JP4597614B2 - Dielectric window fogging prevention plasma processing equipment - Google Patents

Description

  The present invention relates to a plasma processing apparatus provided with a dielectric window having optical transparency for optical measurement from the outside of a reaction chamber. In particular, the present invention relates to a plasma processing apparatus that prevents deposits from gradually accumulating on the dielectric window and causing fogging.

With the recent advancement of micromachine manufacturing technology, the etching depth of the surface of an object to be processed is measured in real time in a plasma processing apparatus. An example of this measurement technique is optical measurement using laser interference or the like, in which a laser is incident from the outside of a dielectric window provided in a part of the reaction chamber, and the etching depth is measured. As another technique, there is plasma emission analysis measurement, and the etching depth is measured in real time by measuring light generated from plasma generated in the reaction chamber outside the dielectric window . In any of these methods, an optical measuring instrument is installed outside the reaction chamber, and measurement is performed by laser or light passing through the dielectric window . It is desirable that the transmittance is always high and constant.

However, when a plasma processing apparatus is used, scattered substances or film formation fine particles generated from the processing object during the etching process or the film forming process adhere to the inner surface of the reaction chamber and deposit to contaminate the reaction chamber. Sometimes. For example, when silicon dioxide (SiO ₂ ) is etched as an object to be processed, a fluorocarbon (CF) gas is used as a reactive gas. ((CF ₂ ) _n ) is likely to occur. These deposit on the surface of the anode side electrode with little ion bombardment and on the inner surface of the reaction chamber.

These scattered objects adhere to and accumulate on the dielectric window . As these are deposited, the light transmittance of the dielectric window decreases, so that the light transmittance of the dielectric window changes between the initial and final measurement. Therefore, when performing optical measurement, accurate measurement cannot be performed continuously.

  So far, measures have been considered to prevent such scattered matter from accumulating inside the reaction chamber. For example, Patent Document 1 discloses an optical excitation process apparatus including a plurality of protective windows for preventing the light transmission window from being fogged and an etching chamber for removing the fogging of the protective window. When one protective window becomes cloudy, it moves to the etching chamber and is subjected to a dry etching process, and another protective window that has already been regenerated and becomes transparent moves to a light transmission window. Thereby, the loss at the time of transmission of excitation light can be reduced.

  Patent Document 2 and Patent Document 3 disclose a reactive ion etching apparatus using a top plate of a vacuum chamber as a floating electrode. When a high frequency current is applied to the floating electrode, a negative bias is applied to the top plate. And the upper top plate is always struck by positive ions, and as a result, the adhesion of the film to the top plate is suppressed.

Japanese Unexamined Patent Publication No. 6-23068 JP 2002-343775 A ([0010]) JP 2003-109947 A ([0014])

  In the configuration of the cited document 1, since the protective window itself is not prevented from being fogged, the light transmittance in the protective window gradually decreases. In addition, processing and measurement must be temporarily stopped while the protective window is replaced, and continuous optical measurement cannot be performed. Further, in the configurations of the cited references 2 and 3, since the entire top plate is an electrode, it is necessary to suppress interference of the high frequency magnetic field with the induction coil adjacent to the top plate, which complicates the apparatus and increases costs. There's a problem. When a window is formed in a part of the top plate that is an electrode, the magnetic field may be disturbed in the window part.

Therefore, the problem to be solved by the present invention is that in a plasma processing apparatus having a dielectric window at the upper part of the reaction chamber, scattered matter adheres and accumulates on the dielectric window , and its light transmittance decreases with time. By preventing this, accurate optical measurement is continuously performed while avoiding complication of the apparatus and an increase in cost.

As a result of intensive studies to solve the above problems, the inventors of the present application provide an excitation auxiliary electrode to which a high-frequency voltage is applied, and by disposing a part of the working part in the vicinity of the dielectric window , The inventors have come up with the idea of preventing the scattered matter from accumulating inside the dielectric window .

