About the 1996 TMS Annual Meeting: Monday Afternoon Sessions (February 5)

MATERIALS SCIENCE OF CONTACTS AND METALLIZATION AND INTERCONNECTS I

Program Organizers: Jagdish Narayan, Dept of Matls Sci & Engrg, Box 7916, NC State University, Raleigh, NC 27695; John Sanchez, Advanced Micro Devices, M3 160, PO Box 3453, Sunnyvale, CA 94088

Room: Orange County 5

Location: Anaheim Marriott Hotel

Session Co-chairs: D. Crawford, National Science Foundation, Arlington, VA 22230; J. Narayan, North Carolina State University, Raleigh, NC 27695-7916

J. Narayan, North Carolina State University, Raleigh, NC 27695- 7916

2:00 pm Invited

THE SCIENCE AND APPLICATION OF LOW TEMPERATURE GROWN GaAs FOR NONALLOYED OHMIC CONTACTS: J.M. Woodall, T.P. Chin, M.R. Melloch, Department of Electrical and Computer Engineering, Purdue University, West Lafayette, IN 47907- 1285; M.P. Patkar, Vittesse Semiconductor Co., Camarillo, CA 93010

In spite of voluminous research on metal contacts to compound semiconductor materials and devices, very little is known about the basic charge transport physics at the metal- semiconductor interface of widely used contacts. For example, there is still no consensus concerning the Schottky barrier physics for metal/GaAs interfaces used for gate electrodes and diodes. Also, the exact transport physics and its relationship to interface structure and chemistry for the Au- Ge- Ni ohmic contact to GaAs is not well understood. Here we discuss the transport physics and ohmic contact applications of well defined MBE grown and non- alloyed contact structures using low temperature grown (LTG) GaAs. For n- type contacts we use a tandem structure of 2 nm of LTG on a 10- 100 nm thick layer of GaAs doped with lx10²⁰ Si atoms- cm^-3. Ohmic electron transport from the metal to the bulk GaAs occurs by a tandem processes, first via a mid- gap band of deep donor states in the LTG GaAs and then via tunneling though the high density space charge layer caused by the highly Si doped layer, with a resulting non- alloy contact resistance of mid 10^{- 7} ohm- cm². For non- alloyed ohmic contacts to p- type GaAs we grow at 350[[ring]]C and dope with lx10²⁰ Be atoms- cm^-3. The key here is that growth at 350[[ring]]C produces As rich GaAs which in turn greatly reduces the rapidly diffusing interstitial Be concentration, hence very high surface space charge densities can be obtained leading to a non- alloyed contract resistance of <10^{- 7} ohm- cm², without degrading device performance by uncontrolled Be diffusion.

2:30 pm Invited

SOLID- PHASE REGROWTH OF COMPOUND SEMICONDUCTORS AT LOW TEMPERATURES: APPLICATION TO SHALLOW, LOW- RESISTANCE OHMIC CONTACTS: T. Sands, Department of Materials Science and Mineral Engineering, University of California, Berkeley, CA 94720- 1760; L.C.Wang, Department of Electrical Engineering, Texas A&M University, College Station, TX 77843- 3128

Bilayer metallizations consisting of a first layer of Pd or Ni and an overlayer of a group III, IV or V element react with III- V semiconductor substrates in two stages. In the first stage, reactions occur independently at both interfaces as the systems move toward local equilibrium. In the second stage, the reaction between the two metallization layers dominates, and the Pd- III- V (or Ni- III- V) reaction product decomposes to release Pd (or Ni) and regrow the III- V compound. Since the proposal and demonstration of this solid- phase regrowth (SPR) process [Sands, Marshall and Wang, J. Mater. Res. 3 (1988) 914], SPR has provided a mechanism for the controlled modification of III- V surfaces at low temperatures (<350deg.C) with principal application in the fabrication of shallow, low- resistance ohmic contacts. In this talk we will review the SPR mechanism and highlight recent advances in the understanding of doping by SPR, the application of SPR contacts to p- InP and the development of SPR contacts to n- GaAs using processing temperatures as low as 150deg.C.

