JPH04183897A - Selective anodic oxidation method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Purpose of the Invention (Industrial Application Field) The present invention relates to a method for forming an oxide film on the surface of metal wiring deposited on a semiconductor substrate, for example in the manufacturing process of a semiconductor device. .

(Prior Art) Anodic oxidation is a method of forming an oxide film on the surface of a metal by applying a positive potential to the metal in a weakly ionized aqueous solution. For example, the following two methods can be used to form an oxide film while selectively leaving exposed metal parts on the surface of a metal thin film deposited on a semiconductor substrate and forming a wiring pattern.

(1) After forming an oxide film on the entire surface of the metal thin film using anodic oxidation or the like, a resist pattern is formed, and the oxide film is selectively removed by chemical or physical etching to expose the underlying metal.

(2) After forming a resist pattern on the surface of the metal thin film, only the portions where there is no resist pattern are selectively oxidized by anodic oxidation (selective anodic oxidation method).

The former method has the disadvantage that the process is complicated because it includes an etching step, and that the underlying metal thin film is damaged during etching. Therefore, the inventors adopted the latter selective anodic oxidation method.

However, in the case of selective anodic oxidation, dielectric breakdown occurs in the resist at the ends of the resist when voltage is applied, and if the adhesion between the resist and the metal thin film is poor, oxidation progresses in the gap, resulting in the accuracy of the shape of the oxide film pattern. will decrease. This causes a reduction in integration density and uncertainties in device design.

(Problems to be Solved by the Invention) An object of the present invention is to provide a selective anodic oxidation method capable of forming an oxide film pattern with high shape accuracy.

[Structure of the Invention (Means and Effects for Solving the Problems) In order to solve the above problems, the selective anodic oxidation method of the present invention changes the resist film thickness by changing the applied voltage according to the electrical resistivity, that is, the insulation property of the resist. On the other hand, by increasing the thickness to a level that does not cause dielectric breakdown, dielectric breakdown at the ends of the resist pattern during anodic oxidation is prevented and formation of an oxide film on the lower part of the resist is suppressed.

In addition, in the selective anodizing method of the present invention, the adhesion between the resist and the metal thin film is maintained by performing post-baking at a temperature below the glass transition point temperature of the resist, or by not performing post-baking at all, and oxidation is prevented from forming the gap between the resist and the metal thin film. This prevents the disease from progressing. (Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 shows the process of forming an oxide film on a metal surface by selective anodic oxidation. A metal thin film (11) made of tantalum is formed on the semiconductor substrate (I3) by a sputtering method, and a phenol novolak resist is screen printed on the surface of the metal thin film (ll) or coated, exposed, and developed to form a resist (11).
12) Form a pattern. Next, post-baking is performed to remove the developer and rinse solution from the resist (12). Next, the semiconductor substrate (10) is submerged in a weakly ionized aqueous solution (15) made of citric acid, and a positive potential is applied to the metal thin film (11) facing the platinum-type cathode (16) to perform anodic oxidation. . This allows the resist (
12) Selective oxide film (14
) to form. After that, the resist (12) is peeled off,
A semiconductor substrate (10) having an oxide film (14) pattern of a desired shape is obtained.

FIG. 2 is a top view and a cross-sectional view of the semiconductor substrate after the oxide film (24) is formed by anodic oxidation. When voltage is applied, the resist (22) may cause dielectric breakdown at the edges or the resist (22) may
22) and the thin metal film (21), an oxide film is formed under the resist (22), resulting in an abnormally grown oxide film portion (25).

Here, the size of the abnormally grown oxide film portion (25) (length of symbol X in the figure) is referred to as the amount of abnormally grown oxide film.

In order to suppress the abnormal growth of the oxide film, ■Improving the dielectric breakdown strength of the resist ■Strengthening the adhesion between the resist and the metal thin film to prevent the oxide film from progressing to the bottom of the resist ■Applying voltage during anodic oxidation Measures can be taken to reduce this and prevent dielectric breakdown of the resist.

The dielectric breakdown strength of a resist changes not only by its physical properties such as electrical resistivity, but also by increasing the thickness of the resist to increase its mechanical strength. FIG. 3 shows the relationship between the resist film thickness and the amount of abnormal growth of the oxide film when selective anodic oxidation is performed at an applied voltage of 150V. If anodic oxidation is performed with a resist film thickness of 1 μm to 3 μm, the resist will cause dielectric breakdown and abnormal growth of the oxide film will be significant, so the resist film thickness must be reinforced to 4 μm or more. The resist used in this example has an electrical resistivity of 1 x 1013 Ω/μm to 1 x 10+4 Ω/μm, but the same effect of preventing dielectric breakdown can be obtained by increasing the resist film thickness according to the electrical resistivity. It will be done. Note that the resist ink can be formed into a pattern by screen printing or roll printing, and the photoresist can be formed into a pattern by applying, exposing, and developing a positive or negative resist. The following methods are used to control the resist film thickness.

