JPH03185843A - Manufacture of gaas field effect transistor - Google Patents

Abstract

PURPOSE:To reduce surface level density by attaching S atoms and improve noise characteristics, by a method wherein, after a gate electrode is formed, an insulating film is formed after the gate electrode is dipped in solution containing ammonium sulfate, after a GaAs surface is exposed. CONSTITUTION:After a source electrode 7 and a drain electrode 8 are formed, an SiO2 film 6 is eliminated by using hydrofluoric acid system etching solution, the surface of a GaAs substrate 1 is exposed; the substrate is dipped in aqueous solution of ammonium sulfate for about an hour and washed with water; thus an s atom attaching film 9 is formed. An FET is completed by depositing an SiO2 film 10 by using, e.g. optical CVD method at a low temperature (lower than or equal to 450 deg.C). The S atom attaching layer is formed on the GaAs surface by ammonium sulfate solution penetrating treatment, a lot of dangling bonds existing on the surface are reduced; surface level density turning to a low frequency noise source is reduced, and noise characteristics are improved. When the temperature of insulating film deposition after ammonium sulfate treatment becomes too high, attached S atoms might evaporate before insulating film deposition, so that the temperature is desirable to be lower than or equal to 450 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for manufacturing a field effect transistor using a compound semiconductor GaAs. (abbreviated as MESFET)!
Although it has the advantages of high speed and low power consumption compared to the conventional 5iFET, it is expected to be used in both the digital and analog IC fields. Recently, a self-alignment type FET using a high-melting point metal gate that can reduce parasitic resistance such as C & source resistance has been developed, and even though high performance has been attempted, the invention has not been resolved. However, these conventional GaAsM E S F E
(Noise increases in the low frequency region (especially below 200 MHz), and analog ICs whose bandwidth is this low frequency region
The present invention has been made in view of the above problems.
In the production of AsFET, the GaAs surface is treated with ammonium sulfide [(NHn)e3 or (NH4)eSx]S
According to the present invention, by treating the GaAs surface with ammonium sulfide, the GaAs surface is passivated with S (sulfur) atoms, which is a source of noise at low frequencies. GaAsF has a surface state density of 41 (reduced) and improved noise characteristics.
In the following examples, a self-alignment type FET using a high-melting point metal gate will be explained as an example of a device that can obtain ET. Using the photoresist film 2A as a mask, 3i111 ions are implanted at an acceleration voltage of 30 KeV and a dose of 8 x 10"cIII-" to form the well layer 3 that will become the channel region, and then the photoresist M2A is removed. As shown in (b), using the sputtering method, WSiN (2000 people)/Ta
A three-layer film 4A of N (500 Å)/Au (4000 Å) was formed, and then Ar ion milling and CFa 10a were applied to a predetermined area using the photoresist film 2B as a mask, as shown in the same figure (c). Anisotropic plasma etching of a mixed gas is performed (to form a Schottky gate electrode 4 made of a part of the three-layer film 4A).Next, photoresist film 2
After removing B, as shown in Figure (d), using the photoresist film 2C as a mask, 312G ions are implanted under the conditions of 50KeV and 5 x 10"cm-" to form the source and drain. Next, the photoresist film 2C was removed while forming a part of the n' layer 5, and a 5iOi film 6 (2,500 layers) was formed on the entire surface as shown in Figure (e). Using membrane 2D as a mask, 160 3i11 ions were passed through the membrane for 5 ins.
KeV, 1" implanted under the conditions of 5 x 10"Cm-"
Next, remove the photoresist film 2D from the n layer 8 which will become part of the drain. As shown in Figure (f), annealing is performed at 800°C for 15 minutes in an arsine atmosphere and ions are implanted. Even if the layer is activated, the same figure (g
), a predetermined region of the SiO*jl 16 was opened using a hydrofluoric acid etching solution using a photoresist film as a mask, and the AuGe was lifted off and heat treated at 430° C. for 3 minutes to form the source electrode 7. Although the drain electrode 8 is shaped like the one shown in the same figure (h)? Q
The 5i02 film 6 was removed using a hydrofluoric acid-based etching solution to expose the surface of the GaAs substrate 1, and the surface of the GaAs substrate 1 was soaked in an aqueous solution of ammonium sulfide [(NHJ)esx] at ℃ for 1 hour, and then washed with water. ．． Although the LS atomic adhesion layer 9 is formed on the GaAs surface, the temperature is lowered again (45
5i02 film 1 using, for example, a photo-CVD method at
0 is deposited to complete the FET. Figure 2 shows the difference between the FET treated with the aqueous solution permeation of ammonium sulfate according to the manufacturing method of the present invention and the FET not subjected to the conventional treatment, as shown in Figure 1. The figure shows the frequency dependence of the noise figure of 4. The gate length of the FET is 1 μm and the gate width is 600 μm0. Although the L threshold voltage is 10.9V, it is clear from the same figure that the FET produced by the manufacturing method of the present invention
It can be seen that the noise figure is drastically reduced in the region (below 00 MHz). This method forms an S atom adhesion layer on the GaAs surface by ammonium sulfate solution infiltration treatment. This may be because the surface state density, which causes noise, is reduced and the noise characteristics are improved. The temperature is preferably below 450°C as there is a risk of evaporation before the formation of the ohmic electrode.
In addition, in the above explanation, the force described for the treatment using l; It goes without saying that the invention can also be applied to the process of manufacturing FETs using epitaxial layers. By doing this, the surface unit density caused by dangling bonds, which exist in large numbers on the GaAs surface and cause noise at low frequencies, is reduced to S.
It is possible to reduce the noise by adhering atoms and improve the noise characteristics, making it possible to obtain high-performance GaAsFET.

[Brief explanation of drawings]

FIG. 1 shows a GaAsM E S F according to an embodiment of the present invention.
The steps showing the manufacturing method of ET are as shown in Fig. 2.
This is a diagram showing the frequency dependence of the noise characteristics of ET.
...GaAs substrate, 3...Well layer, 4...
・・・Gate electrode, 9...Name of Houou Rito with Si original atom

Claims (1)

[Claims] A method for manufacturing a GaAs field effect transistor, comprising the steps of: after forming a gate electrode, exposing the GaAs surface, impregnating it in a solution containing ammonium sulfate, and then forming an insulating film.