JPH11135450A - Method for manufacturing silicon carbide semiconductor device - Google Patents

Abstract

(57) [Summary] [Implementation] Ion implantation is performed to manufacture a silicon carbide semiconductor device.
This prevents deterioration of device characteristics due to roughening of the surface of the silicon carbide substrate during annealing at 500 ° C. or more. (1) After annealing, the substrate surface is etched and smoothed by an etching gas such as a hydrogen-diluted hydrochloric acid gas. (2) Before annealing, a thin film stable at an annealing temperature such as alumina is laminated, and the thin film is removed after annealing to maintain the initial surface roughness.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a semiconductor device made of silicon carbide.

[0002]

2. Description of the Related Art For the purpose of controlling high frequency and high power, a power semiconductor device (hereinafter referred to as a power device) using silicon (hereinafter referred to as Si) has been improved in performance by various means. . However, the power device may be used in the presence of high temperature or radiation, and under such conditions, the Si power device may not be used.

Further, in response to a demand for a device having a higher performance than a Si power device, application of a new material is being studied. Silicon carbide (hereinafter referred to as Si)
The width of the forbidden band (referred to as C) is 3.26 eV for 4H type, 6
Since the H-type has 3.02 eV), the controllability of the electrical conductivity at a high temperature is excellent, and the maximum operating temperature can be increased. Also Si
Since it has a dielectric breakdown voltage that is about one digit higher than that, the on-resistance can be reduced, the power loss in a steady state can be reduced, and application to a high breakdown voltage element is possible. Further, since SiC has an electron saturation drift speed about twice as high as that of Si, it is also suitable for high frequency high power control. If such advantages of SiC can be utilized, it is considered that the characteristics of power devices can be dramatically improved, and MOSFETs, diodes, and the like are currently being prototyped.

[0004] However, in order to apply such excellent physical properties of SiC to power devices, element technologies as sophisticated as Si process technologies are required. That is,
After finishing the surface of the SiC substrate to a mirror surface, it is necessary to establish a process technology such as epitaxially growing a SiC thin film, doping a donor or an acceptor in the process, or forming a metal film or an oxide film.

One of the most important process techniques is a technique for selectively forming impurity regions by introducing impurities. The method includes a thermal diffusion method and an ion implantation method. The thermal diffusion method widely used for Si semiconductor elements is difficult to apply in SiC because the diffusion coefficient of impurities is very small. Therefore, ion implantation is mainly used in SiC.

However, in the ion implantation, a crystal is damaged. In order to recover the damage and activate the implanted impurities, a heat treatment is usually performed at a high temperature of about 1500 ° C. (hereinafter referred to as annealing). As a result, the activation rate of the impurity is improved with the recovery of the damage, and the impurity region can be formed. In the ion implantation of silicon carbide, 800 to 900 to improve the activation rate of the implanted impurities.
Although ion implantation is performed at a high temperature of ℃, activation is still insufficient, and annealing at a higher temperature is required.

[0007]

However, when annealing is performed at 1500 ° C. or higher to further increase the activation rate, irregularities running in the [1,1, −2,0] direction occur on the surface of the SiC crystal. . These irregularities increase as the annealing temperature increases. For example, while annealing at 1500 ° C. in vacuum has a surface roughness of about 95 nm in average amplitude, annealing at 1600 ° C. results in about 200 nm.
It is considered that the unevenness is generated by increasing the vapor pressure of Si in the high temperature region and causing surface desorption. Even in argon, although not as much as in vacuum, 1500
It becomes about 55 nm at ° C.

As a result, there arises a problem that the mobility near the surface is reduced and the contact resistance is increased. In particular, in a MOSFET, carrier transport in a layer induced near the surface is important, and mobility near the surface is greatly affected by the surface state. In view of the above problems, an object of the present invention is to provide a method for manufacturing a silicon carbide semiconductor device which has a smooth surface even when annealing at a high temperature after ion implantation and does not cause deterioration in characteristics. is there.

[0009]

According to the present invention, there is provided a method of manufacturing a silicon carbide semiconductor device in which ions are implanted into a silicon carbide substrate and annealing is performed at a high temperature. Is smoothed. By doing so, a silicon carbide semiconductor device having a smooth surface can be obtained.

In particular, as a step of smoothing the substrate surface,
After the annealing, etching is performed using an etching gas such as a gas containing hydrochloric acid (HCl) gas. By doing so, the etching rate is increased because the probability of HCl molecules flying in the convex portions is high, and the etching rate is small in the concave portions because the probability of HCl molecules flying is low, so that smoothing is performed. It does not leave stress such as mechanical polishing on the silicon carbide substrate.

As another method, a thin film that does not sublime at an annealing temperature such as alumina may be laminated on the substrate surface before annealing, and the thin film may be removed after annealing. When annealing is performed by covering with a high-temperature stable substance such as alumina, evaporation of Si atoms from the surface is suppressed, and surface roughening during annealing is avoided, so that a smooth surface is maintained.

