JPS59181620A - Reactive-ion etching method - Google Patents

Abstract

PURPOSE:To improve the uniformity of etching depth by forming a recessed section to the upper surface of a lower electrode, shaping a specific angle of inclination to the base at a central section in the peripheral section of the recessed section, placing a material to be etched and etching the material. CONSTITUTION:A recessed section 21 for receiving a sample to be etched 6 is formed previously to the upper surface of a lower electrode 3. With the recessed section 17, the base 21 at a central section is flattened, a peripheral section 22 is inclined, and an angle within 90 deg. from 5 deg. to the base 21 at the central section such as approximately 30 deg. is used as the angle of inclination. A distance up to the surface of the sample from plasma is made larger than that up to the upper surface of the lower electrode 3 from plasma on an etching under the state in which the sample 6 is placed on the base 21 at the central section of the recessed section 17.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a reactive ion etching method for etching a sample using a reactive ion etching apparatus having parallel plate electrodes in the manufacturing process of large-scale integrated circuits. In particular, it relates to a method for etching materials whose etching rate is primarily rate-limited by the removal of reaction products.

[Technical background of the invention]

2. Description of the Related Art As devices become more highly integrated and operate at higher speeds, from integrated circuits (ICs) to large-scale integrated circuits (LSIs), microfabricability of devices is required. For this reason, wet etching and chemical dry etching (chemi) are used as manufacturing process technologies.
cal Dry Etching: CDE)'
1. Reactive ion etching, which allows anisotropic etching without side etching, has come to be widely used in place of isotropic etching.

Here, the principle of reactive ion etching will be briefly explained. That is, electrodes are placed facing each other in a vacuum container equipped with an exhaust system, one electrode and the inner wall of the container are all grounded, the sample to be etched is placed on the other electrode, and a reactive gas is introduced into the container. , applying high frequency power to the other electrode to turn the gas into plasma. At this time, negative self-bias occurs in the electrode to which the high frequency is applied due to the difference in mobility between electrons and ions and the difference in area between the electrode to which the high frequency is applied, the counter electrode, and the inner wall of the container. This negative self-bias is called a cathode drop voltage and is expressed as a direct current potential (dc) from the ground potential. The positive ions generated in the plasma are accelerated by the self-bias and collide perpendicularly to the surface of the etching target sample that has adsorbed the etching species, thereby promoting the reaction between the etching species and the etching target material,
Etching progresses by generating volatile substances. That is, etching requires 1, (1L) the reaction rate between the etching species and the material to be etched, Φ) the supply amount of the reactive gas, (C
) The rate is limited by the removal of etching products from the sample surface. The above (a) is called reaction rate-determining, and there are cases where the addition is intended to increase the reaction rate. The above (b) is called supply rate limiting, and a typical example is when a large number of semiconductor wafers are etched at the same time, the etching depth per wafer time (etching rate) is lower than when etching one wafer at a time. There is a loading effect. Further, the removal of the etching product (C) from the sample surface does not pose any problem because it is quickly removed if the etching product is a volatile substance with a high vapor pressure at room temperature.

[Problems with background technology]

However, if the etching product has a low vapor pressure at room temperature, etching does not proceed uniformly on the light surface of the sample, resulting in very poor etching rate uniformity within the sample surface. For example, when molybdenum silicide Mo5i2e is placed on an electrode and etched by the conventional reactive ion etching method, the uniformity of the etching rate is very poor. As a result of intensive investigation into the causes of the above-described phenomenon, the present inventors found that in etching MoSi2, the reaction products MoCl5 or Mo0Ct
It has been found that this is because the removal of x from the sample surface determines the rate of etching.

In other words, the reaction product MoCl5*Mo0Czz
Because the vapor pressure of the sample is low, these reaction products are removed relatively quickly at the sample periphery, and etching progresses from the sample periphery, and the etching depth at the sample periphery is greater than that at the sample center. It became clear that this was because the In this way, if etching is primarily rate-limited by the removal of reaction products, the uniformity of the etching rate will deteriorate if the vapor pressure of the etching products is low;
A problem arises in that productivity is significantly reduced.

[Purpose of the invention]

The present invention has been made in view of the above circumstances, and is a reactive ion etching method that can improve the uniformity of etching depth within the surface of a sample to be etched when the etching rate is mainly determined by the removal of reaction products. The present invention provides a method.

