Detector for low temperature transmission pyrometry

Apparatus and methods of processing substrates include a detector manifold to detect radiation from proximate a processing area in a chamber body; a radiation detector optically coupled to the detector manifold; and a spectral multi-notch filter. Apparatus and methods of processing substrates include detecting transmitted radiation from an emitting surface of a substrate in a chamber body; conveying at least one spectral band of the detected radiation to a photodetector; and analyzing the detected radiation in the at least one spectral band to determine an inferred temperature of the substrate.

FIELD

Embodiments described herein relate to apparatus and methods of processing substrates. More specifically, apparatus and methods described herein relate to temperature measurement by radiation transmission.

BACKGROUND

New trends in anneals feature processing in lamp-based anneal chambers. Such processing calls for accurate temperature assessment at low temperatures. Temperature assessment with mere radiant emission measurements may not be accurate at temperatures below about 400° C. due to a low signal-to-noise ratio. Transmission pyrometry may provide the requisite accuracy and precision.

Transmission pyrometry is a common mode of assessing the thermal state of a substrate (e.g., a silicon substrate). Thermal processing chambers commonly expose a substrate to intense, non-coherent or coherent radiation to raise the temperature of the substrate, either of the whole substrate or a part or surface area of the substrate. The radiation used to heat the substrate creates a strong background radiation environment in the chamber.

High power radiation is used to assess the thermal state of the substrate because it can be differentiated from the background radiation in the chamber. Lasers are typically used because they offer high power, and because they afford the opportunity to select a particular wavelength best suited to the substrate. Lasers produce coherent radiation that, when transmitted through a substrate, can indicate a thermal state of the substrate, which may be registered as a temperature. The transmitted radiation may be detected by a pyrometer, compared to the source radiation, and the result is correlated to infer the substrate thermal state. Heretofore, the source radiation was generally selected to be at a small number (e.g., one or two) of narrow wavelength bands. The transmitted radiation, likewise, was analyzed only at a small number (e.g., one or two) of narrow wavelength bands

There is a need for reliable transmission pyrometric measurements. The detector must be operable in an environment of high radiant noise.

SUMMARY

Embodiments described herein relate to apparatus and methods of processing substrates. More specifically, apparatus and methods described herein relate to temperature measurement by radiation transmission.

In an embodiment, a transmission pyrometry detector includes a detector manifold to detect radiation from proximate a processing area in a chamber body; a radiation detector optically coupled to the detector manifold; and a spectral multi-notch filter.

In an embodiment, a method includes detecting transmitted radiation from an emitting surface of a substrate in a chamber body; conveying at least one spectral band of the detected radiation to a photodetector; and analyzing the detected radiation in the at least one spectral band to determine an inferred temperature of the substrate.

DETAILED DESCRIPTION

A transmission pyrometry detector (“TPD”) generally measures radiation spectra of a substrate (e.g., a silicon substrate) at a range of wavelengths (more than just one or two primary wavelengths) to infer the temperature of the substrate. The TPD may reliably detect transmitted radiation in at least two spectral bands. The spectral bands may be generally separated from one another (e.g., at least 10 nm separation between bands, or at least 25 nm separation between central wavelength) to provide precision in resolving radiant intensity in each. The TPD may be sensitive to radiation in the selected spectral bands, while filtering radiation of other wavelengths. For example, the TPD may detect a spectral band of width about 10 nm-15 nm centered around 1030 nm, and the TPD may also detect a spectral band of width about 10 nm-15 nm centered around 1080 nm. The TPD may filter other wavelengths, for example, to an optical density of about 3.0 (“OD3”). In some embodiments, the spectral bands may be at longer wavelengths (e.g., greater than 1080 nm).

FIG. 1is a partial perspective diagram of a prior art rapid thermal processing (RTP) chamber300. The chamber300generally consists of a lamp assembly310, a chamber body320and a substrate support assembly330. For clarity, the chamber300has been cross-sectioned, and only the upper portion of chamber body320is illustrated inFIG. 1.

Lamp assembly310includes a plurality of lamps311, each of which is positioned inside a reflective light pipe312. The lamps may be incandescent lamps, such as tungsten-halogen, or other high output lamps, such as discharge lamps. Together, the reflective light pipes312form a honeycomb array313inside a water-cooled housing314. A very thin quartz window315forms the bottom surface of lamp assembly310, separating lamp assembly310from the vacuum usually present in chamber300. Quartz is typically used for quartz window315since it is transparent to infrared light. Lamp assembly310is attached to the upper surface of chamber body320in a vacuum-tight manner.

