JP2024098728A - Semiconductor device manufacturing method - Google Patents

Abstract

To effectively mitigate warpage generated in an SiC substrate.SOLUTION: A manufacturing method of a semiconductor device comprises: a first ion implantation process that performs ion implantation of a dopant into a first surface of a SiC substrate; and a second ion implantation process that performs ion implantation of a chemical element into a second surface which is positioned at an opposite side of the first surface of the SiC substrate in higher density than 1×1019 cm-3 after the first ion implantation process. In the first ion implantation process, warpage is generated in the SiC substrate in a direction in which the first surface is protruding. In the second ion implantation process, the warpage of the SiC substrate is mitigated.SELECTED DRAWING: Figure 8

Description

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

Patent Document 1 discloses a method for manufacturing a semiconductor device from a semiconductor substrate (hereinafter referred to as a SiC substrate) made of SiC (i.e., silicon carbide). In this manufacturing method, dopants such as boron and phosphorus are ion-implanted into the front surface of the SiC substrate. When the dopant is ion-implanted into the front surface of the SiC substrate, warping occurs in the SiC substrate. Next, warping-relieving ions are implanted into the rear surface of the SiC substrate. This alleviates the warping that has occurred in the SiC substrate.

JP 2022-153954 A

This specification proposes a technology that effectively reduces warpage in SiC substrates.

The method for manufacturing a semiconductor device disclosed in this specification includes a first ion implantation step and a second ion implantation step. In the first ion implantation step, a dopant is ion-implanted into a first surface of a SiC substrate. In the second ion implantation step, an element is ion-implanted into a second surface of the SiC substrate opposite to the first surface at a concentration higher than 1×10 ¹⁹ cm ⁻³ after the first ion implantation step. In the first ion implantation step, warping occurs in the SiC substrate in a direction such that the first surface is convex. In the second ion implantation step, the warping of the SiC substrate is alleviated.

The element ion-implanted into the SiC substrate in the second ion implantation step may be a dopant or an element other than a dopant.

In addition, the mitigation of the warpage of the SiC substrate in the second ion implantation process means that the warpage of the SiC substrate that occurred in the first ion implantation process (i.e., warpage in a direction that makes the first surface convex) is mitigated. Therefore, warpage in a direction that makes the second surface convex may occur in the second ion implantation process.

When a dopant is ion-implanted into the first surface in the first ion implantation step, the SiC substrate is warped in such a direction that the first surface is convex. When an element is ion-implanted into the second surface of the SiC substrate in the second ion implantation step, the SiC substrate is deformed so as to alleviate the warp caused in the first ion implantation step. When an element is ion-implanted into the second surface in the second ion implantation step at a concentration higher than 1×10 ¹⁹ cm ⁻³ , the SiC substrate can be efficiently deformed in the second ion implantation step. Therefore, according to this manufacturing method, the warp caused in the SiC substrate in the first ion implantation step can be effectively alleviated.

FIG. 2 is a cross-sectional view of a SiC substrate 12 before ion implantation. 4A to 4C are explanatory diagrams of an ion implantation process for the electric field relaxation region 18. 4A to 4C are explanatory diagrams of the epitaxial growth process of the second drift region 20. FIG. 4 is an explanatory diagram of warping of the SiC substrate 12 after the first ion implantation process. FIG. FIG. 4 is an explanatory diagram of warping of the SiC substrate 12 after the second ion implantation process. FIG. 13 is a graph showing the relationship between the amount of warpage and the ion implantation concentration in the second ion implantation process. FIG. FIG. FIG. 1 is a cross-sectional view of a metal-oxide-semiconductor field effect transistor (MOSFET) manufactured by a manufacturing method according to an embodiment.

In the manufacturing method disclosed in the present specification, the second ion implantation step may include ion implanting an element at a concentration lower than 1×10 ²⁰ cm ⁻³ .

It has been found that the amount of deformation occurring in the second ion implantation step is reduced when an element is ion-implanted at a concentration of 1×10 ²⁰ cm ⁻³ or more in the second ion implantation step. By ion-implanting an element at a concentration lower than 1×10 ²⁰ cm ⁻³ in the second ion implantation step, the warpage occurring in the first ion implantation step can be more effectively alleviated.

In the manufacturing method disclosed herein, in the second ion implantation step, an element may be ion-implanted at a concentration higher than the concentration of the dopant implanted into the first surface in the first ion implantation step.

