JPS6258542B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a semiconductor device, and particularly to a method for forming wiring using a lift-off method.

Conventionally, the lift-off method has been used as a method for forming electrode wiring of semiconductor devices.
The most common lift-off method uses only a photoresist as shown in FIGS. 1a-1d. Photoresist layer 12 on semiconductor substrate 11
(FIG. 1A), selectively exposed and developed to form a photoresist pattern 13 (FIG. 1B), and a metal layer 14 to be used as wiring is deposited (FIG. 1C). This method is then treated with an organic solvent to remove the photoresist pattern 13 and the metal layer 14 deposited thereon, leaving a desired wiring pattern on the semiconductor substrate (FIG. 1d).

This method requires that the thickness of the metal layer that is to become the wiring become thinner on the side surfaces of the photoresist pattern 13. Therefore, the thickness of the metal that will become the wiring on the side of the photoresist is
It is generally formed by vapor deposition, which makes it thinner than the flat part. However, when a high melting point metal such as titanium or platinum or a metal that is easily oxidized is used as the electrode wiring, the adhesion strength between the semiconductor substrate and the wiring becomes weak in the vapor deposition method. There are drawbacks such as difficulty in maintaining a high degree of vacuum during vapor deposition, and the film must be formed by sputtering. In this case, when attempting to form wiring by a lift-off method using a photoresist, a problem arises in that the film thickness on the side surfaces of the photoresist becomes considerably thicker than in the case of vapor deposition, resulting in very poor lift-off properties. In the worst case, as shown in FIG. 2, the metal film 14' on the photoresist remains, causing shorts between wiring lines.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a method for forming an electrode interconnection, which is a conventional lift-off method using only a photoresist, but which has easy lift-off properties even in the case of sputtering and has a high yield.

The features of the present invention include a step of forming a photoresist layer with a thickness of 2 microns or more on a semiconductor substrate;
A step of selectively exposing and developing the photoresist layer to form a photoresist pattern, and a step of performing a first heat treatment on the semiconductor substrate including the photoresist pattern at 100° C. to 130° C. for 5 minutes to 30 minutes. After that, a process of depositing a metal film to become an electrode wiring by sputtering, and a second heat treatment on the substrate containing the metal film at 150°C to 250°C for 20 minutes to 60 minutes.
and a step of treating the substrate with trichlene to remove unnecessary portions of the metal film and the photoresist pattern, leaving only electrode wiring.

The reason why the film thickness of the photoresist is set to be 2 micumins or more is as follows. The desired thickness of the metal film usually deposited by sputtering is 4000Å.
This is also the film thickness that is often used in practice. At this time, as shown in FIG. 4, a photoresist film thickness of 2.5 μm or more, which facilitates lift-off under the optimal conditions of the first and second heat treatments described below, was obtained. The lift-off non-defective rate in the figure indicates the ratio of chips with no remaining metal film between desired wirings to the total number of chips on the wafer. However, film thickness
Even with a thickness of 2.0 to 2.5 .mu.m, a 100% yield rate can be obtained by repeating scrubbing with trichlene several times. Therefore, in consideration of practicality, it is necessary to set the film thickness to 2.0 .mu.m or more. Here, scrubbing means treating the substrate with trichlene and mechanically scrubbing the entire surface of the substrate.

Next, the first heat treatment conditions were determined for the following reasons.

FIG. 5 shows an example of the experimental results. Under the general heat treatment conditions of 150°C and 60 minutes, all shots were defective.
When the temperature was lowered as in the present invention (for example, the case of 120° C. is shown), a lift-off rate of 100% was obtained by shortening the time to 5 to 30 minutes. In this case, if the time is further shortened, the rate of non-defective products decreases, and it is not related to the number of times of scrubbing. The reason for this is thought to be that the dilute hydrofluoric acid treatment generally performed before metal film sputtering causes the photoresist pattern to peel due to poor adhesion to the substrate, resulting in poor shorting of the metal wiring. Furthermore, if the first heat treatment time is short, there is a problem that the adhesion strength to the substrate is reduced due to outgas during deposition of the metal film. In the present invention, instead of using general heat treatment conditions as described above, low temperature and
We are working to shorten the time. Also, 120 as shown in Figure 5
A trend in °C was observed in the range of 100°C to 130°C.

Next, the second heat treatment conditions were determined for the following reasons.

