JPH0750287A - Plasma etching treatment - Google Patents

Abstract

PURPOSE:To form a hole pattern having a vertical form uniformly on the surface of a specimen, by forming magnetic field distribution wherein the value of flux density on the specimen surface is in a specified range, and the magnetic flux density on the outer periphery is higher than that of the specimen surface, and performing an etching treatment. CONSTITUTION:An inner coil 21 and an outer coil 22, which constitute a magnetic field generator 20, are arranged under a specimen stand 17, the magnetic field distribution on the specimen S surface is controlled by changing the intensity of applied magnetic field, and an etching process is performed by using reaction gas. That is, a magnetic field distribution is formed as follows: the magnetic flux density on the specimen S surface is uniform, its value is in the range of 0-50 Gauss, and the magnetic flux density on the peripheral part of the specimen S is higher than that of the specimen S surface. An SiO2 film is subjected to anisotropic etching by using fluorocarbon based gas wherein the ratio of the number of atoms is larger than or equal to 0.375. Thereby the pattern shape is uniformed, and the etching selection ratio and the etching rate can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for etching a semiconductor manufacturing process, and more particularly to a method for etching a silicon oxide film.

[0002]

2. Description of the Related Art A method of generating plasma by electron cyclotron resonance (hereinafter referred to as ECR) excitation can generate highly active plasma at a low gas pressure,
A wide range of ion energy can be selected, a large ion current can be obtained, and the ion flow has excellent directivity and uniformity. Therefore, research is being actively conducted as an indispensable process for thin film formation and etching in the production of highly integrated semiconductor devices and the like.

FIG. 4 is a sectional view schematically showing an etching apparatus as an example of a conventional microwave plasma apparatus, and 11 in the figure shows a plasma generation chamber. The peripheral wall of the plasma generation chamber 11 is configured in a double structure, a cooling water flow chamber 11a is formed inside the microwave generation port 11c, and a microwave inlet 11c sealed by a quartz glass plate 11b is formed in the center of the upper wall. A plasma extraction window 11d is formed in the center of the lower wall at a position facing the microwave introduction port 11c. The microwave inlet 11c is connected to one end of a waveguide 12 whose other end is connected to a microwave oscillator (not shown), and the plasma extraction window 11
A sample chamber 13 is arranged so as to face d. Further, an exciting coil 14 is arranged concentrically with the plasma generation chamber 11 and the waveguide 12 connected to the plasma generation chamber 11 so as to surround them.

On the other hand, a sample table 17 is disposed in the sample chamber 13 at a position facing the plasma extraction window 11d, and a sample S such as a wafer can be attached to and detached from the sample table 17 by means such as electrostatic adsorption. An exhaust port 13a is formed on the lower wall of the sample chamber 13 that is placed and connected to an exhaust device (not shown).

Further, 11g in the drawing shows a reaction gas supply system connected to the plasma generation chamber 11, 13g in the drawing shows a reaction gas inlet connected to the sample chamber 13, and 11g in the drawing.
Reference numerals h and 11i denote a cooling water supply system and a cooling water supply system.

In the thus constructed etching apparatus, after the plasma generation chamber 11 and the sample chamber 13 are set to a predetermined vacuum degree, a desired gas is supplied into the plasma generation chamber 11 through the reaction gas supply system 11g. Gas is supplied so as to obtain a pressure, a microwave is introduced into the plasma generation chamber 11 through the microwave introduction port 11c while forming a magnetic field by the excitation coil 14, and the gas is resonantly excited by using the plasma generation chamber 11 as a cavity resonator. Then, plasma is generated. The generated plasma is projected to the periphery of the sample S in the sample chamber 13 by the divergent magnetic field whose magnetic flux density decreases toward the sample chamber 13 side formed by the excitation coil 14, and the sample chamber 1
The surface of the sample S in No. 3 is etched (JP-A-57-133636).

The above-mentioned apparatus is suitable for anisotropic etching because the highly active plasma is generated in the low gas pressure region and the charged particles have a strong directivity.

