JPS6222443B2 - - Google Patents

Abstract

PURPOSE:To form a layer having a sharp impurity distribution by growing one layer when growing in gas phase a plurality of layers having different impurity density, subsequently etching it in the III group element-containing atmosphere in the Periodic Table and then growing next layer. CONSTITUTION:HCl and H2S for feeding AsH3 and Ga are supplied as carrier gases onto a GaAs substrate, thereby growing an N type GaAs layer 1 of 1.2X10<18>cm<-3>. Then, HCl for feeding Ga and HCl are supplied at 10ml/min and 60ml/min for approx. 10 sec, thereby etching the layer 1 in 0.7mum, and AsH3 is further flowed without adding impurity, thereby growing an N type GaAs layer 2 of 1.8X10<15>cm<-3>. Thus, the impurity density distribution forms sharply in the layer, and there can be obtained a layer having preferable performance in forming an IMPATT diode or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for growing a compound semiconductor epitaxial layer exhibiting a steep change in carrier concentration.

Ideally, it is desirable that the carrier concentration of an epitaxial layer used in manufacturing an impact diode, which is a type of microwave solid-state oscillation device, changes as steeply as possible, as shown in FIG.

In Fig. 1, the vertical axis shows the carrier concentration and the horizontal axis shows the thickness. In the figure, 1 indicates a region of high n-type carrier concentration, 2 indicates a region of low n-type carrier concentration, and 3
is a region of high p-type carrier concentration. When using a compound semiconductor consisting of Group and Group elements of the periodic table (hereinafter referred to as "-group semiconductor"), for example GaAs, as a single crystal substrate, since the substrate is n-type, region 1 is formed first, and then Areas 2 and 3
is formed.

The example shown in Figure 1 is an SDR type, that is, a single drift region.
This is an impact diode called a DDR type (double drift region) type, in which the p-type region consists of two regions, a high carrier concentration region and a low carrier concentration region.
drift region) type. Conventionally, after a region corresponding to high carrier concentration region 1 in FIG. was growing.

However, for example, if the carrier concentration is 1×
According to the conventional method, when changing from a region of 10 ¹⁸ /cm ³ to a region of 1×10 ¹⁶ /cm ³ , the carrier concentration decreases in a relatively gentle curve.

That is, the thickness required to transition from a high carrier concentration region to a low carrier concentration region reaches from 1 μm to 4 μm, which is undesirable because it increases series resistance which adversely affects the performance of the device.

The present inventors have arrived at the present invention as a result of intensive research to solve the above problems, and an object of the present invention is to form multiple regions with different carrier concentrations on the surface of a single crystal substrate. An object of the present invention is to provide a novel method for vapor phase epitaxial growth of a - group semiconductor single crystal layer.

The above objects of the invention are achieved by a method of growing regions with one carrier concentration, followed by etching in an air stream containing group elements, and then growing regions with different carrier concentrations. .

When manufacturing epitaxial wafers used for manufacturing varactor diodes, impact diodes, etc., the buffer layer has a carrier concentration of 10 ¹⁸ /cm ^{3 .}
After growing a region with a relatively high carrier concentration to a thickness of 4 to 8 μm using a vapor phase epitaxial growth method, the supply of group and group element components is temporarily stopped. Next, while supplying only group element components,
Etch the above-mentioned high carrier concentration region using HCl or the like.

In this case, by adjusting the supply amount of the group element component, it is possible to adjust the thickness required for transition from a region of high carrier concentration to a region of low carrier concentration.

In the case of GaAs epitaxial layers, transporting Ga
If etching is carried out for 10 to 50 seconds at a HCl flow rate of 10 to 40 ml/min, the carrier concentration can be reduced with an epitaxial layer growth thickness of 1 μm or less.

Further, when the flow rate of HCl for Ga transport is set to 20 ml/min or more, a dip 4 having a carrier concentration as shown in FIG. 2 can be formed. In FIG. 2, the vertical axis is the carrier concentration, and the horizontal axis is the thickness.

Also, when the carrier concentration is changed from a low carrier concentration region to a high carrier concentration region, a steep change in carrier concentration can be obtained by the method of the present invention.

In the case of GaAs, the composition of the gas used for epitaxial growth is AsH ₃ −Ga−Hcl−H ₂ system,
_Ascl3 -Ga-Hcl- _H2 system is suitable.

