JP3303530B2 - Method for manufacturing silicon carbide semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to silicon carbide (hereinafter referred to as Si)
C) which is provided with an electrode that makes ohmic contact with a semiconductor substrate made of SiC.

[0002]

2. Description of the Related Art Considering the performance limit of silicon (Si), which is widely used as a semiconductor material, a semiconductor material which can be used even in a severe environment has been sought. For example, a wide gap semiconductor such as SiC having a band gap of 3 eV is expected to be used as a next-generation semiconductor material. Compared to Si, SiC has characteristics of three times the thermal conductivity, 10 times the maximum electric field strength, and twice the electron drift velocity.

[0003]

In a power semiconductor element through which a large current flows, ohmic contact between a metal and a semiconductor interface is important. Good ohmic contact does not degrade device characteristics. It has been reported that the higher the carrier concentration of SiC, the lower the contact resistance at the metal-semiconductor interface. That is, Appl. Phys. Lett. Vol 62, No. 4
(Jan. 1933) As described in p25, p-type 6H-
In the case of SiC, when the carrier concentration is as low as 5.5 × 10 ¹⁵ cm ³ , Rc between the electrode made of Al—Ti is 2.9 × 1.
It is as high as 0 ^-2 Ω · cm ³ and the carrier concentration is 2.9 × 10 ¹⁹ /
When it is cm ³ , Rc is 1.5 × 10 ⁻⁵ Ω · cm ² .
Although SiC carrier concentration 10 ¹⁵ ~10 ¹⁷ / cm ³ as low as about quality are commercially available, low Rc can not be obtained in the case of manufacturing an element by a commercially available SiC this. Conversely, in the case of a SiC crystal having a high carrier concentration, an electrode having a low Rc can be formed, but it is difficult to obtain a SiC crystal having a higher carrier concentration because of the presence of many crystal defects called micropipes.

An object of the present invention is to solve the above-mentioned problems and to provide a method of manufacturing an SiC semiconductor device in which an electrode having a low Rc is formed on a high-quality low-carrier-concentration SiC crystal.

[0005]

In order to achieve the above object, a method of manufacturing a SiC semiconductor device according to the present invention is directed to a method of manufacturing a SiC semiconductor device, comprising: ion implantation as, and then the surface layer of said one surface is thermally oxidized after removing the resulting oxide layer, a metal electrode on the exposed substrate surface in the step of forming the ohmic contact electrode by adhering, from the substrate surface Ion implantation
Thermal oxidization to a depth where the concentration of the ionic species is at a peak value . Then, the thermal oxidation is preferably performed by steam oxidation. Ma
Was, it is better to perform the removal of the oxide layer with an aqueous solution of hydrofluoric acid.

[0006]

The ion species incident on the semiconductor substrate by the ion implantation stops through the zigzag path. A value obtained by connecting a line from the incident point to the stop point with a straight line and projecting the line to a perpendicular line from the incident point, that is, a depth from the substrate surface is called a projection range.
As a result, the projected range is distributed with a statistical fluctuation range, and it is considered that the implanted ion species have a Gaussian distribution centered on the peak concentration in the semiconductor substrate. Therefore, Si
Ion implantation of a dopant of the same conductivity type as the C base, thermal oxidation of the SiC base from the surface to the position of its peak concentration,
If the oxide layer is removed, the portion of the implanted dopant with the highest concentration and low resistance is exposed, so that the substrate itself forms an ohmic contact electrode having low contact resistance even at a low carrier concentration on the SiC substrate. be able to.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. As shown in FIG. 1, ions were implanted into a substrate 1 made of n-type 6H—SiC using nitrogen as an n-type dopant as an ion species 2. The conditions for the ion implantation are acceleration energy of 100 KeV and a dose of 5 × 10 ¹⁵ / cm ^2.
It is. Thereby, as shown in FIG. 2, the heavily doped layer 3 is formed around the peak value Ro = 0.25 μm of the projected range distribution. FIG. 6 shows that an ion implantation of nitrogen is performed on an n-type 6HSiC substrate under the same conditions as described above,
It is a measurement result of the spreading resistance after annealing at 1200 ° C. for 10 hours. As shown in the figure, the resistance value is Ro of nitrogen.
It shows a Gaussian distribution centered around 0.25 μm and a depth of 0.2.
The resistance sharply drops at the position of 27 to 0.29 μm.
This indicates that the implanted nitrogen hardly diffuses and forms a low-resistance high-concentration layer in situ. Therefore, the sample was oxidized from the surface to the depth of the peak value Ro of the projected range distribution by steam oxidation at 1200 ° C. for 3 hours and 35 minutes. As a result, as shown in FIG. 3, the surface of the substrate 1 was covered with the oxide film 4 having a thickness of 0.49 μm. Wet oxidation such as steam oxidation is suitable for SiC having a slow oxidation rate. The SiC to be oxidized is 0.54 per volume 1 of the oxide film. Thereafter, the oxide film was removed using an etching solution obtained by diluting hydrofluoric acid with water at a volume ratio of 20 times. As a result, as shown in FIG. 4, the low-resistance high-concentration doped layer 3 was exposed. The surface of this highly doped layer 3 was smooth. Next, as shown in FIG. 5, the metal electrode 5 was brought into contact with the highly doped layer 3 using Ni as an electrode material. This electrode exhibited a lower Rc by about 40% or more than an electrode directly attached on n-type 6H-SiC. However, the oxide film 4
Was removed by dry etching, the surface of the highly doped layer 3 became uneven, and a low Rc was not obtained.