FIG. 6 shows an example of the experimental results. FIG. 6 shows the relationship between the heat treatment time at 200° C. and the lift-off yield rate for a sample in which a metal film was sputtered using the film thickness and the optimum conditions for the first heat treatment described above. The lift-off property was improved by heat treatment for 20 minutes or more. A time longer than 60 minutes would be too long to be practical.
When this second heat treatment is performed at a low temperature (an example of 130°C is shown), the lift-off property is extremely poor, and experiments have shown that a temperature of 150°C or higher is required, including when scrubbing is performed several times. Moreover, the same tendency as at 200°C in the same figure was observed at 150°C to 250°C. That is, it is preferable to perform heat treatment in this temperature range for 20 minutes to 60 minutes.

Figures 3a to 3e illustrate a preferred embodiment of the invention. First, a photoresist layer 32 is formed on a semiconductor substrate 31 on which desired P-N junctions, insulating films, contact openings, etc. have been formed (first
Diagram a). The photoresist is OMR (manufactured by Tokyo Ohka Kogyo, trade name), and its thickness is approximately 2μ.
m or more is desirable. Thereafter, a photoresist pattern 33 is formed by selectively continuing exposure using a photomask and performing a phenomenon treatment.
Figure b). Next, a first heat treatment is performed to remove the solvent content of the photoresist. Heat treatment temperature is 100-130
It is preferable that the heat treatment time is 5 to 30 minutes, and that the heat treatment conditions are low temperature and short. Next, a desired metal film 34 is deposited on the entire surface of the substrate including the photoresist pattern by sputtering (FIG. 3c). The metal film is not limited to one layer, and may be one in which two or three layers of different metals are successively deposited. When the thickness of the photoresist is approximately 2.5 μm, the thickness of the metal film is desirably 4000 Å or less, considering the ease of lift-off. However, even if it is more than that, a product with significantly improved lift-off property compared to the conventional method can be obtained. Next, a second heat treatment is performed on the substrate on which the sputtered film has been deposited. The conditions for heat treatment are
Preferably, the temperature is 150 to 250°C for 20 to 60 minutes, and this heat treatment causes the solvent to jump out of the photoresist pattern, causing shrinkage of the photoresist pattern.
Many cracks 35 occur in the metal film on the side surface of the photoresist pattern. The occurrence of this crack is a factor that facilitates the lift-off property (Fig. 3d). Next 60~
Immerse the entire substrate in Triclean heated to 80 °C. As a result, trichlene penetrates into the photoresist pattern 33 through the cracks 35, swells the photoresist, and further facilitates lift-off properties. After that, the entire surface of the substrate is mechanically scrubbed to remove unnecessary metal films on the top and side surfaces of the photoresist pattern, and then the photoresist is removed by treatment with a photoresist stripping solution, and the desired electrodes are removed. Only the wiring remains (Figure 3e).

Compared to conventional methods, the method for forming electrode wiring shown in this example allows for easy lift-off even when the metal film on the side surface of the photoresist is thick, as in the case of sputtering, due to the simple method of heat treatment, which improves yield. High electrode wiring can be obtained.

Although the present invention has been described above, the technical scope of the present invention is not limited to the above embodiments.

[Brief explanation of the drawing]

1a to 1d and 2 are cross-sectional views of each process of a semiconductor device according to the conventional electrode wiring forming method, and FIGS. 3a to 3e are sectional views of the electrode wiring forming method of a semiconductor device according to the present invention. 4, 5, and 6 are cross-sectional views showing one embodiment of the present invention in the order of steps, and are diagrams showing the effects of the present invention. In the figure, 11...semiconductor substrate, 12...
Photoresist layer, 13... Photoresist pattern, 14... Metal film, 14'... Remains of metal film, 31... Semiconductor substrate, 32... Photoresist layer, 33... Photoresist pattern, 34...
...Metal film, 35... Crack in metal film.

Claims (1)

[Claims] a step of forming a photoresist layer with a thickness of 2 microns or more on a semiconductor substrate; a step of selectively exposing and developing the photoresist layer to form a photoresist pattern; and a step of forming a photoresist pattern on the semiconductor substrate. First heat treatment on the substrate at 100℃
A process of heating the metal film at ~130°C for 5 to 30 minutes, followed by a process of depositing a metal film that will become the electrode wiring by sputtering, and a second heat treatment on the substrate containing the metal film at a temperature of 150°C to 250°C for 20 minutes. a step of carrying out the process for 60 minutes to 60 minutes, and treating the substrate with Triclean to remove unnecessary parts of the metal film and the photoresist pattern,
1. A method of manufacturing a semiconductor device, comprising: a step of leaving only electrode wiring.