DE112013003131T5 - Reduction of radiation thermometry deviation errors in a CVD reactor - Google Patents

Abstract

Devices for reducing radiation thermometry error errors in housings such as CVD reactors. In one embodiment, a radiation thermometer uses a non-focused telecentric lens assembly. The unfocused telecentric array is focused at infinity, but is used to capture radiation from a relatively close target (for example, within a few meters) that is out of focus. The capture of collimated radiation from the target reduces the contribution of scattered radiation. In another embodiment, scattered radiation originating from a particular segment of a peripheral heating element may be localized by one of several mechanisms, including reducing the radiation (eg, operating temperature) of the particular segment, or capturing or deflecting a portion of the radiation from the one specific segment is reduced. Radiation thermometers mounted near an axis extending from the center of the wafer receptacle and over the particular segment are less susceptible to radiation and thus provide a more reliable temperature measurement.

Description

BACKGROUND

Organometallic Chemical Vapor Deposition (MOCVD) is a chemical vapor deposition technique for growing crystalline layers in processes such as semiconductor fabrication. The MOCVD process is initiated in a reactor chamber having specially designed flow flanges which produce uniform reactor gas streams to the reactor chamber.

The temperatures of the crystalline layers during the MOCVD process are typically measured using non-contact devices such as radiation thermometers or pyrometers. Such crystalline growth materials include silicon carbide (SiC), zinc selenide (ZnSe) and gallium nitride (GaN) based materials such as GaN and AlGaN. Certain crystalline growth material substrates have radiation properties that limit the operating wavelength that can be used for radiation thermometry. For example, GaN grown on a sapphire substrate may have a transmittance of greater than 50% at process temperatures, for wavelengths greater than 450 nanometers (nm). Thus, at wavelengths greater than 450 nm, a substantial portion of the radiation exiting the surface of a GaN layer originates from the structure under the substrate, which is in the line of sight of the radiation thermometer (eg, a wafer receptacle). The radiation passing through the GaN layer provides no indication of the temperature of the GaN layer. Accordingly, radiation thermometers have been developed which detect radiation at wavelength lengths shorter than 450 nm (approximately corresponding to the blue, violet and ultraviolet wavelengths). See, for example, For example, U.S. Patent Application No. 2011/0064114 to Zettler et al. (hereinafter referred to as "Zettler") which discloses a pyrometer which is adapted to detect radiation in the range of 250 nm to 450 nm.

A problem with the use of radiation thermometers is the detection of unwanted radiation. One source of unwanted radiation is unfiltered radiation detected outside the desired detection bandwidth. Zettler describes a device and technique that takes into account the contribution of unfiltered radiation. Zettler points out that narrowband pass filters do not completely block infrared radiation. The unblocked infrared radiation can be problematic at operating temperatures (about 800 ° C) because the spectral blackbody radiation capability of the target is about nine orders of magnitude higher in the infrared region of the electromagnetic spectrum than in the primary bandpass (this is the desired spectral bandpass for deriving the target temperature). of the narrow bandpass filter. The Zettler method involves the use of a detector sensitive to a broad range of wavelengths (from ultraviolet to infrared) and filtering the incoming radiation with a narrow bandpass filter centered at about 410 nm. A long-pass filter is then used to effectively block the primary bandpass of the narrow bandpass filter, but to allow the unfiltered radiation to pass through the narrow bandpass filter in the infra-red and near-infrared regions of the electromagnetic spectrum. Zettler derives the radiation passing through the primary bandpass of the narrowband pass filter from the difference between the two measurements, i. h., between the signal obtained only with the narrowband pass filter and the signal obtained with both the narrowband pass filter and the longpass filter.

Another source of unwanted radiation is the contribution of "scattered radiation". Scattered radiation is reflected radiation that is deflected by the housing or other structures by means of intermediate reflection to the target and reflected in the line of sight of the radiation thermometer. Imagine a wafer shot with GaN wafers heated to an elevated temperature of 800 ° C, for example, a microwave heating process. The components operated at the elevated temperature, such as the wafer receptacle and the wafers, will emit radiation in all directions, causing radiation within the chamber to be inter-reflected. A portion of the inter-reflected radiation will be incident on the surface to which the radiation thermometer targets and contributes to the radiation detected by the radiation thermometer. For GaN crystalline films at 800 ° C, the reflectance at 410 nm is about 0.2. The scattered contribution can significantly distort the temperature value given by the radiation thermometer.

Scattered radiation is a serious problem when the target is at or near the maximum temperatures in the chamber, which is the case with microwave heaters. However, if radiation is measured in or near the short wavelengths of the visible spectrum (i.e., in the blue, violet, or ultraviolet wavelengths), the problem is exacerbated when there are other sources within the chamber that operate at much higher temperatures, as the goal. Such a heater transfers heat in accordance with the first law of thermodynamics, which requires that the resistance heating element is operated at a temperature which is significantly higher than that of the crystal growth layer. An advantage of thermal radiant heating is that the radiation intensity can be adjusted in order to set a profile via the wafer receptacle, which promotes an equal distribution of the temperature.

For example, consider the black body radiation of a crystalline growth layer at 800 ° C. According to Planck's law, the black body spectral emittance at 410 nm and 800 ° C is about 2.0 × 10 -4 watts / m 2 .mu.m. Consider now a heating source, such as a resistive heating element that transfers heat by radiation and convection to the crystalline growth layer operating at 1800 ° C. The blackbody spectral emissivity at 410 nm and 1800 ° C is about 1.4 x 10 + 3 watts / m 2 .mu.m. This is an increase of about 7 orders of magnitude compared to blackbody spectral emissivity at 800 ° C (a typical operating temperature for a crystal growth layer during the CVD process) at the wavelength of interest ( 1 ). Accordingly, even if only a fraction of a percent of the radiation at the 410 nm wavelength finds its way onto the detector of the radiation thermometer, the deviation of the indicated temperature can be significant. Thus, the stray radiation contribution in chambers using resistive heating elements may be of the same order of magnitude as the unfiltered radiation contribution identified by Zettler.

However, Zettler says nothing about the contribution of scattered radiation or the effects of having radiation sources within a chamber that can ultimately project beyond the radiation emitted by the target. Rather, Zettler treats the target as if it were free-radiant (that is, had no reflected contribution). In fact, however, a target in a CVD chamber operating at temperatures required for crystal growth is not free-radiant.

A radiation thermometer tailored to reduce the effects of unwanted radiation not due to unfiltered radiation but also due to scattered radiation would be welcome.

SUMMARY

Various embodiments of the disclosure use a so-called "telecentric" optical arrangement, but in a non-focused mode, to limit the contribution of the reflected scattered radiation with respect to at least three different aspects. First, in a telecentric optical arrangement, the principal rays captured by the target are substantially parallel to the optical axis, which substantially limits the scatter contribution, particularly if the target has a highly reflective reflection component. Second, telecentric optical arrays can also be tailored so that the solid angle that each point spans on the target is quite small, which also reduces the contribution of scattered radiation. Third, the telecentric optical assembly may be configured to capture a collimated beam emitted from the target, further reducing the solid angle of the radiation detected by the radiation thermometer, and at the same time increasing the size of the target (and the subsequent signal-to-noise ratio) to the effective one Diameter of the front optical elements increased. Upon detection of the collimated beam, the telecentric optical assembly is used in an "off-focus" mode, i. H. it is not used for high quality recording of the surface of the target. Therefore, the components used in the telecentric optical arrangement need not be of the excellent quality typically associated with commercially available telecentric lens systems.

Various embodiments of the disclosure may alternatively or additionally reduce the contribution of stray radiation detected by a radiation thermometer to the reaction chamber and the accessories therein, such that less stray radiation is incident on the target of the radiation thermometer. In the analysis of the scattered radiation for the present work, it was found that the largest contribution of the scattered radiation detected by the radiation thermometer emanates from the peripheral heating elements in a heating element arrangement. It has also been verified by both ray tracing modeling and verification experiments that providing a discontinuity in the portion of the peripheral heating element closest to the target surface of the radiation thermometer significantly reduces the drift error caused by scattered radiation.

"Not Focused" Telecentric Optics

Commercially available telecentric lens systems are used, for example, in image processing systems to provide clear, crisp, high-magnification images. These telecentric lens systems provide a uniform magnification of all the points in an image regardless of the position of the point in that image. That is, telecentric lens systems used in image processing systems provide images that are substantially isometric, as opposed to perspective images provided with standard imaging systems. An advantage of the commercially available telecentric lens systems is that the isometric image can significantly reduce the parallax in the image.

However, the effective range over which a telecentric lens system can provide an isometric image at a given setting is quite limited. This effective range is commonly referred to as the "telecentric depth" (see, e.g., Petrozzo et al., "Telecentric Lenses Simplify Non-Contact Metrology," Test & Measurement World, October 15, 2001, p.5). Thus, a paradigm of telecentric lens systems is that they are operable in a narrow area centered around the object plane. The optical components of an image processing telecentric lens system are of high quality to provide crisp images throughout the image. Furthermore, commercially available telecentric lens systems typically utilize high quality tripods to provide the ability to adjust the depth of focus of the object plane. The exact imaging capabilities of commercially available telecentric lens systems drive up costs.

In various embodiments of the disclosure, the telecentric concept is used in a manner that does not use image processing systems. In one embodiment, the telecentric optical assembly is configured to focus at infinity while being located only a few centimeters from the target. The advantage of this arrangement is that the radiation from each of the points on the target is at substantially the same angle into the target optical system enters. High image quality and the associated costly optics is not required because the goal rather than object imaging is rather radiation collection and detection. That is, the telecentric optical device is used in an unfocused or "off-focus" mode to effectively detect a collimated beam of radiation emitted from the target surface. Such an arrangement does not require high quality imaging optics nor sophisticated mounts for fine tuning an image.

Structurally, an unfocused telecentric optical assembly, in various embodiments of the disclosure, includes an aperture stop and a first or "object" optical component (referred to herein as the "object assembly") of one or more optical components. The aperture stop and the object arrangement may define an optical axis and a first focal length relative to a reference point within the object arrangement, the reference point being disposed on the optical axis. In one embodiment, the aperture stop is located at a distance from the reference point of the object assembly that is substantially equal to the first focal length of the object assembly. By placing the aperture stop in the focal length of the object assembly, the object assembly is effectively focused to infinity, transmitting substantially collimated radiation from a non-focused target through the object assembly, and focusing the radiation from the non-focused target onto the aperture stop.

In some embodiments, a second or "image" optical component assembly (referred to herein as "image arrangement") of one or more optical components may be disposed opposite the object assembly from the aperture stop and configured to move from the object assembly through the aperture stop on the optical axis transmitted radiation, wherein the image arrangement defines a second focal length with respect to a second reference point in the image arrangement, wherein the second reference point is arranged on the optical axis.

In one embodiment, a "bilateral" telecentric optical arrangement is implemented in which the principal rays of both the target and the image are parallel to the optical axis. In the bilateral arrangement, the focal length of the object assembly defines approximately the target distance, with the aperture disposed substantially in the back focal plane of the object assembly and in the front focal plane of the image assembly. In a bilateral telecentric arrangement, not only is the radiation collected by the object optical component array substantially collimated, but also the radiation transmitted from the image-optical component array to the detector is substantially collimated. An advantage of the collimation of the radiation between the image-optical component arrangement and the detector is the additional suppression of scattered light.

In various embodiments, the unfocused telecentric optical assembly is provided as a kit for implementation with a new or existing radiation thermometer in chemical vapor deposition systems. In one embodiment, a telecentric lens assembly is provided that includes an aperture stop and a front optical component assembly for collecting radiation from a target, wherein the telecentric lens assembly is configured to position the aperture stop in the focal length of the front optical component assembly. Further, manufacturer-side instructions are provided which direct the user to align the front optical component assembly to intercept the radiation emitted by a target in a chemical vapor deposition chamber. In one embodiment, the coupling of the telecentric lens assembly to a radiation detector and / or the positioning of the aperture stop in the focal length of the front optical assembly is performed by the manufacturer; In other embodiments, the step of positioning the aperture stop in the focal length of the front optical assembly and / or positioning the aperture stop in the instructions provided by the manufacturer is provided.

Two wavelength pyrometer

Various of the disclosed embodiments also include a two-wavelength pyrometer that utilizes the unfocused telecentric concept to measure radiation in the visible / ultraviolet or "visible / UV" spectrum and in the infrared spectrum. (For purposes of this disclosure, the "visible / UV" spectrum, alternatively referred to as the "optical" spectrum, includes the wavelengths including 300 nm to 700 nm, the "visible" spectrum, the wavelengths including 400 nm to 700 nm and the " Infrared spectrum, including wavelengths of greater than 700 nm to about 10,000 nm.) A common solution for deriving temperature from a radiation measurement is the so-called "quotient" pyrometer. A quotient pyrometer measures the radiation emitted by a target in two different wavelength bandpasses and operates on the principle of correlating the ratio of the received signals with the temperature. For a gray body radiator (i.e., a target having the same radiating power over both the different wavelength bandpasses), the effect of radiating power is effectively canceled by the quotient of the ratio, so that the signal ratios are temperature dependent, as in blackbody calibration. Also, schemes have been developed to correct the indicated temperature of a quotient pyrometer if the target being considered is not a gray body.

