carbide epitaxial film are subjected to heat treatment for activation. A method has been proposed for forming a carbon film on each of the above (see, for example, Patent Document 2 below). In Patent Document 2 below, by forming carbon films on both surfaces of a semiconductor substrate, interfacial dislocations at the interface between the starting substrate and the silicon carbide epitaxial film and warping of the semiconductor substrate, which are caused by activation heat treatment, are eliminated. suppressed.

Japanese Patent No. 6136732 JP 2017-220653 A

However, in the above-described conventional method for manufacturing an epitaxial substrate, when the silicon carbide epitaxial film is epitaxially grown on the front surface of the starting substrate, the raw material gas flows into the rear surface of the starting substrate, which is the contact surface with the tray. Also on the rear surface of the starting substrate, an excessive silicon carbide film adheres to the portion where the raw material gas is supplied. Therefore, a process for removing the excess silicon carbide film on the back surface of the starting substrate is required.

Further, the thicker the silicon carbide epitaxial film epitaxially grown on the starting substrate, the greater the stress in the silicon carbide epitaxial film, and the greater the warpage of the epitaxial substrate formed of the starting substrate and the silicon carbide epitaxial film. When the warp of the epitaxial substrate increases, dislocations occur in the silicon carbide epitaxial film, adversely affecting the characteristics and yield of the semiconductor device, and the epitaxial substrate cannot be transported to various process equipment, causing problems in the manufacturing process. Occur.

SUMMARY OF THE INVENTION In order to solve the above-described problems of the prior art, the present invention provides a semiconductor substrate capable of suppressing adhesion of an excess silicon carbide film to a semiconductor substrate due to epitaxial growth and reducing warpage of the semiconductor substrate. An object of the present invention is to provide a manufacturing method and a manufacturing method of a semiconductor device.

In order to solve the above-described problems and achieve the objects of the present invention, a method for manufacturing a semiconductor substrate according to the present invention provides a semiconductor substrate obtained by epitaxially growing a silicon carbide epitaxial film on a first main surface of a starting substrate made of silicon carbide. and has the following characteristics. First, a first film forming step is performed to cover the second main surface of the starting substrate with a carbon film. Next, a second film formation step is performed to epitaxially grow the silicon carbide epitaxial film on the first main surface of the starting substrate with the second main surface covered with the carbon film. Next, a removing step is performed to selectively remove the carbon film and leave the carbon film at predetermined locations on the second main surface of the starting substrate. The first major surface of the starting substrate is the (0001) plane. The second main surface of the starting substrate is the (000-1) plane.

Further, in the method for manufacturing a semiconductor substrate according to the present invention, in the above-described invention, in the first film forming step, the carbon film is formed in a direction opposite to the first stress applied to the starting substrate by the silicon carbide epitaxial film. In addition, the thickness is such that a second stress is generated in the starting substrate to bring the starting substrate closer to flatness.

Further, in the method for manufacturing a semiconductor substrate according to the present invention, in the above-described invention, in the first film forming step, the second stress is applied to the carbon film by the remainder of the carbon film remaining after the removing step. It is characterized by being the thickness to be generated on the substrate.

Further, in the method of manufacturing a semiconductor substrate according to the present invention, in the above-described invention, the carbon film is made to have a thickness of 50 nm or more and 200 nm or less in the first film forming step.

Further, in the method of manufacturing a semiconductor substrate according to the present invention, in the above-described invention, the carbon film is left in the portion other than the portion to be the semiconductor chip in the removing step.

Further, in the method of manufacturing a semiconductor substrate according to the present invention, in the above-described invention, the carbon film is left in a ring shape along the outer circumference of the starting substrate in the removing step.

Further, in the method of manufacturing a semiconductor substrate according to the present invention, in the above-described invention, in the removing step, the carbon film is left in a grid shape along dicing lines surrounding a portion to be the semiconductor chip. .

Further, in the method for manufacturing a semiconductor substrate according to the present invention, in the above-described invention, in the removing step, the outermost dicing line among the dicing lines surrounding the periphery of the semiconductor chip and the outer periphery of the starting substrate are removed. , and the carbon film is left between.

Further, in the method of manufacturing a semiconductor substrate according to the present invention, in the above-described invention, the carbon film is left at a portion where the warp of the starting substrate becomes large due to the first stress in the removing step.

Further, in the method for manufacturing a semiconductor substrate according to the present invention, in the invention described above, a protecting step and a covering step are performed after the second film forming step and before the removing step. In the protecting step, the silicon carbide epitaxial film is protected with a protective film. In the covering step, the predetermined portion of the carbon film is covered with a metal mask. In the removing step, the carbon film is etched using the metal mask to leave the carbon film at the predetermined location on the second main surface of the starting substrate.

