JPH08316164A - Method of making semiconductor device - Google Patents

Abstract

(57) [Summary] [Object] To provide a local impurity doping method for forming a planar type high breakdown voltage pn junction necessary for manufacturing a high breakdown voltage silicon carbide semiconductor device. [Structure] After forming an impurity layer on the surface of a SiC substrate by ion implantation or CVD, hydrogen ions are irradiated at a high temperature. [Effect] A diffusion layer can be formed in SiC, and a high breakdown voltage p
An n-junction is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor device having a wide band gap such as silicon carbide.

[0002]

2. Description of the Related Art A wide-gap semiconductor reflects a wide bandgap and has physical properties suitable for a high breakdown voltage and a high temperature element such as a high dielectric breakdown electric field and a large saturation drift velocity of electrons.
In particular, silicon carbide (SiC) has many crystal systems,
It has a band gap of 2.3 to 3.0 electron volts due to its crystal structure. Also, in terms of process, both p-type and n-type dopants are present, and the conductivity type can be controlled. SiC
The dopant is aluminum (Al) for p-type,
Regarding boron (B) and n-type, nitrogen (N) and phosphorus (P) are known. Similar to Si, SiC can be formed into a good insulating film by thermal oxidation. Therefore, SiC is S
It is the most promising candidate for the constituent material of the semiconductor device, which is replaced by i.
An element made using SiC is expected to be applied to various electric technical fields such as a high power element, a high temperature element, a radiation resistant element and a photoelectric conversion element.

[0003]

Although it has been known for a long time that SiC is suitable for a high breakdown voltage device because of its physical properties, it is a switching technique that makes full use of the excellent physical properties of SiC because the process technology is difficult. The device has not been created. In particular, a local impurity doping technique for forming a high breakdown voltage planar type pn junction is indispensable for producing a high breakdown voltage device. Although thermal diffusion is generally used for local impurity doping in the production of Si devices, SiC has an extremely small impurity diffusion coefficient and requires a high temperature close to 2000 ° C. for thermal diffusion, which involves sublimation of the surface of SiC. For this reason, the usual impurity diffusion method as applied to Si cannot be applied to SiC. Therefore, the ion implantation method is used for the local impurity doping. However, since the ion implantation method involves the introduction of crystal defects, it is difficult to form a high breakdown voltage pn junction (J.App.
L. Phys., 63, (1988), 922. ).

It is an object of the present invention to provide a local impurity doping method for forming a high breakdown voltage planar type pn junction necessary for manufacturing a high breakdown voltage SiC device.

[0005]

In view of the above problems, the present invention is to form a layer doped with impurities by epitaxial growth or ion implantation on the surface of a silicon carbide single crystal, and then subjecting the silicon carbide single crystal to 500 ° C. to 1500 ° C. ℃
By irradiating hydrogen ions or γ-rays from the surface side while heating at a high temperature, the diffusion of impurities from the impurity-doped layer to the deep portion of the silicon carbide single crystal is accelerated. is there.

[0006]

[Operation] Diffusion of impurities is movement due to exchange of positions of impurity atoms with vacancies. The diffusion rate depends on the density of vacancies in the crystal. The equilibrium vacancy density of the crystal depends on the temperature and increases with increasing temperature. However, since SiC has a strong Si—C bond, the equilibrium vacancy concentration is small and the diffusion rate is extremely small even in the temperature range of 1000 ° C. to 1200 ° C. used for thermal diffusion in Si.

According to the present invention, after forming a layer doped with impurities by epitaxial growth or an ion implantation method on the surface of a silicon carbide single crystal, the silicon carbide is added to 500 times.
By irradiating hydrogen ions or γ-rays from the surface side while heating at 1 ° C to 1500 ° C, excessive vacancies are introduced into the SiC single crystal, so that impurity diffusion can be accelerated. In addition, after the impurity-doped layer is formed by selective epitaxial growth or ion implantation, the silicon carbide single crystal is heated to 500 ° C. to 1 ° C.
From the surface side while heating to 500 ° C, hydrogen ions or γ
Local irradiation is possible by irradiating with a ray. As the dopant, Al, B for forming the p-type layer and N, P for forming the n-type layer may be used.

