Introduction. In-Situ Metrology for Veeco k465i GaN MOCVD WHAT BLUE BANDIT PROVIDES IN REAL-TIME: k-space Associates, Inc.

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1 O C T O B E R k-space Associates, Inc. WHAT BLUE BANDIT PROVIDES IN REAL-TIME: Direct, True GaN Film Temperature During InGaN MQW Growth Direct, Auto- Calibrated Wafer Carrier and Wafer Pocket Temperature Film Thickness and Surface Roughness During InGaN MQW Growth Optical triggering of wafer carrier rotation for plugn-play installation Multi-wafer and Multi-ring Capabilities NEW! - Direct interface to Veeco Nexus control software via Axiom interface NEW! - Full platen scanning capability for 2D Mapping In-Situ Metrology for Veeco k465i GaN MOCVD Introduction For over 10 years, ksa BandiT TM has proven itself to be an invaluable tool for non-contact, non-invasive, realtime, absolute wafer temperature monitoring of semiconductor materials used in today s optoelectronic and electronic devices. Now we have tailored this technology specifically for GaN HBLED deposition monitoring, offering the ksa Blue BandiT in-situ metrology tool. Blue BandiT provides critical wafer and film temperature information that standard NIR/ECP pyrometers cannot measure. This is due to the substrate (e.g. sapphire) and growing film (e.g. GaN, InGaN, AlGaN) being transparent in the infrared regime, where standard pyrometers/ecp s detect radiation. ksa Blue BandiT optics head installed on For pyrometers attempting to collect Veeco k465i MOCVD reactor for GaN HBLED radiation in the absorbing region of in-situ metrology these materials (<450nm), they are starved for signal due to low emission at such short wavelengths. The ksa Blue BandiT tool offers TWO temperature measurements: 1) Direct GaN film temperature via band-edge thermometry (BET), and 2) Pocket/carrier temperature via blackbody radiation analysis of the NIR radiation signal. The BET technique yields absolute film temperature measurement during the crucial InGaN/GaN MQW growth, with resolution of +/- 0.5C and unparalleled run-to-run and tool-to-tool reproducibility. ksa Blue BandiT has been validated for use on the popular Veeco k465i MOCVD reactor platform (including the MaxBright TM series). Blue BandiT on the k465i provides real-time monitoring of GaN/InGaN film temperature, wafer pocket temperature, film thickness, and surface roughness. High speed triggering electronics and laser supplied with Blue BandiT handle the fast rotation speeds of the 465i reactor ( rpm) by synchronizing directly to the carrier rotation, both for symmetric and asymmetric carriers. In addition, a linear scanning stage has been implemented to provide full scanning capability across the slit viewport of the k465i, yielding full carrier/wafer mapping with high spatial resolution. In short, ksa Blue BandiT provides a turn-key in-situ metrology solution with unparalleled control of the crucial InGaN/GaN MQW layers, resulting in better PL uniformity and increased yield for Veeco k465i and Maxbright MOCVD reactors.

