JP7253730B2 - Semiconductor device manufacturing method and semiconductor device - Google Patents

Description

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

In recent years, power devices such as MOSFETs (metal-oxide-semiconductor field-effect transistors) and Schottky barrier diodes using silicon carbide (silicon carbide, silicon carbide, SiC) as a substrate have been developed. A power device using a silicon carbide substrate has excellent characteristics such as high withstand voltage, high speed, energy saving, etc., because the bandgap of the material is wider than that of conventional silicon-based devices. For example, Patent Document 1 proposes a method of manufacturing a semiconductor device using a silicon carbide substrate.

JP 2017-168688 A

The inventors of the present invention have found that the conventional method for manufacturing a semiconductor device using a silicon carbide substrate, such as that disclosed in Patent Document 1, has the following problems. That is, in the conventional manufacturing method, when forming a MOS structure, a polished silicon carbide substrate having a flat surface structure is prepared, and the surface of the prepared silicon carbide substrate is exposed to an oxidizing atmosphere at a high temperature for a long time. , a silicon dioxide film is formed on this surface to function as a gate. During this thermal oxidation treatment, carbon atoms in the silicon carbide substrate are taken into the silicon dioxide film, and an impurity level resulting from the carbon atoms is formed at the interface between the silicon dioxide film and the silicon carbide substrate. . When this impurity level is formed, the electrical characteristics of the semiconductor device deteriorate, such as reducing electron mobility when the MOSFET operates. The inventors of the present invention have found that the conventional manufacturing method has such a problem.

In one aspect, the present invention has been made in view of such circumstances, and an object thereof is to provide a semiconductor device having a silicon carbide substrate and excellent electrical characteristics, and a method of manufacturing the same.

The present invention adopts the following configurations in order to solve the above-described problems.

That is, a method of manufacturing a semiconductor device according to one aspect of the present invention includes steps of preparing a silicon carbide (silicon carbide, silicon carbide, _SiC ) substrate; ) preparing a substrate, and bonding the silicon carbide (SiC) substrate and the silicon dioxide (SiO ₂ ) film of the silicon (Si) substrate by a room temperature direct bonding method.

According to the room-temperature direct bonding method, the silicon dioxide film can be bonded to the surface of the silicon carbide substrate without exposing it to an oxidizing atmosphere at a high temperature for a long time. Therefore, according to the manufacturing method described above, a silicon dioxide film can be formed on the surface of the silicon carbide substrate without incorporating carbon atoms in the silicon carbide substrate into the silicon dioxide film. In other words, it is possible to suppress the formation of impurity levels that cause deterioration of electrical characteristics at the interface between the silicon carbide substrate and the silicon dioxide film. Therefore, according to the manufacturing method described above, a semiconductor device including a silicon carbide substrate and having excellent electrical characteristics can be obtained.

The room temperature direct bonding method is a method of bonding objects at room temperature without an intermediate layer and without heating. Examples of room-temperature direct bonding include surface activation bonding and atomic diffusion bonding.

The method of manufacturing a semiconductor device according to one aspect may further include, after the step of bonding, performing an annealing process (baking process) on the silicon carbide substrate and the silicon substrate that are bonded to each other. Also, the temperature of the annealing treatment may be 500 degrees Celsius to 900 degrees Celsius. According to this manufacturing method, the state of the interface between the silicon carbide substrate and the silicon dioxide film is improved, and a semiconductor device with even better electrical characteristics can be obtained.

A semiconductor device according to one aspect of the present invention includes a silicon carbide substrate, and a silicon dioxide film bonded to one surface of the silicon carbide substrate by a room temperature direct bonding method. According to this configuration, it is possible to provide a semiconductor device including a silicon carbide substrate and having excellent electrical characteristics.