The different wavelength bandpasses of ordinary quotient pyrometers tend to be relatively close to one another on the electromagnetic spectrum, which is due to the general belief that wavelength bandpasses that are close together have a better chance of having the same radiating power (ie graybody behavior) show) compared to wavelength bandpasses farther apart. However, in certain methods it is desirable to obtain information about different portions of the wavelength spectrum to properly control the process. For example, in depositing GaN on sapphire substrates in a MOCVD reactor, one way to control the process is to derive the temperature of the wafer receptacle for primary temperature control with an infrared pyrometer and the temperature of the GaN layer of the wafer derive optical pyrometer for secondary control. Conventional quotient pyrometers are not suitable for this purpose because both wavelength bandpasses are typically in the same electromagnetic range - either in the optical or in the infrared.

In the two-wavelength pyrometer embodiments of the present disclosure, a pair of radiation thermometers measure radiation from identically inspected targets in different wavelength bandpasses. The central wavelengths of the bandpasses may be in different parts of the electromagnetic spectrum, with the first of the wavelength bandpasses in the visible / UV spectrum and the second of the wavelength bandpasses in the infrared spectrum. In one embodiment, the center wavelengths for the infrared and optical wavelength bandpasses are about 900 nm and 400 nm, respectively (for example, 930 nm and 405 nm). The two-wavelength pyrometer of the present disclosure combines the optical (ie visible / UV spectrum) and infrared detectors in one unit so that both measurements are made through a common viewing port. Accordingly, the provision of optical and infrared radiation measurement does not require the use of two viewing ports. A further advantage is that the radiation captured for both the optical and the infrared measurement can be simultaneously captured by the same identical target through the same location on the viewing port window, whereby certain differences resulting from non-simultaneous measurements, which have been obtained from different targets through different viewing aperture windows, can be avoided. Including the unfocused telecentric optics further reduces the contribution of the scattered radiation, which reduces the error of deviation of the temperature measurements.

Some of the two-wavelength pyrometer arrangements disclosed herein optionally include a reflectometer arrangement to compensate for radiation. Deriving the temperature from a radiation signal requires either knowledge or compensation of the radiation ability of the target. A wafer in a CVD chamber may experience significant and non-monotonic changes in emissivity as the layers are built on the wafer, which may cause intermittent destructive interference of the various reflective wafer layers, which may result in a periodic change in reflectivity and emissivity , Certain embodiments of the present disclosure include a reflectometer integrated into the radiation thermometer, comprising one or both of the radiation thermometers of the two-wavelength pyrometer. The reflectometer value may be implemented to derive the emissivity of the target and to provide a correction for the indicated temperature. Including the unfocused telecentric optics further reduces the amount of scattered radiation, which reduces the error of deviation of the emissivity determination.

Structurally, the disclosed two-wavelength telecentric pyrometer may comprise an object array of one or more optical components for transmitting radiation of a non-focused target, the object array defining a focal length with respect to a first reference point in the object array. In this embodiment, a first aperture stop is arranged to receive radiation transmitted from the object assembly, the object assembly and the first aperture stop defining a first optical axis passing through the reference point, the first aperture stop being spaced from the reference point substantially equal to the focal length of the object array, for focusing a first detected portion of the radiation onto the first aperture stop. In this embodiment, a second aperture stop is arranged to receive radiation transmitted from the object assembly, wherein the object assembly and the second aperture stop define a second optical axis passing through the reference point, the second aperture stop spaced apart from the second aperture stop Reference point is arranged, which is substantially equal to the focal length of the object arrangement, for focusing a second detected part of the radiation on the second aperture diaphragm. A second detector of electromagnetic radiation may be arranged to detect the first detected part of the radiation transmitted by the object arrangement through the first aperture stop. Likewise, a second detector of electromagnetic radiation for detecting the second detected part of the radiation transmitted by the object arrangement through the second aperture stop can be arranged, the first detector of electromagnetic radiation and the second detector of electromagnetic radiation generating a first signal or a second signal for deriving a temperature of the unfocused target.

The two-wavelength telecentric pyrometer may further comprise a first reflectometer assembly including a first radiation source for generating a first beam of electromagnetic radiation and a first beam splitter, the first beam splitter being arranged to propagate a portion of the first beam along the first optical axis Irradiation of the unfocused target. Furthermore, a second reflectometer module, comprising a second radiation source for generating a second beam of electromagnetic radiation and a second beam splitter, may be included, the second beam splitter being arranged to propagate a portion of the second beam along the second optical axis for irradiating the unfocused beam target.

In one embodiment, the first detected portion of the radiation is in the infrared spectrum of electromagnetic radiation and the second detected portion of the radiation is in the visible spectrum of electromagnetic radiation. The second detected portion of the radiation may define a wavelength bandpass centered at a wavelength greater than or equal to 400 nm and less than or equal to 410 nm. The first detected portion of the radiation may define a wavelength bandpass having the 930 nm wavelength. Also included was a reduced aperture arrangement for selectively reducing one of the first detected portion of the radiation detected by the first electromagnetic radiation detector and the second detected portion of the radiation detected by the second electromagnetic radiation detector.

Multi-channel pyrometer

Embodiments of the present invention further include a "multi-channel" pyrometer system for deriving a spatial temperature distribution comprising a plurality of unfocused telecentric radiation thermometers for determining the temperature profile of the wafer during manufacture provide. Uniform wafer temperatures are desirable to increase wafer yield. While most of the temperature of the wafer receiver and wafer is controlled by the heating elements, various secondary parameters are available to the operator to improve the uniformity of the temperature between wafers as well as the uniform temperature distribution within a wafer. The present invention includes an arrangement for measuring the uniformity of the wafer temperature. The plurality of radiation thermometers are each designed to inspect another target at a different position on a given wafer, with the data from each target detected simultaneously. The target sizes can be adjusted to achieve almost complete coverage of the inspected wafer for deriving a temperature distribution across the wafer. Temperature uniformity maps can be generated and their accuracy can be improved by using statistical averages of synchronized data over a selected period of time (eg, 1 minute). Including the unfocused telecentric optic reduces the contribution of stray radiation in the chamber which varies substantially with the position of the target on the wafer. The reduction of the stray radiation contribution reduces the error of deviation of the individual temperature measurements and the resulting temperature profile.

In yet other embodiments of the present disclosure, both the multi-channel arrangement and the dual-wavelength concepts (with optional reflectivity capabilities) are combined in the same system. By this arrangement, the temperature profiles may include the improved accuracy provided by the dual wavelengths and / or the radiator balance arrangements.

Structurally, a multichannel pyrometer system for deriving a spatial temperature distribution is disclosed, comprising a plurality of radiation thermometers arranged to inspect a corresponding plurality of adjacent unfocused targets, each of the plurality of radiation thermometers comprising a first telecentric optical assembly. The first telecentric optical arrangement comprises an object arrangement of one or more optical components for transmitting radiation, the object arrangement defining a focal length with respect to a reference point in the object arrangement. Each of the plurality of radiation thermometers further comprises a first aperture stop arranged to receive radiation transmitted from the object array, the object array and the first aperture stop defining a first optical axis passing through the reference point, the first aperture stop being in one Distance from the reference point is arranged, which is substantially equal to the focal length of the object arrangement, for focusing a first detected part of the radiation from the corresponding one of the corresponding plurality of adjacent unfocused targets on the first aperture diaphragm. Each of the plurality of radiation thermometers further comprises a first electromagnetic radiation detector arranged to detect the first detected portion of radiation transmitted by the object assembly through the first aperture diaphragm, the first electromagnetic radiation detector producing a first signal indicative of a temperature of the first detector derived from the corresponding plurality of adjacent non-focused targets. The plurality of radiation thermometers may be arranged to inspect a wafer on a wafer receptacle, wherein the wafer receptacle is disposed within a chemical vapor deposition chamber, and wherein the plurality of adjacent unfocused targets are completely opposed to the wafer. Opposing the unfocused targets by the wafer is periodic due to the rotation of the wafer receiver.

At least one of the plurality of radiation thermometers may comprise a first reflectometer assembly comprising a first beam splitter and a first radiation source for generating a first beam of electromagnetic radiation. The first beam splitter may be arranged to propagate a portion of the first beam along the first optical axis for irradiating the corresponding one of the corresponding plurality of adjacent non-focused targets. A second reflectometer assembly comprising a second beam splitter and a second radiation source for generating a second beam of electromagnetic radiation, the second beam splitter being arranged to propagate a portion of the second beam along the second optical axis may also be included for irradiating the corresponding one of the corresponding plurality from neighboring unfocused targets. In some embodiments, one or both of the first and second reflectometer assemblies or reflectometer assemblies modulates the first beam with a chopper. At least one of the plurality of radiation thermometers may include a reduced aperture arrangement arranged to selectively reduce the first detected portion of the radiation detected by the first detector of electromagnetic radiation.

In one embodiment, at least one of the plurality of radiation thermometers further comprises a second telecentric optical array including a second aperture stop arranged to receive radiation from the object array, the object array and the second aperture stop defining a second optical axis defined by the Reference point runs, with the second Aperture stop is arranged at a distance from the reference point, which is substantially equal to the focal length of the object arrangement, for focusing the second detected part of the corresponding one of the corresponding plurality of adjacent unfocused targets on the second aperture stop; and a second detector of electromagnetic radiation arranged to detect the second detected portion of the radiation transmitted from the object assembly through the second aperture stop, the second detector of electromagnetic radiation generating a second signal from which the temperature of the corresponding one of the corresponding plurality of adjacent ones does not derived from focused goals. The first detected part of the radiation may be in the infrared spectrum of the electromagnetic radiation and the second detected part of the radiation is in the visible spectrum of the electromagnetic radiation. In one embodiment, a cold light mirror is arranged along the first optical axis and the second optical axis, wherein the cold light mirror transmits the first detected part of the radiation and reflects the second detected part of the radiation. The second detected portion of the radiation may define a wavelength bandpass centered at a wavelength greater than or equal to 400 nm and less than or equal to 410 nm, and the first detected portion of the radiation may define a wavelength bandpass having the 930 nm wavelength ,

Scattered radiation control

An operating principle of the various embodiments is to locally reduce the contribution of the radiation of the peripheral heating element in the vicinity of the target of the radiation thermometer. In one embodiment, the local reduction of the radiation contribution is achieved by including a portion of low heat flux in the peripheral heating element so that the radiant heat radiated therefrom at an operating wavelength of the radiation thermometer is significantly less than that of other portions of the peripheral heating element or elements ( for example, more than two orders of magnitude lower). The low heat flux section eliminates the radiation of radiation at the operating wavelength (for example in the visible / UV spectrum), so that, locally, the peripheral heating element does not contribute to stray radiation at the operating wavelength of the radiation thermometer. Analysis and experimentation for this work have shown that reducing the spectral contribution of radiation in the vicinity of the target surface of the radiation thermometer in this way significantly reduces the deviation error due to stray radiation.

In another embodiment, the local reduction of the stray radiation contribution is achieved by a radiation trap positioned in the vicinity of the peripheral heating element. A large part of the radiation originating from the peripheral heating element, of the segment in the vicinity of the radiation trap, is thereby captured and makes no contribution to the scattered radiation contribution.

In another embodiment, the local reduction of the scattered radiation contribution is achieved by deflecting the radiation originating from a segment of the peripheral element. In this embodiment, a baffle is positioned near the peripheral heating element which deflects the radiation emanating from a portion of the peripheral heating element away from the target area of the radiation thermometer. In this way, the scattered contribution is reduced locally.

In one embodiment, a system is described for limiting stray radiation received from a radiation thermometer, comprising a chemical vapor deposition chamber (CVD) and a wafer receptacle configured to rotate about an axis of rotation, the wafer receptacle having a top surface, a bottom surface, and a wafer surface outer edge, wherein the upper surface is substantially planar and defines a target plane. A plurality of heating elements are disposed beneath the wafer receptacle, wherein the plurality of heating elements are configured to irradiate the lower surface of the wafer receptacle. The plurality of heating elements may include a peripheral heating element proximate the outer edge of the wafer receptacle. The peripheral heating element may surround the other heating elements of the plurality of heating elements, or may consist of two or more heating elements surrounding the other heating elements. The peripheral heating element may include a portion of low heat flow along a particular portion of the peripheral heating element, wherein the portion of low heat flux is operated at a significantly reduced temperature relative to other portions of the peripheral heating element. In one embodiment, the low heat flow portion is configured to operate at a temperature of at least 300 ° C below the temperature of any other portion of the heating element when operating at a maximum operating temperature.

In one embodiment, a radiation thermometer is arranged to inspect a target located proximate to a "reduced scattered radiation axis", the reduced scattered radiation axis being coplanar with the target plane and extending from the axis of rotation and over the portion of the beam Heating element with a low heat flux extends. The portion of the low heat flux peripheral heating element may include an electrical connection.