[Summary of the invention]

That is, in the present invention, a reactive gas is introduced into a vacuum container having an exhaust system, high frequency power is applied between upper and lower electrodes facing each other in the container, and a material to be etched is placed on the lower electrode. In the reactive ion etching method, a recess is provided on the upper surface of the lower electrode, and the peripheral parts of these four parts have an inclination angle of 5 degrees or more and 90 degrees or more with respect to the bottom surface of the central part. This method is characterized in that a substance to be etched is placed on the bottom surface of the central part of the substrate, and the etching rate is mainly determined by the removal of reaction products.

As a result, compared to when the sample is placed on the flat top surface of the lower electrode, reaction products are removed at a slightly slower rate around the sample, and reaction products are removed almost uniformly within the sample surface. It becomes like this.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a reactive ion etching apparatus used in the method of the present invention.

That is, 1 is a vacuum container main body made of stainless steel, for example, and an upper electrode 2 and a lower electrode 3, which constitute a parallel plate type electrode, are arranged facing each other so as to be combined with the container main body 1 to form a vacuum container. ing. In this case, the electrodes 2, 3
are insulating rings [for example, tetrafluoride resin] 4 and 5, respectively.
Therefore, it is electrically insulated from the vacuum container body 1. 6
is a sample to be etched placed on the lower electrode 3. The upper electrode 2 and the lower electrode 3 are each cooled/4' inno7
．． It is designed to be water cooled by 8. Reference numeral 9 denotes a gas inlet provided at the center of the upper electrode 2, for example. 1
0 is an exhaust pipe communicating with the side surface of the vacuum container body 1;
Connected to an external exhaust system (e.g. rotary pump, oil diffusion pump, etc.). Reference numeral 11 denotes a high frequency 'it source, and its high frequency output is applied by a changeover switch 12 to the upper electrode 2 via an impedance matching device 13 or to the lower electrode 3 via an impedance matching device 14. 15 is a change-over switch for grounding the upper electrode 2 when no high-frequency output is applied to it, and 16 is a change-over switch for grounding the lower electrode 3 when no high-frequency output is applied to it. The vacuum container body 1 is always grounded.

Further, on the upper surface of the lower electrode 2, there are four parts (spot holes) for accommodating the sample 6 to be etched, as shown in FIG.
21 is provided, and this recess 17 has a flat bottom surface 2 at the center and an inclined peripheral section 22, with an inclination margin of 1.
The angle θ is approximately 30 degrees with respect to the center bottom surface 21, for example. When the sample 6 is placed on the central bottom surface 2 of the recess 17, the distance from the plasma to the sample light surface is assumed to be longer than the distance from the plasma to the upper surface of the lower electrode during etching.

FIG. 3 shows an example of the sample 6 to be etched, in which a silicon oxide film 32 with a thickness of 1700× is formed on a semiconductor substrate, for example, a 4-inch single crystal silicon wafer 31, by thermal oxidation method, and sputtering is performed on the silicon oxide film 32. After depositing molybdenum silicide MO8i233 at 4000X by the method, an etching mask was formed using a positive resist (trade name 0FPR800: Tokyo Applied Chemical Industry Co., Ltd.) 34.

In the method of the present invention, etching is performed using the above-mentioned etching apparatus shown in FIG. 1 under, for example, the following etching conditions.

That is, chlorine (C
62) Using a mixed gas of 358 ccM and 5 secM of oxygen (02), adjust the pressure in the vacuum container to 0.4 Torr, and apply high frequency power 'f' to the lower electrode 3.
13.56 MHz, 0.3 W/cm2, and the lower electrode 2 is grounded. Note that the principle of this etching is as described above, and detailed explanation will be omitted here.

After etching for 1 minute by the above method, the resist 34 of sample 6 is peeled off with a sulfuric acid solution and Mo5t is etched.
The etching depth of 23J was measured at 20 locations on the sample surface (Fig. 4, P1 to
FIG. 5 shows the data measured in (see page 20). As can be seen from this figure, the uniformity of the etching depth within the sample plane is very good. Here, if the average etching depth is represented by ma and the standard deviation of the normal distribution is represented by σ, then 3σ/ma, which indicates the degree of variation in etching depth, is as small as 0.07.

