JPH04318932A - Forming method of metallic pattern - Google Patents

Abstract

PURPOSE:To conduct metallic wiring impossible by wet etching by an acid and alkali such as a compound semiconductor through a safe positive lift-off method. CONSTITUTION:The forming method of a metallic pattern is composed of a process (a), in which a resist material film 14 is formed onto a zinc oxide film 12, a process (b), in which the resist material film in a section forming a pattern in a resist material is removed, a process (c), in which a metallic film 13 is evaporated onto the zinc oxide film, on which the resist material film is left, by a vacuum deposition machine with a planetary mechanism, a process (d), in which a metal evaporated on a resist side surface is wet-etched, and a process (e), in which the left resist and the metallic film on the resist are removed. The thickness of a metallic film evaporated onto the resist side surface only by oblique projection is made thinner than that of the metallic film evaporated on a plane section. The ratio of the thickness of both metallic films is measued previously and experimentally, the metallic film evaporated on the side surface section is taken off through wet etching, and the thickness of the metallic film left on the plane section can be adjusted in specified thickness.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a metal pattern forming method in a semiconductor manufacturing process.

0002

2. Description of the Related Art In the technical field of semiconductor manufacturing processes, group IV semiconductors represented by Si are resistant to acids and alkalis, and when metal wiring is formed by photolithography, As shown in the process diagram, wet etching using an acid or alkali etchant is possible using a resist as a mask.

That is, in the same figure, 1 is a substrate material, 2 is a metal material film, and 3 is a resist material film, FIG. 3(b) is a forming process of the metal material film, and FIG. 3(c) is a resist coating process. FIG. 3(d) shows the pattern forming step by photolithography, FIG. 3(e) shows the etching step of the metal material film using an etching solution, and FIG. 3(f) shows the resist material removal step.

This is because group IV semiconductor metals are much more durable than metals against acid and alkali etchants, and even if the metal melts and the etchant comes into direct contact with the group IV semiconductor, the group IV semiconductor itself will not It takes advantage of the fact that it is not etched.

However, zinc oxide (ZnO) and zinc sulfide (
Group II-VI compound semiconductors such as ZnS or III-V compound semiconductors such as gallium arsenide (GaAs) are not as durable against acid and alkali etchants as Group IV semiconductors such as Si. Figure 3
Wet etching as shown in FIGS. 3(a) to 3(f) is often impossible.

[0006] Therefore, a lift-off method as shown in FIGS. 4(a) to 4(e) has been adopted. This lift-off method uses photolithography to cover areas other than the areas where wiring is desired with resist, then evaporates metal over the entire surface using an appropriate method, then removes the resist with an appropriate solvent, and at the same time removes the metal that was evaporated on the resist. This method removes the metal and leaves the metal only in designated areas.

That is, in the figure, 1 is a substrate material, 2 is a metal material film, and 3 is a resist material film, FIG. 4(b) is a resist coating process, and FIG. 4(c) is a pattern formation process by photolithography. FIG. 4(d) shows the process of forming a metal material film, and FIG. 4(e) shows the process of removing the resist and unnecessary metal parts.

[0008] In the above method, unnecessary metal can be physically removed from the metal to be wired using a resist, so there is no need to use acid or alkaline etchants that harm compound semiconductors, and safe and reliable wiring can be achieved. is possible. However, the disadvantages of the lift-off method include the following. The surface where you want to wire the metal and the surface masked by the resist from which you want to remove the metal should either not be connected after evaporation, or even if they are connected, there should be a level difference in the resist that can be easily separated by physical force (for example, ultrasonic waves, etc.). It is necessary to attach it by In other words, as shown in FIG. 5, if the step is small relative to the thickness of the metal, or if the metal vapor is obliquely incident, the metal will be connected across the step, making it impossible to remove the excess metal.

