Individual Wafers Research Articles

Process-parameter variability in the manufacture of m.o.s. integrated circuits

The integrated circuits produced on a manufacturer's process line incorporate a standardised m.o.s. transistor providing a set of seven process-parameter values per die at the wafer-probe stage. A statistical analysis of the parameters measured on batches of wafers withdrawn in consecutive weeks from the line shows that the batches received different process treatments. A similar analytical procedure applied to the individual wafers of the batches yields the more surprising result that the wafers were also dissimilarly processed.

A microwave evaluation of the velocity-field characteristic in different regions of individual epitaxial gallium-arsenide layers

The velocity (current)-electric field characteristic has been measured in different regions of individual epitaxial gallium-arsenide wafers by a high-power microwave technique. Epitaxial-n layers on semi-insulating substrates ranging in resistivity from approximately 0.5 to 5 Ω cm have been characterized. Trends in high-field microwave properties with normally specified low-field dc material properties are indicated.

Measurement of Flexure in Silicon Wafers by the Lang X-ray Diffraction Technique†

ABSTRACT The Lang x-ray diffraction technique provides a simple non-destructive method for measuring flexure in single-crystal silicon wafers at different stages of integrated circuit fabrication. A molybdenum target provides Kα1 and Kα2 x-radiation which is diffracted from the set of {110} normal to the surface parallel {111}. The widths of the diffracting regions and their separation are simply related to the flexure, which may be expressed as a radius of curvature (p). This method is limited to wafers which do not diffract from the entire region irradiated, i.e. p 1590 in. for a substrate to 203 in. after several processing stages. Non-uniformity in individual wafers is much greater after the material has been through several processing stages.

Reliable electron beam welded micro-connections

Electron beam joining techniques with associated fixturing have been employed to develop a high termination density interconnection system—micro-assembly stack—for the integration of microminiaturized electronic components of the thin film and integrated circuit variety. The interconnecting system embodies ten stacked wafers—0·6 × 0·6 × 0·030 in.—joined by means of peripheral conductor ribbons on all four sides, yielding a structure with 80 interwafer conductors and 800 electron beam-welded joints on 0·025 in. centers. The interconnection technique is suitable for application to most any wafer dimension and geometry. The reliability of the process was demonstrated in terms of the mechanical and electrical characteristics of the interconnections in the as-welded condition, and also after environmental exposure. Pull strength tests were carried out on the copper ribbons welded to the metallized edges of individual wafers as well as to wafer-assemblies simulating conditions in a micro-assembly stack. In the latter instance the pull tests were carried out on weld pairs. The salient points of the reliability study are presented below. Pull strength. Statistical analysis by normal distribution methods of the weld pair pull strengths indicate at a 90 per cent confidence level that no more than 2·6 welds per 200,000 from such a population would fail below 200 g. All the welds failed in the copper conductor immediately adjacent to the fusion zone. All pull strength values exceeded 200 g. Weld resistance. It was demonstrated at a 90 per cent confidence level that no more than three welds out of 1000 weld pair joints from the same population as above would have a resistance greater than 0·010 Ω. Thermal shock. Weld pairs subjected to thermal shock did not exhibit any pull strength degradation. From the statistical analysis of the resistance measurements it was computed that no more than 4·5 welds out of 1,000,000 from such a population would increase more than 0·001 Ω. Extreme ambient temperature test. Weld pair joint resistance was measured from −55°C to 200°C and all measurements were found to be well below 0·010 Ω. Vibration tests. Two micro-assembly stacks were vibrated according to Method 204B of MIL Std 202A without any visible degradation. A modular interconnection system for the integration of thin films, solid state devices and hybrid microcircuits has been developed. This system, based on an electron beam-welded joint of demonstrated reliability, provides a termination and conductor density capability compatible with the high parts density of microcircuits.

半導体用スライシング機の試作について

In this paper is reported a newly designed slicing machine for semiconductor wafers. The distinctive designes of the machine are as follows:(a) A safety device for power stoppage is attached on the machine to prevent the diamond wheel from damage.(b) An optical measuring device for the direction of crystal axis of the workpiece mounted on the machine to avoid the deviation resulting from resetting of the workpiece.(c) A forced lubrication system is employed to the cutting spindle to ensure long running.(d) A hydraulic device is applied to eliminate the backlash of the feeding screw.The performance of the machine has been pursued experimentally in comparison with the similar machines now in popular service and has been concluded as follows.(a) The deviation of the direction of the wafer's crystal axis is within one (1) degree both in X axis and Y axis.(b) The uniformity of thickness among a lot of wafers is within 0.010 mm through 0.015 mm. while it is 0.015 mm through 0.020 mm for the machine now in popular use.(c) The minimum thickness of the wafers which can be sliced by the machine is about 0.200 mm. while it is 0.25 mm for the machines now in popular use.(d) The surface roughness of the wafers is 1.2, 1.8, and 1.4 micron Hmax respectively for the thickness of the wafer of 0.2, 0.25, and 0.3 mm, while it is 2, 2.4, and 2.8 micron Hmax for the machine now in popular use.(e) The parallelism of the wafer expressed by the thickness unifomity of the individual wafer is within 0.010 mm for the machines in popular service.