JPH0551173B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a microwave plasma processing apparatus,
In particular, the present invention relates to a microwave plasma processing apparatus suitable for etching and deposition of semiconductor substrates and the like.

[Conventional technology]

As described in Japanese Patent Application Laid-Open No. 59-103340, a conventional device includes a magnetron at the other end of a waveguide attached around a discharge tube, and a reflective disk or reflective cylinder at the opening of the discharge tube. was installed, and the microwaves from the magnetron were reflected by a reflecting disk or cylinder to efficiently generate plasma within the discharge tube.

[Problem that the invention seeks to solve]

The above-mentioned conventional technology does not take into account the positional relationship between the reflective end and the discharge tube, nor the shape of the discharge tube or the reflective end, resulting in problems in terms of plasma generation efficiency and uniformity of processing speed of the object to be processed. .

In terms of plasma generation efficiency, it was found that the plasma generation efficiency of the incident wave injected into the discharge tube was low, with reflected waves accounting for more than 50% of the incident wave. For this reason, as described in JP-A-59-103340, the microwave power injected into the discharge tube is reflected by a reflecting disk or cylinder, and the reciprocating microwave power is effectively used to generate a plasma. Although the plasma generation efficiency can be improved, it has been found that the plasma generation efficiency varies greatly depending on the distance from the discharge tube to the reflective end, that is, the passage distance of the microwave power injected into the discharge tube.

Regarding the uniformity of the processing speed of the object to be processed, if the object to be processed is etched by generating plasma in a conventional hemispherical discharge tube, the etching rate will be non-uniform. This is because strong plasma is generated along the spherical surface of the discharge tube, and by the time the active particles created in the plasma generation section reach the object to be processed, they mainly lose energy through collisions with neutral particles. It is thought that the number of active particles decreases rapidly as the distance between the object to be processed and the plasma generating section increases along the spherical surface.

SUMMARY OF THE INVENTION An object of the present invention is to provide a microwave plasma processing apparatus that can process an object quickly and uniformly.

[Means for solving problems]

The present invention includes a microwave generation source that generates microwaves, a waveguide that guides the microwaves, and a discharge that transmits the microwaves guided through the waveguide and generates plasma by the transmitted microwaves. a processing chamber having a tube, a sample stand provided below the discharge tube, and a processing chamber provided between the discharge tube and the sample stand, which reflects microwaves that have passed through the discharge tube and arrived at the discharge tube side. A reflective end is provided, and the reflective end is further provided with a large number of active particle passage holes arranged so that active particles in the plasma are uniformly emitted within the processing chamber.

[Effect]

Since the reflective end reflects microwaves, the plasma generation efficiency is improved, and the active particle passage hole through which the active particles in the plasma pass is formed so as to correspond to the shape of the discharge tube, for example, as shown in FIG. Since it is provided at the reflective end, active particles are uniformly discharged into the processing chamber through the passage hole.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 to 6.

FIG. 1 shows a microwave plasma processing apparatus.

A reflecting end 10 having a plurality of small diameter holes is attached to the lower opening of the circular waveguide 7, and further,
A processing chamber 11 is provided in which an object to be processed, in this case a wafer 12, is placed and a sample stage 13 parallel to the reflective end 10 is disposed therein. A heater 14 is provided at the lower part of the sample stage 13 and indirectly heats the wafer 12.

A discharge tube 6 having a concave surface parallel to the sample stage 13 is attached to the upper opening of the circular waveguide 7, and a step conversion device is installed to efficiently convert the microwave transmission mode from rectangular to circular. Vessel 5
A rectangular waveguide 2 is provided via. A magnetron 1, which is a microwave generation source, is attached to the upper end of the waveguide 2. 3 is an isolator for absorbing reflected waves returning within the rectangular waveguide 2;
is a stub-type matching device that performs impedance matching of a load to eliminate reflection of microwaves transmitted through the rectangular waveguide 2.

In this case, the plasma generation chamber includes a circular waveguide 7,
It is surrounded by a reflective end 10 and a discharge tube 6. 9 is a cooling channel for cooling the circular waveguide 7, and 8 is a processing gas inlet for supplying processing gas into the plasma generation chamber. An exhaust device (not shown) is connected to the lower part of the processing chamber 11, and the processing chamber 11 and the plasma generation chamber are evacuated to a predetermined pressure. 15 is a cooling gas inlet for introducing cooling gas for cooling the discharge tube 6.

In this case, the magnetron 1 has a frequency of 2.45 GHz, the rectangular waveguide 2 has a standard size that can transmit TE ₁₀ mode, and the circular waveguide 7 has a size of 113 mm that does not cut off microwaves (for example, TE ₁₁ mode). ), and the discharge tube 6 that allows microwaves to pass through and forms the plasma generation chamber is made of quartz (other materials such as alumina can also be used). . Also,
Discharge tube 6 and reflective end 10 forming a plasma generation chamber
The distance between the two is the microwave internal wavelength λg (156.7mm)
The length of the cylindrical portion of the discharge tube 6 is also approximately λg/4 (40 mm).
The hole in the reflective end 10 has a diameter of 10 mm that can cut and reflect microwaves (for example, 72 mm in the case of TE ₁₁ mode).
It is fine if it is less than mm. ).