In one embodiment, the target is in a rectangular area on the wafer plane that includes a portion of the reduced scattered radiation axis, the rectangular area extending from the spindle to an outer edge of the wafer receptacle, the rectangular area having a width which is approximately the same width as the tangential dimension of the specific portion of the peripheral heating element.

The system may further include a cylinder disposed within the CVD chamber, the cylinder defining a cylinder axis substantially concentric with the axis of rotation, the cylinder having an inner surface and an outer surface, the inner surface defining an inner cylinder diameter Outside surface defines an outer cylinder diameter, wherein the cylinder has an upper edge defining an upper plane which is substantially perpendicular to the cylinder axis. The wafer receiver may define a receiver outside diameter that is larger than the cylinder inside diameter of the cylinder. The system may further include a spindle disposed within the CVD chamber, the spindle being concentric with the axis of rotation and having a distal portion adapted for coupling to the wafer receptacle. In one embodiment, the radiation thermometer may be configured to detect radiation in the visible / UV region of the electromagnetic spectrum.

In various embodiments of the disclosure, various mechanisms for reducing stray radiation emitted by a particular portion of a peripheral heating element are presented. In one embodiment, the mechanism includes one of a radiation trap and a radiation deflector disposed proximate the particular portion of the peripheral heating element.

• • Anordnen der Heizelementanordnung in der chemischen Dampfabscheidungskammer;
• • Anordnen der Wafer-Aufnahme in der chemischen Dampfabscheidungskammer oberhalb der Heizelementanordnung und mit der oberen Oberfläche nach oben;
• • Ausrichten eines Strahlungsthermometers zum Inspizieren eines Zieles, das in der Nähe einer Achse reduzierter gestreuter Strahlung angeordnet ist, wobei die Achse reduzierter gestreuter Strahlung koplanar mit der Zielebene ist und sich von der Drehachse und über den Abschnitt des Heizelements mit einem geringen Wärmefluss erstreckt.

In other embodiments, a method of confining a scattered radiation received from a radiation thermometer that inspects a target in a chemical vapor deposition chamber is presented, the method comprising providing a wafer receptacle and a heater assembly configured for operation in the chemical vapor deposition chamber wherein the wafer receptacle is configured to rotate about an axis of rotation and has a bottom surface and a substantially planar top surface, the top surface defining a target plane, the heater element assembly comprising a peripheral heating element that extends along a portion of low heat flux a certain portion of the peripheral heating element comprises. Instructions on a tangible medium are also provided, including the steps:

• Arranging the heater assembly in the chemical vapor deposition chamber;
• Placing the wafer receiver in the chemical vapor deposition chamber above the heater assembly and with the upper surface up;
• Aligning a radiation thermometer to inspect a target disposed proximate an axis of reduced scattered radiation, wherein the reduced scattered radiation axis is coplanar with the target plane and extends from the axis of rotation and over the portion of the low heat flux heating element.

BRIEF DESCRIPTION OF THE FIGURES

1 Fig. 12 is a diagram of the spectral blackbody radiation energy according to Planck's Law, at various temperatures;

2 Figure 10 is a sectional view of a non-focused telecentric beam thermometer operatively connected to a MOCVD chamber in a disclosed embodiment;

3 Fig. 10 is a sectional view of a non-focused telecentric beam thermometer and a radiation trap operatively connected to an MOCVD chamber in a disclosed embodiment;

4 is an unfocused telecentric optical arrangement in a disclosed embodiment;

5 Fig. 12 is a sectional view of a non-focused telecentric beam thermometer operatively connected to a MOCVD chamber employing a flow extender in a disclosed embodiment;

5A is an enlarged fragmentary sectional view of the MOCVD chamber and the flow extender of 5 ;

6A to 6C show multi-channel arrangements for obtaining spatial temperature distributions of a wafer, in a disclosed embodiment;

7A is a sectional view of a MOCVD chamber with radiation thermometer;

7B is a three-dimensional cutaway view of the MOCVD chamber of 7A with the various accessories for modeling scattered radiation, in a disclosed embodiment;

8th is a schematic representation of the portion of the peripheral heating element of 7A emitted radiation;

9 Figure 11 is a plan view of a heater assembly within a reactor chamber (wafer pick-up removed), in a disclosed embodiment;

10 Fig. 10 is a graph comparing the response of an infrared radiation thermometer and an optical radiation thermometer, both of which inspect a wafer shot during a heating cycle of a heater assembly;

11 is the top view of 9 showing the orientation of the target relative to the heater array for a scattered radiation detection experiment, in a disclosed embodiment;

12A FIG. 12 is a graph comparing the response of a radiation thermometer arranged to inspect outer radial positions of a wafer receptacle proximate a portion of a high heat flux peripheral heating element and near a portion of a low heat flux peripheral heating element. FIG a disclosed embodiment;

12B FIG. 12 is a graph comparing the response of a radiation thermometer arranged to provide mid-span radial positions of a wafer receptacle proximate a portion of a high heat flux peripheral heating element and near a portion of a low heating peripheral element. FIG To consider heat flow, in a disclosed embodiment;

13A Figure 5 is a partial plan view of a wafer receiver in a reactor chamber, with the reactor chamber containing a local radiation trap, in a disclosed embodiment;

13B is a sectional view of the local radiation trap of 13A ;

14 Fig. 12 is a schematic view of a reactor chamber wherein the reactor chamber uses a localized radiation deflector in a disclosed embodiment;

15 Fig. 12 is a schematic view of a two-wavelength pyrometer inspecting a wafer through a viewing port, in a disclosed embodiment;

16A and 16B 4 are representative diagrams of the composite signals received from a pyrometer using a reflectometer assembly, in a disclosed embodiment; and

17 Figure 4 shows a multi-channel arrangement using dual-wavelength pyrometers to obtain spatial temperature distributions of a wafer in a disclosed embodiment.

DETAILED DESCRIPTION

Referring to 1 will be a series of curves 10 showing the spectral blackbody radiation energy according to Planck's law at different temperatures. Also is in 1 the visible spectral range 12 which roughly coincides with the 400 nm to 700 nm wavelength band. With regard to the previous discussion of the effect of temperature on the black body radiation energy at 410 nm, are in 1 first and second reference points 14 and 16 at 1073 K or 2073 K (corresponding to 800 ° C or 1800 ° C).

Referring to the 2 and 3 In disclosed embodiments, it is an MOCVD reactor system 20 which is a radiation thermometer 22 with a non-focused telecentric optical arrangement 24 used. The MOCVD reactor system 20 includes a reactor chamber 26 operating with a flow flange 28 is coupled to a housing 30 define. The flow flange 28 has laminar flow plates 31 on, through which the gases for the MOCVD process enter the reactor chamber 26 be directed. Inside the reactor chamber 26 is a wafer shot 32 arranged, which has an upper surface 34 has, the wafer bags 35 define, and a bottom surface 36 and operatively with a spindle 38 connected, which is a rotation axis 40 Are defined. Each of the wafer bags 35 is to take a wafer 41 educated. A housing closure 42 may be adjacent to the inner wall of the reactor chamber 26 be removably inserted and surrounds the wafer holder 32 ,

A resistance heater assembly 44 is below the wafer intake 32 attached, for radiation-based coupling with the lower surface 36 the wafer recording 32 , The resistance heater assembly 44 can be a peripheral heating element 45 included and from a cylinder 46 be surrounded, and also down through a reflector plate 48 be limited to the radiation-based coupling between the Widerstandheizelementanordnung 44 and the wafer recording 32 to reinforce.

The radiation thermometer 22 is on top of the flow flange 28 mounted and aligned, the upper surface 34 the wafer recording 32 through a viewing port window 52 In one embodiment, the viewing port window is 52 in a recess 54 arranged, which can be actively cooled.

The non-focused telecentric optical arrangement 24 contains a first or front arrangement 62 optical components (hereinafter referred to as "object arrangement" 62 designated) and a second or rear arrangement 64 optical components (hereinafter referred to as "image arrangement") 64 designated). The object arrangement 62 is characterized in that it has an effective radial dimension 65 ( 4 ), that is, a maximum radial dimension, over which the object arrangement 62 the radiation on an aperture stop 66 effectively transmits.

The aperture stop 66 is between the object and image arrangements 62 and 64 arranged. In one embodiment, the object and image arrangements are 62 and 64 and the aperture stop 66 concentric along an optical axis 68 arranged. The optical axis 68 is the axis along which the radiation thermometer 22 detected radiation spreads. The optical axis 68 may be straight, as shown here, or tortuous, for example when planar or focusing mirrors are used for the transmission of radiation. The optical axis 68 can be an unfocused goal 72 centered, which is characterized in that it has a non-focused target area 74 having. The radiation thermometer 22 also contains a detector 76 for the detection of electromagnetic radiation.

It should be understood that for purposes of this disclosure, an "optical component assembly" may include a plurality of optical components (as shown) or a single optical component, such as a single lens. While the optical components illustrated herein include lenses, it will be understood that other optical components such as focusing mirrors and fiber optic bundles may be used to achieve radiation transmission.

In one embodiment, the radiation thermometer becomes 22 aligned so that the optical axis 68 essentially perpendicular to the upper surface 34 the wafer recording 32 ( 2 ). In another embodiment, the radiation thermometer is 22 aligned so that the optical axis 68 at an acute angle 78 relative to a direction perpendicular to the upper surface 34 the wafer recording 32 ( 3 ). In one embodiment, a light trap 82 , in a mirrored angle of the optical axis 68 ( 3 ) arranged in three-dimensional space. That means that the light trap 82 is arranged to a reflection of the optical axis 68 from a hypothetical specular surface on the upper surface 34 the wafer recording 32 oppose.

Referring to 4 becomes the unfocused telecentric optical assembly 24 of the radiation thermometer 22 described in more detail. The object arrangement 62 is characterized in that it has a focal length F1, which is from a reference point 84 on the optical axis, on or within the object arrangement 62 is, is measured. A "focal length" is the distance from the reference point 84 in which to the optical axis 68 parallel rays passing through the object arrangement 62 go through, be focused. For the unfocused telecentric optical arrangement 24 is the aperture stop 66 in this convergence point, ie in the focal length F1 of the object arrangement, positioned.

The unfocused telecentric optical arrangement 24 is further shown as a distance L1 between the image arrangement and the aperture stop and a distance L2 between the image arrangement 64 and the detector 76 having. The aperture stop 66 is further characterized by being a major dimension 86 having. Here is the "main dimension" 86 the diameter of a circular opening or the largest dimension of a non-circular opening (for example, the diagonal of a rectangular opening).

In one embodiment, the distance L1 is substantially equal to the focal length of the image arrangement 64 , so that by the picture arrangement 64 to the detector 76 transmitted radiation is substantially collimated. This arrangement is referred to herein as a "bilateral" telecentric optical arrangement. In a bilateral telecentric arrangement, not only is that due to the object arrangement 62 collected radiation is substantially collimated, but also that of the image arrangement 64 to the detector 76 transmitted radiation is substantially collimated (as shown in the figures). An advantage of collimating the image arrangement 64 to the detector 76 transmitted radiation is that additional stray light is reflected. Such stray radiation originates both from the surfaces of the various optical components in the system and from off-axis radiation entering the radiation thermometer 22 occurs. The collimation of the radiation between the image unit 64 and the detector 76 throws back more of the radiation in the image arrangement 64 at angles that are not parallel to the optical axis 68 are.

In one embodiment, the distance L2 may also be substantially equal to the focal length of the image arrangement 64 be. However, L2 is not limited to a particular dimension in a bilateral telecentric optical arrangement.

A ray of light 88 is characterized as a bundle of rays having a central or "main" ray 92 includes, all from an infinitely small point 94 on the target 72 come. The ray bundle 88 includes all those rays coming from the infinitesimal point 94 going out in one to the main beam 92 centered solid angle 96 are. The main beam 92 is parallel but offset from the optical axis 68 , Every infinitesimal small point 94 in the finish area 74 emits a similar beam through the object array 62 is collected.

The solid angle 96 is a function of the main dimension 86 and a target distance L3, which is the distance from a frontmost surface 95 the object arrangement 62 to the goal 72 is. The smaller the solid angle 96 of the beam 88 is, the closer are the rays in the beam 88 on it, parallel to the optical axis 68 to be, and the greater the rejection of stray light. For a given target distance L3 is the solid angle 96 the smaller, the smaller the main dimension 86 is. Also provides for a given main dimension 86 the aperture stop 66 a longer target distance L3 for a smaller solid angle 96 , for improved rejection of stray light. In general, the target distance L3 has no fixed dimension because of the unfocused parallel beam collection. Non-limiting examples of the target distance L3 for MOCVD chambers are less than two meters. In one embodiment, the target distance L3 is substantially the focal length of the object arrangement 62 representing the rays of a given beam 88 essentially focused when passing through the aperture stop 66 passes through, as in 4 shown. In one embodiment, the target distance L3 is on the order of 200 mm to 300 mm (for example, 250 mm).

