JPS6028237A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To make the end surface of an opening for fitting an electrode steep by using a laminate of a negative type resist film as a foundation and a positive type resist film as an upper layer as masks when the surface of a semiconductor substrte, to which an element region is formed, is adhered with an SiO2 film and the opening is formed through etching while being made to correspond to the element region. CONSTITUTION:The upper section of a semiconductor substrate 1, to which an element region is shaped through diffusion, is coated with an SiO2 film 2, the whole surface is coated with a negative type resist film 3, and an opening corresponding to the element region is bored through photoetching to expose the film 2 as a film 2'. Since the circumferential wall of the opening takes a tapered shape in a negative type resist at that time, a positive type resist film 4 is formed additionally on the film 3, the film 4 is also attached to the side wall of the opening section through the same treatment, and the opening section is brought to a steep shape. The exposed film 2' is removed through etching, the whole surface is coated with a metallic material 5 for an electrode, and the films 4 and 3 are removed together with the material 5 applied on the films 4 and 3, thus obtaining the electrode 5 having a precise pattern on the element region.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to the formation of electrodes for semiconductor devices, and particularly relates to a lift-off method.

<Prior art> The lift-off method is a method in which a photoresist is applied onto a semiconductor substrate to form, for example, an electrode pattern, and then a metal film for electrodes is deposited on the photoresist and the semiconductor substrate, and then a metal film for electrodes is deposited on the photoresist and the semiconductor substrate. This is a method of forming, for example, an electrode by removing the deposited unnecessary metal film at the same time as removing the photoresist.The process is simple, and since no etching solution is used, there is no need to etch the sides of the electrode. It is widely used.

In order to make this method more effective, it is desirable that the metal film deposited on the photoresist and the metal film deposited directly on the substrate be separated by a step difference due to the thickness of the photoresist film. Therefore, the photoresist needs to be thicker than the metal film to be deposited. Especially thick film electrode (1
In the case of a semiconductor device that requires a photoresist thickness of about 0 μm), the photoresist thickness needs to be about 20 μm.

However, when a pattern is formed by increasing the resist film thickness using a negative type photoresist, the sides of the resist after pattern formation tend to become tapered as shown in Figure 1, making it difficult to separate the metal film. .

In FIG. 1, l is a semiconductor substrate on which circuit elements are formed, and the surface of the substrate l is covered with a 5i02 film 2, except for electrode openings where conductors must be adhered. Photoresist 3 is applied. An electrode pattern image is exposed and developed on the applied negative type photoresist 3 to form an electrode opening 2a, and then an electrode metal film 5 is formed by vapor deposition or the like, and unnecessary portions of the metal film 5 are removed from the resist 3. It is removed with peeling. In such a negative type photoresist, when the electrode opening 2a is formed in advance, the opening end surface 3a of the resist is etched into a tapered shape, making it impossible to obtain a steep step, and therefore it is difficult to separate the metal film 5 at the electrode part. There is an inconvenience.

In addition, in the case of positive type resist, although the side surface of the resist after electrode pattern formation is in a step state, the adhesion between the semiconductor substrate and the resist is relatively poor, so it has the disadvantage that it is not suitable for etching the contact insulation film, which requires etching. there were. Therefore, when lift-off is performed using a positive type photoresist, as shown in FIGS. Figure (a)), then after peeling off the negative type photoresist 3, a pattern for lift-off is formed with positive type photoresist 4 (Figure 2 (b)).
)) L, then deposit the metal 5 that will become the electrode (Fig. 2 (C)
) and then peeling off the positive photoresist to create the image shown in Figure 2 (
An electrode 5 like dl was formed. However, even in this improved process G-), there are problems in that the number of steps is large and the resist film is formed only in one layer, which is still insufficient to obtain the required film thickness.

<Purpose of the Invention> The present invention improves the conventional drawbacks, and provides a method for manufacturing a semiconductor device that simplifies the work of removing photoresist during electrode pattern formation using the lift-off method and can obtain a highly reliable pattern. provide a method.

<Example> FIG. 3 (a+ to (dl) are cross-sectional views for explaining process diagrams in which the method of the present invention is applied to a semiconductor device. In order to form a semiconductor element on a semiconductor substrate 1, a predetermined portion is After performing processes such as diffusion of impurities, a silicon dioxide film 2 is deposited as an insulating film on the substrate surface, and then a negative type photoresist 3 is applied, and patterns corresponding to, for example, electrodes are formed using conventional photoetching techniques. (Fig. 3(a))
).

Next, on the pattern of the negative type photoresist 3 formed earlier, a positive type photoresist 4 is applied as shown in FIG. 3(b). A pattern is formed using a conventional photoetching technique using a glass mask that forms a covering shape. That is, the tapered shape of the etched end face, which is a drawback of negative type photoresists, is compensated for and a steep end face is formed. Next, the insulating film 2 of the contact part
' is etched using a known technique, and then a metal material 5 to serve as an electrode is deposited on the photoresist and the substrate (FIG. 3(C)). Next, the semiconductor substrate is immersed in a photoresist stripping agent, and a positive type resist 4. At the same time as the negative type resist 3 is peeled off, unnecessary portions of the metal film deposited on the photoresist are also removed to form electrodes 5 deposited on the substrate 1 as shown in FIG. 3Fdl. At this time, the end face of the electrode opening is steep because it is covered with a positive resist, and the metal film on the resist is easily peeled off.

As explained above, since the method of the present invention is based on a negative type photoresist, there is no problem in etching the insulating film at the contact area, and the positive type photoresist covers the negative type photoresist. Because of the patterned shape, the overall resist film thickness is thick, and the sides of the resist after pattern formation are in a step state, and even in the case of thick film electrodes, unnecessary parts of the metal film on the photoresist and the metal film on the semiconductor substrate are removed. The portion of the metal film that should be left is easily separated, making the work much easier and improving the reliability of the pattern shape. Because it has a two-layered structure consisting of a negative type photoresist and a positive type photoresist, it also has the advantage of extremely reducing the number of pinholes that occur in the resist.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view for explaining the conventional manufacturing method using a negative type photoresistor, Figure 2 (al to Fdl is a diagram of the conventional lift-off process when a positive type photoresistor is used, and Figure 3 is a diagram of the present invention). 2 is a process diagram for explaining one embodiment of the invention. 2.2': silicon dioxide film; 3: negative type photoresist film; 4: positive type photoresist film; 5: metal film for electrode. Agent Patent attorney Aihiko Fuku (2 others) (B No. (C) 3!2I!

Claims (1)

[Claims] 1. A step of forming a pattern using a negative type photoresist on a semiconductor substrate covered with an insulating film, a step of applying a positive type photoresist on the pattern and etching the positive type photoresist into a corresponding pattern, and a step of etching the positive type photoresist into a corresponding pattern. a step of etching an insulating film on the surface of the substrate exposed by etching; a step of depositing a metal film on the photoresist pattern and the exposed semiconductor substrate;
A method for manufacturing a semiconductor device, comprising the steps of: peeling off the remaining photoresist; and simultaneously removing a metal film on the photoresist.