Further, in order to solve the above-described problems and achieve the object of the present invention, a method of manufacturing a semiconductor device according to the present invention comprises epitaxially growing a silicon carbide epitaxial film on a first main surface of a starting substrate made of silicon carbide. A method of manufacturing a semiconductor device using a semiconductor substrate has the following features. First, a first film forming step is performed to cover the second main surface of the starting substrate with a carbon film. Next, a second film formation step is performed to fabricate the semiconductor substrate by epitaxially growing the silicon carbide epitaxial film on the first main surface of the starting substrate with the second main surface covered with the carbon film. Next, a removing step is performed to selectively remove the carbon film and leave the carbon film at predetermined locations on the second main surface of the semiconductor substrate. Next, a first formation step is performed to form a predetermined device structure on the first main surface of the semiconductor substrate while leaving the remainder of the carbon film on the second main surface. Next, a second forming step is performed to form an electrode portion in contact with a portion other than the remaining portion of the carbon film on the second main surface of the semiconductor substrate. Next, a cutting step is performed to cut the semiconductor substrate into individual chips each having the element structure and the electrode portion. The first major surface of the starting substrate is the (0001) plane. The second main surface of the starting substrate is the (000-1) plane.

According to the method for manufacturing a semiconductor substrate and the method for manufacturing a semiconductor device according to the present invention, in manufacturing a semiconductor substrate in which a silicon carbide epitaxial film is epitaxially grown on the front surface of a starting substrate, during the epitaxial growth of the silicon carbide epitaxial film , the back surface of the starting substrate is covered with a carbon film. Therefore, adhesion of an extra silicon carbide film to the semiconductor substrate due to epitaxial growth can be suppressed. Moreover, since the stress applied to the starting substrate by the silicon carbide epitaxial film on the front surface side is opposite to the stress applied to the starting substrate by the carbon film on the back surface side, the warping of the semiconductor substrate can be reduced. It has the effect of being able to

4 is a flow chart showing an overview of a method for manufacturing a semiconductor device according to the first embodiment; FIG. 4 is a plan view showing a state in the middle of manufacturing the semiconductor substrate according to the first embodiment; FIG. 4 is a cross-sectional view showing a state in the middle of manufacturing the semiconductor substrate according to the first embodiment; FIG. 4 is a cross-sectional view showing a state in the middle of manufacturing the semiconductor substrate according to the first embodiment; FIG. 4 is a plan view showing a state in the middle of manufacturing the semiconductor substrate according to the first embodiment; FIG. 4 is a plan view showing a state in the middle of manufacturing the semiconductor substrate according to the first embodiment; 1 is a cross-sectional view showing an example of the structure of a semiconductor device manufactured by the method for manufacturing a semiconductor device according to the first embodiment; FIG. FIG. 10 is a plan view showing an example of a state in the middle of manufacturing the semiconductor substrate according to the second embodiment; FIG. 10 is a plan view showing an example of a state in the middle of manufacturing the semiconductor substrate according to the second embodiment; FIG. 10 is a plan view showing an example of a state in the middle of manufacturing the semiconductor substrate according to the second embodiment; 5 is a chart showing the amount of warp during the manufacture of the semiconductor substrate according to the example. FIG. 4 is a cross-sectional view showing an example of warping of a general semiconductor substrate after forming an epitaxial film;

Preferred embodiments of a method for manufacturing a semiconductor substrate and a method for manufacturing a semiconductor device according to the present invention will be described in detail below with reference to the accompanying drawings. In this specification and the accompanying drawings, layers and regions prefixed with n or p mean that electrons or holes are majority carriers, respectively. Also, + and - attached to n and p mean that the impurity concentration is higher and lower than that of the layer or region not attached, respectively. In the following description of the embodiments and the accompanying drawings, the same configurations are denoted by the same reference numerals, and overlapping descriptions are omitted. In this specification, in the notation of the Miller index, "-" means a bar attached to the index immediately after it, and adding "-" before the index indicates a negative index.

(Embodiment 1)
A method of manufacturing a semiconductor substrate according to the first embodiment and a method of manufacturing a semiconductor device according to the first embodiment which is manufactured (manufactured) using this semiconductor substrate will be described. FIG. 1 is a flow chart showing an outline of a method for manufacturing a semiconductor device according to a first embodiment. Steps S1 to S7 in FIG. 1 are a flow chart showing an overview of the method for manufacturing the semiconductor substrate 11 according to the first embodiment. 2, 5, and 6 are plan views showing states in the middle of manufacturing the semiconductor substrate according to the first embodiment. 3 and 4 are cross-sectional views showing states in the middle of manufacturing the semiconductor substrate according to the first embodiment. FIG. 7 is a cross-sectional view showing an example of the structure of a semiconductor device manufactured by the semiconductor device manufacturing method according to the first embodiment.

FIG. 2 shows the state of the starting substrate 1 before the processing of step S1 in FIG. 1 as viewed from the front surface 1a side. FIG. 3 shows the state of the starting substrate 1 after the processing of step S1 in FIG. FIG. 4 shows the state of the semiconductor substrate 11 after the processing in step S2 of FIG. 5 and 6 respectively show the state of the semiconductor substrate 11 after the processing in steps S5 and S6 of FIG. 1 as seen from the back surface 11b side. FIG. 7 shows a cross-sectional structure of a semiconductor device manufactured using the semiconductor substrate 11 after the processing in step S8 of FIG. FIG. 7 also shows two adjacent unit cells (element functional units) of MOSFETs as an example of a semiconductor device formed in the effective region of the semiconductor substrate 11 . An effective area is an area used as a semiconductor chip.