It should be noted that whether or not "bonded by normal temperature direct bonding" can be determined based on the composition of the silicon dioxide film. That is, if the silicon dioxide film contains many carbon atoms (for example, the concentration of carbon atoms in the silicon dioxide film is above a threshold value), the silicon dioxide film is formed by thermal oxidation treatment instead of the room temperature direct bonding method. It can be determined that On the other hand, when the silicon dioxide film contains almost no carbon atoms (for example, the concentration of carbon atoms in the silicon dioxide film is below a threshold value), the silicon dioxide film is said to be bonded to the silicon carbide substrate by the room temperature direct bonding method. can judge.

According to the present invention, it is possible to provide a semiconductor device having a silicon carbide substrate and excellent electrical characteristics, and a method of manufacturing the same.

FIG. 1 shows an example of a method for manufacturing a semiconductor device according to an embodiment. FIG. 2 schematically illustrates one state of the manufacturing process of the semiconductor device according to the embodiment. FIG. 3 schematically illustrates one state of the manufacturing process of the semiconductor device according to the embodiment. FIG. 4 schematically illustrates one state of the manufacturing process of the semiconductor device according to the embodiment. FIG. 5 schematically illustrates one state of the manufacturing process of the semiconductor device according to the embodiment. FIG. 6 schematically illustrates one state of the manufacturing process of the semiconductor device according to the embodiment. FIG. 7 schematically illustrates one state of the manufacturing process of the semiconductor device according to the embodiment. FIG. 8 schematically illustrates the configuration of the prepared samples. FIG. 9A shows the result of measuring the current-voltage characteristics of a sample that was not annealed. FIG. 9B shows the result of measuring the current-voltage characteristics of the sample subjected to annealing treatment (550 degrees). FIG. 9C shows the result of measuring the current-voltage characteristics of the sample subjected to annealing treatment (900 degrees). FIG. 9D shows the result of measuring the current-voltage characteristics of the sample subjected to annealing treatment (1150 degrees). FIG. 10 shows the results of measuring the leak current of each sample in a state where no voltage is applied.

Hereinafter, an embodiment (hereinafter also referred to as "this embodiment") according to one aspect of the present invention will be described based on the drawings. However, this embodiment described below is merely an example of the present invention in every respect. It goes without saying that various modifications and variations can be made without departing from the scope of the invention. That is, in implementing the present invention, a specific configuration according to the embodiment may be appropriately employed. In addition, in the following description, for convenience of description, the directions in the drawings are used as a reference.

§1 Configuration Example An example of a method for manufacturing a semiconductor device 1 according to the present embodiment will be described with reference to FIGS. 1 to 7. FIG. FIG. 1 is a flow chart showing an example of a method for manufacturing a semiconductor device 1 according to this embodiment. 2 to 7 schematically illustrate one state of the manufacturing process of the semiconductor device 1 according to this embodiment. In addition, well-known apparatuses, such as a semiconductor manufacturing apparatus, may be used for each process below.

(Step S101)
In step S101, as shown in FIG. 2, a silicon carbide (SiC) substrate 10 having a first surface 101 and a second surface 102 facing each other is prepared. The dimensions and shape of the silicon carbide substrate 10 are not particularly limited and may be appropriately selected according to the embodiment. For example, the thickness of the silicon carbide substrate 10, that is, the width between the first surface 101 and the second surface 102 may be 200 μm to 300 μm. The planar shape of the silicon carbide substrate 10 may be circular as shown in FIG.

(Step S102)
In step S102, as shown in FIG. 3, a silicon (Si) substrate 11 having a silicon dioxide (SiO ₂ ) film 12 formed on one surface thereof is prepared. In the example of FIG. 3, the silicon substrate 11 has a first surface 111 and a second surface 112 facing each other, and the silicon dioxide film 12 is formed on the second surface 112 side. After polishing the second surface 112 of the silicon substrate 11 sufficiently smooth, the silicon dioxide film 12 can be formed on the second surface 112 side by performing a thermal oxidation treatment on the second surface 112 . A known method may be employed for the thermal oxidation treatment. Moreover, the conditions of the thermal oxidation treatment (heating temperature, heating time, etc.) may be appropriately set according to the thickness of the silicon dioxide film 12 to be formed.

