JPH01307218A - Patterning method of metallic electrode on amorphous semiconductor thin film - Google Patents

Abstract

PURPOSE:To prevent the short circuit between electrodes on an amorphous semiconductor thin film by etching and eliminating a conductive layer formed on the interface between the amorphous semiconductor thin film and a high melting point metal layer, by using hydrofluoric/nitric acid. CONSTITUTION:On an amorphous semiconductor thin film, a metal film having at least one high melting point metallic layer 16 in contact with the thin film 12 is formed. On said metallic film, a patterned photoresist film 20 is formed, and only the part of the metal film except an electrode forming region is exposed. After that, the metallic film is selectively eliminated by etching, and a conductive layer 14, which is formed on the interface between the amorphous semiconductor thin film 12 and the high melting point metal layer 16 at the time of forming the layer 16, is selectively eliminated by etching with hydrofluoric/nitric acid. As a result, the metallic film on the amorphous semiconductor thin film 12 is patterned together with the conductive layer 14 formed on the interface. Thereby, the generation of short circuit between electrodes can be prevented, and the highly precise patterning is enabled.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for patterning a metal electrode on an amorphous semiconductor thin film, and in particular to a method for forming a patterned metal electrode containing a high melting point metal layer on the thin film. Regarding the method.

[Prior art and problems to be solved by the invention] Conventionally, a metal film is once created on the entire surface of an amorphous semiconductor thin film by a method such as vapor deposition or sputtering, and then this metal film is selectively removed using a photoetching technique. , methods of obtaining patterned metal electrodes have been adopted. Photoetching consists of the steps of photoresist coating, exposure, development, etching, and photoresist removal. In the etching process, a wet etching method or a plasma etching method is usually applied.

Now, in electronic devices using amorphous semiconductors,
To improve its heat resistance, chromium (Cr), nickel (Ni), and molybdenum (M
A high melting point metal film such as (o) is sometimes formed and used as an electrode. However, when forming a film of this high-melting point metal, a conductive layer with relatively low resistivity (for example, in the case of amorphous silicon, a conductive layer that is thought to be silicide) is formed at the interface with the amorphous semiconductor due to mutual diffusion with the high-melting point metal. )
is formed. This conductive layer cannot be removed by the above-mentioned wet etching method or plasma etching method using an ordinary etching solution. Therefore, even if a high melting point metal film is buttered by conventional photoetching, the conductive layer at the interface remains between the electrodes, resulting in a short circuit between the electrodes.

As another patterning method, a mask vapor deposition method is well known. In this method, a metal film is formed by masking the part where no electrode is to be formed, and buttering is performed simultaneously with the film formation.

Therefore, unlike in the case of photoetching, unnecessary conductive layers are not formed. However, in this method, the dimensions of the electrode pattern may be inaccurate due to the wraparound of the vapor deposited particles at the edge of the mask. Further, there was a problem in that it was difficult to position the mask with high precision. Therefore, the mask vapor deposition method is not suitable for forming fine electrode patterns, and the application of this method is limited to cases where the electrode spacing exceeds 1 mm.

The present invention has been made in view of the above points, and is a method of forming a patterned metal electrode containing a high melting point metal layer on an amorphous semiconductor thin film, which prevents short circuits between electrodes and achieves high precision. The purpose is to provide a method that allows both buttering and buttering.

[Means for Solving the Problems] The metal electrode buttering method according to the present invention involves creating a metal film having at least one high-melting point metal layer in contact with the amorphous semiconductor thin film on the amorphous semiconductor thin film; After forming a patterned photoresist film to expose only the part of the metal film other than the electrode formation part, the metal film is selectively removed by etching, and when creating a high melting point metal layer, it is removed by etching. The conductive layer formed at the interface is further selectively removed by etching with hydrofluoric nitric acid.

The amorphous semiconductor in the present invention refers to an amorphous semiconductor such as silicon (Si), germanium (Ge), chalcogen, sulfur (S), selenium (Se), tellurium (Te), or an alloy thereof, i.e., 5i- GesGe-Se, As-8, Ge-As-8'
It means an amorphous semiconductor such as e, Te-As-8i-Ge system, but is not limited to these.

