Patent Application
20090165721
The present invention generally relates to a susceptor for supporting a semiconductor wafer during a chemical vapor deposition process.
Semiconductor wafers may be subjected to a chemical vapor deposition process such as an epitaxial deposition process to grow a thin layer of silicon on the front surface of the wafer. This process allows devices to be fabricated directly on a high quality epitaxial layer. Conventional epitaxial deposition processes are disclosed in U.S. Pat. Nos. 5,904,769 and 5,769,942, which are incorporated herein by reference.
Prior to epitaxial deposition, the semiconductor wafer is loaded into a deposition chamber and lowered onto a susceptor. After the wafer is lowered onto the susceptor, the epitaxial deposition process begins by introducing a cleaning gas, such as hydrogen or a hydrogen and hydrochloric acid mixture, to a front surface of the wafer (i.e., a surface facing away from the susceptor) to pre-heat and clean the front surface of the wafer. The cleaning gas removes native oxide from the front surface, permitting the epitaxial silicon layer to grow continuously and evenly on the surface during a subsequent step of the deposition process. The epitaxial deposition process continues by introducing a vaporous silicon source gas, such as silane or a chlorinated silane, to the front surface of the wafer to deposit and grow an epitaxial layer of silicon on the front surface. A back surface opposite the front surface of the susceptor may be simultaneously subjected to hydrogen gas. The susceptor, which supports the semiconductor wafer in the deposition chamber during the epitaxial deposition, is rotated during the process to ensure the epitaxial layer grows evenly. Prior art susceptors used in epitaxial growth processes are described in U.S. Pat. Nos. 6,652,650; 6,596,095; and 6,444,027, all of which are incorporated herein by reference.
A common susceptor design includes a graphite disk having a recess in an upper face of the susceptor for receiving the wafer. The disk is coated with silicon carbide. In addition, three equally spaced, race-track-shaped openings extend into the susceptor from the lower surface for receiving the upper ends of supports disposed within the deposition chamber. These support openings engage the supports to prevent the susceptor from slipping on the supports as they turn during processing. The susceptor is prone to cracking at the locations of the race-track-shaped openings. Conventional techniques to correct this cracking problem include increasing the thickness of the carbide coating, decreasing the thickness of the carbide coating and using fillets at the inner corners of the recesses.
The applicants determined that each of the aforementioned techniques was met with limited success. Accordingly, a need exists for a susceptor that reduces or eliminates cracking due to its engagement with the support posts.
In one aspect of the present invention, a susceptor for supporting a semiconductor wafer during a chemical vapor deposition process in a chemical vapor deposition device that includes a plurality of support posts generally comprises a body having opposing upper and lower surfaces. At least one recess extends downward from the upper surface of the body for receiving a single semiconductor wafer therein during the chemical vapor deposition process. A plurality of support bosses extend downward from the lower face of the body. Each of the support bosses has a boss opening extending axially toward the lower surface of the body of the susceptor. The boss opening is sized and shaped for receiving a free end of one of the support posts of the chemical vapor deposition device to mount the susceptor on the support posts.
Other objects and features will be in part apparent and in part pointed out hereinafter.
Corresponding reference characters indicate corresponding parts throughout the drawings.
Referring now to the drawings, and in particular to
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Although the susceptor body 20 may have other overall dimensions without departing from the scope of the present invention, in one embodiment the susceptor has an overall diameter of about 14.7 inches. Further, although the susceptor body 20 may be made of other materials without departing from the scope of the present invention, in one embodiment the susceptor body is made of silicon carbide coated graphite. The susceptor body 20 may have a plurality of holes extending from the upper surface 14 to the lower surface 16 as shown and described in U.S. Pat. Nos. 6,652,650 and 6,444,027. It is understood that the susceptor body may take on other configurations than those detailed above. For example, the susceptor body 20 may have a large central opening. Other configurations of the susceptor body that deviate from the above description are within the scope of the present invention.
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Each boss opening 50 has a major diameter 54 (
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In the illustrated embodiment, the wall 46 of the boss 44 has an exterior peripheral surface 58 that is oblong or generally race-track-shaped and is generally concentric with the interior peripheral 48 surface of the wall. The wall 46 has a thickness T1 between the interior and exterior peripheral surfaces 46, 58, respectively, that is generally uniform around the axis A1 of the boss opening 50. As an example and without limitation, the thickness T1 of each boss wall 46 may be about 0.15 cm (0.06 in). It is understood that the exterior peripheral surfaces 58 of the walls 46 may be other shapes and the thicknesses of the walls may be non-uniform.
Although the bosses 4410 may be made of other materials without departing from the scope of the present invention, in one embodiment the bosses are made of silicon carbide coated graphite. The bosses 44 may be formed integrally with the susceptor body 20, such as by machining the bosses and the susceptor body from a single blank of graphite. It is understood that the bosses 44 may be formed separate from the susceptor body 20 and subsequently secured thereto. Other ways of forming the susceptor 10 having the bosses 44 are within the scope of the invention. It is also contemplated that fillets may be formed at internal and external corners where the bosses 44 meet the susceptor body to increase load-bearing capabilities of the bosses.
Referring to
During the epitaxial deposition process, an epitaxial silicon layer grows on the front surface of the semiconductor wafer 12. The wafer 12 is introduced into the chamber 14 and centered on the face 34 of the susceptor 10. First the apparatus performs a pre-heat or cleaning step. A cleaning gas, such as hydrogen or a mixture of hydrogen and hydrochloric acid, is introduced into the chamber 14 at about ambient pressure, at a temperature from about 1000° C. to about 1250° C., and at a flow rate from about five liters per minute to about 100 liters per minute. After a period of time sufficient to remove native oxide layers from both the front and back surfaces of the wafer 12 and to stabilize the temperature in the reaction chamber 14 from about 1000° C. to about 1250° C., a silicon-containing source gas, such as silane or a chlorinated silane, is introduced through the inlet 70 above the front surface of the wafer 12 at a flow rate from about one liter per minute to about fifty liters per minute. The source gas flow continues for a period of time sufficient to grow an epitaxial silicon layer on a front or upper surface of the wafer 12 to a thickness from about 0.1 micrometer to about 200 micrometers. Simultaneously with the source gas being introduced, a purge gas, such as hydrogen, flows through the inlet 72 below the back or lower surface of the wafer 12. The purge gas flow rate is selected so the purge gas contacts the back surface of the semiconductor wafer 12 and carries out-diffused dopant atoms from the back surface to an exhaust outlet 74.
The support bosses 44 of the susceptor 10 replace the conventional support openings formed in the body of susceptor. Accordingly, the susceptor 10 having support bosses 44 does not have thinned locations due to the formation of the support recesses. Therefore, cracking of the susceptor due to these thinned locations is precluded.
When introducing elements of various aspects of the present invention or embodiments thereof, the articles “a”, “an”, “the” and “said” are intended to mean that there are one or more of the elements. The terms “comprising”, “including” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. Moreover, the use of “top” and “bottom”, “front” and “rear”, “above” and “below” and variations of these and other terms of orientation is made for convenience, but does not require any particular orientation of the components.
As various changes could be made in the above constructions, methods and products without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. Further, all dimensional information set forth herein is exemplary and is not intended to limit the scope of the invention.
