JP2921258B2 - Insulating film etching method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an etching method for an insulating film, and more particularly to an etching method for forming a through hole in an interlayer insulating film of a semiconductor integrated circuit device.

[0002]

2. Description of the Related Art In a semiconductor integrated circuit device, a through hole in an interlayer insulating film is etched so that its cross-sectional shape becomes an inverted conical shape. The reason is that in the sputtering method used when forming a conductor layer on the interlayer insulating film after the opening of the through hole, if the cross-sectional shape of the through hole is not made to a certain shape, it is required on the inner side surface of the through hole This is because a conductive film having a small thickness is not attached. Conventionally, as a method of etching through holes in a mortar shape, a method in which a mask film used as a mask at the time of through hole etching is etched in a lateral direction as etching proceeds.

FIGS. 2A to 2E are diagrams showing one example. First, as shown in FIG. 2A, a conductor layer 2 is formed on a silicon substrate 1, an interlayer insulating film 3 is formed, and then an etching mask 4 is formed on the interlayer insulating film 3. At this time, an etching mask whose etching rate is lower by about 1/3 to 1/4 than that of the interlayer insulating film is used. For example, when a polyimide film is used as an interlayer insulating film, a plasma silicon nitride film is used for the etching mask 4.

[0004] Next, as shown in FIG. 2B, the plasma silicon nitride film 4 in a desired region is formed by photolithography.
Is removed. Further, as shown in FIG. 2C, CF ₄ is reduced to about 40 using a parallel plate type reactive ion etching apparatus.
%, 10 m at a pressure 100mtorr with the O ₂ to about 60 percent gas
A high frequency power of about w / cm ² is introduced, and the interlayer insulating film 3 is etched using the plasma silicon nitride film 4 as a mask. At this time, the silicon nitride film is about 400 A / min and the photoresist is about 600 A / min. Then, as shown in FIG. 2 (d), the opening region is widened with the lateral etching of the silicon nitride film, whereby the interlayer insulating film is opened like a slash. Thereafter, as shown in FIG. 2 (e), the the CF ₄ to about 80
The silicon nitride film is removed by plasma etching using a barrel-type dry etching apparatus in which a gas of about 20% and oxygen is introduced and the pressure is about 0.6 torr.

[0005]

However, such a conventional etching method has a problem that the opening diameter of the through-hole increases in proportion to the increase of the etching time. This is an unavoidable problem because the mask is etched in proportion to the etching of the interlayer insulating film as described above. On the other hand, the interlayer insulating film is subjected to a process of flattening a step of a base layer of the interlayer insulating film so that the upper conductive film can be coated with a sufficient thickness.
There are portions where the thickness is partially different. Therefore, the through-holes at the peaks of the steps are etched more than necessary until the through-holes located at the valleys of the steps of the base layer are opened, and as shown in FIG. Those whose bottoms are located in valleys are small, and those that are located in peaks are large.

Further, the controllability of the film thickness of the interlayer insulating film is inevitably about ± 10% of the specified value from the viewpoint of cost. However, as the film thickness increases or decreases, the etching time of the through hole is set. I need to do it again. For this reason, as shown in FIG. 3B, there is a problem that the dimension of the upper portion of the through hole changes.
As described above, the difference in the through hole opening diameter depending on the position imposes restrictions on the characteristics of the arrangement of elements and wirings of the semiconductor integrated circuit device, which causes a problem that the arrangement design becomes difficult. SUMMARY OF THE INVENTION An object of the present invention is to provide a method of etching an insulating film that can form a through hole formed in the insulating film with a uniform opening diameter.

[0007]

SUMMARY OF THE INVENTION The present invention provides a method for selectively etching an insulating film using an etching mask.
In the first stage of the initial stage of etching using an R etching device
Does not supply RF power and reduces RF power in the second stage
However, in the third stage at the end of etching, the RF power is increased.
Etching . Or, the first stage of the initial stage of etching
Increasing the microwave power is a micropower a floor, the second stage
On the floor, make the microwave power smaller than that,
In the third stage at the end of the etching, etching for further reducing the microwave power is performed.

[0008]

Next, the present invention will be described with reference to the drawings. FIG. 1 is a sectional view of a part of a semiconductor chip showing an embodiment of the present invention in the order of manufacturing steps. First, as shown in FIG. 1 (a), a conductor layer 2 is formed on a silicon substrate 1, and a polyimide solution is applied thereon and heated at about 400 ° C. to form a polyimide interlayer insulating film 3 of about 1 μm. It is formed thick. Next, as shown in FIG. 1B, the plasma C
A silicon nitride film 4 is formed to a thickness of about 0.2 μm by the VD method.
Then, as shown in FIG. 1C, after the photoresist 5 is applied, the photoresist 5 is removed only in the through-hole region by using the photolithography technique, and the normal reactive ion etching method is mainly performed using CF ₄ gas. Then, the silicon nitride film 4 in the photoresist opening region is removed.

