JPH0131310B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a - group compound semiconductor device which has excellent heat resistance, and in particular has a high allowable storage and operation temperature.

n-type GaAs such as Gunn diodes, imbat diodes, mixer diodes, field effect transistors, etc.
A semiconductor device using a semiconductor includes at least one ohmic electrode, or the ohmic electrode and another shot barrier electrode. Here, conventional ohmic electrodes are usually made of Au--N-type GaAs, which has a relatively low carrier density, because ohmic contact with low contact resistance can be easily obtained.
It is obtained by thermally alloying a material containing Ge or Sn as an n-type impurity with GaAs as a main component, which is mainly composed of Ib group elements such as Ge, Au-Su, and Ag-In-Ge. Further, typically, an Au layer is further provided as a second layer on the alloyed layer in order to reduce wiring resistance and facilitate bonding.
However, conventional semiconductor devices made of n-type GaAs semiconductors equipped with such ohmic electrodes have the drawback of inferior heat resistance and particularly low allowable temperature compared to Si transistors. The reason for this is, for example, when considering an electrode whose main component is Au, such as Au-Ge, during heat treatment alloying to obtain ohmic contact, Au interacts with Ga in GaAs, and the Au-Ga Forms an alloy. In this case, if the reaction is complete, something close to an Au-Ga eutectic will be produced, which will melt at a relatively low temperature of around 350°C.
In other words, the ohmic electrode whose main component is Au,
Au reacts with GaAs at a low temperature of about 400℃,
This is because the melting point of the reaction product is low. In addition, when using Ag-In-Ge, the second layer of Au easily diffuses at low temperatures and forms a solid solution with Ag.
Since Au reaches the GaAs interface, the situation is similar to that of electrodes whose main component is Au, and the maximum allowable temperature of conventional semiconductor devices made of n-type GaAs semiconductors equipped with these ohmic electrodes is at most 400°C, making them heat resistant. He had the disadvantage of being lacking in sexuality.

SUMMARY OF THE INVENTION An object of the present invention is to provide a highly heat-resistant semiconductor device that eliminates the above-mentioned conventional drawbacks and significantly increases the low allowable temperature.

According to the present invention, the - group compound is characterized by comprising an ohmic contact layer formed by heat-treating a metal film made of 32 to 64% by weight of Ge and Ni, and a wiring layer made of Al in contact with the ohmic contact layer. A semiconductor device is obtained.

The present invention will be explained in detail below with reference to the drawings.

FIG. 1 is a perspective view showing a first embodiment of the present invention, and shows a planar Gunn effect element as a semiconductor device. In the same figure, in contact with n-type GaAs12,
A first electrode layer 13 formed by heat treatment with a metal layer consisting of 32 to 64% by weight of Ge and the balance Ni, and a second electrode layer 14 as a wiring layer made of Al in contact with the first layer.
(note that 11 is a high resistance substrate). Here, the first electrode layer is an n-type
It acts as an ohmic contact to GaAs, and the second layer has the effect of reducing wiring resistance and facilitating lead wire bonding. 1st
The electrode layer is in ohmic contact with n-type GaAs, has a very high melting temperature (over 800°C), and has excellent heat resistance with good stability at high temperatures. However, even if it is the first electrode layer, if an Au layer is used as the second layer as in the past, the heat resistance will be lower than in the case of using an electrode whose main component is Au in the first layer as in the past. Although it is considerably improved, Au will eventually become active and reach the GaAs interface, resulting in a decrease in heat resistance over time.
This will result in a decrease in the allowable temperature. sometimes 500℃
In the above high temperature range, the characteristics of the first layer are greatly reduced. Here, by using Al as the second layer in contact with the first layer as in the present invention, phenomena that reduce the features of the first layer as described above, that is, a decrease in heat resistance and a decrease in allowable temperature, can be prevented. be able to.

The following specific example will be described. high resistance
Carrier density 5×10 ¹⁵ cm ^-3 thickness 7μ on GaAs substrate
A planar Gunn effect element was fabricated using a wafer on which an n-type layer of m was grown. Element length is 30μ
It is m. First, an unnecessary n-type layer was removed by ordinary chemical etching to form an element region. Then, 40% by weight was added to the cathode and anode electrode parts.
An alloy film consisting of Ge and the remainder Ni was deposited to a thickness of 1500 Å and heat treated in hydrogen gas at a temperature of 500° C. for 5 minutes to obtain ohmic contact, that is, to form a first electrode layer. Furthermore, a second layer of Al film having a thickness of 1 μm was formed on the first layer. In this case, the second layer is formed by depositing Al over the entire surface and then etching unnecessary parts, and is limited to the inside of the first layer in plan view. For comparison, the following two types of elements having the same shape and including cathode and anode electrodes were created. One of them (comparative element 1) is that the first layer is the same as in the example of the present invention, and the second layer is the same as in the example of the present invention.
The first layer is a 1 μm thick Au film, and the other is a conventional first layer with Au-Ge-Ni.
The ohmic contact was heat treated at a temperature of 450°C for 30 seconds, and a 1 μm thick Au film was used as the second layer. The heat resistance and allowable temperature of these three types of elements were investigated by storing them at high temperatures. Comparative element 2 had the lowest allowable temperature, for example, at a temperature of 500° C., the second layer of Au reacted instantly and the electrode completely changed in quality. In comparison element 2, 500
After more than 15 minutes at a temperature of °C, deterioration of the electrode began to occur. On the other hand, the element of Example 1 of the present invention has a much higher heat resistance than these comparative elements, and has a heat resistance of 500
No deterioration of the electrode occurred for 1 hour at a temperature of .degree.