In order to easily solve the above problem, it goes without saying that the height difference should be made larger than the thickness of the evaporated metal, but as shown in FIG. I need to come. However, if the metal vapor is introduced vertically, the efficiency of the semiconductor manufacturing process will be considerably reduced. Usually, in vapor deposition, metal placed in a crucible in a high-vacuum chamber is heated by an appropriate means, and the evaporated metal does not collide with other objects, but travels almost straight to the substrate to be evaporated, becoming a metal film. .

To perform lift-off, as shown in FIG. 7, the substrate 1 to be evaporated supported by the holder 5 in the vacuum chamber 4 must be placed in the positional relationship shown in the figure with respect to the metal evaporation source 6. There is. The number of substrates to be processed is determined by the area of the evaporated metal relative to the substrate up to an allowable oblique incident angle (θ).

[0011]

[Problems to be Solved by the Invention] Normally, when metal is evaporated for the purpose of not performing lift-off (in the case of wet etching, etc.), a planetary mechanism shown in FIG. 8 is provided and the planetary is rotated relative to the evaporation source. Therefore, methods have been devised to allow metal to be deposited with a uniform thickness on a large number of substrates. For example, when metal evaporation is performed using vacuum chambers with the same diameter, the number of wafers processed at one time is approximately Many people use a planetary mechanism that is about 10 times more powerful. However, in the planetary mechanism, the metal vapor has many oblique incidences with respect to the substrate. If you try to perform lift-off using this mechanism, metal will also be deposited on the sides of the resist, so the metal will cross over the resist level and become connected, which naturally makes it difficult to physically remove the unnecessary metal. . Moreover, even if most of the unnecessary parts can be removed, burrs often remain on the end faces of the vapor-deposited metal wires, which is not practical. Note that 7 in FIG. 8 is a planetary mechanism, and 8 is a heater.

0012

OBJECTS OF THE INVENTION An object of the present invention is to provide a metal pattern forming method that can perform metal wiring, such as compound semiconductors, which cannot be formed by wet etching using acid or alkali, with high productivity through safe and reliable lift-off. It is in.

[0013]

[Means for Solving the Problems] A metal pattern forming method according to the present invention includes a step of forming a resist material film on a compound semiconductor substrate, and removing a portion of the resist material film where a pattern is to be formed in the resist material film. a step of evaporating a metal film on the substrate on which the resist material film remains using a vacuum evaporator with a planetary mechanism, a step of etching the metal deposited on the side surface of the resist, and a step of etching the remaining resist; The gist is that the method consists of a step of removing the metal film thereon. If a planetary mechanism is not used, the number of sheets processed at one time is extremely small, resulting in poor productivity. Therefore, the planetary mechanism is an essential mechanism for evaporation.

[0014] Metal deposited on the side surface of the resist formed by photolithography by oblique incidence bridges the predetermined metal wiring portion and the metal deposited on the other resist mass portions, using a planetary mechanism. ,
In order to make lift-off possible, the evaporated metal must be removed from the sides of the resist, or it must be made extremely thin so that the bridge is easily cut by physical force such as ultrasonic vibration. Just do it.

[0015] As a result of detailed investigation of the thickness of the metal vapor deposited film deposited by the planetary mechanism, the present inventors found that the metal film deposited only by oblique incidence on the side surface of the resist is as follows.
It was found that the metal film was thinner than the metal film deposited on flat surfaces other than the side surfaces. Therefore, we experimentally measured the thickness ratio of the metal film on the flat surface and the side surface in advance, removed the metal film deposited on the side surface by wet etching, and set the thickness of the metal film remaining on the flat surface to a predetermined value. It was discovered that the film thickness can be adjusted. After this process, lift-off was possible by removing the resist using a normal solvent.

The thickness ratio of the metal film on the side surface portion and the flat surface portion varies depending on the thickness of the resist and the vapor deposition apparatus, so the thickness ratio is confirmed experimentally for each apparatus or determined by calculation. In addition, since the metal film on the side of the resist varies considerably in thickness, it is not necessary to completely remove it; once the thinnest part is completely etched, the remaining part can be easily removed in the next lift-off process. Do you get it. In other words, it is not necessary to precisely etch the metal film on the side surface of the resist, and only rough etching is sufficient, resulting in good workability.

