Ground Silicon Wafers Research Articles

Rotational grinding of silicon wafers—sub-surface damage inspection

Industrial practise in wafer manufacturing indicates that there is not one agreed method available to acquire a conclusive picture of the sub-surface damage, defined as structural inhomogeneities of the crystal lattice. Therefore, various methods have been studied and compared for measurement of the sub-surface damage introduced to single crystal silicon wafers during rotational grinding process. Several probing techniques were used to analyse a controlled set of ground silicon wafers. Optical methods were used to study the strain distribution, scattering-in depth and surface topography of the sample set. Acoustic and X-ray diffraction were used to directly observe variations in the Young’s modulus and the lattice constant, respectively. The techniques used ranged from point analysis to whole-wafer mapping and averaging. The study indicates that the various physical properties of the lattice damage arise from closely linked processes taking place during the grinding process. The correlations between the methods included in this study have been identified and quantified, and the relationships between the various observable quantities of sub-surface damage are discussed.

Actively Controlled Compliance Device for Machining Error Reduction

Deformation of the tool itself, due to cutting forces, is one of the major causes of machining error in precision machining. The authors propose a new solution to the problem that employs an actively controlled compliance device. By applying ‘negative’ compliance of the device, deformation of the machining tool can be compensated, and the machining error can be reduced to zero. This paper reports our analysis of the machining process to compensate machining error using negative compliance. It also evaluates our method through experiments of grinding silicon wafers and turbine blades.

Quantitative material characterization by ultrasonic AFM

In an atomic force microscope equipped with a micromachined cantilever tip, the cantilever vibration spectra in contact with the sample were found to be strongly dependent on the excitation power. However, if the excitation power is small enough, the resonance peak width decreases and the peak frequency increases to a certain limiting value. In this condition the tip–sample contact is kept linear, and satisfactory agreement between the measured and calculated frequency is obtained, assuming a constant contact stiffness; the agreement is further improved by taking into account the lateral stiffness. More quantitative information on the elasticity of the sample is obtained from the contact load dependence of the frequency, where contact stiffness of a non-spherical tip shape is derived from the Sneddon–Maugis formulation, and the tip shape index is estimated by an inverse analysis of the load–frequency relation. A further advantage of evaluating not only the vertical but also the lateral stiffness is demonstrated on a ground silicon wafer by simultaneous measurement of deflection and torsional vibration. Copyright © 1999 John Wiley & Sons, Ltd.

ぜい性材料の超精密研削技術の研究 超精密研削装置の試作

The present paper deals with a ductile mode ultraprecision grinding equipment, which is developed for industrially realizing crack free grinding of semiconductor materials with high shape accuracy. This equipment is composed of ultraprecision systems such as force-operated linear actuator, composite bearing guideway mechanism, stationary spindle structure, 10 nm resolution feedback NC control and so on. By these systems, inching resolution of the grinding wheel head reached 10 nm, and the loop stiffness between grinding axis and rotary-table is 150 N/μm. The thickness of dislocation layer remained on the ground silicon wafer is about 0.5 μm. It is confirmed that there are no cracks remaining under the ground surface from SAM (Scanning Acoustic Microscope) observations. On the other hand, in case of conventional precision grinding machine, many cracks were observed along grinding marks. The LTV (Local Thickness Variation) which describes local flatness for all cells is under 0.4 μm. The TTV (Total Thickness Variation) which describes global flatness is 0.55 μm.

Parallelism Improvement of Ground Silicon Wafers

This paper discusses substituting grinding for lapping in machining processes of silicon wafers. To attain this goal, the rotating wafer grinding method, in which a rotating wafer is ground by continuous infeed of a cup wheel, is investigated. The parallelism of a silicon wafer ground by this method is within 2 μm for a 5 in. (125 mm) wafer.