JP2007227816A - Plasma treatment ending method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide plasma treatment ending techniques with which electric charges on an object to be treated can be removed within a short time, and stable plasma treatment is performed without damage of the object to be treated, conveyance trouble or the like. <P>SOLUTION: With a plasma treatment ending method; a voltage is applied between a pair of electrodes, the plasma of supplied reaction gases is operated on an object to be treated, and plasma treatment is performed and then ended. The method includes a power reduction step of reducing a power to a power W<SB>20</SB>smallest among powers W<SB>2</SB>meeting a condition smaller than a supplied power W<SB>1</SB>during the plasma treatment, but stably maintaining plasma discharging at a time point to end the plasma treatment; a discharging step of stably performing plasma discharging for a predetermined period of time (t) on the condition of the power W<SB>20</SB>reduced in the power reduction step; and a stop step of stopping supplying the power after the discharging step. The reaction gases are similarly supplied from a state under the plasma treatment to the discharging step. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to plasma deposition, plasma etching and other plasma surface treatment techniques, especially plasma treatment after plasma thin film formation and surface treatment using He, Ar, O ₂ or other plasma gas. Regarding the method.

  A technique for forming a thin film on a semiconductor substrate by plasma CVD is widely used today. That is, thin film formation is performed using an apparatus as shown in FIG. In FIG. 2, 1 is a Si wafer, 2 is an electrode on which the Si wafer 1 is placed, 3 is an electrode also serving as a reaction gas supply shower, 4 is a radio frequency (RF) power source, 5 is a matching box, Reference numerals 6a and 6b denote flow meters for controlling the reaction gas supplied to the plasma reaction chamber through the electrode 3. After the Si wafer 1 is placed on the electrode 2, first, the plasma reaction chamber is evacuated. Thereafter, the main reaction gas is supplied into the plasma reaction chamber while being controlled by the flow meter 6a, and the secondary reaction gas is supplied into the plasma reaction chamber while being controlled by the flow meter 6b. Then, the switch of the high-frequency power source 4 is turned on, and a predetermined voltage is applied between the pair of parallel plate electrodes 2 and 3 to form plasma. As a result, a thin film is formed on the Si wafer 1 or the surface of the Si wafer 1 is etched. That is, a predetermined plasma surface treatment is performed. When the desired surface treatment is completed, the switch of the high frequency power supply 4 is turned off. Thereafter, the Si wafer 1 is lifted by lift pins, removed from the lower electrode 2, and carried out of the plasma reaction chamber.

FIG. 3 shows time series changes in the power condition, gas flow rate, and charge charge in the Si wafer 1 in the above series of steps. As can be seen from FIG. 3, the reactive gas (process gas) is supplied (time t ₀ ) before the high frequency power supply 4 is switched on (time t ₁ ), but the high frequency power supply 4 is switched off (time t ₂ ). At the same time, the supply is stopped. The potential on the surface of the Si wafer 1 increases with the start of plasma discharge, and becomes a constant value after a certain time. From the end of the plasma discharge after the predetermined value continues (time t ₂ ), the charge charged in the Si wafer 1 spontaneously discharges through the process gas in the plasma reaction chamber. However, since it is difficult to discharge, it takes time to complete the discharge. Until this discharge is completed, the Si wafer 1 is electrostatically attracted to the lower electrode 2. Therefore, even if the Si wafer 1 electrostatically attracted to the lower electrode 2 is pushed up by the lift pins and peeled off, it cannot be easily performed. That is, forcibly pushing up, the Si wafer 1 is cracked or chipped, or the Si wafer 1 is transported.

Therefore, in order to solve such problems, for example, when cutting off the RF power, (1) a method of gradually reducing the RF power without suddenly decreasing, or (2) the RF power being suddenly reduced to 0 Thereafter, a method has been proposed (JP-A-3-44472) in which power of 50% or less of the applied power at the time of film formation is turned on again.
Japanese Patent Laid-Open No. 3-44472

  According to the proposed technique, the charge on the surface of the Si wafer 1 can escape to the plasma reaction chamber (reaction vessel) on the ground side via the discharge plasma, and a certain effect seems to be achieved.

  However, in the above method (1), when the drop time of the RF power is short, the charged electric charge is not sufficiently removed, and the occurrence of a transportation trouble due to electrostatic adsorption is still recognized. In addition, since the RF power drop rate is fast, impedance matching of the discharge plasma cannot follow, and the convergence operation is continuously repeated, and a state where matching cannot be obtained occurs. For this reason, the problem that plasma discharge became unstable and arcing occurred on the Si wafer 1 was recognized.

