JPH06338489A - Method of manufacturing metal film - Google Patents

Abstract

PURPOSE:To obtain a metal film having an excellent etching precision and stable characteristics by a method wherein the metal film is etched with one etching liquid having a higher concentration out of two etching liquids having different concentrations containing hydrofluoric acid and thereafter the metal film is etched with another etching liquid. CONSTITUTION:When etching a metal film 16 for an electrode composed of Ti, it is continuously etched using two etching liquids 1, 2 having different concentrations composed of HF-NH4F-HNO3-H2O. The concentration of etching liquid 1 is much higher than the etching liquid 2, and an oxide film or an oxide nitride film formed mainly on a surface of the metal film 16 for an electrode is removed. Thereafter, etching is performed with the etching liquid 2 having a lower concentration than the etching liquid 1, whereby the metal film 16 itself for an electrode is etched to form source and drain electrodes 7a, 7b. Thus, Ti is uniformly etched without causing side etching.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a metal film, and more particularly to a method for accurately manufacturing a metal film used as an electrode or wiring in a semiconductor device.

[0002]

2. Description of the Related Art As a metal electrode or a metal wiring in a semiconductor device, a metal film containing, for example, Ti is used. As a means for forming such a metal film into a desired shape, there is a method using wet etching. T
An etching solution containing hydrofluoric acid is suitable as an etching solution used for wet etching a metal film containing i. For example, JP-A-59-12472.
Japanese Unexamined Patent Publication No. 6 discloses that a hydrofluoric acid solution of about 5% is used as the hydrofluoric acid-based etching solution. Also, Th
in Film Processes (Vessen.JL, Kern.W, Academic
Press (1978) shows that a hydrofluoric nitric acid solution containing about 5% hydrofluoric acid is used as an etching solution for the Ti film.

[0003]

However, the etching of the metal film made of Ti has the following problems. That is, when Ti is deposited by a vapor deposition method to form a metal film made of Ti, an oxide film is generated on the surface thereof, and it is difficult to avoid this at present. In addition, when depositing Ti by sputtering, T
In order to secure the stability of the i film, a mixture of Ti and nitrogen is usually sputtered. In this case,
An oxynitride film is formed on the surface of the Ti film. Therefore, at the time of etching, the oxide film or oxynitride film formed on the surface of Ti and the underlying Ti film are etched. However, the oxide film and the oxynitride film are less than Ti. As a result, the etching rate is small and the film thickness is not uniform, so that uniform etching cannot be performed accurately. That is, since the relatively thin portion of the oxide film or the oxynitride film is removed by the etching solution before the other portions, the etching of the Ti film located therebelow is less than that of the surrounding Ti. Will proceed. Therefore, side etching occurs in the Ti film, and after etching, unevenness is generated on the side end surface of the Ti film, so that a metal film with high etching accuracy cannot be obtained.

On the other hand, although Ti has the drawbacks in the etching process as described above, it has the advantage of being excellent in film stress and corrosion resistance. It is difficult to obtain a metal film made of Ti with good etching accuracy while making good use of the stability of Ti, which is a conflicting requirement.

The present invention has been made in view of the above circumstances, and provides a method for producing a metal film capable of obtaining a metal film having good etching accuracy and stable characteristics.

[0006]

In a method for producing a metal film, a metal film having a desired shape is obtained by applying a protective mask to the surface of a metal film mainly composed of Ti and then performing wet etching. 2 with different concentrations
The etching is performed by etching the metal film with one of the two types of etching solutions having a higher concentration and then etching the metal film with the other etching solution.

[0007]

The oxide film or the oxynitride film covering the surface of Ti is removed in a relatively short time by first etching with an etching solution having a high concentration of hydrofluoric acid, and then,
By etching with an etching solution having a hydrofluoric acid content concentration lower than that of the etching solution used first, Ti is etched substantially uniformly without causing side etching.

[0008]

EXAMPLES A method for manufacturing a metal film according to the present invention will be described below with reference to FIGS. Here, FIG.
2 is a vertical sectional view of a thin film transistor using a metal film according to the present invention, and FIGS. 2 and 4 are explanatory views for explaining a manufacturing process of the thin film transistor shown in FIG. First, in the present embodiment, a case in which an electrode in a thin film transistor is manufactured by the method for manufacturing a metal film according to the present invention will be described as an example. First, the structure of the thin film transistor will be described with reference to FIG. The basic structure of this thin film transistor is already known, and the description of the structure here will be briefly described. The difference from the conventional one is that some electrodes are formed by the manufacturing method according to the present invention as described later.

The thin film transistor comprises, for example, a gate electrode 2 made of Ti, a gate insulating layer 3 made of SiNx, and a-Si on an insulating substrate 1 made of an insulating member such as glass.
A semiconductor active layer 4 made of H, a channel protection layer 5 made of SiNx, ohmic contact layers 6a, 6b made of n ⁺ a-Si: H, a source electrode 7a made of Ti and a drain electrode 7b are sequentially laminated and It is configured by patterning. Further, in the thin film transistor, the insulating layer 8 made of polyimide is laminated and the insulating layer 8 is formed.
Contact holes 9a, 9b are formed in the wiring portion 1 and the wiring portion 1 provided on the insulating layer 8 through the contact holes 9a, 9b.
0a, 10b are the source / drain electrodes 7a, 7b
It is connected to. In addition, on the insulating layer 8 and on the channel protection layer 5, a light shielding portion 11 is formed using aluminum.