The dimensions and shape of the silicon substrate 11 are not particularly limited and may be appropriately selected according to the embodiment. Moreover, the thickness of the silicon dioxide film 12 is not particularly limited, and may be appropriately selected according to the embodiment. For example, the thickness of the silicon substrate 11, that is, the width between the first surface 111 and the second surface 112 may be 200 μm to 300 μm. Also, the thickness of the silicon dioxide film 12 (the width in the vertical direction in the figure) may be 10 nm to 300 nm.

(Step S103)
In step S103, as shown in FIG. 4, the silicon carbide substrate 10 and the silicon dioxide film 12 of the silicon substrate 11 are bonded by a room temperature direct bonding method. In the example of FIG. 4, the first surface 101 of the silicon carbide substrate 10 and the silicon dioxide film 12 (second surface 112) of the silicon substrate 11 are bonded together.

The room temperature direct bonding method is a method of bonding objects at room temperature without an intermediate layer and without heating. Examples of room-temperature direct bonding include surface activation bonding and atomic diffusion bonding. A known room temperature bonding apparatus may be used for this room temperature direct bonding method.

In the surface activation bonding method, the surfaces of two objects to be bonded are irradiated with a beam (for example, an argon beam) or plasma to clean and activate each surface, and then pressure is applied to bond the surfaces together. It is a joining method for joining. As an example of the room-temperature direct bonding method, when adopting this surface activation bonding method, the first surface 101 of the silicon carbide substrate 10 is sufficiently smoothed (for example, the arithmetic mean roughness Ra is 1 nm), and then the silicon carbide substrate is polished. The first surface 101 of 10 and the silicon dioxide film 12 surface (second surface 112) of the silicon substrate 11 are made to face each other. Next, the first surface 101 of the silicon carbide substrate 10 and the surface (second surface 112) of the silicon dioxide film 12 are respectively irradiated with a beam or plasma to clean and activate each surface (101, 112). Then, the first surface 101 of the silicon carbide substrate 10 and the surface of the silicon dioxide film 12 are brought into contact with each other and pressed from the outside. Thereby, the first surface 101 of the silicon carbide substrate 10 and the surface of the silicon dioxide film 12 can be firmly bonded.

(Step S104)
In step S104, unnecessary portions of the silicon substrate 11 are removed as shown in FIG. A known patterning method such as photolithography may be used for this removal process. The unnecessary portion to be removed is, for example, a portion on which electrodes are not formed. The unnecessary portion to be removed may be appropriately set according to the embodiment.

In the example of FIG. 5, the silicon substrate 11 has a portion 115 where the silicon dioxide film 12 is not formed. However, the removal process need not be limited to such an example. This portion 115 may be removed.

(Step S105)
In step S105, the silicon carbide substrate 10 and the silicon substrate 11 bonded to each other are annealed (fired). For this annealing treatment, a known non-contamination-free apparatus such as a vertical/horizontal heat treatment furnace or an RTA heat treatment furnace may be used. The temperature of the annealing treatment may be appropriately set according to the embodiment. The annealing temperature is preferably between 500 degrees Celsius and 900 degrees Celsius.

(Step S106)
In step S106, the source and drain are formed. In this embodiment, as shown in FIGS. 6 and 7, the first surface 101 of the silicon carbide substrate 10 is doped with an n-type impurity (such as phosphorus) to form the ring-shaped source region 13 . FIG. 7 schematically illustrates how the semiconductor device 1 is viewed from the first surface 101 side. On the other hand, on the second surface 102 of the silicon carbide substrate 10, the electrode 16 is formed by laminating a metal material (for example, copper, titanium, etc.) and heat-treating the formed metal layer. This electrode 16 serves as a drain. Thereby, the source and drain can be formed.

Thus, the manufacturing of the semiconductor device 1 is completed. This semiconductor device 1 includes a silicon carbide substrate 10 and a silicon dioxide film 12 bonded to one surface (first surface 101) of the silicon carbide substrate 10 by a room temperature direct bonding method. In this embodiment, the semiconductor device 1 is configured to have a MOSFET structure as illustrated in FIG.

