Data processing: measuring – calibrating – or testing – Measurement system – Temperature measuring system
Reexamination Certificate
1999-05-27
2002-02-19
Assouad, Patrick (Department: 2857)
Data processing: measuring, calibrating, or testing
Measurement system
Temperature measuring system
C702S099000, C374S126000
Reexamination Certificate
active
06349270
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method and apparatus for non-contact temperature measurement of a moving semiconductor wafer employing both a pyrometer and a reflectometer to provide temperature and reflectivity data respectively to a general purpose computer.
BACKGROUND OF THE INVENTION
During the fabrication of semiconductor wafers, numerous physical parameters, such as temperature, pressure and flow rate are monitored and regulated to achieve a desired crystal growth. Maintenance of a specific temperature during the wafer fabrication process is particularly important in order to achieve a high quality semiconductor crystal. The semiconductor wafers to be grown are often placed on rapidly rotating carousels, or carriers, so as to provide a uniform surface easily accessible to circulating semiconductor gasses within a reactor chamber for the deposition of the semiconductor materials. Therefore, measurement of the wafer temperature during the deposition process is problematic in that a non-contact method of measurement is required which can accurately measure the temperature of the semiconductor wafers rotating at high speeds; often greater than 1,000 RPMs.
Non-contact temperature measurement of objects is presently possible using devices which measure the radiation reflected from a target object. These devices, known as pyrometers, are used to calculate the temperature of a physical body based on emitted radiation power from the body and a physical characteristic of the body known as its emissivity. A body's emissivity is a measure of the ratio of the emitted radiation from a body to the incident radiation. The body's temperature can be computed given its emissivity (E) and emitted radiation power (P) according to
P
=
E
w
2
π
C
1
∫
0
∞
1
(
λ
T
)
5
(
ⅇ
C
2
/
λ
T
-
1
)
ⅆ
λ
(
1
)
Planck's equation:
Where
E
w
=body emissivity (dependent on body color and surface characteristics)
C
1
, C
2
=traceable universal consants (Planck's Spectral Energy Distribution)
&lgr;=radiation wavelength
T=body temperature
From the emitted radiation power (P), the corresponding temperature of the body (T) may be accurately determined using the above equation if the emissivity of the body is known.
Often, however, the emissivity of the semiconductor wafers whose temperature is to be determined changes during the course of the semiconductor growth process so as to complicate its temperature determination. Therefore, a real-time time determination of the semiconductor wafer emissivity is necessary, in order to properly calculate the temperature of the semiconductor wafers during all phases of the semiconductor growth process.
Further complicating determination of the semiconductor wafer temperature is the fact that the semiconductor wafers are often placed upon a carousel within a chemical vapor deposition (CVD) chamber. The CVD chamber is a sealed environment that allows infused gases to be deposited upon the wafers to grow the semiconductor layers. Rotation of the semiconductor wafers upon the carousel permits an even deposition of infused gases upon the wafers. The rapidly rotating carousel presents difficulties in accurately measuring the semiconductor wafer temperature by the pyrometer, however, in that the pyrometer is typically fixed over a single point along the radius of the carousel such that sequential temperature measurements may include readings from the semiconductor wafers, the carousel itself, or the boundary between the semiconductor wafers and the carousel.
Several possible approaches may be used to make wafer temperature measurements using a high-speed pyrometer positioned over a rapidly rotating wafer carrier. First, a sequence of temperature measurements using a real-time algorithm to separate wafer and carousel temperatures may be used. The problem with this approach is that modem pyrometers can provide high-speed measurements with single point data acquisition times in the range of 0.1 milliseconds, but they often require a much longer time, e.g., on the order of 20 milliseconds or more, between single measurements to perform calculations and self-calibration. As a result, sequential temperature measurements of the wafer carrier and wafer are not easily obtained so as to obtain reliable temperature measurements from the wafer only.
A second approach employs a triggering function in which the pyrometer measurements are taken at a frequency close to the period of rotation for the wafer carrier. With this approach, the pyrometer provides data measurements scanned across the disk, i.e. a stroboscopic effect, to generate temperature data. The “down time” between temperature measurements is used to achieve the above-mentioned calculations and self-calibration. However, this method also has its shortcomings. In particular, modern pyrometers often initiate an autonomous self-calibration with respect to the ongoing measurements of temperatures. Such autonomous self-calibration necessarily interferes with any periodic gathering of temperature data from the pyrometer and makes such temperature determinations on a periodic basis extremely difficult.
To overcome the difficulties of the above solutions, an encoder may be installed on the carousel spindle to provide a “trigger” for the initiation of pyrometer measurements. This approach, however, requires additional system complexity related to the synchronization between the encoder and the wafer locations. Further, the delay in communications between the encoder and the pyrometer requires complex calibration procedures for each different rotation speed of the carousel and, therefore, requires recalibration when changing speeds.
In sum, the present level of pyrometer development does not allow for the implementation of a simple and reliable method of measuring the temperature of semiconductor wafers on a rapidly rotating carousel, particularly where the emissivity of the semiconductor wafer is varying over the measurement time.
SUMMARY OF THE INVENTION
In accordance with the present invention an apparatus has been provided for determining the real-time, non-contact temperature measurement of first and second fast moving entities. The first and second entities have first and second reflectivities, and are disposed in a fixed relationship with respect to each other. Further provided in the apparatus are a pyrometer for providing a series of temperature data related to the temperatures of the first and second entities respectively, each temperature datum having a temperature value, a reflectometer for providing a series of reflectivity data related to the first and second reflectivities, each reflectivity datum having a reflectivity value and correlated with a corresponding temperature datum so as to form a reflectivity-temperature data pair, and a computer having a memory for storing a set of computer instructions. The computer is coupled to the pyrometer and the reflectometer for receiving the series of temperature data and the series of reflectivity data and the set of computer instructions include instructions for creating a data table for storing the reflectivity-temperature data pairs according to a frequency of occurrence of each reflectivity value in the series of reflectivity data, instructions for identifying at least one reflectivity data peak representative of the first reflectivity characteristic within the data table, and instructions for determining at least the temperature of the first entity from the reflectivity data peak based upon the associated reflectivity-temperature data pairs.
In accordance with an embodiment of the present invention, the first entity is a semiconductor wafer and the second entity is a semiconductor wafer carrier, and the first reflectivity of the semiconductor wafer is higher than the second reflectivity of the semiconductor wafer carrier. Similarly, the first reflectivity of the semiconductor wafer is of a
Boguslavskiy Vadim
Gurary Alexander
Patel Ameesh N.
Ramer Jeffrey C.
Assouad Patrick
Barbee Manuel L.
Emcore Corporation
Lerner, David, Littenberg, Kromholz & Mentlik, LLP
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