Coating processes – Interior of hollow article coating – Coating by vapor – gas – mist – or smoke
Reexamination Certificate
2000-02-18
2001-09-04
Beck, Shrive P. (Department: 1762)
Coating processes
Interior of hollow article coating
Coating by vapor, gas, mist, or smoke
C427S255180, C427S255270, C427S255393, C427S314000, C423S349000
Reexamination Certificate
active
06284312
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
This invention relates to chemical vapor deposition of polysilicon directly onto the walls of a reaction chamber. More particularly, it relates to broad surface area chemical vapor deposition where a thin wall casing is used to construct the reaction chamber, and becomes the broad surface area form upon which the polysilicon deposit is made.
2. Background Art
One of the widely practiced conventional methods of polysilicon production is by depositing polysilicon in a chemical vapor deposition (CVD) reactor, and is referred to as Siemens method. In this method, polysilicon is deposited in a CVD reactor on high-purity thin silicon rods called “slim rods”. Because of the high purity silicon from which these slim rods are fabricated, the corresponding electrical resistance of the slim rods is extremely high. Thus it is extremely difficult to heat this silicon “filament” using electric current, during the startup phase of the process.
Sometimes the slim rods are replaced by metallic rods that are more conductive and easier to heat with electrical current. This method is referred to as Rogers Heitz method. However, the introduction of metal into the chemical vapor deposition process introduces metal contamination. This contamination of the polysilicon yield is not acceptable in the semiconductor/microelectronics industry.
In the Siemens method, external heaters are used to raise the temperature of these high purity rods to approximately 400° C. (centigrade) in order to reduce their electrical resisitivity. Sometimes external heating is applied in form of halogen heating or plasma discharge heating. However in a typical method, to accelerate the heating process, a very high voltage, in the order of thousands of volts, is applied to the rods. Under the very high voltage, a small current starts to flow in the slim rods. This initial flowing current generates heat in the slim rods, reducing the electrical resistance of the rods and permitting yet higher current flow and more heat.
This process of sending low current at high voltage continues until the temperature of slim rods reaches about 800° C. At this temperature, the resistance of the high purity silicon rods falls very drastically and the high voltage source is switched to a low voltage source that is capable of supplying high current.
Referring to prior art
FIG. 1
, a CVD reactor consists of a base plate
23
, quartz bell jar
17
, chamber cover
24
, bell jar supports
16
, and heater
18
between the bell jar and the chamber cover. There is incorporated in base plate
23
, a gas inlet
20
and a gas outlet
21
, and electrical feedthroughs
19
. A viewing port
22
provides for visual inspection of the interior.
In the prior art polysilicon manufacturing process by CVD, the silicon slim rod structure is assembled in the form of a hair pin by having a cross rod
2
placed horizontally on two long, spaced apart, vertical rods
1
and
3
. The structure is mounted and connected so as to provide a current path between electrical feedthroughs
19
. During the CVD process, polysilicon deposit accumulates uniformly on the slim rods; the deposit being shown here partially removed to show the slim rod structure.
Different users employ different methods for joining the horizontal rod to the vertical rods. One method requires a groove or a key slot at the top of each vertical rod. A small counter bore or conforming figment is formed on the ends of the horizontal rod so that it can be press fitted into the grooves to bridge the two vertical rods.
A typical prior art reactor consists of a complex array of subsystems. Two power sources are required, one power supply that can provide very high voltages and low current; and a second power supply that can sustain a very high current at relatively lower voltage. Also needed are the slim rod heaters and their corresponding power supply for preheating the slim rods. Another component is the high voltage switch gear. Moreover, the entire startup process is cumbersome and time consuming. Since the current drawn by the slim rods at around 800° C. is of a run away nature, the switching of the high voltage to low voltage needs to be done with extreme care and caution.
Also, through this electric current method for heating the slim rods, the rods become an interior heat source losing tremendous amounts of heat via radiation to the surroundings. There is significant energy loss inherent in the existing practice.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an apparatus and method for more efficient production of polysilicon by chemical vapor deposition, using less power and resulting in lower cost, by using a thin wall tubular casing to construct a reaction chamber, heating the casing from outside the chamber, and depositing polysilicon directly upon the interior wall of the casing.
It is a further object of the invention to provide a method to eliminate many of the costly components of the prior art CVD process reactor by replacing the basic slim rod design of the prior art as the core element and target for deposition, with a thin wall tubular section or casing as the target for broad area deposition.
The availability of large diameter silicon tubes, readily drawn using the EFG (edge-defined film fed growth) method, motivated the research leading to the present invention. Other means for extruding or forming tubular casings or structures suitable for deposition in the manner of the invention as the walls of a reaction chamber or as broad surface area deposition targets within the reaction chamber, are within the scope of the invention.
In accordance with the invention, a chemical vapor deposition reactor is specifically designed to utilize a reaction chamber constructed from a section of tubular material, which may be of silicon, graphite or suitable metals. The chamber is closed at bottom and top ends as may be done with a base plate and cover respectively. The inner surface of the tube becomes the wall of the reaction chamber. When radiant heat is applied from sources external to the chamber, as with jacket heaters applying radiant heat through a quartz envelope, sufficient to heat the chamber walls to the necessary deposition temperature, and a suitable carrier gas and reactant materials containing silicon are admitted into the chamber, the hot chamber walls become a broad surface area available for deposition.
As the chemical vapor deposition proceeds, a continuous, broad surface layer of polysilicon is deposited on the chamber wall, building in thickness so that the interior diameter of the chamber grows progressively smaller. This results in the production of a hollow, tubular bulk quantity of polysilicon with a thin wall tubular casing. The casing can be included or removed prior to further processing of the polysilicon.
A further refinement of the invention provides for the placement of a somewhat smaller diameter thin wall core tube suspended in the center of the reaction chamber formed by the larger diameter shell tube, so that broad area deposition occurs on both the inner and outer surfaces of the core tube concurrently with deposition on the inner surface of the shell tube. This results in a larger yield over the same reaction time, and more efficient use of the reactor.
The most common carrier gas for chemical vapor deposition of polysilicon is hydrogen, although an inert gas could be used. Suitable reactant materials for use with a hydrogen carrier are either silane, SiH4, having a deposition temperature in the order of 800 degrees centigrade, or any of the chlorosilanes, which have a deposition temperature in the order of 1000 to 1200 degrees, depending on the actual composition and process details. The primary product of the process is, of course, a solid deposit of polysilicon on the interior walls of the reaction chamber. The gaseous byproducts of the process are removed continuously through outlet ports, as new carrier gas and reactant materials are admitted into the chamber.
Still other objecti
Chandra Mohan
Gupta Kedar Prasad
Jafri Ijaz Hussain
Prasad Vishwanath
Talbott Jonathan A.
Asmus Scott J.
Barr Michael
Beck Shrive P.
GT Equipment Technologies INC
Maine Vernon C.
LandOfFree
Method and apparatus for chemical vapor deposition of... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for chemical vapor deposition of..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for chemical vapor deposition of... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2451507