First, a method for manufacturing the semiconductor substrate 11 according to the first embodiment will be described. As shown in FIG. 2, a starting substrate (semiconductor wafer) 1 of, for example, 4 inches made of silicon carbide (SiC) is prepared. The starting substrate 1 constitutes, for example, a back surface 11b (see FIG. 4) of a semiconductor substrate (semiconductor wafer) 11, which will be described later. be. The starting substrate 1 may be, for example, a four-layer periodic hexagonal (4H—SiC) single crystal substrate of silicon carbide. The front surface 1a of the starting substrate 1 is the (0001) plane, the so-called Si plane, and the back surface 1b (see FIG. 3) is the (000-1) plane, the so-called C plane.

The starting substrate 1 has, for example, orientation flats 2 a and 2 b that indicate the plane orientation of the starting substrate 1 . In FIG. 2, two orientation flats (linear cutouts) 2a, which are linear in directions X and Y parallel to the front surface of the starting substrate 1 and perpendicular to each other, are provided at the end of the starting substrate 1. 2b is formed. The number of orientation flats can be increased or decreased as long as the plane orientation of the starting substrate 1 can be detected and the position of the starting substrate 1 can be adjusted when transported to the manufacturing apparatus. Notches (V-shaped planar cutouts) may be formed instead of the orientation flats 2a and 2b.

Next, the starting substrate 1 is cleaned by a general semiconductor substrate cleaning method (for example, an organic cleaning method or an RCA cleaning method). Next, a carbon (C) film 3 is formed on the rear surface 1b (that is, the C surface) of the starting substrate 1 by sputtering to cover the entire rear surface 1b of the starting substrate 1 with the carbon film 3 (step S1). In the process of step S1, it is sufficient that a target (not shown) made of carbon and the back surface 1b of the starting substrate 1 are arranged to face each other in a chamber of a sputtering device (not shown). For example, the process of step S1 may be performed by a sputtering-down method in which a target is arranged above the starting substrate 1 . The target, for example, has a carbon purity of about 99.9% or more, and has a disk shape larger than the starting substrate 1 and having an outer shape of about 6 inches, for example.

Specifically, argon (Ar) gas having a gas pressure of 2 Pa, for example, introduced into the chamber of the sputtering apparatus is brought into a plasma state by a high electric field applied between the target and the rear surface 1b of the starting substrate 1. FIG. A DC (Direct Current) power applied between the target and the starting substrate 1 may be about 600 W, for example. Argon ions accelerated by the high electric field between the target and the back surface 1 b of the starting substrate 1 collide (sputter) with the target, and carbon atoms, which are the target material sputtered from the target, are deposited on the back surface 1 b of the starting substrate 1 . Thus, the carbon film 3 is formed. The carbon film 3 functions as a carbon cap that protects the rear surface 1b of the starting substrate 1 regardless of the thickness t1.

Further, after the carbon film 3 is formed, the starting substrate 1 is in a warped state so as to protrude toward the rear surface 1b side, as shown in FIG. The warp amount h1 of the starting substrate 1 is, for example, within a range of approximately 10 μm to 200 μm. The warp amount h1 of the starting substrate 1 is controlled by the thickness t1 of the carbon film 3. FIG. If the thickness t1 of the carbon film 3 is thin, the warp amount h1 of the starting substrate 1 is small, and if the thickness t1 of the carbon film 3 is too thick, the starting substrate 1 may crack. Specifically, the thickness t1 of the carbon film 3 is suitably, for example, about 50 nm or more and 200 nm or less. For example, without heating the starting substrate 1, the carbon film 3 having a thickness t1 of about 130 nm is formed in a film forming time of about 25 minutes. The amount of warp h1 of the starting substrate 1 is the height difference between the apex of the most convex portion toward the back surface 1b side in the thickness direction Z of the starting substrate 1 and the edge of the back surface 1b of the starting substrate 1 .

Next, the starting substrate 1 with the carbon film 3 formed on the rear surface 1b is cleaned by a general semiconductor substrate cleaning method. Next, starting substrate 1 is inserted into a chamber of an epitaxial growth apparatus (not shown), and silicon carbide epitaxial film 4 is formed on front surface 1a of starting substrate 1 (step S2). The epitaxial growth apparatus may be, for example, a CVD (Chemical Vapor Deposition) apparatus. The tray on which the starting substrate 1 is placed when the starting substrate 1 is fixed in the chamber of the epitaxial growth apparatus has, for example, a convex shape on the back surface 1b side of the starting substrate 1 on the surface on which the starting substrate 1 is placed (see FIG. 3). You may have a recessed part (counterbore) so that it may meet.

Through the steps up to this point, as shown in FIG. 4, semiconductor substrate 11, which is an epitaxial substrate in which silicon carbide epitaxial film 4 is laminated on front surface 1a of starting substrate 1, is fabricated. Silicon carbide epitaxial film 4 forms front surface 11 a (that is, Si surface) of semiconductor substrate 11 , and its conductivity type and thickness t 2 are determined by the element structure of the semiconductor device fabricated on semiconductor substrate 11 . The thickness t2 of the silicon carbide epitaxial film 4 is set according to, for example, the breakdown voltage. If there is, it is about 270 μm. The breakdown voltage is the limit voltage at which the leakage current does not increase excessively and the device does not malfunction or break down.

