JPH0955517A - Multilayered metal schottky electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize electrode structure wherein long term reliability of a semiconductor device is ensured and high frequency characteristics are not deteriorated, by forming one or a plurality of lamination films composed of molybdenum laves as the lower layers and titanium layers as the upper layers, arm a semiconductor layer, and forming a conductive metal layer on the lamination films. SOLUTION: Photoresist is spread on a GaAs Schottky contact layer 11. An aperture is formed in a photoresist film by using a reduction projection method and an electron beam exposure method. A molybdenum layer 12, a titanium layer 13 and an aluminum layer 14 are continuosly stuck in order on the whole surface by using a film forming method like an electron beam sputtering method. An electrode having a desired shape is formed in the aperture part, by eliminating the photoresist and lifting off unnecessary metal films on the photoresist. Thereby molybdenum is introduced into a semiconductor interface, and mutual reaction between metal and semiconductor is restrained, so that a device of high reliability can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-layer metal Schottky electrode used as a gate electrode of a field effect transistor (hereinafter referred to as FET).

[0002]

2. Description of the Related Art In an FET using a compound semiconductor, a metal layer that forms a Schottky contact with a semiconductor layer is usually used as a gate electrode. FIG. 10 shows a typical electrode structure of a conventional FET. In this electrode structure, as shown in the figure, a titanium (Ti) layer 102 that forms a Schottky contact with the GaAs Schottky contact layer 101 is formed, and a platinum (Pt) layer serving as a barrier metal layer is formed thereon. ) Layer 103 and a gold (Au) layer 104 as a low resistance metal layer are sequentially laminated. In this electrode structure, the platinum layer prevents the gold layer 104 for lowering the resistance of the upper gate from directly reacting with the lower titanium layer 102, and gallium (Ga) from the surface of the semiconductor Schottky contact layer is external. It has the function of suppressing the diffusion toward

Also, a titanium / aluminum (Ti, Al) -based electrode structure shown in FIG. 11 is often used because of its good workability. That is, it has a structure in which a titanium layer 112 and an aluminum (Al) layer 113 as a low resistance metal layer are stacked on a GaAs Schottky contact layer 111.

Further, in order to improve the transistor characteristics, it is often practiced to make the gate electrode have a T-shaped cross section. Its sectional structure is shown in FIG. The electrode having this structure is manufactured as follows. A photoresist film (not shown) having a T-shaped opening is formed on the GaAs Schottky contact layer 121. Titanium, platinum, and gold are sequentially deposited to form titanium layers 122, 125 and platinum layer 12.
3, 126 and gold layers 124, 127 are formed. By removing the photoresist film together with the metal layer formed thereon, the electrode having the structure shown in FIG. 12 is obtained.

[0005]

In the above-mentioned conventional electrode structure, since titanium is in contact with the interface with the semiconductor, when the FET is used in the active state for a long time, a mutual reaction occurs between the titanium and the semiconductor. As a result, there are drawbacks such as fluctuations in the characteristics of the FET and problems in terms of reliability.

Further, in the conventional electrode structure, platinum is used as a barrier metal. However, the vapor deposition of platinum requires heating at a higher temperature or an electron beam of high energy as compared with other metals, so that it is stable. It was difficult to form a film, and it was difficult to form it with good reproducibility and high yield.

Further, when platinum is contained in the layer forming the multilayer structure, the width of the stacked platinum layers tends to be narrower than the width of the lower layer electrode, and a narrow gold layer grows on it. Therefore, when the T-shaped electrode is formed, as shown in FIG. 12, there is a problem that the upper layer metal and the lower layer metal are not formed in close contact with each other. Therefore, the mechanical strength of the electrode is insufficient, and the gate resistance becomes high, so that a desired high frequency characteristic cannot be obtained.

Therefore, an object of the present invention is to ensure long-term reliability of a semiconductor device and to stably form an electrode structure which does not deteriorate high frequency characteristics with high yield. is there.

[0009]

A multi-layer metal Schottky electrode of a field effect transistor according to the present invention for achieving the above object is a titanium compound having a molybdenum (Mo) film as a lower layer on a III-V compound semiconductor. One or a plurality of laminated films having a (Ti) film as an upper layer are formed, and a good conductive metal layer is formed thereon.

[0010]

Next, embodiments of the present invention will be described with reference to the drawings. Here, a gate electrode structure on gallium arsenide (GaAs) will be described as an example, but the present invention is not limited to this, and any semiconductor material may be used as long as it is an electrode used for a III-V group compound semiconductor element, and lattice matching is possible. It can be applied to both cases of system and strain system.

FIG. 1 is a sectional view of a Schottky electrode for explaining an embodiment of the present invention. To form an electrode having this structure, first, a photoresist is applied on the GaAs Schottky contact layer 11. Next, an opening is formed in the photoresist film by using a reduction projection method or an electron beam exposure method. After that, a molybdenum layer 12, a titanium layer 13, and an aluminum layer 14 are sequentially and continuously deposited on the entire surface by a film forming method such as an electron beam evaporation method. Next, by removing the photoresist and lifting off the unnecessary metal film thereon, an electrode having a desired shape is formed in the opening.

