JPH05160021A - Method and device for ashing - Google Patents

Abstract

PURPOSE:To conduct a uniform ashing operation on a sample by a method wherein the sample is arranged on the downstream side of a down-flowing plasma gas stream, another gas stream is fed from the side of the plasma gas stream, and the flow of the plasma gas stream is controlled. CONSTITUTION:A sample 14 is placed on a stage 18, and O2 gas is introduced from an ashing gas introducing hole 19 while a reaction chamber 15 is being evacuated. On the other hand, micro-waves 24 are introduced from a microwave waveguide tube 23, oxygen plasma is generated in a light-emitting chamber 12, and neutral active species are sent into a reaction chamber from the abovementioned plasma through the hole on a punching board 16. At this time, the control gas such as O2 gas and the like is also fed from a gas introducing hole 21, and a down-flowing plasma gas stream is controlled. When the neutral active species of the plasma gas stream reach the sample 14, the organic resist on the sample 14 is incinerated. As a result, the distribution of ashing speed can be made uniform.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for removing an organic resist in a semiconductor manufacturing process, and more particularly to a downflow type ashing method and apparatus for ashing and removing the organic resist used as an etching mask or the like. Regarding

[0002]

2. Description of the Related Art In a method of manufacturing a semiconductor device having a fine structure, a lithography process using an organic resist (photoresist, EB resist, etc.) is performed. In the lithography process, the used resist needs to be removed thereafter. The process of removing the resist includes a wet process and a dry process, but the dry process has been widely used instead of the wet process.

The dry process for removing the resist is usually performed by a method called ashing. Ashing is a method of activating oxygen in plasma, irradiating the activated oxygen to the organic resist, and ashing (oxidizing) the organic resist to remove it.

Initially, a barrel type ashing device was used. However, since the sample (wafer) is exposed to plasma, high-energy particles collide with the wafer and hit the heavy metal in the resist onto the semiconductor substrate, thereby forming a gate oxide film. There was a problem such as damage.

For this reason, in recent years, a downflow type ashing device has been used in which plasma once generated is downflowed onto a wafer. Since the plasma and the wafer are separated in the downflow type ashing apparatus, the above-mentioned problems rarely occur. In the downflow type ashing device,
Microwaves are often used as a plasma excitation source.

FIG. 6 shows an example of a conventional ashing device. The ashing device has a microwave introducing chamber 10 in the upper portion, and the lower surface of the microwave introducing chamber 10 is adjacent to the light emitting chamber 12 via a microwave transmitting window 11 formed of quartz or the like. The light emitting chamber 12 has an ashing gas introduction port 19 on the side, and the lower surface is separated from the reaction chamber 15 by a punching board 16.

The reaction chamber 15 has an exhaust port 17 on the side,
It is connected to the exhaust system. A stage 18 is provided in the reaction chamber 15, and a sample 14 such as a semiconductor wafer is placed on the stage 18. Reaction chamber 15 and light emitting chamber 12
Has an airtight structure as a whole, and ashing gas such as O ₂ can be introduced from the ashing gas inlet 19 and exhausted to a desired pressure by an exhaust device.

When the microwave 24 is transmitted from the microwave source to the microwave introducing chamber 10, the microwave 24 passes through the microwave transmitting window 11 and enters the light emitting chamber 12, where the plasma 13 can be formed. That is, when O ₂ gas is introduced from the ashing gas inlet 19, oxygen plasma 13 is formed in the light emitting chamber 12.

From the plasma 13, activated oxygen atoms pass through the punching board 16 and flow downward. In this way, the active oxygen flowing out from the punching board 16 reaches the wafer 14 and ashes the organic resist on the wafer 14.

When the microwave 24 is introduced as shown in the figure, the microwave is gradually attenuated.
The plasma density on the side where the is introduced becomes high. For this reason,
The ashing gas is introduced from the direction opposite to the microwave 24.

There is also known a structure in which the distance between the plasma and the sample is made longer without using a punching board for separating the plasma from the sample.

[0012]

However, according to the conventional ashing apparatus, the ashing speed on the sample has a distribution. If there is a distribution in the ashing rate, the ashing rate as a whole will be limited by the portion with the lowest ashing rate.