In order to compare the effect of the above method, a sample 6 similar to that described above was placed on the flat upper surface of the lower electrode 3' without providing a recess in the lower electrode J, as shown in FIG. 6, and etched under the same etching conditions as described above. FIG. 7 shows the results obtained by performing etching and performing the same measurements as described above. As is clear from this figure, the etching depth is larger at the periphery than at the center within the sample surface, the uniformity of the etching depth is very poor, and the depth variation is as large as 0.30.

In other words, when using a lower electrode whose entire upper surface is flat, the reason why the uniformity of etching depth becomes extremely poor is that td-1Mo
In the etching of Si2, the reactive product Mo
Removal of CAs or Mo0C1z from the sample surface determines the etching rate, and MoC75s Mo0C7x
This is because etching proceeds from the sampled surface portion where these are removed relatively quickly due to the low vapor pressure of the etching.

On the other hand, as described above, in the method of the present invention, a recess is provided in the lower electrode, the periphery of the recess is sloped, and the sample is placed within the recess.

As a result, the removal of reaction products around the sample became somewhat slow, and the reaction products were removed almost uniformly within the surface of the sample.

The method of the present invention is applicable not only to MoSi2 in the above embodiment, but also to other materials in general whose rate of etching is mainly determined by the removal of reaction products. In addition, the sample is placed on the flat bottom of the recess, and the angle of inclination that the peripheral part of the recess near the sample periphery makes with respect to the flat bottom is determined by the difference in vapor pressure of the reaction product. The angle can be selected and set within a wide range, such as from about 5 degrees to 90 degrees, depending on the aspect. In addition, when etching multiple samples at the same time, it is possible to improve the uniformity of the etching depth for each sample by making the peripheral inclination angles of the recesses provided at the center and the periphery of the lower electrode different. You can also do this.

〔Effect of the invention〕

As described above, according to the reactive ion etching method of the present invention, when etching is rate-limited mainly by the removal of reaction products, the uniformity of the depth to be etched can be improved, and productivity can be improved. can contribute to improvement.

[Brief explanation of drawings]

FIG. 1 is a configuration explanatory diagram showing an example of a reactive ion etching apparatus used in the plasma etching method according to the present invention, and FIG. 2 is an enlarged view of the concave portion of the lower electrode of the apparatus shown in FIG. 3 is a sectional view showing an example of a sample placed in the recess shown in FIG. 2, and FIG.
Figure 5 is a plan view showing the etching depth measurement location after etching the sample shown in Figure 5, Figure 5 is a diagram showing the etching depth measurement results at the measurement location in Figure 4, and Figure 6 is a diagram showing a method for comparison with the method of the present invention. FIG. 7 is a side sectional view showing the lower electrode used and the mounting state of the sample, and FIG. 7 is a diagram showing the etching depth measurement results after etching the sample in the state of FIG. 6. DESCRIPTION OF SYMBOLS 1...Vacuum container main body, 2...Upper electrode, 3...Lower electrode, 6...Sample, 9...Gas inlet, 10...
・Exhaust pipe, 1...High frequency power supply, 17...Recess, 2
No...Central bottom surface, 22...Peripheral part, 31...Single crystal silicon wafer, 32...Silicon oxidation FJL
33...Molybdenum silicide, 34...Positive resist, θ...Inclination angle. Applicant's agent Patent attorney Takehiko Suzue10

Claims (3)

[Claims] (1) A reactive gas is introduced into a vacuum container equipped with an exhaust system, high-frequency power is applied between upper and lower electrodes facing each other in the container, and the material to be etched is placed on the lower electrode and etched. In the reactive ion etching method, a recess is provided on the upper surface of the lower electrode, and the peripheral part of the recess has an inclination angle of 5 degrees to 90 degrees with respect to the bottom surface of the central part, and A reactive ion etching method characterized in that etching is performed by placing a material to be etched on the bottom surface of a central portion, the etching rate of which is mainly determined by the removal of reaction products. (2) A patented reactive ion etching method characterized in that the material to be etched is formed on a laminated material made of silicon single crystal. (3) The reactive ion etching method according to claim 1 or 2, characterized in that a patterned etching mask is present on the material to be etched.