JPH0669153A - Formation of fine contact hole - Google Patents

Abstract

PURPOSE:To make a fine contact hole highly accurately through dielectric films of a semiconductor device. CONSTITUTION:A first dielectric film 12 and a photoresist 13 are formed sequentially on a semiconductor substrate 11. Assuming the numerical aperture of lens in an aligner is NA and the wavelength of exposing light is lambda, an opening of diameter W(=(0.7-1)lambda/NA) is made through the photoresist 13 by aligning technology, an opening 12a is made through the first dielectric film 12 using the opening made through the photoresist 13, a second dielectric film 14 having thickness (d) is formed thereon, the second dielectric film 14 is subjected to anisotropic etching to leave the second dielectric film 14 on the side wall of the opening l2a made through the first dielectric film 12 thus making a contact hole 15 having diameter W-2d.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for forming fine contact holes for electrically connecting conductive layers above and below an insulating film.

[0002]

2. Description of the Related Art In a semiconductor integrated circuit device, mutual electrical connection between a transistor active region in a substrate and a take-out electrode, or between multi-layer wirings, etc. are all made through contact holes. Therefore, a large number of contact holes are present in one semiconductor integrated circuit device. To form contact holes,
A method using an exposure technique is used. In this method, a mask having a desired contact hole diameter is used for exposure, a resist pattern is formed, and then the contact hole is formed by dry etching. In the formation of contact holes using this exposure technique, contact holes below the resolution limit of the exposure technique cannot be formed. Therefore, a sidewall contact hole formation method is proposed in which the contact holes are once opened and then the contact holes are reduced. ing. (Japanese Patent Application No. 62-172141).

FIG. 2 is a diagram showing a conventional method of forming a contact hole using a side wall. As shown in FIG. 3A, the first insulating film 2 formed on the silicon substrate 21.
2 is coated with a photoresist 23 and projected with irradiation light through a mask 24, so that the photoresist 23 has an opening depending on the mask pattern diameter 24a as shown in FIG. . Next, the first insulating film 22 is etched by using the photoresist 23 as a mask, and the opening 2 is formed in the first insulating film 22 as shown in FIG.
2a is formed.

Thereafter, as shown in FIG. 1D, a silicon oxide insulating film 25 as a second insulating film is deposited on the insulating film 22. Here, if the second insulating film 25 is anisotropically dry-etched, the insulating film 25 having the same thickness as the second insulating film 25 is formed on the sidewall of the opening 22a as shown in FIG.
It is possible to obtain a contact hole having a smaller diameter than the opening 22a.

[0005]

According to such a conventional sidewall contact hole forming method, it is possible to obtain an arbitrary contact hole diameter smaller than the dimension opened by the exposure technique. However, in this method, the second insulating film 25
Since the film is once formed and anisotropically etched, the thickness of the insulating film 25 left in the opening 22a is also changed depending on the degree of this etching, and the diameter of the contact hole to be finally formed and the opening The diameter relationship of 22a (24a) may not be constant.

Therefore, there is a problem that it is not clear how large the opening should be formed with respect to the desired diameter of the contact hole. If the relationship between the diameter of the opening opened by the exposure technique and the diameter of the contact hole to be finally formed is not appropriate, dimensional variations that cannot be ignored occur in the surface of the semiconductor substrate, or fine contact holes are formed. In this case, there is a problem in that the contact hole may be defective. An object of the present invention is to provide a forming method capable of forming fine contact holes with high precision.

[0007]

The forming method of the present invention comprises a step of sequentially forming a first insulating film and a photoresist on a semiconductor substrate, and a step of forming an opening in the photoresist by an exposure technique. A step of forming an opening in the first insulating film by using the opening, and a second insulating film is formed on the entire surface and anisotropically etched to form a sidewall of the opening of the first insulating film. In which the second insulating film is left to form a fine contact hole, and the numerical aperture of the lens of the exposure apparatus used for exposure is NA and the light wavelength of exposure is λ, W [ = (0.7 to 1) λ / NA]
A contact hole having a diameter of W-2d is formed by forming an opening having a diameter of 5 mm and forming the film thickness of the second insulating film by d.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings. As shown in FIG. 1, first, as shown in FIG. 1A, a first insulating film 12 is formed on a silicon substrate 11, a photoresist 13 is formed, and then a photomask not shown is used. Opening 1 in photoresist 13 by exposure technique
3a is formed. Next, as shown in FIG. 3B, the first insulating film 12 is etched using the photoresist 13 to form the opening 12a, and the second insulating film 14 is deposited thereon. Further, by anisotropically etching the second insulating film 14, the second insulating film 14 is left inside the opening 12a, and the second insulating film 14 forms a contact hole 15 having a fine diameter. .

