Multi-wafer System Research Articles

Homoepitaxial Chemical Vapor Deposition of up to 150 μm Thick 4H-SiC Epilayers in a 10×100 mm Batch Reactor

In this paper we present results on the growth of low-doped thick epitaxial layers on 4° off-oriented 4H-SiC using a warm-wall multi-wafer CVD system (Aixtron VP2800WW). Statistical data on doping and thickness of 25 μm to 40 μm layer growth show results similar to standard epilayer growth (5-15 μm). Improvements in thickness and doping uniformity as well as the reduction of epitaxial defects has boosted the quality of 25 μm to 40 μm thick epilayers. Laser light scattering measurements resulted in projected device yields with median values of 83% and 96% for 5×5 mm2 and 2×2 mm2 die size, respectively. This corresponds to a low epitaxial defect density of < 0.75 cm-2 in 25-40 μm thick epilayers. This paper also presents results of 60 μm to 150 μm thick epitaxial layer growth. Excellent results for doping, thickness and carrier lifetime were achieved. As an example results of a fully loaded 10×100mm run with 150 μm thick epilayers are presented. Wafer-to-wafer doping and thickness values of 3.7 % and 3.4% for sigma/mean were accomplished, respectively. Typical average lifetime values of 5 μs to 6 μs were measured on the 150 μm thick layers without post-epi treatments.

Growth of free-standing wurtzite AlGaN by MBE using a highly efficient RF plasma source

Ultraviolet light emitting diodes (UV LEDs) are now being developed for various potential applications including water purification, surface decontamination, optical sensing, and solid-state lighting. The basis for this development is the successful production of AlxGa1−xN UV LEDs grown by either metal-organic vapor phase epitaxy (MOVPE) or molecular beam epitaxy (MBE). Initial studies used mainly sapphire as the substrate, but this result in a high density of defects in the epitaxial films and now bulk GaN or AlN substrates are being used to reduce this to acceptable values. However, the lattice parameters of GaN and AlN are significantly different, so any AlGaN alloy grown on either substrate will still be strained. If, however, AlGaN substrates were available, this problem could be avoided and an overall lattice match achieved. At present, the existing bulk GaN and AlN substrates are produced by MOVPE and physical vapor transport, but thick free-standing films of AlGaN are difficult to produce by either method. The authors have used plasma-assisted MBE to grow free-standing AlxGa1−xN up to 100 μm in thickness using both an HD25 source from Oxford Applied Research and a novel high efficiency source from Riber to provide active nitrogen. Films were grown on 2- and 3-in. diameter sapphire and GaAs (111)B substrates with growth rates ranging from 0.2 to 3 μm/h and with AlN contents of 0% and ∼20%. Secondary ion mass spectrometer studies show uniform incorporation of Al, Ga, and N throughout the films, and strong room temperature photoluminescence is observed in all cases. For films grown on GaAs, the authors obtained free-standing AlGaN substrates for subsequent growth by MOVPE or MBE by removing the GaAs using a standard chemical etchant. The use of high growth rates makes this a potentially viable commercial process since AlxGa1−xN free-standing films can be grown in a single day and potentially this method could be extended to a multiwafer system with a suitable plasma source.

Double pulse doped InGaAs/AlGaAs/GaAs pseudomorphic high-electron-mobility transistor heterostructures

Double pulse doped (δ-doped) InGaAs/AlGaAs/GaAs pseudomorphic high-electron-mobility transistor (HEMT) heterostructures were grown by molecular-beam epitaxy using a multiwafer technological system. The room-temperature electron mobility was determined by the Hall method as 6550 and 6000 cm2/(V s) at sheet electron densities of 3.00 × 1012 and 3.36 × 1012 cm−2, respectively. HEMT heterostructures fabricated in a single process feature high uniformity of structural and electrical characteristics over the entire area of wafers 76.2 mm in diameter and high reproducibility of characteristics from process to process.

High-Performance Multi-Wafer SiC Epitaxy – First Results of Using a 10x100mm Reactor

In this paper, we present first results of epitaxial layer deposition using a novel warm-wall CVD multi-wafer system AIX 2800G4 WW from AIXTRON with a capability of processing 10x100mm wafers per run. Intra-wafer and wafer-to-wafer homogeneities of doping and thickness for full-loaded 10x100mm runs will be shown and compared to results of the 6x100mm setup of our hot-wall reactor VP2000HW by AIXTRON used for device production since 2001.

