JPS5941829A - Forming method of ohmic contact with compound semiconductor - Google Patents

Abstract

PURPOSE:To execute the formation of a high-concentration layer, the formation of an ohmic electrode and relative positioning by a simple process by forming a hole in which the opening section of a first layer is than that of a second layer, etching the compound semiconductor while using the thin-film of the first layer as a mask and vapor-growing an element. CONSTITUTION:An electrode pattern is formed by a photo-resist 14, a nitride film 13 and an oxide film 12 are etched through dry etching using CF4 gas while using the pattern as a mask, and the hole in which the opening section of the oxide film 12 of the first layer is wider than that of the nitride film of the second layer on the oxide film is formed. Gallium arsenide 11 is etched by using a mixed liquid of sulfuric acid, hydrogen peroxide and water while using the oxide film 12 as a mask and entered in a thermal decomposition system growth oven employing arsine-organic gallium-hydrogen, and a gallium aresenide crystal 15 in high concentration is grown selectively. When metals 16, 17 forming the ohmic contact are evaporated while using the nitride film 13 as a mask, step broken sections 18, 18' can be formed, the metals are alloyed through heat treatment, and the excellent ohmic contact is obtained.

Description

[Detailed Description of the Invention] With the development of communication systems such as microwave line-of-sight communication and satellite communication, it has become desirable to send more information. It has become desired. Conventionally, silicon has been the mainstream material for semiconductor devices, but compound semiconductors are currently attracting attention as materials for high-frequency devices because of their high electron mobility. Among these, research on gallium arsenide is particularly advanced, and field-effect transistors using gallium arsenide have already reached a practical level.

In field effect transistors, it is important to shorten the gate length and lower the source resistance in order to obtain good performance.

As a method of lowering the source resistance, a method is conventionally known in which a crystal having a concentration one order of magnitude higher than that of the active layer is buried in a portion where an ohmic contact is to be formed. However, in the case of compound semiconductors, the impurity concentration is 2x 10t
It is difficult to increase the resistivity higher than cML-3, and it is not possible to make the resistivity sufficiently low compared to metals. Therefore, in order to lower the source resistance, it is necessary to not only bring the high-density crystal close to the gate, but also to use ohmic The electrode metal also needs to be close to the gate. - The accuracy of relative alignment of photoresist patterns using an exposure machine is ±0.5μ
It is about m. Therefore, after forming a high concentration layer by selective growth,
When forming a new ohmic electrode pattern using photoresist, in order to apply pressure so that the positions of both patterns do not reverse, ohmic polarization pattern 2tj: It is necessary that the pattern is at least 0.5 μm or more smaller than the pattern 1 of the high temperature [14].

FIG. 1(a) is a plan view showing the relationship between the high concentration I@ pattern and the polarization pattern, and FIG. 1(b) is a cross-sectional view thereof.

This is not only disadvantageous in terms of device characteristics, but also
Since difficult positioning is required, this method has the disadvantage of lowering the manufacturing yield.

The present invention has been made in response to the above problems, and it is possible to form a high a degree layer and ohmic polarization through a simple process, and at the same time, to perform ohmic polarization and formation of a compound semiconductor with suitable relative alignment. To provide a contact formation method.

The gist of the present invention is to form a hole in which two layers of thin films with different properties are deposited on a compound semiconductor, and the layer on the compound semiconductor side (layer X) has a wider opening than the layer above it (second layer). a first step in which the compound semiconductor is etched using the first layer thin film as a mask, and then a high concentration compound semiconductor is selectively grown by vapor phase growth; a third step of forming a metal on the high concentration region to obtain ohmic contact, removing the first and second layer thin films, and simultaneously removing the metal on the second layer thin film;
A method for forming an ohmic contact to a compound semiconductor, comprising a fourth step of performing high-temperature treatment to alloy the metal and a high-temperature compound semiconductor.

The present invention will be described in detail below based on embodiments.

