Thermal measuring and testing – Thermal testing of a nonthermal quantity
Reexamination Certificate
1998-10-28
2001-04-17
Bennett, G. Bradley (Department: 2859)
Thermal measuring and testing
Thermal testing of a nonthermal quantity
C374S161000, C374S129000, C374S123000, C374S133000, C374S128000, C374S126000, C414S936000, C414S937000
Reexamination Certificate
active
06217212
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method for detecting an incorrect position of a semiconductor wafer during a high-temperature treatment of the semiconductor wafer in a quartz chamber which is heated by IR radiators. The semiconductor wafer is lying on a rotating support and is held at a specific temperature with the aid of a control system. The invention also relates to a device for carrying out the method.
2. The Prior Art
A semiconductor wafer is subjected to a high-temperature treatment in a quartz chamber, when it is intended to condition the semiconductor wafer. Examples of conditioning include annealing, rapid thermal annealing and rapid thermal processing (RTP). Other high-temperature treatment includes doping the wafer or depositing a layer of material on one or both sides of the semiconductor wafer (chemical vapor deposition (CVD), atmospheric pressure CVD (ACVD), reduced pressure CVD (RCVD), epitaxy). For this purpose, the semiconductor wafer has to lie on a support. The support is rotated during the treatment to ensure that the semiconductor wafer is treated as uniformly as possible.
One decisive factor in the success of the high-temperature treatment is that the semiconductor wafer lies in the planned position on the support and maintains this position throughout the treatment. Even a slightly incorrect position of the semiconductor wafer in which the semiconductor wafer does not lie parallel to the support may have undesirable consequences. For example, if the semiconductor wafer, during a coating treatment, does not lie parallel to the support, but rather is tilted slightly out of the parallel position on the support, the thickness of the layer deposited may not be uniform. Crystal defects within the semiconductor wafer may occur.
Often, the support for the semiconductor wafer is raised in the edge region. The intention is to avoid incorrect positions and to allow the semiconductor wafer to be centered. Despite such precautionary measures, it is still possible that the semiconductor wafer may lie in an undesired position on the support. Semiconductor wafers which are faulty for this reason have to be identified and separated out following the treatment. This procedure is complex and uneconomical.
SUMMARY OF THE INVENTION
The present invention makes it possible to prevent these problems. The invention provides a way of recognizing that the semiconductor wafer is in an incorrect position even during the treatment of a semiconductor wafer.
The invention relates to a method for detecting an incorrect position of a semiconductor wafer during a high-temperature treatment of the semiconductor wafer in a quartz chamber which is heated by IR radiators, the semiconductor wafer lying on a rotating support and being held at a specific temperature with the aid of a control system, comprising
a) recording thermal radiation which is emitted by the semiconductor wafer and the IR radiators using a pyrometer;
b) determining the radiation temperature of the recorded thermal radiation; and
c) determining the semiconductor wafer to be in an incorrect position if the radiation temperature of the recorded thermal radiation fluctuates to such an extent over time that the fluctuation has a width that lies outside a permissible temperature fluctuation range &Dgr;T.
The invention also relates to a device for carrying out the method, in which this device will detect an incorrect position of a semiconductor wafer during a high-temperature treatment of the semiconductor wafer in a quartz chamber which is heated by IR radiators. The semiconductor wafer is lying on a rotating support and is held at a specific temperature by means of a control system. The device has a pyrometer which records thermal radiation emitted by the semiconductor wafer and the IR radiators. The pyrometer is connected to a unit which determines the radiation temperature of the recorded thermal radiation. This unit generates a signal if the radiation temperature of the recorded thermal radiation fluctuates to such an extent over the course of time that the fluctuation amplitude lies outside a permissible temperature fluctuation range &Dgr;T.
By using the invention, there is no need for an involved search for semiconductor wafers which are faulty as a result of being incorrectly positioned during a high-temperature treatment. Such semiconductor wafers are identified as early as at the start of or during the high-temperature treatment and are separated out, for example following the high-temperature treatment. However, it is preferred to interrupt the high-temperature treatment after it has been established that the semiconductor wafer is in an incorrect position. The semiconductor wafer is then moved into the desired position and the high-temperature treatment is continued. This is advantageous in those cases in which, at the time an incorrect position is established, the semiconductor wafer has not yet undergone any material change, for example a coating.
An incorrect position of the semiconductor wafer is regarded as a position which deviates to an impermissible extent from a horizontal position of the semiconductor wafer. An incorrect position is established by measuring thermal radiation with the aid of a pyrometer which is sensitive to this radiation. The pyrometer records thermal radiation which is emitted by the semiconductor wafer. This thermal radiation has radiation components which emanate from the IR radiators and are reflected by the semiconductor wafer. Under stationary conditions, the intensity of the radiation components reflected and recorded by the pyrometer depends on the corresponding angle of reflection. If the semiconductor wafer is in an incorrect position, the intensity of the thermal radiation recorded by the pyrometer fluctuates significantly. This is because the angle of reflection varies during each revolution of the support. The oscillations of the thermal radiation are correlated with the frequency of the wafer rotation.
By contrast, if the semiconductor wafer is in the planned horizontal position during the high-temperature treatment, this has practically no effect on the angle of reflection and there are no fluctuations in intensity. The radiation intensity recorded by the pyrometer is proportional to a radiation temperature. The semiconductor wafer is assumed to be in an incorrect position if the radiation intensity or the radiation temperature derived therefrom fluctuates in the following manner. There is temperature fluctuation to such an extent over the course of time that the temperature fluctuation amplitude lies outside a temperature fluctuation range &Dgr;T which is regarded as permissible. The fluctuation range which is regarded as permissible can be determined by routine experimentation. It preferably corresponds to a natural fluctuation range which is established when the semiconductor wafer is lying in the horizontal position on the support in the correct position.
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Brenninger Georg
Fürfanger Martin
Hansson Per-Ove
Sedlmeier Wolfgang
Bennett G. Bradley
Collard & Roe P.C.
Verbitsky Gail
Wacker Siltronic Gesellschaft fur Halbleitermaterialien AG
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