However, since the plasma extracted by the divergent magnetic field spreads according to the lines of magnetic force, the distribution of the plasma density on the sample surface is high at the central portion and becomes lower toward the periphery. Further, in the peripheral portion, the lines of magnetic force are obliquely incident on the sample, and accordingly, plasma is also obliquely incident on the sample. By the way, FIG. 5 shows the radial distribution of the magnetic flux density Bz in the direction perpendicular to the sample table on the sample table 17 at this time. In FIG. 5, the horizontal axis represents the radial position (mm) from the center of the sample table, and the vertical axis represents the vertical magnetic flux density (Gauss). The magnetic flux density Bz is the sample S
The distribution has a maximum value at the center of, and decreases monotonically toward the outside of the sample S in the radial direction. FIG. 6 shows a sectional view of the etching shape in the central portion and the peripheral portion of the sample S in this magnetic field distribution. As the sample S, a Si substrate 41
A SiO ₂ film 42 was formed on the SiO ₂ film 42, a photoresist film 43 was formed on the SiO ₂ film 42, and a pattern of holes 44 was formed on the photoresist film 43. During this etching, the SiO ₂ film of the sample S is vertically etched according to this hole pattern and
It is preferable to etch at a uniform rate throughout the top. However, when the cross-sectional view of the etching shape of FIG. 6 is seen, the SiO ₂ film 42 is obliquely etched in the peripheral portion, and the etching rate is slower than that in the peripheral portion although the SiO ₂ film 42 is vertically etched in the central portion. The result is shown. That is, in the peripheral portion, the plasma obliquely enters the sample S in accordance with the oblique incidence of the lines of magnetic force, so that the etching proceeds obliquely, and in the central portion, the plasma density is higher than in the peripheral portion, so that the high-frequency energy applied to the sample stage is Considering how each ion is given, the etching rate in the central portion is lower than that in the peripheral portion because the central portion is smaller than the peripheral portion. Therefore, under the magnetic field distribution of this divergent magnetic field, it is difficult to perform etching with a good etching shape and a uniform etching rate.

Therefore, the present applicant has previously proposed the plasma processing apparatus shown in FIG. 7 in Japanese Patent Laid-Open No. 64-8624 as a measure against the above problem. FIG. 7 is an enlarged cross-sectional view of the vicinity of the sample table, and a magnetic field generator 20 is arranged below the sample table 17 on which the sample S is placed. The magnetic field generator 20 has a double-structured cylindrical shape. An outer coil 22 is arranged outside and an inner coil 21 is arranged inside the yoke 2.
It is arranged in a form surrounded by 3.

The above-mentioned outer coil 22 is the excitation coil 14
A magnetic field is formed in the same direction as the magnetic line of force of the divergent magnetic field from (FIG. 4), and the inner coil 21 forms a magnetic field in the opposite direction to the outer coil 22.

The inner coil 21 can reduce the magnetic flux density Bz in the direction perpendicular to the sample S and expand the plasma in the radial direction of the sample. However, this alone does not limit the spread, and the plasma spreads too much, the plasma density decreases, and the etching processing speed decreases. Therefore, when a magnetic field having the same direction as the divergent magnetic field from the exciting coil 14 is formed by the outer coil 22, a strong magnetic field is formed above the yoke 23. The plasma expanded by the magnetic field formed by the inner coil 21 is
The strong magnetic field prevents the magnetic field from spreading outward, is confined in the inner region where the magnetic field is weak, and there is no constraint of the plasma due to the strong magnetic field, so that the region is made uniform. Therefore, the plasma distribution can be controlled by changing the magnitudes of the magnetic fields generated by the outer coil 22 and the inner coil 21, respectively.

[0012]

FIG. 8 shows an example of the magnetic flux density Bz in the vertical direction on the sample stage 17 with respect to the radial direction (r direction) of the sample stage 17 in the above-mentioned apparatus. Further, FIG. 9 shows a cross-sectional view showing the etching shapes in the sample central portion and the sample outer peripheral portion at this time. As shown in FIG.
It can be seen that the plasma density in the central portion of the sample S is low. When the anisotropic etching treatment of the surface of the SiO ₂ film 42 is performed, the plasma density becomes small in the central portion of the sample S, and as shown in FIG.
While the desired etching of the O ₂ film 42 is obtained, in the outer peripheral portion of the sample S, the magnetic force lines of the divergent magnetic field are inclined,
Therefore, the plasma obliquely enters the outer periphery of the sample S, the SiO ₂ film 42 is etched into an inclined pattern shape, and the plasma density further increases, so that the ion potential decreases due to the decrease in the bias potential per ion. However, there has been a problem that micro-loading occurs because the amount of the polymerized film deposited by the carbon radicals generated by the dissociation of the fluorocarbon reaction gas increases.

