JPS60102733A - Forming method of ohmic electrode - Google Patents

Abstract

PURPOSE:To lower contact resistance, to improve the morphology of the surface of an ohmic electrode and to reduce the area of the electrode by forming a first layer for the ohmic electrode having multilayer structure to an N type GaAs layer in an AuGe layer and bringing the thickness of the first layer to 350Angstrom or less. CONSTITUTION:An N type GaAs layer 2 is formed on a semi-insulating GaAs substrate 1. The N type GaAs layer 2 is formed by implanting Si ions at 1.5X 10<13>does/cm<2>.100keV and activating the ions. An AuGe layer 3, an Ni layer 4 and an Au layer 5 are shaped on the layer 2. These layers 3, 4, 5 are formed through several evaporation in thickness of 300Angstrom , 300Angstrom and 1,000Angstrom and patterning by a lift-off method. An ohmic contact is obtained between the N type GaAs layer 2 and the AuGe layer 3 through ohmic heat treatment. The morphology of the surface is improved by bringing the thickness of the AuGe layer 3 to 350Angstrom or less.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a method for forming an ohmic electrode on an n-type GaAs layer.

(Prior art) As one of the methods for forming this type of ohmic electrode, n-type G
An Au Ge layer is deposited on the surface of the aAs layer, and then ohmic treatment is performed to form an alloy layer with an n+ type region,
A method of obtaining ohmic contact with the n-type GaAs layer by this is known.

In addition, in order to improve the surface morphology of the AuGe layer (1
), or a two-layer structure with a coating layer of Ni or PT to reduce ball up.
Alternatively, it is also known to form a three-layer structure including an Au layer and an Au layer in order to further prevent oxidation of the coating layer.

In a typical example, a 12 wt% GeoAuGe layer is deposited at 1000λ, on top of which a Ni layer is deposited at 300X;
On top of that, 10ool of Au was deposited, and then 400℃~400℃
Ohmic heat treatment is performed at a temperature of 50° C. for about 1 minute.

According to this method, a low-resistance ohmic contact can be obtained, but the surface morphology of the electrode is sensitive to the ohmic processing temperature, and the surface morphology at the ohmic processing temperature where the lowest resistance is obtained is not necessarily good. This includes problems when a fine electrode shape is required.

The present inventors believe that the ohmic contact made by the AuGe alloy is
The Au by alloying reaction with AuGe/n-type GaAs
Since it utilizes the phenomenon of forming an n+ layer at the Ge/n-type GaAs interface, it depends on the thickness of the AuGe layer (
2) As a result of experiments based on the assumption that the thickness of the reaction layer with GaAs is different and that this can be a factor controlling the physical properties of ohmic contact, we are confident that the AuGe thickness is the dominant factor for the surface moholozor. It's arrived.

(Object of the Invention) The present invention has been achieved based on such knowledge, and its object is to provide a method for forming an ohmic electrode having good ohmic contact resistance and good electrode surface moholonau. In particular, it is an object of the present invention to provide a method that has a wide tolerance range for ohmic processing temperature fluctuations and is excellent in stability.

(Structure of the Invention) The present invention achieves the above object in a method of forming an ohmic contact to an n-type GaAs layer using an AuGe alloy.
This was achieved by setting the AuGeO layer thickness to 350X or less, and will be described in detail below.

(Example) FIG. 1 is a cross-sectional view for explaining the present invention in detail, and in FIG. 1, l is a semi-insulating GaAs substrate;
2 is an n-type GaAs layer. The n-type GaAs layer 2 is made of St
ion 1-, 5 X 1.015doesAyn2.
1. It is formed by implanting and activating it under the condition of 0 keV. In FIG. 1, 3 to 5 are ohmic electrodes having a three-layer structure, 3 is AuGe, 4 is N:, and 5 is Au. These three layers of AuGe/Ni/Au are each 300X
It is formed by continuous vapor deposition to a thickness of /300X/100OX and patterning using a lift-off method. Thereafter, ohmic heat treatment is performed to obtain ohmic contact between the n-type GaAs and AuGe layers.