3:00 pm Invited

ELECTRICAL AND MICROSTRUCTURAL CHARACTERISTICS OF Cu/Ge OHMIC CONTACTS TO N- TYPE GaAs: M.O. Aboelfotoh, S. Oktyabrsky, J. Narayan, Department of Materials Science and Engineering, North Carolina State University, Raleigh, NC 27695- 7916

We show that Cu- Ge alloys prepared by depositing sequentially Cu and Ge layers onto GaAs substrates at room temperature followed by annealing at 400deg.C form a low- resistance ohmic contact to n- type GaAs over a wide range of Ge concentration that extends from 15 to 40 at %. A contact resistivity of (4- 6)10^{- 7} [[Omega]]cm² is obtained on n- type GaAs with doping concentrations of ~lx10^l7 cm^-3. The contact resistivity is little affected by varying the Ge concentration in the range studied and is not influenced by the deposition sequence of the Cu and Ge layers. In addition, the contacts are electrically stable during annealing at 450deg.C after contact formation. Cross- sectional high- resolution TEM results show that Cu reacts only with Ge to form the [[xi]] and [[epsilon]]1,- Cu3Ge phases, and that the interface between the contact metal and the GaAs substrate is planar and structurally abrupt. The results suggest that the formation of the [[xi]], and [[epsilon]]1- Cu3Ge phases leads to the formation of a highly doped n⁺- GaAs surface layer which results in the low contact resistivity.

3:30 pm BREAK

4:00 pm Invited

RECENT DEVELOPMENT OF OHMIC CONTACTS FOR COMPOUND SEMICONDUCTORS: M. Murakami, T. Oku, Y. Koide, and K. Tsukui,, Department of Materials Science and Engineering, Division of Engineering Science, Kyoto University, Sakyo- ku, Kyoto 606- 01 Japan

Recent several breakthroughs in wide energy gap compound semiconductor materials have inspired many researchers to develop new electronic devices capable of high temperature and/or high power operation, blue light- emitting- diodes,and ultra- short wave length lazer- diodes. One of the restrictions for mass production of these devices is lack of low resistance Ohmic contact materials which satisfy the device requirements. In this paper our current status of development of Ohmic contacts for n- GaAs, p- GaN, and p- ZnSe are: briefly reviewed. Special emphasis will be made on recent progress of the intermetallic compound contacts to n- GaAs.

4:30 pm Invited

CRYSTAL STRUCTURE AND CHEMISTRY OF NOVEL Cu- Ge OHMIC CONTACT LAYERS: S. Oktyabrsky, M.O. Aboelfotoh, J. Narayan, Department of Materials Science and Engineering, North Carolina State University, Raleigh, NC 27695- 7916

We report systematic studies of chemistry, structure and electrical characteristics of novel Cu- Ge alloyed ohmic contacts to n- GaAs with very low specific contact resistivity (4x10^-7 cm² for n~lxl0^l7cm^-3). Results of TEM investigations on chemistry of phase formation, crystal structure and defect microstructure in Cu- Ge alloyed layers are presented. Structure and properties of Cu- Ge contact layers having lower and higher Ge concentrations from the stoichiometric Cu3Ge composition are compared. Unique properties of the contact layers, namely low specific contact resistivity, high thermal stability, interface sharpness and high contact layer uniformity are related to the formation of an ordered orthorhombic [[epsilon]]1- Cu3Ge phase with average lattice parameters: 5.30, 4.20 and 4.56 Å. High- resolution TEM has been used to study the ordering in the [[epsilon]]1Cu3Ge which is responsible for orthorhombic distortion of the parent hexagonal [[xi]]-phase. No compounds due to the chemical reactions with GaAs were found in the alloyed layer as well as in the interface region, demonstrating chemical inertness of the [[epsilon]]1- Cu3Ge ordered phase with respect to GaAs.

5:00 pm Invited

METAL CONTACTS TO III-V COMPOUND SEMICONDUCTORS: W.O. Barnard, G. Myburg, F. D. Auret, W. E. Meyer, Department of Physiscs, University of Pretoria, South Africa

In this talk a summary will be given of Schottky barrier height data on (100) OMVPE grown GaAs, as well as on methods to improve Schottky and ohmic contacts to InP. The Schottky barrier height data of 41 metals processed in the same laboratory, following the same cleaning procedure and using the same high quality OMVPE grown (100) n- type GaAs, will be presenteL From I- V and C- V measurements it was found that there exist no obvious linear relationship between Schottky barrier height and metal work function as is suggested by the Schottky- Mott theory, if all the above- mentioned metals are taken into account. Similar results were obtained if the metal work function was replaced by the Pauling or Meidema electronegativities. In contrast with this, if only metals are chosen with high melting points which were deposited by means of an electron gun, a linear relationship does exist belween Schottksy barrier height and metal work function. The Schottky barrier heights of Ru contacts to InP showed a dramatic increase from 0.49 eV befare passivation to about 0.88 eV afler wet chemical passivation in an acid containg Ru ions.