JP3672300B2 - Lift pin for thin film growth apparatus, method of forming the same, and lift pin head - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to lift pins and lift pin heads for lifting an object to be processed such as a semiconductor wafer in a heat treatment apparatus such as an epitaxial growth apparatus.
[0002]
[Prior art]
The epitaxial growth apparatus includes a susceptor as a wafer support in a processing chamber. This susceptor is provided with through holes penetrating vertically at a plurality of locations, typically three locations. A lift pin is fitted in the through hole. When the wafer is supported, the lift pin head is substantially flush with the upper surface of the susceptor. When the wafer processing is completed, the susceptor is lowered. Since the stopper is arranged at a position corresponding to the lift pin, the lift pin hits the stopper and stops descending. As the susceptor continues to descend, the lift pins protrude from the upper surface of the susceptor and lift the wafer.
[0003]
In this manner, the transfer robot takes out the wafer from the processing apparatus in a state where the wafer is lifted by the three lift pins. When the wafer is carried into the processing apparatus, a process substantially opposite to this is performed. That is, the transfer robot carries the wafer to the upper side of the susceptor. Three lift pins are raised by the pin lift mechanism, and the wafer is supported by the lift pins. After the transfer robot moves backward, the lift pins are lowered to place the wafer on the susceptor.
[0004]
The lift pins that were coated with SiC on the base of carbon have been conventionally used. SiC is the material used for the susceptor, and the same material was used to ensure a uniform heat distribution across the entire surface of the susceptor. However, the lift pin has a portion that protrudes long downward from the susceptor, and the temperature of the lift pin head is lower than the temperature of the upper surface of the susceptor due to the heat dissipation effect of the protrusion. It has been found that this temperature drop causes a slight dent at a position corresponding to the lift pins of the wafer on which the film formation process has been completed.
[0005]
As a countermeasure against this problem, the inventors of the present invention proposed in JP-A-2001-199791 that two quartz members having different infrared transmittance or thermal conductivity are joined to form a lift pin. However, quartz lift pins give satisfactory results when used in a low-temperature epitaxial device of about 700 ° C, but when used in a high-temperature epitaxial growth device exceeding 1000 ° C, Si adheres to the surface and is repeatedly used in the chamber cleaning process. It was found that when exposed, it was etched and deteriorated.
[0006]
Patent registration No. 3098001 describes that the film thickness of the wafer is dented due to a temperature drop due to the heat dissipation effect of the lift pins, and in order to solve this problem, a base having a lower thermal conductivity than the susceptor substrate. The use of lift pins made of material is described. The specific structure of the lift pin is proposed that the graphite base material is coated with SiC, the SiC base material is coated with SiC, the whole is composed of glassy carbon, or the whole is composed of quartz. Has been.
[0007]
[Problems to be solved by the invention]
The inventor of the present application has found that a quartz lift pin is not suitable for use in a high temperature epitaxial growth apparatus as described above, and has tested a lift pin obtained by machining glassy carbon by machining. It was found to be unfavorable for the epitaxial growth process because it is fragile than SiC, which is the material of the material, and the lift pins are scraped by friction when the susceptor is moved up and down, generating fine powder. It was also found that the lift pins cannot be sufficiently durable due to wear due to friction or damage such as HCl etching at high temperatures.
[0008]
[Means for Solving the Problems]
According to one aspect of the present invention, the lift pin includes a hollow sheath portion made of SiC and a glassy carbon head portion fitted in the sheath portion. Since the portion of the pin that frictions with the through hole of the susceptor when the susceptor is raised or lowered is formed of SiC of the same material as the susceptor, the phenomenon that the lift pin is scraped by friction can be reduced.
[0009]
According to another embodiment of the present invention, the length of the portion of the glassy carbon head fitted into the sheath portion is set so as to obtain desired lift pin characteristics. By doing so, the influence of the cooling effect of the lift pin sheath on the lift pin head can be adjusted.
[0010]
In one aspect, the present invention provides a method for forming a lift pin. According to this method, a lift pin formed by coating SiC on a pin-shaped carbon base as a whole is prepared, the top of the base is exposed by cutting the top of the lift pin, and the top of the base is exposed. Is heated in the presence of oxygen to remove the base to form a hollow sheath, and a glass-like carbon lift pin head is fitted into the sheath.
[0011]
According to another aspect of the present invention, when a silicon single crystal thin film is inserted into a through hole formed in a susceptor of a thin film growth apparatus for vapor-phase growth of a silicon single crystal thin film, a wafer is carried into the growth apparatus or taken out from the growth apparatus. Provides a head for lift pins to lift the wafer. This head is made of glassy carbon and is used by being fitted into a hollow sheath made of SiC.