  Conventionally, at the time when the plasma processing is completed, for example, the introduction of the main reaction gas for film formation is stopped, and the processing is performed using plasma of only the secondary reaction gas. For this reason, the discharge impedance is different from that at the time of film formation, and it is difficult to obtain impedance matching. Therefore, in order to completely remove the charge charge, it is necessary to take a sufficiently long drop time of the power value. By the way, as a descent speed that plasma impedance matching can follow, about 15 W / sec is considered under normal working conditions. For this reason, it takes about 20 seconds to lower the RF power source 4 from 300 W to 0 W, for example. In this case, the processing time becomes long, and it is disadvantageous to advance the TAT (Turn Around Time).

  By the way, although the technique (1) in the technique of the above-mentioned patent document 1 is intended to reduce the RF power continuously and gradually, it is conceivable to reduce the power stepwise. Also in this case, in order to ensure the impedance matching of the discharge and stabilize the discharge, one step requires 3 seconds or more under normal working conditions. Therefore, for example, when the power is lowered from RF power of 300 W in steps of 50 W in 3 seconds, it takes 18 seconds in 6 steps. That is, it cannot be completed in a short time. Further, when the RF power is lowered continuously or stepwise, the plasma discharge continues, so that film formation proceeds under unstable conditions where impedance matching cannot be obtained. And it is easily understood that it is not preferable to continue the plasma treatment under such unstable conditions. For example, in the film formation by plasma discharge, there is a close relationship between the applied power and the film thickness / film quality, and the film formation under the unstable condition as described above deteriorates the film quality. Incidentally, the discharge characteristic of the charge charged on the Si wafer 1 in this case is shown in FIG.

  On the other hand, the method (2) in the technique of the above-mentioned Patent Document 1 temporarily stops the plasma discharge by setting the power to 0 W, and again generates the discharge at a low power. However, since the input power for the second discharge is small and the discharge has already stopped, it is difficult to obtain RF matching, and no discharge occurs if the discharge step is set to a short time of about 5 seconds. The step ends, and the charge charge, which is the original purpose, cannot be removed. Therefore, since it is necessary to operate the step of lowering the RF power to 0 W and the step of stabilizing by supplying the plasma again to generate plasma discharge, 10 to 15 seconds or more are necessary, and the effect of shortening the time is lost. . Further, since the RF power is once cut off, in order to resume, the generation of plasma becomes unstable at the lowest power, so it is necessary to start with a power value higher than the lowest power. In this case as well, plasma processing under unstable conditions proceeds as in the case of (1). Incidentally, the discharge characteristic of the charge charged on the Si wafer 1 in this case is shown in FIG.

Further, in both methods (1) and (2) of Patent Document 1, since RF power is applied while flowing only the side reaction gas that does not cause film growth, the film having poor plasma resistance is damaged. There is also.
For these reasons, the technique of Patent Document 1 is not satisfactory.

  Accordingly, the problem to be solved by the present invention is that the charge charged to the object to be processed can be removed in a short time, and there is no damage to the object to be processed, no transportation trouble, etc., and stable plasma processing is performed. It is to provide a plasma processing termination technique.

The above-mentioned problem is a plasma processing end method for applying a voltage between a pair of electrodes to cause a plasma of a supplied reaction gas to act on an object to be processed, and then ending the plasma processing.
A power reduction step that reduces the power W ₂ to a condition that is less than the supply power W ₁ during the plasma treatment, but which satisfies the condition that the plasma discharge is stably maintained, at the time of ending the plasma treatment;
In the power reduction power W ₂ condition that is lowered in step, the predetermined time t, the discharge step occupying performed a plasma discharge stable,
After the discharging step, comprising a stopping step of stopping the power supply,
The problem is solved by the plasma processing termination method in which the reaction gas is supplied in the same manner during the plasma processing and the discharge step.

In particular, a plasma processing end method for ending plasma processing after applying a voltage between a pair of electrodes to cause plasma of a supplied reaction gas to act on a workpiece to perform plasma processing,
At the time it is intended to end the plasma processing, smaller than the supply power W ₁ during plasma processing, however plasma discharge power decreases to reduce to the smallest power W ₂₀ Among satisfy power W ₂ to be stably maintained Steps,
A discharge step of stably performing plasma discharge for a predetermined time t under the condition of power W ₂₀ reduced in the power reduction step;
After the discharging step, comprising a stopping step of stopping the power supply,
The problem is solved by the plasma processing termination method in which the reaction gas is supplied in the same manner during the plasma processing and the discharge step.

  Note that the discharge step in the plasma processing termination method is preferably maintained until the static electricity charged to the object to be processed by the discharge step substantially disappears.

  Further, in the power reduction step in the plasma processing termination method, the power reduction rate is preferably as high as possible.

  When the plasma processing is terminated as described above, the power value is lowered under the condition that the discharge that is easy to obtain impedance matching is stable, and the time during which the plasma is maintained at a low power value is obtained. Since it is provided, the workpiece can be taken out in a short time.