Optionally, the radiation thermometer 22 with a reduced size opening arrangement 97 and / or a closure assembly 98 be equipped. In one embodiment, the size reduced opening arrangement comprises 97 and the shutter assembly 98 one on each actuator 100 attached plate 99 , For the size reduced opening arrangement 97 includes the plate 99 an opening 101 that compared to opening the aperture stop 66 is of a reduced size, thereby giving it at least the main dimension 86 the aperture stop 66 superimposed. The plate 99 the closure assembly 98 however, is blank.

In operation, the plates can 99 be positioned independently of each other, ie either not in the way of the through the aperture 66 be through radiation or through the aperture 66 partially or completely block radiation passing through. For the size reduced opening arrangement 97 can, when in an operational position, open 101 around the optical axis 68 be centered, whereby the radiation is partially blocked and the effective opening of the radiation thermometer 22 is reduced. In the closure arrangement 98 keeps the positioning of the plate 99 from the standby position to the deployed position, the target radiation from reaching the detector 76 completely off. Both the size reduced opening arrangement 97 as well as the closure assembly 98 are in 4 shown in the deployment position. In one embodiment, the opening 101 a diameter in the range of 1 to 12 mm.

Functionally, the size reduced opening arrangement 97 can be implemented to prevent saturation of the detector during a temperature rise. As discussed above, the blackbody spectral emittance energy can increase by several orders of magnitude, especially in the visible / UV spectrum. The size-reduced opening arrangement 97 Can be used to control the level of radiation that the detector 76 reduces, thereby preventing saturation. Likewise, the closure assembly 98 be used to the detector 76 to protect against radiation in extreme conditions radiation conditions.

The illustrated actuator (s) 100 are of a rotary type that the plate (s) 99 in the optical axis 68 turns when in use position and the plate (s) 100 away from the optical axis when in the standby position. It should be understood that this arrangement is not restrictive, as any of a number of actuator arrangements can be implemented, including a linear motion assembly that supports the disk (s). 99 moved linearly in and out of the optical path or an adjustable iris device for actively controlling the aperture size.

It is understood by those skilled in the art that there is a tradeoff between the size of the required solid angle 96 and the size of the required target area 74 to achieve a given signal-to-noise ratio. That is, for a given target distance L3, smaller solid angles 96 (eg smaller main dimensions 86 ) for larger target areas 74 can be used, which generally improves the rejection of stray radiation, whereas for smaller target areas 74 larger solid angles 96 (eg larger main dimensions 86 ) are needed. The target size is determined by other factors, such as the dimension of the viewing port window 52 , the effective radial dimension of the image arrangement 64 and the desired field of view of the target 72 on the wafer recording 32 limited. Thus, for smaller target areas 74 that have a larger main dimension 86 the aperture stop 66 and at shorter target distances require L3, the stray light rejection of the unfocused telecentric optical assembly 24 be affected.

In certain non-limiting embodiments, the major dimension is 86 the aperture stop 66 about 1/3 or less of the effective radial dimension 65 the object arrangement 62 , In one embodiment, the main dimension is 86 the aperture stop 66 in the range of 1 mm to 20 mm.

For a typical target of crystalline growth material, there has been inter-reflected radiation coming from the target 72 is reflected, a strong mirror component. That is, much of the radiation incident on the surface of the crystal growth structure will be reflected at the same angle as the angle of incidence. Accordingly, a disproportionately high proportion of the scattered radiation entering standard radiation thermometers (ie, one without telecentric optical arrangement) will enter the target 72 reflected off in angles that are not parallel to the optical axis 68 are. Accordingly, by reducing the solid angle 96 of the beam 88 the contribution of scattered radiation is considerably reduced.

Consider the orientation of the radiation thermometer 22 in 2 , Radiation mirroring the target 72 and into the radiation thermometer 22 must first be inter-reflected or from the viewport window 52 be radiated. The viewing aperture may be configured to reduce the amount of radiation reflected therefrom, e.g. By the use of antireflective coatings and / or by arranging the viewing port window 52 in the depression 54 that can be actively cooled to reduce the amount of radiation on the viewing window 52 comes to mind, limit.

Consider the orientation of the radiation thermometer 22 in 3 , The light trap 82 arranged as generally described and in 3 shown, the function fulfills radiation that would otherwise target the target 72 at the angle of specular reflection for the optical axis 68 would come to mind. The light trap 82 may also, as discussed above - for example, with an anti-reflective window in a recess 54 - be adapted to the transmission of inter-reflected radiation to the target 72 to limit.

To the theory of operation of the unfocused telecentric optical arrangement 24 to check was the geometry and operating conditions of the container 30 as in essence 2 and described herein, using the Advanced System Analysis Program (ASAP), a three-dimensional ray tracing program modeled by Breault Research Organization, Inc. of Tucson, Ariz., USA. The ASAP model was performed to identify the stray radiation pathways and Scattered radiation entering the viewport window 52 enters, analyze. The peripheral heating element 45 was set as a radiation source operating at a temperature of 1800 ° C. The wafer shot 32 (modeled as wafer in the wafer bags 35 comprising) was modeled both as a radiation source at 800 ° C and as a scattering medium. Regarding the wafer bags 35 was supposed to be wafers 41 with an emissivity of 0.8 at the wavelengths of interest. The blackbody radiation energy for the radiation sources at a wavelength of 405 nm was derived based on Planck's law. The inner walls of the housing 30 (including the housing closure 42 , the laminar flow plates 31 and the viewport window 52 were also modeled as scatter media.

The radiation thermometer 22 was modeled for two different collection optics: a "standard" optical arrangement with a target diameter of 10 mm at a 1: 1 magnification; and the unfocused telecentric optical assembly as illustrated and described herein, with a target diameter of about 30 mm. The amount of the target 24 radiated and directly into the radiation thermometer 22 entering 405 nm radiation ("signal radiation") was with that in the housing 30 between-reflected and in the radiation thermometer 22 amount of 405 nm radiation ("scattered radiation") compared for each optical arrangement. The results are shown in Table 1. Table 1: ASAP model results predict the fraction of the radiation wavelength attributed to the signal and scattered radiation at 405 nm for standard and telecentric optical arrangement (target at 800 ° C, peripheral heating element at 1800 ° C) Standard lens Non-Focused Telecentric Optics signal radiation 30% 61% scattered radiation 70% 39% Temperature error at 405 nm wavelength 41 ° C 16 ° C

The ASAP model previously predicted that for a radiation thermometer using standard optics, about 70% of the radiation flux to the detector at the 405 nm wavelength would be due to stray radiation. Use of unfocused telecentric optical arrangement 24 reduced the stray contribution to 39%. These stray light contributions cause temperature deviation errors of about 41 ° C and 16 ° C, respectively. That is, the deviation error of the temperature measurement for the unfocused telecentric optical assembly 24 for the non-axial telecentric optical arrangement is almost 2/3 less than with a standard lens system.

Referring to the 5 and 5A was the efficiency of the unfocused telecentric optical arrangement 24 also verified experimentally. For this experiment, a MOCVD reactor system that uses a flow extender 104 used. The flow extender 104 includes an upper end 106 that extends over the top surface 34 the wafer recording 32 extends and by means of connectors 108 on the housing closure 42 is attached. Flow exciters are used to improve the flow and thermal properties of the crystal growth environment, but also tend to be affected by radiation thermometers that capture the wafer 32 and wafers 41 inspect to drastically increase received stray radiation signal. The reactor system was operated for an extended period of time with wafer holding at about 800 ° C (including GaN crystalline growth material on the wafers in the wafer pockets) so that the thermal environment within the housing was in a quasi-steady state (i.e. means that the components of the MOCVD reactor system were thermally saturated). A measurement with a radiation thermometer was carried out when the resistance heating element arrangement was energized. Then the power supply to the resistance heater assembly was interrupted and a second measurement was made with the radiation thermometer within a ten second period. At the 405 nm wavelength, the stray radiation of the resistive heater assembly disappears almost immediately after the power supply is cut off, while because of the heat capacity of the target, the target continues to emit radiation at substantially the same emission energy as just prior to the power interruption. Accordingly, it was assumed that the first measurement included a stray radiation component of the resistive heater array at the 405 nm wavelength, while the second measurement did not. The experiment was conducted for both a standard optical pyrometer using a conventional focused optics array and a radiation thermometer incorporating the unfocused telecentric optical array 24 used. Both radiation thermometers were nominally operated at the wavelength of 405 nm. The results are shown in Table 2. Table 2: Measurement results determine the fraction of the radiation wavelength attributed to the signal and scattered radiation at 405 nm for a standard and a telecentric optical array (800 ° C target; flow extender chamber) Standard optics Non-Focused Telecentric Optics signal radiation 36% 69% scattered radiation 64% 31% Temperature error at 405 nm wavelength 34 ° C 12 ° C

The measurement results show that with a radiation thermometer using standard optics, about 64% of the radiation flux to the detector at the wavelength of 405 nm is due to scattered radiation. Use of unfocused telecentric optical arrangement 24 reduced the stray contribution, however, to about 31%. These stray light contributions cause temperature deviation errors of about 34 ° C and 12 ° C, respectively. This means, as stated, that the deviation error of the temperature measurement for the unfocused telecentric optical arrangement 24 for the non-axial telecentric optical arrangement is almost 2/3 less than with a standard lens system.

In an embodiment, the detector comprises 76 a photon counter (ie, a photomultiplier tube or PMT) having a cut-off wavelength of 700 nm and is therefore insensitive to infrared radiation. Therefore, the use of a PMT as a detector largely eliminates the concerns of insufficient filtering in the infrared region of the spectrum identified in Zettler. A filter device 102 can be used to filter the PMT so that only wavelengths primarily in the range of blue, violet or ultraviolet light are detected.

Another advantage of the PMT is the fast time response it provides, which is a factor in CVD chambers that use high wafer rate rotation speeds, such as the TURBODISC systems manufactured by Veeco Instruments of Somerset, New Jersey, USA is. The TURBODISC system is commonly available from Mitrovic, et. al., "Reactor Design Optimization Based on 3D CFD Modeling of Nitride Deposition in MOCVD Vertical Rotating Disc Reactors", June 2005 (available at http://www.wpi.edu/academics/che/HMTL/CFD_in_CRE_IV/Mitrovic.pdf). last visited on June 16, 2012). The high speeds of such systems can be detected by the radiation detector 76 Demand data acquisition rates on the order of 10 kHz that PMTs can deliver.

Non-limiting examples of the spectra transmitted by the filter device include a central wavelength in the range of 380 nm to 420 nm and a bandwidth (half-width) in the range of 10 nm to 70 nm. In one embodiment, the filter device comprises 102 Furthermore, a bandpass filter in combination with a color glass filter. A non-limiting example of a filter combination is the Newport 10BPF25-400 bandpass filter (center wavelength of 400 ± 3.5 nm, half width of 25 ± 3.5 nm) with a Thorlabs FGB25 color glass filter (local cut-off wavelength of 400 nm ), which together define a primary bandpass that transmits radiation nominally in the 390 nm to 420 nm bandpass.

In one embodiment, a non-limiting example includes component matching and layout for the unfocused telecentric optical assembly 24 : the object arrangement 62 comprising a plano-convex lens having a diameter of 50.8 mm and a focal length of 249.2 mm (eg LA1301-A from Thorlabs, Inc.) arranged at a distance F1 of 249.2 mm from the aperture stop 66 ; the object arrangement 64 comprising a plano-convex lens having a diameter of 25.4 mm and a focal length of 75.0 mm (for example LA1608-A from Thorlabs, Inc.) arranged at a distance L1 of 75 mm from the aperture stop 66 and at a distance of 75 mm from the detector. In another embodiment, the object arrangement comprises 62 Further, an achromatic doublet having a diameter of 50.8 mm and a focal length of 100 mm (for example, AC508-100-A of Thorlabs) in combination with the plano-convex lens from above to the focal length F1 of the object arrangement To shorten approximately 87 mm, as well as to shorten the overall length of the arrangement. In this latter arrangement, an achromatic Duplicate with a shorter focal length (for example, 30 mm) z. B. as an image arrangement 64 used for closer proximity to the port (eg, AC254-030-A from Thorlabs).

The lenses in the above examples may comprise any material suitable for transmission of visible / UV radiation of the electromagnetic spectrum, such as borosilicate glass, barium fluoride and quartz glass. They can also be coated with antireflection coatings.

Alternatively, other filtering devices and techniques may be used in conjunction with the non-focused telecentric optical device illustrated herein 24 be implemented. For example, the detector and filter arrangement Zettler can be implemented. In some embodiments, a water cooled CCD or a solid state detector such as an avalanche photodiode may be used.

In operation, the wafer receiving is about the axis of rotation 40 rotated while being radiation-based from the heater assembly 44 is heated. The rotation speed of the wafer holder 32 around the axis of rotation 40 can vary significantly depending on the operating parameters and design criteria of the MOCVD reactor system 20 ,

The radiation thermometer 22 and the unfocused telecentric optical assembly 24 are not limited to systems that implement heat sources other than resistance-based heat sources. The various embodiments of the disclosure may be used, e.g. For example, some CVD reactor systems use microwave heating sources.