In the above configuration, the wafer 12 on which photoresist is to be ashed is placed on the sample stage 13, and 200 _SCCM of O ₂ gas is introduced into the circular waveguide 7 as a processing gas, and the pressure is maintained at 1 Torr, and the wafer 12 is heated at 700 W. A microwave is applied and impedance matching of the load is performed using the stub type matching device 4, and the plasma is supplied to the plasma generation chamber.
When O ₂ gas plasma is generated, as shown in the figure, plasma is generated near the inner surface of the discharge tube 6, and as shown in FIG. Ashing processing was performed.

This is because the surface of the discharge tube 6 has approximately the same area as the sample stage 13 and is parallel to it, that is, parallel to the entire surface of the wafer 12. When the active particles exit into the processing chamber 11 through the hole at the reflective end, they mainly collide with neutral particles in the plasma generated at the same time in the plasma generation chamber, and lose energy and become inert particles. However, since the distance for the active particles to reach the wafer 12 is the same over the entire surface of the wafer 12, it is thought that the number of active particles reaching the wafer 12 is almost uniform and the etching rate becomes uniform.

In order to confirm this, photoresist was ashed using the apparatus shown in FIG. In this figure, the same reference numerals as in FIG. 1 indicate the same members, and the difference between this figure and FIG. A circular waveguide 7a with a parallel plate-shaped discharge tube 6a and a circular waveguide 7 of different height is used.

Using the apparatus configured as described above, 200 _SCCM of O ₂ gas is introduced into the circular waveguide 7a, and while the pressure is maintained at 1 Torr, a 500 W microwave is applied to the discharge tube 6.
As a result of etching the wafer 12 by changing the distance l between a and the wafer 12, it was found that the etching efficiency rapidly decreased as the distance l increased, as shown in FIG. Further, when an approximate formula was obtained from this experiment, it was found that it is expressed by the following formula: y=y ₀ ·e−(0.02 to 0.06)(x−x ₀ ) (1). Note that here, y is the amount of etching at distance x, and _y0 is the amount of etching at distance _x0 .

In addition, the high etching rate was obtained because
As shown in FIG. 5, by setting the distance between the discharge tube 6 and the reflection end 10 to about 1/4 of the tube wavelength λg of the microwave, the incident microwave and the reflection end This is considered to be because the electrolytic strength _Ex in the vicinity of the inner surface of the discharge tube 6 becomes maximum due to the microwaves opposed in 10, and the plasma generation efficiency improves.

In order to confirm this, the distance L _d between the discharge tube 6 and the reflective end 10 shown in FIG.
When I measured P _r , as shown in Figure 6,
When the distance L _d is 1/4 of the microwave tube wavelength λg, that is, 40 mm, the reflected power P _r reaches its minimum,
It can be seen that the reflected power P _r increases when L _d is 40 mm or less. In other words, it can be seen that when the distance L _d is less than 1/4 of the tube wavelength λg of the microwave, the reflected power is large and does not effectively contribute to plasma generation. Furthermore, this tendency becomes more noticeable as the input power P _f becomes larger, and tends to be alleviated as the input power P _f becomes smaller.

Further, in this case, the efficiency of plasma generation reached its maximum when the distance L _d was 40 mm, and it was not possible to generate plasma when L _d was 10 mm.

Note that the plasma generation efficiency is maximum at λg/4 or more, but as the distance L _d becomes shorter, the distance to the wafer also becomes shorter, which increases the probability that the number of remaining active particles will increase. The distance L _d is λg/8 or more, in other words, λg/8 to λg/
4 is optimal. However, if the wafer can be brought close to the discharge tube, a high etching rate can be obtained even at λg/4 or more.

As described above, according to this embodiment, by setting the distance between the discharge tube 6 and the reflective end 10 to λg/8 or more, efficient plasma generation can be obtained, and the distance between the reflective end 10 and the wafer 10 is By providing the surfaces parallel to each other, uniform ashing processing can be performed over the entire surface of the wafer 12.
This has the effect that the wafer 12 can be processed quickly and uniformly.

Next, another embodiment of the present invention will be described with reference to FIGS. 7 to 9.

In FIG. 7, the same reference numerals as in FIG. 1 indicate the same members, and the difference between this figure and FIG. 1 is that the discharge tube 6 and the wafer 12 are shaped like a hemisphere and move away from each other as the distance from the wafer 12 increases outward from the center of the wafer 12. Discharge tube 6
8, and the reflective end 10 is made into a reflective end 10a having a plurality of holes that become larger from the center toward the outside, as shown in FIG.