Alternatively, as shown in FIG. 10, depending on the location of the sample S, the plasma density decreases, so that the ion energy increases due to the increase of the bias potential and the sputtering effect becomes stronger, and the hole 4 of the photoresist 43 is increased.
There is a problem that the side wall portion 47 of 4 is etched and the resist recedes, and as a result, a hole 48 larger than the normal hole 44 is etched.

The present invention has been made in view of the above problems, and provides a plasma processing method capable of forming a hole pattern formed by anisotropic etching in a vertical shape and in a uniform state on a sample surface. The purpose is to do.

[0015]

In order to achieve the above object, a plasma etching method according to the present invention applies a high frequency electric field by a microwave and a magnetic field formed by an exciting coil to a gas introduced in a plasma generating chamber. In the plasma etching method, the plasma is generated by introducing the plasma into the sample chamber communicating with the plasma generation chamber by the magnetic field, and the sample placed in the sample chamber is etched. By the generator
The magnetic flux density on the surface of the sample is uniform and its value is 0 to
A magnetic field distribution having a value in a range of 50 gauss and having a higher magnetic flux density outside the peripheral portion of the sample than on the sample surface is subjected to etching treatment. To do.

[0016]

[Function] Even if the magnetic field distribution on the sample table is controlled by the double magnetic coil under the sample table to make the magnetic field distribution uniform under the constant divergent magnetic field by the exciting coil, the magnitude of the magnetic field is large. Depending on the thickness, the distribution of the pattern shape after anisotropic etching of the silicon oxide film changes.

When the magnetic flux density in the direction perpendicular to the sample is 0 Gauss or less, the cyclotron radius of the charged particles generated by gas dissociation becomes long, so that the plasma near the center of the sample spreads in the radial direction of the sample. Since the plasma density becomes small in the center of the sample, the ion energy increases due to the increase in bias potential, and the sputtering effect becomes stronger. As a result, the sidewalls of the photoresist pattern are sputtered at an angle, the resist recedes, and the pattern size increases. On the contrary, since the plasma density becomes higher in the peripheral area of the sample, the ion energy decreases due to the decrease of the bias potential, and the deposition amount of the polymer film due to the carbon-based radicals generated by the dissociation of the fluorocarbon-based reaction gas increases to slow the etching rate. Become.

On the other hand, when the magnetic flux density in the direction perpendicular to the sample is set to a uniform magnetic field of 50 Gauss or more on the sample, the plasma density distribution becomes dense in the center of the sample and the pattern shape distribution is 0 Gauss or less. It has the opposite distribution.

Further, when a uniform magnetic field is formed within the range of 0 to 50 Gauss on the sample, the plasma uniformly spreads in the sample plane, and thus a vertical hole pattern is uniformly formed in the sample plane. It will be.

According to the above-mentioned method of the present invention, the magnetic flux density on the sample surface is set so that the magnetic flux density on the outside of the sample is higher than the magnetic flux density on the sample surface, and the magnetic flux on the sample surface is set. Density 0-50
Since Gauss is set, the hole pattern formed by anisotropic etching has a vertical shape, and the uniformity of the pattern shape on the sample surface is improved.

When the surface of the SiO ₂ film is subjected to the plasma etching treatment, it is desirable that the etching rate of the SiO ₂ film is high and the etching selection ratio with respect to the photoresist film is large. When a fluorocarbon-based gas is used as the reaction gas, the reaction gas is dissociated in plasma, and the dissociated carbon-based radical species are deposited as a polymerized film on the sample surface. This polymer film has the effect of reducing the etching rate of the resist more than the amount of decrease of the etching rate of the SiO ₂ film, so that the above selection ratio becomes large.

A fluorocarbon-based gas having a carbon to fluorine atomic ratio of 0.375 or more, that is, C
_{The 3} F ₈ gas or C ₄ F ₈ gas is suitable for anisotropic etching of a SiO ₂ film because it has a higher etching rate and a larger selection ratio than those of gases of less than that.

Therefore, the double magnetic coil which is the magnetic field generator shown in FIG. 7 is arranged under the sample stage, and the magnetic field distribution on the sample surface is controlled so as to satisfy the above-mentioned conditions, and the reaction gas By anisotropically etching the SiO ₂ film using the same, the pattern shape can be made uniform, the selection ratio and the etching rate can be improved.

[0024]

Embodiments of the plasma processing method according to the present invention will be described below with reference to the drawings. The plasma processing apparatus used is the same as the conventional one shown in FIG. 7, and the description of the apparatus will be omitted. First, when anisotropic etching of a SiO ₂ film is performed, when C ₃ F ₈ or C ₄ F ₈ gas is used as a reaction gas and the magnetic field distribution on the sample stage is changed, the shape change of the hole and its in-plane We observed changes in distribution and searched for appropriate conditions.

