Lehrstuhl Werkstoffe der Elektrotechnik Sapphire Crystal Growth Matthias Bickermann Vortrag auf der WET-Klausurtagung in Silberbach/Selb, 14. 16. Februar 2008 Lehrstuhl Werkstoffe der Elektrotechnik (WW6), Universität Erlangen-Nürnberg, Martensstr. 7, 91058 Erlangen, Germany
Lehrstuhl Werkstoffe der Elektrotechnik Sapphire Crystal Growth Outline: 1. Introduction 3. Verneuil technique 4. Czochralski technique 2. Applications 5. Kyropoulos technique 6. Shaped Growth 8. Outlook 7. Gradient Freeze / HEM
M. Bickermann: Sapphire Crystal Growth 1. Introduction Sapphire is used here for single crystals of alumina. alumina: -Al O 2 3 corundum: the mineral and the crystal structure (A B, trigonal 3m) 2 3 Single crystals: leukosapphire: transparent sapphire: blue ruby: red padparadscha: pink-orange fancy color sapphire [Wikipedia]
Products and Applications of Artificial Sapphire: (1) Mechanical Parts Sapphire is strong, rigid, inert, wear-resistant, corrosion-free, heat-cabable, transparent,... Applications: Glasses e.g. for wrist watches Biomaterials Medical applications Protections Wear-resistant windows Lamp tubes Semiconductor handling tools M. Bickermann: Sapphire Crystal Growth 2. Applications Sapphire can be grown in arbitrary shapes! [Kyocera, Saint Gobain]
Products and Applications of Artificial Sapphire: (1) Mechanical Parts Sapphire is strong, rigid, inert, wear-resistant, corrosion-free, heat-cabable, transparent,... Applications: Glasses e.g. for wrist watches Biomaterials Medical applications Protections Wear-resistant windows Lamp tubes Semiconductor handling tools M. Bickermann: Sapphire Crystal Growth 2. Applications [Kyocera] Sapphire can be grown in arbitrary shapes!
Products and Applications of Artificial Sapphire: (2) Optical Parts Excellent optical transmission from mid-uv to mid-ir M. Bickermann: Sapphire Crystal Growth 2. Applications 100 80 60 Applications: Optical equipment (blanks, lenses, rods) Laser rods (doped) LCD projector windows (coated) 40 20 0.1.2.3.4.5.7 1.0 2.0 3.0 5.0 7.0 wavelength [µm] [Kyocera] Sapphire can be grown with high structural perfection!
Products and Applications of Artificial Sapphire: (2) Optical Parts Excellent optical transmission from mid-uv to mid-ir M. Bickermann: Sapphire Crystal Growth 2. Applications Applications: Optical equipment (blanks, lenses, rods) Laser rods (ruby, TiSa) LCD projector windows (coated) [Crystal Systems] [Kyocera] Sapphire can be grown with high structural perfection!
Products and Applications of Artificial Sapphire: (3) Substrates M. Bickermann: Sapphire Crystal Growth 2. Applications a-axis sapphire was used in the 70s for silicon-on-sapphire (SOI/SOS) c-axis sapphire is now widely used for III-nitride epitaxial growth (white LEDs, blue lasers,...) Status: orientation: a-axis is easier to grow size: 8-inch (4-inch perfect quality) defects: 100 dislocations/cm², no bubbles [Kyocera] no inclusions, few low-angle grain boundaries wafering/polish is the costly step cost-competition: strong
The Verneuil (Flame Fusion) Technique. A. L. Verneuil (1890): First synthetic ruby ( Ø 6mm, L=25mm) Industrial production since 1900 250t of crystals produced per year ( Ø up to 30mm) yielding ~3 t of gems + easy setup + high growth rate difficult growth control 108dislocations/cm² gas bubble inclusions cracking due to T-gradients M. Bickermann: Sapphire Crystal Growth 3. Verneuil [Wikipedia]
M. Bickermann: Sapphire Crystal Growth 3. Verneuil The Verneuil (Flame Fusion) Technique. A. L. Verneuil (1890): First synthetic ruby (Ø 6mm, L=25mm) Grain selection: Industrial production since 1900 250t of crystals produced per year (Ø up to 30mm) yielding ~3 t of gems + easy setup + high growth rate difficult growth control 108 dislocations/cm² gas bubble inclusions cracking due to T-gradients [Scheel]
The Czochralski (Crystal Pulling) Technique. First ruby laser (1960): Demand for high quality crystals Czochralski Crystals at Union Carbide Today: Ø 200mm, L=600mm crystals by Saint Gobain Crystals and Honeywell a-/m-axis growth (reduced pressure, 2% oxygen) Cr-, Ti-doping for laser rods + mature technique 2 + 10 dislocations/cm² M. Bickermann: Sapphire Crystal Growth 4. Czochralski low growth rate to suppress bubbles expensive iridium crucible low yield for c-axis materials [Harris]
