JPS6120334A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To process the aperture of the insulation film in taper form with photo resist left in the other part by a method wherein, even in a state of unexposure of a positive resist, the aperture window of the photo resist is enlarged by utilizing that it slightly melts in its developer. CONSTITUTION:An aperture window 26 is formed in part of the third positive photo resist 25 by the photolithography technique. An aperture window 28 is formed in the same shape at the position of the aperture window 26 in the second negative photo resist 24 and the first positive photo resist 23 by derective dry etching 27. A vertical aperture 30 is formed in the insulation film 22 by corresponding to the aperture window 28 by the directive dry etching 29 of the insulation film 22. The aperture window 28 at the part of the first positive photo resist 23 around the aperture window 28 is enlarged by dipping in a positive developer. Then, the aperture 30 is processed in taper form by removing the exposed rectangular part of the insulation film 22 by wet etching with a buffer solution of hydrofluoric acid or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for opening holes in an insulating film.

(Prior Art) In semiconductor devices, openings are formed in an insulating film for connection between conductor layers. A conventional method for forming the opening will be explained with reference to FIG. 2. Second
Figure (a) is a diagram in which an interlayer insulating film is formed after forming a MOS transistor on a semiconductor substrate, in which 11 is a semiconductor substrate, 12 is a diffusion layer, 13 is an r-upper electrode, 14 is a thermal oxide film,
15 is an interlayer insulating film. When forming an opening in this interlayer insulating film 15, first, a photoresist pattern F having an opening window 16 at a desired position is formed on this interlayer insulating film 15 as shown in FIG. 2(b). After that, as shown in FIG. 2(b), this photoresist pattern 17 is
By dry etching the interlayer insulating film 15 using as a mask, a vertical opening 18 is temporarily formed in the interlayer insulating film 15 at the position of the opening window 16 and having the same dimensions. Thereafter, the photoresist pattern 17 is peeled off.

Then, wet etching is performed on the entire surface without the photoresist pattern 17, as shown in FIG. 2(e).
As shown in FIG. 1, when the thermal oxide film 14 in the portion of the opening 18 is removed, the opening 18 is made into a tapered shape.

Further, by this whole-surface wet etching process, the stepped portion of the interlayer insulating film 15 becomes a slope 19. Thereafter, a wiring metal layer 20 is formed on the interlayer insulating film 15 including the opening 18, as shown in FIG. 2(d), and then this wiring metal layer 20 is patterned (not shown).

(Problems to be Solved by the Invention) However, such conventional methods have the disadvantages of lowering the interlayer breakdown voltage, increasing the film capacitance, and further causing interlayer short circuits. That is, in the conventional method described above, the opening 18 is tapered by wet etching the entire surface by taking advantage of the high etching rate at the corners of the interlayer insulating film 15. A film hole or a pinhole may be formed locally in the interlayer insulation film 15, resulting in a decrease in interlayer breakdown voltage, an increase in oxide film capacitance, and an interlayer short circuit. Note that since the etching rate of the corners is high, the photoresist pattern 17
Even if etching is performed to remove the thermal oxide film 14 and at the same time make the opening 18 tapered, it is difficult to make the opening 18 tapered.

(Means for solving the interpolation point problem) Therefore, in the present invention, by widening the aperture window of the photoresist by utilizing the property that the positive photoresist is slightly soluble in the developer even in an unexposed state, To process an opening in an insulating film into a tapered shape while leaving photoresist in other parts.

(Function) According to this method, the openings in the insulating film are tapered with photoresist remaining in areas other than the q openings. Pinholes are no longer formed.

(Embodiment) FIG. 1 shows an embodiment of the present invention. This embodiment will be described below.

In FIG. 1(a), 21 is a semiconductor substrate, 22 is an insulating film thereon), and first, a positive type first photoresist 23. is applied on this insulating film 22. A negative type second photoresist 24 and a positive type third photoresist 25 are sequentially applied. Then, a desired opening window 26 is formed in a part of the positive type third photoresist 25 by a well-known photolithography technique. First and second photoresists 2a, 2+
The thickness of i is about 3000λ, and the thickness of the third photoresist 25 is about aoooA. By using such a photoresist thickness, a good opening shape can be obtained through the following steps.

