U.S. patent application number 10/431120 was filed with the patent office on 2004-11-11 for method for increasing polysilicon granin size.
Invention is credited to Chen, Bu-Fun, Huang, David, Huang, Yao-Hui, Lee, Tung-Li, Lin, Chih-Hao, Lin, Yen-Fei, Sun, James.
Application Number | 20040224533 10/431120 |
Document ID | / |
Family ID | 33416387 |
Filed Date | 2004-11-11 |
United States Patent
Application |
20040224533 |
Kind Code |
A1 |
Huang, Yao-Hui ; et
al. |
November 11, 2004 |
Method for increasing polysilicon granin size
Abstract
The present invention relates to a method for increasing the
grain size of a polysilicon layer, which includes exposing a
silicon oxide wafer in a deposition chamber to an amount, effective
for the purpose, of nitrogen at a flow rate of at least about 240
standard liters per minute (slm).
Inventors: |
Huang, Yao-Hui; (Taipei,
TW) ; Lee, Tung-Li; (Hsin-Chu, TW) ; Lin,
Chih-Hao; (Taipei, TW) ; Lin, Yen-Fei;
(Ping-Dong, TW) ; Sun, James; (Taipei, TW)
; Chen, Bu-Fun; (Taipei, TW) ; Huang, David;
(Taipei, TW) |
Correspondence
Address: |
DUANE MORRIS, LLP
IP DEPARTMENT
ONE LIBERTY PLACE
PHILADELPHIA
PA
19103-7396
US
|
Family ID: |
33416387 |
Appl. No.: |
10/431120 |
Filed: |
May 7, 2003 |
Current U.S.
Class: |
438/775 ;
257/E21.166 |
Current CPC
Class: |
C23C 16/24 20130101;
H01L 21/28525 20130101; C23C 16/0218 20130101 |
Class at
Publication: |
438/775 |
International
Class: |
H01L 021/31; H01L
021/469 |
Claims
What is claimed is:
1. In the manufacture of semiconductor devices, a method for
increasing the grain size of a polysilicon layer in a furnace,
which comprises exposing a silicon oxide wafer in a deposition
chamber of the furnace to an amount, effective for the purpose, of
nitrogen at a flow rate of at least about 240 standard liters per
minute.
2. The method as recited in claim 1, wherein the flow of nitrogen
is achieved through nitrogen shower.
3. The method as recited in claim 1, wherein the increasing of
grain size results in an increase in semiconductor device speed.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to semiconductor
device manufacturing, and, more particularly, to a method for
controlling device speed by adjusting polysilicon grain size.
BACKGROUND OF THE INVENTION
[0002] In the manufacture of semiconductor devices, wafers, such as
silicon wafers, are subjected to a number of processing steps. The
processing steps include depositing or forming layers, patterning
the layers, and removing portions of the layers to define features
on the wafer. One such process used to form the layers is a
procedure known as chemical vapor deposition (CVD), where reactive
gases are introduced into a vessel containing the semiconductor
wafers. The reactive gases facilitate a chemical reaction that
causes a layer to form on the wafers.
[0003] One deposition process involves the formation of
polycrystalline silicon (polysilicon) layers on the wafer by
decomposing SiH.sub.4 molecules to Si atoms, which in turn combine
to form Si grains, or "polysilicon.". There are numerous factors
that affect the deposition rate and deposition polysilicon film
characteristics of a deposition tool. These factors include, e.g.,
the flow rate of reactive gases through the chamber and the
temperature/pressure of the chamber.
[0004] Polysilicon furnaces both within and without a nitrogen box
(the furnace wafer loading area immediately below the furnace main
body) may play an important role in controlling polysilicon grain
size, thereby governing device speed. An important consideration is
the actual N.sub.2 (nitrogen) flow which continuously treats the
silicon wafer surface in the N.sub.2 box. A continual need exists
for effective mechanisms for increasing the grain size of a silicon
wafer.
SUMMARY OF THE INVENTION
[0005] The present invention relates to a method for increasing the
grain size of a polysilicon layer in a furnace, which includes
exposing a silicon oxide wafer in a deposition chamber to an
amount, effective for the purpose, of nitrogen at a flow rate of at
least about 240 standard liters per minute (slm).