[0012]
The lift pin head can be replaced because it is a built-in type. It is considered that the influence of the heat dissipation effect of the sheath portion on the temperature of the lift pin head changes depending on the length of the portion extending from the lift pin head portion to the sheath portion. Various lengths of lift pin heads can be made and tested, and an optimal length lift pin head can be employed. Further, only the lift pin head can be exchanged while keeping the sheath portion unchanged according to the degree of pain of the lift pin head.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Next, specific embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a single wafer epitaxial growth apparatus as an example of a thin film growth apparatus according to the present invention. The epitaxial growth apparatus 1 includes a processing chamber 2 made of quartz glass, and a gas supply 3 and a gas exhaust port 4 are provided on the side wall of the processing chamber 2 so as to face each other. Above and below the processing chamber 2, a plurality of infrared lamps 5 for heating the wafer are arranged radially with respect to the center of the processing chamber 2. The infrared lamp 5 may be either a near infrared lamp or a far infrared lamp.
[0014]
A disc-shaped susceptor (support base) 6 is disposed in the processing chamber 2. The susceptor 6 is made of a carbon graphite material coated with silicon carbide (SiC). A wafer W is placed on the upper surface portion of the susceptor 6 and is supported from the back surface side at three points by a quartz glass support shaft 7 provided at the lower portion of the processing chamber 2 so that the upper surface portion is horizontal. Yes.
[0015]
As shown in FIG. 2, the susceptor 6 is formed with a plurality of through-holes 8 extending in the vertical direction at equal intervals on the circumference of the required radius with respect to the center portion thereof. FIG. 3 is a cross-sectional view showing a state where the lift pins 9 of the prior art are inserted into the through holes 8. The through hole 8 has a small diameter portion 8a, a tapered surface portion 8b formed above the small diameter portion 8a, and a large diameter portion 8c formed above the tapered surface portion 8b. A pin-like lift pin 9 is slidably inserted into each through hole 8. The upper end of the lift pin 9 forms a substantially flat surface with the upper surface of the susceptor 6, and the wafer W is placed on this surface.
[0016]
Referring again to FIG. 1, the epitaxial growth apparatus 1 includes a pin lift mechanism 10. The pin lift mechanism 10 includes a lift tube 11 that can be moved up and down arranged to surround the main shaft of the support shaft 7, a drive device 12 that drives the lift tube 11, and the number of lift pins 9 that extend radially from the lift tube 11. A corresponding number of lift arms 13 are provided. A pin receiving portion 14 for receiving the lift pin 9 is attached to the tip of each lift arm 13.
[0017]
In film formation, first, the wafer W is introduced to the upper side of the susceptor 6 by controlling a transfer means such as a transfer robot. In this state, the lift pins 9 are raised by driving the pin lift mechanism 10. When the lift tube 11 is raised by the drive device 12, the pin receiving portion 14 of each lift arm 13 comes into contact with the lower end of the lift pin 9 and pushes up the lift pin 9.
[0018]
Thus, the head portion 9b of the lift pin 9 protrudes upward from the upper surface of the susceptor 6 and receives the wafer W from the transfer means. The arm of the transfer robot is retracted from above the susceptor 6, the pin lift mechanism is driven, the lift pins 9 are lowered, and the wafer W is placed on the susceptor 6.
[0019]
Thereafter, the following epitaxial growth process is performed. While the wafer W is heated by the infrared lamp 5, the susceptor 6 is rotated by a rotation driving device (not shown), and a reactive gas such as trichlorosilane (SiHCl ₃ ) gas or dichlorosilane (SiH ₂ Cl ₂ ) gas is used. The gas is supplied from the gas supply port 3 into the processing chamber 2. These reaction gases may be diluted with hydrogen gas and flowed. Then, the reaction gas flows in a laminar flow state along the surface of the wafer W heated to a predetermined temperature, and a single crystal of silicon is epitaxially grown on the surface of the wafer W.
[0020]
FIG. 4 shows the structure of the lift pin 30 and the manufacturing process thereof in one embodiment of the present invention. FIG. 4A shows a cross-sectional structure of a conventional lift pin in which an SiC coating 21 is applied to a carbon substrate 23 by CVD. This lift pin is cut along the alternate long and short dash line AA ′. This cutting can be performed using a saw used for cutting the wafer, and can also be performed by shaving the tops of the lift pins with a grinder. The structure shown in FIG. 4B is obtained by scraping off the flange portion of the structure thus obtained along the circumference according to the alternate long and short dashed lines BB ′ and CC ′.