Silicon carbide epitaxial film 4 on front surface 1a of starting substrate 1 causes starting substrate 1 to warp in a direction opposite to carbon film 3 on rear surface 1b of starting substrate 1 . That is, silicon carbide epitaxial film 4 causes stress in starting substrate 1 in the direction of reducing warp amount h1 (see FIG. 3) of starting substrate 1 having carbon film 3 formed on rear surface 1b. Therefore, the warp amount h1' of the starting substrate 1 after the silicon carbide epitaxial film 4 is formed is smaller than the warp amount h1 of the starting substrate 1 before the silicon carbide epitaxial film 4 is formed. A warp amount h1' of starting substrate 1 after deposition of silicon carbide epitaxial film 4 is preferably within a range of, for example, about 0 μm or more and 100 μm or less. A warp amount h1' of starting substrate 1 after deposition of silicon carbide epitaxial film 4 is a warp amount h11 of semiconductor substrate 11 with carbon film 3 deposited on back surface 11b.

Next, the semiconductor substrate 11 is taken out from the epitaxial growth apparatus and cleaned by a general semiconductor substrate cleaning method. Next, a resist is applied to the front surface 11a of the semiconductor substrate 11 (that is, the surface of the silicon carbide epitaxial film 4) using a coater and a developer, and the semiconductor substrate 11 is exposed to light. The front surface 11a of is protected with a resist film having a thickness of about 2 μm, for example (step S3). Next, the semiconductor substrate 11 whose front surface 11a is protected with a resist film is inserted into a chamber of a dry etching apparatus and dry-etched to remove an excess silicon carbide film adhering to the back surface 11b of the semiconductor substrate 11. , the entire surface of the carbon film 3 is exposed (step S4).

In the process of step S4, for example, sulfur hexafluoride (SF ₆ ) gas introduced as an etching gas into the chamber of the dry etching apparatus is ionized or radicalized by plasma generated in the chamber, and this reactive ion species is converted into Reactive ion etching in which etching is performed using a ions may also be used. In the process of step S4, the tray on which the semiconductor substrate 11 is placed when fixing the semiconductor substrate 11 in the chamber of the dry etching apparatus may have a flat surface on which the semiconductor substrate 11 is placed. If no excess silicon carbide film adheres to the surface of the portion of carbon film 3 to be left after the process of step S6, which will be described later, the process of step S4 may be omitted.

Next, the semiconductor substrate 11 is removed from the dry etching apparatus, and as shown in FIG. 5, a predetermined portion of the carbon film 3 is covered with a metal mask 21 (step S5). The predetermined portion of the carbon film 3 is the portion of the carbon film 3 that remains after the process of step S6, which will be described later. Specifically, the predetermined portion of the carbon film 3 is, for example, the portion of the carbon film 3 along the outer circumference of the semiconductor substrate 11 . The metal mask 21 is disk-shaped and ring-shaped and has an outer shape larger than that of the semiconductor substrate 11 . That is, the portion of the carbon film 3 along the outer periphery of the semiconductor substrate 11 is covered with a ring-shaped metal mask 21 , and the central portion is exposed through the opening of the metal mask 21 . In FIG. 5, the outer circumference of the semiconductor substrate 11 is indicated by a dashed line. Orientation flats 12 a and 12 b of the semiconductor substrate 11 are formed at positions corresponding to the orientation flats 2 a and 2 b of the starting substrate 1 .

More specifically, in the process of step S5, the main surface on which the carbon film 3 is formed (that is, the back surface 11b) is placed on a tray on which the semiconductor substrate 11 is placed when the semiconductor substrate 11 is fixed in the chamber of the dry etching apparatus. ) facing up, the semiconductor substrate 11 is placed. A metal mask 21 is fixed to the tray so as to face the carbon film 3 , and the portion of the carbon film 3 along the outer periphery of the semiconductor substrate 11 is covered with the metal mask 21 . The metal mask 21 has screw holes 22 for fixing the metal mask 21 to a tray on which the semiconductor substrate 11 is placed with screws (not shown). The tray on which the semiconductor substrate 11 is placed in the process of step S5 may have, for example, a concave portion (counterbore) corresponding to the thickness of the semiconductor substrate 11 on the surface on which the semiconductor substrate 11 is placed.

Next, the semiconductor substrate 11 with a predetermined portion of the carbon film 3 covered with the metal mask 21 is inserted into a chamber of a dry etching apparatus and dry etched to remove the portion of the carbon film 3 not covered with the metal mask 21 . (step S6). As a result of the processing in step S6, as shown in FIG. 6, only the portion 3a (hatched portion) of the carbon film 3 along the outer periphery of the semiconductor substrate 11 covered with the metal mask 21 remains in a ring shape. In the process of step S6, for example, oxygen (O ₂ ) gas introduced as an etching gas into the chamber of the dry etching apparatus is ionized or radicalized by plasma generated in the chamber, and etching is performed using this reactive ion species. may be reactive ion etching.

A portion 3a of the carbon film 3 left in a ring shape along the outer circumference of the semiconductor substrate 11 (hereinafter referred to as a remainder) 3a covers an ineffective region of the semiconductor substrate 11, which is not used as a semiconductor chip, for example. part. The width w1 of the remaining portion 3a of the carbon film 3 may be, for example, about 2 mm or more and 3 mm or less. Further, the semiconductor substrate 11 receives stress in opposite directions from the silicon carbide epitaxial film 4 on the front surface 11a side and the carbon film 3 on the back surface 11b, and is warped by a predetermined amount h11 (see FIG. 4). It is in a warped state.

