JPS6141131B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for forming minute patterns required for semiconductor devices and the like, and an object of the present invention is to form fine patterns with high yield.

That is, the present invention uses a solution that simultaneously removes both a part of the metal film and the photosensitive resin under the metal film when forming a metal film pattern on a semiconductor substrate by the lift-off method.
Furthermore, by removing the metal film and introducing a means for easily dissolving the photosensitive resin, the pattern formation yield is significantly improved, and the correlation between the photosensitive resin film thickness and the metal film thickness is allowed. The aim is to increase the difference and stabilize the lift-off process. In particular, the present invention is applicable to fine patterns (approximately 2
Suitable for forming micrometers (μm width).

For example, it is necessary to form a metal film pattern in IC, LSI, surface acoustic wave, etc., but conventionally, this type of pattern formation involves forming a pattern using photosensitive resin on the metal film, and then etching the metal film. A so-called chemical etching method is used to remove the exposed metal film portion by etching with a liquid, or a part of the metal film is made into an oxide film using the photosensitive resin pattern, and this oxide film is used as an etching mask for chemical etching. method was used. In either case, these methods involve so-called wet etching using a solution, so the solution gets under the photosensitive resin and oxide film used as an etching mask, resulting in the so-called under-etching phenomenon, and the desired etching is not achieved. A pattern is formed smaller than the pattern width. For this reason, when attempting to form a pattern with a width of about 1 to 2 .mu.m, the pattern becomes significantly smaller or disappears due to the underetching, making it impossible to form a normal and highly accurate pattern.

On the other hand, in order to solve this problem, the lift-off method shown in FIG. 1 is sometimes used. In this method, the pattern width of the metal film is determined by the pattern width of the photosensitive resin initially formed.
Highly accurate pattern formation is possible.

A conventional lift-off method will be explained with reference to FIG. First, a pattern 2 made of photosensitive resin is formed on a semiconductor substrate 1 on which elements are formed. Next, metal films 3, 3' are deposited on the entire surface by means such as vacuum evaporation. Here, 3 is a metal film on the photosensitive resin pattern 2, and 3' is a metal film on the semiconductor substrate 1. If the thickness of the metal film and the photosensitive resin film are selected appropriately, the metal film will not adhere to the step 4 between the metal film and the photosensitive resin (Fig. 1b), or only a very thin film will be formed. Not attached. Therefore, when immersed in a solution that dissolves the photosensitive resin, the photosensitive resin is removed and at the same time, the metal film 3 on the photosensitive resin 2 is also removed, and as shown in FIG. Only the metal film 3' is formed.

However, in the conventional lift-off method,
For example, as shown in Figure 2 I, the aluminum film thickness is 0.8μ.
In the case of m, the lift-off achievement rate (yield) for forming a 6 μm wide pattern with a photosensitive resin film thickness of 1.65 μm is only 80%. In order to obtain the highest yield, experiments have shown that the photosensitive resin film needs to be approximately three times or more thicker than the aluminum film. In other words, the aluminum film thickness is 1 μm, which is normally used for IC and LS1 wiring.
If the thickness of the photosensitive resin film is small, the thickness of the photosensitive resin film must be at least about 3 μm. In the photolithography method for forming a pattern width of about 1 to 2 μm, increasing the thickness of the photosensitive resin film lowers the yield of pattern formation using the photosensitive resin before increasing the yield of the lift-off method. Finally 1~2μ
It becomes impossible to form a pattern on the photosensitive resin of m.

In general, the reason for the decrease in the yield of the lift-off method is presumed to be that the aluminum film adheres thickly to the corners (arrow 4) of the photosensitive resin pattern 2 on the semiconductor substrate 1, as shown in Fig. 1. . That is, when the aluminum film thickness is constant, the thinner the photosensitive resin film is, the thicker the aluminum film is as indicated by the arrow 4, making lift-off difficult.

Furthermore, in order to reduce the thickness of the aluminum film at the portion indicated by arrow 4, there is a method of etching the aluminum surface layer using an aluminum etching solution after aluminum evaporation.
However, in this method, aluminum and photosensitive resin are etched separately, and lift-off cannot be determined until the two steps are completed.
If the lift-off is insufficient, two steps are repeated again, which is undesirable because it increases the number of steps, lowers yield, and lowers reliability.

The present invention enables easy and reliable lift-off without causing such inconveniences. That is, when forming a metal film pattern on a semiconductor substrate, for example, the present invention uses a solution that dissolves both the photosensitive resin and the metal film and has a higher dissolution rate for the photosensitive resin mask than the metal film, and further This method is characterized by applying ultrasonic vibration as a means to easily dissolve the photosensitive resin.

