JPH0834224B2 - Method for manufacturing field effect transistor - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing a field effect transistor, and more particularly to a method for manufacturing a field effect transistor in which a low resistance metal is covered on a gate electrode.

[Conventional technology]

Field effect transistors have been developed as a low-power, high-speed switching element for a long time. In particular, a GaAs Schottky barrier gate type field effect transistor (hereinafter referred to as GaAs MESFET) using n-type gallium arsenide (GaAs) as an operating layer is It is attracting attention as a key device for next-generation ultra-high speed computers. The most important parameter that can characterize the characteristics of GaAs MESFETs is the transfer conductance (gm), and various device processes have been devised to improve gm.

[Problems to be solved by the invention]

FIG. 3 shows a cross-sectional shape of a GaAs MESFET using the so-called self-alignment method. After the semiconductor operating layer 12 is formed in the semi-insulating substrate 11 by the ion implantation method, a refractory metal such as tungsten silicide ( Wsi) gate electrode 13 is formed, high concentration ions are implanted using it as a mask, and source electrode 14 and drain electrode 1 of the gate electrode are formed.
A low resistance region 16 is formed on the 5 side. The reason why the refractory metal is used as the gate electrode is that it is necessary to withstand the annealing treatment (usually 700 ° C. or higher) for activating the implanted ions. In this structure, since the low resistance region is provided on both sides of the gate electrode, the series parasitic resistance is small,
Although high gm can be obtained, refractory metals generally have high specific resistance and thus have a drawback of increasing gate resistance. In order to reduce the gate resistance, as shown in Fig. 4, Au-Ti
A method using N-Wsi three-layer metal 31 is also proposed,
In this case, since the low resistance metal (TiN) -Au is in contact with only the upper surface of the Wsi gate electrode, the adhesion is weak,
Accidents in which the low-resistance metal peeled off from the high-melting metal also often occurred.

[Means for solving problems]

The present invention has been made in view of the above-mentioned drawbacks of conventional field effect transistors, and an object thereof is to provide a method for manufacturing a field effect transistor having a gate electrode having low gate resistance and high mechanical strength. To do.

The method for manufacturing a field effect transistor of the present invention comprises a step of forming a gate electrode made of a refractory metal on a semiconductor operating layer provided on a semi-insulating substrate, a photoresist is applied to the entire surface, and then the entire surface is dry-etched. And exposing a portion of the upper surface and side surfaces of the gate electrode by etching the photoresist by a predetermined amount, and then forming a low resistance metal on the entire surface by vapor deposition, and exposing the low resistance metal. And a step of removing the photoresist, the step of patterning the upper surface and the side surface of the gate electrode so as to wrap it, and a hat-shaped low resistance metal contacting from the upper surface of the gate electrode to a predetermined side surface is formed. Form.

〔Example〕

Next, the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view of one embodiment of the present invention, showing a specific resistance of 10 ⁷ So-cm.
An n-type GaAs semiconductor operating layer is formed on the above semi-insulating GaAs substrate 11.
12 (carrier density 2 × 10 ¹⁷ cm ⁻³ , thickness 0.1 μm) are provided by the ion implantation method. A source electrode 14 and a drain electrode 15 made of an AuGe alloy are provided on the surface of the semiconductor operating layer 12, and a gate electrode 13 made of a Wsi refractory metal is provided between the source electrode 14 and the drain electrode 15. A low resistance region (thickness 0.3 μm, carrier density 5 × 10 ¹⁷ cm ⁻³ ) 16 is provided on both sides of the gate electrode to reduce series parasitic resistance. In the figure, the gate electrode thickness and length are both 0.5 μm. The essence of the field-effect transistor according to the present invention is the upper surface 17 and a part of the side surface of the gate electrode 13.
Hat-shaped low resistance metal (Ti-Pt) formed over 18
-Au) 19. The thickness of the low resistance metal is 0.5 μm,
The upper surface 17 of the gate electrode and the side surface 0.2 μm down from the shoulder 1
It is in contact with the gate electrode at 8.

Next, one example of a method of manufacturing the field effect transistor shown in FIG. 1 will be described with reference to FIG. FIG. 2A shows a source 14, a drain 15 and a gate 13 on a semi-insulating substrate by a usual method.
3 shows a state in which each electrode is provided. The gate length of the WSi gate electrode is 0.5 μm, and the gate electrode is also 0.5 μm. Next, a photoresist 21 is applied to the entire surface in FIG. 2B, and then the entire surface is dry-etched from the vertical direction as shown in FIG. 2C, so that the head 22 of the gate electrode 13 is exposed. Next, in the same figure (D), Ti (200Å) -Pt (200Å)-
Au (5000Å) 19 is vapor-deposited, a predetermined photoresist mask 23 is provided as shown in (E), the above Ti-Pt-Au film is etched, and the unnecessary photoresist is removed at the end, as shown in FIG. A field effect transistor is obtained.

〔The invention's effect〕

As described above, in the field effect transistor according to the present invention, the high-melting-point metal gate electrode has the hat-shaped low resistance metal provided on the head thereof, so that the gate resistance can be reduced and the high-frequency characteristic is excellent. Is obtained. Further, since the low resistance metal is in contact not only with the upper surface of the gate electrode but also with the side surface thereof, the mechanical strength is sufficient.

Although the GaAs MESFET is shown in the embodiment of the present invention, it is needless to say that the field effect transistor is not limited to the GaAs MESFET and can be applied to other field effect transistors (including MOSFET) using a high melting point gate metal.

[Brief description of drawings]

FIG. 1 is a sectional view of one embodiment of the present invention, and FIG.
(E) is a process sectional view showing an example of the manufacturing method,
FIG. 4 and FIG. 4 are sectional views of a conventional field effect transistor. 11 ... Semi-insulating substrate, 12 ... Semiconductor operating layer, 13 ... Gate electrode, 14 ... Source electrode, 15 ... Drain electrode, 16 ...
… Low resistance region, 17 …… Gate electrode top surface, 18 …… Side surface, 19
...... Low resistance metal, 21 ...... Photoresist, 22 ...... Gate electrode head, 23 ...... Photoresist pattern, 31 ...... Ti-Pt-
Au film.

Claims (1)

[Claims] 1. A step of forming a gate electrode made of a refractory metal on a semiconductor operating layer provided on a semi-insulating substrate, a photoresist is applied to the entire surface, and then the entire surface is dry-etched to leave the photoresist. A step of exposing a part of an upper surface portion and a side surface of the gate electrode by quantitative etching; a step of forming a low resistance metal on the entire surface by vapor deposition; and a step of exposing the low resistance metal to the upper surface of the gate electrode. And forming a hat-shaped low-resistance metal in contact with a predetermined side surface portion from the upper surface portion of the gate electrode, and a step of patterning the portion and the side surface portion so as to enclose the portion and the side surface portion. Of manufacturing a field effect transistor having