Advances in Multi- and Single-Wafer SiC Epitaxy for the Production and Development of Power Diodes

In this paper, we present results of epitaxial layer deposition for production needs using our hot-wall CVD multi-wafer system VP2000HW from Epigress with a capability of processing 7×3” or 6×100mm wafers per run in a new 100mm setup. Intra-wafer and wafer-to-wafer homogeneities of doping and thickness for full-loaded 6×100mm and 7×3” runs will be shown. Results on Schottky Barrier Diodes (SBD) processed in the multi-wafer system will be given. Furthermore, we show results for n- and p-type SiC homoepitaxial growth on 3”, 4° off-oriented substrates using a single-wafer hot-wall reactor VP508GFR from Epigress for the development of PiN-diodes with blocking voltages above 6.5 kV. Characteristics of n- and p-type epilayers and doping memory effects are discussed. 6.5 kV PiN-diodes were fabricated and electrically characterized. Results on reverse blocking behaviour, forward characteristics and drift stability will be presented.

Suitability of 4H-SiC Homoepitaxy for the Production and Development of Power Devices

ABSTRACTIn this paper, we present results of epitaxial layer deposition for production needs using our hot-wall CVD multi-wafer system VP2000HW from Epigress with a capability of processing 6×100mm wafers per run. Intra-wafer and wafer-to-wafer homogeneities of doping and thickness for full-loaded 6×100mm runs will be shown and compared to results of the former 7×3″ setup. The characteristic of the run-to-run reproducibility for the 6×100mm setup will be discussed. To demonstrate the suitability of the reactor for device production results on Schottky Barrier Diodes (SBD) processed in the multi-wafer system will be given. Furthermore, we show results for n- and p-type SiC homoepitaxial growth on 3″, 4° off-oriented substrates using a single-wafer hot-wall reactor VP508GFR from Epigress for the development of PiN-diodes with blocking voltages above 6.5 kV. Characteristics of n- and p-type epilayers and doping memory effects are discussed. 6.5 kV PiN-diodes were fabricated and electrically characterized. Results on reverse blocking behaviour, forward characteristics and drift stability will be presented.

Challenges in Large-Area Multi-Wafer SiC Epitaxy for Production Needs

The rapid market development for SiC-devices during the last years can be attributed particularly to the success in supplying high-quality SiC wafers and corresponding epitaxial layers. The device quality could be enhanced and the costs were reduced by enlarging the wafer size as well as by a significant progress in epitaxial growth of active layers by using multi-wafer CVD systems. In this paper we want to give an overview of CVD multi-wafer systems used for SiC growth in the past and today. We present recent results of SiC homoepitaxial growth using our multi-wafer hot-wall CVD system. This equipment exhibits a capacity of 5×3” wafers per run and can be upgraded to a 7×3” or 5×4” setup. By optimizing the process conditions epitaxial layers with excellent crystal quality, purity and homogeneity of doping and thickness have been grown. Issues like reproducibility, drift of parameters and system stability over several runs will be discussed.

Advances in 4H-SiC Homoepitaxy for Production and Development of Power Devices

AbstractIn this paper we present results of epitaxial layer deposition for production needs using our hot-wall CVD multi-wafer system. This equipment exhibits a capacity of 7x3” wafers per run and can be upgraded to a 6x4” setup. Characteristics of epilayers and reproducibility of the proc-esses are reported. Furthermore, we show recent results of p-type SiC homoepitaxial growth on 3” 4° off-oriented substrates using a single-wafer hot-wall CVD. The dependence of layer prop-erties on growth parameters, doping and thickness uniformity as well as doping memory effects are discussed. For the characterization of epitaxially grown pn-junctions first research grade pin-diodes were fabricated. The p-type emitters were either deposited in the same growth run to-gether with the n-type buffer and drift layers (continuous growth) or the n- and p-layers were grown in two different growth runs (separate growth).

