We present an analysis of nonuniform mask undercut which occurs during fabrication of V-grooves by anisotropic etching of silicon. Mask undercut is known to be highly sensitive to alignment of the etch window with the <110> crystal direction. We show that the configuration of the mask patterns defining the end of the groove has a strong influence on the uniformity of the mask undercut and whether the V-groove sidewalls are true {111} or near [111] planes. Mask patterns with closed ends result in V-grooves whose sides are true (111) planes after long etches; open-ended mask patterns result in V-grooves with near (111) planes. These results can be explained in terms of step generation and movement during the etching process. Displacements of the V-groove centerline as a function of mask misalignment angle and wafer surface misorientation are calculated.

We present silicon etch rate measurements from wagon wheel patterns and widely separated V-grooves etched in KOH solutions. The data indicates there is a reactant depletion effect when using wagon wheel patterns, which obscures the true surface-reaction-rate-limited etch rate. Etch rates obtained from widely separated V-grooves, which are less influenced by reactant transport, indicate the activation energy of {111} etching is less than that of {100} etching, in contrast to previous reports. Our experiments yield activation energies of 0.53 eV for {111} planes and 0.62 eV for {100} planes. The apparent activation energy is highly sensitive to slight angular misalignments off the {111}.

Optical circuits based on low-loss glass waveguide on silicon are a practical and promising approach to integrate different functional components. Fiber attachment to planar waveguide provides a practical application for optical communications. Microwave Plasma Assisted Chemical Vapor Deposition (MPACVD) produces superior quality, low birefringence, low-loss, planar waveguides for integrated optical devices. Microwave plasma initiates the chemical vapor of SiCl4, GeCl4 and oxygen. A Ge-doped silica layer is thus deposited with a compatible high growth rate (i.e. 0.4 - 0.5 micrometer/min). Film properties are based on various parameters, such as chemical flow rates, chamber pressure and temperature, power level and injector design. The resultant refractive index can be varied between 1.46 (i.e. pure silica) and 1.60 (i.e. pure germania). Waveguides can be fabricated with any desired refractive index profile. Standard photolithography defines the waveguide pattern on a mask layer. The core layer is removed by plasma dry etch which has been investigated by both reactive ion etch (RIE) and inductively coupled plasma (ICP) etch. Etch rates of 3000 - 4000 angstrom/min have been achieved using ICP compared to typical etch rates of 200 - 300 angstrom/min using conventional RIE. Planar waveguides offer good mode matching to optical fiber. A polished fiber end can be glued to the end facet of waveguide with a very low optical coupling loss. In addition, anisotropic etching of silicon V- grooves provides a passive alignment capability. Epoxy and solder were used to fix the fiber within the guiding groove. Several designs of waveguide-fiber attachment will be discussed.

Optical circuits based on low-loss glass waveguide are the practical and promising approaches to integrate different functional components for optical communication system. Microwave plasma assisted chemical vapor deposition produces superior quality, low birefringence, low-loss, planar waveguides for integrated optical devices. A microwave plasma initiates the chemical vapor of SiCl4, GeCl4 and oxygen. A Ge-doped silica layer thus deposited on the substrates with reasonable high growth rate. Film properties are based on various parameters, such as chemical flow rates, chamber pressure and temperature, power level and injector design. The main emphasis has been on optimizing the deposition parameters and reproducibility. An uniform, low-loss film can be made by properly balancing the precursor flows. The refractive index of deposited film can also be controlled by adjusting the flow ratio of SiCl4 and GeCl4 bubblers. Deposited films was characterized by prism coupler, loss measurement, residual stress, and composition analysis. The resulted refractive index step can be varied between 1.46 to 1.60. Waveguide can be fabricated with any desired refractive index profile. Standard photolithography defines the waveguide pattern on mask layer. Core layer was remove by the plasma dry etch which has been investigated by both reactive ion etch (RIE) and inductively coupled plasma etch. Etch rate of 3000-4000 angstrom/min has been achieved by using ICP compared to typical etch rate of 200-300 angstrom/min by using conventional RIE.

Flip-chip solder joint technology has been widely used in the integrated circuit (IC) packaging and optoelectronics packaging. Several solder deposition techniques have been developed. In this paper, we will report on an electroplating technique to form Pb/Sn (both eutectic and 95/5% Pb and Sn) solder joints in any shape. For some optoelectronic applications, we successfully plated the Pb/Sn solder pads larger than the under bump metallurgy (UBM). In addition to solder shape and size, solder pad profile (cross section) is one of the most important issues for passive alignment flip chip bonding of optoelectronic devices where the vertical clearance is sometimes limited to less than one micron. Our experiments show that the solder pads surface profile is highly dependent on the process conditions. We found that in addition to an electric field effect, electrolyte diffusion played a very important role in forming the solder pad profile. Based on our model, we optimized plating conditions and improved the thickness uniformity to 0.1 /spl mu/m (standard deviation) over 2-inch wafers for an average solder pad thickness of 4.6 /spl mu/m. This process reduces the cost of solder deposition as well as providing a means for controlling airborne Pb toxicity which might be found for pads deposited by vacuum deposition methods.

We have studied the formation of etch hillock defects during anisotropic etching of (100) silicon in KOH, Defect density is correlated with low etchant concentration and high etch temperature. Cathodic etch experiments indicate that hillocks form under conditions of decreased OH- ion concentration, The activation energy for defect formation is 1.2 eV, considerably higher than the energy associated with silicon removal, We propose a mechanism to explain hillock formation that involves nucleation by silicon redeposited from the etch solution, The incidence of hillocks in this model is the result of a competition between the forward and reverse etch reactions, Examination of defects by electron microscopy suggests that growth occurs preferentially on slow-etching planes, in agreement with the model predictions. [151]

Anisotropically etched v-grooves on silicon substrate for the positioning of optical fibers have been widely implemented in fiber optics and optoelectronic applications. Because the anisotropic etching depends upon the crystallographic orientation of silicon, the v-grooves are normally formed parallel to the <110> direction. However, some applications, such as optical switches, and wavelength division multiplexing/demultiplexing devices, fan-in and fan-out configuration for fiber positioning are required. In this paper, we will report a single mode refractive plate switch where a micromachined silicon waferboard was implemented for passively positioning optical fibers. We successfully demonstrated a 2 X 2 single mode optical switch with less than 0.64 dB loss.