Browse Prior Art Database

Coating for Ultra High Voltage Pyrex Viewports to Prevent Boron Outgassing

IP.com Disclosure Number: IPCOM000113934D
Original Publication Date: 1994-Oct-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 2 page(s) / 66K

Publishing Venue

IBM

Related People

Delage, SL: AUTHOR [+4]

Abstract

Viewports are a common feature in most vacuum systems. This is especially true in the case of large Ultra High Voltage (UHV) systems such as Molecular Beam Epitaxy (MBE) systems, where they are used for a variety of reasons from visual monitoring of sources and transfer mechanisms to optical coupling of visible and IR radiation into the system.

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Coating for Ultra High Voltage Pyrex Viewports to Prevent Boron Outgassing

      Viewports are a common feature in most vacuum systems.  This is
especially true in the case of large Ultra High Voltage (UHV) systems
such as Molecular Beam Epitaxy (MBE) systems, where they are used for
a variety of reasons from visual monitoring of sources and transfer
mechanisms to optical coupling of visible and IR radiation into the
system.

      In Si MBE there have been indications that there is significant
contamination of Si with boron.  This is undesirable because B is a p
type dopant in Si.  In fact, it has been observed that there is a
pile-up of B at the interface.

      The problem has been isolated as due to B&sub2.O&sub3.  or
sub-oxides evaporating from the pyrex viewports.  Pyrex is basically
a borosilicate glass.  During cleaning and also during growth the
substrate is taken to high temperatures.  The viewports in the
vicinity of the sample heat up (by radiation).  The temperature is
high enough to cause dissociation of Boron oxide, a volatile
compound, and this dopes the growing silicon film.

      Pyrex viewports may be replaced by quartz or sapphire
viewports.  However, there are some problems in that they have
different transmission characteristics, they cannot be made in large
sizes (six inch diameter is very difficult) and they are very
expensive (3 to 10 times).  Also, they cannot be baked to
temperatures >  250ºC because of the delicate seal and they
are not as reliable.  Hence, pyrex ports are preferred.

      This publication describes a technique to prevent B out
diffusion and deposition on the substrate.  It consists of coatin...