The plasma processing apparatus according to the present invention based on such considerations is connected to a high-frequency power source, and an excitation coil having a spiral shape that gradually separates from the object to be processed from the peripheral part to the central part is provided in the reaction chamber. A plasma processing apparatus that is provided outside and includes a dielectric window having optical transparency in a part of a reaction chamber, wherein an excitation auxiliary electrode connected to a high frequency power source is provided outside the reaction chamber, and the excitation auxiliary electrode Is connected in series to the high frequency power supply side end of the excitation coil, and a working portion having a non-linear portion consisting of a flat plate and a U-shaped bent portion, which is a part of the auxiliary excitation electrode, It is arranged close to the surface of the body window.

According to the plasma processing apparatus of the present invention, it is possible to prevent the scattered matter from adhering to the dielectric window inside the reaction chamber during the plasma processing and gradually causing fogging. Therefore, when measuring the etching depth etc. of the surface of the processing object optically through the dielectric window , accurate measurement can always be performed. Furthermore, the present invention can be realized by a very simple configuration in which an excitation auxiliary electrode to which a high-frequency voltage is applied is provided and an action part that is a part of the auxiliary electrode is disposed in the vicinity of the dielectric window. Can be implemented.

  First, the excitation coil and excitation auxiliary electrode used for the plasma treatment of the present invention will be described. The excitation coil may be any one that has been conventionally used in a plasma processing apparatus, such as a single annular shape, a double shape, or a multi-coil shape, which can gasify the gas inside the reaction chamber. A material having a spiral shape that gradually separates from the object to be processed from the periphery to the center as described in No. 228056 can be suitably used (FIG. 2). Here, a mechanism for adjusting the distance between the excitation coil and the dielectric window as described in the same document may be further provided. Furthermore, by providing a mechanism for raising and lowering the height of the central portion of the coil, it is possible to easily realize a uniform magnetic field, that is, a uniform plasma density, in the lower plane of the excitation coil.

The excitation auxiliary electrode is connected to a high frequency power source, and a part of the excitation auxiliary electrode is disposed in the vicinity of the dielectric window. In the present application, a part of the auxiliary excitation electrode arranged close to the dielectric window is referred to as an action part. When a high-frequency current is supplied to the action part, a magnetic field is generated, and a sputtering effect is generated in the reaction chamber. As a result, even if scattered matter, polymer or the like adheres to the inner surface of the dielectric window , the attached matter is removed, and as a result, fogging of the dielectric window is prevented. In order to sufficiently exhibit such an anti-fogging action, the action part is preferably arranged at a distance of 5 mm to 30 mm from the surface of the dielectric window.

The wire constituting the excitation auxiliary electrode may be the same as that of the excitation coil, or may be of a different shape / material. However, it is desirable that at least the action portion of the auxiliary excitation electrode has a flat plate shape as shown in FIG. By doing so, the magnetic field generated by the high-frequency current flowing through the action part is efficiently introduced into the reaction chamber through the dielectric window .

  A dedicated power source may be provided as the high frequency power source for the excitation auxiliary electrode, but the high frequency power source for the excitation coil may be used as it is. In this case, the excitation auxiliary electrode and the excitation coil may be connected to the common power source by either a serial or parallel method, but the plasma in the reaction vessel is more stable when connected in series. In addition, in the case of parallel connection, the voltage of the power supply is applied to the auxiliary electrode as it is. Therefore, in order to prevent discharge from the auxiliary electrode, the voltage must be adjusted through a capacitor. For these reasons, a series connection is preferable. In the case of series connection, it is desirable to connect the excitation auxiliary electrode to the high frequency power supply side end of the excitation coil. In this case, since the high frequency power becomes stronger than when connected to the other end, a larger sputtering effect can be obtained.

  In the plasma processing apparatus according to the present invention, a light-impermeable protective sheet is disposed on the inner surface of the dielectric window on the reaction chamber side, and a part of the protective sheet is provided with a light-transmissive window. You may do it. The size of the transmission window is sufficient as long as it can transmit light necessary for measuring the etching depth and the like. Thereby, the area | region which must take the countermeasure against fogging can be minimized. In this case, the action part is arranged in the vicinity of the transmission window outside the reaction chamber.

