Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Composite having voids in a component
Reexamination Certificate
1998-12-18
2001-10-23
Copenheaver, Blaine (Department: 1771)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Composite having voids in a component
C428S142000, C428S212000, C428S318600, C428S319100, C428S428000
Reexamination Certificate
active
06306489
ABSTRACT:
The invention relates to a quartz glass component for a reactor housing, comprising a substrate body made of a first quartz glass quality with an inside surface facing the interior of the reactor which inside surface has in at least one roughness zone a median roughness depth R
a
of more than 1 &mgr;m. Further, the invention concerns a method for the manufacture of a quartz glass component for a reactor housing, in particular for a reactor chamber of a plasma etching device, comprising the following steps: a) the forming of a blank made of a granulate containing SiO
2
, and
1. Field of the Invention
b) the partial or complete vitrification of the blank by heating to a temperature above 1,000° C.
2. Discussion of the Prior Art
Quartz glass components of the kind indicated above are used for example as quartz glass bells for reactor chambers in plasma etching devices. Such etching devices are used for the etching of semiconductor wafers. The surface of semiconductor wafers is commonly coated, after a chemical pre-treatment, by dielectric coatings such as oxide and nitride coatings, or electrically conductive coatings such as silicide or polysilicide layers. To manufacture a free silicon surface these coats are removed by means of a plasma process. During this process the removed materials in turn are deposited as layers on the inner surfaces of the reactor chamber. When these layers reach a certain thickness they break off and lead to particulate problems. In order to prevent this the affected surfaces are cleaned from time to time. The cleaning of the surfaces is costly in terms of time and money. In order to reduce the expenses it is desirable to keep the periods between the cleaning steps as long as possible.
It is known that roughened surfaces are able to hold thicker layers. Sandblasting is commonly used for the roughening of quartz glass bells. Normally, an average roughness of at least 1 &mgr;m is desired. The average roughness R
a
is established according to DIN 4768.
Even though on the one hand sandblasting produces structures on the quartz glass surfaces which contribute to a stronger adhesion of coatings, on the other hand fractures develop starting at the surface, in turn causing the layers to break off. This results in particle problems in the reactor space. In addition, a homogenous treatment of the entire inner surface of quartz glass bells and the maintaining of precise dimensioning during sandblasting is problematic. The roughness of the inner surface changes as a result of repeated sandblasting. This can adversely affect the bell's continued usefulness and therefore its life expectancy.
Pour-in technology may be used to manufacture a quartz glass bell, as is used in the manufacture of quartz glass crucibles. A process for the manufacture of a quartz glass bell for the reactor chamber of a CVD-coating apparatus is described in EP-A 2,715,342. First, a metallic casting mold is filled with crystalline or amorphous SiO
2
powder which, under rotation of the casting form about its vertical axis, forms into an granular outer layer having a thickness of about 200 mm. The outer layer is then heated from the inside by means of an electric arc and is melted or sintered. The inner surface of a quartz glass blank manufactured in this manner is compact and smooth. The above-proposed sandblasting method is suitable for the roughening. A quartz glass bell is completed by fusing a flange to the blank.
The known process is particularly sensitive in respect to the homogeneity of the temperature field during the pouring of the granulate and during vitrification. The roughness of the inner surface after sandblasting depends on it. The reproducible maintenance of the roughness requires high expenditures.
SUMMARY OF THE INVENTION
The object of the invention is to provide a quartz glass component which produces as far as possible no particles in the reactor chamber and which is distinguished by high adhesiveness for coatings, and by a particularly long service life. Furthermore, the object of the invention is to provide a simple method for the manufacture of such a quartz glass component which method would make possible a reproducible adjustment of a predetermined surface roughness.
Concerning the quartz glass component, the object is accomplished on the basis of the above-described quartz glass bell in that an open-pore bubble layer of a second quartz glass quality is formed on the substrate in the roughness zone.
The roughness zone encompasses that portion of the inner surface of the quartz glass component facing the inner space of the reactor, on which for example deposition of material layers is expected during the intended use of the quartz glass component. It may encompass the entire inner surface of the quartz glass component. Deposition of material layers may take place due to chemical reactions or physical processes such as heating, vaporizing, smelting, sublimating, etc. Not only can the adhesion of material layers be improved by means of the bubble layer, but the optical properties of the component such as transmission or absorption in the roughness zone can be specifically controlled.
The open pores in the roughness zone result in a particularly suitable type of surface roughness as regards firm adhesion of material layers deposited thereon. The open pores form a surface microstructure in the roughness zone which structure is distinguished by a plurality of places of adhesion and points of attack for the layers deposited thereon. In addition, the porous structure contributes to a beneficial distribution of tension between the quartz glass and the coating material by assuring a three-dimensional distribution of the resulting tensions. A particularly high adhesiveness for the material layers is achieved due to the open pores and it permits deposition of especially thick material layers on the inner surface of the quartz glass component without the risk of breaking-off. The time periods between cleanings can therefore be extended which makes the service life of the quartz glass component longer.
This is also aided by the fact that a porous bubble layer is provided in the roughened zone. In addition to the open pores in an area close to the surface, the bubble layer also contains pores which do not end immediately near the inner surface. These pores may be closed. These deeply embedded pores become open pores immediately near the surface as a result of removal of the porous layer near the surface, for example during designated use of quartz glass component in an etching apparatus or during removal of deposited layers by means of etching or sandblasting. Therefore the surface microstructure characterized by the open porosity does not change or does so only insignificantly as long as the bubble layer is not removed. This contributes to a time-constant roughness of the inner surface and thus to a long service life of the quartz glass component.
The bubble layer is formed on the substrate. It thus forms only a portion of the wall thickness of the quartz glass component in the roughness zone. The component therefore comprises at least two layers of differing quartz glass qualities, the term “quality” here meaning the sum of chemical, physical or optical properties of each quartz glass. The bubble layer which comprises only a portion of the component may for example be optimized as regards the adhesiveness of material layers while the substrate may have advantages as regards other properties such as transmission, mechanical stability or manufacturing costs.
In what follows, the term “reactor” is meant to be a reaction vessel in which chemical reactions or physical processes such as heating, vaporizing, smelting, sublimating, etc. take place partially or completely. The quartz glass component may for example serve as a cover for a reactor housing or as the reactor housing itself. Such housings are known in many forms for example as bells, tubes or bowls.
The average thickness of the porous bubble layer is advantageously between 0.5 mm and 5 mm, while being imbedded in a non-
Hellmann Dietmar
Leist Johann
Copenheaver Blaine
Heraeus Quarzglas GmbH
Tiajoloff Andrew L.
Vo Hai
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