M. Bickermann: Sapphire Crystal Growth 4. Czochralski The Czochralski (Crystal Pulling) Technique. First ruby laser (1960): Demand for high quality crystals Czochralski Crystals at Union Carbide Today: Ø 200mm, L=600mm crystals by Saint Gobain Crystals and Honeywell a-/m-axis growth (reduced pressure, 2% oxygen) Cr-, Ti-doping for laser rods + mature technique 2 + 10 dislocations/cm² low growth rate to suppress bubbles expensive iridium crucible low yield for c-axis materials [Honeywell]
The Kyropoulos Technique. Idea of Kyropoulos (1926) M. Bickermann: Sapphire Crystal Growth 5. Kyropoulos Sapphire growth developed at the Vavilov State Optical Institute (GOI), St. Petersburg from 1960 Crystal grows into the melt Seed is actively cooled and slowly pulled out [Scheel] [Monocrystal]
The Kyropoulos Technique. M. Bickermann: Sapphire Crystal Growth 5. Kyropoulos Russian plant Analog at Stavropol (1972) produces Ø 80 mm crystals Today, Monocrystal PLC: Ø 250mm boules, 4 c-axis substrates, 8 a- and m-plane blanks 2 + no bubbles (growth at 10 mbar) 3 + 10 dislocations/cm² low growth rate difficult thermal management low yield for c-axis materials [Monocrystal]
M. Bickermann: Sapphire Crystal Growth 6. Stepanov Shaped Crystal Growth: Stepanov and Related Techniques. Stepanov method developed in Russia in the 60s (Monocrystal PLC) EFG method by LaBelle (Saphikon, now Kyocera) [Harris] As-grown crystals of ANY shape! [Kyocera]
M. Bickermann: Sapphire Crystal Growth 6. Stepanov Shaped Crystal Growth: Stepanov and Related Techniques. Stepanov method developed in Russia in the 60s EFG method by LaBelle (Saphikon/Kyocera, Saint Gobain Crystals) Today: Ribbons of up to 300 mm x2mx12mm(!) Windows of up to 1000 mm x 500 mm. Substrates of up to 8-inch diameter. Rods, Tubes, Domes, even variable compositions and changing geometries are produceable. + mature technique + easy and cheap set-up + As-grown crystals of ANY shape! bubbles (molybdenum crucible and shaper) diameter limitation for rods and tubes 5 10 dislocations/cm², inclusions
M. Bickermann: Sapphire Crystal Growth 6. Stepanov Shaped Crystal Growth: Stepanov and Related Techniques. NCS: Non-Capillary Shaping Technique for growth of bigger-diameter rods (Kurlov 1997) (No commercial application) [Kurlov] The scheme of monolithic crystal growth by the NCS method: (a) seeding, (b) growing a hollow closed shape, (c) growing a monolithic crystal. (1) crucible, (2) melt, (3) die, (4) capillary channel, (5) seed, (6) hollow closed shape of the crystal, (7) monolithic crystal.
M. Bickermann: Sapphire Crystal Growth 7. HEM The Heat Exchange Method (Schmid-Viechnicki Technique). Developed 1967 by Schmid (US Army) (Ø 76 mm blanks) Crystal Systems (founded 1971) now produces Ø 380 mm, L=380 mm bulk Seed at crucible bottom, actively cooled by He gas (heat exchange) Melt kept under constant temperature Crystal spreads until the whole melt is solidified: Crucible-contact method [Crystal Systems]
M. Bickermann: Sapphire Crystal Growth 7. HEM The Heat Exchanger Method (Schmid-Viechnicki Technique). [Khattak & Schmid] + biggest bulk sapphire crystals difficult thermal management bubbles (molybdenum crucible) radial low-angle grain boundaries 4 10 dislocations/cm² low yield for c-axis substrates
M. Bickermann: Sapphire Crystal Growth 7. HEM The Heat Exchanger Method (Schmid-Viechnicki Technique). Best crystals are grown in a-/m-axis direction Coring of c-axis rods (up to 4-inch diameter) out of cross-sections of the boule [Khattak & Schmid] Variations: Thermal Gradient Techique (TGT) no seed cooling, complicated 3D-heater management
The Summary: M. Bickermann: Sapphire Crystal Growth 8. Conclusions Every Technique Found its Commercial Application! Cheap Production (Windows, Gems) Verneuil (Gemstones) Largest Size (Windows, Rods) EFG (Windows) Perfect Quality (Optics, Substrates) Czochralski (doped) EFG (Windows, shaped parts) HEM (Rods, Blanks) Kyropoulos (pure)
The Summary: M. Bickermann: Sapphire Crystal Growth 8. Conclusions Every Technique Found its Commercial Application! Cheap Production (Windows, Gems) Active in the III-Nitride Substrate market: BAIKOVSKY + others...