Next, a lift-off method according to an embodiment of the present invention will be explained with reference to FIG. In the examples shown below, in addition to the above methods, exposure to ultraviolet light and boiling of the solution were performed. In FIG. 3a, a positive photosensitive resin (AZ
-1350J) is applied to form a desired pattern 22, and the entire surface is irradiated with ultraviolet light with an amount of light sufficient to decompose the photosensitive resin. Next, a metal film (for example, Al) is deposited on the semiconductor substrate 21. At this time, the metal film is deposited on the photosensitive resin pattern 22 and the exposed surface of the semiconductor substrate 21, forming metal films 23 and 23', respectively. However, a thin metal film is also attached to the corners 24 of the photosensitive resin pattern 22. This is shown in Figure 3b.

Next, it is immersed in a solution such as acetone, isopropyl alcohol, methyl alcohol, or ethyl alcohol that easily dissolves the positive photosensitive resin, and then boiled for about 5 to 20 minutes. As a result, the positive photosensitive resin is swollen and a portion of it begins to dissolve. Through this step, the positive photosensitive resin is irradiated with sufficient ultraviolet light before the metal film is attached, so that the positive photosensitive resin pattern 22
is in a state where it decomposes and is easily dissolved in a solution.

Next, ultrasonic vibrations are applied to the solution that removes the photosensitive resin and part of the metal film. As a result, the metal film of the stepped portion 24 becomes thinner actively from the broken line to the solid line in FIG. 3c, and due to ultrasonic vibration,
While the melted photosensitive resin 21 is ejected from the gap between the steps 24, the mechanically weak steps 24 are cut off, forming a minute metal film pattern 23' on the substrate as shown in FIG. 3d. I can do it.

Next, another embodiment of the present invention will be described with reference to FIG.

First, a positive photosensitive resin (AZ-1350J) is applied onto the semiconductor substrate 21 on which elements are formed, a desired pattern 22 is formed, and ultraviolet light is applied to the entire surface with a sufficient amount of light to decompose the photosensitive resin. (Figure 3a). Next, a metal film (for example, Al) is deposited on the semiconductor substrate 21. At this time, the metal film is deposited on the photosensitive resin pattern 22 and the exposed surface of the semiconductor substrate 21 to form 23 and 23', respectively. A thin metal film is also attached to the corners 24 of the photosensitive resin pattern 22b.

The photosensitive resin and part of the metal film are then immersed and boiled in a solution that removes them, and ultrasonic vibrations are applied.
Through this step, the metal film on the stepped portion 24 becomes thinner, although very slightly, as shown in FIG. 3c. In this state, the photosensitive resin pattern 22 easily dissolves into the solution, and the metal film 23 on the photosensitive resin pattern 22 is removed, leaving only the metal film 23' on the semiconductor substrate 21 as shown in FIG. The remaining metal film can form a pattern.

As described above, the purpose of the present invention is to actively dissolve the photosensitive resin, and furthermore, in the process, for example, irradiating the entire surface with ultraviolet light does not cause the positive photosensitive resin to be significantly dissolved by the solvent. In addition, boiling in a solution swells the positive photosensitive resin, making it easier to dissolve in the solution. Furthermore, while the solution used in the present invention dissolves the photosensitive resin, it also dissolves a part of the attached metal film at the same time, reducing the thickness of the stepped portion 24 in FIG. 3b and increasing the number of pinholes. By enlarging the diameter of the pinhole, the photosensitive resin 22 surrounded by the metal film is actively dissolved. Furthermore, the ultrasonic vibration in the present invention actively assists in dissolving the photosensitive resin, and has a special effect on the reliable removal of the photosensitive resin. As described above, according to the present invention, the yield can be improved by lift-off.

Next, the study results of the present invention will be explained in detail. As shown in FIG. 1 or 3, by providing a photosensitive resin pattern, adhering a metal film, and removing the photosensitive resin pattern, the metal film on the photosensitive resin pattern is removed. What is important in the so-called lift-off method for forming a pattern is the thickness of the metal film at the stepped portions shown at 4 in FIG. 1 and 24 in FIG. 3, and the prompt removal of the photosensitive resin. Generally, the thinner the metal film is, the higher the incidence of pinholes. FIG. 4 shows the incidence of pinholes in the aluminum film at the stepped portions, measured using a scanning electron microscope. The thinner the film thickness of the stepped portion is, the more pinholes will occur. For this reason, the photosensitive resin surrounded by the metal film is dissolved and removed through this pinhole, but in order to make the film thickness T at the step part less than 500 Å, the aluminum film thickness is set to 0.8 μm. In this case, the thickness of the photosensitive resin required for lift-off is at least 2.4 μm. In IC, LS1, etc., using a resin film thickness of 2.4 μm in a miniaturization process that requires a pattern width of 1 to 2 μm is not only extremely difficult in forming miniaturized patterns, but also reduces yield. This results in an extreme decrease in

However, in the method of the present invention, the number of pinholes in the stepped portion can be increased and the pinholes can also be enlarged, which is suitable for forming fine patterns.