This configuration can more effectively mitigate the warpage that occurs during the first ion implantation process.

In the manufacturing method disclosed herein, in the second ion implantation step, a carbon agglomeration layer may be formed within the implantation range of the element in the second ion implantation step of the SiC substrate.

This configuration can more effectively mitigate the warpage that occurs during the first ion implantation process.

In the manufacturing method disclosed herein, the SiC substrate may be made of 4H-SiC or 6H-SiC. In the second ion implantation step, 3C-SiC may be formed within the implantation range of the element in the second ion implantation step of the SiC substrate.

This configuration can more effectively mitigate the warpage that occurs during the first ion implantation process.

The manufacturing method disclosed herein may further include a third ion implantation step of ion-implanting a dopant into the first surface after the second ion implantation step. In the second ion implantation step, the SiC substrate may be warped such that the second surface is convex. In the third ion implantation step, the SiC substrate may be warped such that the first surface is convex.

With this manufacturing method, the second ion implantation process can mitigate the warping that occurs in the first and third ion implantation processes.

The manufacturing method disclosed herein may further include, after the second ion implantation step, a step of removing the implanted area of the element in the second ion implantation step in the SiC substrate.

In the manufacturing method of the embodiment, a semiconductor device is manufactured from a SiC substrate 12 shown in FIG. 1. The SiC substrate 12 is made of 4H-SiC or 6H-SiC. The SiC substrate 12 has an n-type drain region 14 and an n-type first drift region 16. The first drift region 16 is disposed above the drain region 14. The n-type impurity concentration of the first drift region 16 is lower than the n-type impurity concentration of the drain region 14.

First, as shown in FIG. 2, p-type impurities are selectively ion-implanted into the upper surface 12a of the SiC substrate 12 through a mask to form multiple p-type electric field relaxation regions 18 in the first drift region 16. Next, as shown in FIG. 3, an n-type second drift region 20 is epitaxially grown on top of the first drift region 16. The n-type impurity concentration of the second drift region 20 is approximately equal to the n-type impurity concentration of the first drift region 16. At this stage, no significant warping has occurred in the SiC substrate 12.

(First ion implantation process)
Next, a first ion implantation step is performed. In the first ion implantation step, as shown in FIG. 4, a p-type body region 22 is formed in the second drift region 20 by selectively ion-implanting p-type impurities into the upper surface 12a of the SiC substrate 12 through a mask. Here, the p-type impurities are ion-implanted at a concentration of less than 1×10 ¹⁸ cm ⁻³ . Here, the body region 22 is formed in a wide range exposed to the upper surface 12a. Here, the p-type impurities are ion-implanted multiple times while changing the implantation depth, thereby forming a thick body region 22. Here, the second drift region 20 is left under the body region 22. When the p-type impurities are ion-implanted into the upper surface 12a, the SiC substrate 12 expands in the region (i.e., the body region 22) in which the p-type impurities are implanted near the upper surface 12a. Since the range in which the body region 22 is formed is wide, the SiC substrate 12 expands greatly near the upper surface 12a. On the other hand, in the first ion implantation step, the region near the lower surface 12b of the SiC substrate 12 does not expand. Therefore, as shown in FIG. 5, the SiC substrate 12 is warped in a direction in which the upper surface 12a is convex. Hereinafter, when the SiC substrate 12 is placed on a horizontal plane, a portion in the upper surface 12a that has the largest displacement in the vertical direction relative to the outer peripheral end 12r of the upper surface 12a is referred to as the maximum displacement portion 12d. In addition, the position of the maximum displacement portion 12d in the vertical direction relative to the outer peripheral end 12r (more specifically, the position measured with the upper side being positive) is referred to as the warpage amount S. A positive value of the warpage amount S means that the upper surface 12a is convex, and a negative value of the warpage amount S means that the lower surface 12b is convex. If the absolute value of the warpage amount S is large, a malfunction occurs in the manufacturing equipment (for example, a conveying device for the SiC substrate 12, etc.). Therefore, in the manufacturing process of the semiconductor device, the absolute value of the warpage amount S of the SiC substrate 12 is controlled to be equal to or less than the reference value Smax. In the first ion implantation process, the amount of warpage S has a positive value. In the first ion implantation process, the amount of warpage S does not reach the reference value Smax, but increases to a value close to the reference value Smax.