Characteristics of back-illuminated visible–blind UV photodetector based on Al xGa 1−xN p–i–n photodiodes

In this work, we reported the growth, fabrication and characterization of an Al x Ga 1− x N heteroepitaxial back-illuminated visible–blind UV photodetector designed for flip–chip mounting. This device was grown on one side of a polished sapphire substrate using a low-temperature AlN buffer layer created by six-pocket multi-wafer system metalorganic chemical vapor deposition (MOCVD) with a vertical reactor. In order to obtain the wavelength of the visible–blind region, the Al x Ga 1− x N layer was grown under various conditions of growth time and gas flow rate, after optimizing the AlN buffer layer. This device consisted of a 1.3 μm thick Al 0.15Ga 0.85N “window layer”, a 0.16 μm thick Al 0.08Ga 0.92N i-layer, a 0.46 μm thick Al 0.08Ga 0.92N p-layer, a 0.1 μm thick GaN p-layer, followed by a 30 nm GaN:Mg p +-contact layer. All of the device processing was completed using standard semiconductor processing techniques that included photolithography, metallization and etching. In this device, the zero-bias peak responsivity was found around 0.052 A/W at 340 nm, corresponding to an external quantum efficiency of 19%. The rise and fall time of the photoresponse was 20.8 ns. Moreover, this device exhibits a low dark current density of 17 pA/cm 2 at zero-bias.

Multiwafer reactor boosts antimonide prospects

For some compound materials the production of crystalline epilayers has become routine. In this activity synergy is everything. Now the processes developed for the growth of arsenides, phosphides and nitrides, etc, are coming to the antimonides. Aixtron AG and the Fraunhofer Institute for Solar Systems ISE have developed what they see as the world's first practical multiwafer system for the antimonides.

Epitaxial Growth of SiC in a Vertical Multi-Wafer CVD System: Already Suited as Production Process?

ABSTRACTResults about a new CVD system suited for epitaxial growth on six 2 inch SiC-wafers at a time are presented. Excellent gas flow stability is achieved for this new reactor type as shown by in- situ observations of the gas flow dynamics in the reactor chamber. These experimental results agree favorably with numerical process simulation results.The epitaxial layers grown in the multi-wafer system so far show a by an order of magnitude higher background impurity level (≤1015 cm−3) as reported previously for layers grown in single-wafer systems by the authors and other groups (≤ 1014 cm−3). On the other hand, the doping homogeneity achieved until today is very encouraging. The variation on a 2 inch wafer is less than ± 20% at about 1*1016 cm−3. The wafer to wafer variation of the average doping value both within a run and from run to run is within 15 %. The reproducibility and uniformity of the layer thickness is even better (total thickness variation ≤5% on a 2 inch wafer). The surface of the epitaxial layers is very smooth with a typical growth step height of 0.5 nm (4H, 8° off orientation). First measurements on Schottky diodes build on these layers show low leakage current values indicating low point defect density in the epitaxial layers.

MOVPE growth of high quality III-nitride material for light emitting device applications in a multiwafer system

Processes for mass production of GaN and its related alloys, InGaN and AlGaN, have been optimized to achieve high device yield and low cost of ownership. Here we present some of the latest results obtained from AIX 2000HT Planetary Reactors® in a configuration of 7×2″ which provides unique uniformity capabilities due to the twofold rotation of the substrates. GaN single layers with background electron concentrations below 5×1016cm−3 and intended doping levels up to 1018cm−3 p-type and 1020cm−3 n-type with state of the art homogeneities have been achieved. Thickness homogeneities have been shown to be better than 1% standard deviation on full 2″ wafers, while composition uniformity of ternary material is determined by room temperature photoluminescence mappings. Low-temperature photoluminescence and reflectance spectra of single-layer GaN revealed free-exciton transitions

Multiwafer molecular beam epitaxy for high volume production of GaAs/AlGaAs heterojunction bipolar transistor wafers

Circuits incorporating GaAs/AlGaAs heterojunction bipolar transistors (HBTs) are being increasingly used in commercial applications with volume requirements that can only be met using multiwafer reactors. HBT wafers grown in single and multiwafer molecular beam epitaxy (MBE) reactors are found to be very similar in terms of both material characteristics and resultant device performance. Postgrowth defect levels are reduced by an order of magnitude with the multiwafer system compared to single wafer systems and are similar to those obtained on commercially purchased metal organic chemical vapor deposition wafers. Multiwafer MBE systems are thus shown to be a viable means for the high volume production of HBT wafers.