The characteristic points of the Schottky electrode according to the present invention are the following two points. The metal that contacts the semiconductor layer and forms a Schottky contact therewith is molybdenum. Do not use platinum.

The Schottky electrode of the field effect transistor according to the present invention can take the following embodiments. A gold layer is used instead of the aluminum layer as the good conductive metal film. A titanium layer is formed on the good-conductivity metal film to improve the adhesion with the upper metal layer. A laminated film of a molybdenum layer and a titanium layer is laminated in two or more layers. A barrier metal layer such as a molybdenum layer is interposed between the good conductive metal and the underlying titanium film. An electrode is formed by a lift-off method using a photoresist film having a T-shaped opening.

In the multilayer electrode formed as described above, since the GaAs Schottky contact layer 11 and the molybdenum layer 12 do not react with each other even in the active state,
A stable Schottky contact is secured for a long period of time.
Moreover, since platinum is not contained in the multilayer structure, it is possible to form the layer easily with good reproducibility and with high yield. Furthermore, since platinum is not used, when the T-shaped electrode is formed, electrode thinning does not occur, so that the adhesiveness between the upper layer and the lower layer does not deteriorate, and the high frequency characteristics of the device may deteriorate. Disappear.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. [First Embodiment] FIG. 1 shows a sectional structure of the first embodiment. As shown in FIG. 1, a film thickness of 10 nm is formed on the GaAs Schottky contact layer 11 by an electron beam evaporation method.
A molybdenum layer 12, a titanium layer 13 having a film thickness of 20 nm, and an aluminum layer 14 having a film thickness of 420 nm were sequentially formed. This laminated film was patterned by a lift-off method using a photoresist.

[Second Embodiment] FIG. 2 is a sectional view showing a second embodiment of the present invention. As shown in the figure, GaA
On the s-Schottky contact layer 21, a molybdenum layer 22 having a thickness of 10 nm and a thickness of 2 are formed by using an electron beam evaporation method.
A 0 nm titanium layer 23, a 400 nm thick aluminum layer 24, and a 20 nm thick titanium layer 25 were successively and successively formed, and patterned by a lift-off method.

[Third Embodiment] FIG. 3 is a sectional view showing a third embodiment of the present invention. As shown in the figure, GaA
On the s-Schottky contact layer 31, a molybdenum layer 32 with a thickness of 10 nm, a titanium layer 33 with a thickness of 20 nm, and a molybdenum layer 34 as a barrier metal layer with a thickness of 10 nm are formed by electron beam evaporation. Then, a gold layer 35 as a good conductive metal layer was sequentially and continuously formed to a thickness of 410 nm and patterned by a lift-off method.

[Fourth Embodiment] FIG. 4 is a sectional view showing a fourth embodiment of the present invention. As shown in the figure, GaA
On the s-Schottky contact layer 41, a molybdenum layer 42 having a thickness of 10 nm, a titanium layer 43 having a thickness of 20 nm, and a molybdenum layer 44 serving as a barrier metal layer having a thickness of 20 nm are formed by electron beam evaporation. Then, a gold layer 45 as a good conductive metal layer having a film thickness of 380 nm and a titanium layer 46 as an adhesion layer having a film thickness of 20 nm were successively formed successively and patterned by a lift-off method.

[Fifth Embodiment] FIG. 5 is a sectional view showing a fifth embodiment of the present invention. As shown in the figure, GaA
On the s Schottky contact layer 51, a molybdenum layer 52 having a film thickness of 10 nm and a film thickness of 1 were formed by using an electron beam evaporation method.
0 nm titanium layer 53, 10 nm thick molybdenum layer 5
4. Titanium layer 55 with 10 nm thickness and 410 nm thickness
The aluminum layer 56 was sequentially formed and patterned by the lift-off method.

In the electrode having this structure, the thickness of molybdenum required for one vapor deposition can be reduced, so that the film formation becomes easier and the process can be stabilized.
In this embodiment, (molybdenum, titanium) is set to 2 units, but the unit is not limited to this, and it is possible to repeat only desired units.

[Sixth Embodiment] FIG. 6 is a sectional view showing a sixth embodiment of the present invention. As shown in the figure, GaA
On the s-Schottky contact layer 61, a molybdenum layer 62 having a thickness of 10 nm and a thickness of 1 are formed by using an electron beam evaporation method.
0 nm titanium layer 63, 10 nm thick molybdenum layer 6
4. A titanium layer 65 having a film thickness of 10 nm, an aluminum layer 66 having a film thickness of 390 nm, and a titanium layer 67 having a film thickness of 20 nm were successively and successively formed, and patterned by a lift-off method.

[Seventh Embodiment] FIG. 7 is a sectional view showing a seventh embodiment of the present invention. As shown in the figure, GaA
On the s-Schottky contact layer 71, a molybdenum layer 72 having a thickness of 10 nm and a thickness of 1 are formed by an electron beam evaporation method.
0 nm titanium layer 73 and 10 nm thick molybdenum layer 7
4. After stacking a titanium layer 75 having a film thickness of 10 nm, a molybdenum layer 76 as a barrier metal layer having a film thickness of 10 nm and a gold layer 77 as a good conductive metal layer having a film thickness of 400 nm are successively formed.
The film thickness was sequentially and continuously formed and patterned by the lift-off method.