  That is, when the RF power is lowered to a small power that is not 0 W, impedance matching of the discharge plasma may not be successfully performed, but if a power change is generated instantaneously without changing the plasma conditions other than the RF power, After finding that stable plasma can be maintained and plasma discharge under such circumstances is secured, the charge charged to the object can be discharged well and the object to be processed can be removed quickly. It became possible.

  In spite of application with a small electric power, the plasma is stable, so that there is no possibility that a poor film is added in the film formation, and there is no possibility that the film is damaged.

The plasma processing termination method according to the present invention is such that a voltage is applied between a pair of electrodes and plasma based on the supplied reaction gas is applied to an object to be processed placed on one electrode, and then the plasma processing is terminated. It is a method to make it. Then, at the point of time when the plasma processing is to be terminated, there is a power reduction step that lowers the power W ₂ to satisfy the condition that the plasma power is kept stable, which is smaller than the supply power W ₁ during the plasma processing. In particular, at the time it is intended to end the plasma processing, smaller than the supply power W ₁ during plasma processing, however reduced to the smallest power W ₂₀ Among satisfy power W ₂ where plasma discharge is stably maintained A power reduction step. In addition, there is a discharge step in which plasma discharge is stably performed for a predetermined time t under the condition of power W ₂ (particularly W ₂₀ ) reduced in the power reduction step. After the discharging step, there is a stopping step of stopping power supply. The reaction gas is supplied in the same manner during the plasma treatment and the discharge step. The discharge step in the plasma processing termination method is preferably maintained until the static electricity charged to the object to be processed by the discharge step substantially disappears. Further, in the power reduction step in the plasma processing termination method, the power reduction rate is preferably as high as possible.
This will be described in more detail below.

  FIG. 1 is a time chart of RF power, process gas, and electric charge charged on a Si wafer when plasma processing is performed using a plasma CVD apparatus.

In the present invention, the plasma CVD apparatus shown in FIG. 2 can be used.
First, the Si wafer 1 is transported into the plasma reaction chamber and placed on the electrode 2 held at 300 to 400 ° C. Then, after evacuating the plasma reaction chamber to a vacuum level of 0.4 Pa or less, a predetermined amount of reaction gas (main reaction gas and sub reaction gas: process gas) is introduced, and the RF power supply 4 is turned on to supply RF power. Apply. Thereby, a predetermined plasma process is performed. For example, a predetermined film is formed on the Si wafer 1.

  Thereafter, the plasma processing is finished and the Si wafer 1 is taken out from the plasma reaction chamber. Therefore, first, the RF power is lowered to the lowest power that can stably maintain the plasma discharge. And it maintains for several seconds under this state. During this time, the process gas, that is, both the main reaction gas and the side reaction gas maintain the flow rate and pressure. In other words, the conditions are not changed except for reducing the RF power.

  The electric charge that has been charged in the Si wafer 1 is discharged by the above process, so the RF power is cut off and the supply of the process gas is stopped.

  As can be seen from FIG. 1 in which the situation of the above steps is shown, when the RF power at the time of film formation is lowered to the minimum power value, charges still remain on the surface of the Si wafer 1. However, while the discharge is maintained at the lowest power that can stably maintain the plasma discharge, the electric charge is discharged to the ground (vessel constituting the plasma reaction chamber) through the plasma. . As a result, the residual charge is negligible or disappears in a short time. Therefore, at this stage, when the Si wafer 1 is lifted by the lift pins, the Si wafer 1 can be easily removed from the lower electrode 2. And it can be smoothly carried out of the plasma reaction chamber.

  Incidentally, the minimum power at which the plasma discharge can be stably maintained is, for example, about 50 W. However, there are some differences depending on the electrode shape, the frequency of the high frequency, and the distance between the electrodes (the distance between the cathode electrode to which the RF power is applied and the ground or the bias application electrode). Therefore, the process gas flow rate, pressure, distance between electrodes, etc. are set to the same conditions as during plasma processing (for example, film formation), and only the RF power is gradually reduced from the value during film formation, and the reflected wave output is It may be searched while visually confirming whether the plasma discharge state is stable below the value.

  Further, the time for maintaining the plasma discharge at the lowest power is the time necessary for releasing the electric charge charged on the surface of the Si wafer 1 through the plasma. However, if the discharge is stable, the time is sufficient for a moment. . However, considering that the impedance matching of the plasma discharge can be reliably obtained and depends on whether or not the discharge can be stably maintained, generally, it takes about 2 to 5 seconds, particularly about 3 seconds. However, when the discharge becomes unstable, a potential gradient is formed in the plasma, and the phenomenon that the charge charge on the surface of the Si wafer increases conversely, or the plasma impedance changes and a state in which static elimination due to discharge cannot be performed occurs. Therefore, finally, it is sufficient to confirm the discharge by visual inspection and confirm that the reflected wave output is not more than a predetermined value, and determine the discharge time of the minimum power.

