A method for determining average damage depth of sawn crystalline silicon wafers.

The depth of surface damage (or simply, damage) in crystalline silicon wafers, caused by wire sawing of ingots, is determined by performing a series of minority carrier lifetime (MCLT) measurements. Samples are sequentially etched to remove thin layers from each surface and MCLT is measured after each etch step. The thickness-removed (δt) at which the lifetime reaches a peak value corresponds to the damage depth. This technique also allows the damage to be quantified in terms of effective surface recombination velocity (Seff). To accomplish this, the MCLT data are converted into an Seff vs δt plot, which represents a quantitative distribution of the degree of damage within the surface layer. We describe a wafer preparation procedure to attain reproducible etching and MCLT measurement results. We also describe important characteristics of an etchant used for controllably removing thin layers from the wafer surfaces. Some typical results showing changes in the MCLT vs δt plots for different cutting parameters are given.

Use of optical scattering to characterize dislocations in semiconductors.

Optical scattering from a defect-etched semiconductor sample is used to characterize dislocations in the material. It is shown that when the sample is illuminated normally with a He-Ne (lambda = 6328-A) laser beam the reflection pattern can be used to identify the shapes of the etch pits and hence the directions of the dislocation propagation. The integrated light flux scattered by the illuminated sample, normalized by the incident flux, is shown to be proportional to the dislocation density. This principle is applied in two ways to count dislocations at the sample surface. In one case the defect-etched sample is scanned under a light beam, and the scattered flux is collected by an integrating sphere and measured. In the second case the defect-etched sample is illuminated with incoherent light of a broad angular spectrum, and a photographic transparency is produced which registers an image of the dislocation density distribution of the original sample. These two methods for counting dislocations, mapping dislocation distribution, and measuring average dislocation density of the sample are discussed.

Optical diffraction technique for determination of crystal orientations.

An optical technique for determination of crystal orientations is described. This technique uses texture etching to generate pseudoperiodic surface structures whose groove shape is characteristic of the surface orientation. When such a textured surface is illuminated with monochromatic light, a far-field diffraction pattern characteristic of the surface orientation is observed. A procedure for analysis of diffraction patterns to determine crystal orientations is discussed. Results obtained by this technique agree very well with those using the x-ray Laue technique.

Efficient optical waveguide coupler.

A new method for high-efficiency interconnection of two planar optical waveguides is described. This technique is based on mode-matched coupling and is particularly useful when the difference between the refractive indices of the individual guides is large. The method consists of etching a deep vertical step in the highindex waveguide followed by the deposition of low-index waveguide on the etched section so that the two guides remain connected end to end. A theoretical treatment for the design of the coupler and for determination of fabricational tolerences is given. Couplers were fabricted using high-index waveguides like GaAs and LiNbO(3) and low-index waveguides made up of glass or solution-deposited (polyurethane or photoresist) films on SiO(2) substrate. It is shown that by controlling the junction profile, efficiencies close to theoretical values can be obtained. Some applications of such a coupler are given.

Focused laser lithographic system.

A focused laser lithographic system (FLLS) has been constructed. Details of the construction of this system and its performance are given. Results indicate that certain modifications to the system will enable it to rival much more expensive systems.

Propagation characteristics of GaAsP heterostructure waveguides for 1.06 microm and 0.905 mum wavelengths: an evaluation.

Propagation characteristics of GaAs/GaAs (1-x)P(x) and GaAs (1-y)Py/GaAs(1-x)P(x) waveguides are evaluated at 1.06-mum. and 0.905-mum wavelengths. Attenuation of the lowest order mode in single-mode and two-mode waveguides is 1.2 dB/cm at 1.06 mum. At 0.905 mum the measured attenuation rate for the GaAs(0.80)P(0.20)/GaAs(0.65)P(0.35) waveguide is 1.5 dB/cm. Multimode waveguides have considerable mode conversion due to surface undulations caused by grading dislocations. Refractive indices have also been calculated from experimental data at 1.06 mum for GaAs and GaAs(0.65)P(0.35)to be 3.47 and 3.325, respectively.

GaAs optical waveguide structures at 10.6-microm wavelength.

A comparison of GaAs/n(+)GaAs, GaAs/GaAsP, and GaAs/AlGaAs waveguide structures is presented. Their fabrication processes and their transmission properties at 10.6-microm wavelength are described. The loss due to the free carrier absorption of the substrate is analyzed. Experimentally, an attenuation rate of 2 dB/cm in a single mode (~7 microm) GaAs/GaAsp waveguide with a maximum dimension of the order of 7 cm has been achieved.