[Eighth Embodiment] FIG. 8 is a sectional view showing an eighth embodiment of the present invention. As shown in the figure, GaA
On the s-Schottky contact layer 81, a molybdenum layer 82 having a thickness of 10 nm and a thickness of 1 are formed by using an electron beam evaporation method.
0 nm titanium layer 83 and 10 nm thick molybdenum layer 8
4. After laminating a titanium layer 85 having a film thickness of 10 nm, a molybdenum layer 86 as a barrier metal layer having a film thickness of 10 nm and a gold layer 87 as a good conductive metal layer having a film thickness of 380 nm are successively formed.
Then, a titanium layer 88 as an adhesion layer having a thickness of 20 nm was successively and continuously formed to a thickness of 20 nm and patterned by a lift-off method.

[Ninth Embodiment] FIG. 9 is a sectional view showing a ninth embodiment of the present invention. After forming a photoresist film (not shown) having a T-shaped opening on the GaAs Schottky contact layer 91 by photolithography, molybdenum, titanium, molybdenum, and gold are respectively formed by electron beam evaporation. 10nm, 20nm, 1
It was deposited to a film thickness of 0 nm and 410 nm. Next, the unnecessary metal film is removed together with the photoresist to remove the molybdenum layers 92 and 96, the titanium layers 93 and 97, the molybdenum layer 94,
A Schottky electrode composed of 98 and gold layers 95 and 99 was formed. In the electrode formed as described above, the adhesion between the upper and lower metal layers was good, and a low resistance gate electrode could be formed.

[0025]

As described above, according to the present invention,
As an electrode structure of a III-V group compound semiconductor, since molybdenum is introduced into the semiconductor interface, a metal-semiconductor interaction is suppressed, so that a highly reliable device can be obtained. Further, since platinum having a high vapor deposition temperature is not included as a barrier layer, the process is easy and the reproducibility and the yield can be improved. Furthermore, since platinum is not included, there is no reduction in the electrode width seen in the electrode structure containing platinum, and in the case of a T-shaped electrode, it is possible to secure the adhesion between the upper and lower metal layers. . Therefore, a low resistance fine electrode structure can be manufactured, and deterioration of the high frequency characteristics of the FET can be prevented.

[Brief description of drawings]

FIG. 1 is a cross-sectional view for explaining an embodiment mode and a first embodiment example of the present invention.

FIG. 2 is a sectional view for explaining a second embodiment of the present invention.

FIG. 3 is a sectional view for explaining a third embodiment of the present invention.

FIG. 4 is a sectional view for explaining a fourth embodiment of the present invention.

FIG. 5 is a sectional view for explaining a fifth embodiment of the present invention.

FIG. 6 is a sectional view for explaining a sixth embodiment of the present invention.

FIG. 7 is a sectional view for explaining a seventh embodiment of the present invention.

FIG. 8 is a sectional view for explaining an eighth embodiment of the present invention.

FIG. 9 is a sectional view for explaining a ninth embodiment of the present invention.

FIG. 10 is a cross-sectional view showing a first conventional example.

FIG. 11 is a sectional view showing a second conventional example.

FIG. 12 is a sectional view showing a third conventional example.

[Explanation of symbols]

11, 21, 31, 41, 51, 61, 71, 81, 9
1, 101, 111, 121 GaAs Schottky contact layer 12, 22, 32, 34, 42, 44, 52, 54, 6
2, 64, 72, 74, 76, 82, 84, 86, 9
2, 94, 96, 98 Molybdenum layer 13, 23, 25, 33, 43, 46, 53, 55, 6
3, 65, 67, 73, 75, 83, 85, 88, 9
3, 97, 102, 112, 122, 125 Titanium layer 14, 24, 56, 66, 113 Aluminum layer 35, 45, 77, 87, 95, 99, 104, 12
4,127 Gold layer 103,123,126 Platinum layer

Claims (5)

[Claims] 1. A multi-layer metal Schottky electrode for a field effect transistor using a III-V compound semiconductor, wherein a molybdenum (Mo) layer is a lower layer and a titanium (Ti) layer is an upper layer on a semiconductor layer. A multi-layer metal Schottky electrode, wherein one or more laminated films are formed, and a good conductive metal layer is formed thereon. 2. The good conductive metal layer is made of aluminum (A
The multi-layer metal Schottky electrode according to claim 1, which is formed of 1) or gold (Au). 3. The multilayer metal Schottky electrode according to claim 1, wherein a titanium layer serving as an adhesion layer is formed on the good conductive metal layer. 4. The multi-layer metal Schottky electrode according to claim 1, wherein a barrier metal layer is formed between the laminated film and the good conductive metal layer. 5. The multi-layer metal Schottky electrode according to claim 4, wherein the barrier metal layer is a molybdenum layer.