JPS6341987B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a dry etching method, and particularly to an improvement in a method for chemically dry etching a silicon nitride film, a polycrystalline silicon film, etc. deposited on a semiconductor substrate.

[Technical background of the invention and its problems]

In the manufacture of semiconductor integrated circuits, a process is performed in which various films are deposited on a semiconductor substrate such as silicon, and then the films are selectively etched using a resist pattern formed by photolithography as a mask. . As an etching method in this process, a wet etching method has conventionally been adopted, but it not only involves dangerous work but also poses problems such as the generation of pollution due to the disposal of the etching solution.

For these reasons, there has recently been a shift toward dry etching methods that utilize gas reactions. Various dry etching methods are known, among which the chemical dry etching method (CDE method) has high selectivity in isotropic shapes.
This CDE method excites a reactive gas with microwave plasma, transports the generated active species to a reaction chamber separated from the plasma chamber, and reacts with the material to be etched in the reaction chamber to perform etching.

However, when attempting to process multiple materials to be etched (for example, large-diameter wafers) at once in a reaction chamber with a limited volume using the above-mentioned CDE method, the wafer position is restricted, and in particular, the etching process within the wafer plane is limited. There was a problem that uniformity deteriorated. . The main reason for this is that as the etching area increases, the etching reaction becomes rate-limiting due to the loading effect, and active species are consumed around the wafer and do not reach the center of the wafer.

[Purpose of the invention]

The present invention aims to provide a dry etching method that improves the uniformity of etching within the surface of a material to be etched as well as between materials to be etched.

[Summary of the Invention] The present invention is a dry etching method in which a reactive gas is excited by microwave plasma, the generated active species are transported to a reaction chamber separated from a plasma chamber, and reacted with a material to be etched. In,
The method is characterized in that He is added to the reactive gas. According to the present invention, by adding He to the reactive gas and increasing the total flow rate of the gas containing active species, the active species can be uniformly supplied over the entire surface of the material to be etched, and as a result, Able to perform uniform etching.

[Embodiments of the invention]

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a sectional view of an etching apparatus used in the CDE of this embodiment, and FIG. 2 is a sectional view of a main part of a cassette loaded into the vacuum chamber of FIG. 1. Reference numeral 1 in the figure indicates a vacuum chamber, and a support base 2 is rotatably disposed at the center of the chamber 1, which is pivotally attached to a shaft 2 that penetrates from the bottom surface of the chamber 1. Chamber 1 of the shaft 2
A bearing 4 is provided at a portion located outside the shaft 2, and the lower end of the shaft 2 is pivotally connected to a drive shaft 6 of a motor 5 via a belt 7. Further, a cassette 8 shown in FIG. 2 is placed on the support stand 3.
The cassette 8 has an open side on one side and support plates on three sides, and a plurality of grooves 9 are formed in the vertical direction on the inner side of each support plate. In these grooves 9, aluminum shielding plates 10 are installed every other row. A gas introduction pipe 11 for introducing a gas containing active species is provided on the left side wall of the chamber 1, and a gas exhaust pipe 12 is provided on the right side wall of the chamber 1. These gas introduction pipe 11 and exhaust pipe 1
Near the entrance of the second chamber 1, first dispersion plates 13, 13 each having a large number of slits are arranged. Further, second dispersion plates 14, 14 each having a large number of slits are disposed between the gas introduction pipe 11 and the support stand 3, and between the exhaust pipe 12 and the support stand 3. There is.

Next, dry etching of a polycrystalline silicon film on a wafer using the apparatus shown in FIGS. 1 and 2 will be described.

First, a single crystal silicon wafer 2 with a diameter of 6 inches
1 is thermally oxidized to form a silicon oxide film 22 with a thickness of about 200 Å, and then the oxide film 2 is further removed by CVD.
After depositing an impurity-free polycrystalline silicon film 23 with a thickness of about 4000 Å on the polycrystalline silicon film 23, a resist pattern 24 was formed on the polycrystalline silicon film 23 by photolithography (as shown in FIG. 3).

Next, 25 wafers 21 shown in FIG. 3 are inserted horizontally into the groove 9 between the shielding plates 10 of the cassette 8 as shown in FIG. did. Next, CF ₄ , O ₂ and N ₂ were added at 100 sccm each into a plasma chamber (not shown).
In addition to supplying He under conditions of 50sccm and 50sccm,
is supplied at a predetermined ratio to the CF ₄ and O ₂ ,
The gas was excited by 2.45 GHz microwave. Subsequently, the active species diluted with He is introduced into the vacuum chamber 1 at a pressure of 20 Pa through the gas introduction pipe 11 through the exhaust pipe 12, and the cassette 8 on the support base 3 is slowly rotated by the motor 5. Then, the exposed polycrystalline silicon film 23 on the plurality of wafers 21 placed in the cassette 8 was subjected to chemical dry etching.