The solution used in the present invention not only dissolves the photosensitive resin but also dissolves a small amount of aluminum film, and therefore the etching rate of the photosensitive resin is much higher than that of aluminum.
The solution is a mixture of NaOH and H ₂ O, or
A mixture of H ₃ PO ₄ and an organic solution is preferred.
In the case of a mixture of NaOH and H ₂ O, NaoH exhibits dissolving power for both aluminum film and positive photosensitive resin. Further, H ₃ PO ₄ dissolves the aluminum film, and organic solutions such as isopropyl alcohol, methyl alcohol, ethyl alcohol, and ascent dissolve the positive photosensitive resin.

Experiments show that in a solution of NaOH:H ₂ O, 29KC
In a solution with a mixing ratio of NaOH:H ₂ O = 1:6400 during ultrasonic vibration, the etching rate of Al was approximately 200%.
Å/min, and in a solution of H ₃ PO ₄ :acetone, H ₃ PO ₄ :acetone=
At 20:80, the etching rate of Al was about 110 Å/min. The solution can be used before or after the above-mentioned mixing ratio.

Furthermore, the effect of ultraviolet irradiation on photosensitive resin is
For AZ-1350J resin with a film thickness of 1.65 μm, it took about 10 seconds to completely dissolve the unirradiated resin in an acetone solution, and only a small amount was dissolved in a NaOH solution, but the resin that had been irradiated with ultraviolet rays in advance takes about 3 seconds to dissolve in acetone,
The NaOH solution required 120 seconds. It is clear that irradiation with ultraviolet light is effective. Also, looking at the effects of immersion and boiling in a solution after the metal film has been attached,
For example, a sample that was not immersed in a solution or boiled was subjected to ultrasonication for approximately 80 hours under the conditions of an aluminum film thickness of 0.8 μm, a positive photosensitive resin film thickness of 1.65 μm, and a solution of NaOH:H ₂ O = 1:6400. The samples soaked and boiled according to the process of the present invention required only about 10 to 20 minutes of ultrasound time.

According to the above method, the lift-off achievement rate for the lift-off method using the conventional process and the process based on the present invention is shown in FIG. As is clear from FIG. 2, not only is there a significant difference in lift-off yield, but the range of lift-off conditions is wide. For example, in the conventional method, the peak resin film thickness is 1.65 μm, but according to the method of the present invention, the resin film thickness is in the range of 1.15 to 2.15 μm, so it is possible to have considerable tolerance in the process and achieve a high lift-off yield. This is something that can be achieved.

As mentioned above, irradiation with ultraviolet rays, immersion in a solution, and boiling before depositing the metal film not only shorten the working time of the process, but also increase the lift-off yield by promoting the solubility of the resin.

In the above explanation, a metal film pattern was formed using a positive photosensitive resin, but the method of the present invention can be widely applied to the formation of other minute patterns.

Furthermore, since the metal film is removed at the same time as the photosensitive resin, there are no disadvantages to the process, and the state of metal film pattern formation can be confirmed during this process, resulting in good controllability and minimal etching of the metal film. This does not cause the inconvenience of unnecessarily reducing the thickness of the metal film.

As described above, according to the method of the present invention, fine patterns in semiconductor devices etc. can be obtained with high precision and high yield, and it greatly contributes to the formation of fine patterns.It is also simple in terms of process and industrially large. It has value.

[Brief explanation of the drawing]

Figures 1 a to c are process diagrams of the conventional lift-off method;
FIG. 2 is a curve diagram showing the lift-off yield according to the conventional method and the method of the present invention, FIG. 3 a to d is a process diagram of the lift-off method according to the embodiment of the present invention, and FIG. It is a relationship diagram between and film thickness. 21... Semiconductor substrate, 22... Photosensitive resin pattern, 23, 23'... Metal film pattern.

Claims (1)

[Claims] 1. A step of forming a mask pattern on a substrate;
A step of depositing a metal film on the mask pattern and the substrate, and immersing the substrate in a solution that dissolves and removes a part of the mask pattern and the film and has a higher dissolution rate for the mask than the metal film, and applying sonic vibration to simultaneously dissolve the mask pattern and the coating in the solution, removing the mask pattern and the coating thereon, and selectively forming a pattern of the coating on the substrate. A pattern forming method characterized by: 2. The pattern forming method according to claim 1, wherein the substrate is immersed in a solution that dissolves at least the mask and the solution is boiled before applying the ultrasonic vibration. 3. The pattern forming method according to claim 1 or 2, wherein the substrate is a semiconductor substrate and the mask pattern is made of a positive photosensitive resin. 4. The pattern forming method according to claim 3, wherein after forming the mask pattern, the entire surface is irradiated with ultraviolet light.