(Second ion implantation process)
Next, a second ion implantation step is performed. In the second ion implantation step, as shown in FIG. 6, a warpage adjusting element 42 is ion-implanted into the lower surface 12b of the SiC substrate 12. In this embodiment, aluminum (Al), which is a kind of p-type impurity, is used as the warpage adjusting element 42. However, the warpage adjusting element 42 is not particularly limited. The warpage adjusting element 42 may be a dopant (i.e., a p-type impurity or an n-type impurity), or may be another element (i.e., an element that does not affect the conductivity of the SiC substrate 12). In addition, here, the warpage adjusting element 42 is ion-implanted to a constant depth without changing the implantation depth. When the warpage adjusting element 42 is ion-implanted into the lower surface 12b, crystal defects are formed in the region where the warpage adjusting element 42 is implanted near the lower surface 12b. Hereinafter, the region where crystal defects are formed by ion implantation of the warpage adjusting element 42 is referred to as a crystal defect region 40. When the crystal defect region 40 is formed, the SiC substrate 12 expands in the crystal defect region 40 (i.e., the region near the lower surface 12b). On the other hand, in the second ion implantation process, the region near the upper surface 12a of the SiC substrate 12 does not expand. Therefore, the SiC substrate 12 deforms so as to reduce the amount of warping S. That is, the SiC substrate 12 deforms so as to alleviate the warping caused in the first ion implantation process. Here, the warping amount S is reduced to a negative value by implanting the warping adjustment element 42 at a higher concentration than the p-type impurity implanted in the first ion implantation process. That is, as shown in FIG. 7, the SiC substrate 12 is warped so that the lower surface 12b of the SiC substrate 12 becomes convex. The absolute value of the amount of warping S after the second ion implantation process is controlled to a value lower than the reference value Smax.

FIG. 8 shows the relationship between the warpage ratio S2/S1 and the ion implantation concentration D of the warpage adjusting element 42. The warpage ratio S2/S1 shows the absolute value of the change S2 of the warpage S caused in the second ion implantation process divided by the change S1 of the warpage S caused in the first ion implantation process. S2/S1>1 means that the lower surface 12b of the SiC substrate 12 becomes convex in the second ion implantation process. S2/S1<1 means that the upper surface 12a of the SiC substrate 12 is maintained in a convex state in the second ion implantation process. As shown in FIG. 8, when the ion implantation concentration D in the second ion implantation process exceeds 1×10 ¹⁹ cm ⁻³ , the ratio S2/S1 rises sharply. Therefore, in the second ion implantation process, the warpage S can be efficiently changed by ion implanting the warpage adjusting element 42 at a concentration higher than 1×10 ¹⁹ cm ⁻³ . In particular, when the ion implantation concentration D exceeds 1×10 ¹⁹ cm ⁻³ , the ratio S2/S1 exceeds 1, and therefore it is possible to cause the SiC substrate 12 to warp so that the lower surface 12b becomes convex.

The reason why the ratio S2/S1 rises sharply when the ion implantation concentration D in the second ion implantation step exceeds 1×10 ¹⁹ cm ⁻³ is considered to be as follows. When ions are implanted at an ion implantation concentration exceeding 1×10 ¹⁹ cm ⁻³ in the second ion implantation step, at least one of a carbon aggregate layer and a 3C-SiC layer is detected when the cross section of the crystal defect region 40 is analyzed. The carbon aggregate layer is a layer in which carbon aggregates in the SiC substrate 12. The 3C-SiC layer is a layer in which the crystal structure in the SiC substrate 12 changes to a 3C-SiC crystal structure. When the ion implantation concentration D in the second ion implantation step exceeds 1×10 ¹⁹ cm ⁻³ , it is considered that the carbon aggregate layer or the 3C-SiC layer is formed in the crystal defect region 40, and the crystal defect region 40 expands greatly. Therefore, it is considered that the ratio S2/S1 of the warpage amount rises sharply when the ion implantation concentration D exceeds 1×10 ¹⁹ cm ⁻³ .

Furthermore, when the ion implantation concentration D is higher than 1×10 ²⁰ cm ⁻³ , the ratio S2/S1 gradually decreases as the ion implantation concentration D increases. Therefore, in the second ion implantation step, when the warpage adjustment element 42 is ion-implanted at a concentration lower than 1×10 ²⁰ cm ⁻³ , the warpage amount S can be changed efficiently.