Referring to the 6A and 6B are multi-channel arrangements 110 and 111 for detecting the spatial temperature change on the wafer 41 in one embodiment of the disclosure. In the illustrated embodiment, a plurality of radiation thermometers 22a . 22b and 22c , each containing the unfocused telecentric optical assembly 24 Implement, present, at the same time respective goals 72a . 72b and 72c on the wafer 41 to inspect when the wafer 41 at the sight opening 52 rotates past. The variety of radiation thermometers 22a . 22b and 22c can be configured and arranged to all goals 72a . 72b and 72c of the wafer 41 be opposed when the wafer shot 32 a certain rotational orientation around the axis of rotation 40 occupies.

In one embodiment, the plurality of radiation thermometers 22a . 22b and 22c arranged so that the goals 72a . 72b and 72c along a line 112 centered substantially along a radial coordinate R extending from the axis of rotation 40 extends radially outward and through the center of the wafer 41 ( 6A ) runs. In a further embodiment, the plurality of radiation thermometers 22a . 22b and 22c arranged so that the goals 72a . 72b and 72c along a line 114 centered substantially at right angles to the radial coordinate R and through the center of the wafer 41 ( 6A ). Still other embodiments may also define other patterns, such as targets that form a nonlinear pattern or that lie along a line that forms an acute angle relative to the radial coordinate r.

Referring to 6C , becomes a multichannel cluster 120 of radiation thermometers 22a to 22e in a disclosed embodiment, for measuring a pattern of targets 72a to 72e , The multichannel cluster 120 can be two-dimensional information about the temperature distribution of the wafer 41 deploy, for example, along the lines 112 and 114 ,

The different in the 6A to 6C Embodiments shown may implement a "blue light" wavelength centered around a wavelength, for example, in the wavelength range of 400 nm to 410 nm (for example, 405 nm). In one embodiment, the plurality of radiation detectors (eg, radiation detectors 22a to 22c from 6A ) a single mount for the radiation collection lenses, closures / openings, filters and detector lenses to provide a more compact design for better spatial resolution. In a non-limiting embodiment, the size of the target 72 (for example 72a to 72e from 6C ) 11 mm x 22 mm and still provide sufficient signal-to-noise ratios. Considering spaces between 1.5mm to 10mm between targets, such an arrangement allows the use of a range of radiation thermometers 22 , in a density of a radiation thermometer 22 or less for about every inch of the diameter of the wafer 41 (ie, a series of three thermometers for a 3-inch wafer, a series of six thermometers for a 6-inch wafer, a series of eight thermometers for an 8-inch wafer, etc.).

The output signals of the radiation thermometer 22a . 22b and 22c can be captured and stored on a data acquisition system 115 get saved. In one embodiment, the data acquisition system comprises a signal processor 116 receiving the signals from the radiation thermometers 22a . 22b and 22c conditioned and digitized, a storage device 117 which stores the digital data and a control unit 118 like a computer. The signal data of each of the radiation thermometers 22a . 22b and 22c over time can be detected and stored in the storage device 117 get saved. The control unit 118 can also handle real-time tasks, such as converting the signal data into temperatures, averaging and standard deviation calculations, and recording the temperature profiles of the wafers 41 and / or the wafer holder 32 , The data acquisition system 115 is for use in the configuration of 6A but can be used with any of the radiation thermometers shown here. Also, various systems are available to the person skilled in the art for data acquisition.

The data acquisition system 115 may also be configured to process the data streams for processing data obtained when a given wafer 41 with regard to the radiation thermometer is properly oriented to synchronize. Synchronization allows the extraction of the relevant portions of the data stream, which is the same when inspecting, e.g. B. the goals 72a . 72b and 72c , received signals corresponds. These relevant portions of the data stream may be averaged over time for statistical treatment. In one embodiment, both synchronization and statistical treatment of the data occur in real time. An exemplary synchronization routine is in US Pat. 6349270 by Gurary, et al. ("Gurary") revealed.

Referring to the 7A and 7B is a MOCVD reactor system 220 shown which is a radiation thermometer 222 used, which is arranged to a target 224 within the MOCVD reactor system 220 to inspect. The MOCVD reactor system 220 includes a reactor chamber 226 operating with a flow flange 228 is coupled to a housing 230 define. The flow flange 228 has laminar flow plates 231 on, through which the gases for the MOCVD process enter the reactor chamber 226 be directed. Inside the reactor chamber 226 is a wafer shot 232 arranged, which has an upper surface 234 that has a goal level 233 defined on which the target of the radiation thermometer is substantially fixed. The upper surface also defines wafer pockets 235 for receiving substrates or wafers 237 , The wafer shot 232 also includes a bottom surface 236 and is operative with a spindle 238 connected to a rotation axis 240 Are defined. A housing closure 242 may be adjacent to the inner wall of the reactor chamber 226 be removably inserted and surrounds the wafer holder 232 ,

A heating element arrangement 244 is under the wafer recording 232 attached, for radiation-based coupling with the lower surface 236 the wafer recording 232 , The resistance heater assembly 244 can from a cylinder 246 be surrounded and also down by a heating wire mounting plate 248 be limited to the radiation-based coupling between the Widerstandheizelementanordnung 244 and the wafer recording 232 to reinforce. The cylinder 246 defines a cylinder axis 250 that is essentially concentric with the axis of rotation 240 is.

The radiation thermometer 222 is on top of the flow flange 228 mounted and aligned, the upper surface 234 the wafer recording 232 through a viewing port window 252 In one embodiment, the viewing port window is 252 in a recess 254 arranged, which can be actively cooled.

The heating element arrangement 244 can be a peripheral heating element 264 include. The peripheral heating element 264 is called so because it is the outer periphery of the heating element assembly 244 Are defined. While the peripheral heating element shown here 264 is a single heating element, a heating arrangement in which the peripheral (outermost) heating elements consist of two or more heating elements is also contemplated.

To promote uniform heating, the peripheral heating element 264 in the illustrated embodiment, one near the inner surface 266 the cylinder arranged peripheral heating element. A variety of rays 2 ' are as of the peripheral heating element 264 radiated inside the housing 230 between-reflected and into the radiation thermometer 222 entering, presented.

Referring to 8th the area is near an upper edge 272 of the cylinder 246 and an outer edge 274 the wafer recording 232 in a disclosed embodiment. A gap 276 is between the outer edge 274 and the top edge 272 Defines it to the wafer shot 232 to allow you to turn freely. The as from the peripheral heating element 264 emitted rays shown 268a . 268b and 268c , make three types of radiation, the gap 276 leaves: ray 268a represents direct radiation, which is the gap 276 leaves without being reflected; beam 268b represents radiation from the inner surface 266 of the cylinder 246 and the outer edge 274 the wafer recording 232 is scattered; and beam 268c represents the radiation coming from the lower surface 236 the wafer recording 232 and the heating wire mounting plate 248 is scattered.

In operation, the wafer bags 235 with substrates 237 be loaded (eg sapphire). The wafer shot 232 becomes about the rotation axis 240 rotated and the heater assembly 244 energized to a temperature of around 1800 ° C. Gases are passing through the laminar flow plates 231 introduced to a crystalline growth material (for example, GaN) on the wafer holder 232 including the wafer bags 235 and any substrate contained therein 237 , The temperature of the crystalline growth material in operation is on the order of 800 ° C.

The operating conditions of the housing 230 as in essence 7A and 7B were three-dimensionally modeled using a ray tracing program. The ray tracing program was performed to identify the stray radiation paths and stray radiation entering the viewing port window 252 enters, analyze. The peripheral heating element 264 was assumed to be contiguous and set as a radiation source operated at a temperature of 1800 ° C. The wafer shot 32 (modeled as a wafer 237 in the wafer bags 35 comprising) was modeled both as a radiation source at 800 ° C and as a scattering medium. The blackbody radiation energy for the radiation sources was derived based on Planck's law at a wavelength of 405 nm. The inner walls of the housing 230 (including the housing closure 242 , the laminar flow plates 231 and the sight opening 252 were also modeled as scatter media.

The radiation thermometer 222 was modeled at two different positions: an "outer" position at a radius R near the center of the outermost wafer pockets 235 (in 7A shown); and a mid-span position centered at about 2/3 R between the outer position and the axis of rotation 240 , The amount of the target 224 radiated and directly into the radiation thermometer 222 entering 405 nm radiation ("signal radiation") was with that in the housing 230 between-reflected and in the radiation thermometer 222 amount of 405 nm radiation ("scattered radiation"). The results are shown in Table 3. Table 3: Predicted fraction of the radiation wavelength attributed to the signal and scattered radiation at 405 nm (target at 800 ° C; peripheral heating element at 1800 ° C) Outer position center position signal radiation 3% 30% scattered radiation 97% 70% Temperature error at 405 nm wavelength 127 ° C 41 ° C

The ray tracing model predicted that for a peripheral heating element 264 forming a continuous ring and the radiation thermometer centered at the outer position 222 Approximately 97% of the radiation flux to the detector of a standard radiation thermometer at the wavelength of 405 nm is attributable to scattered radiation. In the center position, it is predicted that the scattered radiation accounts for approximately 70% of the total signal. These stray light contributions cause temperature deviation errors of approximately 127 ° C and 41 ° C, respectively. Furthermore, the results of the ray-tracing model show that approximately 92% of the scattered radiation reaching the detector of the radiation thermometer comes from the lower surface 236 the wafer recording 232 and the filament heating wire mounting plate 248 is scattered (as by beam 268c in 8th shown).

Referring to 9 is a heating element arrangement 244a in a disclosed embodiment, which is an internal heating element 304 and a peripheral heating element 264a includes. The flow flange 228 and the wafer shot 232 are removed in this view, the arrangement of the heating element assembly 244a to show clearly. The spindle 238 , the housing closure 242 and the heating wire mounting plate 248 are also visible in this view. The heating elements 264a and 304 include electrical connections 306 respectively. 308 ,

The connection connection 306 occupies an arc segment 310 the peripheral heating element 264a , in which the electrical resistance is significantly reduced compared to other arc segments of the peripheral heating element of the same length. That means that the arc segment 310 a section 312 the peripheral heating element 264a forms with a low heat flow. The connection connection 306 operates compared to the high resistance portion of the peripheral heating element 264a with a significantly reduced temperature. For example, in one non-limiting embodiment, the peripheral heating element operates 264a with a maximum operating temperature of nominal 2000 ° C. In this operating state, the connection connection works 306 at about 1500 ° C and it is assumed that the nominal temperature on the arc segment 310 at 1700 ° C or less, or at least 300 ° C lower than the operating temperature of the high resistance portion of the peripheral heating element 264a , Thus, the section works 312 (that is, the electrical connection 306 ) with a low heat flux of the peripheral heating element 264a in terms of operating temperature, at a substantially lower temperature than the remainder of the peripheral heating element 264a , so that the radiation contribution of the section 312 with a low heat flux at 405 nm is smaller by about two orders of magnitude than that of the high resistance portion of the peripheral heating element 264a (please refer 1 ).

The inner heating element 304 the heating element arrangement 244a is arranged so that a first half-length 314 within a first semicircle and a second half-length 316 within a second semicircle. Accordingly, there is a discontinuity line 318 between the first and second half-length 314 and 316 that lies just at one point near the spindle 238 and the electrical connection 308 is bridged.

An experiment was performed to determine the relative contribution of the peripheral heating element 264a to the scattering contribution at the 405 nm wavelength as compared to the heater array 244a as a whole, to determine. The inner heating element 304 and the peripheral heating element 264a were fully powered and controlled, the wafer shot 232 at a steady state temperature near 800 ° C, as would be done in a normal crystal growth process. Then the power was supplied to the peripheral heating element 264a limited, so that the peripheral heating element 264a could only be operated at about half power while still controlling the system, the wafer shot 232 to heat to or near the 800 ° C temperature. In this way, the radiation contribution of the peripheral heating element 264a at the 405 nm wavelength reduced to negligible while recording the wafer 232 essentially remained at temperature and the inner heating element 304 was actually operated at a slightly higher temperature to the lower heat input from the peripheral heating element 264a compensate. Then the power supply of the inner heating element 304 also limited to about half capacity. It was a measurement with the radiation thermometer 222 under all three operating conditions, the third condition (both the peripheral heating element 264a as well as the inner heating element 304 at half power) immediately after limiting the power of the inner heater element 304 was made. Based on these measurements, it was found that the peripheral heating element 264a between 80% and 90% of that emitted by the radiation thermometer 222 received scattered radiation contributed. Thus, the simplification of modeling has been made, only that of the peripheral heating element 264 outgoing radiation instead of the entire heating element arrangement 244 from 7A , validated.

A theory has been developed that with so much of the scattered radiation from the peripheral heating element 264 The scattered radiation can be locally controlled by limiting the emission of the peripheral heating element. That is, if the goal 224 of the radiation thermometer 222 on an area of the target level 233 which is near a zone of the peripheral heating element 264 whose emitted radiation is substantially reduced, trapped or conducted away, the stray radiation received by the radiation thermometer should be reduced.