Since the shape of the discharge tube 6b is hemispherical, the aperture ratio of the hole in the reflective end 10a is such that the distance to the wafer 12 is 50 mm different between the central lower end and the peripheral portion of the discharge tube 6b. Since the amount of active particles reaching the wafer 12 is not uniform over the entire surface of the wafer 12, the amount of etching in each part of the wafer 12 was predicted using equation (1) above, and the aperture ratio was changed accordingly. In this case, the aperture ratio at the periphery of the reflective end 10a is approximately 10 times that at the center.

When the wafer 12 was ashed using the apparatus having the above configuration under the same conditions as the apparatus shown in FIG. 1, as shown in FIG. Can be ashed at a rate.

FIG. 9A shows the case where the reflecting end 10a is ashed using the apparatus shown in FIG. 7 with the hole size uniform as in the case of the apparatus shown in FIG. In this case, it is clearly seen that the distance between the discharge tube 6b and the wafer 12 increases from the center toward the outside, and the etching rate also decreases.

As described above, according to the book and other embodiments, even if the distances from the discharge tubes 6b from the wafer 12 are not equal, the aperture ratio of the reflective end 10a can be adjusted from the discharge tube 6b to the wafer 12.
By changing the distance to wafer 1
Since the amount of active particles reaching the wafer 12 can be made almost uniform over the entire surface of the wafer 12, the wafer can be processed uniformly as in the previous embodiment. In addition, the hemispherical lower end of the discharge tube 6b and the reflective end 1
By setting the distance from 0a to λg/8 or more, efficient plasma generation can be performed as in the previous embodiment, and the wafer processing speed can be increased.

In this embodiment, a downwardly convex discharge tube is used, but an upwardly convex discharge tube may also be used. However, this is disadvantageous because the distance between the wafer and the inner surface of the discharge tube becomes long.

Furthermore, the reason why the length of the cylindrical portion of the discharge tube 6 in FIG. However, unnecessarily increasing the length of the cylindrical part in order to increase the area will make the device larger and increase the distance from the inner surface of the discharge tube (plasma generation part) to the wafer, which will actually reduce the effectiveness. becomes smaller.

Furthermore, although this embodiment has been described in the case of etching a wafer, it can also be applied to the case where a deposition is generated on a wafer using plasma.

〔Effect of the invention〕

According to the present invention, the distance between the discharge tube and the reflection end is set to 1/8 or more of the tube wavelength of the microwave, and the equalizing means is provided to uniformize the amount of active particles released into the processing chamber. This has the effect that the processed material can be processed quickly and uniformly.

[Brief explanation of the drawing]

Fig. 1 is a longitudinal cross-sectional view showing a microwave plasma processing apparatus which is an embodiment of the present invention, Fig. 2 is a view showing the etching state by the apparatus shown in Fig. 1, and Fig. 3 is a longitudinal cross-sectional view of the apparatus used in the experiment. Figure 4 is a diagram showing the experimental results using the apparatus shown in Figure 3, Figure 5 is a diagram showing the microwave standing wave electric field between the discharge tube and the reflecting end, and Figure 6 is a diagram showing the results of the experiment using the apparatus shown in Figure 3. A diagram showing the relationship between the distance to the reflection end and the reflected power of microwaves, FIG. 7 is a longitudinal cross-sectional view showing a microwave plasma processing apparatus according to another embodiment of the present invention, and FIG. FIG. 9 is a plan view of the reflective end viewed from the direction A, and is a diagram showing the etching state when the aperture ratio of the reflective end is made the same and when the aperture ratio is changed by the apparatus of FIG. 7. 1... Magnetron, 2... Rectangular waveguide, 6...
...Discharge tube, 7...Circular waveguide, 10...Reflection end,
11...processing chamber, 13...sample stand.

Claims (1)

[Claims] 1. A microwave generation source that generates microwaves, a waveguide that guides the microwaves, and a microwave that transmits the microwaves that are guided through the waveguide, and that generates plasma by the transmitted microwaves. A processing chamber having a discharge tube to be generated, a sample stand provided below the discharge tube, and a processing chamber provided between the discharge tube and the sample stand to direct microwaves transmitted through the discharge tube and into the discharge tube. and a reflective end that reflects the plasma to the side, and the reflective end has a large number of active particle passage holes arranged so that active particles in the plasma are uniformly emitted within the processing chamber. Wave plasma treatment equipment. 2. In the microwave plasma processing apparatus according to claim 1, the distance between the lower surface of the discharge tube facing the sample stage and the reflection end is selected to be 1/8 or more of the tube wavelength of the microwave. Features of microwave plasma processing equipment. 3. The microwave plasma processing apparatus according to claim 1, wherein the distance between the lower surface of the discharge tube facing the sample stage and the reflection end is 1/8 to 1/4 of the tube wavelength of the microwave.
Microwave plasma processing equipment characterized by being selected by