JPH04199681A - Semiconductor device - Google Patents

Abstract

PURPOSE:To obtain a transistor excellent in characteristics by a method wherein an electrode composed of a first metal layer in rectifying contact with a semiconductor layer, a nichrome alloy layer deposited thereon, and a second metal layer metal layer formed thereon is provided. CONSTITUTION:An electrode G composed of a first metal layer or an intermetallic compound layer 3 in rectifying contact with a semiconductor layer 1, a nichrome alloy layer 4 deposited thereon, and a second metal layer metal layer 5 formed thereon is provided. That is, a gate electrode G is composed of a tungsten silicide (WxSiy) layer 3, a nichrome alloy layer 4, and an Au layer 5. Nichrome alloy is excellent in adhesion to metal or metal compound and small in electrode potential difference to metal such as gold, platinum, or the like. Therefore, an electromotive force is hardly induced between the layers which constitute the electrode G, so that an interface between a nichrome alloy layer and its upper or lower layer can be protected against local corrosion. By this setup, a semiconductor device of this design can be prevented from increasing in resistance and enhanced in transistor characteristics.

Description

[Detailed Description of the Invention] [Summary] Regarding a semiconductor device in which a rectifying contact electrode is provided on a compound semiconductor, the resistance of the electrode does not increase even when exposed to solutions such as hydrofluoric acid and hydrochloric acid, and the semiconductor device has a good performance. A first metal layer or metal compound layer in rectifying contact with the semiconductor layer, a nichrome or alloy layer laminated on the first metal layer or metal compound layer, and a nichrome alloy layer for the purpose of obtaining transistor characteristics. The second metal layer is formed on the alloy layer and includes an electrode.

[Industrial application field]

The present invention relates to a semiconductor device, and more particularly, to a semiconductor device in which a compound semiconductor is provided with an electrode in rectifying contact with the compound semiconductor.

[Prior Art] As a compound semiconductor device, for example, a GaAs metal gate field effect transistor (GaAs-MESFET) is used.
is proposed.

This transistor, as illustrated in FIG. 4(a),
An n-GaAs active layer 42 is formed on a GaAs substrate 41, and a gate electrode 43 that makes Schottky contact with the active layer 42, and a source electrode 44 and a drain electrode 45 that make resistive contact with the active layer 42 on both sides thereof are provided. It has a similar structure.

By the way, in order to ensure long-term stable operation of the device, the gate electrode 43 has a multilayer structure in which a film of a material that does not easily react with GaAs and a metal having low resistivity are superimposed.

For example, tungsten silicide (WXSi) is formed on the GaAs active layer 42 by a sputtering method.
layer 46, a titanium (T1) layer 47, and a platinum (Pt) layer 4, which are successively deposited thereon by electron beam evaporation or the like.
8. A gate electrode 43 is constituted by a gold (Au) layer 49. In this case, the thickness of each layer 46 to 49 is, for example, −X
Si, layer 46 has 2000 people, 74 layer 47 has 50 people, p
There are 1,500 people in the T layer 48 and 5,000 people in the Au layer 49.

Here, the reason why the 74 layer 47 is inserted between the Wx Si layer 46 and the PT layer 4 is that because L Siy is chemically inert, interdiffusion between metals is difficult to occur. This is because, if not inserted, the adhesive strength between the J Si layer 46 and the PT layer 48 would be significantly reduced.

[Problem to be solved by the invention:- However, when the gate electrode 43 having the above structure is exposed to a solution such as buffered hydrofluoric acid or hydrochloric acid in the manufacturing process of a semiconductor device, -X Si and the layer 46 are formed due to electrochemical action. Local corrosion occurs at the interface with the 74th layer 47, and as shown in FIG. 4(b), the T
The side of i1i47 will be removed. Moreover, if this effect appears significantly, ++'+ Siy film 4
The layer above 6 will peel off.

This is because the GaAs active layer 42 and the WXSi layer 46 are in rectifying contact, and an electromotive force is generated between the 74 layer 47 and the PT layer 48 due to different metals. This is because the gold layer 48 or the gold layer 49 serves as a cathode, and buffered hydrofluoric acid or the like acts as an electrolyte.

Furthermore, it has been confirmed that the exposed Si2 layer 46 due to the corrosion of the 74th layer 47 is also corroded due to the stress applied to the IS+ layer 4G during film formation.

