Coating processes – Coating by vapor – gas – or smoke
Reexamination Certificate
1998-08-14
2001-03-13
Lund, Jeffrie R. (Department: 1763)
Coating processes
Coating by vapor, gas, or smoke
C427S008000, C427S314000, C427S010000, C118S725000, C118S728000, C118S729000, C118S730000, C118S666000, C118S712000, C118S713000, C118S724000, C219S390000, C219S405000, C219S411000, C392S416000, C392S418000, C374S126000, C374S130000, C374S131000, C374S141000
Reexamination Certificate
active
06200634
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The field of the present invention relates in general to semiconductor processing. More particularly, the field of the invention relates to a system and method for detecting and measuring semiconductor substrate properties, such as temperature, temperature uniformity, and emissivity, using optical pyrometry.
2. Background
In rapid thermal processing (RTP) of semiconductor device materials (such as a semiconductor wafer or other substrate), one of the critical process parameters is temperature. Repeatable, precise, and process-independent measurements of the wafer temperature are among the most important requirements of semiconductor processing equipment (such as RTP) in integrated circuit manufacturing.
Contact temperature sensors, such as thermocouples and thermistors, are commonly used to measure temperature. However, these sensors are not well-suited to many wafer processing environments. Such temperature sensors typically must be placed in contact with a wafer which may affect the uniformity of heating and expose the wafer to contaminants under certain conditions. In addition, it is difficult to achieve repeatable temperature measurement conditions due to inconsistent contact areas and other variations in heat transfer to the sensor.
As a result, noninvasive temperature measurement techniques, such as optical pyrometry, have been used in many RTP systems. Unlike temperature measurement using contact sensors, such as thermocouples and thermistors, temperature measurement using optical pyrometry does not require contact with the wafer and as a result does not expose the wafer to metallic contaminants during processing. Optical pyrometers may determine temperature based upon optical electromagnetic radiation (hereinafter “light”) emitted from an object. Optical pyrometers typically use a high temperature optical fiber, light pipe, lens, or other light collecting device to transmit light to a light sensitive device that measures the flux density or intensity of the light emitted by the object. See, e.g., U.S. Pat. No. 4,859,079 to Wickerstein et al. and U.S. Pat. Nos. 4,750,139 and 4,845,647 to Dils et al., each of which is incorporated herein by reference. The temperature is then determined using Planck's equation which defines the relationship between the temperature of an object, the flux density of light being emitted from that object, and the light emitting characteristics of the object's surface (emissivity).
The advantages of optical pyrometry for RTP include its noninvasive nature and relatively fast measurement speed which is critical in controlling the rapid heating and cooling in RTP. However, accurate optical temperature measurement using pyrometry depends upon the accurate measurement of the flux density of light emitted from the wafer and upon the wafer's light emitting characteristics or emissivity. Emissivity is typically wafer dependent and depends on a range of parameters, including temperature, chamber reflectivity, the wafer material (including dopant concentration), surface roughness, and surface layers (including the type and thickness of sub-layers), and will change dynamically during processing as layers grow on the surface of the wafer.
Among other things, the emissivity of a semiconductor wafer depends upon the wavelength of light that is being measured.
FIG. 1
is a graph of emissivity as a function of wavelength and temperature for a pure silicon wafer. As shown in
FIG. 1
, emissivity is temperature dependent and may vary greatly at wavelengths greater than the absorption band of silicon, which is slightly less than one and two tenths (1.2) micrometers. The effects of emissivity with respect to temperature on optical pyrometry for silicon can be minimized by using a sensor with maximum sensitivity within a range of about eight tenths (0.8) to about one and one tenth (1.1) micrometers wavelength, as indicated at 100 in FIG.
1
. See also U.S. Pat. No. 5,166,080 to Schietinger et al. which is incorporated herein by reference. However, the wavelength/emissivity characteristic of a wafer will differ for doped silicon and other semiconductor materials such as gallium arsenide. In addition, the emissivity of a given wafer will typically change during processing as materials, such as silicon dioxide, are deposited on the wafer surface. Therefore, it is very difficult to control the effects of emissivity on temperature measurement based solely upon the wavelength of light that is used for pyrometry.
A short wavelength less than one (1) micrometer is often preferred for optical pyrometry since it provides certain benefits. For instance, a short wavelength improves the sensitivity of the temperature measurement which is based on Planck black-body emission. Sensitivity is defined as the fractional change in radiance per fractional change in temperature and from the equations for Planck black-body emission it can be shown that sensitivity is inversely proportional to wavelength. Therefore, shorter wavelengths are preferred for improved sensitivity in temperature measurement.
However, the ability to use a short wavelength of light in optical pyrometry is severely limited in many conventional rapid thermal processors due to interference from radiant energy heating sources. The heat needed for RTP is typically provided by a heating lamp module which consists of high intensity lamps (usually tungsten-halogen lamps or arc lamps).
FIG. 2
illustrates a conventional RTP processing chamber, generally indicated at
200
, using two banks of heating lamps
202
and
203
to heat a semiconductor wafer
204
through optical windows
206
and
207
. An optical pyrometer
208
may be used to measure the wafer temperature by detecting the flux density of light within cone of vision
210
. However, most radiant energy heating sources, including tungsten filament and arc lamp systems, provide their peak energy intensity at a wavelength of about one micrometer which interferes with optical pyrometer
208
. Optical pyrometer
208
will detect light reflected off of wafer
204
from heating lamps
202
and
203
as well as light emitted from the wafer. This reflected lamp light erroneously augments the measured intensity of light emitted from the wafer surface and results in inaccurate temperature measurement.
Therefore, some conventional systems have used a longer wavelength of light to measure temperature so that the spectral distribution of the heating lamps has minimal overlap with the pyrometer's operating spectral band or wavelength. However, measuring the intensity of emitted light at a longer wavelength to reduce interference can lead to similar interference problems from light emitted by hot chamber surfaces which, at longer wavelengths, becomes significant enough to cause errors in the measured light intensity. For instance, quartz, which is typically used in RTP processing chambers, re-emits light predominantly at longer wavelengths (typically greater than 3.5 micrometers). An alternative approach is to measure and compensate for reflected light. Two optical pyrometers may be used—one for measuring the light from the lamps and one for measuring the light from the wafer. The strength of the characteristic AC ripple in light emanated from the lamp can be compared to the strength of the AC ripple reflected from the wafer to determine the wafer's reflectivity. This, in turn, can be used to essentially subtract out reflected light in order to isolate the emitted light from the wafer for determining temperature using Planck's equation. See, e.g., U.S. Pat. No. 5,166,080 to Schietinger et al. However, such systems may require complex circuitry to isolate the AC ripple and perform the calculations that effectively eliminate reflected light. Such systems also require an additional light pipe and other components.
FIG. 3A
illustrates an RTP processing chamber, generally indicated at
300
, with a single set of heating lamps
302
for heating wafer
304
. Typically, wafer
304
is supported by
Johnsgard Kristian E.
McDiarmid James
Lund Jeffrie R.
Mattson Technology Inc.
Wilson Sonsini Goodrich & Rosati
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