2 Laser Triggering for Synchronization Most high speed MOCVD reactors use a spindle drive mechanism which is in contact with the wafer carrier and drives the rotation speed upwards of 1000 rpm or more. This spindle and wafer carrier system is typically a friction fit and not mechanically coupled, which leads to unpredictable carrier slip during rotation. This slip makes wafer-sorted in-situ optical metrology a challenge. To solve this issue, k-space developed a high speed laser and photo detector optic, coupled with a microprocessor and wafer/web identification algorithms (patent pending), to synchronize to the carrier rotation at any rotation speed, and regardless of carrier slip. Using this new setup, an internal trigger is generated via real-time analysis of the web widths as seen by the laser reflectance, and this trigger is sent to the Blue BandiT spectrometers for triggered data acquisition. In this manner, a hard spindle trigger is not needed, and carrier slip is no longer an issue. This new technique has been validated over many full device runs on both 6 x 6 and 14 x 4 symmetric and asymmetric carriers. With this implementation, Blue BandiT is now stand-alone as it does not require any trigger or other electrical connection to the k465i. Laser reflectivity changes between substrate and web (in between wafers) is used to identify wafer positions and synchronize with rotation speed for wafer-specific real-time metrology. Trace below shows typical laser reflectance signal generated by Blue BandiT during high-speed rotation. Direct GaN Film Temperature Capability: Control Of InGaN MQW Temperature for Ultimate LED Emission Wavelength Control ksa Bandit's patented, band-edge based temperature measurement technology relies on the shift in band gap energy with change in material temperature. Blue BandiT uses a high-resolution solid-state spectrometer to measure the optical absorption edge of the semiconductor in real time. The measured absorption edge is used to determine the absolute film temperature via a GaN calibration file, which maps band edge to temperature. The calibration file is generated using calibrated vacuum heating chambers at k-space to ensure the highest possible temperature accuracy. As a result, direct, accurate, and repeatable measurement of the GaN film temperature is guaranteed with ksa Blue BandiT, and unmatched by any other optical temperature monitoring technique. Temperature resolution during MQW growth is +/- 0.5C or better. Because BandiT s technology is insensitive to changing viewport transmission, stray heater radiation, and sample wobble, Blue BandiT is the most accurate and repeatable optical method available for measuring true GaN temperature during InGaN MQW growth. The ability to directly measure and control the actual GaN temperature during InGaN MQW growth becomes critical to control the emission wavelength of the LED. The amount of Indium incorporation within the quantum wells determines the overall LED emission wavelength and is very sensitive to temperature. For every 1 C change in temperature, a corresponding 1.3 nm shift in LED PL emission is expected. In order to control the LED device yield to within a typical 2 nm bin size, temperature control of better than 1 C must be obtained during the InGaN MQW growth. ksa Blue BandiT provides this level of measurement resolution, accuracy, and repeatability across all MQW growth temperature ranges. In- S i t u M e t r o l o g y f o r V e e c o k i G a N M O C V D

3 When growing GaN films on bare sapphire substrates, ksa BandiT can determine the material band edge with as little as 500 Å of material. However, since the GaN layer is thin, the optical absorption characteristics of the GaN are still changing and need to be accounted for to properly determine the actual band edge and corresponding temperature. ksa BandiT uses a patentpending approach to compensate for the dynamic growth of GaN on sapphire, whereby the measured band edge of the GaN film is adjusted based upon the film s thickness, which is also measured by Blue BandiT in real time. With this new approach, repeatability of the band-edge measurements can be maintained to within +/- 0.5 C after the initial GaN buffer layer is complete. This level of repeatability becomes extremely important during the growth of layers which are critical to overall device performance and yield, such as during the InGaN MQW step during HBLED layer growth. This novel band-edge temperature measurement of the GaN film provides a means for accurate temperature measurement during the critical InGaN MQW growth steps. Representative ksa Blue BandiT data on a Veeco k465i production MOCVD reactor is shown at right. A customer-supplied GaN template was sent to k-space for vacuum chamber calibrations (temperature versus band-edge wavelength) to ensure accuracy, and the real-time thickness compensation routines were implemented. In this case, six 6 wafers were monitored by Blue BandiT to observe the temperature behavior during the entire InGaN MQW growth (upper chart). The system was able to directly measure the temperature on all wafers during the growth with high resolution (+/- 0.5 C) and speed during sample rotation up to 1000 rpm. Temperature during an individual quantum well on 2 separate growth runs is also shown in the bottom two charts. ksa Blue BandiT sheds light on the dynamic temperature fluctuations during this critical layer. BET GaN Film Temperature During InGaN MQW Growth Wafer Center Data (6 wafers) GaN film temperature during entire InGaN MQW growth (above). Monitoring of GaN film temperature during single MQW showing significant temperature drift during single well growth (wafer center temperatures of all 6 wafers). GaN Temperature During InGaN MQW Growth Run #1 GaN Temperature During InGaN MQW Growth Run #2

4 PL Wavelength (nm) PL (nm) at ksa Blue BandiT Measurement Spot Area Control of LED Emission Wavelength with ksa Blue BandiT Ex-Situ LED Photoluminescence λ vs. GaN Band-Edge Temperature During MQW Growth Validation of the direct temperature measurement technique offered by Blue BandiT comes in comparing MQW BET with photoluminescence (PL) data from the as-grown devices. Multiple growth runs were performed over multiple reactors. Typical temperature and PL vs wa- GaN BET Average During InGaN MQW Growth (Deg C) fer plots are shown to the right and below. There is a direct and strong correlation between measured MQW temperature and PL wavelength. An increase in well growth temperature means increased In content in the InGaN well layer, which shifts the PL wavelength to shorter wavelengths. Closed loop control of the well and barrier temperature via Blue BandiiT will result in tighter LED emission wavelength range, and hence increased yields. In addition, since BET technology is a diffuse measurement, any sample curvature or bow near the wafer edges will not impact the measurement viability or accuracy. Note that full wafer area mapping capabilities are also available with ksa Blue BandiT. Band Edge Temperature (Degrees C) MOCVD InGaN MQW Growth Run ksa BandiT Temperature Vs. PL Wafer In- S i t u M e t r o l o g y f o r V e e c o k i G a N M O C V D

