Growth of high crystal quality gallium oxide (Ga₂O₃) at large production scale throughput is not available in the market due to (a) a ready high-volume supply of large wafers for homoepitaxy, (b) MOCVD tools explicitly configured for large area MOCVD growth of Ga₂O₃ homo- or heteroepitaxy. One of the primary factors is the unavailability of manufacturing scale substrates and growth tools.

Our company “Structured Materials Industries, Inc, (SMI)” has designed, sold, and fielded several Ga₂O₃ MOCVD growth tools as well as adapted several pre-existing (for different materials) tools to grow Ga₂O₃ and operated in-house tools for growth on single (cm² scale, 50mm, 100mm, 150mm, and 200mm) and multiple wafer tools (3×50mm, 19×50mm, and 38×50mm wafer diameters) or multiple 100mm) depositions. These tools have operated using a range of heating systems – induction, radiant filament, and lamps to operate over a range of growth temperatures (~400°C to ~1100°C) using a multiple of binary and alloy growth precursors (O₂, N₂O, H₂O, TEGa, TMGa, TMIn, TMAl, TEAl, GaCl₃), process enhancers such as HCl, and dopants (SiH₄, TEOS, TMSn) and are compatible with a wide range of other elements.

The results of these works have led SMI to refine a series of reactors for research to production applications – spanning single to multiple wafer tools employing a multiple of growth parameters and heater types. In this presentation, we will review our series of reactor designs and how they are best applied – for example few through multiple small or large wafer epitaxy is best produced using advanced patented (US7573004 B1) high temperature oxide compatible designed filaments in rotating disc reactors supporting growth through 900°C whereas very high temperature growth – through 1100°C is best produced using induction heating when such high temperatures are warranted, whereas enclosed filament geometries are best for large single wafer processing. We note that filament heating is sufficient for most applications and can be used to produce uniform temperature heating. Reactor designs, supported by simulations of a variety of parameters, such as gas mixtures, flows, temperatures, pressures, carrier flows, flow rates of precursors, and the gap between showerhead and susceptor, for example, are reviewed along with areas of demonstrated results. Overall, production tool designs are based upon optimized parameters and they are reviewed.

As an ultra-wide bandgap semiconductor(UWBG), β-Ga₂O₃ is a very promising materials for various applications such as UV photodetectors, power rectifiers, gas sensors, MOSFETs, SBDs, and LEDs because β-Ga₂O₃ has a wide bandgap of 4.9eV and a high breakdown voltage of 8MV/cm. Furthermore, since β-Ga₂O₃ is capable of melt growth, it is possible to obtain a higher growth rate and a lower manufacturing cost than other WBG semiconductors such as SiC, GaN, and Diamond.[1,2]

In this study, the quality improvement of Sn-doped β-Ga₂O₃ crystal was systematically investigated with controlling temperature gradient in growth cell of edge-defined film-fed growth (EFG) method. Flat-shaped β-Ga₂O₃crystal ribbons were typically grown by the EFG method. The principal surface and the growth direction were set to be (001) and [010], respectively. To prepare Sn-doped n-type bulk crystals, different amounts of Sn powder were added to Ga₂O₃ source powder. The temperature gradient in growth cell was controlled by changing structure of surrounding refractory materials and using the after-heater(A/H). The doping characteristics and crystal quality of various β-Ga₂O₃ crystal ribbons grown with changing the temperature gradient were systematically analyzed. A phase analysis of β-Ga₂O₃ bulk crystals was performed by Raman analysis, and the quality of the crystals was analyzed by a high-resolution X-ray diffraction (HRXRD). Electrical properties and impurity concentration of unintentionally doped (UID) β-Ga₂O₃ and Sn-doped β-Ga₂O₃ crystals were analyzed using the Hall effect measurement system and the secondary ion mass spectrometry (SIMS), respectively.

High-quality Sn-doped (001) β-Ga₂O₃ crystal with a full width at half maximum (FWHM) of 38 arcsec and an etch pit density (EPD) of 3700/cm² was obtained with optimizing temperature gradient. Proper temperature gradient resulted in the reduction of SnO₂ volatilization during the growth process and the uniform distribution of bluish color throughout the entire ribbon. The carrier concentration of ≥10¹⁸/cm³ was obtained on Hall effect measurement.