A scattered radiation detection experiment was conducted to test this theory. The radiation thermometer 222 was designed to detect electromagnetic radiation over a narrow bandpass centered nominally around 405 nm. A second infrared radiation thermometer 320 ( 7A ) was adapted to detect electromagnetic radiation via a bandpass centered nominally at 900 nm. It will be recalled that, as described above, the change in spectral blackbody emission energy at 405 nm is extremely sensitive to changes in temperature (Fig 14 and 16 . 1 ). Accordingly, the radiation thermometer reacts 222 , which is designed to detect radiation nominally at 405 nm, extremely sensitive to stray radiation from the peripheral heating element 264 comes. However, in the relevant temperature range (nominally 2100 K), the change in the spectral blackbody radiation energy at 900 nm wavelength (under renewed with reference to 1 and Planck's Law) are very insensitive to temperature change at 900 nm (see reference numeral 322 . 1 ). Accordingly, the infrared radiation thermometer operating at 900 nm 320 much less sensitive to stray radiation from the peripheral heating element 264 is, and instead more sensitive to changes in the temperature of the wafer recording 232 (nominal at 1100 K, see reference numeral 324 . 1 ).

Therefore, the scattered radiation detection experiment is based on a comparison of that of a detector which is very sensitive to scattered radiation (the radiation thermometer 222 ), and of a reference device which is insensitive to scattered radiation (the infrared radiation based on thermometer 320 ), indicated temperatures.

Referring to 10 is a typical stray radiation signature 330 shown. The scattered radiation signature 330 based on a comparison of an infrared temperature signal 332 , which from the infrared radiation thermometer 320 was generated, and an optical or "blue light" temperature signal 334 that of the radiation thermometer 222 , which detects radiation at nominal 405 nm, was generated. At the in 10 The data shown both inspect the radiation thermometer 222 as well as the infrared radiation thermometer 320 Destinations at the destination level 233 that are similarly located (ie in similar radii from the axis of rotation 240 ). Also the data in 10 were normalized so that the initial temperatures shown on initial cooling (first zone I of 10 ) pursue the same.

For the scattered radiation detection experiment, the MOCVD reactor system was used 220 operated to bring the wafer recording to a first control temperature. Then the control temperature was set down to a lower setpoint temperature, below the first elevated temperature. A first zone I of the scattered radiation signature 330 provides the cooling of the wafer shot 232 as a steady drop in the temperature signals 332 and 334 a second zone 11 the scattered radiation signature 330 represents a stabilization of the temperature signals 332 and 334 where the temperature controller of the MOCVD system 220 establishes a controlled equilibrium at the lower setpoint temperature.

The infrared temperature signal 332 follows essentially the true temperature profile of the wafer shot during the process described above. That is, the actual temperature of the wafer recording 232 in the zone II part of the scattered radiation signature 330 a gradual reversal 336 followed by a substantially monotonic increase in temperature 338 experiences. The gradual reversal 336 and the monotonous temperature rise 338 are a result of the thermal mass of the wafer receptacle 232 ,

The optical temperature signal 334 However, this is due to a sharp reversal 342 followed by a significant overshoot 344 and a slight undershoot 346 in the zone II part of the scattered radiation signature 330 characterized before it is at a controlled equilibrium temperature 348 levels off. The optical temperature signal 334 is a mix of the wafer shot 232 emitted signal 232 and the scattered radiation on the target 224 at the target level 233 invades and into the radiation thermometer 222 is reflected. The overshoot 344 and the undershoot 346 are for a proportionally enhanced temperature profile, which is the heating element arrangement 244 when reacting to a new setpoint experiences, characteristic. It is assumed that the optical temperature signal 334 the control temperature profile of the heating element arrangement 244 closely follows, because the optical temperature signal 334 is dominated by the scattered radiation component as predicted by the ray tracing model.

Therefore, one can qualitatively determine whether that of the radiation thermometer 222 received radiation has a strong scattered radiation component. Temperature signals that have a similar profile as the infrared radiation signal 332 (gradual inversion with monotonic increase) are not dominated by scattered radiation, while temperature signals have a profile similar to that of the optical radiation signal 332 (sharp reversal with significant overshoot) follow, dominated by scattered radiation.

Referring to 11 became the scattered radiation detection experiment by inspecting the targets 224a . 224b . 224c and 224d with the radiation thermometer 222 Again, it was set up to detect radiation at 405 nm nominal wavelength, at several different positions at the target level 233 repeated. While 11 an exposed heater element assembly 244a It should be understood that during the scattered radiation detection experiment, the wafer shot 232 was in place and worked in a rotary mode. According to shows 11 the orientation of the heating element arrangement 244a relative to where the goals are 224a to 224d at the target level 233 extending above the heater assembly 244a is located.

To test the theory that the stray radiation near a portion of the peripheral heating element 264a is reduced with low heat flow, the heating element arrangement 244a arranged so that the section with low heat flow 312 near the goals 224a and 224b was while the section of the peripheral heating element 264a that is near the goals 224c and 224d was, a continuous section 350 was and had a high heat flow. The goals 224a and 224d although diametrically opposite, were both at a radial distance of about 7.68 inches (195 mm) from the axis of rotation 240 centered. Likewise, the goals became 224b and 224c although diametrically opposite, both at a radial distance of about 5.6 inches from the axis of rotation 240 centered.

Referring to the 12A and 12B , the results of the tests are shown. Optical temperature signals 352 and 354 from 12A were from the goals 224a and 224d obtained, ie at an outer radial position. Note that the optical temperature signal 354 that is near a portion of the peripheral heating element 264a obtained with a high heat flux, a temperature profile characteristic of a high stray radiation component (sharp inversion 342a with a strong overshoot 344a ) having. However, the optical temperature signal has 352 which is near the zone 312 the peripheral heating element 264a with low heat flow 312 was obtained, the same temperature profile characteristics as the infrared radiation signal 332 from 10 (gradual reversal 336a with monotonous temperature rise 338a ).

Regarding 12B , were the optical temperature signals 356 and 358 from the goals 224b respectively. 224c attained, ie in middle positions. Note that the optical temperature signal 358 that is near the continuous section of the peripheral heating element 264a obtained with a high heat flux, a temperature profile characteristic of a high stray radiation component (sharp inversion 342b with a strong overshoot 144b ) having. However, the optical temperature signal has 356 which is at a middle position near the zone 312 the peripheral heating element 264a with low heat flow 312 was obtained, the same temperature profile characteristic, as the infrared radiation signal 332 from 10 (gradual reversal 336b with monotonous temperature rise 338b ).

Accordingly, there is an axis of reduced scattered radiation 362 ( 11 ) as at the target level 233 radially from the axis of rotation 240 and over the middle of the zone 312 Defined extending with low heat flux. aims 224 on the target area 233 near the axis 362 are, have a reduced stray radiation component, which, compared to elsewhere on the target level 233 inspected targets a reduced deviation error in the temperature determination is induced. In one embodiment, the goal is 224 along an axis 362 centers or otherwise touches or overlaps them. In another embodiment, the goal falls 224 in a rectangular area 364 reduced scattered radiation, defined as a length 366 having, extending from the axis of rotation 240 down to the outer edge 274 the wafer recording 232 (in 11 not shown), and an approximate width 368 having, through the tendon of the arch segment 310 is defined.

Referring to the 13A and 13B In a disclosed embodiment, it becomes a radiation trap 372 for picking up a portion of the radiation coming from a particular section 374 the peripheral heating element 264 is emitted, shown. In one embodiment, the radiation trap comprises 372 a depression 376 that in the housing closure 242 , which is a tangential dimension 378 has defined. In one embodiment, the particular section is 374 the peripheral heating element 264 defined as the arc segment immediately adjacent to the radiation trap 372 is arranged and the same tangential dimension 378 having.

In operation, part of the particular section 374 radiated radiation 380 in the cavity 376 directed, either by direct irradiation or by reflection at the various surfaces in the vicinity of the radiation trap 372 , The radiation trap 372 thus limits locally the propagation of radiation by trapping the radiation 380 , In this embodiment, the axis is reduced scattered radiation 362 at the target level 233 defined and extends from the axis of rotation 240 and through the tangential center of the depression 376 , The width 368 the rectangular zone 364 Reduced scattered radiation is due to the tendon of the tangential dimension 378 Are defined.

Referring to 14 In one disclosed embodiment, a radiation deflector 392 for deflecting a portion of the radiation coming from a particular section 394 the peripheral heating element 264 is emitted, shown. In one embodiment, the radiation deflector comprises 392 a bulge 396 that is radially inward near the outer edge 274 the wafer recording 232 protrudes. The bulge 396 can be considered a tangential dimension 398 to be characterized. In One embodiment is the particular section 394 the peripheral heating element 264 defined as the arc segment, immediately adjacent to the radiation deflector 392 is arranged and the same tangential dimension 398 like the bulge 396 having.

In operation, part of the particular section 374 radiated radiation 402 in the bulge 396 directed, either by direct irradiation or by reflection at the various surfaces in the vicinity of the radiation deflector 392 , The radiation deflector 392 thus limits local radiation incidence by scattering the radiation 402 , away from a plane 404 passing through the axis of rotation 240 is defined and through the bulge 396 runs. In this embodiment, the axis is reduced scattered radiation 362 by cutting the target plane 233 and the plane 404 defined and extends from the axis of rotation 240 through the radiation deflector 392 , The width 368 the rectangular zone 364 Reduced scattered radiation is due to the tendon of the tangential dimension 398 of the radiation deflector 392 Are defined.

In a disclosed embodiment, the heating element is equipped with hardware for implementing at least one of the techniques for locally reducing stray radiation described herein. A set of instructions is also provided on a tangible medium (eg, paper copy described or computer-accessible), which instructions describe how to align a radiation thermometer relative to the orientation of the heater for a reduced stray radiation component as described herein. Such a combination can be used, for example, to retrofit existing CVD reactor systems.

Referring to 15 becomes a two-wavelength pyrometer 420 in a disclosed embodiment. The two-wavelength pyrometer 420 consists of two radiation thermometers 422 and 424 each adapted to consider a different central wavelength, for example the 930 nm and the 405 nm wavelength, respectively. Each of the radiation thermometers 422 and 424 can also be the unfocused telecentric optical arrangement 24 include, their components in 15 are identified with the same reference numerals as already used.

In one embodiment, the radiation thermometers divide 422 and 424 of the two-wavelength pyrometer 420 a common object arrangement 62 , A cold light mirror 426 Can be used to create a visible / UV spectrum beam 434 to the radiation thermometer 424 to transmit (reflect) while an infrared ray bundle 432 to the radiation thermometer 422 is transmitted. Alternatively, instead of the cold light mirror 426 a beam splitter (not shown) may be used.

Functionally, the two-wavelength pyrometer allows 420 as shown, the simultaneous measurement of a common goal 72 radiated radiation signal. The cold light mirror 426 allows a large proportion of visible / UV spectrum radiation to the radiation thermometer 424 while transmitting a large portion of the infrared radiation through the radiation thermometer 422 passes. For example, cold light mirrors are available that reflect more than 90% of the visible or visible / UV radiation while maintaining a minimum of 83% transmission for wavelengths greater than 800 nm. See "Cold Mirrors," DichroTec Thin Films LLC (available at http://www.dtthinfilms.com/cold-mirrors.html, last visited on May 30, 2013). For embodiments where the filtered wavelengths of both radiation thermometers 422 and 424 either in the visible / UV or in the infrared spectrum, a suitable beam splitter can be used instead. The size-reduced opening arrangement 97 can also, as described above and as for the radiation thermometer 424 in 15 shown for one or both radiation thermometers 422 . 424 be used.

In various embodiments, one or both of the radiation thermometers may be used 422 . 424 with a reflectometer module 442 be equipped. The reflectometer module 442 can be a radiation source 444 have (as a radiation source 444a and 444b for the radiation thermometer 422 respectively. 424 designated), a detector 446 and a beam splitter 448 include. The radiation sources 444a and 444b are tailored or selected, a bundle of rays 452 which has a spectral emission in the wavelength band emitted by the respective filter device 102 and 102b of the respective radiation thermometer 422 or 424 is allowed through. The bundles of rays 452 as well as the optical axes 68 , be in 15 for the radiation thermometer 422 respectively. 424 from each other as a bundle of rays 452a and 452b and optical axes 68a and 68b , distinguished. The bundles of rays 452a and 452b are generically referred to below as bundles of rays 452 and together as a bundle of rays 452 designated. The detector 446 (for the radiation thermometer 422 respectively. 424 as a detector 446a and 446b is selected), to a wavelength in which by the filter device 102 of the respective radiation thermometer 422 or 424 transmitted and from the respective radiation source 444a and 444b radiated tape to respond. In one embodiment, the reflectometer assembly includes 442 a chopper 458 for modulating the beam 452 when he is out of the radiation source 444 exit.