An object of the present invention is to provide an ashing method capable of performing more uniform ashing on a sample. Another object of the present invention is to provide an ashing device that can perform more uniform ashing on a sample.

[0014]

The downflow ashing method of the present invention is a method of arranging a sample downstream of a downflowing plasma gas flow and ashing the sample, wherein Another gas stream is supplied to control the flow of the plasma gas stream.

[0015]

[Operation] From the side of the down-flowing plasma gas flow,
By supplying another gas flow, the in-plane distribution of the ashing rate could be controlled.

[0016]

FIG. 1 shows an ashing device according to an embodiment of the present invention. The ashing device comprises a microwave introducing chamber 10 at the top, a light emitting chamber 12 below the microwave introducing chamber 10, and a reaction chamber 15 below that.
Have. The sample 14 is placed on the stage 18 in the reaction chamber 15.

The microwave introducing chamber 10 is laterally connected to the microwave waveguide 23. Microwave introduction room 10
The light emitting chamber 12 and the light emitting chamber 12 are separated by the microwave transmitting window 11 while maintaining an airtight state, but microwaves can pass through the microwave transmitting window 11. The microwave transmission window 11 is formed of, for example, a quartz plate or the like. The light emitting chamber 12 is separated from the reaction chamber 15 by a punching board 16.

The punching board 16 has a function of confining plasma in the light emitting chamber 12, but gas is used for the light emitting chamber 1.
2. It can flow between the reaction chambers 15. An ashing gas introduction port 19 is provided in the light emitting chamber 12 on the side opposite to the microwave waveguide 23 so that an ashing gas such as O ₂ can be introduced.

The reaction chamber 15 has a stage 18 for mounting the sample 14 therein. Further, an exhaust device for maintaining the inside of the reaction chamber 15 at a predetermined atmospheric pressure (vacuum degree) has an exhaust port 17
It is connected to the.

Further, a pair of gas inlets 21 are arranged on the side wall of the reaction chamber 15 in a planar arrangement shape so as to sandwich the microwave waveguide 23. FIG. 2 shows a planar arrangement of the gas inlet 21. A pair of gas inlets 21 are arranged substantially radially from the sample 14 so as to sandwich the microwave traveling direction 30.

The punching board 16 has a large number of holes having a diameter of, for example, about 1.5 mm. 6 inches ~
When processing a wafer having a diameter of 8 inches, the diameter of the reaction chamber 15 is about 25 to 30 cm. The distance from the wafer 14 to the punching board 16 is about 5 cm.
During the ashing, the pressure in the reaction chamber 15 is, for example, 0.8.
The gas is exhausted by the exhaust device so as to be about Torr.

From the gas inlet 21, for example, the same gas as the ashing gas such as O ₂ or an inert gas such as Ar or N ₂ is supplied in a small amount so as not to excessively reduce the active neutral species.

When performing ashing, the stage 18
The sample 14 is placed on top, and while the reaction chamber 15 is being evacuated, O ₂ gas is introduced from the ashing gas introduction port 19. Also,
At this time, a small amount of O ₂ gas, for example, about 1/10 of the ashing gas is supplied from the gas inlet 21.

A microwave 24 having a frequency of 2.45 GHz is supplied from the microwave waveguide 23 to the microwave introducing chamber 1.
When introduced into 0, the microwave 24 passes through the microwave transmitting window 11 made of quartz, and oxygen plasma is generated in the light emitting chamber 12.

Neutral active species (oxygen atom radicals) from the plasma pass through the holes of the punching board 16 and the reaction chamber 1
Sent to 5. At this time, O _{2 is} also supplied from the gas inlet 21.
A control gas such as a gas is supplied to control the plasma gas flow that flows down. When the neutral active species of the plasma gas flow reach the sample 14, the organic resist on the sample 14 is incinerated.

The sample 14 is heated to, for example, about 180 ° C. by the heater embedded in the stage 18. While continuously supplying ashing gas and control gas,
By exhausting with the exhaust device, the pressure in the reaction chamber 15 is maintained at a constant pressure of about 0.8 Torr.

