Wafer Bending Research Articles

Effect of Biaxial Stress on Solid Phase Epitaxy of Silicon

ABSTRACTThe effect of biaxial stress on solid phase epitaxial growth (SPEG) rate of crystalline Si(100) into self-implanted amorphous surface layer has been measured. Biaxial stresses in the crystalline and amorphous phases were generated by bending the silicon wafer using the residual stresses in Ge films deposited on the back side of the wafer. Stresses were determined at SPEG temperatures by optical measurements of wafer bending curvatures. Tensile stresses up to 13 MPa in the crystalline phase and 34 MPa in the amorphous phasewere achieved during SPEG at 530ºC. An optical system based on the time-resolved reflectivity (TRR) technique was devised to measure the growth rates of two adjacent samples during a single SPEG run. This enables a direct comparison of the growth rates under different stress conditions without concern for run-to-run temperature variations. We found that the growth kinetics in all the samples were retarded as the c/a interface approached the free surface. However, the extent of this rateretardation was reducedin the stressed samples, leading to stress-enhanced growth kinetics. We speculate that the application of the biaxial tensile stresses might slow down the incorporation of hydrogen into the amorphous phase, a mechanism for the rate-retardation.

Slip band formation during bending of GaAs wafers

Slip band formation during bending of GaAs wafers

Slip band formation during bending of GaAs wafers

Slip bands which appear after 4-point bending of liquid encapsulated Czochralski grown zinc doped GaAs (001) wafers at (412…447)°C have been characterized quantitatively both by reflection and transmission microscopy. Slip is initiated at the edges of the tensile part of the specimen. Deformation proceeds by the growth of slip bands in length through the whole specimen and in height up to ≈ 200 nm. Their average distance goes down to ≈ 20 μm within the bending angle interval (0.2…5.9)° investigated. Residual stresses σ1 – σ2 ≈ (8…30) MPa have been detected by stress-induced birefringence measurements in the bent crystals.

Slip band formation during bending of gap wafers

Abstract{001} LEC‐GaP:S wafers were deformed between 470 °C and 640 °C. {111} slip planes of maximum resolved shear stress were activated. Heights and densities of slip steps have been measured by optical and electron microscopy. At lower temperatures deformation proceeds mainly by growth of step heights whereas at higher temperatures bending is accomplished by the increase of slip band density rather than of height.

The dislocation structure of GaP crystals after 6–10° bending

More than one thousand individual dislocations have been examined by TEM in S-doped LEC-GaP after three-point bending of (001) wafers at temperatures in the range 605-615°C. A linear variation of d...

High-Temperature Treatment of Porous Silicon

en

Stress‐Induced Spectral Changes in Raman Spectra of n ‐ GaAs Encapsulated with Si3 N 4 Films

Raman spectra and wafer bending of encapsulated with films were observed. The stresses which are estimated from wafer bending by the Timoshenko relation depend on the thickness of encapsulated films. The changes in Raman spectra also depend on the film thickness. There is good correlation between the variation of the ratio of peak heights of longitudinal optical to coupled plasmon‐longitudinal optical modes in the Raman spectra, (LO/L‐), and the variation of stress deduced from wafer bending. The variation of the LO/L‐ modes with film thickness was explained by the change in space charge layer thickness and disordering by inhomogeneous strain.

Band Gap Energy and Stress of GaAs Grown on Si by MOCVD

The band gap gap energy and stress of GaAs grown on Si using (GaP/GaAsP) and (GaAsP/GaAs) superlattice intermediate layers were measured by electro-reflectance and wafer bending. It was found that high-density dislocations or defects which can relax stress exist during the early stages of the growth and decrease with the growth sequence; the growth temperatures have significant effects on crystal perfection.

The Contrast of Dislocations in X-Ray Topographs of Homogeneously Bent Silicon Crystals

ABSTRACTThe contrast of dislocations in X-ray transmission topographs has been studied as a function of specimen curvature. It has been shown that in the symmetric Laue geometry, contrast differences between Lang and Hirst Curved Crystal topographs are attributable to inhomogeneous bending of the specimen wafers.

Lattice Bending in LEC-Grown Semi-Insulating GaAs Wafers

Lattice bending in LEC-grown semi-insulating GaAs crystal wafers was investigated by X-ray diffraction. Various distributions in the lattice bending were observed in wafers from different boules. Prominent bends, with radii of curvature of about 20 m, were observed at places where the relevant topographs showed the presence of fine cellular dislocation networks. The apparent wafer bending was also examined optically and was found to be caused mainly by back surface damage.

Effect of phosphorus doping on stress in silicon and polycrystalline silicon

An investigation of the polysilicon stress properties as a function of film thicknesses and phosphorus doping showed that as-deposited films are moderately compressive, and become less compressive with increasing film thickness. High temperature PBr3 diffusion in silicon produces wafer bending corresponding to a tensile stress in wafer. Following a PBr3 diffusion, polysilicon films, however, become less compressive. Subsequent oxidation introduces an additional compressive stress component of the order of 2−3×109 dyne/cm2 for oxidation temperatures between ∼900−1000 °C. The thermal expansion coefficients were similar for doped and undoped films (α∼2.9 ppm/°C) and slightly less than for 〈100〉 silicon, while the doped films were found to be less stiff than undoped ones but both were less stiff than 〈100〉 silicon. The observed changes in polysilicon stress due to film thickness and phosphorus doping have been interpreted in terms of a grain growth model wherein those factors which lead to enhanced grain growth also result in reduced compressive stresses.