Reference

[1] S. Ohira et al., Thin Solid Films 516, 5763-5767 (2008)

[2] Stephan Lany, APL Mater. 6, 046103 (2018)

β-Ga₂O₃ 4.9eV의. It has a wide bandgap and a high breakdown voltage of 8MV/cm, so it is receiving a lot of attention for power device applications. In addition, it has the outstanding advantage of being able to grow a single crystal with a higher growth rate and lower manufacturing cost than other WBG semiconductor materials such as SiC, GaN, and diamond. [1-4] In this study, a β-Ga₂O₃ crystal block with a thickness of 10 mm was grown on an Ir die with a multi-slit structure through an edge-define film-fed growth (EFG) process. The growth direction and main surface of the β-Ga₂O₃ crystal were set to the [010] direction and the (100)/(001) plane, respectively, and the crystal growth rate was set to about 12 mm/h. . The crystalline blocks were annealed in a nitrogen environment to reduce residual stress in the crystals before preparing crystal substrates with different orientations. A chemical mechanical polishing (CMP) process using Hastilite Ditron 3.0 slurry was chosen as the final processing step to create an epi-ready surface of the β-Ga₂O₃ crystal substrate. Raman spectra showed successful growth of β-Ga₂O₃ bulk crystals. Crystal quality was assessed by high-resolution X-ray diffraction (HRXRD). Etch pit density (EPD) and defect types were measured on crystal surfaces etched with H₃PO₄ solution.

Etch pit density (EPD) and defect type were measured on the liquid etched crystal surfaces. A typical Sn-doped Ga 2 O 3 crystal block grown by the EFG method was bluish. The X-ray rocking curve values ​​of the Ga₂O₃ single crystal ribbon depend on the Sn doping concentration and show slightly different values ​​depending on the measurement position in the Ga₂O₃ crystal ribbon, indicating the spatial change of the Ga₂O₃ crystal quality. decision. The crystal quality and surface properties of various β-Ga2O3 crystal substrates with (100), (001), (-201), and (hkl) orientations after CMP process were systematically investigated.

Reference:

[1] JY Tsao 등, Adv. 전자. 엄마. 4, 1600501 (2018)

[2] M. Higashiwaki, GH Jessen, Appl. Physics Rhett. Man 112, 060401 (2018)

[3] Kun Zhang 외, J. Alloys and Compounds,881,160665 (2021)

[4] Shengnan Zhang 외, J. Semicond. 39, 083003 (2018)

Gallium oxide (Ga₂O₃) has been highlighted as an emerging material for power semiconductor applications [1]. Recent achievements in bulk substrates and epitaxy pave a way for demonstrating several kV level power devices. However, various defects in β-Ga₂O₃ such as dislocations, stacking faults, and twin defects have been still issued, requiring further crystal quality with defect analysis.X-ray topography is one of powerful techniques to observe defect distribution in a non-destructive way [2].The etch pit technique destructively visualize the defect distribution of the substrate as it chemically etches down the defect regions with an acid (or base). In this study, we compare the defect characteristics of (100) and (001) β-Ga₂O₃ single crystals grown by edge-defined film-fed growth (EFG).

In experiment, the etch pits of (100) and (001) β-Ga₂O₃ single crystals were formed by wet etching with 85 wt% phosphoric acid (H₃PO₄) solution at 140 °C for 120 min. The profile of etched surfaces was observed using atomic force microscope. In addition, (001)-oriented β-Ga₂O₃ single crystal was analyzed using an X-ray topography (Beamline 09, Synchrotron Radiation Facility SAGA-LS).

Figure 1 shows the AFM images of the etched surface for (100) and (001) surfaces. The etch pit of (100) plane are shallower and narrower compared to (001) plane as the (100) plane is parallel to the dislocation direction and has a cleavage property [3]. The density of the etch pits in the (100) and (001) planes were counted to be ~3.8×10⁵ cm^-2 and ~6.0×10⁴ cm^-2, respectively. Figure 2 shows the XRT image of (001) β-Ga₂O₃ with a diffraction vector, g=605. It was found that the dominant features were dot, line along [010] direction, and curved line contrasts. The line contrasts are mostly associated with b-axis screw dislocations with Burgers vectors (b) parallel to [010], and the dot contrasts are related to edge dislocations with <001> burgers vectors [4]. In addition, many wandering dislocations are observed on the (001) surface, which show curved contrasts. This defect observation might assist to improve the crystal quality of Ga₂O₃ substrates as we perform further in-depth characterization in the future.

References

[1] J. Y. Tsao, et al., Adv. Electron. Mater. 4, 1600501 (2018)

[2] M. Higashiwaki, et al., Appl. Phys. Lett. 100, 013504 (2012).

[3] Kun Zhang, et al., J. Alloys and Compounds, 881,160665 (2021)

[4] Shengnan Zhang, et al., J. Semicond. 39, 083003 (2018)