Lateral coupling of InP/GaInAsP/InP structures by selective area MOMBE

Lateral couplings of InP/GaInAsP/InP structures selectively grown by metalorganic molecular beam epitaxy (MOMBE) are presented. The heterostructures were grown by either using the hydrides AsH3 and PH3 or tertiarybutylphosphine and tertiarybutylarsine as group V precursors in a prototype multiwafer (MOMBE) system. The base heterostructures of the first epitaxy were patterned with SiO 2 mask stripes and trenches were reactive-ion etched. Heterostructures were selectively filled in by a second growth run forming lateral heterojunctions of different quaternary materials. The structures exhibit a bright photoluminescence and a sharp transition at the boundary of the locally grown material indicating a high crystal quality up to the lateral junction with only a minor change in the PL wavelength ( < 2 nm). These optimized lateral couplings were applied to laser/waveguide butt-couplings. Optical coupling losses were determined by means of reactive-ion etched waveguides across cascades of coupled GaInAsP layers with an emission wavelength of λ G 1050 nm. Values as low as 0.12 dB/coupling were determined in cut-back measurements.

Recent progress in multi-wafer CBE systems

Abstract We describe the recent progress of multi-wafer CBE systems demonstrating their potential capability of producing III–V semiconductor device structures with excellent uniformity and state-of-the-art performance. Up to three 4 inch wafers can be grown simultaneously with excellent uniformity and extremely small wafer-to-wafer variation (x in AlxGa1−x As: 0.2136 ± 0.0014). A specifically designed high-conductance metalorganic gas cell with a tilted aperture without any diffuser gives a high uniformity together with a fast switching at the heterointerfaces. An intrinsic difficulty for obtaining good compositional uniformity of ternary alloys containing indium is overcome by improvement in the design of an In-free substrate holder showing a uniform temperature profile within ± 0.9°C across a whole wafer. To extend the capability of CBE, an in situ cleaning method which combines hydrogen radical cleaning and As-free cleaning was investigated. The n-type GaAs epilayers showed a reduced depletion of electrons at the air-exposed regrown interface. From SIMS analysis, hydrogen radical and As-free cleaning show stronger effects on gettering carbon, and oxygen, respectively. Some C contamination during the 2nd As-free cleaning procedure is expected to be eliminated by decreasing the treatment temperature from the separately optimized one. The successful cleaning of InP substrates using trisdimethylaminophosphorous (TDMAP) would also extend the capability of CBE for the reproducible growth of large area (> 3 × 3 inch) InP-based materials.

A Synergistic Approach to Environmental Concerns in Large Scale MOCVD Processes

AbstractProcesses used in the production of epitaxial III-V semiconducting materials employ a wide variety of materials that are environmentally hazardous. As production volumes increase, the need to manage these materials becomes a serious concern. As the leading supplier of production scale single and multi-wafer MOCVD systems, we have taken the approach of minimizing the generation of waste by designing our reactor for high reactant utilization efficiency, and then trapping the remainder so that the exhaust stream is clean. We have paid particular attention to both operational efficiency and operator safety. The traps may be simply removed and replaced, with cleaning being performed off line. The trapped materials are reduced to an inert state for subsequent commercial disposal; this is particularly important for phosphorus, which can be highly flammable if improperly handled. The reactor chamber deposits occur below the wafer level and typically are cleaned only after several hundred deposition cycles. These factors contribute to a quick cycle time and high uptime, both of which increase throughput. These issues become more important as the reactor size is increased and when multiple shifts are utilized. These points are exemplified by our operational experience with our new Enterprise series, which holds four 100mm wafers (or seventeen 50mm wafers) per run. We will discuss the progressive trapping of solid As and P compounds and those hydride gases which are not completely decomposed in the reaction chamber. The use of computer modeling to scale the process to larger dimensions and to optimize the deposition conditions will also be discussed.

