JP2863780B2 - Multi-layer metal Schottky electrode - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multilayer 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 a FET using a compound semiconductor, a metal layer forming 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 for forming a Schottky contact therewith is formed on a GaAs Schottky contact layer 101, and platinum (Pt) serving as a barrier metal layer is formed thereon. ) A 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 and the lower titanium layer 102 from directly reacting with each other, and gallium (Ga) is externally applied from the surface of the semiconductor Schottky contact layer. It has the function of suppressing the diffusion toward.

Further, 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 the GaAs Schottky contact layer 111.

In order to improve the transistor characteristics, the gate electrode is often formed in a T-shaped cross section. FIG. 12 shows the cross-sectional structure. The electrode having this structure is manufactured as follows. On the GaAs Schottky contact layer 121, a photoresist film (not shown) having a T-shaped opening is formed. Titanium, platinum, and gold are sequentially deposited to form titanium layers 122 and 125 and a platinum layer 12.
3, 126 and gold layers 124, 127 are formed. If the photoresist film is removed together with the metal layer formed thereon, an electrode having the structure shown in FIG. 12 is obtained.

[0005]

In the above-mentioned conventional electrode structure, titanium is in contact with the interface with the semiconductor. Therefore, when the FET is used in an active state for a long time, an interaction occurs between titanium and the semiconductor. Therefore, there have been drawbacks such as fluctuations in the characteristics of FETs and problems in reliability.

In the conventional electrode structure, platinum is used as a barrier metal. However, since platinum deposition requires heating at a higher temperature or a higher energy electron beam than in the case of other metals, it is stable. Film formation is difficult, and it is difficult to form a film with high reproducibility and high yield.

Further, when platinum is contained in the layers constituting the multilayer structure, the width of the laminated platinum layer tends to be narrower than the width of the lower electrode, and a narrow gold layer grows thereon. Therefore, when the T-shaped electrode is formed, there is a problem that the upper metal and the lower metal are not formed in close contact as shown in FIG. Therefore, in addition to the insufficient mechanical strength of the electrode, there have been problems such as an increase in gate resistance and a failure in obtaining desired high-frequency characteristics.

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

[0009]

In order to achieve the above object, a multilayer metal Schottky electrode of a field effect transistor according to the present invention comprises a group III-V compound semiconductor on which a molybdenum (Mo) film is formed as a lower layer and a titanium layer is formed. One or more laminated films having a (Ti) film as an upper layer are formed, a good conductive metal layer is formed thereon, and the thickness of the lowermost molybdenum layer is 10 nm. It is characterized by the following.

[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. However, the present invention is not limited to this, and any electrode may be used for a III-V group compound semiconductor device, regardless of the semiconductor material and lattice matching. The present invention can be applied to any of the system and the strain system.

FIG. 1 is a cross-sectional view of a Schottky electrode for describing an embodiment of the present invention. In order 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 using a reduction projection method or an electron beam exposure method. Thereafter, a molybdenum layer 12, a titanium layer 13, and an aluminum layer 14 are sequentially and entirely deposited by using 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 Schottky electrode according to the present invention has the following two features. The metal that contacts the semiconductor layer and forms a Schottky contact therewith is molybdenum with a thickness of 10 nm . Do not use platinum.

The Schottky electrode of the field-effect transistor according to the present invention can adopt the following embodiments. A gold layer is used as the good conductive metal film instead of the aluminum layer. A titanium layer is formed on the good conductive metal film to improve the adhesion with the metal layer formed thereon. Two or more stacked films of a molybdenum layer and a titanium layer are stacked. A barrier metal layer such as a molybdenum layer is interposed between the good conductive metal and the titanium film thereunder. 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, the GaAs Schottky contact layer 11 and the molybdenum layer 12 do not react with each other even in the active state.
A long-term stable Schottky contact is secured.
In addition, since platinum is not contained in the multilayer structure, it is easy to manufacture and can be formed with high reproducibility and high yield. Furthermore, since platinum is not used, when the T-shaped electrode is formed, the electrode does not become thin, so that the adhesion between the upper layer and the lower layer does not deteriorate, and the high-frequency characteristics of the device can be deteriorated. Disappears.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a cross-sectional structure of a 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 titanium layer 13 having a thickness of 20 nm, and an aluminum layer 14 having a thickness of 420 nm. 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 FIG.
On the Schottky contact layer 21, a 10-nm thick molybdenum layer 22 and a 2
A 0-nm-thick titanium layer 23, a 400-nm-thick aluminum layer 24, and a 20-nm-thick titanium layer 25 were 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 FIG.
On the Schottky contact layer 31, the molybdenum layer 32 is formed to a thickness of 10 nm, the titanium layer 33 is formed to a thickness of 20 nm, and the molybdenum layer 34 as a barrier metal layer is formed to a thickness of 10 nm by using an electron beam evaporation method. Then, a gold layer 35 as a good conductive metal layer was successively formed to a thickness of 410 nm sequentially 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 FIG.
On the Schottky contact layer 41, a molybdenum layer 42 is formed to a thickness of 10 nm, a titanium layer 43 is formed to a thickness of 20 nm, and a molybdenum layer 44 as a barrier metal layer is formed to a thickness of 20 nm by electron beam evaporation. Then, a gold layer 45 as a good conductive metal layer was successively formed to a thickness of 380 nm and a titanium layer 46 as an adhesion layer was successively formed to a thickness of 20 nm, 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 FIG.
On the Schottky contact layer 51, a 10 nm-thick molybdenum layer 52 was formed by using an electron beam evaporation method.
0 nm titanium layer 53, 10 nm thick molybdenum layer 5
4. Titanium layer 55 having a thickness of 10 nm and a thickness of 410 nm
Was successively formed into a film and patterned by a 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 can be more easily formed and the process can be stabilized.
In this embodiment, (molybdenum, titanium) is two units, but the present invention is not limited to this, and it is possible to repeat a desired unit.