Next, a manufacturing process of the thin film transistor having the above structure will be described with reference to FIGS. First, a metal film 12 made of, for example, Ta (Cr, Ti, W, Mo, etc. is also suitable) is formed on the insulating substrate 1 by vapor deposition or sputtering.
The entire surface is deposited to a thickness of about 00 Å (see FIG. 2A). Then, a photoresist pattern (not shown) is formed on the metal film 12, and the gate electrode 2 is formed by dry etching (see FIG. 2B). For this dry etching, for example, SF ₆ is used as an etching gas.

Next, using a P-CVD apparatus, SiNx
A gate insulating layer 3 made of a, a semiconductor active layer film 13 made of a-Si: H, and a channel protective layer film 14 made of SiNx, respectively.
A film of about 0 Å and 1500 Å is deposited on the entire surface (see FIG. 2B), and then the semiconductor layer film 13 and the channel protective layer film 13 are subjected to photolithography to obtain a semiconductor having a desired shape. An active layer 4 and a channel protection layer 5 are obtained (see FIG. 3 (a)).

Then, an ohmic contact layer film 15 made of n ⁺ a-Si: H is deposited over the entire surface to a thickness of about 1000 Å (see FIG. 3B), and an electrode metal made of Ti is further formed. The film 16 is deposited on the entire surface by the vapor deposition method or the sputtering method to a thickness of about 2000 angstroms (see FIG. 3).
(See (b)). Then, the source electrode 7a and the drain electrode 7b are formed by the photolithography method (see FIG. 3C). Here, the etching of the electrode metal film 16 made of Ti performs continuous etching using two different etchants density consisting _{HF-NH 4 F-HNO 3} -H 2 O. As the two types of etching solutions having different concentrations, for example, those having a composition ratio shown in Table 1 are suitable.

When using the etching solutions shown in Table 1, first, the surface of the electrode metal film 16 is etched with the etching solution 1. The concentration of the etching solution 1 is considerably higher than that of the etching solution 2, and the oxide film or the oxynitride film formed mainly on the surface of the electrode metal film 16 by using the etching solution 1 having such a high concentration is used. (Not shown) will be removed. After that, the electrode metal film 16 itself is etched by etching with an etching liquid 2 having a concentration lower than that of the etching liquid 1 to form the source / drain electrodes 7a and 7b. After this,
By patterning the film 15 for the ohmic contact layer, the ohmic contact layers 6a and 6b are formed.

[0014]

[Table 1]

Next, polyimide is applied by a roll coat or a spin coat to a thickness of about 1 μm to form an insulating layer 8 (see FIG. 4A). Then, contact holes 9a and 9b are formed on the insulating layer 8 and in the portions located on the source electrode 7a and the drain electrode 7b, respectively (FIG. 4).
(See (a)). Finally, for example, a conductive material such as aluminum is deposited to a thickness of about 1 μm by a vapor deposition method or a sputtering method, and the wiring portions 10a and 10b and the channel light shielding film 11 are formed.
Thus, the thin film transistor is completed by respectively forming (see FIG. 4B).

In the present embodiment, when the source electrode 7a and the drain electrode 7b were etched, etching solutions having different concentrations shown in Table 1 were used. The etching solution concentrations are shown in Table 1. The thickness of the oxide film or the oxynitride film is not limited to the above, and can be changed appropriately according to the degree of the film thickness of the oxide film or the oxynitride film. After that, it suffices that Ti itself can be etched with an etching liquid having a concentration lower than that of the etching liquid used first.

Further, since the source / drain electrodes 7a and 7b are formed by the method for manufacturing the metal film according to the present embodiment, the end portions of the source / drain electrodes 7a and 7b, particularly the channel protection layer 5 are formed. It is possible to form a metal film with high accuracy on the side surface portion b (see FIG. 1) of the end portion a of the upper portion, which does not have unevenness after etching as in the conventional case. Also, the source / drain electrode 7
The edges a of 7a and 7b (see FIG. 1) are surely bonded to the channel protection layer 5 on the channel protection layer 5, and therefore the current when the thin film transistor is conducting is different from the conventional one. Will disappear.

[0018]

As described above, according to the present invention,
When etching the metal film made of Ti, the oxide film or oxynitride film formed on the surface of Ti is removed at a stroke, and then the Ti itself is etched. Since the metal film is not partially etched, it is possible to provide a metal film with high etching accuracy without side etching.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of an example of a thin film transistor using an electrode formed by using the method for manufacturing a metal film according to the present invention. Is.

FIG. 2 is an explanatory diagram for explaining a manufacturing process by the method for manufacturing a metal film according to the present invention.

FIG. 3 is an explanatory diagram for explaining a manufacturing process by the method for manufacturing a metal film according to the present invention.

FIG. 4 is an explanatory diagram for explaining a manufacturing process by the method for manufacturing a metal film according to the present invention.

[Explanation of symbols]

4 ... Semiconductor active layer, 5 ... Channel protection layer, 6a,
6b ... Ohmic contact layer, 7a ... Source electrode,
7b ... drain electrode

Claims (1)

[Claims] 1. A method of manufacturing a metal film, wherein a metal film having a desired shape is obtained by applying a protective mask to the surface of a metal film mainly made of Ti and then performing wet etching, wherein the concentration of hydrofluoric acid is different. A method for producing a metal film, which comprises etching the metal film with one of the two types of etching solutions having a higher concentration and then etching the metal film with the other etching solution.