JPH02273922A - Formation of through hole - Google Patents

Abstract

PURPOSE:To make the etching rate of the upper layer of an interlayer insulating film differ from that of the lower layer of the insulating film and to make it possible to form properly the taper angle of a through hole by a method wherein the film quality of the upper layer is made to differ from that of the lower layer. CONSTITUTION:An interlayer insulating film 14 is constituted of a lower layer 15, which is a silicon nitride film of fine film quality, and an upper layer 16, which is a silicon nitride film of rough film quality. That is, as the etching rate of the silicon nitride film, which is the upper layer 16 of rough film quality, is larger than that of the silicon nitride film, which is the lower layer 15 of fine film quality, a through hole 19 having a proper taper angle of 30 to 50 deg. can be formed by performing an isotropic etching using a resist pattern 17 as a mask.

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application The present invention relates to a method of forming a through hole having an appropriate taper angle.

(b) Conventional technology Multilayer wiring structures are frequently used in semiconductor devices due to their increasing density, and through holes for connecting upper and lower wiring layers are tapered to improve step coverage of upper layer wiring. For example, JP-A-62-
It is described in Publication No. 9638.

FIG. 2 shows an example of a through hole in a conventional multilayer wiring structure. In the figure, (1) is a semiconductor substrate, (2)
is a Sin, film, (3) is the first layer Ae wiring layer, (4)
is the interlayer insulating film, 5) is the through hole, and (6) is the second layer A! This is a wiring layer.

The through hole (5) is the first layer Affi wiring layer (3)
An interlayer insulating film (4) such as a silicon nitride film is deposited thereon, a resist pattern is formed thereon, and isotropic etching is performed using plasma etching using the resist pattern as a mask, thereby forming the side walls into a tapered shape. Ta.

(c) Problems to be Solved by the Invention However, in order for a silicon nitride film to have moisture resistance and other appropriate properties as a high-performance insulating film (4), it is desirable to have a dense film quality; If the density is increased, the taper angle θ of the through hole (5) will increase, and the second layer AP wiring (
6) The step coverage gradually deteriorates, resulting in failures such as disconnection.

(d) Means for Solving the Problems The present invention has been made in view of the above-mentioned conventional problems.
The present invention provides a method for forming a through-hole that can obtain a good tapered shape by forming the through-hole (5) and Jl (16), which has a rough film quality.

(E) Effect According to the present invention, the silicon nitride film of the upper layer (16), which has a rougher film quality, is etched more than the silicon nitride film of the lower layer (15), which has a denser film quality. By performing isotropic etching using (17) as a mask, a through hole (19) having an appropriate taper angle of 30 to 50 degrees can be formed.

(F) EXAMPLE An example of the present invention will be described below in detail with reference to the drawings.

FIGS. 1A to 1F are cross-sectional views showing the method for forming through holes according to the present invention in the order of steps. First, as shown in FIG. (1
An electrode material such as aluminum (A2) is formed on the surface of 1) via a silicon oxide film (12), and this is patterned to form a first wiring layer (13).

Next, as shown in FIG. 1B, the first
The film thickness is 10,000~ to cover the wiring layer (13).
A lower layer (15) of an interlayer insulating film (14) made of a silicon nitride film (SixNy) of 20,000 yen is formed. The plasma nitride film is formed in a (SiH4+NHs) or (SiHa+N*) gas system for several hours at a production temperature of 2.
The plasma nitride film is heated under the conditions of 00 to 400°C and a generation pressure of 0.1 to I Torr, and the composition of the plasma nitride film represented by Si, N is as low as possible by Si, N, which is formed by opposite thermal decomposition.
.

The film is formed so that it is close to the film and has a dense film quality (excellent film density).

Then, as shown in FIG. 1C, a silicon nitride film having a rougher quality than the silicon nitride film of the lower layer II (15) is deposited on the lower layer (15) again to a thickness of 100 to 1000 using the plasma CVD method.
This layer is deposited on top to form the upper layer (16) of the interlayer insulating film (14). The film quality can be controlled by substrate temperature, production pressure, gas flow rate, applied high frequency and power, etc., and the composition is such that the etching rate is lower than that of the lower layer (16). Also, after depositing the lower layer (16), a part of the wafer is taken out and the lower layer (15) is deposited again using the same apparatus.
), it is possible to form a thin silicon nitride film with rough film quality by performing the deposition process for several minutes after the device is turned on under the same formation conditions. This is probably due to a drop in wafer temperature due to the removal of a portion of the wafer, or a decrease in the temperature and pressure inside the plasma CVD equipment due to the short processing time (
16) This is thought to be because the film is formed under unstable conditions before the conditions at the time of formation are reached.

Then, as shown in the first diagram, a resist (17) is spin-on coated on the upper fl<16) surface, exposed, and developed to form the opening (
18) and then conduct a CF using the resist (17) as a mask as shown in Figure 1E.
By performing plasma etching using gas, the interlayer insulating film (14) is isotropically etched to form a tapered through hole (19). The interlayer insulating film (14) is etched in the thickness direction of the interlayer insulating film (14) due to the difference in film quality between the upper layer (16) and the lower layer (15).The upper layer (16) has a higher etching rate. Above J
! (16) proceeds faster when removed laterally. Therefore, by this etching, the upper layer of the interlayer insulating film (14) is opened more widely, and the taper angle .theta. of the through hole (19) can be formed at a smaller and appropriate angle of 30 to 50 degrees than in the past. In addition to this example in which the entire film quality is isotropically etched, isotropic etching by plasma etching and R/E etching are also used.
Anisotropic etching may also be used.

Then, as shown in FIG. 1F, after removing the resist (17), aluminum (Af!) is formed by sputtering or electron beam evaporation, and by buttering this, the through hole (19) is formed. and the first wiring layer (1
A second WI wiring layer (20) is formed in contact with 3).

According to such a formation method, the through hole (19) has an appropriate taper angle and has a gentle step, so that the step coverage of the 2Mth wiring layer (20) is excellent and it is possible to prevent defects such as broken lines.

Although this example refers to a 2M structure, 3-layer, 4-layer
Needless to say, the same applies to the layered structure.

(g) Effects of the invention As explained above, according to the present invention, a through ball (1
Since the taper angle (9) can be appropriately formed, a semiconductor device with high reliability of interlayer connections can be provided. In addition, since a silicon nitride film is used as the interlayer insulating film (14),
A structure with better moisture resistance, pressure resistance, and step coverage than that of a Sin film can be obtained, and since the etching rate can be changed by changing the film quality, it has the advantage that the process does not need to be particularly complicated.

[Brief explanation of drawings]

1A to 1F are cross-sectional views showing the forming method of the present invention in the order of steps, and FIG. 2 is a cross-sectional view for explaining a conventional example.

Claims (2)

[Claims] (1) A step of forming wiring metal on a semiconductor substrate, in which multiple layers of insulating films are formed on the wiring metal, with an upper layer of an insulating film of rough quality that has a higher etching rate than the underlying insulating film. forming a resist pattern on the uppermost insulating film, and using the resist pattern as a mask, etching the plurality of layers of insulating films to form a tapered through hole. How to form a through hole. (2) The method for forming a through hole according to claim 1, wherein the insulating film is a silicon nitride film (Si_xN_y) formed by plasma CVD.