(Third ion implantation process)
Next, a third ion implantation step is performed. In the third ion implantation step, as shown in FIG. 9, a plurality of n-type source regions 24 and a plurality of p-type contact regions 26 are formed by selectively ion-implanting p-type impurities and n-type impurities into the upper surface 12a of the SiC substrate 12 through a mask. Either the ion implantation of n-type impurities into the source region 24 or the ion implantation of p-type impurities into the contact region 26 may be performed first. Here, n-type impurities and p-type impurities are ion-implanted at a concentration higher than 1×10 ¹⁸ and lower than 1×10 ¹⁹ cm ⁻³ . That is, the concentration of the n-type impurity ion-implanted into the source region 24 and the concentration of the p-type impurity ion-implanted into the contact region 26 are higher than the concentration of the p-type impurity ion-implanted into the body region 22 and lower than the concentration of the element ion-implanted into the crystal defect region 40. Here, the source region 24 and the contact region 26 are formed in a wide range exposed to the upper surface 12a. The body region 22 is left under the source region 24 and the contact region 26. When n-type impurities and p-type impurities are ion-implanted into the upper surface 12a, the SiC substrate 12 expands in the region where the impurities are implanted near the upper surface 12a (i.e., the source region 24 and the contact region 26). Since the range in which the source region 24 and the contact region 26 are formed is wide, the SiC substrate 12 expands greatly near the upper surface 12a. On the other hand, in the third ion implantation step, the region near the lower surface 12b of the SiC substrate 12 does not expand. Therefore, the SiC substrate 12 deforms so as to increase the amount of warping S. That is, the SiC substrate 12 deforms so as to alleviate the warping caused in the second ion implantation step. Here, the amount of warping S increases to a positive value. That is, similar to FIG. 5, the SiC substrate 12 warps so that the upper surface 12a of the SiC substrate 12 becomes convex. Since the SiC substrate 12 is warped so that the lower surface 12b becomes convex after the second ion implantation step is performed, the amount of warpage S is prevented from becoming excessive when the upper surface 12a of the SiC substrate 12 becomes convex in the third ion implantation step. Therefore, the amount of warpage S in the third ion implantation step is controlled to a value lower than the reference value Smax.

Next, the SiC substrate 12 is annealed to activate the n-type impurities and p-type impurities ion-implanted into the SiC substrate 12. Next, as shown in FIG. 10, the upper surface 12a of the SiC substrate 12 is etched to form a plurality of trenches 28 that penetrate the source region 24, the body region 22, and the second drift region 20 and reach the electric field relaxation region 18.

Next, as shown in FIG. 11, the lower surface 12b of the SiC substrate 12 is polished, etched, or the like to remove the crystal defect region 40 and reduce the thickness of the drain region 14.

Next, as shown in FIG. 12, a gate insulating film 30 and a gate electrode 32 are formed in the trench 28. A source electrode 34 is formed on the upper surface 12a of the SiC substrate 12. A drain electrode 36 is formed on the lower surface 12b of the SiC substrate 12. Through the above steps, the MOSFET shown in FIG. 12 is completed.

As described above, in this embodiment, in the second ion implantation step, an element is ion-implanted into the lower surface 12b at a concentration higher than 1×10 ¹⁹ cm ⁻³ . Therefore, in the second ion implantation step, the amount of warpage S of the SiC substrate 12 can be efficiently reduced. Also, in the second ion implantation step, an element is ion-implanted into the lower surface 12b at a concentration lower than 1×10 ²⁰ cm ⁻³ , so that it is possible to prevent a deterioration in the efficiency of change in the amount of warpage S due to an excessive amount of ion implantation.

In addition, in this embodiment, in the second ion implantation process, an element is ion-implanted at a concentration higher than the concentration of the p-type impurity ion-implanted in the first ion implantation process. Therefore, in the first ion implantation process, the upper surface 12a becomes convex, and in the second ion implantation process, the lower surface 12b becomes convex. Furthermore, in the third ion implantation process after the second ion implantation process, the upper surface 12a becomes convex. Therefore, the warp generated in the second ion implantation process can offset both the warp generated in the first ion implantation process and the warp generated in the third ion implantation process. Therefore, even if the number of times of ion implantation of an element into the lower surface 12b is small, the warp amount S of the SiC substrate 12 can be managed to a low value.

In the above embodiment, the process of ion-implanting an element into the lower surface 12b is performed only once. However, the process of ion-implanting a dopant into the upper surface 12a and the process of ion-implanting an element into the lower surface 12b may be repeated alternately multiple times.