Further, a thin film which does not sublime at the annealing temperature may be laminated on the substrate surface before the ion implantation, and after the ion implantation and annealing, the thin film may be removed.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION

[Embodiment 1] FIGS. 1A to 1C are cross-sectional views showing main steps in the order of manufacturing steps of a silicon carbide semiconductor device according to the present invention. An n-type 4H-SiC wafer 1 having a main surface slightly inclined from the (0001) plane was prepared, and an epitaxial layer 2 of about 10 μm was grown. The initial surface roughness is about 20 nm on average amplitude. On this SiC wafer, 900
At 180 ° C, 100 keV, 50 ke
V, ions of aluminum (Al) were implanted under the conditions of a total dose of 5 × 10 ¹³ cm ⁻² [FIG. 1 (a)]. The depth of the ion-implanted layer 3 is about 0.5 μm, which results in a substantially flat impurity profile.

Next, the wafer is placed in a vacuum at 160
Annealing was performed at 0 ° C. for 30 minutes [FIG. Thereafter, the surface roughness was about 200 nm. Then, the surface was placed in 1% HCl gas diluted with hydrogen (H ₂ ) for 13 minutes.
Etching was performed at 00 ° C. for 5 minutes [FIG.
As a result, the surface roughness was reduced to about 40 nm. In addition, the surface roughness was calculated from the observation result of the scanning tunnel microscope.

For this sample, the carrier mobility was evaluated by the van der Pauw method. That is, nickel (Ni) electrodes are formed at four corners on the epitaxial layer of the sample by a sputtering method using a metal mask. The diameter of the electrode is 200 μm and the thickness is 400 nm. Thereafter, argon (Ar) is used to make ohmic contact except for rectification.
Anneal at 1050 ° C. for 5 minutes in an atmosphere.

As a result, the mobility is 60 cm ² /
Vs and almost twice as large as those without the HCl etching. Further, the contact resistance of the ohmic contact with the metal electrode could be reduced by about 20%. Since the depth of the ion implantation was about 0.5 μm and had a substantially flat impurity profile, even if the roughened surface layer was removed by etching, the sheet resistance did not increase significantly.

Example 2 After ion implantation was performed in the same manner as in Example 1, an alumina (Al ₂ O ₃ ) layer 4 was deposited on the ion implantation layer 3 by sputtering to a thickness of 100 nm [FIG.
(A)]. Thereafter, high-temperature annealing was performed under the same conditions as in Example 1. Thereafter, the Al ₂ O ₃ layer 4 was removed with an HF solution [FIG.

As a result, the surface roughness was kept almost at the initial value. When the carrier mobility of this sample was evaluated in the same manner as in Example 1, it was found to be about 80 cm ² / V.
s. The contact resistance of the ohmic contact with the metal electrode was also reduced by about 30%. [Embodiment 3] Before the implantation of impurity ions, a thin film for surface protection may be deposited.

First, alumina (Al ₂
After depositing O ₃ ) to a thickness of 100 nm, the same ion implantation and high-temperature annealing as in Example 1 were performed. Then H
The Al ₂ O ₃ film was removed by the F solution. Also in this case, the surface roughness was kept almost at the initial value, and the carrier mobility was almost the same as in Example 2.

[0020]

As described above, according to the present invention, in a method of manufacturing a silicon carbide semiconductor device in which ion implantation is performed and annealing is performed at a high temperature, the surface of the substrate is smoothed after annealing, or the substrate is etched before annealing. By stacking a thin film on the surface, the smoothness of the substrate surface is maintained, whereby a silicon carbide semiconductor element having a smooth surface can be obtained. As a result, the carrier mobility of the surface layer is particularly increased, and the ohmic contact resistance of the metal electrode is reduced. All of these lead to a reduction in the on-resistance and make a great contribution to reducing the loss of the semiconductor element. Further, the characteristics of the manufactured semiconductor device element can be made uniform.

[Brief description of the drawings]

FIG. 1 (a) after ion implantation, (b) after annealing,
(C) is a schematic cross-sectional view of the SiC substrate after etching with HCl.

FIG. 2A shows ion implantation and Al ₂ O ₃ deposition,
(B) is a schematic cross-sectional view of the SiC substrate after annealing and removal of Al ₂ O ₃ .

[Explanation of symbols]

1 ... SiC wafer 2 ... Epi layer 3 ... Ion implantation layer 4 ... Al ₂ O ₃ layer

Claims (6)

[Claims] 1. A method of manufacturing a silicon carbide semiconductor device, comprising: ion-implanting a silicon carbide substrate and performing annealing at a high temperature, wherein the substrate surface is smoothed after annealing. Production method. 2. The method for manufacturing a silicon carbide semiconductor device according to claim 1, wherein the step of smoothing the surface of the substrate includes etching with an etching gas after annealing. 3. The method for manufacturing a silicon carbide semiconductor device according to claim 2, wherein a gas containing hydrochloric acid gas is used as an etching gas. 4. A method for manufacturing a silicon carbide semiconductor device in which ions are implanted into a silicon carbide substrate and annealing is performed at a high temperature, wherein a thin film that does not sublimate at the annealing temperature is laminated on the substrate surface before annealing, and after the annealing, A method for manufacturing a silicon carbide semiconductor device, comprising removing a thin film. 5. A method for manufacturing a silicon carbide semiconductor device in which ions are implanted into a silicon carbide substrate and annealing is performed at a high temperature, wherein a thin film that does not sublime at the annealing temperature is laminated on the surface of the substrate before the ion implantation. And a method of manufacturing a silicon carbide semiconductor device, wherein the thin film is removed after annealing. 6. The method for manufacturing a silicon carbide semiconductor device according to claim 4, wherein alumina is formed as a thin film.