5 Wafer Carrier/Pocket Temperature Monitoring ksa Blue BandiT also combines a new, patented blackbody emission fitting technology. The spectral radiation intensity from the pocket is collected via a solid state spectrometer and is fit in real time to Planck s equation to determine temperature. This novel technique provides a direct measurement of the underlying graphite wafer carrier or pocket. Automated in-situ calibration via blackbody radiation curve fitting ensures run-to-run repeatability and unmatched resolution (better than 0.1 C). ksa Blue BandiT band edge and blackbody methods can be used simultaneously for direct temperature monitoring of both the GaN film/ substrate and underlying graphite wafer carrier to help minimize temperature non-uniformities and completely characterize both temperatures during growth. Differences in thermal mass, gas flow influences to surface temperature, and wafer bow can be readily monitored and compensated for to ensure process temperatures used for control lead to accurate uniformity profiles and correct temperatures during each step in the LED growth process. GaN film temperature (BET) and wafer pocket temperature (Blackbody) measured simultaneously. Note differences in absolute temperature, stability, overshoot/undershoot. Wafer Pocket and GaN Film Temperature During Single InGaN Well Wafer Center Data Wafer Pocket & GaN Film Temperature During InGaN MQW Growth Wafer Center Data

6 High Resolution Film Thickness Monitoring By using the same broadband light source and visible range spectrometer, Blue BandiT can determine thin-film thickness and deposition rate utilizing the wavelength-dependent interference fringes present in the GaN/Sapphire or GaN/Silicon spectra. By analysis of extrema positions in the below-gap spectra and knowledge of the temperature-dependent index of refraction dispersion, the thickness of the GaN film can be determined to within 0.5% accuracy for a typical LED structure. Blue BandiT even has high enough resolution to determine the film thickness changes observed during InGaN MQW growth for which each layer is typically less than 5nm. Since this diffuse spectra fitting capability is performed using the full spectrometer wavelength range, it can also be used to fingerprint layer interface quality based upon the magnitude and/or shape of the peak/valley positions from run to run. Total film thickness GaN thickness fitting of interference fringes due to GaN film on Sapphire (upper plot). Change in thickness during InGaN MQW growth (lower plot). Blue BandiT can measure the thickness of each MQW layer. Film Thickness During InGaN MQW Growth Wafer Center Data In- S i t u M e t r o l o g y f o r V e e c o k i G a N M O C V D

7 High Sensitivity Surface Roughness Monitoring By monitoring changes in diffuse reflectivity signal vs. wavelength, ksa BandiT can provide a real-time, qualitative measurement of surface roughness. The ksa BandiT light source signal can be monitored across a spectral region where the semiconductor should be absorbing (i.e nm for GaN at 750 C), and thus limited signal should enter the detector in the diffuse reflection geometry used with Blue BandiT. Signal increases/decreases in this above-gap region (i.e. to the left of the material band edge), is directly related to surface roughness changes. This measurement can also be made quantitative via sample-specific measurements of true roughness (i.e. AFM) and included software mapping functions to map diffuse reflectivity values to absolute roughness. Since shorter wavelengths are used for this technique, the signal changes are very sensitive to surface morphology. As such, even roughness changes during the InGaN MQW layers can be monitored and tailored to optimize the LED performance (see plots below). Roughness ( nm) Rougher Roughness Changes During InGaN MQW Growth Wafer Center Data