Hereinafter, a more specific example will be described.
First, an embodiment in forming a film such as SiOC will be described with reference to the CVD apparatus in FIG.

The Si wafer 1 was transferred into the plasma reaction chamber and placed on the lower electrode 2 held at 300 to 400 ° C. Then, the plasma reaction chamber was evacuated to 0.4 Pa or less, and 800 sccm of TMS (trimethylsilane), 2000 sccm of O ₂ , and 400 sccm of He were introduced at time (t ₀ ).

Thereafter, for example, 300 W of RF power (13.56 MHz) was applied at time (t ₁ ).

Then, at a time (t ₂ ) at which a predetermined time has elapsed, the RF power was instantaneously reduced to 50 W (the lowest RF power value at which the plasma discharge being examined in advance can be stably maintained). This state is maintained for 3 seconds. Note that the process gas is supplied in the same manner for 3 seconds.

At the time (t ₃ ) after the elapse of 3 seconds, the RF power was cut off and the introduction of process gas (TMS, O ₂ , He) was stopped.

As a result, the electric charge charged on the surface of the Si wafer flowed to the ground side, and it was extremely small or disappeared. Therefore, the Si wafer 1 can be taken out smoothly and without problems. And since the time of about 3 seconds required for static elimination is a short time, the film formed while maintaining the discharge is very small and does not cause a problem. In addition, since the charge removal process is performed under the same gas atmosphere conditions as in the film formation, there is no impact on the Si wafer by ions of a side reaction gas such as O ₂ or N ₂ that does not grow the film, and the Si wafer may be damaged No.

In the above embodiment, the case of film formation has been described. In this embodiment, the case of plasma surface treatment without film growth will be described. For example, the plasma surface treatment using He, Ar, O ₂ or the like can be applied to the case of plasma etching using CF ₄ , CHCl _3, or the like.

First, the Si wafer 1 was transferred into the plasma reaction chamber and placed on the lower electrode 2 maintained at 300 to 400 ° C. Then, the plasma reaction chamber was evacuated to 0.4 Pa or less, and 2800 sccm of He was introduced to a pressure of 800 Pa.
Thereafter, for example, 300 W of RF power (13.56 MHz) was applied.

  Then, at the time when the desired surface treatment is performed after a predetermined time has elapsed, the RF power is instantaneously reduced to 50 W (the lowest RF power value at which the plasma discharge being examined in advance can be stably maintained), and this state is reached. For 3 seconds. It should be noted that He is supplied in the same manner for 3 seconds.

  At the time after the elapse of 3 seconds, the RF power was cut off (set to 0) and the introduction of the process gas (He) was stopped.

  As a result, charges are accumulated on the surface of the Si wafer 1 even in He plasma. However, while maintaining low power (50 W), the charge charges flow to the ground side through the plasma, and the charge charges disappear. Therefore, when removing the Si wafer with the RF power set to 0, it can be easily removed without being attracted to the lower electrode 2.

Time chart of plasma processing of the present invention Schematic diagram of plasma CVD equipment Conventional plasma processing time chart Time chart of the technique of Japanese Patent Laid-Open No. 3-44472 Time chart of the technique of Japanese Patent Laid-Open No. 3-44472

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Si wafer 2, 3 Electrode 4 High frequency power supply 5 RF matching box 6a Main reaction gas flowmeter 6b Side reaction gas flowmeter

Patent applicant Next-generation semiconductor material technology research association
Representative Katsumi Udaka

Claims (3)

A plasma processing end method for applying a voltage between a pair of electrodes to cause a plasma of a supplied reaction gas to act on an object to be processed and then ending the plasma processing.
A power reduction step that reduces the power W ₂ to a condition that is less than the supply power W ₁ during the plasma treatment, but which satisfies the condition that the plasma discharge is stably maintained, at the time of ending the plasma treatment;
In the power reduction power W ₂ condition that is lowered in step, the predetermined time t, the discharge step occupying performed a plasma discharge stable,
After the discharging step, comprising a stopping step of stopping the power supply,
The plasma processing end method is characterized in that the reaction gas is supplied in the same manner during the plasma processing and the discharge step. Power W ₂ to be reduced in power reduction step, plasma treatment termination method of claim 1, wherein the plasma discharge is the smallest power W ₂₀ among power to be maintained stably. 2. The plasma processing termination method according to claim 1, wherein the discharging step is maintained until the static electricity charged to the object to be processed by the discharging step substantially disappears.

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