Glenn Wherry Cullen

Reduced pressure silicon epitaxy; A review

Abstract As the critical dimensions of IC circuits are decreased, more demands are put on the characteristics of epitaxial silicon layers. Reduced pressure provides an additional control parameter to use in efforts to achieve the required characteristics in the epitaxial deposits. In this review we discuss the impact of reduced pressure epitaxial growth on: the growth temperature, arsenic autodoping, pattern integrity, thickness and resistivity uniformity, and deposition rate. Epitaxial growth has been achieved at temperatures well under 900°C at reduced pressures, but low temperature pre-epitaxial substrate surface conditioning methods still need to be developed. Very significant improvement in the control of arsenic autodoping, pattern integrity, and resistivity and thickness uniformity has been achieved at reduced deposition pressures. The impact of pressure on autodoping is, at least qualitatively, understood. A number of aspects of the impact of pressure on pattern integrity are not understood.

Heteroepitaxial silicon characterization: Microstructure as related to UV reflectometry

Abstract Some uncertainties have arisen with regard to the relationship between the crystalline quality of heteroepitaxial silicon and data collected by UV reflectometry. Only ≌ 100 A of the silicon most remote from the substrate is sampled in UV reflectometry, while the primary defect structure in the heteroepitaxial silicon consists of {221} twin domains which are initiated at, and concentrated near, the silicon/substrate interface. The correlation between data collected by X-ray pole-figure analysis, cross-sectional TEM and UV reflectometry demonstrates unambiguously that there is a physical relationship between the deposit crystallinity and UV reflectometry. This correlation can be understood through the observation that the degree to which the twin domains propagate to the surface is a function of the volume percent of the twins integrated over the volume of the deposit sampled.

The characterization of CVD single-crystal silicon on insulators: Heteroepitaxy and epitaxial lateral overgrowth

Abstract In the development of the heteroepitaxial silicon technology, progress had been impeled because of the labor and time involved in the evaluation of the crystalline quality of the deposits by transmission electron microscopy and device performance. Therefore an important part of our program has been directed toward the development of rapid and non-destructive methods for the characterization of the silicon crystallinity. It is essential that the results of such methods relate to device performance. In this paper, we update earlier reports on this effort. Emphasis has been placed on the use of UV reflectometry for probing the near-surface silicon quality, photovoltage spectroscopy for probing the “bulk” of the film, interference photovoltage spectroscopy for probing the near-substrate portion of the silicon, and infrared multiple reflectometry to assess the crystalline quality of the substrate surface. The silicon-on-insulator effort has recently been extended on the growth of dielectrically isolated silicon by CVD epitaxial lateral overgrowth. The evaluation of these deposits by transmission electron microscopy is described.

Relationship between crystallinity and electronic properties of silicon-on-sapphire

Abstract A comparative study of electronic properties (determined by photovoltage spectroscopy) and of the crystalline perfection (determined by UV reflection technique) was carried out on a series of silicon-on-sapphire wafers of different crystallinity. It was found that the improvement of crystallinity led to a significant reduction of the concentration of deep levels in the middle of the energy gap. Differences in the as-deposited crystalline quality can be related to differences in the electronic properties even after the deposits were ion implanted, oxidized and annealed. Recently discovered slight amorphization of silicon-on-sapphire was quantitatively analyzed in terms of the amorphization factor, η. It was found that η decreases with improvement of crystallinity and its value for SOS films was one to two orders of magnitude smaller than in a typical a-Si.