Next, as shown in FIG. 1(b), by subjecting the photoresist to directional dry etching 27, the negative type second photoresist 24 and the positive type first photoresist 23 are coated with the positive type third photoresist. Opening window 2 of photoresist 25
An aperture window 28 is formed in the same shape at position 6. At this time,
There is no problem even if the positive type third photoresist 25#2 is removed (in this example, it is all removed), but it is desirable to reduce thermal changes in the remaining first photoresist 23 as much as possible. . For this reason, for example, a heat-resistant resin is used for at least the first photoresist 23, and dry etching is performed while cooling. It must be soluble in a positive developing solution.

Next, as shown in FIG. 1(e), using the remaining photoresist 24, 23 as a mask, directional dry etching 29 of the insulating film 22 is applied to the insulating film 22 in the opening window 28. Correspondingly, vertical apertures 30 are formed.

Thereafter, by immersing the substrate in a positive developer, or by sprinkling a positive developer without rotating the substrate side (this is called a spin image), the positive developer around the aperture window 28 is formed. By slightly dissolving the first photoresist 23, the opening window 28 in the first photoresist 23 portion is formed.
Spread out as shown in Figure 1(d). That is, in a positive photoresist, the exposed area is usually removed by a developer, but even in a wood-exposed state, if the resist is prevented from becoming hot, it will be dissolved by the developer. By making full use of this property, a positive type first photoresist 23 is formed.
hμ A corner of the insulating film 22 at the upper end VC of the hole 30 is exposed with the first photoresist 23 remaining on the other side.

Finally, the exposed corner portions of the insulating film 22 are removed by wet etching using K such as a hydrofluoric acid buffer, thereby forming the openings 30 into a tapered shape as shown in FIG. 1(6). After this, although not shown, wiring and the like are performed by known means to complete the semiconductor device.

(Effects of the Invention) As described in detail above, according to the method V of the present invention, the opening windows of the photoresist can be formed by utilizing the property that the pot-shaped photoresist is slightly dissolved in the developer even in an unexposed state. By widening the opening, the opening in the insulating film can be tapered with the photoresist remaining in areas other than the opening. Therefore, it is possible to prevent the juxtaposition caused by the whole-surface wet etching process, that is, the fall of the insulating film, and the generation of pinholes, thereby preventing a decrease in interlayer breakdown voltage, an increase in oxide film capacitance, and the occurrence of interlayer short circuits.

Further, according to the present invention, a combination of three layers of photoresist is used to form a small aperture window when forming a perpendicular aperture in the insulating film and a large aperture window when forming the aperture into a tapered shape. Since polysilicon or loose metal is not required to form such an aperture window, the process is easy and the number of man-hours can be reduced.

Furthermore, the expansion of the aperture window (formation of a large aperture window) is carried out by dissolving a small amount of photoresist in an unexposed state in the 01m solution, so the aperture window can be expanded with high precision. Can be controlled.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an embodiment of the method for manufacturing a semiconductor device according to the present invention, and FIG. 2 is a sectional view showing a conventional method for forming an opening in an insulating film. 21... Semiconductor substrate, 22... Insulating film, 23...
positive type first photoresist, 24... negative type second photoresist;
photoresist, 25... positive type third photoresist, 26... aperture window, 27... directional dry etching, 28... aperture window, 29... directional dry etching, 30... Open hole.

Claims (1)

[Claims] A positive type first photoresist, a negative type second photoresist, and a positive type third photoresist are sequentially applied onto the insulating film on the semiconductor substrate, and a desired opening window is formed in the positive type third photoresist. By performing a directional etching of the photoresist after this step, the negative-tone second photoresist and the positive-tone first photoresist are made to have the same aperture window position in the positive-tone third photoresist. a step of forming an aperture window in the shape, and then forming an aperture portion in the insulating film corresponding to the aperture window by directional dry etching the insulating film using the photoresist as a mask; Thereafter, a step of widening the aperture window of the positive first photoresist by dissolving the first photoresist around the aperture window with a positive developer, and a step of widening the aperture window by this step. A method of manufacturing a semiconductor device, comprising the step of forming an opening in the insulating film into a tapered shape by etching away the exposed corner of the insulating film.