After the process in step S6, the surface area of the carbon film 3 is reduced, so that the stress generated in the semiconductor substrate 11 by the carbon film 3 is slightly reduced. maintained. Specifically, the remaining portion 3a of the carbon film 3 is in a state in which the semiconductor substrate 11 is slightly warped so that the back surface 1b side is convex, in a state in which the semiconductor substrate 11 is not warped, or in a state in which the semiconductor substrate 11 is located on the front surface 1a. Keep it in a slightly warped state so that the side is convex.

The processing after step S6 is performed with the remaining portion 3a of the carbon film 3 left on the back surface 11b of the semiconductor substrate 11. As shown in FIG. The warp amount of the semiconductor substrate 11 after the processing in step S6 is as small as possible due to the stress balance between the silicon carbide epitaxial film 4 on the front surface 11a side and the carbon film 3 on the back surface 11b. preferable. Therefore, it is preferable to set the thickness t1 (see FIG. 3) of the carbon film 3 so that the warp amount h11 of the semiconductor substrate 11 due to the remaining portion 3a of the carbon film 3 after the process of step S6 is as small as possible.

Further, in the processing after step S6, the remaining portion 3a of the carbon film 3 functions as a reinforcing material for maintaining the strength of the semiconductor substrate 11. As shown in FIG. Further, since the portion of the rear surface 11b of the semiconductor substrate 11 exposed after the process of step S6 was protected by the carbon film 3, no extra silicon carbide film adhered in the process of step S2. Therefore, the process of polishing the back surface 11b of the semiconductor substrate 11 after the process of step S6 can be omitted.

Next, the semiconductor substrate 11 is taken out from the dry etching apparatus, and the resist film on the front surface 11a of the semiconductor substrate 11 is removed by a general method (step S7). Instead of the resist film, the front surface 11a of the semiconductor substrate 11 may be protected with a silicon oxide (SiO ₂ ) film which is less adversely affected by plasma than the resist film. Next, it is cleaned by a common semiconductor substrate cleaning method. Thus, the semiconductor substrate 11 according to the first embodiment is completed.

Next, a predetermined element structure is formed on this semiconductor substrate 11 (step S8). For example, as the semiconductor device according to the first embodiment, an n-channel MOSFET (Metal Oxide Semiconductor Field Effect Transistor: MOS field effect transistor having an insulated gate with a three-layer structure of metal-oxide-semiconductor) is manufactured. In this case, as shown in FIG. 7, an n ⁺ -type starting substrate 1 to be the n ⁺ -type drain region 31 is prepared.

In addition, in the process of step S2, each silicon carbide epitaxial film 41 that becomes the n ⁻ -type drift region 32 and the p-type base region 33 as the silicon carbide epitaxial film 4 on the front surface 1a of the n ⁺ -type starting substrate 1. , 42 are sequentially epitaxially grown to fabricate the semiconductor substrate 11 . A MOS gate, a source electrode 39 and a drain electrode 40 may be formed on this semiconductor substrate 11 in the process of step S8.

Specifically, in the process of step S8, a set of photolithography and ion implantation is repeatedly performed under different conditions, and the n ^{+ -type} source region 34 is formed in the p-type silicon carbide epitaxial film 42 that becomes the p-type base region 33. , p ⁺ -type contact regions 35 and n-type JFET (Junction FET) regions 32a are selectively formed. The n ⁺ -type source region 34 and the p ⁺ -type contact region 35 are each selectively formed inside the p-type silicon carbide epitaxial film 42 .

N-type JFET region 32 a penetrates p-type silicon carbide epitaxial film 42 in thickness direction Z to reach n ⁻ -type silicon carbide epitaxial film 41 . A portion of p-type silicon carbide epitaxial film 42 excluding n ⁺ -type source region 34 , p ⁺ -type contact region 35 and n-type JFET region 32 a is p-type base region 33 . Next, a gate electrode 37 is formed on the surface of the portion of the p-type base region 33 sandwiched between the n ⁺ -type source region 34 and the n-type JFET region 32a with a gate insulating film 36 interposed therebetween. The gate electrode 37 may extend onto the surface of the n-type JFET region 32a through the gate insulating film 36. As shown in FIG.

When a trench gate structure is formed instead of the planar gate structure, instead of the n-type JFET region ^32a , the n − -type drift region 32 penetrates the n ⁺ -type source region 34 and the p-type base region 33 in the thickness direction Z. , and the gate electrode 37 is formed inside the trench with the gate insulating film 36 interposed therebetween. Next, an interlayer insulating film 38 is formed on the front surface 11 a of the semiconductor substrate 11 so as to cover the gate electrode 37 . Next, a contact hole 38 a is formed through the interlayer insulating film 38 in the thickness direction Z to expose the n ⁺ -type source region 34 and the p ⁺ -type contact region 35 .

Next, the interlayer insulating film 38 is flattened by heat treatment (reflow). Next, by a general method, a source electrode 39 is formed on the front surface 11a of the semiconductor substrate 11 so as to be in ohmic contact with the n ⁺ -type source region 34 and the p ⁺ -type contact region 35 so as to fill the contact hole 38a. do. A drain electrode 40 is formed on the back surface 11 b of the semiconductor substrate 11 so as to be in ohmic contact with the n ⁺ -type drain region 31 . As described above, the carbon film 3 on the back surface 11b of the semiconductor substrate 11 is formed in the ineffective region, so the drain electrode 40 may be formed while leaving the carbon film 3 on the back surface 11b of the semiconductor substrate 11. FIG.