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

FIG. 7 is a sectional view showing a seventh embodiment of the present invention. As shown in FIG.
A 10-nm-thick molybdenum layer 72 and a 1-nm-thick
0 nm titanium layer 73, 10 nm thick molybdenum layer 7
4. After laminating a titanium layer 75 having a thickness of 10 nm, a molybdenum layer 76 as a barrier metal layer is formed to a thickness of 10 nm, and a gold layer 77 as a good conductive metal layer is formed to a thickness of 400 nm.
The film was successively formed to have a film thickness of, and was patterned by a lift-off method.

[Eighth Embodiment] FIG. 8 is a sectional view showing an eighth embodiment of the present invention. As shown in FIG.
A 10-nm thick molybdenum layer 82 and a 1-nm thick
0 nm titanium layer 83, 10 nm thick molybdenum layer 8
4. After laminating a 10 nm-thick titanium layer 85, a molybdenum layer 86 as a barrier metal layer is formed to a thickness of 10 nm, and a gold layer 87 as a good conductive metal layer is formed to 380 nm.
Then, a titanium layer 88 as an adhesion layer was sequentially formed into a film having a thickness of 20 nm to a thickness of 20 nm, and was patterned by a lift-off method.

[Ninth Embodiment] FIG. 9 is a sectional view showing a ninth embodiment of the present invention. After a photoresist film (not shown) having a T-shaped opening is formed on the GaAs Schottky contact layer 91 by photolithography, molybdenum, titanium, molybdenum, and gold are respectively deposited by electron beam evaporation. 10 nm, 20 nm, 1
It deposited to a film thickness of 0 nm and 410 nm. Next, the unnecessary metal film is removed together with the photoresist, and 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 the electrode structure of the III-V compound semiconductor, molybdenum is introduced at the semiconductor interface, so that a metal-semiconductor interaction is suppressed, so that a highly reliable device can be obtained. Further, since platinum having a high deposition temperature is not included as a barrier layer, the process is easy, and reproducibility and yield can be improved. Furthermore, since platinum is not contained, there is no decrease 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 microelectrode structure can be manufactured, and deterioration of the high-frequency characteristics of the FET can be prevented.

[Brief description of the drawings]

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

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 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 layers 12, 22, 32, 34, 42, 44, 52, 54, 6
2, 64, 72, 74, 76, 82, 84, 86, 9
2, 94, 96, 98 Molybdenum layers 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

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-1-319974 (JP, A) JP-A-2-226770 (JP, A) JP-A-6-84967 (JP, A) JP-A-54-1979 127280 (JP, A) Japanese Utility Model 60-181058 (JP, U) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01L 21/28-21/288 H01L 21/44-21/445 H01L 29/40-29/51 H01L 29/872

Claims (5)

(57) [Claims] 1. A multi-layered film having a molybdenum (Mo) layer as a lower layer and a titanium (Ti) layer as an upper layer is formed on a group III-V compound semiconductor layer. A multilayer metal Schottky electrode of a field effect transistor having a layer formed thereon, wherein the lowermost molybdenum layer has a thickness of 10 nm . 2. The method according to claim 1, wherein said highly conductive metal layer is made of aluminum (A).
2. The multilayer metal Schottky electrode according to claim 1, wherein the electrode is made 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 said good conductive metal layer. 4. The multilayer metal Schottky electrode according to claim 1, wherein a barrier metal layer is formed between said laminated film and said good conductive metal layer. 5. The multilayer metal Schottky electrode according to claim 4, wherein said barrier metal layer is a molybdenum layer.