By carrying out the method of the present invention, it is possible to obtain - group semiconductor epitaxial wafers suitable for manufacturing microwave solid-state devices such as impact diodes and varactor diodes, which require steep changes in carrier concentration. The utility value is extremely large.

The method of the present invention will be explained in more detail below based on Examples and Comparative Examples.

Example 1 A GaAs single crystal substrate doped with Si and having a carrier concentration of 2.1×10 ¹⁸ /cm ³ and whose surface crystallographic orientation is 3° inclined from the (100) plane and a container containing Ga were prepared. A vertical epitaxial reactor was charged.

While supplying hydrogen at a flow rate of 3500 ml/min, the substrate temperature was raised to 750°C and the Ga container to 800°C. After the reactor reached the specified temperature, 100 ml/min of _AsH3 diluted to 10% with hydrogen gas and 10 ml/min of HCl for Ga transfer were added.
600 ml/min of hydrogen gas containing 50 ppm _H2S
Carrier concentration 1.2 after 20 minutes of supply at ml/min
An n-type GaAs epitaxial layer of ×10 ¹⁸ /cm ³ and 6 μm thick was grown.

After that, the supply of AsH ₃ , H ₂ S and Hcl was stopped, and
The substrate temperature was raised to 770°C over about 1 hour.

Next, while flowing Hcl for Ga transfer at 10ml/minute, Hcl
was supplied for 10 seconds at a flow rate of 60 ml/min to etch the layer having a carrier concentration of 1.2×10 ¹⁸ /cm ³ by 0.7 μm.

After etching was completed, HCl for Ga transfer was supplied for an additional 50 seconds.

Next, AsH ₃ (concentration 10%) was supplied at 100 ml/min to increase the carrier concentration for 10 minutes without adding any impurities.
An n-type GaAs epitaxial layer of 1.8×10 ¹⁵ /cm ³ and 3 μm thick was grown.

In the obtained GaAs epitaxial wafer, the carrier concentration ranged from 1.2×10 ¹⁸ /cm ³ to 1.8×
The thickness of the epitaxial layer required for transition to the region of 10 ¹⁵ /cm ³ was 0.35 μm.

Example 2 During etching, the supply amount of HCl for Ga transfer was set at 40
n in the same manner as in Example 1 except that the setting was ml/min.
A type GaAs epitaxial layer was grown by vapor phase.

In the obtained GaAs epitaxial wafer, the carrier concentration ranged from 1.2×10 ¹⁸ /cm ³ to 1.8×
The thickness of the epitaxial layer required for transition to the 10 ¹⁵ /cm ³ region was 0.2 μm, and a dip with a width of 0.6 μm was formed.

Example 3 Carrier concentration 1.2× in the same manner as Example 1
After growing and etching a GaAs epitaxial layer of 10 ¹⁸ /cm ³ , the molar ratio of both Ga and As components was set to 4:1 in growing the low carrier concentration region.

That is, 40 ml/min of HCl for Ga transfer, AsH ₃
(concentration 10%) was supplied at 100 ml/min to grow an n-type GaAs epitaxial layer with a carrier concentration of 1.8×10 ¹⁵ /cm ³ and a thickness of 3 μm for 10 minutes without adding any impurities.

In the obtained GaAs epitaxial layer, the carrier concentration ranges from 1.2×10 ¹⁸ /cm ³ to 1.8×10 ¹⁵ /cm ³
The thickness of the epitaxial film required for transition to the region was 0.1 μm.

Comparative Example The carrier concentration was changed in the same manner as in the example except that the supply amount of AsH ₃ was 100 ml (concentration 10%), the supply amount of HCl for Ga transfer was 10 ml/min, and the substrate temperature was 750°C. 1.1×10 ¹⁸ /cm ³ and 1.7×10 ¹⁶ /
An epitaxial film with two layers of cm ³ was grown in the vapor phase.

The transition from the high carrier concentration layer to the low carrier concentration layer required 3 μm.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing changes in carrier concentration of an SDR type impact diode. FIG. 2 is a diagram showing changes in carrier density with dips. 1... N-type high carrier concentration region, 2... N-type low carrier concentration region, 3... P-type high carrier concentration region, 4... Deep.

Claims (1)

[Claims] 1. In vapor phase epitaxial growth of a compound semiconductor single crystal layer made of elements of Groups and Groups of the periodic table having multiple regions with different carrier concentrations on the surface of a single crystal substrate, a region with a single carrier concentration is used. 1. A method characterized in that after growing regions with different carrier concentrations, following etching in an air stream containing a group element.