Next, by dicing (cutting) the semiconductor substrate 11 along dicing lines (not shown) into individual chips (step S9), the MOSFET shown in FIG. 7 is completed.

As described above, according to the first embodiment, in manufacturing a semiconductor substrate in which a silicon carbide epitaxial film is epitaxially grown on the front surface of the starting substrate, silicon carbide epitaxial film is formed on the front surface of the starting substrate. A carbon film is deposited on the entire back surface of the starting substrate before the film is epitaxially grown. The carbon film induces a stress in the starting substrate that opposes the stress exerted on the starting substrate by the silicon carbide epitaxial film. Therefore, by adjusting the thickness of the carbon film, the amount of warpage of the starting substrate can be reduced. Therefore, it is possible to reduce the warp amount of the semiconductor substrate obtained by epitaxially growing the silicon carbide epitaxial film on the front surface of the starting substrate, and to make the semiconductor substrate nearly flat.

Moreover, since the amount of warpage of the semiconductor substrate is reduced, cracking of the semiconductor substrate during the manufacturing process can be suppressed. In addition, since the amount of warpage of the semiconductor substrate is reduced, it is possible to improve the accuracy of photolithography and avoid defects in the manufacturing process caused by the inability to transfer the semiconductor substrate to various process apparatuses. Further, since the amount of warpage of the semiconductor substrate is reduced, the generation of dislocations in the silicon carbide epitaxial film can be reduced, so that the yield can be improved.

Further, according to the first embodiment, during the epitaxial growth of the silicon carbide epitaxial film, the back surface of the starting substrate is covered with the carbon film, so that an extra silicon carbide film can be prevented from adhering to the back surface of the starting substrate. can be done. The silicon carbide epitaxial film adhering to the carbon film can be removed together with the carbon film in subsequent steps. Therefore, when forming an element structure on a semiconductor substrate obtained by epitaxially growing a silicon carbide epitaxial film on the front surface of a starting substrate, the step of polishing the back surface of the semiconductor substrate can be omitted.

(Embodiment 2)
Next, a method for manufacturing the semiconductor device according to the second embodiment will be described. 8 to 10 are plan views showing an example of a state in the middle of manufacturing the semiconductor substrate according to the second embodiment. 8 to 10 show an example of the state of the semiconductor substrate 11 after the processing in step S6 of FIG. 1, viewed from the back surface 11b side. In the manufacturing method of the semiconductor device according to the second embodiment, the layout of the portions (residual portions) 3b to 3d (hatched portions) of the carbon film 3 left on the rear surface 11b of the semiconductor substrate 11 after the processing of step S6 is the same as that of the first embodiment. It is different from the manufacturing method of such a semiconductor device.

Specifically, as shown in FIG. 8, the remaining portion 3b of the carbon film 3 may be left in a grid pattern on the dicing lines 13 of the semiconductor substrate 11 along the dicing lines 13 by the process of step S6. In FIG. 8, the dicing lines 13 of the semiconductor substrate 11 are indicated by dashed lines (the same applies to FIG. 10). A portion of the semiconductor substrate 11 surrounded by the remaining portion 3b of the carbon film 3 is a portion that becomes a semiconductor chip when diced in the process of step S9. The portions of the semiconductor substrate 11 that will become the semiconductor chips are exposed in a substantially rectangular shape and arranged in a matrix.

Further, as shown in FIG. 9, the process of step S6 leaves the remaining portion 3c of the carbon film 3 in a straight line extending in one direction (for example, the direction X or the direction Y) parallel to the back surface 11b of the semiconductor substrate 11. may For example, the semiconductor substrate 11 is reinforced by leaving the remaining portion 3c of the carbon film 3 in a straight line passing through a portion where the silicon carbide epitaxial film causes the semiconductor substrate 11 to warp greatly and a substantially central portion of the semiconductor substrate 11. . In this case, for example, the carbon film 3 formed on the entire surface of the back surface 11b of the semiconductor substrate 11 may be removed in a substantially rectangular shape so as to leave a linear residual portion 3c. FIG. 9 shows a state in which two regions of the carbon film 3 adjacent to each other across the linear portion left as the remaining portion 3c are removed into two substantially rectangular regions each having a surface area approximately half the surface area of the semiconductor substrate 11. FIG.

The warp amount h11 (see FIG. 4) of the semiconductor substrate 11 differs in any direction parallel to the back surface 11b of the semiconductor substrate 11. As shown in FIG. Therefore, by leaving the remaining portion 3c of the carbon film 3 so as to extend in the direction in which the amount of warp of the semiconductor substrate 11 increases (the direction Y in FIG. 9), the amount of warp h11 of the semiconductor substrate 11 is reduced to They can be adjusted to be substantially the same in any direction parallel to the back surface 11b. The direction in which the remaining portion 3c of the carbon film 3 extends, the number of lines, the line width and the interval between them can be changed variously. Alternatively, a plurality of linear residual portions 3c of the carbon film 3 may be left, and the linear residual portions 3c of the carbon film 3 may be arranged so as to cross each other at an arbitrary angle.

