Non-contact Polishing Research Articles

Radiation response of CMOS/SOI devices formed by wafer bond and etchback

The fabrication process and defect characteristics of thin-film silicon-on-insulator (SOI) devices prepared by the bond and etchback process (BESOI) utilizing diamond matching and noncontact polishing were studied. MOS devices were fabricated and were characterized electrically before and after radiation exposure. Analysis by TEM shows that a defect-free film is produced by the BESOI process. CMOS devices show high mobility and low leakage current (less than 1.0 pA/ mu m). The radiation responses of the top and edge oxide are comparable to those of bulk devices. Positive charge trapping and interface-trap generation were -0.8 and 0.8 V, respectively, at a dose of 10 Mrad (SiO/sub 2/). >

Noncontact laminar-flow polishing for GaAs

Laminar-flow polishing is a noncontact polishing technique capable of producing a highly polished surface with no subsurface mechanical damage. The method utilizes the hydrodynamic condition of laminar flow to provide the transport mechanisms responsible for the removal of the GaAs surface. The method is well suited to the preparation of semiconductor wafers for experiments where high-quality damage-free substrates are required. In addition, the ease of controlling the polishing conditions makes this method a useful technique in production where a high throughput of wafers with uniform and damage-free surfaces are essential.

Polishing of lithium niobate by ion-beam etching

Ion-beam etching has previously been used to enable coupling of light from an optical fibre to a titanium indiffused waveguide on LiNbO3 [1]. The fibre diameter was reduced so that the fibre could be placed in an ion-etched groove in the LiNbO3 coaxial with the waveguide. Here, an alternative use of ion etching, as a non-contact polishing method, is reported. This is of value in a solution to a problem encountered by Lefevre et al. [2]. They found that Michelson fringes arising from Fresnel reflections at the outputs of an integrated optic phase modulator determined the lower limit of detection of Sagnac fringes in a fibre optic gyroscope. One way to overcome this limit is to cut back one branch of the modulator by more than half the coherence length of the source, so that the reflections are incoherent. However, this leaves the end of the waveguide in a corner inaccessible to conventional end-polishing methods. It was thought that by adjusting the angle of incidence of the ion beam on the sawn surface to the angle for which the etch rate was greatest, 0 . . . . all features would be suppressed and the surface would tend to be flat. Because 0m~, was not known, it had first to be guessed and then inferred from early results. However, in the region of interest for optical coupling, near to the waveguide face, pairs of facets were formed (Fig. 1). The facets were a few micrometres wide and much improved in finish over the original sawn surface (Fig. 2). As yet, however, a facet perpendicular to the waveguide face has not been produced and no measurements of coupling efficiency have been made. The requirement for a perpendicular facet is not likely to be very stringent. Lefevre et al. [2] deliberately introduce a 10 ° lateral misalignment with minimal loss. Thus a facet a few degrees off perpendicular should not be a problem. The etching geometry is shown in Fig. 3. Three angles of incidence, 0, were tried. These were 0 °, 321⁄2 ° and 45 ° . The general pattern for 45 ° etching was two overhanging facets, (Fig. 1) the one meeting the waveguide face being at a lesser angle. For 321⁄2 ° etch-

Effects of substrate polishing on double-heterostructure AlyGa1−yAs-AlxGa1−xAs lasers grown by molecular beam expitaxy

Data are presented indicating that remnant damage retained beneath the surface of GaAs substrates as a result of polishing has an adverse effect on the performance of semiconductor laser diodes. Deep subsurface damage, observed on the etched/polished substrates provided by the crystal manufacturer, can be removed with an extended etch using a bromine-methanol solution or with a noncontact polishing process developed at ARACOR. Data are shown for laser structures with both GaAs and AlxGa1−xAs active layers, grown by molecular beam epitaxy on substrates prepared to compare the effects of the three polishing techniques. Laser structures grown on substrates prepared by bromine-methanol and noncontact polishing show lower threshold current densities and a marked increase in device uniformity.