Electric heating – Heating devices – Combined with container – enclosure – or support for material...
Reexamination Certificate
2001-02-16
2002-04-09
Walberg, Teresa (Department: 3742)
Electric heating
Heating devices
Combined with container, enclosure, or support for material...
C219S390000, C219S552000, C392S416000, C392S418000, C374S009000, C374S126000, C250S492200
Reexamination Certificate
active
06369363
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method of measuring electromagnetic radiation that is radiated from a surface of an object that is irradiated by electromagnetic radiation given off by at least one radiation source, whereby the radiation given off by the radiation source is determined by at least one first detector, and the radiation given off by the irradiated object is determined by at least one second detector that measures the radiation.
A method of this type is known, for example, from U.S. Pat. No. 5,490,728 A in conjunction with the manufacture of semiconductor substrates in a reaction chamber. In this case, the electromagnetic radiation given off by the radiation source is naturally superimposed with a waviness that is undesired and occurs due to fluctuations of the line voltage or due to phase controls. Unfortunately, no influence can be had on this waviness, and can also not be intentionally selected. The waviness is therefore only suitable, if at all, to a limited extent for an intentional utilization as a characteristic of the radiation given off by the radiation source.
Reference is also made to DE-A-26 27 753, which discloses an apparatus for measuring and controlling the thickness of optically effective thin layers during build up thereof in vacuum coating units. The measurement and control is achieved by detecting the reflection or transmission characteristic of layer thicknesses between fractions of and multiples of the essentially monochromatic measurement light that is utilized, and by interruption of the coating process when a predetermined layer thickness has been achieved. The apparatus comprises a measurement light source for a focused measurement light beam, a chopper, a beam splitter that is disposed in the axis of the measurement light beam at an angle of 45°, a measurement light receiver that is connected in series with a monochromatic illuminator, as well as a differentiator for the measurement signal and an interrupter for the coating process. Furthermore, DE-A-42 24 435 discloses an optical interface for the infrared monitoring of transparent disks, whereby the light of an infrared radiation source is conducted by a beam wave guide into the interior of the interface where it is emitted for exposing the surface of the disk. The radiation reflected at the disk that is to be monitored is received by the input of another beam wave guide and is conveyed by the beam wave guide via a daylight filter to a photo detector. U.S. Pat. No. 5,270,222 furthermore discloses a method and an apparatus for a diagnosis and prognosis during the manufacture of semiconductor devices. The apparatus has a sensor for the diagnosis and prognosis that measures various optical characteristics of a semiconductor wafer. The sensor has a sensor arm and an optoelectronic control box for conducting coherent electromagnetic or optical energy in the direction of the semiconductor wafer.
It is therefore an object of the present invention to provide a method of the aforementioned general type with which the measurement of electromagnetic radiation, and the determination of the pyrometers and values drived therefrom, can be carried out in a straightforward manner and more precisely.
The stated object is inventively realized in that the radiation given off from at least one radiation source is actively modulated with at least one characteristic pyrometer, and in that the radiation determined by the second detector is corrected by the radiation determined by the first detector to compensate for the radiation of the radiation source reflected from the object. The radiation source is, preferably a heat lamp and the irradiated object is preferably a semiconductor substrate that is subjected to a thermal treatment.
Due to the intentional, active and hence known modulation of the radiation source with a characteristic pyrometer it is possible to more precisely differentiate the difference between the radiation radiated from the object itself, and necessary for the determination of the characteristics of the object, from the radiation of the radiation source reflected from the object. In this way, it is possible to determine more precisely and in real time the characteristics of the object, for example the temperature, the emissivity, the transivity, the reflectivity, or the layer thicknesses or characteristics of a material that is on the object and differs from the material of the object.
Pursuant to one particularly advantageous embodiment of the invention, the active modulation of the radiation given off by the radiation source for the characterization thereof, is used during the correction of the radiation determined by the second detector. Due to the active and hence known modulation of the radiation given off by the radiation source, the characterization and hence differentiation of this radiation from the actually to be measured radiation that is given off by the object is particularly simple, reliable and quantitatively accurate.
The radiation given off by the radiation source is preferably modulated with respect to amplitude, frequency and/or phase. Depending upon the existing conditions and requirements, the type of modulation can be selected as desired, whereby the type of modulation can be selected in particular also with respect to the simplicity and reliability of the modulation process, but also of the evaluation process and of the detection process. In this connection, amplitude modulation means the modulation of the modulation amplitude. However, the process preferably involves intensity modulation, the amplitude of which is not modulated, but rather possibly slowly varied.
In addition to the type of modulation, it is also possible to utilize every signal shape of the modulation. However, particularly advantageous, during an amplitude modulation, is the use of a signal shape having a signal pattern that is as continuous as possible. This has the advantage that also during a Fourrier transformation high frequencies essentially do not occur and therefore the number of scans per unit of time during the detection or processing of the detected signal can remain low, so even with a simple evaluation process a good and accurate measurement can be carried out.
In general, the modulation of the characteristic pyrometer can be effected with a periodic or non periodic signal. A non periodic modulation can be obtained, for example, in that the characteristic pyrometer is linked with a positive or negative increment which is generated by means of a random mechanism, via a linking operation (e.g. addition, multiplication or a linking with a look-up-table). In this connection, after a certain interval of time has elapsed the increment is respectively predetermined pursuant to a random principle. The time interval itself can in this connection be constantly determined pursuant to a predefined function or again pursuant to a random principle. The important thing with the non periodic modulation is that the pyrometer (increment and/or time interval) determined by random principles be known and be available within an evaluation device or an evaluation process for signal analysis. The pyrometers (increment and/or time interval) determined by a random principle can satisfy an arbitrarily predefined distribution function. They can, for example, be distributed uniformly, in a Gaussian fashion or pursuant to a Poisson distribution, as a result of which the respective expected values of the pyrometers are similarly predefined. The advantage of a non periodic modulation is that as a result periodic disruptive influences can be suppressed.
A further advantageous embodiment of the invention consists in that the radiation source comprises a plurality of individual radiation sources, for example a plurality of lamps, that can be combined into one or more lamp banks. Pursuant to advantageous embodiments in conjunction with radiation sources that comprise a plurality of lamps, the radiation of at least one of the lamps is modulated. Although the modulation of the radiation of
Balthasar Horst
Hauf Markus
Knarr Thomas
Möller Uwe
Walk Heinrich
Becker R. W.
Fuqua Shawntina T.
R.W. Becker & Associates
Steag Ast
Walberg Teresa
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