Further, as shown in FIG. 10, the remaining portion 3d of the carbon film 3 may be left between the outer periphery of the semiconductor substrate 11 and the outermost dicing line 13a of the semiconductor substrate 11 by the processing of step S6. A space between the outer periphery of the semiconductor substrate 11 and the outermost dicing line 13 a of the semiconductor substrate 11 is an invalid region of the semiconductor substrate 11 . Compared to the case where the remaining portion 3a of the carbon film 3 is left in a ring shape (FIG. 6), the surface area of the remaining portion 3d of the carbon film 3 is increased. More effective as a material.

As described above, according to the second embodiment, when partially leaving the carbon film formed on the back surface of the starting substrate after forming the silicon carbide epitaxial film on the front surface of the starting substrate, Even if the layout of the remainder of the carbon film is changed, the same effect as in the first embodiment can be obtained.

(Example)
Next, the warp amounts h1 and h1' of the starting substrate 1 and the warp amount h11 of the semiconductor substrate 11 (see FIGS. 3 and 4) were verified. FIG. 11 is a chart showing the amount of warp during the manufacture of the semiconductor substrate according to the example. In FIG. 11 , the starting substrate 1 or the semiconductor substrate 11 is the semiconductor substrate for which the “direction of warpage” and the “amount of warpage” of the example are verified. Concave or convex in the "direction of warpage" indicates the cross-sectional shape of the semiconductor substrate when the front surface (Si surface) is the upper surface and the back surface (C surface) is the lower surface.

Specifically, in FIG. 11, "the direction of the warp is concave" means that the front surface of the semiconductor substrate is concave downward and the back surface is protruding downward, that is, the semiconductor substrate is convex toward the back surface. It is in a warped state. "The direction of warp is convex" means a state in which the front surface of the semiconductor substrate protrudes upward and the back surface is recessed, that is, the semiconductor substrate is warped so as to protrude toward the front surface. FIG. 12 is a cross-sectional view showing an example of general warp of a semiconductor substrate after forming an epitaxial film.

In general, the starting substrate 101 before forming the silicon carbide epitaxial film 104 is in a state of being warped so that the back surface 101b side is convex, or in a state of not being warped (not shown). As shown in FIG. 12, semiconductor substrate 111 obtained by forming silicon carbide epitaxial film 104 on front surface 101a of starting substrate 101 is greatly warped so that front surface 111a is convex. state (hereinafter referred to as a conventional example).

In the conventional example, the portion where the semiconductor substrate 111 bends in the plane is mainly the central portion 121, and the outer portion 122 surrounding the central portion 121 is almost flat in a cross section parallel to the thickness direction Z. That is, by bending the central portion 121 of the semiconductor substrate 111, the semiconductor substrate 111 is greatly warped so as to protrude toward the front surface 111a (shown as "no C film" in FIG. 11). Therefore, it is presumed that warping of semiconductor substrate 111 can be reduced if stress can be generated in a direction that cancels the stress applied to central portion 121 of semiconductor substrate 111 after silicon carbide epitaxial film 104 is formed. .

In the example, the semiconductor substrate 11 was manufactured under the above conditions according to the method of manufacturing the semiconductor device according to the first embodiment. Like the general starting substrate 101, the starting substrate 1 before the process is in a state of being warped so as to protrude toward the back surface 1b side, or in a state of no warping, and the amount of warping is small (see FIG. 11 " shown as "Before Process Input"). In addition, the starting substrate 1 on which the carbon film 3 having a thickness t1 of 130 nm was formed on the back surface 1b by the processing in step S1 was warped to be convex toward the back surface 1b side more than before the process was started. was confirmed (indicated in FIG. 11 as “after forming a C film on the C surface”).

Further, the semiconductor substrate 11 formed by forming the silicon carbide epitaxial film 4 with a thickness t2 of 65 μm on the front surface 1a of the starting substrate 1 by the processing of step S2 is the starting film before the silicon carbide epitaxial film 4 is formed. It was confirmed that the warped state to be convex toward the back surface 11b side was smaller than that of the substrate 1 (shown as "after epitaxial growth" in FIG. 11). In addition, the semiconductor substrate 11 in which the ring-shaped carbon film 3 was left along the outer circumference of the semiconductor substrate 11 by the processing in step S6 was in a state of being warped so as to protrude toward the front surface 11a. It was confirmed that the amount of warpage was small (shown as "after selective removal of C film" in FIG. 11).

From these results, in the example, the stress applied to the semiconductor substrate 11 by the silicon carbide epitaxial film 4 on the front surface 11a side of the semiconductor substrate 11 was reduced to the remaining portion 3a of the carbon film 3 formed on the back surface 1b of the semiconductor substrate 11. It has been confirmed that the stress applied to the semiconductor substrate 11 can be substantially canceled by the above. As a result, it has been confirmed that the processing of step S8 (formation of the element structure) can be performed while maintaining the state of the semiconductor substrate 11 slightly warped so as to protrude toward the back surface 11b side or the front surface 1a side. rice field.

As described above, the present invention is not limited to the above-described embodiment, and can be variously modified without departing from the scope of the present invention. For example, in each of the above-described embodiments, the area and planar shape of the remaining portion of the carbon film left on the back surface of the semiconductor substrate can be variously changed. In the above-described embodiments, MOSFETs are described as examples, but the present invention is also applicable to SBDs (Schottky Barrier Diodes) and IGBTs (Insulated Gate Bipolar Transistors). It is possible. Moreover, the present invention is similarly established even if the conductivity type (n-type, p-type) is reversed.

