Ruby E. Robertson

Silicon dioxide deposition at 100 °C using vacuum ultraviolet light

A new photochemical reaction for low‐temperature deposition of silicon dioxide has been developed. In this process silane is reacted with nitrogen dioxide in the presence of vacuum ultraviolet radiation. The electrical and mechanical properties of films grown at 100 °C are reported. Capacitance voltage measurements on metal‐oxide‐semiconductor structures on silicon indicate an interface state density <5×1011/cm2. Several possible reaction mechanisms are discussed, and evidence is presented indicating surface photochemistry may be important.

Integrated TiC coatings for moving MEMS

The application of wear-resistant coatings to microelectromechanical systems (MEMS) devices offers the potential of addressing the reliability of moving MEMS devices. However, coating non-line-of-sight, concealed surfaces in fully released 3D MEMS structures, especially those behind micron-sized apertures, is a difficult problem to overcome with most deposition techniques. A practical and viable solution to this problem is the direct integration of wear-resistant coatings into the MEMS fabrication process. Using this approach we have inserted pulsed-laser-deposited titanium carbide (TiC) coatings between critical polysilicon interfaces during fabrication of a MEMS device. This paper describes the details of inserting laser-ablated TiC coatings into a user-friendly surface micromachining process for MEMS to protect key sliding Si surfaces in MEMS motors. This hybrid technology is an effective way of inserting wear-resistant coatings such as TiC into the MEMS fabrication scheme.

Pulsed-laser deposited TiC coatings for MEMS

Titanium carbide (TiC) thin films have very desirable properties that make them ideally suited for applications to MEMS devices. TiC has been one of the preferred coatings for improving the performance of macroscopic moving mechanical components due to its established wear-resistance. Pulsed laser deposition (PLD) has been an excellent method for the deposition of TiC because unlike any other deposition process for TiC, PLD offers the capability of producing high-quality films even at room-temperature. Using a patented PLD technique, especially designed and optimized for the deposition of high-hardness, particulate-free films, we have deposited TiC coatings on a variety of surfaces, including Si and several MEMS compatible film-layers. Our results have demonstrated that TiC coatings also offer a high wear-resistance to Si surfaces. This, together with the excellent chemical and mechanical properties, and thermal stability of our PLD TiC coatings, has led to our application of TiC to moving MEMS devices fabricated from Si. The fabrication of Si MEMS devices is quite well established, however, the reliability and performance of MEMS devices such as microgears, micromotors and microactuators, which involve sliding Si surfaces, remain an open question. The short functional life of these devices is attributed to the excessive wear rate of Si induced by high friction. The work presented here describes a hybrid process whereby PLD is used in conjunction with the Aerospace MEMS fabrication process (AIMMOS) for inserting TiC coatings into critical interfaces in MEMS devices that would involve sliding contact between two Si surfaces. The PLD of TiC, the spectroscopy of the plume, and the properties and applications of PLD-TiC for MEMS will be discussed.

Development of released micromachined structures for millimeterwave device applications: preliminary results

The exploding interest in miniaturized subsystems for mobile and satellite communications applications has revealed a dire need for higher levels of integration, performance, and cost-effectiveness from millimeter-wave components. Monolithic microwave integrated circuit (MMIC) technology has enabled tremendous strides in efforts to miniaturize analog communications circuits and deliver advanced performance at the higher, less-crowded millimeter-wave frequency regime. Similarly, microelectromechanical systems (MEMS) technologies have realized their own successes in the likes of accelerometers for air-bag deployment systems and miniaturized motors. The strengths of MMICs and MEMS, two areas whose applications have largely developed independently, can now be synthesized to yield the types of components that will deliver the high performance, space efficiency, and low cost demanded by the current communications technology needs. This paper reports preliminary progress in the development of released surface-micromachined structures suitable for use in such millimeter-wave device applications. Several experimental structures are described, with a brief overview of the fabrication process used and the eventual millimeter-wave circuit context for the structures.

Photoassisted Deposition of Silicon Dioxide from Silane and Nitrogen Dioxide

Abstract : Three new reactions for depositing silicon dioxide at low temperatures using vacuum ultraviolet and ultraviolet radiation to initiate a reaction between silane and nitrogen dioxide have been developed. The optical and electrical properties of these films are reported. The effect of ion implantation on the infrared spectra of oxides grown by vacuum ultraviolet irradiation is also presented. Keywords: Photochemical deposition; Silicon dioxide; Silane; Nitrogen dioxide; ion implant; Effects; Silicon dioxide films.

Studies of Boron Implantation Through Photochemically Deposited SiO2 Films on Hg1-xCdxTe

Variable temperature Hall and resistivity measurements have been used to monitor the changes in carrier behavior in p-type Hg1-xCdxTe when boron ions are implanted through photochemically deposited SiO2. The formation of an n-type layer is demonstrated. Quantitative and non-destructive determinations of the absolute 10B concentration and distribution has been obtained by the novel method of neutron depth profiling. As expected, the boron distributions in the SiO2 films and Hg1-xCdxTe are strongly dependent upon the ion implant energy. However, negligible changes in the boron depth profiles were found after 200°C anneals. The present results are briefly related to the performance behavior of mid-wavelength infrared (MWIR) sensors produced via generic ion implantation procedures.