Heating – Heating or heat retaining work chamber structure
Reexamination Certificate
2003-10-14
2004-10-12
Wilson, Gregory (Department: 3749)
Heating
Heating or heat retaining work chamber structure
C118S725000, C392S416000, C392S418000
Reexamination Certificate
active
06802712
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The present invention relates to a heating system, a reactor, and a method for heating a reactor for one of deposition and oxidation.
During the manufacture of integrated circuits such as memory product substrates, especially semiconductor wafers, are processed in high-temperature ovens, called reactors, in order to deposit layers of isolating, semiconducting or conducting material. These reactors can be suited for the processing of a plurality of wafers at one time. The wafers are placed on a wafer support inside the reactor. The deposition reactor and, thus, the wafers are heated to a desired temperature. Typically, reactant gases are passed over the heated wafer, causing the chemical vapor deposition of a thin layer of the reactant material on the wafer. Alternatively, reactant gases passing over the heated wafer will immediately react with the substrate material, as is the case in thermal oxidation.
FIG. 1
shows an exemplary deposition reactor that is suited for low-pressure chemical vapor deposition processes. A large number of wafers (typically at least 100) is carried by a wafer carrier, for example a slotted quartz boat, so that the gas flowing direction, which is defined by the line connecting gas inlet and gas outlet and which is parallel to the longitudinal axis of the reactor, is orthogonal to the wafer surfaces. Heating means are provided in order to heat the reactor to a predetermined temperature. As soon as the predetermined temperature is reached, the reactant gases are introduced into the deposition reactor in order to effect the deposition reaction. According to the prior art method, the temperature of the deposition reactor is maintained constant during deposition.
In order to deposit silicon dioxide, for example TEOS, (Si(OC
2
H
5
)
4
) is reacted at a temperature of 700° C. and a pressure of 40 Pa. Silicon nitride layers can be generated by reacting SiH
2
Cl
2
and NH
3
at a temperature of 750° C. and a pressure of 30 Pa.
As is generally known, the deposition rate depends on the deposition temperature and the pressure inside the deposition reactor. More specifically, a higher deposition temperature results in a higher deposition rate. Accordingly, usually a temperature gradient is applied in a direction parallel to the gas flowing direction in order to compensate for the depletion of the reactant gases in that direction. Consequently, the temperature at the reactant gas outlet is higher than the temperature at the reactant gas inlet. By these measures, it is possible to deposit a homogenous layer thickness onto all wafers that are simultaneously processed.
However, it is not possible to achieve a sufficient in-plane uniformity of the layer thickness. More specifically, the layers on the wafers close to the gas outlet tend to assume a bowl shape in which the layer thickness at the edge of the wafer is greater than the layer thickness in the middle of the wafer. Typically, the difference between layer thickness at the edge and layer thickness in the middle is approximately 10 nm at a mean value of the layer thickness of 200 nm. On the other side, the layers on the wafer close to the gas inlet tend to assume a pillow shape in which the layer thickness at the edge of the wafer is smaller than the layer thickness in the middle of the wafer.
U.S. Pat. No. 5,775,889 to Kobayashi et al. discloses a reactor for high temperature treatment of semiconductor wafers. The wafers are held perpendicularly with respect to a reactant gas flow direction parallel to a longitudinal axis of the reactor. The heating system performs a rising and falling temperature profile during wafer processing in order to avoid crystal defects called slip. When the reaction tube has reached about 1,100° C., oxidation gases are fed into the reaction tube.
International patent application no. WO 00/39840 discloses a vertical oven system for boron doping of semiconductor wafers. The wafers are vertically disposed. The oven includes several temperature zones that can be heated independently.
To provide a heating system and a method for heating a reactor for one of deposition and oxidation by which the in-plane uniformity of the deposited or oxidized layer thickness is improved.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a heating system, a method for heating a deposition or oxidation reactor, and a reactor including the heating system that overcome the hereinafore-mentioned disadvantages of the heretofore-known devices and methods of this general type and that improve the in-plane uniformity of the deposited layers by changing the reactor temperature during the deposition process.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a heating system adapted to change a temperature within a reactor during processing. The heating system includes a plurality of heating elements. The plurality of heating elements correspond to the plurality of reactor zones. Each of the plurality of heating elements correspond to a given one of the plurality of reactor zones. The reactor zones are adapted to perform a temperature behavior according to a temperature profile versus time. A heating element corresponding to a zone nearest the gas inlet is adapted to perform a temperature behavior according to a temperature profile that rises during the process. A heating element corresponding to a zone nearest the gas outlet is adapted to perform a temperature behavior according to a temperature profile that falls during the process.
With the objects of the invention in view, there is also provided a reactor that includes the above-described heating system. With the objects of the invention in view, there is also provided a method for heating a reactor during a process involving one of deposition and oxidation of a plurality of semiconductor wafers. The method includes providing a reactor having a gas inlet for feeding at least one reactant gas, a gas outlet for exhausting the at least one reactant gas, a longitudinal axis between the gas inlet and the gas outlet, and a plurality of reactor zones along the longitudinal axis. The next step is holding a plurality of wafers perpendicularly to a reactant gas flow direction aligned parallel to the longitudinal axis to enable the process. The next step is heating each of the reactor zones according to different temperature profiles versus time during the process. The next step is increasing a temperature of a given one of the reactor zones nearest the gas inlet during the process. The next step is decreasing the temperature of a given one of the reactor zones nearest the gas outlet during the process.
Accordingly, in the embodiments of the invention, the reactor temperature is no longer held at a constant value but it is changed. For example, the temperature can be lowered, raised, or changed in an arbitrary manner. Exemplary temperature profiles that are applied in all the zones of the reactor are illustrated in
FIGS. 2 and 3
. As is shown in
FIG. 2
, the temperature is ramped down by 40 K, whereas in
FIG. 3
, during deposition that starts at point A and ends at point B, the temperature is first ramped up by 60 K and then again ramped down by 60 K. The time is depicted in arbitrary units (a.u.). It is to be noted that deposition and oxidation are exchangeable in this invention. A feature of the invention that is described for a deposition reaction can equally be used for an oxidation reaction.
According to a preferred embodiment, the deposition (or oxidation) reactor is divided into a plurality (usually five) of zones along the reactant gas flowing direction. The heating system is divided into heating elements and each of the heating elements is separately controlled so as to provide a different temperature profile indicating the temperature of the specific temperature element versus time as is shown schematically in FIG.
4
. The number of heating elements can be the same as the number of zones. As can be seen from
FIG. 4
, in zone
1
,
Bernhardt Henry
Seidemann Thomas
Stadtmueller Michael
Infineon Technologies SC300 GmbH & Co. KG
Wilson Gregory
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