INDUSTRIAL APPLICABILITY As described above, the method for manufacturing a semiconductor substrate and the method for manufacturing a semiconductor device according to the present invention are useful for power semiconductor devices used in power converters and power supply devices for various industrial machines.

REFERENCE SIGNS LIST 1 starting substrate 1a front surface of starting substrate 1b rear surface of starting substrate 2a, 2b, 12a, 12b orientation flat 3 carbon film 3a to 3d remainder of carbon film 4 silicon carbide epitaxial film 11 semiconductor substrate 11a front surface of semiconductor substrate surface 11b back surface of semiconductor substrate 13 dicing line 13a outermost dicing line 21 metal mask 22 screw hole in metal mask 31 n ⁺ type drain region 32 n ⁻ type drift region 32a n type JFET region 33 p type base region 34 n ⁺ type source region 35 p ⁺ -type contact region 36 gate insulating film 37 gate electrode 38 interlayer insulating film 38a contact hole 39 source electrode 40 drain electrode 41 n ^- -type silicon carbide epitaxial film 42 p-type silicon carbide epitaxial film h1, h1' Amount of warp h11 Amount of warp of semiconductor substrate t1 Thickness of carbon film t2 Thickness of semiconductor substrate w1 Width of remainder of carbon film X, Y Direction parallel to main surface of semiconductor substrate Z Thickness direction

Claims (11)

A method for manufacturing a semiconductor substrate by epitaxially growing a silicon carbide epitaxial film on a first main surface of a starting substrate made of silicon carbide,
a first film forming step of covering the second main surface of the starting substrate with a carbon film;
a second film forming step of epitaxially growing the silicon carbide epitaxial film on the first main surface of the starting substrate with the second main surface covered with the carbon film;
a removing step of selectively removing the carbon film to leave the carbon film on a predetermined portion of the second main surface of the starting substrate;
including
The first main surface of the starting substrate is the (0001) plane,
A method of manufacturing a semiconductor substrate , wherein the second main surface of the starting substrate is a (000-1) plane . In the first film forming step, the carbon film is caused to generate a second stress on the starting substrate in a direction opposite to the first stress applied to the starting substrate by the silicon carbide epitaxial film and for making the starting substrate flattened. 2. The method of manufacturing a semiconductor substrate according to claim 1, wherein the thickness is 3. The method according to claim 2, wherein in the first film forming step, the carbon film has a thickness such that a remainder of the carbon film remaining after the removing step causes the second stress in the starting substrate. A method for manufacturing a semiconductor substrate. 4. The method of manufacturing a semiconductor substrate according to claim 1, wherein in the first film forming step, the carbon film is formed to have a thickness of 50 nm or more and 200 nm or less. 5. The method of manufacturing a semiconductor substrate according to claim 1, wherein in said removing step, said carbon film is left on a portion other than a portion to be a semiconductor chip. 6. The method of manufacturing a semiconductor substrate according to claim 1, wherein in said removing step, said carbon film is left in a ring shape along the outer periphery of said starting substrate. 6. The method of manufacturing a semiconductor substrate according to claim 1, wherein in the removing step, the carbon film is left in a grid shape along dicing lines surrounding the portion to be the semiconductor chip. . 1-, wherein in the removing step, the carbon film is left between the outermost dicing line among the dicing lines surrounding the periphery of the portion to be the semiconductor chip and the outer periphery of the starting substrate. 6. The method for manufacturing a semiconductor substrate according to any one of 5. 4. The method of manufacturing a semiconductor substrate according to claim 2, wherein, in said removing step, said carbon film is left at a portion where warping of said starting substrate increases due to said first stress. After the second film formation step and before the removal step,
a protective step of protecting the silicon carbide epitaxial film with a protective film;
a covering step of covering the predetermined portion of the carbon film with a metal mask;
10. The removing step includes etching the carbon film using the metal mask to leave the carbon film at the predetermined location on the second main surface of the starting substrate. 1. A method of manufacturing a semiconductor substrate according to claim 1. A method for manufacturing a semiconductor device using a semiconductor substrate obtained by epitaxially growing a silicon carbide epitaxial film on a first main surface of a starting substrate made of silicon carbide,
a first film forming step of covering the second main surface of the starting substrate with a carbon film;
a second film forming step of epitaxially growing the silicon carbide epitaxial film on the first main surface of the starting substrate with the second main surface covered with the carbon film to fabricate the semiconductor substrate;
a removing step of selectively removing the carbon film to leave the carbon film on a predetermined portion of the second main surface of the semiconductor substrate;
a first forming step of forming a predetermined element structure on the first main surface of the semiconductor substrate while leaving the remainder of the carbon film on the second main surface;
a second forming step of forming an electrode portion in contact with a portion of the second main surface of the semiconductor substrate other than the remaining portion of the carbon film;
a cutting step of cutting the semiconductor substrate into individual chips having the element structure and the electrode portion;
including
The first main surface of the starting substrate is the (0001) plane,
A method of manufacturing a semiconductor device , wherein the second main surface of the starting substrate is a (000-1) plane .

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