FIGS. 1A to 1F show the sample table 17 when the magnitude of the magnetic flux density Bz on the surface of the sample S is changed.
2A to 2F are magnetic flux density distribution diagrams in the radial direction (r direction) of FIGS. 2A to 2F corresponding to the magnetic flux density distributions of FIGS. 1A to 1F. It is sectional drawing which showed the etching shape in the outer peripheral part. At this time, the divergent magnetic flux from the exciting coil is made constant, and the magnitude of the magnetic field applied to the inner coil 21 and the outer coil 22 is changed to change the magnitude of the sample stand 17
The magnetic flux density Bz above was set uniformly within the surface of the sample S. The magnetic flux density Bz is set to have a maximum value on the yoke 23 so that the magnetic flux density Bz outside the peripheral edge of the sample S is higher than the magnetic flux density Bz in the surface of the sample S. The set value was 80 to 200 gauss.

As shown in FIGS. 1 (a) and 2 (a), when the magnetic flux density Bz = 100 Gauss in the sample S, the etching rate is lowered in the central portion of the sample S. It is considered that this is because the cyclotron radius of the charged particles generated by the dissociation of the gas is shortened and the plasma density is increased in the vicinity of the center of the sample S, and as a result, the deposition amount of the fluorocarbon polymer film is increased. Further, in the outer peripheral portion of the sample, since the plasma density is small, the ion energy is increased, the sputtering effect is increased, and the hole 4
The side wall portion 47 of the photoresist film 43 of No. 4 is cut obliquely and etched larger than the desired hole shape.

As shown in FIGS. 1B and 2B, when the magnetic flux density Bz = 75 Gauss in the sample S,
In the central portion of the sample S, the decrease of the etching rate is smaller than that in the case of Bz = 100 gauss, and in the outer peripheral portion of the sample S, the SiO ₂ film 42 is vertically etched.

Further, FIGS. 1 (c) to 1 (e) and 2 (c).
~ (E), the magnetic flux density Bz on the surface of the sample S
Of 50 to 0 Gauss, the SiO ₂ film 42 was vertically etched both in the central portion of the sample S and the outer peripheral portion of the sample S, and the uniformity within the surface of the sample S was good.

As shown in FIGS. 1 (f) and 2 (f), when the magnetic flux density Bz = -25 Gauss in the sample S, the plasma density is small in the central portion of the sample S, so that the ion energy increases. The sputtering effect was increased, the sidewall portion 47 of the photoresist film 43 of the hole 44 was obliquely cut, and etching was performed to a size larger than the desired shape of the hole 44, and the etching rate was lowered in the outer peripheral portion of the sample S.

FIG. 3 is a graph showing the relationship between the etching rate of the SiO ₂ film and the resist selectivity with respect to the resist when the reactive gas species are different. Normally, the range of high etching rate is 4
The range is 00 nm / min or more, and the range in which the selectivity to resist is high is 5 or more. The reaction gas that fills both regions, that is, the hatched region in the figure, is C ₃ F ₈
And C ₄ F ₈ . From this, it can be said that a fluorocarbon-based gas having a carbon atom number ratio to fluorine of 0.375 or more is a gas that can obtain a high etching rate and a high selection ratio.

As is clear from the above description, in the plasma processing method according to the embodiment, when the SiO ₂ film 42 is etched, it has a maximum value at the outer peripheral portion of the sample S, that is, on the yoke 23. By fixing the magnetic flux density of 80 to 200 gausses and setting the magnetic flux density on the sample S within the range of 0 to 50 gausses, vertical etching can be performed along the holes 44 of the photoresist film 43. . Further, by using a fluorocarbon-based gas having a carbon atom number ratio to fluorine of 0.375 or more as the reaction gas at this time, a high etching rate and a high selection ratio can be obtained.

[0032]

As described above in detail, in the plasma processing method according to the present invention, the magnetic field density is set so that the magnetic flux density outside the sample is higher than the magnetic flux density on the sample surface. At the same time, since the magnetic flux density on the surface of the sample is set to 0 to 50 gauss, the plasma can be uniformly spread in the surface of the sample and can be etched into a vertical shape, and the uniformity can be improved in the surface of the sample. You can

In the above plasma processing method, when a fluorocarbon-based gas having a carbon to fluorine atomic ratio of 0.375 or more is used as the reaction gas,
The etching rate is high and the selection ratio can be high.

