Papers

AVS1996 Session PS2-TuM: Etching of III-V Materials

Tuesday, October 15, 1996 8:40 AM in Room 201B

Tuesday Morning

Start	Invited?	Item
8:40 AM		PS2-TuM-2 Ultrahigh Vacuum Chemically Assisted Ion Beam Etching System with a Three Grid Ion Source J. Hryniewicz, Y. Chen, S. Hsu, C. Lee, G. Porkolab (University of Maryland, Baltimore County & the Laboratory for Physical Sciences, College Park) A chemically assisted ion beam etching system has been developed which performs high quality, highly anisotropic etching of AlGaAs/GaAs at relatively low ion energies (200 eV). The use of three grid ion optics in a Kaufman ion source allows etching at low energies with reasonable rates without loss of profile verticality. All-UHV etching chamber construction with a high-throughput turbomolecular pump and high vacuum loadlock provide routine high quality etching of AlGaAs without the use of etch ch amber cryo panels or cryo pumps. Low ion energy and a clean vacuum environment permit the use of a single level, non hard baked photoresist mask. Benefits include high pattern resolution and fidelity, low mask erosion rate, good dimensional control, and easy, complete mask stripping as well as reduced substrate damage.
9:00 AM		PS2-TuM-3 Dry Etching of InGaP in Magnetron Enhanced BCl\sub3\ Plasmas G. McLane, M. Wood, D. Eckart (Army Research Laboratory); J. Lee, K. Lee, S. Pearton, C. Abernathy (University of Florida) Recently, In\sub0.5\Ga\sub0.5\P/GaAs heterostructures have been investigated for replacement of the AlGaAs/GaAs material system in devices such as heterojunction bipolar transistors, diode lasers, and high electron mobility transistors. InGaP is less prone to oxidation, contains fewer deep level states, and has a lower surface recombination velocity than AlGaAs. InGaP has been successfully dry etched using electron cyclotron resonance in BCl\sub3\, Cl\sub2\, and in CH\sub4\/H\sub2\/Ar gas mixtures. We report here on dry etch investigations of InGaP in magnetron enhanced BCl\sub3\ plasmas. InGaP etch rates were determined as a function of power(0.2-0.5 W/cm\super2\), BCl\sub3\ flow rate (3-12 sccm), and pressure (2-10 mTorr), with rates as high as 0.35 micron/min achieved. Scanning electron micrographs showed etched surfaces to be smooth, with vertical sidewalls free of undercut. Auger electron spectroscopy measurements of etched samples revealed the presence of a boron residue, with surface composition remaining essentially unchanged upon etching. The addition of N\sub2\, Ar, and O\sub2\ to the BCl\sub3\ plasma was ineffective in producing an etch rate increase. Changes in sheet resistance and photoluminescence of n-type and p-type InGaP exposed to BCl\sub3\ plasmas were also investigated as a function of power, pressure, and etch duration time. The n-type material was found to be more susceptible to etch-induced damage than p-type material, suggesting that electron traps are produced by ion bombardment.
9:20 AM		PS2-TuM-4 Dry Etch Damage in III-V Semiconductors C. Wilkinson, S. Murad, S. Beaumont (University of Glasgow, United Kingdom) Dry etching is the preferred route for the patterning of the III-V semiconducting material used in very high speed field effect transistors and optoelectronic devices as it gives higher yield and control of the profile of the feature being etched. However damage - that is deterioration of the electrical and optical properties - can be caused by the bombardment of the energetic ions which typically have energy in the range 50 to 500 eV. This energy penetrates deeply into the material. After making a distinction between surface and sidewall damage, methods of measuring both will be given. The data show the very damaging nature of physical sputtering using rare gases and the advantage of having a chemical component to the etching. Models for the formation of damage will be discussed and a summary of the current position of our understanding of how it is created will be given. Two essentially damage free processes will be discussed - one for GaAs/GaAlAs and the other for In containing compounds. In both cases while the bias voltage is less than 100eV, excellent control of the profile is possible. Recommendations for designing low damage processes will be given.