Chamber body320includes the walls and floor of chamber300as well as a substrate opening321and exhaust opening322. Substrates are delivered into and removed from chamber300through substrate opening321, and a vacuum pump (not shown) evacuates chamber300through exhaust opening322. Slit or gate valves (not shown) may be used to seal substrate opening321and exhaust opening322when necessary.

The substrate support assembly330is contained inside chamber body320and includes an edge ring331, a rotating quartz cylinder332, a reflector plate333and an array of photo probes334(e.g., optical fibers). Edge ring331rests on rotating quartz cylinder332. During substrate processing, edge ring331supports the substrate (not shown for clarity) approximately 25 mm below quartz window315. Rotating quartz cylinder332rotates between about 50 rpm and about 300 rpm during substrate processing to maximize substrate temperature uniformity during processing by minimizing the effect of thermal asymmetries in chamber300on the substrate. Reflector plate333is positioned about 5 mm beneath the substrate. Photo probes334penetrate reflector plate333and are directed at the bottom of the substrate during thermal processing. Photo probes334transmit radiant energy from the substrate to one or more photodetectors337for determining substrate temperature, substrate front side emissivity, and/or reflectivity during thermal processing. When lamps311are incandescent lamps, the pyrometers are typically adapted to measure broadband emissions from the backside of the substrate in a selected range of wavelengths (e.g., between wavelengths of about 200 nm to about 5000 nm).

The photodetector337may include a filter that may provide a spectral response sensitive to the wavelength of the absorption gap at the substrate temperatures between about 100° C. and about 350° C. Photodetector337may be a silicon photodetector for temperatures below about 350° C., since the absorption gap of silicon varies from about 1000 nm to about 1200 nm for temperatures from room temperature to 350° C. A silicon photodetector may be insensitive to radiation having a wavelength greater than about 1100 nm. For temperatures higher than about 350° C., the absorption edge may be beyond the detection limits of the silicon photodetector, so any further increases in the absorption edge wavelength may not be readily detected.

Transmission pyrometry generally utilizes a radiation source that generates mid-infrared radiation (e.g., ranging in wavelength from about 1000 nm to about 1500 nm). The source may produce highly collimated radiation. The collimated radiation may be transmitted through a beam guide (e.g., a single mode optical fiber) onto a silicon substrate. A portion of the collimated radiation may transmit through the substrate. The amplitude of the transmitted radiation may be a function of temperature of the substrate and of the wavelength of the source radiation. A pyrometer probe (e.g., a light pipe) may be aligned to receive the transmitted radiation. For example, the pyrometer probe may be aligned with the beam guide. The pyrometer probe may direct the transmitted radiation to one or more transmission pyrometers. The transmission pyrometers may include components such as filters, diffraction gratings, cylinder lenses, photodetectors, and/or spectrometers. For example, the pyrometer probe may direct the transmitted radiation to a spectral band filter. The spectral band filter may only allow transmission of radiation at selected spectral bands. The non-filtered radiation may be directed to a diffraction grating. The diffraction grating may separate the transmitted radiation in different directions as a function of wavelength. A collimating lens may focus the diffracted radiation to one or more focus points. One or more photodetectors may then measure the radiation as a function of direction, which thereby is a function of wavelength. For example, an indium gallium arsenide linear array may be positioned at the back focal plane of the collimating lens to measure power as a function of wavelength. The power spectrum (as a function of wavelength) of the transmitted radiation in the selected spectral bands may be compared to the power spectrum of the source radiation. The two power spectra may be used to calculate the transmission of the substrate as a function of wavelength. This may then be used to infer temperature of the substrate. In some embodiments, zones of the substrate may be identified, and transmission pyrometry may be done on each zone to create a temperature map of the substrate. In some embodiments, longer wavelengths (e.g., greater than 1080 nm) of source radiation may be utilized.

An exemplary graph of radiation transmitted by a silicon substrate as a function of wavelength of the source radiation and temperature of the substrate is shown inFIG. 2. Sixteen different lines P(λ) show transmission as a function of temperature for sixteen different source wavelengths (in nm). Blackbody radiation as a function of temperature P(bb) is also shown. It should be understood that the detected signal degrades as noise from the blackbody radiation increases. Consequently, source wavelengths may be selected to provide adequate signal-to-noise ratios. As illustrated inFIG. 2, a source wavelength of about 1030 nm may have adequate signal-to-noise ratio in the temperature band T(1030) from about 10° C. to about 275° C.; and a source wavelength of about 1080 nm may have adequate signal-to-noise ratio in the temperature band T(1080) from about 125° C. to about 375° C. As can be seen inFIG. 2, longer wavelengths of source radiation may allow for higher temperature measurements.