In certain embodiments, the reflectometer assembly 442 also one or more focusing elements 454 . 456 such as lenses or spherical mirrors that comprise the beam 452 focus or collimate. In one embodiment, the focusing element 454 a lens group similar to the object arrangement 62 or the image arrangement 64 for telecentric operation.

In operation, the beam becomes 452 from the radiation source 444 the reflectometer module 442 through the beam splitter 448 directed. In one embodiment, a first part occurs 462a or 462b of the beam 452 through the beam splitter 448 and hits the detector 446 , That of the detector 446 generated signal provides an indication of the intensity of the beam 452 , Because of the orientation of the beam splitter 448 sees the detector 446 effectively no radiation, either from the target 72 comes from or from the target 72 is reflected. A second part 464 (when 464a and 464b for the radiation thermometer 422 respectively. 424 and generally as 464 designated) of the beam 452 is from the beam splitter 448 reflected and aligned, substantially along the respective optical axis 68a or 68b and over the cold mirror 426 on the target 72 spread. A share of the second part 464 of the beam 452 then gets off the target 72 along the respective optical axis 68a or 68b of the respective radiation thermometer 422 or 424 over the cold light mirror 426 reflected back and passes through the beam splitter 448 and the filter device 102 , for detection by the respective detector 76a . 76b of the radiation thermometer 422 or 424 ,

In one embodiment, the layout and components of the reflectometer assembly or assemblies 442 specified that the second part 464 of the beam 452 in combination with the two passes through the object arrangement 62 and the passage through the respective image arrangement 64a or 64b is brought to itself on the image plane of the respective detector 76a . 76b to focus. Also, the reflectometer assembly 442 be specified so that the reflectometer irradiation is the target 72 "Underfilled". That is, the area of the target 72 by the radiation from the reflectometer assembly 442 is irradiated, smaller than the target 72 and completely at the finish 72 is included.

Functionally represents the underfilling of the target 72 in measuring reflectivity, provide spatial tolerance to misalignment that may occur. Briefly explained may be the wafer 41 during the CVD process due to the presence of thermal gradients within the wafer 41 deformed or "arched". The bulge may cause the proportion of the second part 464 of the beam 452 , that of the target 72 reflected and from the detector 76a respectively. 76b is received, is redirected, especially if the target is highly reflective. The deflection of this reflected portion causes the reflected radiation laterally in the image plane of the detector 76a or 76b emigrated. By underfilling the target 72 For example, the reflected portion may migrate laterally to some degree and still be fully opposite and therefore through the detector 76a or 76b be completely detected.

While the presentation of the 15 the reflectometer assemblies 442 in both radiation thermometers 422 and 424 It goes without saying that the Refelektometer sources 442 are optional and through both radiation thermometers 422 and 424 , by only a radiation thermometer 422 or 424 or none of the radiation thermometers can be implemented. Likewise, the use of the chopper 458 or other beam modulating means is also optional and need not be compatible with the reflectometer assembly or sources 442 be implemented.

Referring to the 16A and 16B are each through the detector 76a or 76b who is a radiating target 72 considered which of the reflectometer assembly 442 irradiated generated composite signals 472a and 472b in a disclosed embodiment. The composite signal 472a is for a through a reflectometer assembly 442 generated signal representing the optional chopper 458 or other modulation means implemented, characteristically. The composite signal 472a can be considered a modulated signal 474 that a baseline signal 476 modulated. A baseline size 478 the baseline signal 476 shows the radiation energy of the target 72 at. A valley-to-peak amplitude 482 the modulated signal 474 shows the proportion of the second part 464 of the beam 452 to that of the target 72 is reflected.

The composite signal 472b is characteristic of a by a Refelktometer source 442 generated signal that the beam 452 not modulated. Rather, the compound includes signal 472b a pulse or a step signal 484 with a size 485 the the baseline signal 476 surmounted. The step signal 484 can by turning on the radiation source 444 generated, whereby the step signal 484 during the duration of the step signal 484 can drift. To compensate for the drift can be the step signal 484 opposite the signal from the detector 446 , the intensity of the beam 452 tracked, normalized to a normalized signal 486 provide. The amplitude of the normalized signal 486 shows the reflectivity of the target 72 at.

The reflectometer module 442 For example, it can be implemented to change the radiation of the target 72 to compensate. The radiating power of the target can be derived from the measurement of the reflectivity, for example as in US Pat. 6349270 by Gurary, et al. ("Gurary"), which discloses how to derive the emissivity from a measurement of reflectivity in the context of wafers on a wafer shot in a CVD process. An indication of the target emittance may be used to improve the accuracy of the temperature determination.

The share of the second part 464 of the beam 452 that through the detector 76a or 76b is subject to the same collimation as that of the target 72 radiated radiation, described in the above 4 accompanying discussion. That is, only the reflected radiation from the second part 464 which is essentially parallel to a main beam 92 ( 4 ) is reflected by the detector 76a or 76b is detected, so that there is very little or no involvement of radiation first from the target 72 or the sight opening 52 is scattered. Therefore, the contribution of the scattered radiation is that of your second part 464 of the beam 452 Little, regardless of where the target 72 on the wafer 41 lies. By substantially eliminating the stray radiation component, the resulting displayed reflective properties between targets can be more consistent.

In the illustrated arrangement of the two-wavelength pyrometer 420 becomes the second part 464 the beam 452a and 452b before reaching the respective detector 76a . 76b twice through the beam splitter 448 , the cold mirror 426 , the object arrangement 62 and the viewing aperture 52 toned down, and once through the target 72 , the filter device 102 and the picture arrangement 64 , Accordingly, the second part 464 of the beam 452 be exposed to significant attenuation, which requires that the radiation source 444 is provided with sufficient power to provide a detectable reflectivity signal. A non-limiting example of a sufficiently powerful radiation source is a light emitting diode (LED) operating in a range of about 1 mW to about 10 mW. Light-emitting diodes can be tailored to deliver energy in a narrow spectral range through the filter device 102 of the respective radiation detector 422 or 424 passes. For example, for a filter device 102 with a center wavelength of about 405 nm and a bandpass on the order of 25 nm, a non-limiting example of an LED radiation source is the LED405E, manufactured by Thorolabs, Inc. of Newton, NJ, USA, having a center wavelength of 405 nm ± 10 nm and a spectral bandpass (half width) of about 15 nm. For a filter device 102 With a center wavelength of about 930 nm and a bandpass of the order of 10 nm, a non-limiting example of an LED radiation source is the OD-1390 available from Opto Diode Corp. from Newbury Park, CA, USA, which has a center wavelength of about 943 nm and a spectral bandpass (half width) of about 60 nm.

Referring to 17 becomes a multichannel pyrometer 490 in a disclosed embodiment. In the illustrated embodiment, a plurality of two-wavelength pyrometers 420a . 420b and 420c arranged to goals 72a . 72b and 72c along the line 114 consider. Each two-wavelength pyrometer 420a . 420b . 420c includes a respective pair of radiation thermometers 422a / 424a . 422b / 424b . 422c / 424c wherein each member of a given pair is adapted to inspect a selected wavelength bandpass as described with reference to FIG 15 described.

The radiation thermometer 422 and 424 of the double wavelength pyrometer 420 may be arranged so that the propagation axes of the optical components lie in a common plane (eg plane 492 , in 17 represented as by the elongated axes of the radiation thermometer 422c and 424c Gradient). In addition, the internal components of the radiation thermometer 422 and 424 be arranged so that a width 494 orthogonal to the common plane 492 the same is how the width of the radiation thermometer 22a . 22b and 22c from 6A and 6B , One such arrangement is the two-wavelength pyrometer 420 with the same lateral dimensions as the radiation thermometer 22 ready what it is the two-wavelength pyrometer 420a . 420b and 420c allows to be arranged to inspect targets along any line or in other patterns in the same way as above with reference to Figs 6A and 6B discussed and how in 17 shown.

In an alternative embodiment, only one of the pyrometers of a multi-channel arrangement is a two-wavelength pyrometer. In this arrangement, an assumption is made that the temperature correction and / or the emissivity compensation derived from the single two-wavelength pyrometer applies to the entire wafer and hence all targets.

Accordingly, the combined multi-channel, two-wavelength system 490 provide improved accuracy of the two-wavelength, non-focused telecentric array while providing spatial uniformity temperature information.

While the description herein focuses primarily on application in MOCVD reactor systems, it is noted that the principles discussed herein may apply to other types of CVD chambers, as well as generally to chambers using radiation thermometers. Also, for purposes of this disclosure, the terms "pyrometer" and "radiation thermometer" are synonymous, a "detector" is a detector of electromagnetic radiation and a "beam" is a beam of electromagnetic radiation.

References to relative terms such as top and bottom, front and back, left and right, or the like, are intended to simplify the description and are not limited to any particular orientation. All dimensions shown in the figures may vary with a potential design and intended use of a specific embodiment without departing from its scope.

Any of the additional figures and methods disclosed herein may be used separately or in conjunction with other features and methods to provide improved apparatus, systems and methods for making and using the same. Therefore, combinations of features and methods disclosed herein may not be required to broadly embody the disclosed embodiments, and instead are merely disclosed to specifically describe representative embodiments.

For the purposes of interpreting the claims of the present application, it is expressly intended that the provisions of Section 112, sixth paragraph, 35 USC will not apply unless the specific terms "means to" or "step to" are used in the claim in question used.

Claims (57)