Next, as shown in FIG. 1D, after the photoresist 5 is removed with an organic solvent, an ECR etching apparatus is used, and as a first stage etching, an oxygen gas containing 10% of SF ₆ gas is used, and a pressure of 1 mtorr. and then, to set the microwave 2.45 GHz _Z was 200w applied magnetic field 875 Gauss immediately above the wafer to generate the etching gas plasma by electron resonance is about 0.3μm etched in the polyimide depth. At this time, SF ₆ was used as an etching gas component.
The reason for mixing the gas is that polyimide for semiconductors generally contains a silicon component. If the polyimide film does not contain a silicon component, a fluoride gas is not particularly necessary.

Further, as shown in FIG. 1E, RF power is applied to the substrate via the substrate holder as the second stage etching. RF power 100 mw / cm of this time 13.56MH _Z
^{2 was} applied, and the polyimide was further etched by 0.3 μm. Thereafter, as shown in FIG. 1F, the RF power was set to 600 mw / cm ² as the third stage etching, and the etching was performed by 0.8 μm in terms of polyimide etching. The substrate bias at this time was about 100V.

As described above, by increasing the RF power, the etchant involved in the etching is relatively large in the first-stage etching, whereas the ion-etching effect is large in the third-stage etching. Etching is achieved. At this time, when the interlayer insulating film is thick, the third-stage etching time may be increased according to the increase in the film thickness. In the third-stage etching, the opening diameter of the silicon nitride film mask hardly changes even if the etching time is increased, so that the opening diameter of the through-hole does not change up and down in the sectional structure. Here, the same effect can be obtained by increasing the microwave power at the beginning and decreasing it at the end instead of increasing the RF power.

It should be noted that a silicon oxide film can be used as an interlayer insulating film and a photoresist film can be used as an etching mask. That is, after forming an interlayer insulating film and a photoresist mask as in the above embodiment, through-hole etching is performed using an ECR etching apparatus as in the above embodiment. The difference in the etching conditions at this time from the above embodiment is the component ratio of the etching gas. In this case, in order to increase the etching rate of the silicon oxide film as compared with the photoresist, CF ₄ 80%,
By using a gas of O ₂ 20%, a through hole having the same shape as that of the above embodiment was obtained.

When the interlayer insulating film is a siloxane-containing polyimide film, the following can be used as the etching mask. A silicon nitride film formed by plasma CVD, a silicon nitride / oxide film formed by plasma CVD, a silicon oxide film formed by plasma CVD, an aluminum film formed by sputtering, a tungsten silicide film formed by sputtering, and a titanium film formed by sputtering. Also, a silicon oxide film formed by thermal oxidation of silicon as a interlayer insulating film, a silicon oxide film containing phosphorus and boron by a thermal CVD method, a silicon nitride film by a plasma CVD method, a silicon nitride / oxide film by a plasma CVD method, and a plasma CVD method
In the case of a silicon oxide film formed by a method, a silicon oxide film formed by a solution coating method, or a laminated film of these, a photoresist film can be used as an etching mask.

[0014]

As described above, according to the present invention, the RF power or microwave power in the ECR etching apparatus is changed from the first stage at the beginning of etching to the first stage at the end of etching.
Since the insulating film is etched while being gradually changed over three stages , the insulating film can be etched without substantially etching the etching mask, and a local thickness difference of the insulating film and a film at the time of forming the insulating film can be obtained. Even if the through-hole etching time is changed due to the thickness deviation, a through-hole having a uniform opening diameter is formed, so that there is an effect that the design of the semiconductor integrated circuit device becomes easy. In the first stage,
Notched part and part etched in the third stage
Is due to the part etched in the second stage in between.
And the inner surface is smooth
A through hole can be formed.

[Brief description of the drawings]

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

FIG. 2 is a sectional view showing a conventional manufacturing method in the order of steps.

FIG. 3 is a cross-sectional view for explaining a problem of the conventional method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Silicon substrate 2 Conductive layer 3 Interlayer insulating film 4 Silicon nitride film 5 Photoresist

Continued on the front page (58) Fields surveyed (Int.Cl. ⁶ , DB name) H01L 21/28-21/288 H01L 21/302 H01L 21/3205-21/3213 H01L 21/768

Claims (3)

(57) [Claims] A step of forming an insulating film on a semiconductor substrate, and forming an etching mask having an etching selectivity with the insulating film in a required pattern on the insulating film, and selecting the insulating film using the etching mask. An ECR etching apparatus is used for the selective etching, and RF power is used in the first stage of the initial etching.
An etching method for an insulating film, characterized in that an RF power is reduced in a second stage without applying force and an RF power is increased in a third stage at the end of etching. 2. A step of forming an insulating film on a semiconductor substrate, and forming an etching mask having an etching selectivity with the insulating film in a required pattern on the insulating film, and selecting the insulating film using the etching mask. An ECR etching apparatus is used for the selective etching, the microwave power is increased in the first stage of the etching , and the microwave power is increased in the second stage.
Microwave power, and the third
An etching method for an insulating film, wherein, in the step , etching for further reducing microwave power is performed. 3. The method for etching an insulating film according to claim 1, wherein the etching in the ECR etching apparatus uses an etching gas mainly composed of an oxygen gas and a fluoride gas.