A chamber300suitable for transmission pyrometry is illustrated inFIG. 3A. As before, the chamber300includes a lamp assembly310, a chamber body320and a substrate support assembly330. The substrate support assembly330may define a processing area335, proximate which, during operations, a substrate may be typically disposed. As illustrated, a radiation source400is located outside of chamber300. Other embodiments may have the radiation source400inside of the lamp assembly310, attached to the lamp assembly310, immediately outside of lamp assembly310, or otherwise located to suit operational specifications. The source400is configured to generate radiation for input to source manifold410. The source radiation may travel through source manifold410and ultimately reach an incident area of a receiving surface of the substrate (i.e., proximate the processing area335). For example, source manifold410may include a plurality of beam guides415interspersed with the reflective light pipes312. A collimating lens420may be located at an end of beam guide415. The collimating lens420may direct the source radiation onto an incident area of the receiving surface of the substrate (i.e., proximate the processing area335). A portion of the source radiation from each beam guide415may be transmitted from the receiving surface of the substrate to the opposite, emitting surface of the substrate. For example, the source radiation may be incident on the receiving surface of the substrate at the incident area, and the transmitted radiation may exit the emitting surface of the substrate at the emanating area. The incident area may thereby be opposite the emanating area.

In some embodiments, source400may be configured so that source radiation may be selected over and/or distinguished from background radiation. For example, source400may be a bright source so that any background radiation is negligible in comparison. As another example, source400may be turned off periodically to sample the background radiation for calibration and/or normalization. In some embodiment, source400may be a high-power radiant source, for example a quantum sources such as a laser and/or LED. In some embodiments, source400may emit in wavelengths selected to match, or otherwise complement, the spectral characteristics of the TPD. In some embodiments, source400may be a directed radiation source, for example a collimated or partially collimated source, to direct radiation through the substrate to be received by the TPD. Collimation may be selected to match the radiation to the numerical aperture of the TPD, and thereby improve the source-to-noise ratio of the system.

A TPD500may detect the transmitted radiation. The TPD500may include a detector manifold530, one or more radiation detectors537, and a spectral multi-notch filter536(seeFIG. 4). As illustrated, radiation detectors537are located outside of chamber300. Other embodiments may have the radiation detectors537inside of the chamber body320, attached to the chamber body320, immediately outside of chamber body320, or otherwise located to suit operational specifications. The detector manifold530may include a plurality of pyrometer probes534. For example, a pyrometer probe534may be aligned with a beam guide415to detect the transmitted radiation. In some embodiments, each beam guide415of the source manifold410may have an aligned pyrometer probe534. In other embodiments, there may be more beam guides415than pyrometer probes534. In still other embodiments, there may be more pyrometer probes534than beam guides415.

The transmitted radiation may travel through detector manifold530and ultimately reach the one or more radiation detectors537. In some embodiments, a single radiation detector537may receive transmitted radiation from all of the pyrometer probes534. In some embodiments, multiple radiation detectors537may be utilized. In some embodiments, detector manifold530connects a subset of the pyrometer probes534with each radiation detector537. In some embodiments, detector manifold530connects a single pyrometer probe534with each radiation detector537. In some embodiments, detector manifold530may utilize optical splitters to deliver transmitted radiation from one pyrometer probe534to multiple radiation detectors537. In some embodiments, detector manifold530may utilize optical combiners to deliver transmitted radiation from multiple pyrometer probes534to a single radiation detector537.