[0017]

[Function] According to the above metal pattern forming method, metal wiring, which cannot be achieved by wet etching using acid or alkali, such as compound semiconductors, can be reliably formed by lift-off.

[0018]

EXAMPLE An example of wiring aluminum metal to a zinc oxide (ZnO) film deposited on a 3-inch silicon substrate will be described with reference to process diagrams shown in FIGS. 1(a) to 1(e). The structure of the device is shown in Figure 2. In the figure, 10 is a silicon substrate, 11 is a silicon oxide film (SiO2), 1
2 is a zinc oxide film, and 13 is an aluminum metal wiring. A ZnO film has no durability at all against acids and alkalis, and it is completely impossible to perform a wet etching method as shown in FIG. 3 when wiring aluminum.

FIG. 1(a) A resist 14 is applied on the zinc oxide film 12.

FIG. 1(b) A wiring pattern is formed by resist photolithography.

FIG. 1(c) Aluminum evaporation is performed using a vacuum evaporation machine equipped with a planetary mechanism. The desired thickness of the aluminum metal film for wiring is about 0.3 μm. It has been found that when aluminum is deposited using a planetary mechanism, aluminum metal with a minimum thickness of about 0.15 μm is deposited on the side surface of the resist, compared to 0.5 μm of aluminum metal deposited on the flat surface.

FIG. 1(d) Therefore, in order to obtain aluminum wiring with a thickness of 0.3μ and to etch the aluminum metal on the side surface of the resist to a minimum thickness, aluminum metal with a thickness of 4.2μ is evaporated using a planetary mechanism. and aluminum film thickness 1.2μ
When wet etching is performed uniformly, most of the aluminum metal on the sides of the resist is removed. Therefore, an etching solution mainly containing phosphoric acid with an etching rate of about 0.2 μ/min was prepared, and wet etching was performed for 6 minutes.

FIG. 1(e) Thereafter, a normal lift-off process was carried out to remove the resist using a solvent and the accompanying aluminum metal on the resist, thereby making it possible to obtain a predetermined aluminum wiring.

[0024]

[Effects of the Invention] As described above, according to the present invention,
Metal wiring, such as compound semiconductors, which cannot be formed by wet etching using acid or alkali, can be formed with high productivity through safe and reliable lift-off.

[Brief explanation of drawings]

[Figure 1] (a), (b), (c), (d), (e
) is a process diagram showing one embodiment of the present invention.

FIG. 2 is a side view of the device structure of the example.

[Figure 3] (a), (b), (c), (d), (e
) and (f) are pattern forming process diagrams by conventional etching.

[Figure 4] (a), (b), (c), (d), (e
) is a diagram of a pattern forming process using conventional lift-off.

FIG. 5 is a side view of the vapor deposition state when metal vapor is obliquely incident.

FIG. 6 is a side view of the vapor deposition state when metal vapor is vertically incident.

FIG. 7 is a side view of the metal evaporation machine showing the positional relationship between the metal evaporation source and the substrate to be evaporated, which is suitable for lift-off.

FIG. 8 is a side view of a vacuum evaporation machine with a planetary mechanism.

[Explanation of symbols]

1 Substrate material 2 Metal material film 3 Resist material film 4 Vacuum chamber 5　Substrate holder 6 Metal evaporation source 7 Planetary mechanism 8 Heater 10 Silicon substrate 11 Silicon oxide film 12 Zinc oxide film 13 Aluminum metal wiring

Claims (1)

[Claims] 1. A step of forming a resist material film on a compound semiconductor substrate, a step of removing the resist material film in a portion of the resist material film where a pattern is to be formed, and a step of forming a resist material film on the substrate on which the resist material film remains. The method consists of a step of depositing a metal film using a vacuum evaporator with a planetary mechanism, a step of etching the metal deposited on the side surface of the resist, and a step of removing the remaining resist and the space between the metals thereon. A metal pattern forming method characterized by: