JP7392524B2 - Inner wall member for plasma processing equipment and plasma processing equipment - Google Patents

Description

The present invention relates to an inner wall member for a plasma processing apparatus and a plasma processing apparatus using the inner wall member.

A plasma processing apparatus such as a plasma etching apparatus or a plasma CVD apparatus used in a semiconductor device manufacturing process has an upper electrode and a lower electrode connected to a high-frequency power source arranged vertically opposite each other in a chamber. With a silicon wafer placed on the electrode, plasma is generated by applying a high-frequency voltage while flowing processing gas toward the substrate to be processed through a through hole formed in the upper electrode, and etching, etc. is performed on the substrate to be processed. It is configured to perform the following processing.

In such a plasma processing apparatus, since the inner surface of the peripheral wall of the chamber is exposed to the plasma region, it is necessary to take measures to prevent the generation of particles from the inner surface of the peripheral wall.
For example, Patent Document 1 describes that an aluminum material or an alumite-processed aluminum material is used for the peripheral wall of the chamber, and that the inner surface of the chamber is periodically cleaned to prevent generation of particles.

Further, in Patent Document 2, aluminum trioxide is used as an aluminum-based material for the chamber peripheral wall, and this aluminum trioxide is resistant to penetration by helium gas, hydrogen gas, and neon gas, and has low reactivity with gases. It is described as having certain characteristics.
In Patent Document 3, a cylindrical liner is provided inside the peripheral wall of the chamber to prevent plasma from coming into contact with the peripheral wall of the chamber. The liner used is a body made of stainless steel, silicone, etc. coated with erbium oxide or the like.

Japanese Patent Application Publication No. 2009-152539 Japanese Patent Application Publication No. 2013-98172 JP 2017-11265 Publication

However, simply cleaning the inner surface of the chamber periodically as in Patent Document 1 is not sufficient to prevent particle generation. Further, even if the chamber peripheral wall described in Patent Document 2 is made of aluminum trioxide or the liner described in Patent Document 3 is provided, if these are etched, generation of particles cannot be completely prevented.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an inner wall member for a plasma processing apparatus that is less likely to generate particles, and to improve the quality of plasma processing.

To solve the above problem, it is conceivable to form the peripheral wall of the chamber with silicon (Si) in order to eliminate impurity adhesion to the silicon wafer that is the target of plasma processing. However, single crystal silicon can only be manufactured up to a diameter of about 500 mm and cannot be used as a peripheral wall of a large chamber. On the other hand, if the peripheral wall is made of polycrystalline silicon, which can be manufactured without any size restrictions, each crystal grain has a different susceptibility to etching, so if etched for a long time, irregular irregularities corresponding to the grain boundaries will appear. arise. Since the unevenness provides resistance to the flow of processing gas such as etching gas, particles are likely to be generated due to loss of crystal grains and outflow of impurities present at grain boundaries. Therefore, it is necessary that the material hardly generates particles even when etched. Based on this knowledge, the present invention has been made into the following solution.

That is, the inner wall member for a plasma processing apparatus of the present invention is a cylindrical inner wall member that surrounds a space between a pair of electrodes facing each other in a chamber of a plasma processing apparatus, and the plurality of crystal grains are formed in the inner wall member. It is made of columnar silicon crystals extending substantially parallel to the axis of.

Columnar crystal silicon is silicon having an anisotropic columnar crystal structure in which a plurality of crystal grains are grown in one direction by a method such as unidirectional solidification. In the inner wall member formed by growing this columnar silicon in a direction substantially parallel to the axis, many grain boundaries are arranged along the direction substantially parallel to the axis. The axial direction of this inner wall member is parallel to the opposing direction of both electrodes, and parallel to the flow direction of the processing gas. Therefore, even if unevenness occurs when exposed to the plasma generation region for a long time and etched, the shape follows the flow of the processing gas. Therefore, resistance to the flow of processing gas is small, and particles are less likely to be generated.
In addition, in each crystal grain, if the diameter along the length direction of the inner wall member is longer than the diameter along the circumferential direction, it is determined that the crystal grain extends in a direction substantially parallel to the axis.

In one embodiment of the inner wall member for a plasma processing apparatus, the crystal grains have a length in the direction parallel to the axis as X and a length in the direction perpendicular to the axis as Y. It is preferable that the average value of the ratio X/Y is 1.5 or more.
When the average value of the ratio X/Y of these lengths (average aspect ratio) is less than 1.5, the ratio of grain boundaries extending in a direction substantially parallel to the axis decreases, making it difficult to obtain the above-mentioned effects.

In another embodiment of the inner wall member for a plasma processing apparatus, the average grain size of the crystal grains is preferably 5.0 mm or more in equivalent circle diameter.
If the average grain size of the crystal grains is less than 5.0 mm , the number of grain boundaries increases, which increases the resistance to the flow of the processing gas and reduces the effect of preventing particle generation.

Further, the arithmetic mean roughness Ra of the inner circumferential surface of the inner wall member is preferably 5.0 μm or less. When the arithmetic mean roughness Ra exceeds 5.0 μm, the number of particles tends to increase slightly in the initial stage of operation.

In yet another embodiment of the inner wall member for a plasma processing apparatus, at least the inner peripheral surface is a cylindrical surface.
If the inner circumferential surface exposed to the plasma generation region is a cylindrical surface without corners, resistance to the flow of the processing gas is less likely to occur, and generation of particles can be more reliably prevented.

In the plasma processing apparatus of the present invention, the inner wall member is arranged so as to surround the space between the electrodes in the chamber. In this case, the peripheral wall of the chamber itself may be constituted by an inner wall member, or the inner wall may be formed as a liner member that covers the inner peripheral surface of the peripheral wall of the chamber, or as a cylindrical wall disposed concentrically inside the peripheral wall of the chamber. You may arrange a member.

The inner wall member for a plasma processing apparatus of the present invention hardly generates particles even when etched, and by using the inner wall member, it is possible to improve the quality of plasma processing.

1 is a schematic configuration diagram of a plasma processing apparatus according to an embodiment. FIG. 2 is a perspective view schematically showing an inner wall member of one embodiment. 3 is a front view schematically showing crystal grains in the inner wall member of FIG. 2. FIG.

Embodiments of the present invention will be described below with reference to the drawings.
First, a plasma etching apparatus 1 will be described as an example of a plasma processing apparatus.
As shown in the schematic cross-sectional view of FIG. 1, this plasma etching apparatus 1 includes a flat plate-shaped upper electrode 3 provided at the upper part of a chamber 2, and a lower electrode 4 which is vertically movable at the lower part. They are arranged parallel to each other and spaced apart from each other. In this case, the upper electrode 3 is supported in an insulated manner against the wall of the chamber 2 by an insulator 5, and an electrostatic chuck 6 and a focus ring 7 surrounding it are placed on the lower electrode 4. A silicon wafer (substrate to be processed) 8 is placed on the electrostatic chuck 6 with its peripheral edge supported by a focus ring 7 .

Further, an etching gas supply pipe 9 is provided in the upper part of the chamber 2, and the etching gas sent from the etching gas supply pipe 9 passes through a diffusion chamber 10, and then passes through a gas passage hole 11 provided in the upper electrode 3. It is configured to flow toward the wafer 8 through the chamber 2 and to be discharged to the outside from the discharge port 12 on the side of the chamber 2. On the other hand, a high frequency voltage is applied between the upper electrode 3 and the lower electrode 4 by a high frequency power supply 13.

Further, the upper electrode 3 is formed into a disk shape of silicon, and a cooling plate 14 made of aluminum or the like having excellent thermal conductivity is fixed to the back side of the upper electrode 3, and this cooling plate 14 also has a gas passage through the electrode plate 3. Through holes 15 are formed at the same pitch as the gas passage holes 11 so as to communicate with the holes 11 . Then, the electrode plate 3 is fixed in the plasma processing apparatus 1 by screws or the like with the back surface in contact with the cooling plate.

Moreover, a cylindrical inner wall member 21 is provided inside the chamber 2 so as to surround the space between the upper electrode 3 and the lower electrode 4. In the example shown in FIG. 1, the upper end of the inner wall member 21 is attached and fixed to the member to which the upper electrode 3 is fixed, and is spaced apart from the peripheral wall 2a of the chamber 2 and arranged concentrically with the peripheral wall 2a. There is.
As schematically shown in FIG. 2, the inner wall member 21 is made of columnar crystal silicon in which a plurality of crystal grains 21a extend substantially parallel to the axis C of the cylinder. The columnar crystal silicon constituting the inner wall member 21 is silicon having an anisotropic columnar crystal structure in which a plurality of crystal grains 21a are grown in a direction substantially parallel to the axis C by a method such as unidirectional solidification. It is. As shown in FIG. 1, the inner wall member 21 is attached to the plasma etching apparatus 1 with the axis C disposed in the opposite direction of the electrodes 3 and 4, that is, in the vertical direction. Therefore, the direction of the axis C is approximately parallel to the flow direction of the etching gas flowing out from the gas passage hole 11 of the upper electrode 3 as shown by the arrow.

The purity of silicon of this inner wall member 21 is preferably 99.999% by mass or more. Although impurities may exist at grain boundaries of crystals, if the impurities are 10 mass ppm (0.001 mass %) or less, the influence on the silicon wafer is small. Further, the crystal grains 21a of the inner wall member 21 are the average of the ratio of these lengths, where X is the length in the direction parallel to the axis C of the cylinder and Y is the length in the direction perpendicular to the axis C. (Average aspect ratio) X/Y is 1.5 or more. When the ratio X/Y is less than 1.5, the ratio of grain boundaries along the direction parallel to the axis C decreases, and the effect of preventing particle generation becomes poor. This ratio X/Y is preferably 1.8 or more. There is no particular upper limit, but as a manufacturing limit, for example, X/Y is 1000.

The average grain size of the crystal grains 21a is 5.0 mm or more in equivalent circle diameter (square root of (4×area/π)) determined from the area thereof. If the average grain size of the crystal grains 21a is less than 5.0 mm , the number of grain boundaries increases, so resistance to the flow of etching gas increases, and the effect of preventing particle generation becomes poor. The average grain size of the crystal grains 21a is preferably 10 mm or more. The upper limit is not particularly limited, but is, for example, 1000 mm as a range that can be manufactured under normal conditions.
This inner wall member 21 tightly covers the inner circumferential surface of the chamber 2 with an outer circumferential surface formed as a cylindrical surface, and exposes the inner circumferential surface formed as a cylindrical surface to the space between the upper electrode 3 and the lower electrode 4. The plasma generating region P is surrounded by the inner circumferential surface of the plasma generating region P.

To manufacture this inner wall member 21, a molten silicon is poured into a vertically arranged cylindrical mold and cooled from below in the axial direction. By solidifying in the direction and extracting the center part of the obtained cylindrical silicon ingot by coring, it is possible to obtain the inner wall member 21 of columnar crystals in which crystals are grown in a direction substantially parallel to the axis C of the cylinder. . It is also possible to obtain a cylindrical inner wall member by forming a mold cavity into a cylindrical shape, injecting molten silicon, and solidifying it in one direction from below. Finally, the surface is ground and polished by machining to finish the inner wall member 21 of a desired size.

The dimensions of this inner wall member 21 are not necessarily limited, but for example, the thickness T is 5 mm to 20 mm, the height H is 50 mm to 100 mm, and the diameter (inner diameter) D is 300 mm to 600 mm. Further, the inner circumferential surface exposed to the plasma generation region P is preferably smooth to prevent generation of particles as much as possible, and its arithmetic mean roughness Ra is preferably 5.0 μm or less. When Ra is 5.0 μm or less, generation of particles can be effectively prevented even at the initial stage of etching. The arithmetic mean roughness Ra of this inner peripheral surface is more preferably 3.0 μm or less. The lower limit is not particularly limited, but is, for example, 0.01 μm as a range that can be manufactured under normal conditions.