Figure 2 shows the case where the temperature during ohmic heat treatment of an ohmic electrode having a three-layer structure of AuGe/Ni/Au is plotted on the horizontal axis and the contact resistance value is plotted on the vertical axis. If the thickness of is 300X,
Characteristic (b) is for the case where the AuGe layer thickness is 100OX, and the Ni/Au (D thickness is 3ooX/1oooX)
The ohmic heat treatment time is 1 minute. This second
As is clear from the figure, the contact resistivity is lower when the thickness of the AuGe layer is 300X, and a more or less constant contact resistivity can be obtained over a wide range of ohmic processing temperatures.

Figure 3 shows the change in contact resistivity over time when acing was performed at 250°C. Characteristic (a) is for the case where the thickness of the AuGe layer is 300X, and characteristic (b) is for the case where the thickness of the AuGe layer is 300X.
This is the case where the thickness of the Ge layer is 100OX, and this third
As is clear from the figure, when the thickness of the AuGe layer is 300X, it is excellent even in the aging test, and the contact resistivity is stable.

FIGS. 4 and 5 show the surface morphology of the Au layer 5 after the ohmic heat treatment, and are copies of optical micrographs.

In Figure 4(a), the thickness of the AuGe layer is 300X and 430X.
Figure 4(b) shows the surface after ohmic heat treatment for 1 minute at ℃.
In addition, the surface is shown under the same conditions as above.

Figure 5 (,) shows that the thickness of the AuGe layer is 300X and 450X.
Figure 5(b) shows the surface after ohmic heat treatment at ℃ for 1 minute.
In addition, the surface is shown under the same conditions (5).

As is clear from Figures 4 and 5, the AuGe layer is
When set to 00X, the ohmic heat treatment temperature is set to 430
When ohmic heat treatment is carried out at 450°C, it is observed that a 6μ-sized altered region occupies about 16 inches, and when ohmic heat treatment is carried out at 450°C, agglomeration occurs on the entire surface, causing unevenness and extremely deteriorating the surface mohorozo. On the other hand, the AuGe layer is 300
When X is used, no altered region is observed under a 500x optical microscope.

In the above embodiments, the GaAs layer is 300X thick, but the same effect can be obtained even if the thickness is 100X or 11350X. Note that the AuGe layer is 4
00X thickness is relatively good, but 500X thickness is 43
When ohmic heat treatment is performed at 0° C. for 1 minute, a deterioration region of about 11 coefficients is generated. Therefore, when considering the thickness variation of the AuGe layer, the thickness of the AuGe layer should be set to 350X or less.

(Effects of the Invention) As explained above, the present invention provides an ohmic electrode type with a two-layer or three-layer structure in which an AuGe layer is the bottom layer on the surface of an n-type GaAs layer (6), by making the AuGe layer sufficiently thin. As a result, low contact resistivity and good surface morphology can be obtained over a wide range of ohmic processing temperatures, and the stability of contact resistivity is also good, making it possible to reduce the ohmic electrode area with higher integration. The method for forming an ohmic electrode according to the present invention is fully effective when the following is required.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of the structure of the ohmic electrode according to the present invention, Figure 2 is a diagram showing the ohmic contact resistivity versus ohmic treatment temperature, and Figure 3 is a diagram showing the temporal change in ohmic contact resistivity after aging at 250°C. The figures shown, Figures 4 and 5, are
It is a diagram illustrating the surface morphology of an Au film and is a reproduction of an optical micrograph. 1... Semi-insulating GaAs substrate, 2... N-type GaAs
Layer, 3...AuCxe film, 4...Ni film, 5-A
u membrane. (7) Figure 2 Ohmi Tsuk treatment temperature FCI

Claims (1)

[Claims] As an ohmic electrode structure for the n-type GaAs layer, AuG
A method for forming an ohmic electrode with a two-layer or multilayer structure in which the e-layer is the first layer, the method comprising making the AuGe layer thickness of the first layer 350X or less.