JP3790291B2 - Plasma processing equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a plasma processing apparatus such as a plasma etching apparatus, a plasma CVD apparatus, and a plasma surface processing apparatus.
[0002]
[Prior art]
The trend toward higher integration and larger area of semiconductor elements is still unknown, and there is a further demand for development of processing technology corresponding to them. Further, further improvement in processing speed is desired. The problem on the plasma processing apparatus side in response to such a request is to increase the density of plasma and make it uniform over a large area. In other words, high aspect ratio processing (vertical processability) is necessary to ensure fine processing, but the plasma density is controlled even if the direction of ions is controlled by a strong electric field or magnetic field under low pressure. If it is not sufficient, it is impossible to secure a process with sufficient direction at high speed. Similarly, even if high-density plasma is generated in the plasma generation unit, if the distance from the object to be processed is long in order to ensure uniformity, it is difficult to perform high speed and high aspect ratio processing.
[0003]
For the generation of high-density plasma, an inductively coupled plasma generating apparatus using a high frequency coil is more suitable than a capacitively coupled type using parallel plate electrodes. In order to shorten the distance from the plasma generation unit to the object to be processed, it is desirable to use a planar coil in the inductively coupled plasma generation apparatus. Many literatures and patent applications have already been issued for plasma generators using planar excitation coils (for example, Japanese Patent Laid-Open No. 3-79025).
[0004]
However, in the planar coil type plasma generating apparatus, it is very difficult to increase the area of the coil and make the plasma density uniform within the large area while shortening the distance between the coil and the object to be processed. For such a problem, an apparatus has been proposed in which two or more planar coils are used so that adjacent coils generate a high-frequency magnetic field having an opposite phase (Japanese Patent Laid-Open No. 7-245195). . According to this, by using a plurality of coils and changing the arrangement and number of turns of the coils, the distribution of the high-frequency magnetic field can be controlled to generate uniform plasma over the entire surface above the electrode on which the workpiece is placed. It is described that it can be done (paragraph 0017 of the publication).
[0005]
[Problems to be solved by the invention]
In order to make the plasma density uniform with the plasma processing apparatus described in the above-mentioned JP-A-7-245195, it is necessary to adjust the positions of a plurality of coils and the high-frequency currents / voltages flowing through the coils. Is a very subtle and time consuming task. Further, in order to make the plasma density more uniform, the number of coils must be increased. However, when the number of coils is increased, the number of parameters to be adjusted increases, and the adjustment work becomes extremely difficult in practice. In addition, as the number of coils increases, the peripheral circuit also becomes complicated accordingly, so that an increase in cost becomes a problem.
[0006]
The present invention has been made to solve the above-described problems, and provides a plasma processing apparatus that can make the plasma density uniform over a wide area and is easy to adjust while having a simple configuration. It is.
[0007]
[Means for Solving the Problems]
The plasma processing apparatus according to the present invention, which has been made to solve the above-mentioned problems, is characterized by comprising an excitation coil having a spiral shape that gradually separates from the surface of the object to be processed from the peripheral part to the central part. To do. That is, all the conventional excitation coils of this type have a flat spiral shape (spiral shape) as shown in FIG. 3, but the excitation coil of the plasma processing apparatus according to the present invention has a three-dimensional spiral shape (as shown in FIG. Hereinafter, it is called an inverted tornado type).
[0008]
In addition, you may make it provide the mechanism for moving the center part of such an excitation coil in parallel with the surface of a to-be-processed object, perpendicular | vertical, or three-dimensionally.
[0009]
Similarly, a mechanism for moving the central portion of the conventional planar spiral excitation coil in parallel, perpendicularly or three-dimensionally to the surface of the workpiece may be provided.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
The density of the plasma generated by the high frequency coil depends on the strength of the electric field generated by the coil. According to the theory of antennas, when taking spherical coordinates with a certain minute portion of the coil as the origin, the θ component Eθ of the electric field generated at the position (r, θ, φ) represents the current flowing through the coil as I ₀ · exp ( j · ω · t)
Eθ = A · {−1 / (k · r) + j / (k · r) ² + 1 / (k · r) ³ } · sin θ (1)
(A is a constant, k is the wave number of electromagnetic waves). The magnitude of the electric field generated at that position by the entire coil is a value obtained by integrating the above equation (1) with the entire coil. In Equation (1), the first term on the right side corresponds to the electromagnetic wave propagating far away, the other term is a near field localized near the coil (k · r << 1), and the second term is Inductive near field induced by time change of magnetic field, the third term corresponds to capacitive near field induced by electric charge (Hideo Sakurai, "New development of low-pressure and high-density plasma", "Applied Physics" 63, No. 6, p.560). Since the second term is dominant in the coil-type plasma generating apparatus in which the excitation coil is brought close to the object to be processed and a high-frequency current is passed through the coil, the electric field E in the vicinity of the object to be processed by this term (the integral value thereof) is uniform. It is necessary to adjust the coil shape, winding method, etc.
[0011]
Naturally, the strength of the magnetic field excited by the conventional planar spiral coil is weak in the peripheral portion where there is no adjacent portion and strong in the central portion. In order to compensate for this and make the magnetic field uniform, the winding density of the spiral wire must be increased at the periphery and the winding density must be decreased at the center, but the strength of the magnetic field must be uniform. It is difficult to adjust the winding density of each part of the spiral so that even if such adjustment work can be done, the winding density of the spiral made of metal wire is different between the peripheral part and the central part, It is very difficult to fix.