By locally irradiating hydrogen ions or γ-rays using a mask, it is possible to accelerate local diffusion. In addition, p formed by the above method
In the -n junction, the concentration distribution of impurities can be accurately controlled stepwise from the junction interface toward the surface of the semiconductor element by controlling the irradiation conditions of hydrogen ions.

Since the impurity doping method according to the present invention uses substitution of vacancies for impurity atoms, a high impurity concentration of 1 × 10 ¹⁹ cm ⁻³ or more can be obtained in the diffusion layer. In addition, the activation rate of impurities is high. Therefore, the silicon carbide semiconductor device having the pn junction thus formed has a high breakdown voltage and low resistance, and exhibits stable characteristics even at high temperatures.

The method for producing a semiconductor device according to the present invention is particularly effective when silicon carbide is used as a semiconductor material, but the band gap is not limited to silicon carbide and has a band gap of 2.0e.
It is effective for a wide-gap semiconductor having V or more, that is, a semiconductor material such as diamond and nitride, which has a strong bond between atoms and is less likely to diffuse by a normal method.

[0011]

【Example】

(Example 1) n-type SiC having a carrier concentration of 2 × 10 ¹⁸ cm ^-3
After the n-type epitaxial layer (12) having a carrier concentration of 1 × 10 ¹⁶ cm ⁻³ is formed on the single crystal substrate (11) by thermal CVD, the accelerating voltage is 50 k while heating SiC to 1000 ° C.
Ion implantation of Al is performed under the conditions of eV and a dose amount of 5 × 10 ¹⁴ cm ^-2 (FIG. 1A). Further, while heating SiC at 1000 ° C., hydrogen ions are accelerated at an acceleration voltage of 15 keV and 1 × 1.
Irradiate at 0 ¹² cm ^-2 sec ^-1 for 30, 60 min (Fig. 1
(B)). When the acceleration voltage is the same, the penetration depth of hydrogen ions is approximately 2/3 of Si. Therefore, in order to obtain the same diffusion depth, the acceleration voltage of hydrogen ions is approximately 1.5 times that of Si. FIG. 2 shows the depthwise distribution of the impurity concentration by SIMS. As the irradiation time increases, Al diffuses in the depth direction. Also, when the crystal damage due to hydrogen ion irradiation was examined by Rutherford backscattering method (RBS), R
The backscattering intensity obtained from BS was similar to that of perfect crystals (Fig. 3). After performing mesa etching by reactive ion etching (RIE), SiO ₂ passivation (17) is formed by thermal oxidation and sputtering, and then Ni (18) electrode on the n-type side and Al (16) electrode on the p-type side. After formation 1
Heat treatment in vacuum for several minutes at around 000 ° C (Fig. 1
(C)). FIG. 3 shows the I of the pn junction formed according to the present invention.
The -V characteristic is shown. The pn junction formed using the method of the present invention exhibits a high breakdown voltage of about 1000V.

When hydrogen ion irradiation is used, the penetration depth can be controlled by the acceleration voltage, so that the diffusion depth can be set accurately.

Example 2 Carrier Concentration 2 × 10 ¹⁸ cm ^-3
Carrier concentration 1 × on n-type SiC single crystal substrate (11)
Thermal CVD of 10 ¹⁶ cm ^-3 n-type epitaxial layer (12)
Formed by SiO ₂ by thermal oxidation and sputtering.
An ion implantation mask (19) is formed. SiC 100
While heating to 0 ℃, acceleration voltage 50keV, dose 5 ×
Ion implantation of Al is performed under the condition of 10 ¹⁴ cm ^-2 (Fig. 5).
(A)). Further, while heating SiC at 1000 ° C., hydrogen ions are irradiated for 30 and 60 minutes at an acceleration voltage of 15 keV and 1 × 10 ¹² cm ⁻² sec ⁻¹ (FIG. 5B). Ni on the n-type side
(18), after forming Al (16) electrode on p-type side, 1000 ℃
Heat treatment is performed in a vacuum for several minutes before and after (FIG. 5C). The planar type pn junction formed by using the method of the present invention is 1000
It shows a high breakdown voltage close to V.