  Hereinafter, the configuration of a plasma processing apparatus according to an embodiment of the present invention will be described in detail with reference to FIG.

  A flat lower electrode 12 is provided in the sealed reaction chamber 11, and the lower electrode 12 is connected to a bias AC power source 13. The upper surface of the reaction chamber 11 is constituted by a dielectric window 14. The material constituting the dielectric window 14 can be selected from materials having light and electromagnetic wave transmission properties such as quartz, sapphire, and calcium fluoride. A protective sheet 31 for preventing the dielectric window itself from being etched is disposed on the lower surface (reaction chamber side inner surface) of the dielectric window 14. The protective sheet 31 is made of a material having high resistance to sputtering, such as aluminum oxide, and hardly generating oxides. Furthermore, a transmission window 32 made of a material having light and electromagnetic wave transmission properties such as sapphire is formed in a part of the protective sheet 31.

  An excitation coil 15 is disposed immediately above the dielectric window 14 (outside the reaction chamber 11) so as to be parallel to the workpiece 20 placed in the reaction chamber. The excitation coil 15 is an excitation coil having the above spiral shape. The excitation coil 15 is made of, for example, a copper tube, but its linear shape may be a hollow flat plate like the excitation auxiliary electrode described below. Both ends thereof are connected to a high-frequency circuit 17 for flowing a high-frequency current through the coil 15 and a cooling water supply device 18 for circulating cooling water through the coil 15. The distance between the excitation coil 15 and the dielectric window can be adjusted by a position adjusting mechanism (not shown), and the plasma density in the reaction chamber can be set appropriately. The high-frequency circuit 17 shown in FIG. 1 is an example, and other various excitation circuits can be used.

As shown in FIG. 1, the excitation auxiliary electrode 40 is connected in series to the excitation coil 15 on the high-frequency current application side. When the dielectric window 14 is made of quartz and has a thickness of 20 to 25 mm, the action portion 41 is disposed in parallel to the window at a distance of 5 to 30 mm from the dielectric window . If the distance between the action part 41 and the dielectric window 14 is smaller than 5 mm, the sputtering effect on the dielectric window 14 is increased and the anti-fogging effect is enhanced, but ions are incident on the workpiece 20 in the reaction chamber. Therefore, when the distance is longer than 30 mm, the sputtering effect on the dielectric window 14 is reduced, and the fog prevention effect cannot be sufficiently obtained.

The distance is appropriately changed depending on the type of the workpiece 20. For example, in the case of the configuration of the present embodiment, when the object to be processed 20 is SiO ₂ or the like that is mainly etched with ionic species, if the distance is too close, the etching rate decreases, so 15 mm or more is appropriate. In the case of Si or the like that is etched with radical species, the etching rate does not decrease even if the distance is relatively close, so the thickness is set to 5 mm or more. If the thickness of the dielectric window 14 changes, the distance from the dielectric window of the action part 41 also needs to be changed accordingly. However, the dielectric constant of the dielectric window 14 is several times higher than that of air. Therefore (for example, the relative dielectric constant of quartz is 3.8), the adjustment amount of the distance with respect to the change in the thickness of the dielectric window 14 is relatively small.

The shape of the action part 41 will be described with reference to FIG. The shape of the action part can be a simple flat plate as shown in FIG. 3A, but the shape of the action part has a circular part having concentric holes as shown in FIG. A shape having a circular hole opening on one side of the long side as shown in c) or a shape having a U-shaped bent portion as shown in FIG. 3D (hereinafter, the shape of (b) is referred to as O). (C) is a C shape, and (d) is a U shape.) By making the shape of the action portion 41 in this way, unlike the flat plate shape as shown in FIG. 3A, the transmission window is not blocked, so that an optical measurement laser or the like is applied to the inner surface of the dielectric window . It is easy to introduce and light generated from the plasma is easily received outside the dielectric window . That is, it becomes easy to install the optical measuring instrument.