In some embodiments, both photodetector337(FIG. 1) and the radiation detector537(FIG. 3A) are utilized to measure the temperature of a substrate during processing, and a detection assembly is utilized to separate radiation from the probe534(or334) to the photodetector337and the radiation detector537.FIG. 3Bis a schematic side view of a detection assembly360according to embodiments disclosed herein. As shown inFIG. 3B, the detection assembly360includes a reflector362, the photodetector337, and the radiation detector537. A first radiation364and a second radiation366exit the probe534(or334). The first radiation364is the radiation emitted from the substrate and is un-collimated. The first radiation364thus has a large numerical aperture. The second radiation366is the transmitted radiation from the collimated radiation and is collimated. The second radiation366thus has a small numerical aperture. The reflector362may be any suitable device that can redirect radiation. In one embodiment, the reflector362is a mirror. The reflector362is disposed along a path of the second radiation366and the reflector362reflects all, or a substantial portion of, the second radiation366to the radiation detector537. Thus, the reflector362is aligned with both the probe534and the radiation detector537. In one embodiment, the probe534is disposed along an axis that is substantially perpendicular to a major axis of the radiation detector537. Because the second radiation366is highly collimated, the size of the reflector362and the detecting surface of the radiation detector537can be relatively small. The first radiation364is transmitted to the photodetector337. Because the first radiation364is un-collimated, the detection surface of the photodetector337is relatively large as shown compared to the detection surface of the radiation detector537. Furthermore, even though the reflector362is disposed along the path of the first radiation364, the reflector362does not significantly change the amount of radiation transmitted to the photodetector337due to the relatively small size of the reflector362. The detection assembly360is utilized to separate the first radiation364and the second radiation366based on the numerical aperture of the radiations364,366.

An exemplary TPD500is illustrated inFIG. 4. Transmitted radiation may enter the radiation detector537from detector manifold530. The transmitted radiation may travel through a diffraction grating531and/or a cylinder lens532to be split by wavelength λninto various directions. The split radiation may thus be incident on a focal plane533. A detector array535(e.g., an indium gallium arsenide linear detector array) may be arranged to receive the radiation at the focal plane533and measure the power as a function of wavelength P(λn).

TPD500may include one or more spectral multi-notch filters536. For example, a spectral multi-notch filter536may be incorporated into one or more pyrometer probe534of detector manifold530. The transmitted radiation may thereby be filtered by spectral multi-notch filter536within chamber body320. As another example, a spectral multi-notch filter536may be incorporated into the optical coupling between detector manifold530and radiation detector537. As another example, a spectral multi-notch filter536may be a component of radiation detector537. Spectral multi-notch filter536may convey multiple (e.g., two, three, four, or more) spectral bands with at least about 80% efficiency. Spectral multi-notch filter536may filter, remove, or reduce radiation of other wavelengths, for example to OD3. Each of the spectral bands may have a band of width about 10 nm-15 nm. Each of the spectral bands may be generally separated from one another (e.g., at least 10 nm separation between bands, or at least 25 nm separation between central wavelengths). For example, a spectral multi-notch filter536may convey a spectral band of width about 10 nm-15 nm centered around 1030 nm, and the spectral multi-notch filter536may also convey a spectral band of width about 10 nm-15 nm centered around 1080 nm.

In some embodiments, a scanning photodetector may be utilized in conjunction with or in lieu of detector array535. For example, a scanning photodetector may have an optical window that moves along focal plane533at a known speed. As the optical window moves, the scanning photodetector measures power as a function of time P(tn), which can be converted to power as a function of wavelength P(λn) based on the speed of the optical window.

In some embodiments, the radiation detector537may be one or more fiber optic spectrometers.

In some embodiments, detector manifold530may include one or more optical switches. For example, an optical switch may be identified with a subset of the pyrometer probes534. When the optical switch is “on”, the detector manifold530may direct radiation from that subset of pyrometer probes534to the radiation detector537. When the optical switch is “off”, the detector manifold530may not allow radiation from that subset of pyrometer probes534to reach the radiation detector537. In some embodiments, the subset of pyrometer probes identified with each optical switch may be selected to isolate zones of the substrate. Transmission pyrometry may thereby be done on each zone without requiring additional radiation detectors537.

FIG. 5illustrates an example of a power spectrum600generated by TPD500. As illustrated, the power spectrum600has two peak bands610,620. Peak band610is centered on about 1033 nm, while peak band620is centered on about 1081 nm. The width of peak band610is about 15 nm, while the width of peak band620is about 20 nm. The signal within each peak band610,620varies as a function of wavelength. The power spectrum600may be compared to the power spectrum of the source radiation to calculate the transmission of the substrate as a function of wavelength. This may then be used to infer temperature of the substrate.

In some embodiments, power spectrum600may have more than two peak bands (e.g., three peak bands). For example, the source radiation may have wavelengths longer than 1080 nm (e.g., 1120 nm). The TPD500may thus be sensitive to radiation with wavelengths between about 1000 nm and 1500 nm.