Large-scale MOVPE production systems

High-performance ICs and OEICs rely on complex epitaxial heterostructures with tight bandgap engineering. Related development and production require homogeneous material, manufacturing of batches of comparable wafers, in-situ multiwafer fabrication, reduced surface contamination and defect density along with proven heterostructure processes for many combinations of III—V materials. The application of substrate rotation always seemed to cause technical problems, such as particle generation, mechanical feed troughs etc., rather than to improve the process from a production point of view. This paper summarizes the breakthrough in III—V multiwafer MOVPE mass production applications using the planetary multiwafer reactor with gas foil rotation (5 × 3″/7 × 2″ or 5 × 4″/8 × 3″) which was originally developed and patented by Philips LEP for growth of GaAs/AlGaAs heterostructures and has been used successfully since then for HEMT production, laser fabrication, and GaInP deposition. In similar Planetary Reactors, GaAs- and InP-based materials for a wide range of optoelectronic applications have been produced. The use of low pressures is not only advantageous for the handling of phosphorus-containing compounds and reduction of overall gas consumption, but also allows to drastically reduce the amount of H 2 required for driving the wafer support. The variation of thickness in these multiwafer systems is reduced to the order of 1–2% for GaAs, AlGaAs, GaInP, InP, GaInAs and GaInAsP (1.55, 1.3, 1.05 μm). Thus, one major advantage in comparison to MBE is that these reactors are capable of handling both GaAs- and InP-based processes with high concentration of phosphorus. Processes for the production of visible lasers (AlGaInP), GaInP HBTs, or complex solar cell structures have also been developed. This finally makes this MOVPE technology by far superior over MBE for production application. The relatively simple realization of a variety of different wafer sizes emphasizes the efforts to create even larger reaction chambers capable for large-area epitaxial growth of different material systems. The use of silicon wafers as substrates for advanced device structures is no longer limited to 2″ or 3″ wafers, also 4″, 6″, and 8″ wafers can be used, and rectangular arrangements for solar cell production are being developed.

Advances in MOVPE, MBE, and CBE

In epitaxial growth technology, both metalorganic vapor phase epitaxy (MOVPE) and molecular beam epitaxy (MBE) have become the dominant techniques after more than two decades of development. On the horizon, it is the emerging of chemical beam epitaxy (CBE) which has been proven to be a very powerful combination of MOVPE and MBE. Very significant progress has been made in multi-wafer system designs for both MBE and MOVPE. Great success in material uniformity has been demonstrated. At present, it is fair to say that MOVPE has dominated the growth and device applications of phosphorus containing compound semiconductors, e.g. AlGaInP and InGaAsP, and MBE has dominated over the AlGaAs, while CBE is demonstrating its unusual capabilities as a combination of both techniques and is gaining very significant momentum. For CBE, very rapid progress has been made in both AlGaAs and InGaAsP systems. State-of-the-art electronic and photonic devices have been fabricated. When future demand for compound semiconductor devices and circuits becomes substantial, without doubt, CBE will be an important player.

Growth of highly uniform, reproducible InGaAs films in a multiwafer rotating disk reactor by MOCVD

Much of the work on InGaAs film growth has been limited to small single wafer systems with little reported information on the wafer-to-wafer and run-to-run repeatability of the films. We report here on the growth of highly uniform films in a multiwafer system with good run-to-run repeatability. The uniformity of the film properties across the susceptor results from the careful design of the reaction chamber using fluid dynamical modeling. The control of the composition during the course of the run and from run-to-run was improved by careful design of the trimethylindium solid source container.

Very uniform epitaxy

A comprehensive evaluation of the T-shaped reactor, in view of its use as a production tool for 1300 nm optoelectronic devices, was carried out. The material obtained was of excellent quality and exhibited a very high degree of uniformity and good reproducibility, despite the difficulties associated with the control of two composition ratios, particularly with the As/P one. The extension to other compositions is obvious. Ternary and quasi-ternary materials ( InGaAs, InGaAlAs ) can be handled with even greater ease, not to speak about binaries and quasi-binaries ( GaAs, GaAlAs ). The system lends itself naturally to extension toward larger wafer sizes. A multi-wafer system based on the same principles can also be implemented ; very recently, such a system was proposed by Frijlink [16].