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Original Publication Date: 2000-Jan-01
Included in the Prior Art Database: 2002-Sep-10
Document File: 3 page(s) / 145K

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Doug Bishop: AUTHOR [+2]


This paper relates to the field of vacuum seals. More specifically, this paper relates to a vacuum seal for low-pressure chemical vapor deposition applications.

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Technical M-LA @ Developments


by Doug Bishop and Sheldon Quick


  This paper relates to the field of vacuum seals. More specifically, this paper relates to a vacuum seal for low-pressure chemical vapor deposition applications.


  Semiconductor substrates are fabricated using low-pressure chemical vapor deposition (LPCVD) processes. During this process, an LPCVD chamber is used to contain semiconductor substrates and cer- tain chemicals at high temperatures. The LPCVD chamber is heated using a coil furnace. During LPCVD processing, the LPCVD chamber is evacu- ated to form a vacuum therein at a pressure near 1 mTorr.

  The LPCVD chamber of choice is frequently a quartz tube fabricated with a quartz neck and quartz ball socket. The end of the quartz tube connecting the neck and the ball socket is called the 'back' end. The quartz ball socket and a stainless steel ball cover form an interface between the LPCVD cham- ber and the vacuum system. The low-pressure vacu- um system consists of a pump capable of achieving pressures below 1 mTorr, a control valve, and a stainless steel vacuum line that connects to the ball cover.

  The prior art ball junction arrangement uses an Elastomer O-ring gasket inserted into the ball junc- tion between the quartz ball junction and the metal cover to provide a vacuum seal. A thin receiving groove is cut within the metal ball cover for place- ment of the Elastomer O-ring.


  The prior art ball junction design fails to create a long-lasting vacuum system due to high temperature

processing required during LPCVD processing. The O-ring becomes denatured at temperatures near 180 degrees Celsius and above, while the temperature of the LPCVD chamber is typically maintained at tem- peratures between 710°C and 790°C. Under atmos- pheric pressure, the temperature gradient between the vacuum seal and the back end of the tube is not high enough, resulting in temperatures exceeding the O-ring's threshold of 180°C. Under vacuum, the temperature gradient is much larger, with the ball socket and O-ring reaching temperatures between 140°C and 160°C.

  In addition to the maximum O-ring temperature of lSO"C, low temperatures can be detrimental to an LPCVD process using the prior art with cooling. Side reactions of some chemicals used for LPCVD processes (e.g., dichlorosilane and ammonia) can form unwanted byproducts (e.g., ammonium chlo- ride) and tend to condense sublime around the ball junction if the back end temperature is not main- tained high enough (e.g., above 140°C). Resublimination of ammonium chloride creates unwanted substrate haze and particulates that build up within the chamber and will reduce yield.

  To achieve an adequate vacuum seal, a double clamp system is used in the prior art design to align the quartz ball socket with the metal cover. The double clamp assembly is constructed of Aluminum, which expands and contracts with high temperatures achie...