  When the action part 41 is formed asymmetrically as shown in FIGS. 3C and 3D, the direction of the current flowing through the non-linear part (center part) of this action part and the current in the excitation coil It is important to arrange the action parts so that their directions coincide. Here, let us consider a case where the current flows clockwise in the excitation coil 15 formed in a spiral shape, and the current flows from the left side to the right side in the action portion depicted in FIG. As shown by the arrows, the current in the central portion of the action portion has a counterclockwise flow in FIG. 3C-1 and a clockwise flow in FIG. 3C-2. At this time, the magnetic field generated in the excitation coil 15 and the magnetic field generated in the central portion of the action part 41 in FIG. If it does so, sufficient sputtering effect will not arise in reaction chamber 11, and it will become impossible to prevent fogging which arises in a permeation window certainly. On the other hand, in the action part having the shape of FIGS. 3C-2 and 3D, the magnetic field generated by the excitation coil 15 is not canceled, and the inner surface of the dielectric window is prevented from fogging without causing a decrease in etching rate. Is possible.

  A method of using this plasma etching apparatus 10 is as follows. First, the workpiece 20 is placed on the upper surface of the lower electrode 12 and the air in the reaction chamber 11 is discharged. Thereafter, a gas having reactivity with the object to be processed 20 is placed in the reaction chamber 11 until a predetermined pressure is reached, and a high-frequency current is passed through the coil 15. As a result, a sheet-like plasma cloud 21 is formed on the workpiece 20 in the reaction chamber 11, and ions in the plasma 21 collide with the surface of the workpiece 20 by the bias voltage applied to the lower electrode 12. To do. By controlling this bias voltage, ion collision energy is optimized. During the etching process, the surface state such as the etching depth of the workpiece 20 is constantly measured by the optical measuring device 19 installed on the upper part of the dielectric window 14. The transmission window 32 is not fogged and accurate measurement can be performed continuously.

[Experimental Example 1]
In order to demonstrate the effect of the plasma processing apparatus according to the present invention, the present inventors conducted the following experiment. First, the following experiment was performed for the purpose of confirming the sputtering effect.

  A plasma etching processing apparatus in which an excitation auxiliary electrode is connected to the high-frequency current application side end of the excitation coil, and the action part is arranged in parallel with the plane of the window on a dielectric window made of quartz having a thickness of 25 mm. Using. The width A of the action part was 30 mm. The excitation coil was a spiral coil formed so as to gradually move away from the surface of the workpiece from the peripheral part to the central part. In addition, a protective sheet made of aluminum oxide having a thickness of 1 mm was disposed immediately below the dielectric window, and a transmission window made of sapphire having a thickness of 0.5 mm was provided in the central part of the protective sheet. As the etching gas, a mixed gas containing argon at 50 sccm and SF6 at 10 sccm was used. This SF6 is a highly depositable gas, but here it was used to measure the amount of scattered matter adhering to the transmission window. The pressure in the reaction chamber was adjusted to 0.6 Pa. The ICP (Inductively Coupled Plasma) power was 500 W, the bias power was 200 W, and the etching time was 15 minutes.

In the above setting, etching was performed under the conditions shown in Table 1 (FIG. 4), and the following two points were measured and observed.
(1) The thickness of the silicon plate attached to the lower surface of the transmission window with a double-sided tape (made of carbon) is measured, and the etching amount is measured by comparing with the pre-measured thickness before processing (2). Observe the amount of deposit adhering and observe the cloudiness of the transmission window

  In Experiments 2 and 3 in this experiment, the U-shaped action part was installed so that the direction of the current flowing through the U-shaped action part (FIG. 3D) coincided with the direction of the current flowing through the excitation coil.

[Results and discussion]
The results of this experiment are shown in FIG. 4 (Table 1). As a comparative example, an experiment was performed using an excitation coil having the same configuration as that of the prior art and having no excitation auxiliary electrode (Comparative Example 1). According to this, the etching amount of the silicon plate was 0.78 μm, and the transmission window was fogged. That is, it was confirmed that the sputtering effect hardly occurred in the vicinity of the transmission window in the conventional configuration.