Further, the high melting point metal is a metal that usually exhibits a melting point of 1000°C or higher, preferably 1500°C or higher, and chromium (Cr
), nickel (Ni), molybdenum (Mo), titanium (Ti), vanadium (V), tungsten (W), platinum (Pt), zirconium (Zr), niobium (Nb)
, tantalum (Ta), manganese (Mn), palladium (
The term refers to metals such as Pd), and also refers to alloys containing these high-melting point metals, but is not limited thereto.

[Function] A metal film and a photoresist film are sequentially formed on an amorphous semiconductor thin film by a normal method.

The photoresist film is patterned in a conventional manner. At this time, only the portion of the metal film to be removed is exposed. The exposed metal film, including the refractory metal layer, is removed with a conventional etchant. However, at this point, the conductive layer formed at the interface with the amorphous semiconductor thin film during the creation of the high melting point metal layer remains.

The exposed portions of the remaining conductive layer are selectively removed by etching with hydrofluoric nitric acid. As a result, the metal film on the amorphous semiconductor thin film, including the conductive layer formed at the interface, is patterned.

Thereafter, by removing the photoresist film using a conventional method, the metal film containing the high melting point metal layer can be used as an electrode on the amorphous semiconductor thin film.

[Example] Next, the present invention will be explained based on an example in which amorphous silicon is used as an amorphous semiconductor.
The present invention is not limited to the following examples.

FIG. 1 is a cross-sectional view showing steps of a method for patterning a metal electrode on an amorphous silicon thin film according to an embodiment of the present invention.

As shown in Figure (a), a high melting point metal, chromium (
Cr) and aluminum (1), which is a low melting point metal, are sequentially deposited in the same chamber to create a metal film consisting of two layers: a Cr layer (16) and an Ag layer (18) thereon.

As for the deposition conditions, for example, the substrate temperature is 100° C., and the deposition rate is 300 persons/min for both layers (16, 18). The film thickness is, for example, 500 for the Cr layer (1B) and 15,000 for the Ag layer (18). However, Cr layer (1B
), this layer and an amorphous silicon thin film (
A conductive layer (14), which is considered to be chromium silicide having a relatively low resistivity, is formed at the interface with the conductive layer (12).

After creating a metal film consisting of two layers, the Cr layer (16) and the Ag layer (18), as described above, photoresist was further coated on the entire surface of the A47 layer (18), as shown in Figure (b). A photoresist film (20) is formed as shown in . The photoresist is, for example, 0FP manufactured by Tokyo Ohka Kogyo Co., Ltd.
R-800 positive resist can be used. This photoresist is applied to a thickness of about 1 μm by spin coating, and then prebaked at 90° C. for 1 hour in a dryer. After that, exposure and development are performed using a photomask to form a photoresist film (2
0) is patterned.

At this time, only the portion of the A1 layer (18) other than the electrode forming portion is exposed. After this, another photoresist film (2
0) was post-baked at 130°C for 1 hour in a dryer.

After the above steps, first, the etching solution for Al7 is phosphoric acid (H3PO4): acetic acid (CH3c00H): nitric acid (
Af using a solution of HNO3):water-16:2:1:1
By selectively removing the exposed portion of the i-layer (18), A
Butter one layer (18). The state after etching is shown in FIG. 4(d). Since C'' is not dissolved in the Al etching solution, the Cr layer (IB) remains.

Next, Cr etching solution, ceric ammonium nitrate [(NH4) 2Ce (N03)6]:
Perchloric acid (HCII04): Water - 100g: 26
mu: 400mj! Cr layer (16) using a solution of
The Cr layer is patterned by selectively removing the exposed portions of the Cr layer. The state after etching is shown in the same figure (e).

Since the conductive layer (14) at the interface between the Cr layer (16) and the amorphous silicon thin film (2) is not dissolved in the Cr etching solution, the conductive layer (14) remains.

Further, etching is performed by immersing the film in a hydrofluoric nitric acid solution, that is, a solution of hydrofluoric acid (HF):nitric acid:water (1:1:100) for 10 minutes. By this etching, exposed portions of the remaining conductive layer (14) are selectively removed, and the layer believed to be chromium silicide is buttered. The same figure shows the state after etching (
f). At the time of completion of this etching, the metal film on the amorphous silicon thin film (12) has already formed on the conductive layer (12).
Everything including 4) is buttered. If the concentration of the fluoronitric acid solution is too high, it will also etch the amorphous silicon thin film (12). On the other hand, if it is too low, the etching rate of the conductive layer (14) becomes extremely slow, making it impractical. Therefore, hydrofluoric acid:
Nitric acid -5°1 to 1:100, (hydrofluoric acid + nitric acid): water -1
A mixing ratio in the range of :1 to 1:1000 is preferred.

