Device for insulating and sealing electrode holders in CVD reactors
Improved sealing of Siemens reactor electrodes which results in improved reactor campaign times, is accomplished by use of an electrically insulating ring in combination with two seals, a first seal located in a groove in the insulating ring or in a groove in the reactor base plate adjacent the insulating ring, and a second seal not contained in a groove.
1. An apparatus for insulating and sealing electrode holders in CVD reactors having an electrode suitable for accommodating a filament rod disposed atop an electrode holder made of an electrically conductive material and mounted in a recess in a floor plate, comprising:
an electrically insulating ring made of a material of construction having a specific thermal conductivity at room temperature of 0.2-50 W/mK, a minimum flexural strength of greater than 120 MPa, and a specific electrical resistance at room temperature of greater than 10 9 Ωcm, located between the electrode holder and the floor plate,
wherein at least two ring-shaped sealing elements for sealing between the electrode holder and the floor plate are present, wherein the electrically insulating ring or the electrode holder or the floor plate comprises at least one groove in which a first sealing element is secured, wherein at least one second sealing element not secured in a groove is present between the electrically insulating ring and the floor plate or between the electrically insulating ring and the electrode holder, and wherein the at least two ring-shaped sealing elements are not located on the same side of the electrically insulating ring.
2. The apparatus of claim 1 , wherein the material of construction of the electrically insulating ring is selected from the group consisting of aluminum oxide, silicon nitride, boron nitride, zirconium oxide, and yttrium-oxide-, magnesium-oxide- or calcium-oxide-stabilized zirconium oxide.
3. The apparatus of claim 2 , wherein the first sealing element is a graphite foil ring.
4. The apparatus of claim 1 , wherein the first sealing element is a graphite foil ring.
5. The apparatus of claim 1 , wherein the first sealing element is a metallic O-ring or a metallic seal having an open profile having a spring action.
6. The apparatus of claim 5 , wherein the metallic seal has a C-profile and is coated with silver.
7. The apparatus of claim 1 , wherein the second sealing element is a gasket comprising graphite or PTFE.
8. The apparatus of claim 7 , wherein the gasket is chambered on the reactor-side seal circumference as a result of metal or silver foil being flanged around the reactor-side sealing surface of the gasket.
9. A process for producing polycrystalline silicon, comprising introducing a reaction gas comprising a silicon-comprising component and hydrogen into a CVD reactor comprising at least one filament rod which is disposed atop an apparatus of claim 1 , the filament rod supplied with current via the electrode and thus heated by direct passage of current to a temperature at which polycrystalline silicon deposits on the filament rod.