10:00 AM		PS2-TuM-6 Anisotropic Etching of InP with Low Sidewall and Surface Induced Damage in Inductive Plasma Etching using SiCl\sub 4\ J. Etrillard, P. Ossart, G. Patriarche, F. Bresse, C. Daguet, M. Juhel (France Telecom, CNET/PAB) We report on the sidewall and surface characterization of InP etched patterns obtained by Inductice Coupled Plasma (ICP). The fabrication of InP based optoelectronic integrated circuits requires etching processes usually in CH4/H2 gas mixture will low induced damage, high and reproducible etch rate, controlled etch directivity. These requirements imply the use of a high density plasma source which allows to reduce the energy of ions impinging on the wafer surface while keeping a sufficient etch rate. However, this high density plasma usually gives rise to isotropic etching. We introduce here the use of an ICP to etch InP. We show that one can obtain anisotropic processes in SiCl4 chemistry avoiding the carrier compensation due to the H+ bombardment. The surface morphology and the pattern profiles are observed by Scanning Electron Microscopy (SEM) and by Atomic Force Microscopy (AFM). Auger Electron Spectroscopy (AES) and Secondary Ion Mass Spectroscopy (SIMS) are used to obtain the elemental composition in the top 30 nm of the etched surface and to evaluate contamination. Transmission Electron Microscopy (TEM) is used to observe the sidewall damage on patterns obtained by e-beam lithography. The effects of ion density, ion energy, pressure, reactor environment and surface temperature are observed. Finally, surface damage induced on InP etched substrates are characterized through photoluminescence (PL) intensity. The destructive effects of high ion energy etching processes already observed in CH4/H2 chemistry, are also identified. Some very low bias voltage processes (as low as 5V) have been studied in the JCP equipment. It will be shown that extremely low surface damage level and very low sidewall amorphization can be obtained in such processes while keeping high etch rate and anisotropy.
10:20 AM		PS2-TuM-7 Comparison of CH\sub 4\/Ar and CH\sub 4\/H\sub 2\/CO\sub 2\ Plasma Chemistries in Hydrocarbon RIE of InP-based Optoelectronic Devices D. Melville, S. Ohja, R Moore, F. Shepherd (Nortel Technology, Canada) CH\sub 4\/Ar and CO\sub 2\/CH\sub 4\/H\sub 2\ plasmas have been investigated to control the slope of the etched sidewall in different devices. For the fabrication of the Y-junctions in a Mach-Zhender modulator, a controlled slope with an angle from the vertical of 6 to 10 degrees is required. This is achieved with a CH\sub 4\/Ar plasma and, at an 8/67 flow ratio, an angle of 8 degrees is obtained at a power level of 150mW. For structures such as reflectors within a waveguide, the etched facet should be vertical and smooth. The CH\sub 4\/Ar or CH\sub 4\/H\sub 2\ plasmas do not give this result. However, good quality etched facets have been obtained using a CH\sub 4\/H\sub 2\/CO\sub 2\ plasma. Optimized conditions are found to be dependent on exposed area of the wafer and, for the mask levels investigated, these conditions are 3sccm CO\sub 2\, 20sccm CH\sub 4\, 90sccm H\sub 2\, 250W RF and 50mTorr. These parameters give rise to etch rates of 500\Ao\/min and sidewall angles of better than 1 degree from vertical, even in heterostructure material. Application of this process to a passive optical splitter device will be demonstrated. Finally, it will be shown that the CH\sub 4\/H\sub 2\/CO\sub 2\ process also gives a significant improvement in etch depth uniformity of at least a factor of two over the CH\sub 4\/Ar process. It will be shown how this feature, when combined with a laser end-point detection system, can be used to advantage for several devices where the requirement is to dry etch close to (but not into) a thin selective wet etch stop layer.