In the plasma etching apparatus 1 configured as described above, when an etching gas is supplied from the gas supply pipe 9 while a high frequency voltage is applied from the high frequency power source 13 between the upper electrode 3 and the lower electrode 4, this etching gas The gas is sent into the gas diffusion chamber 10 formed at the tip of the gas supply pipe 9, passes through the ventilation hole 11 of the upper electrode 3, and is released into the space between the upper electrode 3 and the lower electrode 4. The plasma becomes plasma and hits the silicon wafer 8, and the surface of the silicon wafer 8 is etched by a physical reaction caused by sputtering of this plasma and a chemical reaction caused by the etching gas.

During this plasma treatment, the etching gas also collides with the inner circumferential surface of the inner wall member 21 provided on the inner circumferential surface of the chamber 2, but since the inner circumferential surface of this inner wall member 21 is smooth, the etching gas is Low resistance to gas flow and less generation of particles. In addition, since this inner wall member 21 is made of columnar silicon whose crystal grains are aligned in a direction substantially parallel to the axis C, many grain boundaries are aligned in a direction parallel to the axis C, that is, along the flow direction of the etching gas. Because of the arrangement, even if unevenness occurs when etching is performed in the plasma generation region P, the unevenness has a shape that follows the flow of the etching gas. Therefore, resistance to the flow of etching gas is small, and particles are less likely to be generated.
By using this plasma etching apparatus 1, it is possible to perform high-quality etching processing with less generation of particles and therefore less contamination.

Note that the present invention is not limited to the above embodiments, and various changes can be made without departing from the spirit of the present invention.
In the above embodiment, the inner wall member 21 is arranged concentrically inside the circumferential wall 2a of the chamber 2 with a space therebetween, but the inner wall member 21 is used as a liner member that covers the inner circumferential surface of the circumferential wall 2a of the chamber 2. may be placed. Alternatively, the peripheral wall 2a of the chamber 2 itself may be constituted by an inner wall member. Even when an inner wall member is provided as the peripheral wall 2a of the chamber 2 itself or as a liner member covering the peripheral wall 2a, it is made of columnar crystal silicon formed by unidirectional solidification, so unlike the case of single crystal silicon, it is necessary to use a large diameter one. It is also easy to apply.

The inner circumferential surface of the inner wall member 21 is preferably a smooth cylindrical surface, but since the generation of particles is suppressed by being made of columnar crystal silicon, the inner circumferential surface of the inner wall member 21 does not need to be a strictly cylindrical surface. This does not exclude that the shape may be a polygonal shape close to a circle.
Further, the present invention can be applied not only to the plasma etching apparatus 1 of the embodiment but also to general plasma processing apparatuses such as plasma CVD apparatuses.

A cylindrical inner wall member having a thickness of 15 mm, a height of 100 mm, and an inner diameter of 410 mm was fabricated from columnar silicon and polycrystalline silicon. The manufacturing method for these is as follows.

(Inner wall member made of columnar crystal silicon)
A cylindrical cavity is formed using a cylindrical mold, and molten silicon is poured into the cavity and solidified in one direction by cooling from below, resulting in columnar crystal grains that grow approximately parallel to the axial direction. Obtained silicon ingot. Here, the average aspect ratio and average grain size of crystal grains were adjusted by changing the cooling speed. Next, the center of the silicon ingot was extracted using a coring ring, and then machined to obtain a cylindrical inner wall member with a thickness of 15 mm, a height of 100 mm, and a diameter of 410 mm. Finally, the inner peripheral surface of the inner wall member was polished.

In addition, when the composition of the obtained inner wall member was measured using an ICP (Inductively Coupled Plasma) emission spectrometer, the amount of impurities was 10 mass ppm or less, and the purity was 99.999 mass % or more. Met.

(Polycrystalline silicon inner wall member)
A cylindrical cavity was formed using a cylindrical mold, and molten silicon was poured into the cavity and cooled from the entire circumference of the mold to obtain a polycrystalline silicon ingot with irregular grain growth directions. Here, the average aspect ratio and average grain size of crystal grains were adjusted by changing the cooling speed. Next, the center of the silicon ingot was extracted using a coring ring, and then machined to obtain a cylindrical inner wall member with a thickness of 15 mm, a height of 100 mm, and a diameter of 410 mm. Finally, the inner peripheral surface of the inner wall member was polished.
In addition, when the composition of the obtained inner wall member was measured using ICP, the amount of impurities was 10 mass ppm or less, and the purity was 99.999 mass % or more.