■In the roll printing method, the resist film thickness is controlled by the amount of push of the roller.■In the screen printing method, the screen thickness becomes the resist film thickness.■When applying photoresist, adjust the rotation speed of the rotary coating machine. The resist film thickness is controlled by controlling the resist film thickness by
It is not possible to form a film in excess of this amount.

-〇- Figure 4 shows the relationship between the post-baking temperature and the amount of abnormal growth of the oxide film. Resist film thickness is 10 μm 1 Applied voltage is 15
It was set to 0v. Post-baking is performed after resist pattern formation, and in the past, post-baking was performed at 120° C., near the glass transition temperature of the resist, for about 5 minutes in order to make the resist structure dense enough to withstand etching. However, due to thermal changes in the resist, the adhesion and properties with the metal thin film deteriorate, and oxidation progresses in the gap between the resist and the metal thin film.
Abnormally grown oxide film portions of 0 μm to 200 μm were observed. Therefore, by setting the post-baking temperature below the glass transition point temperature or not performing post-baking at all, it is possible to avoid adhesion deterioration due to thermal changes in the resist and suppress the amount of abnormal oxide film growth to 50 μm or less. be. In the case of etching, the selective anodizing method does not require the strength of the resist, so there is no problem with post-baking at low temperatures.

FIG. 5 shows the relationship between the applied voltage and the amount of abnormal growth of the oxide film when the resist is post-baked at a temperature below the glass transition temperature and selectively anodized. The resist film thickness was 10 μm. Since the amount of abnormal growth of the oxide film increases in proportion to the applied voltage, the accuracy of the oxide film pattern shape can be improved by reducing the applied voltage. However, an applied voltage of 50 V or more is required to form a normal oxide film. Furthermore, the dielectric breakdown voltage of the above resist at a maximum coating thickness of 20 μm is 200 μm.
It is v.

To summarize the above, a resist pattern with a film thickness of 4 μm to 20 μm is formed, and post-baking is performed at 110° C. or lower for about 5 minutes, or selective anodization is performed at an applied voltage of 50 V to 200 V without post-baking at all. By doing so, it is possible to form an oxide film pattern with high shape accuracy and an oxide film abnormal growth amount of less than 50 μm.

Note that similar effects can be obtained by using aluminum, magnesium, titanium, nickel, or niobium in addition to tantalum as the metal thin film, and by using tartaric acid or boric acid in addition to citric acid as the weakly ionized aqueous solution.

[Effects of the Invention] As detailed above, according to the present invention, it is possible to provide a selective anodic oxidation method capable of forming an oxide film pattern with high shape accuracy.

[Brief explanation of drawings]

Figure 1 is a process and equipment configuration diagram of selective anodization, Figure 2 is a top view of a semiconductor substrate with an oxide film formed on a metal thin film by selective anodic oxidation, and its A-B sectional view. A diagram showing the relationship between the resist film thickness and the amount of abnormal growth of the oxide film, Figure 4 is a diagram showing the relationship between the post-baking temperature and the amount of abnormal growth of the oxide film, and Figure 5 is a diagram showing the relationship between the applied voltage during anodic oxidation and the amount of abnormal growth of the oxide film. FIG. 6 is a process diagram of a method for forming an oxide film pattern by etching. Mouth...Semiconductor substrate, 11...Metal thin film, I2...
Resist, 13... Semiconductor substrate, 14... Oxide film,
15... Weakly ionized aqueous solution, 16... Cathode, 17...
- Ammeter, 18... Variable DC power supply, 21... Metal thin film pattern, 22... Resist, 24... Oxide film,
25... Abnormal growth part of oxide film, 61... Metal thin film,
62...Resist, 63...Semiconductor substrate, 64...
·Oxide film. -1 9-

Claims (2)

[Claims] (1) In the selective anodic oxidation method, in which a resist pattern is formed on a metal surface and then anodized to form an oxide film while selectively leaving exposed metal parts, the thickness of the resist film is determined according to the electrical resistivity of the resist. A selective anodizing method characterized by adjusting. (2) The selective anodizing method according to claim 1, wherein the post-baking of the resist is performed at a temperature below the glass transition point temperature of the resist, or no post-baking is performed at all.