The results of each experiment were as follows.
Experiment 1: In the case of the O-shaped working portion (FIG. 3B) having a distance of 5 mm from the dielectric window, fogging did not occur in the transmission window. Moreover, since the etching amount was 14.4 μm, it was confirmed that the sputtering effect was generated.
Experiment 2: Similarly, in the case of the U-shaped action portion (FIG. 3 (d)) having a distance of 5 mm from the dielectric window, fogging of the transmission window did not occur. The etching amount was 15.3 μm.
Experiment 3: In the case of the U-shaped working portion whose distance from the dielectric window was 15 mm, the etching amount was 0.8 μm, which was lower than that in the case of Experiment 2. The transmission window was slightly fogged.

  As a result of this experiment, when the action part is arranged in the vicinity of the dielectric window, the spattering effect is generated regardless of whether the action part is O-shaped or U-shaped, and fogging of the transmission window is prevented. Was confirmed. From the results of Experiment 3, it was confirmed that when the distance between the action part and the dielectric window is increased, the sputtering effect is reduced and the transmission window is fogged.

[Experiment 2]
Subsequently, the following experiment was conducted for the purpose of confirming the etching rate and in-plane uniformity of the object to be processed.

  As in the previous experiment, on a dielectric window made of quartz with a thickness of 25 mm, an excitation auxiliary electrode is connected to the high frequency current application side end of the excitation coil, and the plasma is arranged so that the action part is parallel to the plane of the window Etching processing was performed using an etching processing apparatus. The width A of the action part was 30 mm. The excitation coil was a spiral coil formed so as to gradually move away from the surface of the workpiece from the peripheral part to the central part. In addition, a protective sheet made of aluminum oxide having a thickness of 1 mm was disposed immediately below the dielectric window, and a transmission window made of sapphire having a thickness of 0.5 mm was provided in the central part of the protective sheet. As an etching gas, a mixed gas was used in which argon was 50 sccm and CHF3 having a high deposition property as in Experimental Example 1 was 50 sccm. The pressure in the reaction chamber was adjusted to 1.0 Pa. The ICP power was 200 W, the bias power was 100 W, and the etching time was 5 minutes. Then, a thermal oxide film silicon substrate having a diameter of 6 inches (152.4 mm) was placed on the upper surface of the lower electrode in the reaction chamber.

  Using ellipsometer (Model No. ESM01A, ULVAC), at one point in the center of the base, 4 points on the circumference 17.5mm from the center of the base, and 4 points on the circumference 35mm from the center of the base, a total of 9 points The substrate thickness before and after the etching treatment was measured, and the average value of these nine points was calculated as the etching rate value. Further, among the nine points measured, a value obtained by dividing the difference between the maximum value and the minimum value by the value obtained by doubling the average value was calculated as the uniformity value.

In the above settings, after performing the etching process under the conditions shown in Table 2 (FIG. 5), the following three points were measured and observed.
(1) Measure the etching rate value (2) Measure the uniformity value (3) Observe the deposit amount and observe the fogging of the transmission window

  In this experiment, the direction of the current around the opening in the central part of FIG. 3 (c-1) is opposite to the direction of the current flowing through the excitation coil, and FIG. In FIG. 3 (d), each action portion was installed so that the direction of the current in the central portion and the direction of the current in the excitation coil coincide.

[Results and discussion]
The results of this experiment are shown in FIG. 5 (Table 2). As a comparative example, an experiment was performed using an excitation coil having the same configuration as that of the related art and having no excitation auxiliary electrode (Comparative Example 2). According to this, the etching rate value was 89.5 nm / min, and the uniformity value was 6.20%. The transmission window was cloudy.

The results of each experiment in which the excitation auxiliary electrode was installed were as follows.
Experiment 4: In the straight action part (FIG. 3A), the transmission window is not fogged.
Experiment 5: In the O-shaped action part (FIG. 3B), the transmission window was not fogged, but the etching rate value was reduced. This is presumably because a magnetic field was generated based on the shape of the action part, and cancellation with the magnetic field of the excitation coil occurred.
Experiment 6: In the shape of FIG. 3 (c-1) among the C-shaped action portions, both the etching rate value and the uniformity value were lowered. This shape is considered to be due to the cancellation of the magnetic field.
Experiment 7: In the shape of FIG. 3C-2 in the C-shaped action portion, an etching rate value almost similar to that of Comparative Example 2 was obtained, and the uniformity value was improved as compared with Comparative Example 2. There was almost no fogging of the transmission window, but some deposits were attached.

