Browse Prior Art Database

Method for In-Situ Measurement of Amorphous Si Oxidized Layer Thickness Using Laser without Considering Time-Dependent Refractive Index and Density of Amorphous Si

IP.com Disclosure Number: IPCOM000122936D
Original Publication Date: 1998-Jan-01
Included in the Prior Art Database: 2005-Apr-04
Document File: 8 page(s) / 298K

Publishing Venue

IBM

Related People

Takeuchi, M: AUTHOR

Abstract

Disclosed is a method for in-situ measurement of oxide layer thickness grown on a-Si (amorphous Si) film in furnace using laser beam intensity reflected from it without considering characteristic parameters, such as the refractive index of amorphous Si, its density which changes in the middle of the oxide layer-growing process. The oxide layer grows in furnace. At the same time, a-Si changes its phase from amorphous to crystalline continuously. Amorphous-Si has been adopted as a material for floating gate of flash memory, and that gate oxide film, which is between floating gate and control gate, is formed by the oxidation of this a-Si floating gate itself.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 25% of the total text.

Method for In-Situ Measurement of Amorphous Si Oxidized Layer Thickness
Using Laser without Considering Time-Dependent Refractive Index and
Density of Amorphous Si

      Disclosed is a method for in-situ measurement of oxide layer
thickness grown on a-Si (amorphous Si) film in furnace using laser
beam intensity reflected from it without considering characteristic
parameters, such as the refractive index of amorphous Si, its density
which changes in the middle of the oxide layer-growing process.  The
oxide layer grows in furnace.  At the same time, a-Si changes its
phase from amorphous to crystalline continuously.  Amorphous-Si has
been adopted as a material for floating gate of flash memory, and
that gate oxide film, which is between floating gate and control
gate, is formed by the oxidation of this a-Si floating gate itself.
Concerned about how to control the thickness of gate oxidation film,
monitoring the oxide film thickness of Si wafer, which is put into
the furnace tube together with production wafers, has been commonly
used.  The film  thickness of oxidized film grown on Si wafer is
measured with laser used  thickness measurement equipment, and after
that, the estimated oxide layer thickness grown on a-Si from the
thickness of oxide layer on Si wafer based on the relation of
oxidation speed between on the surface of  Si wafer and on that of
a-Si.  In this method, the thickness of oxide layer on floating gate
would not be obtained directly, furthermore, it  cannot be estimated
until the deposition process is fully completed. The  speed of
oxidation for a-Si film is about 1.6 times faster than that for  a Si
substrate.  And this factor could fluctuate according to the
characteristics of a-Si film on which oxide is grown.  The method of
estimating the oxide thickness on a-Si from the measured oxide
thickness on Si wafer would be insufficient because the indirectly
estimated oxide thickness of a-Si would have potential error to some
extent. As  this thickness information cannot be obtained until the
deposition process is fully completed, once abnormality takes place
during the oxidation of a-Si process which leads to thicker or
thinner oxide film  than target value, all wafers processed in that
charge would be all scrapped.  As seen so far, the conventional way
for obtaining the oxide  thickness on a-Si has shortcomings to be
overcome, as described below:
  1.  Including error in the measurement thickness value, which
       originated from the indirect estimation of oxide film
       thickness.
  2.  Film thickness will be obtained only after the deposition
       process is fully completed (not in-situ monitoring).

      The problem to be solved by this invention is establishing
in-situ monitoring of both the oxide thickness and crystalline state
without concern about the time dependence of complex refractive index
and density of a-Si which changes as a-Si changes its crystalline
state fro...