In the above embodiment, the amount of warping S is reduced to a negative value in the second ion implantation process. However, in other examples, the amount of warping S after the second ion implantation process may be a positive value. Even with this configuration, the warping caused in the first ion implantation process can be mitigated in the second ion implantation process.

The configurations of the techniques disclosed in this specification are listed below.
(Configuration 1)
A method for manufacturing a semiconductor device, comprising:
A first ion implantation step of ion-implanting a dopant into a first surface of a SiC substrate;
a second ion implantation step of ion-implanting an element into a second surface of the SiC substrate opposite to the first surface at a concentration higher than 1×10 ¹⁹ cm ⁻³ after the first ion implantation step;
having
In the first ion implantation step, warping occurs in the SiC substrate in a direction such that the first surface is convex,
In the second ion implantation step, the warpage of the SiC substrate is alleviated.
Production method.
(Configuration 2)
2. The method according to claim 1, wherein the second ion implantation step implants the element at a concentration lower than 1×10 ²⁰ cm ⁻³ .
(Configuration 3)
3. The manufacturing method according to claim 1, wherein in the second ion implantation step, an element is ion-implanted at a concentration higher than a concentration of a dopant implanted in the first surface in the first ion implantation step.
(Configuration 4)
The manufacturing method according to any one of configurations 1 to 3, wherein in the second ion implantation step, a carbon aggregate layer is formed within an implantation range of the element in the second ion implantation step of the SiC substrate.
(Configuration 5)
the SiC substrate is made of 4H—SiC or 6H—SiC,
The manufacturing method according to any one of configurations 1 to 3, wherein in the second ion implantation step, 3C-SiC is formed within an implantation range of the element in the second ion implantation step of the SiC substrate.
(Configuration 6)
a third ion implantation step of ion-implanting a dopant into the first surface after the second ion implantation step,
In the second ion implantation step, warpage occurs in the SiC substrate in a direction such that the second surface is convex,
In the third ion implantation step, warping occurs in the SiC substrate in a direction in which the first surface is convex.
The method for producing the present invention according to any one of claims 1 to 5.
(Configuration 7)
The manufacturing method according to any one of configurations 1 to 6, further comprising a step of removing an implanted area of the element in the second ion implantation step of the SiC substrate after the second ion implantation step.

Although the embodiments have been described in detail above, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and variations of the specific examples given above. The technical elements described in this specification or drawings demonstrate technical utility either alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. Furthermore, the technology exemplified in this specification or drawings achieves multiple objectives simultaneously, and achieving one of these objectives is itself technically useful.

12: SiC substrate, 22: body region, 24: source region, 26: contact region, 40: crystal defect region

Claims (7)

A method for manufacturing a semiconductor device, comprising:
A first ion implantation step of ion-implanting a dopant into a first surface (12a) of a SiC substrate (12);
a second ion implantation step of ion-implanting an element into a second surface (12b) located on the opposite side of the first surface of the SiC substrate at a concentration higher than 1×10 ¹⁹ cm ⁻³ after the first ion implantation step;
having
In the first ion implantation step, warping occurs in the SiC substrate in a direction such that the first surface is convex,
In the second ion implantation step, the warpage of the SiC substrate is alleviated.
Production method. 2. The method according to claim 1, wherein in the second ion implantation step, the element is ion-implanted at a concentration lower than 1×10 ²⁰ cm ⁻³ . The manufacturing method according to claim 1 or 2, wherein in the second ion implantation step, an element is ion-implanted at a concentration higher than the concentration of the dopant implanted into the first surface in the first ion implantation step. The manufacturing method according to claim 1 or 2, wherein in the second ion implantation step, a carbon condensation layer is formed within the implantation range of the element in the second ion implantation step of the SiC substrate. the SiC substrate is made of 4H—SiC or 6H—SiC,
3. The manufacturing method according to claim 1, wherein in the second ion implantation step, 3C-SiC is formed within an implantation range of the element in the second ion implantation step of the SiC substrate. a third ion implantation step of ion-implanting a dopant into the first surface after the second ion implantation step,
In the second ion implantation step, warping occurs in the SiC substrate in a direction such that the second surface is convex,
In the third ion implantation step, warping occurs in the SiC substrate in a direction in which the first surface is convex.
The method according to claim 1 or 2. 3 . The manufacturing method according to claim 1 , further comprising the step of removing an implanted area of the element in the second ion implantation step of the SiC substrate after the second ion implantation step.

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