Semiconductor device manufacturing: process – Radiation or energy treatment modifying properties of... – By differential heating
Reexamination Certificate
2000-04-21
2001-12-11
Mills, Gregory (Department: 1763)
Semiconductor device manufacturing: process
Radiation or energy treatment modifying properties of...
By differential heating
C438S795000, C427S482000, C118S724000, C118S718000, C219S411000
Reexamination Certificate
active
06329304
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a floating wafer reactor, comprising a processing area at least bounded by walls, wherein heating means are arranged, wherein temperature sensors are arranged which are connected to a controller for the regulation of those heating means.
BACKGROUND OF THE INVENTION
Such a reactor is generally known in the state of the arts There, a wafer is held at a very small distance from facing walls of the reactor by gas flowing from both sides of the wafer. This gas comprises the required reactants. Such a reaction can take place at a comparatively high temperature such as approximately 1000° C. To that end, the walls or plates of the floating wafer reactor are heated, which takes place with the help of heating elements. The energy supply to these electrical heating elements takes place by means of a controller which is regulated by sensors which are either close to the processing area or somewhat deeper in the walls of the floating wafer reactor. The gas supplied to the processing area is heated to the desired temperature beforehand. Apart from the entering and leaving of wafers, the temperature control is comparatively easy and, temperature-wise, a very stable system arises, as the furnace should preferably be continually at the same temperature.
Problems occur during the entering of the wafers in the processing area, however. These will generally be at a comparatively low temperature, for example, at room temperature. Due to the small distance between the walls of the reactor and the wafer, a very rapid heating of the wafer takes place, typically from some seconds to some minutes. The heat capacity of the wafer is much smaller than the heat capacity of the walls. In a typical case, when the temperature of the wafer is elevated from room temperature to 1000° C., a lowering of the temperature by approximately 10° C. occurs immediately on the border between the walls and the processing area of the reactor. Internally of the walls, that is, further away from the border with the processing area, this temperature decrease will be smaller and, if no fiber measures are taken, a temperature drop of the walls of approximately 3° C. can be caused in the long term. This is obviously compensated for by the detection of the sensors present in the walls which will supply extra energy via the controller to the heating elements.
As the heating elements are some distance from the processing area, and the area in between will generally be filled with a ceramic material with a certain heat capacity where the heat is not optimally conducted, there will be some time lag.
For a number of processes, this is particularly undesirable. There, it is important that the temperature in the processing chamber is kept within a narrow range and may not be too high or too low, to be able to correctly control the reaction which takes place in the processing chamber.
SUMMARY OF THE INVENTION
The present invention aims to provide a floating wafer reactor wherein the temperature is controlled such that the entering of a wafer at a comparatively low temperature does not have the negative effects discussed here, that is, that an immediate, adequate reaction occurs to the instantly occurring temperature drop on the boundary surface between the walls of the reactor and the processing area.
This aim is achieved in a floating wafer reactor described above in that means are arranged which, during the entering of the wafer into the processing area, influence the controller such that an amount of energy is supplied to the heating means for a certain time independently of the sensors.
By immediately supplying the heating elements with a pulse of energy during the entering of the wafer, the slowness of the measuring of the temperature drop by the sensors, on the one hand, and the transfer of heat from the heating elements to the processing chamber, on the other hand, is largely or completely removed. “During the entering” has to be understood as both some time before the entry of the wafer, the moment of entering of the wafer and some time thereafter. All of those clearly expressed in seconds or a shorter time, such that this time is substantially shorter than the reaction time of the sensors and the heat exchange between the heating elements and the boundary between the processing area and the walls of the reactor, respectively.
The control of the heating elements can comprise any construction known in the state of the art, but is preferably realized as a cascade control system. Such a cascade control system can be realized with the help of two thermocouples or sensors, wherein one thermocouple is arranged close to a wafer and another thermocouple is arranged closer to the heating element.
According to the invention, a temperature control system consists of two parts. A first part that works with the help of sensors and keeps the temperature of the sensors in the processing area constant in the long term, and a second part that reacts to the introduction of a wafer in the processing area and gives an adequate energy pulse to entirely or largely compensate for the energy absorbed by the wafer.
Due to the presence of the second control part, it is advantageous that the sensor of the first control part which is close to the wafer is not arranged as close as possible to the wafer but at some distance from the boundary between the processing area. A value of 20 mm is given as an example. In this way, the short, sharp temperature fluctuations caused by the introduction of the wafers is only detected by this sensor in a very damped manner.
The invention also relates to a method for the controlling of the temperature in a floating wafer reactor comprising the supply of energy to the heating elements by a controller, which controller is influenced by sensors arranged in the walls of the floating wafer reactor. According to the invention, the controller is influenced during the entry of a wafer in the processing area of a floating wafer reactor such that an amount of energy is added to the electrical heating elements, independently of the sensors. The heating elements can be arranged in the walls but can also comprise lamps and the like.
According to an advantageous embodiment of the invention, the amount of energy supplied to the heating elements is such that this compensates exactly for the amount of energy which is required to heat the said wafer.
It is possible to supply the extra energy pulse, caused by the entering of the wafer, to the heating elements according to some shape known in the state of the art. According to an advantageous embodiment of the invention, the extra pulse is a block pulse, that is, the same amount of energy is supplied constantly during a comparatively short time such as 3-15 seconds.
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Granneman Ernst Hendrik August
Kuznetsov Vladimir Ivanovich
A.S.M. International N.V.
Hassanzedeh P.
Knobbe Martens Olson & Bear LLP
Mills Gregory
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