[0021]
When the structure of FIG. 4B is placed in a furnace and heated in the presence of oxygen, the carbon 23 reacts with oxygen to change to carbon dioxide and is discharged from the furnace as carbon dioxide gas. In this way, carbon 23 is removed from the structure shown in FIG. 4B to obtain a sheath portion 21 ′ made of SiC. On the other hand, a lift pin head 27 shown in FIG. 4C is made by machining from commercially available rod-like glassy carbon. A lift pin 30 is obtained by fitting the lift pin head 27 thus made to the sheath portion 21 '. The length of the lift pins is about 57 mm for an 8 inch (200 mm) wafer and about 110 mm for a 12 inch (300 mm) wafer.
[0022]
SiC used for the susceptor has a thermal conductivity of about 67 W / mK at 25 ° C., whereas glassy carbon used for the lift pin head 27 generally has a thermal conductivity of 8 W / mK or less at 25 ° C. The inventors of the present invention have found that the thermal conductivity of the lift pin head varies slightly depending on the production lot, and that the thermal conductivity of 5.5 to 6.5 W / mK at 25 ° C. is most preferable for the film forming process. It was.
[0023]
When epitaxial growth was performed using the conventional lift pins of FIG. 4A, it was observed that the film thickness of the epitaxial growth film was 1% or more thinner than other wafer portions at positions corresponding to the lift pins on the wafer. This phenomenon is considered to be caused by the temperature of the pin head being lower than the surface temperature of the susceptor due to the heat dissipation effect of the long pin portion of the lift pin.
[0024]
When epitaxial growth was performed using the lift pins 30 of one embodiment of the present invention shown in FIG. 4C, the film thickness reduction at the position corresponding to the lift pins on the wafer was less than 1%. This is presumably because the lift pin head 27 is only slightly affected by the heat dissipation effect of the pin sheath because the glassy carbon has a low thermal conductivity.
[0025]
In the embodiment shown in FIG. 4C, the sheath portion 21 ′ that is a part of the lift pin 30 that contacts the through hole 8 a of the susceptor 6 is made of the same Sic as the susceptor 6. The sheath portion 21 ′ is not worn by friction or contact with the through hole 8 a of the susceptor 6.
[0026]
The lift pin head portion 27 is affected by the heat radiation effect of the sheath portion 21 ′ by the portion extending to the sheath portion 21 ′ (the portion indicated by the length d in the drawing). Therefore, in order to reduce the influence of the heat radiation effect by the sheath portion 21 ′, it is preferable to reduce the length d. For some reason, when it is desired to increase the influence of the high thermal conductivity of the sheath portion 21 ', the length d should be increased. By adjusting the length d in this manner, the influence of the sheath portion 21 ′ can be controlled.
[0027]
FIG. 5 shows another embodiment of the present invention. The length d of the portion extending from the lift pin head 27 into the SiC sheath portion 21 ′ is considerably shorter than that of the embodiment of FIG. 4 (c) to reduce the influence of the heat dissipation effect by the sheath portion 21 ′. Yes.
[0028]
Although the present invention has been described above with reference to specific embodiments, the present invention is not limited to such embodiments.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an example of a thin film growth apparatus using a lift pin of the present invention.
FIG. 2 is a plan view showing a through hole for a lift pin provided in the susceptor.
FIG. 3 is a cross-sectional view showing a state in which a conventional lift pin is inserted into a through hole of a susceptor.
FIG. 4 is a cross-sectional view showing a process of making a lift pin according to an embodiment of the present invention.
FIG. 5 is a sectional view of a lift pin according to another embodiment of the present invention.
[Explanation of symbols]
21 'sheath part 27 lift pin head 30 lift pin

Claims (5)

A lift pin that is inserted into a through hole formed in a susceptor of a thin film growth apparatus for vapor-phase-growing a silicon single crystal thin film and lifts the wafer when the wafer is carried into or out of the growth apparatus. ,
A hollow sheath made of SiC,
A glassy carbon lift pin head fitted in the sheath;
Lift pin with.   The lift pin according to claim 1, wherein the lift pin head has a thermal conductivity of 5.5 to 6.5 W / mK. Prepare a lift pin formed by coating SiC on a pin-shaped carbon base as a whole,
Cutting the top of the lift pin to expose the top of the base;
The lift pin with the top of the base exposed is heated in the presence of oxygen to remove the base to form a hollow sheath,
Including fitting a glassy carbon lift pin head to the sheath;
Lift pin formation method.   The forming method according to claim 3, wherein the lift pin head is formed by shaving from a glassy carbon rod.   A lift pin inserted into a through-hole formed in a susceptor of a thin film growth apparatus for vapor phase growth of a silicon single crystal thin film and lifts the wafer when the wafer is carried into or out of the growth apparatus. A lift pin head made of glassy carbon and fitted into a hollow sheath made of SiC.

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