(Embodiment 3) FIG. 6 is a schematic view of an electrostatic induction diode formed by using the impurity doping method according to the present invention. N-type Si with carrier concentration 2 × 10 ¹⁸ cm ^-3
N with a carrier concentration of 1 × 10 ¹⁶ cm ^-3 on a C single crystal substrate (11)
A type epitaxial layer (12) is formed by thermal CVD. 50k acceleration voltage while heating SiC to 1000 ° C
Al ions are locally implanted through a mask under the conditions of eV and a dose of 5 × 10 ¹⁴ cm ^-2 . In addition, SiC 10
While heating at 00 ° C., hydrogen ions of 1 × 10 ¹² cm ⁻² sec ⁻¹ are irradiated at an accelerating voltage of 15 keV for 60 minutes. Irradiation is continuously performed for 60 minutes at an acceleration voltage of 50 keV. The junction depth is about 0.7 μm. SiO ₂ by thermal oxidation and sputtering
After forming the passivation (17), Ni on the cathode side
(18), Al (16) is used to form an electrode on the anode side. The SiC electrostatic induction diode formed by the present invention has high withstand voltage, low resistance, and stable characteristics even at high temperatures.

[0015]

As described above according to the present invention, Si
Also in C, local impurity doping due to diffusion becomes possible. The element formed by this method has high withstand voltage and low resistance, and exhibits stable characteristics even at high temperatures.

[Brief description of drawings]

FIG. 1 shows an impurity doping method according to the present invention.

FIG. 2 is a depth distribution of impurities.

FIG. 3: Crystallinity evaluation.

FIG. 4 shows pn junction characteristics.

FIG. 5 is a planer type pn junction forming method according to the present invention.

FIG. 6 is an electrostatic induction diode manufactured by using the present invention.

[Explanation of symbols]

11 ... SiC single crystal substrate, 12 ... SiC epitaxial growth film, 13 ... Impurity doping region, 14 ... Al ion, 15 ... Hydrogen ion, 16 ... Anode electrode (Al), 17
... passivation (SiO _2), 18 ... cathode electrode (Ni), 19 ... ion implantation mask (SiO _2).

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical indication location H01L 29/861 H01L 29/91 F (72) Inventor Tsutomu Yao 7-1, Omika-cho, Hitachi-shi, Ibaraki No. 1 Hitachi Ltd. Hitachi Research Laboratory

Claims (6)

[Claims] 1. A method for producing a semiconductor device composed of a semiconductor single crystal having a bandgap of 2.0 eV or more, which comprises: forming a layer doped with impurities by epitaxial growth or ion implantation on the surface side of the single crystal; A semiconductor device characterized by diffusing impurities from the impurity doping layer to the deep part of the single crystal by irradiating hydrogen ions or γ rays from the surface side while heating the semiconductor single crystal to 500 ° C to 1500 ° C. How to create. 2. A method for producing a semiconductor device composed of a silicon carbide single crystal, wherein a layer doped with impurities by epitaxial growth or ion implantation is formed on the surface side of the single crystal, and then the silicon carbide single crystal is formed into
A method of manufacturing a semiconductor device, comprising: diffusing impurities from the impurity doping layer to the single crystal deep portion by irradiating hydrogen ions or γ rays from the surface side while heating at 100 ° C. to 1500 ° C. 3. The method for producing a semiconductor element according to claim 2, wherein any one of Al, B, N and P is used as a dopant. 4. The method for producing a semiconductor device according to claim 2, wherein after a layer doped with impurities is selectively formed on a predetermined portion by epitaxial growth or ion implantation, the silicon carbide single crystal is formed into 500 Semiconductors characterized by accelerating the diffusion of impurities by irradiating hydrogen ions or γ-rays while heating at ℃ to 1500 ℃, and selectively doping impurities from the predetermined portion to the single crystal deep portion. How to make a device. 5. The method for producing a semiconductor device according to any one of claims 2 to 4, wherein a predetermined portion of the silicon carbide semiconductor single crystal is irradiated with hydrogen ions or γ-rays only on a predetermined portion of the surface. A method of manufacturing a semiconductor device, characterized in that impurities are diffused into the semiconductor. 6. The method of manufacturing a silicon carbide semiconductor device according to claim 2, wherein the impurity concentration of the diffusion layer is 1 × 10.
^A pn junction having a size of ¹⁹ cm ^-3 or more.