8 Multi-Wafer Software and OEM Growth Control Interface The ksa Blue BandiT software controls and monitors the light source, spectrometers, and all data I/O. Real-time display of temperature, thickness, surface roughness, and growth rate as well as processed spectra and curve fitting routines are easily performed. A library of wafer band gap/temperature look-up tables can be selected, and new look-up tables can be added to the library. The Blue BandiT hardware is interfaced to the software via a single USB port and cable, and hence can be easily run using a laptop or existing control computer. The ksa Blue BandiT utilizes GUI-based, easy-to use software which allows graphics export to common file formats (.tif,.bmp,.wmf), as well as data export to Excel spreadsheets and standard ASCII text files. A newly developed TCP/IP module is now available for full integration of single, multiple wafer, or full 2D mapping data acquired by Blue BandiT. This integration module can be used to directly communicate with the Veeco Nexus growth control software used on the k465i platforms. By utilizing the Blue BandiT monitoring system along with the laser-based reflectivity, full platen/susceptor temperature, thickness, and surface roughness analysis of all wafers in real-time is now possible during each step of the GaN MOCVD growth. A special acquisition mode allows for user-selectable marker positions to be placed on a visual wafer/platen reflectivity trace showing each wafer profile. These marker positions (either single point, or average area) are used to define up to 256 measurement positions during rotation. Shown below is a Blue BandiT screenshot of the software during InGaN MQW growth showing the following: 1. GaN Film Temperature Analysis spectrum and 6 individual wafer positions being tracked in real-time 2. Blackbody Temperature Analysis spectrum and 6 individual wafers being tracked in real-time 3. Film Thickness Analysis spectrum and 6 individual wafer positions being tracked in real-time In- S i t u M e t r o l o g y f o r V e e c o k i G a N M O C V D

9 Scanning Hardware for On-Tool 2D Wafer Mapping The Veeco 465i MOCVD system incorporates a full slit style viewport which covers the full wafer carrier radius. By using the same Blue BandiT optics hardware and rotational triggering electronics mated to a linear scanning drive, a full 2D map of any parameter can be obtained during growth. The system is the only monitoring technique that can provide real-time 2-dimensional temperature (both GaN film and underlying wafer pocket), thickness, or surface roughness information of all wafers during wafer carrier rotation and growth. Thermal uniformity profiles can now be monitored and adjusted via typical multiple filament heating zones used on the k465i MOCVD systems. Film thickness uniformity and surface roughness profiles can also be obtained before any wafers ksa BandiT k465i hardware with linear scanning mount (Top) and 2D have even left the growth chamber. profiles (bottom) for all wafers, even during InGaN MQW growth. GaN Film Temperature Wafer Pocket Temperature Total GaN Film Thickness Surface Roughness

10 Substrate ksa Blue BandiT Performance Specifications ksa Technology Used Temperature Range ( C) Accuracy ( C) Repeatability ( C) GaN/Sapphire Template (>2um) Temperature GaN/Sapphire Template or Freestanding GaN (>10um) Temperature Graphite Wafer Carrier or Pocket Temperature Band Edge Thermometry Band Edge Thermometry Blackbody Curve Fitting ± 2 ± ± 2 ± ± 2 ±0.5 Film Thickness Accuracy (>2um GaN) Surface Roughness Change (% relative change) +/- 1nm 0.1% ksa Blue BandiT for Veeco k465i GaN MOCVD Summary Leveraging over 20 years of in-situ monitoring technology and expertise, k-space has successfully integrated and can now offer its established real-time ksa BandiT product technology for Veeco s k465i MOCVD reactor line. The newly developed ksa Blue BandiT in-situ metrology tool can provide the following key GaN MOCVD growth parameters: 1) direct GaN film temperature during InGaN MQW growth; 2) wafer carrier and wafer pocket temperature; 3) high resolution surface roughness; 4) total film thickness and MQW thickness. In addition to providing individual wafer measurements on any wafer and wafer carrier configuration, linear scanning harware now allows for full 2D wafer profile maps to obtain important yield information even before the wafers have exited the MOCVD reactor. k-space Associates, Inc. Dexter, MI USA Phone: Fax: k-space Associates, Inc., is a leading supplier to the semiconductor, surface science, and thin-film technology industries. Since 1992, we ve delivered the most advanced thin-film characterization tools and software, thanks to close collaboration with our worldwide customer base. We realize the best products are developed with our customers input, so we re good listeners. For your real-time surface analysis, curvature/stress, temperature, deposition rate, or custom project, we look forward to helping you with your thin-film characterization needs. Rev7 10/10/2012