When the gate electrode 43 becomes thinner due to local corrosion, the input resistance of the gate electrode 43 increases, which manifests itself as an increase in the noise figure (NF) in a low-noise element, the magnitude of which is shown in Figure 5. As shown in FIG.

Note that even if the electrodes having the above-mentioned structure are formed on silicon, local corrosion will not occur because these form resistive contact.

The present invention has been made in view of these problems, and provides a semiconductor device that can obtain good transistor characteristics without increasing electrode resistance even when exposed to fJ liquids such as hydrochloric acid and hydrochloric acid. The purpose is to provide.

[Means for Solving the Problems] The above-mentioned problems are solved by the semiconductor layer 1 as illustrated in FIG.
a first metal layer or metal compound layer 3 in rectifying contact with;
It is characterized by having an electrode G constituted by a nichrome alloy layer 4 laminated on the first metal film or metal compound layer 3 and a second metal layer 5 formed on the nichrome alloy layer 4. This is achieved by a semiconductor device that

[For production]

According to the present invention, a nichrome alloy layer 4 is laminated on the metal layer or metal compound layer 3 in rectifying contact with the semiconductor layer l to form the electrode G, and a metal layer 5 of gold, platinum, etc. is further laminated. The electrode is made up of:

By the way, nichrome alloy is a material that has excellent adhesion to metals and metal compounds, and has a small electrode potential difference with respect to metals such as gold and platinum.

Therefore, even if the semiconductor layer 1 and the electrode G are immersed in a solution such as hydrofluoric acid, hydrochloric acid, nitric acid, etc., the electromotive force is extremely small, so they remain inactive, and local corrosion will not occur at their interface. do not have.

Therefore, the nichrome alloy layer 4 does not become thinner, and the resistance becomes smaller. For example, in a low-noise device, the noise figure
Gain is improved.

〔Example〕

Therefore, the details of the present invention will be explained below based on the drawings.

FIG. 1 is a cross-sectional diagram showing a MESFET according to an embodiment of the present invention.

Reference numeral 1 in the figure is an n-GaAs active layer epitaxially grown on a semi-insulating GaAs substrate 2, and in the center of the transistor formation region thereon, a tungsten silicide (Wx Siy) layer 3, a nichrome alloy (NiCr) A gate electrode G consisting of a layer 4 and a gold (Au) layer 5 is formed,
Further, on both sides thereof, drain electrodes and source electrodes S made of gold/germanium (AuGe) N 6 and Nikel (Ni) layers 7 are laminated at regular intervals.
For GaAs active layer 1, -, Si, layer 3 is Schiller/
) key contact and the AuGe layer 6 is configured for resistive contact.

The steps for forming this transistor will be explained below.

First, as shown in FIG. 2(a), a GaAs substrate 2
An n-GaAs active layer 1 and a SiO□ film 8 are laminated thereon.

Thereafter, a photoresist 9 is applied, exposed and developed to open a window 10 in the photoresist 9 in the gate formation region.

Next, the 5in2 film 8 exposed through the window 10 is etched with hydrofluoric acid or the like to form an opening 11, and the n-Ga layer below is etched.
The As active layer 1 is exposed (FIG. 2(b)). after that,
Photoresist 9 is removed.

Following this, by sputtering, layer 3 was made of Si, layer 3 was made of 2000 layers, NiCr layer 4 was made of 50 to 100 layers, and Au
After about 5,000 layers 5 are successively stacked, a new photoresist 12 is applied, exposed and developed to cover only the gate formation region and its surroundings (FIG. 2(C)). Note that a PT layer may be formed between the NiCr layer 4 and the gold layer 5.

In this case, the NiCr layer 4 has good adhesion to metals and metal compounds, and is thinly formed, thereby reducing contact resistance and increasing the adhesive strength between the WXSi layer 3 and the Au layer 5. It works like this.

After this, the Au layer 5 exposed from the photoresist 12,
The NiCr layer 4, Hz Si layer, and layer 3 are etched in order (FIG. 2(d)), and this is used as a gate electrode G.

Thereafter, as shown in FIG. 2(e), the 5i02 film 8 is removed with buffered hydrofluoric acid, but no local corrosion occurs in the gate at the pole G.