Next, the experimental results of the ashing process in the above device will be described. As the ashing conditions, the total flow rate of oxygen introduced was 1 slm (1000 sccm), the oxygen gas introduction amount in the light emitting chamber was 900 sccm, and the oxygen gas introduction amount in the reaction chamber was 50 sccm × 2 places.

The pressure in the reaction chamber is 0.8 Torr, the microwave power is 1.5 kW, and the wafer temperature is 180 ° C.
The ashing time was 15 seconds. As a sample, a silicon wafer coated with an organic resist film in a thickness of 1.5 μm was used. The organic resist is a novolac-based positive resist.

In this ashing experiment, the ashing speed was measured using five points (a to e) on the surface of the wafer 14 as shown in FIG. 3 as sample points. Table 1 shows the measurement results of the ashing rate.

For comparison, an experiment was also conducted in which the gas inlet 21 of the reaction chamber 15 was closed and the plasma gas flow was not controlled (similar to the prior art) under the same conditions as above. The results are shown in Table 2.

[0031]

[Table 1]

[0032]

[Table 2] Considering the experimental results shown in Tables 1 and 2, by supplying the control gas from the side wall of the reaction chamber, the ashing rate distribution is reduced from 23% to 7.5%. Further, the ashing speed also rises from 1.57 μm / min to 1.94 μm / min as an average value. That is, it is understood that the introduction of the control gas makes the ashing speed uniform and further increases the ashing speed.

The reason why the ashing rate distribution is made uniform and the ashing rate is improved by the embodiment of the present invention is considered as follows. In the case of the conventional technique, as shown in FIG. 7, the plasma gas flow 22 that has passed from the plasma 13 through the punching board 16 flows downward due to a difference in atmospheric pressure due to exhaust and hits the sample 14. At this time, since the sample 14 blocks the plasma gas flow 22, the plasma gas flow may be stagnant on the sample 14.

The opportunity for the stagnant plasma gas to be replaced with fresh plasma gas varies in a complicated manner depending on the arrangement of the sample 14, the arrangement of the exhaust device, the arrangement of the gas supply source, etc., but it is considered that the control is not performed at all. Be done. Also,
The distribution of neutral active species due to the distribution of microwave absorption would be inevitable. Therefore, the ashing rate on the sample 14 may have a distribution.

Further, since a gas stagnation layer is formed on the sample 14 and the supply of fresh ashing gas is hindered, there is a considerable amount of neutral active species exhausted without contacting the sample 14, and the ashing rate is also high. Will it be low?

On the other hand, according to the ashing of the embodiment, since the control gas is supplied from the side to the plasma gas flow which flows down, the plasma gas flow can be controlled.

FIG. 4 conceptually shows the plasma gas flow thus controlled. The plasma gas flow 22 supplied from the plasma 13 gradually progresses downward due to a pressure difference or the like, but the control gas 2 supplied from the gas inlet 21 on the way.
The flow is controlled by 0.

That is, the plasma gas flow 22 which is trying to spread laterally may be pushed back by the control gas 20 and intensively sprayed onto the sample 14. If the plasma gas flow 22 flows into the central portion of the sample 14, it will be easy to prevent the stagnant layer from forming on the surface of the sample 14 in a laminar flow.

The control gas introduction port was provided on the microwave introduction side. Therefore, it seems that the high neutral active species concentration could be distributed relatively uniformly on the sample 14 on the microwave introduction side.

The present inventors further conducted an experiment in which the introduction amount of the light emitting chamber and the introduction amount of the reaction chamber were changed without changing the total flow rate of oxygen gas. The results are shown in Table 3. In this experiment, the total flow rate of oxygen introduced was 1 slm (1000 sccm).
However, the amount of oxygen gas introduced into the light emitting chamber was reduced to 600 sccm, and the amount of oxygen gas introduced into the reaction chamber was 200 sccm ×
Increased to 2 places. The other experimental conditions are the same as those in Table 1 above.