[feature]
As described above, in the manufacturing method according to the present embodiment, the silicon dioxide film 12 is bonded to the first surface 101 of the silicon carbide substrate 10 by the room temperature direct bonding method. According to this room-temperature direct bonding method, the silicon dioxide film 12 can be bonded to the first surface 101 of the silicon carbide substrate 10 without exposing it to an oxidizing atmosphere at a high temperature for a long time. Therefore, according to the manufacturing method of the present embodiment, diffusion of carbon atoms in the silicon carbide substrate 10 into the silicon dioxide film 12 can be avoided. That is, at the interface between the silicon carbide substrate 10 and the silicon dioxide film 12, it is possible to suppress the formation of impurity levels that cause deterioration of electrical characteristics. Therefore, according to the manufacturing method according to this embodiment, the semiconductor device 1 having the silicon carbide substrate 10 and having excellent electrical characteristics can be obtained.

Whether or not the silicon dioxide film included in the semiconductor device is bonded to the silicon carbide substrate by the normal temperature direct bonding method is included in the silicon dioxide film portion measured by analyzing the composition of the cross section of the semiconductor device. It can be determined based on the concentration of carbon atoms. That is, if the silicon dioxide film contains many carbon atoms (for example, the concentration of carbon atoms in the silicon dioxide film is above a threshold value), the silicon dioxide film is formed by thermal oxidation treatment instead of the room temperature direct bonding method. It can be determined that On the other hand, when the silicon dioxide film contains almost no carbon atoms (for example, the concentration of carbon atoms in the silicon dioxide film is below a threshold value), the silicon dioxide film is said to be bonded to the silicon carbide substrate by the room temperature direct bonding method. can judge. For the analysis of the composition, for example, WDX method, photoelectron spectroscopy, or SIMS analysis method from the surface of silicon dioxide can be used for the cross section of the material.

§2 Modifications Although the embodiments of the present invention have been described in detail, the descriptions up to this point are merely examples of the present invention in every respect. It goes without saying that various modifications and variations can be made without departing from the scope of the invention. That is, regarding the configuration of the semiconductor device 1 described above, components may be omitted, replaced, or added as appropriate. Further, in the manufacturing method described above, it is possible to omit, replace, or add steps as appropriate according to the embodiment. For example, the following changes are possible. In addition, below, the same code|symbol is used about the component similar to the said embodiment, and description is abbreviate|omitted suitably about the point similar to the said embodiment. The following modified examples can be combined as appropriate.

<2.1>
The processing order of the above manufacturing method may be changed as appropriate according to the embodiment. For example, the processing order of steps S101 and S102 may be interchanged. The above steps S101 and S102 may be performed simultaneously. The process of step S105 may be performed at any timing after step S103 (joining step). The process of step S105 may be omitted. The processing order of steps S106 and S107 may be interchanged.

<2.2>
The configuration of the semiconductor device 1 may be appropriately changed according to the embodiment. For example, the semiconductor device 1 may include other components such as protective members depending on the embodiment. Further, the semiconductor device 1 has a MOSFET structure. However, the configuration of the semiconductor device 1 need not be limited to such an example as long as it has a MOS structure, and may be appropriately determined according to the embodiment.

§ Experimental example In order to confirm the effectiveness of the annealing treatment, the following experiment was conducted. That is, each sample of the semiconductor device was manufactured by the manufacturing method of the present invention, and annealing treatment was not applied to some of the manufactured samples, and annealing treatment at different temperatures was applied to the other samples. Then, the electrical properties of each obtained sample were measured.