Regarding the inner wall member produced as described above, the average aspect ratio of crystal grains, the average grain size of crystal grains, and the surface roughness (arithmetic mean roughness) Ra of the inner peripheral surface were measured.
The average aspect ratio of crystal grains is determined by observing with a SEM (Scanning Electron Microscope) and determining the maximum length X of the crystal grains along the axial direction of the inner wall member and the maximum length Y in the direction perpendicular to the axial direction. It was measured and Y/X was calculated. The average value of 100 crystal grains for one inner wall member was determined.
The average grain size of a crystal grain is determined by observing it with a SEM (scanning electron microscope) and calculating the equivalent circle diameter (diameter of a circle with the same area as the projected area of a crystal grain) from the projected area of the crystal grain. did. The average value of 100 crystal grains for one inner wall member was determined.
The surface roughness (arithmetic mean roughness) Ra was measured by scanning the inner circumferential surface of the inner wall member in the axial direction by a method in accordance with JIS-B0601. Measurements were taken at four locations on one inner wall member, and the average value was determined.

(Evaluation method)
The inner wall members of each example and comparative example were set so as to surround the plasma generation area of a plasma etching apparatus, and plasma etching was performed on a silicon wafer having a diameter of 300 mm under the following conditions.
Chamber internal pressure: 10 ⁻¹ Torr,
Etching gas composition: A mixed gas of CHF ₃ +O ₂ +He, and the flow rate was 90 sccm (CHF ₃ )+4 sccm (O ₂ )+150 sccm (He).
High frequency power: 2kW
Frequency: 20kHz

The number of particles on the silicon wafer was measured at 50 hours and 300 hours after the start of etching, and the results are shown in Table 1. To measure the number of particles, use a particle counter (WM-3000 manufactured by Topcon Corporation) to scan the wafer surface with a laser beam and measure the intensity of light scattering from the attached particles to determine the position and size of the particles. This was done by recognizing.
These results are shown in Table 1.

As shown in Table 1, the inner wall member of the example made of columnar silicon had fewer particles after 300 hours than the inner wall member of the comparative example made of polycrystalline silicon. Among the examples, Examples 1 and 2 in which the average aspect ratio of the crystal grains is 1.5 or more, the average grain size is 5.0 mm or more, and the surface roughness Ra of the inner peripheral surface is 5.0 μm or less, Particle generation is suppressed even after a long period of time, and high quality plasma etching can be performed. Example 5 also suppresses the number of particles generated after a long period of time, but since the surface roughness Ra exceeds 5.0 μm, the number of particles generated after 50 hours is slightly higher than in Examples 1 and 2. It has become.
On the other hand, in Comparative Example 1, the number of particles generated after a long period of time was greater than in the Example.

1 Plasma etching apparatus 2 Chamber 2a Peripheral wall 3 Upper electrode 4 Lower electrode 5 Insulator 6 Electrostatic chuck 8 Silicon wafer (substrate to be processed)
9 Etching gas supply pipe 10 Diffusion chamber 11 Gas passage hole 12 Discharge port 13 High frequency power source 14 Cooling plate 15 Through hole 21 Inner wall member 21a Crystal grain P Plasma generation region C Axis

Claims (3)

A cylindrical inner wall member that surrounds a space between a pair of electrodes facing each other in a chamber of a plasma processing apparatus, and is made of columnar crystal silicon in which a plurality of crystal grains extend approximately parallel to the axis of the inner wall member. It is configured,
The average grain size of the crystal grains is 14.9 mm or more in equivalent circle diameter,
An inner wall member for a plasma processing apparatus, characterized in that the arithmetic mean roughness Ra of the inner peripheral surface is 5.0 μm or less . The inner wall member for a plasma processing apparatus according to claim 1, wherein at least the inner peripheral surface is a cylindrical surface. A plasma processing apparatus, wherein the inner wall member for a plasma processing apparatus according to claim 1 or 2 is arranged to surround a space between a pair of electrodes facing each other within a chamber.

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