Coating apparatus – Gas or vapor deposition – Crucible or evaporator structure
Reexamination Certificate
2000-07-13
2001-05-08
Bueker, Richard (Department: 1765)
Coating apparatus
Gas or vapor deposition
Crucible or evaporator structure
C392S400000, C392S402000
Reexamination Certificate
active
06228175
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention is directed to apparatus for generating a heated stream of oxygen and water vapor for use in connection with semiconductor processing equipment. In particular, the heated stream of oxygen and water vapor is used to grow thermal oxide films (S
i
O
2
) on semiconductor wafers and also is suitable for use in the deposition of oxide films.
The oxidation of silicon plays a significant part in the use of integrated silicon device technology. The role of the oxide began with the formation of diffusion masks, extended to the use of the oxide as a protective layer and moved on in significance to the use of oxide in integrated circuits. When silicon is exposed to an oxidizing gas, such as oxygen or water vapor, at an elevated temperature, an oxide forms on the surface. An oxide so formed is termed a thermal oxide and is grown on silicon surfaces prepared by chemical or mechanical surface preparation techniques.
While the formation of an oxide layer on silicon can be accomplished using high temperature water vapor or dry oxygen, wet oxygen oxidation wherein an oxygen stream is combined with water vapor provides additional flexibility in the layer formation. The water content of the gaseous stream supplied to the furnace containing the wafers is an important variable for determining oxide thickness. Uniformity and predictability of the characteristics of the oxide layer are dependent on maintaining the ratio of oxygen and water vapor constant.
Typically, the dry tank oxygen is passed through a water bath prior to being introduced into the oxidation furnace. The oxygen travels upwardly through the water vessel with the result that the ratio of oxygen to water is determined in part by the length of the path through the water. As the water level in the vessel changes, the path length of the oxygen gas changes as well and the ratio of the components of the output steam varies as well. The result is that the time required to form an oxide layer of desired thickness is often unpredictable.
An alternative to the passage of an oxygen stream through a water vessel over a period of several hours is the use of controlled hydrogen and oxygen streams combined in a pyrogenic reaction taking place within the furnace. This process typically requires expensive mass flow measurement and ratio control apparatus for each gas stream as well as an under-temperature shut down system. In addition, the safety standards for use of hydrogen in the clean room of a manufacturing facility require extensive shielding. The costs involved in conforming the facility to the local codes and ordinances reduces the desirability of this method of forming an oxide layer on silicon wafers.
Accordingly, the present invention is directed to apparatus for use in the generation of a wet oxygen stream for use in the manufacture of semiconductor components wherein the ratio of water and oxygen is constant during the generation of the stream. Further, the apparatus permits the establishment of the desired ratio prior to introduction of the oxygen and water into a vaporizing vessel. The ability to control the ratio over an extended period of many hours is found to improve the predictability and uniformity of oxide layer formed. The use of this apparatus eliminates the need to modify the facility to conform to safety requirements and thus provides a significant advantage when contrasted with apparatus using a stream of hydrogen to form an oxide layer.
SUMMARY OF THE INVENTION
The invention is directed to the generation of a wet stream of oxygen to be used in a semiconductor furnace for the production of oxide films on semiconductor wafers. The apparatus which is the subject of the present invention utilizes a mixture of water and oxygen injected into a high temperature vessel to produce a gas stream supplied to the semiconductor furnace.
The apparatus includes a quartz vessel open at the top which is nested in a body of high thermal conductivity material. The vessel is in contact with the body. Within the body are inserted means for heating the combination of body and vessel to an elevated temperature of the order of 450° C. A quartz cover having input and output ports is used to close the vessel.
An input tube which contains a mixture of oxygen and water at a predetermined ratio extends from the input port in the quartz cover to a level proximate to the bottom of the vessel. The vessel is substantially filled by chips of inert material so that the chips surround the input tube. The quartz cover includes an output port which contains an output tube that extends downwardly from the port a short distance to a region proximate to the underside of the cover.
During operation, the vessel is first purged and partially heated. The heaters embedded in the body then serve to elevate the temperature of the vessel and the inert chips contained therein. The input tube is then used to deliver a mixture of oxygen and water to the bottom of the vessel. The heating of the vessel and the inert chips to an elevated temperature causes essentially instantaneous vaporization of the water. The flow rate and mixture ratio of oxygen and water are preselected in accordance with the desired growth rate of the oxide film to be produced. The output tube is coupled to the semiconductor furnace.
In contrast to the bubbling of an oxygen stream through a water containing vessel wherein the oxygen and water vapor ratio varies as the process continues, the present apparatus enables the operator to regulate both the ratio and flow rate if desired. Should variation of these parameters not be desired, the flow rate and oxygen-water ratio can be maintained for the period necessary to grow the desired thickness of oxide layer. The use of this apparatus to grow oxide layers enables the operator to control the process by external adjustment.
Alternatively, the apparatus can be used in the deposition of a silicon dioxide layer on the surface of a semiconductor wafer. The input combination of water and oxygen is replaced by nitrogen and tetraethyl orthosilicate (TEOS). The TEOS is vaporized and exits the apparatus mixed with the nitrogen. Oxygen is injected into the output line downstream of the apparatus. The final mixture is provided to the furnace wherein deposition of the oxide film takes place.
REFERENCES:
patent: 3778593 (1973-12-01), Wikstrom
patent: 5467424 (1995-11-01), Davies
Howard Robert W.
Ricker Richard B.
Ridgeway Kent
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