[0041]

[Table 3] As a result of this experiment, it can be seen that if the amount of oxygen gas supplied from the gas introduction port 21 of the reaction chamber 15 is too large, the ashing rate is rather decreased and the uniformity is deteriorated. It is considered that this is because if the oxygen gas that controls the plasma gas flow is too large, the plasma gas flow is rather disturbed and the active radicals are killed by the inert oxygen gas, which lowers the ashing reaction.

Therefore, the flow rate of the control gas supplied from the gas inlet should be sufficient to control the plasma gas flow, but the neutral active species in the plasma gas flow should be substantially reduced. It should not be too much.

Considering the ashing speed shown in Table 1,
Although the ashing velocity distribution has been improved, it can be seen that some distribution still remains. Further, the ashing rates of the sample points a, e, c along the introduction direction of the microwave and the control gas are relatively low, and the ashing rates of the sample points b, d on both sides are relatively high. It is considered that this is because the plasma gas flow 22 mainly flows from top to bottom in the plane arrangement of FIG.

In order to efficiently control the plasma gas flow by introducing a small amount of control gas, it may be desirable that a plurality of gas introduction ports surround the plasma gas flow. FIG. 5 shows the arrangement of control gas inlets in an ashing device according to another embodiment of the present invention. A control gas passage 26 is formed so as to be connected to the control gas supply port 25 and surround the reaction chamber 15, and control gas introduction ports 21a, 21b, 21 for blowing out the control gas from four sides of the reaction chamber 15 are formed.
c and 21d are provided.

By supplying the control gas to the reaction chamber 15 from the four gas inlets 21a to 21d, it becomes possible to converge the down-flowing plasma gas flow from the four directions to the center. In this way, the plasma gas flow that flows down more efficiently is converged so that it flows over the sample 14 in a total flow.

Although the configuration example in which four gas introduction ports are provided is shown, the number of gas introduction ports can be arbitrarily selected. For example, the control gas may be supplied from three sides of the reaction chamber, or may be supplied from five sides or more. One introduction port may be provided at the same circumferential position as the microwave introduction port. When a plurality of gas inlets are provided, the flow rate of the control gas supplied to each gas inlet may be independently controlled by a mass flow controller or the like.

The μ wave may be introduced not from the side but from above. The exhaust port connected to the exhaust device may be provided below the reaction chamber instead of on the side. It is not necessary to use a punching board.

The present invention has been described above with reference to the embodiments.
The present invention is not limited to these. For example,
It will be apparent to those skilled in the art that various modifications, improvements, combinations and the like can be made.

[0049]

As described above, according to the present invention,
Since the downflowing plasma gas flow can be controlled by the control gas, it is possible to make the ashing rate distribution uniform.

Further, it is possible to improve the ashing rate by controlling the plasma gas flow that flows down.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing an ashing device according to an embodiment of the present invention.

FIG. 2 is a schematic plan view showing the arrangement of gas introduction ports in the ashing device of FIG.

FIG. 3 is a plan view showing sample points on a sample in an experiment.

FIG. 4 is a conceptual diagram in which the function of the control gas in the example is considered.

FIG. 5 is a schematic plan view showing another embodiment of the present invention.

FIG. 6 is a cross-sectional view schematically showing an ashing device according to a conventional technique.

FIG. 7 is a conceptual diagram in which a gas flow in ashing according to a conventional technique is considered.

[Explanation of symbols]

 10 microwave introduction chamber 11 microwave transmission window 12 light emission chamber 13 plasma 14 sample (wafer) 15 reaction chamber 16 punching board 17 exhaust passage 18 stage 19 ashing gas inlet 20 control gas (flow) 21 gas inlet 22 plasma gas flow 23 microwave waveguide 24 microwave 25 control gas supply port 26 control gas passage 30 microwave traveling direction

Claims (2)

[Claims] 1. A downflowing plasma gas flow (2
The sample (14) is placed on the downstream side of 2)
In the method for ashing a plasma gas flow (22), a gas flow (20) is supplied from the side of the plasma gas flow (22) to control the flow of the plasma gas flow (22). .. 2. A plasma gas flow (2
The sample (14) is placed on the downstream side of 2)
In the apparatus for ashing, the downflow ashing apparatus is provided with a gas outlet (21) for supplying another gas flow (20) to the side of the downflowing plasma gas flow (22).