Experiment 8: In the U-shaped action portion disposed at a distance of 5 mm from the dielectric window, an etching rate value almost similar to that of Comparative Example 2 was obtained, and the uniformity value was improved as compared with Comparative Example 2. Moreover, there was no cloudiness of the transmission window.
Experiment 9: In the U-shaped action portion disposed at a distance of 15 mm from the dielectric window, an etching rate value almost similar to that of Comparative Example 2 was obtained as in Experiment 8 above, and the uniformity value was also higher than that of Comparative Example 2. Improved. However, some cloudiness was seen on the transmission window. It can be said that when the distance from the dielectric window of the action part is changed from 5 mm to 15 mm, the etching rate is improved, but the fogging prevention effect of the window is reduced.

  From these experiments, by arranging the action part of the excitation auxiliary electrode on the top of the dielectric window, it is possible to prevent fogging of the transmission window, and the action part has a shape such as a C shape or a U-shape. If the direction of the current flowing through these is arranged so as to match the direction of the current flowing through the excitation coil, the etching rate and processing of the object to be processed can be compared with the conventional configuration in which the excitation auxiliary electrode is not installed. It was confirmed that prevention of fogging of the transmission window can be realized without reducing the uniformity of the transmission window.

  In addition, the inventors of the present application conducted experiments using the same excitation auxiliary electrode, and the effect of fogging is enhanced if the action part is brought close to the dielectric window, but if the action part is brought too close, the processing uniformity of the object to be processed is increased. I found it to decline. The reason is considered to be that when the action part is close to the dielectric window, ion components in the reaction chamber are attracted to the dielectric window side, and ion incidence to the lower substrate is reduced. Based on these results, it became clear that the position of the action part is optimally about 5 mm to 30 mm from the dielectric window.

  Note that the plasma processing apparatus of the present invention is not limited to the plasma etching apparatus described in this specification, and can be applied to any apparatus that performs plasma processing, such as a plasma CVD apparatus and a plasma surface processing apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS The schematic block diagram of the plasma etching apparatus which is one Example of this invention. The conceptual diagram of an example of a spiral shape type excitation coil. The top view of the action part of the excitation auxiliary electrode which concerns on this invention. The table | surface which shows the experimental condition and result of Experimental example 1. FIG. The table | surface which shows the experimental condition and result of Experimental example 2. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Plasma etching apparatus 11 ... Reaction chamber 12 ... Lower electrode 13 ... Bias AC power supply 14 ... Dielectric window 15 ... Excitation coil 17 ... High frequency circuit 19 ... Optical measuring device 20 ... To-be-processed object 21 ... Plasma cloud 31 ... Protection sheet 32 ... Transmission window 40 ... Excitation auxiliary electrode 41 ... Action part

Claims (3)

An excitation coil connected to a high-frequency power source and having a spiral shape that gradually separates from the object to be processed from the peripheral part to the central part is provided outside the reaction chamber, and a light-transmitting dielectric window is provided in a part of the reaction chamber. A plasma processing apparatus for
An excitation auxiliary electrode connected to a high frequency power source is provided outside the reaction chamber, and the excitation auxiliary electrode is connected in series to the high frequency power source side end of the excitation coil and is a part of the excitation auxiliary electrode . A plasma processing apparatus, wherein a working portion having a non-linear portion formed of a flat plate and having a U-shaped bent portion is disposed close to the surface of the dielectric window. A light-impermeable protective sheet is disposed on the inner surface of the dielectric window on the reaction chamber side,
The plasma processing apparatus according to claim 1, wherein a part of the protective sheet is provided with a light transmission window. 3. The plasma processing apparatus according to claim 1, wherein the action portion is arranged so that a direction of a current flowing through the non-linear portion matches a direction of a current flowing through the excitation coil.

Images