That is, the standard electrode potential of NiCr has a small difference from that of Au and Pt, and an electrochemical reaction using a hydrofluoric acid solution as an electrolyte does not occur between them, so that the electrode potential at the interface between the NiCr layer 4 and the Au layer 5 Local corrosion will not progress. Moreover, NiCr
Layer 4 is a metal that is inert to an aqueous solution of hydrofluoric acid and is not corroded by itself.

After selectively removing only the SiO□ film 8 in this way, the regions other than the drain formation region and the source formation region are covered with a resist mask 13, and then the AuGe layer 6 and the N4 layer 7 are laminated (Fig. 2(f) )). Then, by removing the resist and mask 13, the metal layer 6.7 thereon is peeled off.

As a result, A is formed in the drain formation region and the source formation region.
The uGe layer 6 and the N4 layer 7 remain, and #6.7 of them becomes the drain electrode D and the source electrode S (FIG. 2(g)).

This completes the transistor.

In the above embodiment, -, Si was used as the metal in rectifying contact with the n-GaAs active layer 1, but other examples include tungsten nitride (W, Ny), titanium (Ti), platinum ( Pt), lanthanide hexaboride (L
It is also possible to use metals or metal compounds such as aBJ and the like.

Further, in the above-described embodiment, the case where the gate electrode G is immersed in a hydrofluoric acid aqueous solution has been described, but local corrosion does not occur when the gate electrode G is immersed in an aqueous solution such as hydrochloric acid or citric acid for the same reason.

Furthermore, in the above embodiment, GaAs-MESF
Although ET has been described as an example, there are other cases in which an electrode is brought into rectifying contact with a compound semiconductor, such as the gate electrode of an IEMT (as shown in FIG. 3) or the metal of a Schottky diode (not shown). Additionally, NiCr may be provided as an intermediate layer of the electrode.

In FIG. 3, reference numeral 12 indicates a semi-insulating GaAs substrate, 13 indicates a 1-GaAs layer formed on the substrate 12, and 14 indicates an n-AlG layer laminated on the 1-GaAs layer 12.
The aAs layer 15 is a gate electrode made of kXSi/NiCr/Au, 16 is a drain electrode made of AuGe/Au, and 17 is a source electrode made of AuGe/Au.

〔Effect of the invention〕

As described above, according to the present invention, a nichrome alloy layer is laminated on a metal layer or metal compound layer in rectifying contact with a semiconductor layer to form an electrode, and a metal layer such as gold or platinum is further laminated. Since the electrodes were formed by using the nichrome alloy layer, almost no electromotive force is generated between each layer of the electrode even when the electrodes are placed in a solution such as hydrofluoric acid, hydrochloric acid, or nitric acid. Corrosion is prevented, and an increase in resistance due to thinning of the electrode can be prevented.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing a first embodiment of the device of the present invention, FIG. 2 is a cross-sectional view showing the manufacturing process of the first embodiment of the device of the present invention, and FIG. 3 is a cross-sectional view of a second embodiment of the present invention. 4 is a sectional view showing an example of a conventional device, and FIG. 5 is a sectional view showing an example of a conventional device.
aAs) is a characteristic diagram showing the relationship between gate resistance and noise figure of a transistor. (Explanation of symbols) 1-n-GaAs active layer, 2... GaAs substrate, 3... tungsten silicide layer, 4... nichrome alloy layer, 5... gold layer, 6... gold germanium layer , 7... Nickel layer, 8... S+OtM, 9... Opening, 10... Window, 11... Resist mask, G... Gate electrode, S... Source electrode, D. ...Drain electrode. Applicant Fujitsu Co., Ltd.

Claims (3)

[Claims] (1) A first metal layer or metal compound layer (3) in rectifying contact with the semiconductor layer (1), and a nichrome alloy layer (4) laminated on the first metal layer or metal compound layer (3). ); and a second metal layer (5) formed on the nichrome alloy layer (4). (2) the first metal layer is titanium or platinum,
3. The semiconductor device according to claim 1, wherein the metal compound layer (3) is tungsten silicide, tungsten nitride, or lanthanide hexaboride. (3) The semiconductor device according to claim 1 or 2, wherein the electrode (G) is a gate electrode of a transistor or an electrode of a Schottky transistor.