[Brief description of drawings]

1A to 1F are radial directions (r direction) of a sample table.
5 is a diagram showing a distribution of magnetic flux density Bz in the vertical direction on the sample table in FIG.

2A to 2F are schematic cross-sectional views showing etching shapes in a sample central portion and a sample peripheral portion corresponding to FIGS. 1A to 1F.

FIG. 3 is a graph showing a relationship between an etching rate according to gas and an etching selection ratio with respect to a photoresist.

FIG. 4 is a schematic cross-sectional view showing a conventional plasma device.

FIG. 5 is a diagram showing the distribution of the magnetic flux density Bz in the vertical direction on the sample stage in the radial direction (r direction) of the conventional sample stage.

FIG. 6 is a schematic cross-sectional view showing etching shapes of a sample central portion and a sample peripheral portion when an etching process is performed using a conventional apparatus.

FIG. 7 is an enlarged cross-sectional view showing a main part of the improved plasma device.

FIG. 8 is a diagram showing the distribution of the magnetic flux density Bz in the vertical direction on the sample table in the radial direction (r direction) of the sample table when a double coil is arranged below the sample table.

FIG. 9 is a schematic cross-sectional view showing etching shapes of a sample central portion and a sample peripheral portion when a double coil is arranged below the sample table and an etching process is performed.

FIG. 10 is a schematic cross-sectional view showing an etching shape of a sample when a double coil is arranged below the sample table and an etching process is performed.

[Explanation of symbols]

 11 Plasma Generation Chamber 13 Sample Chamber 14 Excitation Coil 20 Magnetic Field Generator

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[Procedure amendment]

[Submission date] February 23, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Brief description of the drawing

[Correction method] Change

[Correction content]

[Brief description of drawings]

[1 in FIG. 1] and

1 (a) to 1 (f) are diagrams showing the distribution of the magnetic flux density Bz in the vertical direction on the sample table in the radial direction (r direction) of the sample table.

[1 of FIG. 2] and

2 (a) to 2 (f) are schematic cross-sectional views showing etching shapes in a sample central portion and a sample peripheral portion corresponding to FIGS. 1 (a) to 1 (f).

FIG. 3 is a graph showing a relationship between an etching rate according to gas and an etching selection ratio with respect to a photoresist.

FIG. 4 is a schematic cross-sectional view showing a conventional plasma device.

FIG. 5 is a diagram showing the distribution of the magnetic flux density Bz in the vertical direction on the sample stage in the radial direction (r direction) of the conventional sample stage.

FIG. 6 is a schematic cross-sectional view showing etching shapes of a sample central portion and a sample peripheral portion when an etching process is performed using a conventional apparatus.

FIG. 7 is an enlarged cross-sectional view showing a main part of the improved plasma device.

FIG. 8 is a diagram showing the distribution of the magnetic flux density Bz in the vertical direction on the sample table in the radial direction (r direction) of the sample table when a double coil is arranged below the sample table.

FIG. 9 is a schematic cross-sectional view showing etching shapes of a sample central portion and a sample peripheral portion when a double coil is arranged below the sample table and an etching process is performed.

FIG. 10 is a schematic cross-sectional view showing an etching shape of a sample when a double coil is arranged below the sample table and an etching process is performed.

[Explanation of Codes] 11 Plasma Generation Chamber 13 Sample Chamber 14 Excitation Coil 20 Magnetic Field Generator

[Procedure Amendment 2]

[Document name to be corrected] Drawing

[Correction target item name] All drawings

[Correction method] Change

[Correction content]

[Fig. 06]

[Fig. 09]

[1 of FIG. 01]

[2 of FIG. 01]

FIG. 03

[Fig. 04]

[No. 1 in FIG. 02]

[FIG. 02-2]

[Fig. 05]

[Fig. 07]

[Fig. 08]

[Figure 10]

Claims (1)

[Claims] 1. In the plasma generation chamber, a high-frequency electric field generated by microwaves and a magnetic field formed by an exciting coil act on the introduced gas to generate plasma, and the plasma is communicated with the plasma generation chamber by the magnetic field. In a plasma etching treatment method in which a sample placed in the sample chamber is subjected to an etching treatment, the magnetic flux density on the surface of the sample is uniform and its value is 0 to 50 by a magnetic field generator. A plasma etching method, wherein a magnetic field distribution having a Gaussian range that is higher than the magnetic flux density on the surface of the sample is higher than the magnetic flux density on the surface of the sample, and etching is performed.