In addition to hydrofluoric acid and nitric acid, the hydrofluoric nitric acid may contain other components such as hydrochloric acid and sulfuric acid to the extent that the amorphous silicon thin film (12) is not etched (usually at 10% by weight or less of the total acid component). .

Finally, the remaining photoresist film (20) is removed. For this purpose, for example, Stripping Liquid-502 manufactured by the same company can be used.

Through the above steps, amorphous silicon thin film 11! Cr layer (1B) on I (12)
A patterned metal electrode is formed, consisting of two layers: and one layer (18). Moreover, amorphous silicon thin film (
Since the conductive layer (14) at the interface between the conductive layer (12) and the Cr layer (1B) is also patterned in the same shape as the electrodes, there will be no short circuit between the formed electrodes.

Note that as the first layer metal formed on the amorphous semiconductor thin film, a high melting point metal is used to improve the heat resistance of the amorphous semiconductor electronic device as described above, but in addition to Cr, Ni, Mo, etc. The aforementioned metals or alloys thereof can be used. If this layer is too thin, thermal degradation of the device is likely to occur. Moreover, if it is too thick, cracks are likely to occur. Therefore, the thickness of the first layer of the metal film used as an electrode is 50 Å or more.
00 Å or less, preferably 100 Å or more and 2000 Å or less
Å or less.

Further, in the above description, the second layer of the metal film is one layer (18), but a single layer without the second layer may be used. Also, Al
The above-mentioned high melting point metal may be used in place of p, or gold (
Au), copper (Cu), silver (Ag), magnesium (Mg
), tin (Sn), indium (In), lead (Pb),
Other metals such as germanium (<II; e) or alloys thereof may also be used. Further, the metal film may have three or more layers as long as the first layer is a high melting point metal layer.

The resist used for the photoresist film (20) may be either a positive type or a negative type, but since a relatively highly corrosive fluoronitric acid solution is used, the resist must be post-baked at a temperature of 100°C or higher. It is preferable to do so. Bost baking at this temperature improves corrosion resistance.

According to the patterning method of the present invention described above, the interval between metal electrodes can be reduced to 1 μm. Note that an electrode spacing of 1 μm or more is a value that can be achieved by a commonly used photoetching technique. Considering that patterning with an electrode spacing of more than 1 mm can be achieved by conventional mask vapor deposition, the patterning method of the present invention is particularly effective when the electrode spacing is 1 μm or more and 1 mm or less.

[Effects of the Invention] As explained above, in the method for patterning metal electrodes on an amorphous semiconductor thin film according to the present invention, the conductive layer formed at the interface between the amorphous semiconductor thin film and the high melting point metal layer is etched away using hydrofluoric nitric acid. Therefore, short circuits between the electrodes on the amorphous semiconductor thin film formed by the metal film can be prevented. Moreover, since it is based on a photoetching method, highly accurate patterning is possible, and it is particularly effective when the electrode spacing is 1 μm or more and 1 mm or less.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the steps of a method for patterning a metal electrode on an amorphous silicon thin film according to an embodiment of the present invention. Description of symbols 1O...Glass substrate, 12...Amorphous silicon thin film, 14...Interface conductive layer, 16...Cr layer (high melting point metal layer), 18...A] layer (low melting point metal layer) metal layer), 20... photoresist film. Patent applicant Kanebuchi Chemical Industry Co., Ltd.

Claims (1)

[Claims] 1. A metal film having at least one high melting point metal layer in contact with the thin film is created on the amorphous semiconductor thin film, and a patterned photoresist film is formed on the metal film to form an electrode forming portion of the metal film. After exposing only the portion to be removed, the metal film is selectively removed by etching, and the conductive layer formed at the interface with the amorphous semiconductor thin film during the creation of the high melting point metal layer is further selected by etching with hydrofluoric nitric acid. A method for patterning a metal electrode on an amorphous semiconductor thin film, the method comprising removing the metal electrode.