FIG. 3 shows the calculated light intensity distribution in the cross section of the contact hole, where I is the light intensity, X is the lateral distance, and W is the diameter of the contact hole. Here, the slope of the light intensity at the edge of the opening of the photomask is defined as dI
Assuming / dX, the contact hole diameter size dependent characteristic of dI / dX is as shown in FIG. The horizontal axis is represented by the spatial frequency 1 (= λ / NA · 2W) for generality. Here, λ is the exposure wavelength, and NA is the lens numerical aperture of the exposure optical system.

As can be seen from FIG. 4, dI / dX is 1
It has the property of taking the maximum value between 0.5 and 0.7. In general, the larger dI / dX, the closer the sidewall angle of the photoresist pattern of the contact hole becomes to the vertical. If the side wall angle of the opening 13a of the photoresist 13 approaches a vertical angle, the system dimensional error of the contact hole formed by dry etching can be reduced and the dimensional variation in the silicon substrate can be reduced. Therefore, dI / dX can be reduced. Largest condition, (W = 0.7-1) λ
It is preferable to expose with / NA.

Now, the photoresist 1 in the process of FIG.
A description will be given of the case of forming a contact hole having a desired diameter dimension Y (= 0.3 μm) using an exposure apparatus having an i-line NA of 0.5 when forming the third opening 13a. The maximum value of dI / dX is shown in FIG. 3 where 1 is 0.66, that is, W is 0.56 μm.
Exposure to the photoresist 13,
Development is performed to form 0.56 μm openings 13a. Then, with respect to the desired diameter Y of the finally obtained contact hole,
The thickness of the second insulating film 14 is d = 0.13 μm (d = (Y−
After W) / 2) is deposited on the entire surface of the silicon substrate 11, anisotropic etching is performed by dry etching to obtain a desired contact hole diameter dimension of 0.3 μm (W-2 · d).

Also, an excimer laser (wavelength 0.248 n
m) as a light source and an exposure device with an NA of 0.42
When forming a contact hole of μm, the maximum value of dI / dX is obtained when W is 0.45 μm, so the contact hole is first formed using a mask equivalent to 0.45 μm (W). To do. Next, the thickness is 0.75 μm (d = (Y−W)
/ 2) second insulating film is deposited on the entire surface of the silicon substrate, and then anisotropic etching is performed by dry etching to obtain a desired contact hole diameter dimension of 0.3 μm (W-2 · d). .

[0013]

As described above, according to the present invention, an opening having a diameter of W [= (0.7 to 1) λ / NA] is formed in the photoresist, and the film thickness of the second insulating film is changed. Since the second insulating film is left on the side wall of the opening of the first insulating film to form a fine contact hole, a contact hole having a diameter of W-2d is formed. Since a favorable opening having a sidewall angle that is almost vertical is formed in the resist, a fine contact hole can be accurately formed.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention in the order of manufacturing steps.

FIG. 2 is a cross-sectional view showing a conventional manufacturing method in process order.

FIG. 3 is a diagram showing a light intensity distribution characteristic in a cross section of a contact hole.

FIG. 4 is a characteristic diagram of the contact hole diameter size dependence of dI / dX.

[Explanation of symbols]

 11 Silicon substrate 12 Insulating film 13 Photoresist

Claims (1)

[Claims] 1. A step of sequentially forming a first insulating film and a photoresist on a semiconductor substrate, a step of forming an opening in the photoresist by an exposure technique, and a first insulating film utilizing the opening. And forming a second insulating film on the entire surface, and anisotropically etching the second insulating film to leave the second insulating film on the side wall of the opening of the first insulating film and leave it fine. When the numerical aperture of the lens of the exposure device used for the exposure is NA and the light wavelength of the exposure is λ including the step of forming a contact hole, W [=
A contact hole having a diameter of W-2d is formed by forming an opening having a diameter of (0.7 to 1) λ / NA] and setting the thickness of the second insulating film to d. And a method of forming a fine contact hole.