A telecentric optical arrangement for a radiation thermometer, comprising: an aperture stop; an object array of one or optical components arranged to transmit radiation to the aperture diaphragm, the object array and the aperture diaphragm defining an optical axis, the object array defining a first focal length with respect to a first reference point in the object array, the first reference point is at a distance from the aperture stop on the optical axis that is substantially equal to the first focal length of the object assembly, for transmitting substantially collimated radiation from an unfocused target through the object assembly, and for focusing the radiation from unfocused target on the aperture stop; and a detector of electromagnetic radiation arranged to detect at least a portion of the radiation transmitted by the object assembly through the aperture stop, the detector of electromagnetic radiation generating a signal from which a temperature of the unfocused target is derived. The telecentric optical assembly of claim 1, further comprising an image array of one or optical components disposed opposite the object array from the aperture stop and configured to receive radiation transmitted from the object array through the aperture stop on the optical axis, the image array defines a second focal length with respect to a second reference point in the image arrangement, the second reference point being disposed on the optical axis. The telecentric optical assembly of claim 2, wherein the second reference point of the image array is located at a distance from the aperture substantially equal to the second focal length of the aperture Image arrangement is to collimate the radiation transmitted from the aperture stop through the image assembly and onto the detector. The telecentric optical assembly of claim 1, 2 or 3, wherein the aperture stop defines a major dimension that is about 1/3 or less of an effective radial dimension of the object assembly. A telecentric optical device according to any one of claims 1-4, wherein the electromagnetic radiation detector is a photon counter having a cut-off wavelength of about 700 nm. The telecentric optical assembly of any one of claims 1-5, further comprising a filter device having a primary bandpass at wavelengths less than 450 nm, the filter device configured to filter radiation incident on a detection region of the electromagnetic radiation detector. The telecentric optical device of claim 6, wherein the primary bandpass of the filter device has a center wavelength in the range of 380 nm to 420 nm and has a bandwidth in the range of 20 nm to 50 nm. The telecentric optical device of claim 6, wherein the filter means comprises a bandpass filter. The telecentric optical assembly of any one of claims 1-8, wherein a distance between the unfocused target and the object assembly is less than two meters. A telecentric optical assembly according to any of claims 1-9, wherein the object assembly comprises at least one lens. A method for reducing stray radiation in a radiation thermometer used in a chemical vapor deposition chamber, comprising: Providing a telecentric lens assembly comprising an aperture stop and a first optical component assembly for collecting radiation from a target, the telecentric lens assembly being adapted to receive the aperture stop within the focal length of the first optical component assembly for capturing collimated radiation emitted from the target will, to position; Providing instructions on a tangible medium, the instructions comprising: Orienting the first optical component assembly to intercept the radiation emitted by a target in the chemical vapor deposition chamber. The method of claim 11, wherein the instructions provided in the step of providing instructions include positioning the aperture stop in the focal length of the first optical component array. The method of claim 11 or claim 12, wherein the instructions provided in the step of providing instructions further comprise operatively coupling the telecentric lens assembly to a detector of electromagnetic radiation. The method of claim 11, 12 or 13, further comprising positioning the aperture stop in the focal length of the first optical component array. The method of any of claims 11-14, further comprising operatively coupling the telecentric lens assembly to a detector of electromagnetic radiation. A system for measuring a temperature of a target in a chemical vapor deposition chamber, comprising: a radiation thermometer operatively coupled to the chemical vapor deposition chamber, the radiation thermometer including means for defining an unfocused target within the chemical vapor deposition chamber. Pyrometer system for deriving a spatial temperature distribution, comprising: a plurality of radiation thermometers arranged to inspect a corresponding plurality of adjacent unfocused targets, each of the plurality of radiation thermometers comprising a first telecentric optical assembly including: an object assembly of one or more optical components for transmitting radiation, wherein the object arrangement defines a first focal length with respect to a first reference point in the object arrangement; a first aperture stop arranged to receive radiation transmitted from the object array, the object array and the first aperture stop defining a first optical axis passing through the reference point, the first aperture stop being spaced from the reference point; substantially equal to the focal length of the object array, for focusing a first detected portion of the radiation from the corresponding one of the corresponding plurality of adjacent non-focused targets onto the first aperture stop; and a first detector of electromagnetic radiation arranged to detect the first detected portion of the radiation transmitted by the object assembly through the first aperture stop, wherein the first electromagnetic radiation detector generates a first signal from which a temperature of the corresponding one of the corresponding plurality of adjacent ones does not derived from focused goals. The pyrometer system of claim 17, wherein adjacent ones of the plurality of adjacent unfocused targets define a corresponding space therebetween. The pyrometer system of claim 17, wherein the plurality of radiation thermometers for viewing a wafer are disposed on a wafer receptacle, wherein the wafer receptacle is disposed within a chemical vapor deposition chamber and wherein the plurality of adjacent unfocused targets are completely opposed by the wafer. The pyrometer system of claim 19, wherein the confronting of the unfocused targets by the wafer is periodic. The pyrometer system of claim 17, wherein at least one of the plurality of radiation thermometers comprises a first reflectometer assembly comprising a first beam splitter and a first radiation source for generating a first beam of electromagnetic radiation, the first beam splitter propagating along a portion of the first beam the first optical axis is arranged to irradiate the corresponding one of the corresponding plurality of adjacent unfocused targets. The pyrometer system of claim 21, wherein the first reflectometer assembly modulates the first beam. The pyrometer system of claim 22, wherein the first reflectometer assembly modulates the first beam with a chopper. The pyrometer system of any one of claims 17-23, wherein at least one of the plurality of radiation thermometers includes a reduced aperture array for selectively reducing the first detected portion of the radiation detected by the first electromagnetic radiation detector. The pyrometer system of any one of claims 17 to 24, wherein at least one of the plurality of radiation thermometers includes a second telecentric optical assembly comprising: a second aperture stop arranged to receive radiation from the object array, the object array and the second aperture stop defining a second optical axis passing through the reference point, the second aperture stop being at a distance from the reference point substantially equal to the focal length the object arrangement is for focusing the second detected part of the radiation from the corresponding one of the corresponding plurality of adjacent unfocused targets onto the second aperture stop; and a second detector of electromagnetic radiation arranged to detect the second detected portion of the radiation transmitted by the object assembly through the second aperture stop, the second detector of electromagnetic radiation to generate a second signal indicative of the temperature of the corresponding one of the corresponding plurality of adjacent non-focused ones Goals is derived. The pyrometer system of claim 25, wherein the first detected portion of the radiation is in the infrared spectrum of electromagnetic radiation and the second detected portion of the radiation is in the visible spectrum of electromagnetic radiation. The pyrometer system of claim 25, further comprising a cold mirror disposed along the first optical axis and the second optical axis, wherein the cold mirror transmits the first detected portion of the radiation and reflects the second detected portion of the radiation. The pyrometer system of claim 26 or claim 27, wherein the second detected portion of the radiation defines a wavelength bandpass centered at a wavelength greater than or equal to 400 nm and less than or equal to 410 nm. The pyrometer system of claim 26, 27 or 28, wherein the first detected portion of the radiation defines a wavelength bandpass having the 930 nm wavelength. The pyrometer system of any one of claims 21-29, wherein at least one of the plurality of radiation thermometers comprises a second reflectometer assembly including a second beam splitter and a second radiation source for generating a second beam of electromagnetic radiation, the second beam splitter propagating a portion of the second beam the second optical axis is arranged to irradiate the corresponding one of the corresponding plurality of adjacent unfocused targets. The pyrometer system of claim 30, wherein the second reflectometer assembly modulates the second beam. The pyrometer system of claim 31, wherein the second reflectometer assembly modulates the second beam with a chopper. A telecentric two-wavelength pyrometer comprising: an object assembly of one or more optical components for transmitting radiation from an unfocused target, the object assembly defining a focal length with respect to a reference point in the object assembly; a first aperture end arranged to receive radiation transmitted from the object assembly, the object assembly and the first aperture end defining a first optical axis passing through the reference point, the first aperture end disposed at a distance from the reference point located in Substantially equal to the focal length of the object array, for focusing a first detected portion of the radiation onto the first aperture end; a second aperture stop arranged to receive radiation transmitted from the object array, the object array and the second aperture stop defining a second optical axis passing through the reference point, the second aperture stop located at a distance from the reference point located in Substantially equal to the focal length of the object array, for focusing a second detected portion of the radiation onto the second aperture stop; a second detector of electromagnetic radiation arranged to detect the first detected portion of the radiation transmitted from the object assembly through the first aperture stop; and a second detector of electromagnetic radiation arranged to detect the second detected portion of radiation transmitted from the object assembly through the second aperture end, the first electromagnetic radiation detector and the second electromagnetic radiation detector producing a first signal and a second signal, respectively a temperature of the unfocused target. The two-wavelength telecentric pyrometer of claim 33, further comprising a first reflectometer assembly including a first radiation source for generating a first beam of electromagnetic radiation and a first beam splitter, the first beam splitter for propagating a portion of the first beam along the first optical axis for irradiating the corresponding one of the corresponding plurality of adjacent unfocused targets. The two-wavelength telecentric pyrometer of claim 34, further comprising a second reflectometer assembly comprising a second radiation source for generating a second beam of electromagnetic radiation and a second beam splitter, the second beam splitter being arranged to propagate a portion of the second beam along the second optical axis for irradiating the corresponding one of the corresponding plurality of adjacent unfocused targets. A telecentric two-wavelength pyrometer according to any one of claims 33-35, wherein the first detected portion of the radiation is in the infrared spectrum of electromagnetic radiation and the second detected portion of the radiation is in the visible spectrum of electromagnetic radiation. A telecentric two-wavelength pyrometer according to any one of claims 33-36, wherein the second detected portion of the radiation defines a wavelength bandpass centered at a wavelength greater than or equal to 400 nm and less than or equal to 410 nm, and the first detected portion of the Radiation defines a wavelength bandpass having the 930 nm wavelength. A two-wavelength telecentric pyrometer according to any one of claims 33-37, further comprising a reduced aperture array arranged to selectively reduce one of the first detected portion of the radiation detected by the first electromagnetic radiation detector and the second detected portion of the radiation is detected by the second detector of electromagnetic radiation. A system for limiting stray radiation received by a radiation thermometer comprising: a chemical vapor deposition chamber (CVD); a wafer receptacle configured to rotate about an axis of rotation and comprising an upper surface, a lower surface and an outer edge, the upper surface being substantially planar and defining a target plane; a plurality of heating elements disposed beneath the wafer receptacle, the plurality of heating elements configured to irradiate the lower surface of the wafer receptacle, the plurality of heating elements comprising a peripheral heating element proximate the outer edge of the wafer receptacle, wherein the peripheral heating element includes a portion of low heat flow along a particular portion of the peripheral heating element, the portion having a low heat flux operating relative to other portions of the peripheral heating element at a significantly reduced temperature; and a radiation thermometer for inspecting a target disposed proximate an axis of reduced scattered radiation, wherein the reduced scattered radiation axis is coplanar with the target plane and extends from the axis of rotation and over the portion of the low heat flux heating element. The system of claim 39, wherein the radiation thermometer is arranged to inspect a target that is in a rectangular area on the wafer plane that includes a portion of the reduced scattered radiation axis, the rectangular area extending from the spindle to a plane outer edge of the wafer holder, wherein the rectangular portion has a width which is approximately the same width as the tangential dimension of the specific portion of the peripheral heating element. The system of claim 39 or claim 40, wherein the portion of the low heat flux peripheral heating element comprises an electrical connection. The system of claim 39, 40 or 41, further comprising a cylinder disposed within the CVD chamber, the cylinder defining a cylinder axis substantially concentric with the axis of rotation, the cylinder having an inner surface and an outer surface, the inner surface defines an inner cylinder diameter, the outer surface defines an outer cylinder diameter, the cylinder having an upper edge defining an upper plane substantially perpendicular to the cylinder axis. The system of claim 42, wherein the wafer receptacle defines a receiving exterior diameter greater than the cylinder interior diameter of the cylinder. The system of any of claims 39-43, wherein the peripheral heating element substantially surrounds the others of the plurality of heating elements. The system of any one of claims 39-44, wherein the radiation thermometer is adapted to detect radiation in the visible / UV region of the electromagnetic spectrum. The system of any of claims 39-45, further comprising a spindle disposed within the CVD chamber, the spindle being concentric with the axis of rotation and having a distal portion adapted for coupling to the wafer receptacle. A system according to any one of claims 39-46, wherein the low heat flow portion is adapted to operate at a temperature of at least 300 ° C below the temperature of any other portion of the heating element when operating at a maximum operating temperature. A method of reducing scattered radiation received from a radiation thermometer that inspects a target in a chemical vapor deposition chamber, the method comprising: Providing a wafer receiver and a heater assembly adapted for operation in the chemical vapor deposition chamber, the wafer receiver adapted to rotate about an axis of rotation and having a bottom surface and a substantially planar top surface, the top surface of which Defining a target plane, the heater element assembly comprising a peripheral heating element comprising a portion of low heat flux along a particular portion of the peripheral heating element; Providing instructions on a tangible medium, the instructions comprising: Arranging the heater assembly in the chemical vapor deposition chamber; Placing the wafer receiver in the chemical vapor deposition chamber above the heater assembly and with the top surface facing up; Aligning a radiation thermometer to inspect a target disposed proximate an axis of reduced scattered radiation, wherein the reduced scattered radiation axis is coplanar with the target plane and extends from the axis of rotation and over the portion of the low heat flux heating element. The method of claim 48, wherein the target aligned in the aligning step is in a rectangular area at the target plane comprising a portion of the reduced scattered radiation axis, the rectangular area extending from the axis of rotation to an outer edge of the wafer nest wherein the rectangular area has a width that is approximately the same width as the tangential dimension of the particular portion of the peripheral heating element. The method of claim 48 or claim 49, wherein the target aligned in the aligning step comprises a portion of the axis. A system for limiting stray radiation received by a radiation thermometer comprising: a chemical vapor deposition chamber (CVD); a cylinder disposed within the CVD chamber, the cylinder defining a cylinder axis and having an inner surface and an outer surface, the inner surface defining an inner cylinder diameter, the outer surface defining an outer cylinder diameter, and the cylinder having an upper edge, which defines an upper plane that is substantially perpendicular to the cylinder axis. a peripheral heating element disposed within the cylinder and near the inner surface of the cylinder; a spindle disposed in the cylinder and extending through the peripheral heating element, the spindle having a distal portion extending across the top plane of the cylinder; a wafer receptacle having a top surface that is substantially planar and defines a target plane, the wafer receptacle configured for connection to the distal portion of the spindle for suspension over the peripheral heating element; Means for reducing scattered radiation emitted from a particular portion of the peripheral heating element, wherein the means for reducing scattered radiation is disposed in the vicinity of the peripheral heating element; and a radiation thermometer adapted to inspect a target at the target plane located proximate an axis of reduced scattered radiation, wherein the reduced scattered radiation axis is coplanar with the target plane and has an origin in the axis of rotation that is in a direction of the means extends to reduce scattered radiation. The system of claim 51, wherein the target is in a wafer-level rectangular area that includes a portion of the reduced scattered radiation axis, the rectangular area extending from the spindle to an outer edge of the wafer receptacle, wherein the rectangular Area has a width which is approximately the same width as the tangential dimension of the means for reducing scattered radiation. The system of claim 51 or claim 52, wherein the means for reducing scattered radiation comprises electrical connection of the peripheral heating element. The system of claim 51, 52 or 53, wherein the means for reducing scattered radiation comprises one of a radiation trap and a radiation deflector located proximate the particular portion of the peripheral heating element. A system for limiting stray radiation received by a radiation thermometer comprising: a chemical vapor deposition chamber (CVD); a wafer receptacle configured to rotate about an axis of rotation, the wafer receptacle comprising a top surface, a bottom surface, and an outer edge, the top surface defining a target plane substantially perpendicular to the axis of rotation; a heating element disposed opposite the lower surface of the wafer receptacle, the heating element being proximate the outer edge of the wafer receptacle, the heating element comprising a low heat flow portion adapted to be at a temperature of at least 300 ° C to operate at the temperature of any other portion of the heating element when operating at a maximum operating temperature; and a viewing aperture for a radiation thermometer, wherein the viewing aperture is arranged to inspect a target disposed near an axis of reduced scattered radiation, the reduced scattered axis axis being coplanar with the target plane and extending from the axis of rotation and over the portion of the beam Heating element with a low heat flux extends. The system of claim 55, further comprising a radiation thermometer arranged to inspect a target through the viewing aperture, the target being in the vicinity of the reduced scattered radiation axis. The system of claim 56, wherein the radiation thermometer is adapted to detect radiation in the visible / UV region of the electromagnetic spectrum.

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