[0008] When the substrate is made of p-type SiC, aluminum is used as the ion species 2. Steam oxidation time is
It depends on the projection range of the dopant to be ion-implanted. In addition, as the material of the metal electrode 5, a metal material other than Ni can be used.

[0009]

According to the present invention, a dopant having the same conductivity type as that of the substrate is ion-implanted from the surface of the SiC substrate as an ion species, and then the depth of the peak concentration is removed by a combination of thermal oxidation and etching to achieve a high concentration. The carrier concentration layer is exposed on the surface. Therefore, if a metal electrode is formed on this surface, the substrate itself will be in ohmic contact even at a low carrier concentration, and it has become possible to manufacture a semiconductor device using high quality SiC crystals.

[Brief description of the drawings]

FIG. 1 shows an example of Si during ion implantation according to an embodiment of the present invention.
Cross section of C board

FIG. 2 is a cross-sectional view of the SiC substrate after the ion implantation of FIG.

FIG. 3 is a sectional view of the SiC substrate after thermal oxidation, following FIG. 2;

FIG. 4 is a sectional view of the SiC substrate after the removal of the oxide film, following FIG. 3;

FIG. 5 is a sectional view of the SiC substrate after the formation of the metal electrode, following FIG. 4;

FIG. 6 is a diagram showing a spreading resistance distribution in the depth direction of the SiC substrate after nitrogen ion annealing.

[Description of Signs] 1 SiC substrate 2 ion species 3 highly doped layer 4 oxide film 5 metal electrode

Continuation of the front page (56) References JP-A-64-33925 (JP, A) JP-A-59-145539 (JP, A) JP-A-56-67966 (JP, A) JP-A-2-196421 (JP) JP-A-47-9415 (JP, A) JP-A-8-64802 (JP, A) JP-A-5-90206 (JP, A) JP-A-57-207372 (JP, A) 5-90280 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 21/28 301 H01L 29/161

Claims (3)

(57) [Claims] An ion implantation of a dopant having the same conductivity type is performed from one surface of a silicon carbide semiconductor substrate of one conductivity type as an ion species, and then the surface layer of the one surface is thermally oxidized to remove the generated oxide layer. , a metal electrode on the exposed substrate surface in the step of forming the ohmic contact electrode by adhering, the heat
Oxidation reduces the concentration of ion species implanted from the substrate surface.
A method for producing a silicon carbide semiconductor device, comprising thermally oxidizing to a depth at a peak value . 2. A method for manufacturing a silicon carbide semiconductor device according to claim 1, wherein the thermal oxidation is performed in steam oxidation. 3. The method for producing a silicon carbide semiconductor device according to claim 1 or claim 2, wherein an aqueous solution of hydrofluoric acid to remove the oxide layer.