FIGS. 2(a) to 2(h) are process sectional views for explaining one embodiment of the present invention. An embodiment of the present invention will be described with reference to an example in which the present invention is applied to manufacturing a gallium arsenide field effect transistor. That is, (1) a first layer oxide film 12 with a thickness of 4000X and a second layer nitride film 13 with a thickness of 200OA are grown on the gallium arsenide crystal 11 by the EVA method (see FIG. 2(a)).
)).

(2) Next, an electrode pattern is formed using a 7-photoresist 14 (see FIG. 2(b)). Using this pattern 14 as a mask, the nitride film 13 and oxide film 12 are etched by dry etching using Cir'4 gas ( Figure 2 (C)).

(3) Next, add a mixture of hydrofluoric acid and ammonium fluoride to
0 papermaking degree etching is performed. At this time, the oxide film is 100A
/second, but the nitride film is hardly etched, so the first oxide film 12 is etched into the second layer above it.
Holes having openings wider than the nitride layer can be formed.

Thereafter, the photoresist is removed (FIG. 2(d)).

(4) Next, using the oxide film 12 as a mask, the gallium arsenide is etched by approximately 3000λ using a mixed solution of sulfuric acid, hydrogen peroxide, and water (FIG. 2(e)).

(5) In this state, put this crystal in a pyrolysis type growth furnace using arsine (AsHs)-organic gallium-hydrogen,
High concentration gallium arsenide crystals are selectively grown to a thickness of approximately 300 OA. In this case, as organic gallium, for example, '
By using a(Cz Hs)zCl and selecting appropriate conditions, no gallium arsenide crystals will grow on the attenuated film (FIG. 2(f)).

(6) Next, using the nitride film 13 as a mask, 150% of gold (Au)-gel manila A (Ue) (ue/Au 12 W%) is used as a metal for forming ohmic contact.
Deposit 500^ of 0At nickel (Ni). At this time, since the oxide film 2 has a wider opening than the nitride film 13 above it, the high concentration gallium arsenide crystal and the ohmic electrode are aligned correctly, and the gold/germanium-nickel layer is stepped. A cut part 18.18' is formed (second
Figure (g)).

(7) Next, when this wafer is soaked in a mixed solution of hexafluoric acid and ammonium fluoride for about 2 hours, the etching solution enters the gold/germanium nickel step shown at 18°18' and oxidizes. Membrane 2 is etched. When the oxide film is completely etched, the nitride film and gold/metal layer on the oxide film are removed.
The germanium nickel is stripped from the wafer.

In this state, when this wafer is heat-treated in hydrogen at 480° C., gallium arsenide and gold/germanium/nickel are alloyed, and good ohmic contact is obtained.

In the above embodiments, there is no ohmic contact with gallium arsenide.

As explained above, according to the present invention, an ohmic electrode with a highly concentrated compound semiconductor can be formed by forming a photoresist pattern only once, and the pattern can be arranged correctly in minute dimensions. be able to.

[Brief explanation of the drawing]

FIGS. 1(a) and 1(b) are plan views and cross-sectional views showing the positional relationship between the high-concentration buried layer and the ohmic electrode metal pattern, and FIGS. It is a sectional view of the work type for explaining an example. 1.1'...Pattern of high concentration buried layer, 2.2
'・・・Ohmic 'electrode metal pattern, 3
．． 3'...High concentration buried layer, 11...Gallium arsenide crystal, 12...--Oxide film, 13...
...Nitride film, 14...Photoresist, 15
...High concentration of gallium arsenide, 16...
Gold, kermanium, 17...nickel [L18
118'...Step break part. 1 picture of shadow 2 picture

Claims (1)

[Claims] Two thin films with different properties are deposited on the compound semiconductor, and the layer on the compound semiconductor side (first layer) is the layer above it (the 214th layer).
The first step is to form a hole with a wider opening, and the second step is to etch the compound semiconductor using the first layer thin film as a mask, and then selectively grow a high concentration compound semiconductor.
The second layer thin film is used as a mask to form metal on the high concentration region to obtain ohmic contact, and the first and second layer thin films are removed while the metal on the second layer thin film is also removed. A method for forming an ohmic contact to a compound semiconductor, comprising a third step of removing the metal and a fourth step of alloying the metal and the high concentration compound semiconductor by performing high-temperature treatment.