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] The present invention may be understood by reference to the
following description taken in conjunction with the accompanying
drawings, in which:
[0007] FIG. 1 is a graph of the effect of increased nitrogen flow
in a furnace; and
[0008] FIG. 2 is a graph of polysilicon film volume fraction versus
control wafer resistivity in a furnace.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0009] According to the method of the present invention, a
maximizing of polysilicon grain size results in an increase in
device speed. In the method of the present invention, when an oxide
wafer (i.e., a surface capped with a thin O.sub.2 boundary layer)
was placed in an N.sub.2 box, the wafer was exposed to bulk N.sub.2
flow, with absorbed O.sub.2 being removed as a result. Upon
treatment with the N.sub.2 flow, absorbed oxygen bonded with oxide
molecules, and the oxygen depletion site was filled with N.sub.2
molecules. Nitrogen molecules "interfere" with silicon in forming a
polysilicon seed; therefore fewer seeds, and a larger grain size
was the result.
[0010] A prototypical furnace includes four tube furnaces, which
are used for curing polymers, sintering, and growing oxides and
nitrides on silicon wafers. There are also four gas flow timers for
the furnace. The orientation of the timers matches the orientation
of the tubes with which they correspond; with a maximum time of
twelve hours, the flow timers are used to control the time the gas
flows in the furnaces. The minimum amount of time for the process
to function correctly is about two hours. When the timer reaches
zero, the gas discontinues to flow.
[0011] There are three flow meters located just below the gas flow
timers. Beneath each of the flow meters are two flow meter valves.
The cut-off valves are the valves closest to the flow meters. The
handles are at a 90.degree. angle when the flow meters are closed.
When the handles are parallel with the flow meter, they are open.
The lower valves are the needle valves, which control the gas flow
into the flow meters. To the right of the flow meters is the
three-way valve. This valve controls which gas flows into the
middle flow meter (tube 2). The two selectable gases are oxygen and
nitrogen. The narrow, pointed end of the handle points to the gas
that is being used. When tube 2 is not in use, the valve is turned
to the off position. When furnace tube 2 is used, which performs
oxidation, the oxygen cylinder in the chase behind the furnace is
on. Note that in order to check that the gas pressure is
sufficient, the cylinder gauge closest to the cylinder is read. The
gauge to the left indicates the gas line pressure; it is set to
approximately 25 psi.
[0012] The furnace temperature is controlled by a programmable
temperature control unit. There is one control for every furnace;
there are programmable temperature controllers on each of the
temperature control units. These controllers monitor each of the
furnace zone heaters, and allow the programming of several process
steps. Thus, in order to operate the furnaces, the following steps
are performed: (1) set the appropriate atmosphere, (2) load the
furnace, (3) set the temperature program, (4) run the process, (5)
end the run.
[0013] The first step in setting the atmosphere is to set the gas
flow timer to the length of the particular run. This prevents the
waste of gas in the system. The next step is to set the flow of gas
using the flow meters.
[0014] The first step in loading the furnace is to place a sample
into a quartz boat, which is found in the nitrogen box next to the
furnace. The cap on the end of the tube is removed, and the boat
placed just inside the opening. A metal rod is used in order to
carefully push the boat to the middle of the furnace tube. The
desired temperature in degrees Celsius is set for the controllers,
and the temperature cooled to about room temperature when the
program is done. In order to remove the boat from the furnace, the
loading procedure is reversed.
[0015] In the testing of the present invention, an analysis of the
effect of an increase in nitrogen flow, via nitrogen shower or
other acceptable method was conducted in a furnace. As shown in
FIG. 1, the V.sub.f (the polysilicon film volume fraction, which is
an index of polysilicon grain size) trends down (i.e., larger grain
size, as nitrogen flow increased). In FIG. 2, note that R.sub.s
(control wafer resistivity) trends down (i.e., higher speed) as
V.sub.f trends down (i.e., a larger grain size). Therefore, it is
apparent that device speed is significantly enhanced by the amount
of the N.sub.2 flow rate in a furnace.
[0016] While this invention has been described with respect to
particular embodiments thereof, it is apparent that numerous other
forms and modifications of this invention will be obvious to those
skilled in the art. The appended claims and this invention
generally should be construed to cover all such obvious forms and
modifications which are within the true spirit and scope of the
present invention.
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