Next, as a second embodiment of the present invention, an n-type transistor having an ohmic electrode and a shot barrier gate or an insulated gate electrode, such as a field effect transistor, is described.
A semiconductor device made of GaAs will be described. In the field effect transistor, an ohmic electrode is formed by a first layer formed by heat treating Ni-Ge and a second layer of Al, and a gate electrode is formed by Al forming the second layer. In addition to high heat resistance as in the first embodiment, significant advantages can be obtained in terms of manufacturing technology. That is, since Al forms a good shot junction with n-GaAs, the second layer of the ohmic electrode can be formed in the same step at the same time as the formation of the gate electrode, allowing for simple manufacturing. This advantage becomes even more effective when the semiconductor device forms an integrated circuit. This will be explained using drawings. FIG. 2a shows an equivalent circuit consisting of two field effect transistors, which are the basic units of an integrated circuit, and FIG. 2b is a perspective view of a specific implementation structure. For example, when one unit of the integrated circuit shown in the equivalent circuit diagram of FIG. 2a is formed as shown in FIG.
The process of wiring, such as wiring of the source and drain ohmic contact layers 23a, 23b, 23c, and connection of the gate 25b of the FET used as a load with the source of the load FET and the drain 23b of the drive FET, Immediately after formation, it can be performed using a single layer of Al alone in the same step as forming the gates 25a and 25b of the transistors, which is extremely simple. Note that 21 is a high resistance substrate, and 22 is n
type GaAs active layer.

Naturally, the case where the Al wiring portion of the second layer protrudes from the ohmic contact portion of the first layer is also included. In this case, the Al wiring part will be in direct contact with GaAs, but this part is not considered to be a metal bond.
It is equivalent to an Al shot barrier gate, and there is no factor that reduces heat resistance. Now, in the conventional technology, such a wiring part is, for example, Cr-Pt-
Although Au is sometimes used, Cr, Pt, and Au all easily react with GaAs at temperatures below 500°C.
The heat resistance is not comparable to that of the device of the present invention. Moreover, the wiring part made of this Cr-Pt-Au is, for example, SiO ₂
Even if the device is stacked on top, it is not possible to prevent the reaction from progressing at the ohmic electrode portion as described above, and as a result, the heat resistance of the device of the present invention, particularly the allowable temperature, is far below.

A specific example in this case will be described.
Carrier density 2×10 ¹⁷ cm ^-3 on high resistance GaAs substrate
A shot barrier gate with a gate length of 1.5 μm using a wafer grown with a 0.15 μm thick n-type layer
A GaAs field effect transistor was fabricated. A first layer was formed on the source and drain electrode portions in the same process as in Example 1. After that, Al was vapor-deposited to a thickness of 0.4 μm over the entire surface, and then a mask was formed using photoresist to cover the gate electrode portion and the bonding pad portions of the source and drain electrodes. Subsequently, Al was etched to simultaneously form a gate electrode and a second layer of source and drain electrodes, ie bonding pads, to form a field effect transistor. When the transistor of the second embodiment of the present invention was subjected to a high temperature accelerated deterioration test, the average life of the conventional transistor was ¹⁰⁸ hours, whereas
The transistor had a long life of more than 10 ⁹ hours.

[Brief explanation of drawings]

FIG. 1 is a perspective view of a Brehner-type Gunn effect element showing a first embodiment of the present invention, and FIGS. 2a and 2b are diagrams showing a second embodiment of the present invention. It shows 1 unit. In the figure, 11,
21 is a high resistance substrate, 12 and 22 are n-type GaAs active layers, 13, 23a, 23b, and 23c are ohmic contact layers formed by heat-treating Ge-Ni films, 14, 24
a, 24b, 24c are wiring layers of Al film, 25a,
25b is an Al gate.

Claims (1)

[Claims] 1 32-64 wt% Ge and balance on n-type GaAs
1. A - group compound semiconductor device comprising: an ohmic contact layer formed by heat-treating a metal layer made of Ni; and a wiring layer made of Al in contact with the ohmic contact layer.