After the chemical dry etching according to the above embodiment, the cassette 8 was taken out from the vacuum chamber 1, the 25 wafers 21 placed in the cassette 8 were taken out, and the He
When the uniformity of etching of the polycrystalline silicon film was investigated with respect to the amount of He added (CF ₄ +O ₂ ), a characteristic line shown at A in FIG. 4 was obtained. The uniformity of etching is determined by determining the maximum value (Max) and minimum value (Min) of etching on 25 wafers taken out from cassette 8, and calculating the etching uniformity by [(Max-Min)/(Max+
Min)] × 100 (%). Further, when the etching rate of the polycrystalline silicon film was investigated with respect to the amount of He added, a characteristic line shown at A in FIG. 5 was obtained. As is clear from FIG. 4, etching uniformity within the wafer surface and between wafers can be improved by performing chemical dry etching using active species containing 100% or more He. On the other hand, regarding the upper limit of the amount of He added, as shown in Figure 5, as the amount of He added increases, the etching rate becomes less than 250 Å/min.
It is desirable that the amount added be 400% or less.

In addition, chemical dry etching was performed on a polycrystalline silicon film doped with an impurity (for example, phosphorus) instead of a polycrystalline silicon film with no impurity added, under the same conditions as in the example. When we investigated the etching uniformity of the film and the etching rate of the phosphorus-doped polycrystalline silicon film with respect to the amount of He added, we found that:
Characteristic lines shown in B in FIG. 4 and B in FIG. 5 were obtained.
From these Figures 4 and 5, when an impurity-doped polycrystalline silicon film is used as the material to be etched, the lower limit of He is set to 250 from the viewpoint of uniformity of etching.
%, and its upper limit from the etching rate point of view.
It turns out that it is desirable to set it to 400%.

As shown in the above embodiment, when etching is performed with a plurality of wafers 21 placed in the cassette 8, an aluminum shielding plate 10 is placed between the wafers 21.
By arranging the wafers 21, it is possible to prevent vertically adjacent wafers 21 from being mutually heated by the radiant heat of infrared rays emitted from the wafers 21, and to prevent non-uniform etching due to an increase in the temperature of the wafers. . As a result, a plurality of wafers can be etched at once, resulting in a marked improvement in productivity.

〔Effect of the invention〕

As detailed above, according to the present invention, by adding He to the reactive gas and increasing the total flow rate of the gas containing active species, the active species can be distributed uniformly over the entire surface of the material to be etched. Therefore, it is possible to provide a dry etching method that can provide a uniform etching process and achieve etching uniformity.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing one form of etching apparatus used in an embodiment of the present invention, FIG. 2 is a cross-sectional view of a main part of a cassette loaded into the vacuum chamber of FIG. 1, and FIG. 4 is a cross-sectional view showing the state of a wafer used in the example; FIG. 4 is a characteristic diagram showing the etching uniformity of an impurity-free polycrystalline silicon film and an impurity-doped polycrystalline silicon film with respect to the amount of He added;
FIG. 5 is a characteristic diagram showing the etching rate of an impurity-free polycrystalline silicon film and an impurity-doped polycrystalline silicon film with respect to the amount of He added. 1... Vacuum chamber, 3... Support stand, 5... Motor,
8...Cassette, 10...Aluminum shielding plate,
DESCRIPTION OF SYMBOLS 11... Gas introduction pipe, 12... Exhaust pipe, 21... Wafer, 22... Silicon oxide film, 23... Impurity-free polycrystalline silicon film, 24... Resist pattern.

Claims (1)

[Scope of Claims] 1. A method of dry etching by exciting a reactive gas with microwave plasma, transporting the generated active species to a reaction chamber separate from the plasma chamber, and reacting with the material to be etched, A dry etching method characterized in that He is added to the reactive gas. 2 Mixed gas of CF ₄ and O ₂ as reactive gas or
The dry etching method according to claim 1, characterized in that a mixed gas of CF ₄ , O ₂ and N ₂ is used. 3. The dry etching method according to claim 1, wherein the material to be etched is a wafer, and the dry etching is performed with a plurality of wafers arranged in multiple stages in a reaction chamber.