[0012]
In the plasma processing apparatus according to the present invention, the excitation coil is in an inverted tornado shape, so that the strength of the magnetic field in the central portion is relatively weaker than that in the peripheral portion on the plane below the excitation coil. It is only necessary to change the height of the central part to adjust the strength, and it is much easier than adjusting the winding density of each part of the spiral. Further, fixing the coil shape after adjustment is much easier than the case where it is necessary to consider the return of height due to elasticity, and it is necessary to fix the coil shape while changing the winding density.
[0013]
The above is the case where the shape of the excitation coil is fixed to the inverted tornado shape, and furthermore, a mechanism for moving the central portion horizontally, vertically or three-dimensionally is provided in the plasma processing apparatus. By providing it, it is possible to compensate for various fluctuation factors that occur during actual work on the spot and to further improve the uniformity of the plasma density in the vicinity of the workpiece.
[0014]
The same applies to a conventional planar spiral excitation coil provided with a mechanism for moving the central portion thereof horizontally, vertically or three-dimensionally.
[0015]
As will be fully understood from the above description, the principle of the present invention is not related to the processing contents such as etching, CVD, plasma surface treatment and the like. Therefore, as described above, the present invention can be applied to any of these plasma processing apparatuses.
[0016]
【Example】
As an embodiment of the present invention, a plasma etching apparatus 10 is shown in 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 composed of a quartz plate 14, and an excitation coil 15 is arranged immediately above (outside the reaction chamber 11). The excitation coil 15 is the above-described inverted tornado coil. The coil 15 is formed of a copper tube, and both ends thereof are connected to a high-frequency circuit 16 for flowing a high-frequency current through the coil 15 and a cooling water supply device 17 for circulating cooling water inside the coil 15. By allowing the cooling water to flow through the coil, the third term on the right side of the equation (1) can be reduced. The high-frequency circuit 16 shown in FIG. 1 is an example, and other various excitation circuits can be used.
[0017]
When using the plasma etching apparatus 10 of the present embodiment, 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 reactive to the object to be processed 20 is put into the reaction chamber 11 until a predetermined pressure is reached, and a high-frequency current (usually 13.56 MHz) 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.
[0018]
In the plasma etching apparatus 10 of the present embodiment, the degree of etching of each part of the entire surface of the workpiece 20 is examined by preliminary treatment, and the height and horizontal position of the central part of the inverted tornado coil 15 are determined based on the result. By determining, a uniform etching rate can be obtained over the entire surface of the workpiece 20.
[0019]
In order to further facilitate such adjustment, a mechanism for moving the central portion of the inverted tornado coil 15 three-dimensionally may be provided. An example is shown in FIG. 4. In this mechanism 30, the head 32 moves up and down and rotates with respect to the base 31, and the beam 33 that holds the central portion of the coil 15 expands and contracts from the head 32. Yes.
[0020]
In addition to such a three-dimensional movement, a mechanism for twisting the central portion of the coil 15 may be provided. This is exactly the same as winding the mainspring, and by twisting the central portion of the coil 15, the winding of the spiral (both in the case of the planar spiral type and in the case of the inverted tornado type) becomes stronger or weaker, and the coil 15 is configured. The distribution density of the lines to be changed can be changed between the central portion and the peripheral portion.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a plasma etching apparatus according to an embodiment of the present invention.
FIG. 2 is a perspective view of an inverted tornado excitation coil used in the plasma processing apparatus according to the present invention.
FIG. 3 is a perspective view of a planar spiral excitation coil used in a conventional inductively coupled plasma processing apparatus.
FIG. 4 is a schematic configuration diagram of a plasma processing apparatus according to another embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Plasma etching apparatus 11 ... Reaction chamber 12 ... Lower electrode 13 ... AC power supply 14 for bias ... Quartz plate 15 ... Excitation coil 16 ... High frequency circuit 17 ... Cooling water supply apparatus 20 ... To-be-processed object 21 ... Plasma cloud 30 ... Coil center Part moving mechanism

Claims (5)

In a plasma processing apparatus having an excitation coil having a spiral shape that gradually moves away from the surface of an object to be processed from the peripheral part to the center part, the object to be processed is arranged with respect to the fixed position of the coil peripheral part . A plasma processing apparatus comprising a mechanism for moving in parallel and / or perpendicular to the surface of the substrate. In a plasma processing apparatus having a planar spiral excitation coil parallel to the surface of an object to be processed, the central portion of the excitation coil is parallel to and / or perpendicular to the surface of the object to be processed with respect to a fixed position on the periphery of the coil. A plasma processing apparatus provided with a mechanism for moving. In a plasma processing apparatus having an excitation coil having a spiral shape or a planar spiral shape that gradually moves away from the surface of the workpiece from the peripheral portion to the central portion, for twisting the central portion of the excitation coil with respect to the coil peripheral portion A plasma processing apparatus comprising a mechanism.   The plasma processing apparatus according to claim 1, further comprising a high-frequency circuit that supplies a high-frequency current between both ends of the excitation coil. The plasma processing apparatus according to any one of claims 1-4, characterized in that it comprises a cooling water supply device for circulating cooling water therein該Reiki coil.

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