Electric heating – Heating devices – Combined with container – enclosure – or support for material...
Reexamination Certificate
1999-02-19
2001-06-12
Pelham, Joseph (Department: 3742)
Electric heating
Heating devices
Combined with container, enclosure, or support for material...
C134S001000, C134S037000, C438S905000
Reexamination Certificate
active
06246029
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to cleaning semiconductor manufacturing equipment, and, more particularly, to cleaning unwanted deposits from components of semiconductor crystal growing furnaces.
BACKGROUND OF THE INVENTION
In the semiconductor industry, crystal growing furnaces are used to produce ingots of semiconductor material. According to the most common crystal growing technique, the Czochralski Method, purified polycrystalliie silicon is heated to a molten liquid inside a crystal growing furnace. A small, monocrystalline silicon seed is introduced to the silicon melt, and is rotated slowly and pulled from the melt. As the seed is slowly withdrawn, molten silicon solidifies on the seed, thereby increasing its size. By varying the rotation and pull rates, a resultant monocrystalline silicon ingot of a desired shape and size may be produced. Typically, silicon ingots are produced in industry-standard 200 mm or 300 mm diameter cylinders.
Crystal growing furnaces typically include a pair of concentric quartz and graphite crucibles into which raw polycrystalline silicon material is placed for melting. Surrounding the crucibles is a generally cylindrical-shaped graphite heating element. Surrounding the heating element, in turn, are one or more graphite heat shields and a water-cooled jacket, typically of stainless steel material.
The region within and immediately outside the heating element is termed the “hot zone” because during the crystal growing process the temperatures therein are above the melting point of the silicon melt, which is approximately 1410° C. for pure silicon. The regions of the furnace outside of the hot zone, including the neck region into which the solidified silicon ingot is pulled, typically are maintained at lower temperatures than the hot zone. Therefore, the silicon is able to solidify as it is withdrawn from the melt into a region of lower temperature.
To decrease contamination due to reaction of the silicon with oxygen and other atmospheric gases, the crystal growing process takes places in an inert gas environment. The crystal growing furnace typically includes a graphite purge tube, extending from the neck region to just above the silicon melt to guide the inert gas to the melt, and a graphite chimney, surrounding the purge tube, to decrease turbulence in the flow of the inert gas through the crystal growing furnace.
One common problem experienced by users of crystal growing furnaces is the build-up of deposits such as oxides on certain components in the crystal growing furnace that are located outside the hot zone during the crystal growing process. For example the graphite chimneys and purge tubes commonly experience build-up of deposits along their inner surfaces. Deposits also accumulate on quartz windows located in the purge tube. In addition, ceramic insulators configured to insulate electrodes that supply current to the heating element also commonly experience build-up of deposits on their surfaces.
These deposits are thought to be silicon dioxide, and also may contain trace quantities of boron, antimony, and/or phosphorous, among other materials, and may be of various other material compositions. These deposits, if left uncleaned, may fall into the silicon melt during crystal growth, thereby contaminating the silicon. In addition, because the deposits may cool at a different rate from the materials upon which they have accumulated, they may flake off during heating or cooling of the furnace. If they do not flake off, the deposits may induce thermal stresses that cause certain components, such as the chimneys, to explode or crack during heating and cooling. Build-up on the ceramic insulators may cause arcing to occur from the electrode to nearby metal parts, especially in crystal growing furnaces used with silicon containing high concentrations of conductive dopants, such as antimony.
Several methods of cleaning the deposits from the components currently are known. Vacuums may remove certain dust-like particles; however, they fail to remove hard, caked-on build-up. Machines with abrasive grinders including embedded diamond material are capable of removing the build-up from the graphite purge tubes and chimneys; however, the grinding causes severe damage to the surface of the graphite. Abrasive methods also cause damage to the underlying surfaces of quartz and ceramic components. Blasting methods, such as glass bead and frozen carbon dioxide pellet blasting, are less capable of removing the hard, caked-on deposits, and cause severe pitting of component surfaces.
Because known cleaning methods damage the underlying surface of the furnace components, the components experience a decreased life span, thereby increasing the cost of manufacturing the silicon ingots. Damage resulting from the most efficient of the known cleaning methods, abrasive grinding, has resulted in actual lifetimes for the furnace components of less than one-sixth of their expected lifetimes. It will be appreciated that the aggregate cost of damage resulting from the build-up of deposits on components outside the hot zone of crystal growing furnaces is great.
SUMMARY OF THE INVENTION
A method is provided for cleaning deposits from a component of a semiconductor crystal growing furnace, where the furnace includes a hot zone and where the component is positioned outside the hot zone during the crystal growing process. The method typically includes providing the furnace including the component, removing the component from outside the hot zone, placing the component within the hot zone, and heating the hot zone to clean the component. The component may be virtually any furnace component, including a graphite chimney, purge tube, quartz window, or ceramic insulator. The method may include positioning the component inward of a heating element of the furnace. Where the component is a chimney, the method may also include providing an inner heat shield mounted in the furnace in a predetermined location extending around the hot zone outward of the heating element, removing the inner heat shield from the predetermined location in the furnace, and positioning the chimney outward of the heating element in the predetermined location.
The advantages of the present invention will be understood more readily after a consideration of the drawings and the following description of the invention.
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Kolisch Hartwell Dickinson & McCormack & Heuser
Pelham Joseph
SEH America Inc.
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