At&t Bell Laboratories

At+t Corp.

Adrian B Emerson

Stephen W Downey

Erdmann F Schubert

Fan Ren

Rose F Kopf

James D Sinclair

William D Reents, Jr

Amy J Muller

Anthony M Mujsce

Alka Swanson

Disclosed is an apparatus which can serve to detect, count, size discriminate and analyze the chemical composition of particles in the air or process gases. In a preferred embodiment, the particles enter via a capillary into a differentially pumped chamber. A pulsed laser which is continuously fired is focused at an opening in the chamber. When the particles come into the path of the laser beam, the particles are fragmented and ionized. A dual time of flight mass spectrum is produced, recorded with an oscilloscope and analyzed with a computer. The mass spectrum information enables the determination of the chemical nature and concentration of the species of the particles, the particle size and the elemental composition of airborne particles in real time. Once these parameters are determined the source of the particles can be determined and eliminated from the environment and process. Thus, the inventive apparatus is advantageously used in conjunction with a facility, i.e., a semiconductor manufacturing facility, that requires ultra-clean conditions.

Laser induced mass spectrometry

It has been found that in the preparation of devices having repetitive layers, such as distributed Bragg reflectors, the dopant introduced during processing redistributes itself in a deleterious manner. In particular, this dopant through various effects segregates and diffuses from one layer into the interface region of the second layer. As a result, properties such as electrical resistance of the structure become unacceptably high. By utilizing various expedients such as carbon doping this segregation and its associated deleterious effects are avoided.

Devices having repetitive layers

This invention is concerned with the production of Schottky barrier gate contacts in MESFET devices. The contact is produced by wet-chemical removal of native oxide in a sealed inert gas ambient and blow-drying the wet-etched surface with the inert gas prior to deposition of gate electrode metal on GaAs by electron beam evaporation in an inert gas ambient. Use of Pt, due to its higher metal work function, as the gate contact metal results in a Schottky barrier height of 0.98 eV for Pt on n-type GaAs. This is considerably higher than the barrier height of conventionally processed TiPtAu contacts (0.78 eV). To lower the sheet resistivity of the gate contact, Pt is preferably used as a milti-layer contact in combination with metal having lower sheet resistivity, with Pt being in direct contact with the n-type GaAs surface, MESFETs fabricated using PtAu bilayer contacts show reverse currents an order of magnitude lower than TiPtAu-contacted companion devices, higher reverse breakdown voltages and much lower gate leakage. The use of this technology of native oxide removal and the PtAu bilayer contact provides a much simpler method of enhancing the barrier height on n-type GaAs than other techniques such as counter-doping the near-surface or inserting an interfacial layer.

GaAs MESFETs with enhanced Schottky barrier

Growing community of inventors

Piscataway, NJ, United States of America

Adrian B Emerson