FIG. 8 schematically illustrates the structure of the fabricated sample. In this experimental example, first, a silicon carbide substrate 30 was prepared. Subsequently, using a thermal oxidation method, the silicon substrate 31 was thermally oxidized to form a silicon dioxide film. Thereafter, the silicon dioxide film on the upper and lower surfaces of the silicon carbide substrate 30 was removed to prepare a silicon substrate 31 having a silicon dioxide film 32 (thickness: 30 nm). Then, using a room temperature bonding apparatus, the upper surface of the silicon carbide substrate 30 and the surface (lower surface) of the silicon substrate 31 on the side of the silicon dioxide film 32 were bonded by a room temperature direct bonding method (surface activation bonding method). That is, the upper surface of the silicon carbide substrate 30 and the surface of the silicon substrate 31 on the side of the silicon dioxide film 32 are each irradiated with an argon ion beam by an ion gun in a high degree of vacuum (10 to 6 Pa). An activated surface was formed on the upper surface and the surface of the silicon substrate 31 on the side of the silicon dioxide film 32, and then the upper surface of the silicon carbide substrate 30 and the surface of the silicon substrate 31 on the side of the silicon dioxide film 32 were bonded at 20 kN or less. . At this time, the thickness of the silicon carbide substrate 30 was 300 μm. The thickness of the silicon substrate 31 was 300 μm. After that, by stacking a titanium-based metal material on the lower surface of the silicon carbide substrate 30 and the upper surface of the silicon substrate 31, electrodes (35, 36) having a thickness of 0.5 μm were formed.

In this experimental example, four types of samples were produced, and three of them were subjected to annealing treatment (60 minutes) using a heat treatment furnace before forming the electrodes (35, 36). carried out. Specifically, the samples of the first type were not annealed. A second type of sample was subjected to a 550 degree Celsius annealing treatment. A third type of sample was annealed at 900 degrees Celsius. A fourth type of sample was annealed at 1150 degrees Celsius. Thus, samples of each type were produced. Prepare 15 to 20 samples of each type, apply a voltage from -10 V to +10 V to each electrode (35, 36) of each prepared sample using an IV measurement device, and the current of each sample - Voltage characteristics were measured.

FIG. 9A shows the result of measuring the current-voltage characteristics of the first type sample. FIG. 9B shows the result of measuring the current-voltage characteristics of the second type sample. FIG. 9C shows the result of measuring the current-voltage characteristics of the third type sample. FIG. 9D shows the result of measuring the current-voltage characteristics of the fourth type sample. FIG. 10 shows the relationship between the current value when the voltage is 0 V and the annealing temperature of each type of sample in the measurement of the current-voltage characteristics of each type of sample.

As shown in FIGS. 9A to 9D, the current noise near 0 V was large in the samples that were not annealed. On the other hand, the samples annealed at 550 degrees Celsius and 900 degrees Celsius were able to suppress current noise near 0V. In the sample that was annealed at 1150 degrees Celsius, some current noise occurred near 0V.

In addition, as shown in FIG. 10, the leak current at zero bias could be suppressed in the samples that were annealed at a relatively low temperature of 550 degrees Celsius compared to the samples that were not annealed. . However, the leakage current increased as the annealing temperature increased.

From these results, it was found that the noise level can be suppressed while suppressing the leakage current at the interface between the silicon carbide substrate and the silicon dioxide film by performing the annealing treatment at 500 degrees Celsius to 900 degrees Celsius. Therefore, in order to improve the state of the interface between the silicon carbide substrate and the silicon dioxide film and further improve the electrical characteristics of the semiconductor device, after bonding the silicon carbide substrate and the silicon dioxide film, a temperature of 500 degrees Celsius to 900 degrees Celsius is required. It was found that it is preferable to perform the annealing treatment of

1 ... semiconductor device,
10... Silicon carbide (SiC) substrate,
101... First surface, 102... Second surface,
11... Silicon (Si) substrate,
111... First surface, 112... Second surface,
12... Silicon dioxide (SiO ₂ ) film,
13 ... source region,
16... electrode

Claims (1)

providing a silicon carbide substrate;
preparing a silicon substrate having a silicon dioxide film formed on one surface thereof;
bonding the silicon carbide substrate and the silicon dioxide film on the silicon substrate by a room temperature direct bonding method;
After the step of bonding, annealing the silicon carbide substrate and the silicon substrate that are bonded to each other;
with
The temperature of the annealing treatment is 500 degrees to 900 degrees,
A method of manufacturing a semiconductor device.

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