10:40 AM		PS2-TuM-8 High-Density Plasma Etching of Compound Semiconductors R. Shul, G. McClellan, D. Rieger (Sandia National Laboratories); S. Pearton, C. Abernathy (University of Florida); C. Constantine (Plasma-Therm, Inc.) The realization of advanced compound semiconductor devices relies heavily on the ability to etch reproducibly with smooth surface morphologies, etch rates often exceeding 1 =B5m/min, and a low degree of plasma-induced damage. High-density plasma etching is becoming the technique of choice due to higher etch rates and lower damage as compared to reactive ion etching (RIE). High-density etch systems, including inductively coupled plasma (ICP) and electron cyclotron resonance (ECR), can decouple ion energy and ion density thus establishing a highly flexible etch technique. Such flexibility enables diverse applications from extremely high GaAs etch rates exceeding 4.0 =B5m/min with conical profiles for backside via connections to waveguide etching where anisotropic profiles and sidewall smoothness are critical to optimize device performance. In this study, ICP etching of GaP, GaAs, GaN, and InP is reported and compared to ECR etch results as a function of plasma chemistry, chamber pressure, plasma power, and rf-biasing. The etches are characterized in terms of etch rate and anisotropy using scanning electron microscopy (SEM) and surface morphology using atomic force microscopy (AFM). The etch rates for GaP and GaAs increased monotonically as the Cl concentration increased in ICP- and ECR-generated Cl\sub2\- and BCl\sub3\-based plasmas. InP etch rates were much lower and independent of etch technique and plasma chemistry due to the low volatility of the InCl\subx\ etch products. GaN etch rates obtained in an ICP-generated plasma were slightly higher than those obtained under comparable ECR conditions possible due to the generation of higher concentrations of reactive neutrals. Optical emission spectroscopy (OES) will be incorporated to identify plasma species and possible etch mechanisms for III-V etching in ICP and ECR plasmas.
11:00 AM		PS2-TuM-9 Plasma Etching of III-Nitrides in ICl and IBr C. Vartuli, J. Lee, J. MacKenzie, C. Abernathy, S. Pearton (University of Florida, Gainesville); R. Shul (Sandia National Laboratories) Electron cyclotron resonance (ECR) etch rates for GaN, InN, InAlN, AlN and InGaN were measured for new plasme chemistries, ICl/Ar and IBr/Ar. The effect of etch chemistry, microwave and rf power on the etch rates for these materials were examined. InN proved to be the most sensitive to the plasma composition and ion density. The GaN, InN and InGaN etch rates reached ~ 13000 \Ao\/min, 11500 \Ao\/min and 7000 \Ao\/min respectively at 250 W rf and 1000 W microwave power for ICl discharges. This is the fastest yet reported for these materials. The etched surface of GaN was found to be smooth, with no significant preferential loss of N from the surface at low rf powers, and no significant residue on the surface after etch.
11:20 AM		PS2-TuM-10 ECR RIE-Enhanced Low Pressure Plasma Etching of GaN/InGaN/AlGaN B. Humphreys, M. Govett (Oxford Instruments, England) A room temperature (RT) plasma etch process has been developed to non-selectively etch GaN/InGaN/AlGaN structures grown on sapphire substrates, using an electron cyclotron resonance (ECR) plasma source with RIE enhancement. The process chemistry chosen was Cl\sub 2\CH\sub 4\ based in order to facilitate the formation of volitle etch by-products, typically to form group III halides and group V hydrides, although In is more likely to form an organo-metallic compound as opposed to a chloride. A characteristic of this process is the very smooth sidewall features obtained and the controllibility of the etch profile via ECR power, table bias, and/or gas flow. Typical results obtained using a RT process were etch rates above 100 nm/min, selectivity to a resist mask of 30:1 and a smooth anisotropic profile at low ion energies (<100 eV). The process etch rate showed a characteristic increase with increasing table bias (above 130 nm/min) with only small changes in the relative etch rate of each compound (i.e, selectivity maintained at roughly 1:1) however, this etch relies upon competing etching and deposition mechanisms and thus too large a variation in one parameter without a corresponding compensation with another leads to a rough surface and a more selective etch. The process has also been demonstrates using a metal mask (e.g. Ni) and present work is progressing onto other gas combinations and the use of high temperature electrodes.
11:40 AM		PS2-TuM-11 Control of the Etching of III-V Semiconductors and Related Materials N. Ianno, A. Pittal, B. Wigert, P. Snyder (University of Nebraska, Lincoln); S. Pittal (J.A. Woollam Co. Inc.) In situ spectroscopy ellipsometry has been used as a feedback control for the electron cyclotron resonance (ECR) etching of an AlGaAs/GaAs heterostructure in a CH\sub4\-Ar-H\sub2\plasma, and multilayer stacks of photoresist in O\sub2\ and N\sub2\O plasmas. Development of the control algorithm will be presented. Further, in order to characterize the etching of GaAs, a statistical, two level factorial approach was used to identify the process critical variables, their effects and interactions. During the characterization studies of GaAs etching, an etch induced damage layer was identified. Ex situ ellipsometric characterization and Auger spectroscopy were used to investigate the cause and form of the damage. The damage was identified as a thin, strained layer caused by preferential removal of As by hydrogen in the near surface region.