X‐Ray topographic study of the influence of thermal annealing on the bending of 49BF2+‐implanted Si wafers

AbstractThe influence of thermal annealing on the image contrast of the boundaries of 49BF2+‐implanted regions in Si is investigated by means of X‐ray topography. The contrast is used for studying the wafer bending and the stress types. It is shown that the final state of deformation is determined by: (1) the expansion of the surface layer caused by the implantation, (2) the contraction of this layer caused by the annealing. Effect (1) or (2) dominates depending on the implantation dose and annealing conditions. The possibility of compensating both effects leading to complete elimination of the bending of the implanted wafers is established. The results are discussed on the basis of the correlation between the deformation state of the wafers and the percentage B atoms occupying substitutionally Si‐lattice sites.

Automatic x-ray diffraction measurement of the lattice curvature of substrate wafers for the determination of linear strain patterns

An x-ray diffraction topography goniometer (Lang camera) under computer control has been used to measure localized bending of silicon wafers. The wafer, mounted free from external stresses, is set for Bragg reflection in transmission by lattice planes perpendicular to the surface (Laue case) and it traverses across the x-ray beam in steps of 0.01 mm or multiples thereof. At each step the angular position and the intensity of the peak of the Bragg reflection is determined by least-squares methods from the peak profile with a precision better than the minimum angular step of 0.001°. The lattice curvature obtained from the peak shift is a direct measure of the magnitude of the strains imposed on the wafer by oxide layers, thin films, implantation, and other manufacturing processes. Therefore linear strain maps, showing, for instance, strain gradients occurring at film edges, can be measured quantitatively with high resolution, fully automatically and nondestructively in several direction across a substrate wafer. Measuring substrates of high crystalline perfection and controlling the ambient temperature, the radius of curvature R (in meters) of a uniformly curved substrate can be measured with a probable relative error ΔR/R=R/(1700 m).

The bending of silicon wafers by thin polycrystalline silicon film deposition and by film doping using boron diffusion

The existence of stress at the interface between a monocrystalline silicon substrate and a thin (under 1 μm) polycrystalline silicon film was demonstrated using X-ray topography. The wafer-bending direction was studied for a polycrystalline film doped by boron prediffusion and by prediffusion followed by drive-in diffusion. Wafer bending in the presence of SiO 2 thermal growth between the monocrystalline substrate and the polycrystalline film was also investigated. The causes of the wafer bending and its change during polycrystalline film doping are discussed.

Surface Morphology of GaAs Layers Grown by Liquid-Phase Epitaxy

The surface morphology of liquid-phase epitaxial layers is discussed from the viewpoint of step kinetics. Macroscopic terraces on the grown surface are produced by the kinetic process of an advancing step train. An equation is deduced which gives the terrace size as a function of the surface binding energy. According to the present theory, when a substrate is bent concavely in the growth direction, the binding energy increases and hence the terrace size decreases. If the terrace size when a substrate is not bent is 31 µm, for example, the terrace size when bent concavely is calculated to be less than 0.1 µm, under the same growth conditions. This means the growth surface (e.g. cellular) is transformed into a smoother one (e.g. wave- or mirror-like) by wafer bending. In this paper, the origins of cellular, wave-like, and mirror-like morphologies and their relations are discussed.

Correlation between the defect structure and electrical properties of deformed Si surfaces

Deformation by bending of Si wafers with [112], [111], and [100] surface orientation was produced by sputtering tantalum films on clean Si and on Si surface with a thermally grown oxide. Deposition of 0.5–1-μm Ta films produced radii of curvature in the Si wafers of from 350 to 50 m, respectively, as measured by the ABAC method. Stress on the Si surface as a function of annealing temperature exhibited a maximum of 400°C of 500 g/mm2 and 650 g/mm2 with and without oxide layer. Stress on tantalum films at 400°C was found to be 276.3 kg/mm2. At 300°C, stress on Ta film increased with Ta film thickness from 70 to 150 kg/mm2. Transverse and sectional x-ray topographs have revealed small dislocation loops at the deformed Si surface. Defect structure produced by bending was correlated with the electrical measurements on the Si MOS configuration with thin and thick oxide, using conductance and capacitance methods. The effects of induced defects were studied by measuring the density and energy distribution of the surface states, surface potential, and flat band voltage. I–V characteristics of the oxide film indicated Ta diffusion through SiO2 to the Si surface.

Anticlastic Bending of Silicon Wafers Induced during Thermal Cycling

Bending of single crystal wafers of silicon during thermal cycling is studied. For both {100} and {111} wafers, the form of bending is anticlastic and the locus of maximum points and that of minimum points meet at right angles. In the case of {100} wafers, plastic deformation in two {100} directions occurs. Whereas {111} wafers have two modes of directions of the bending, although the mechanism of bending seems to be the same as that for {100} wafers. This bending occurs neither at temperatures below 1000°C, nor when wafers are heated and cooled very slowly. It is larger when wafers are placed in the middle of a parallel row of wafers. Therefore, this bending is introduced by thermal stresses due to the radiation shielding effect of neighboring wafers. This bending is enhanced when SiO2 layers are grown on one or two surfaces of a wafer.

Surface piezoelectric effect in non-centrosymmetric semiconductors: Cds

It was found that mechanical bending of CdS wafers with the (00.1) orientation causes pronounced changes in the contact potential difference. The changes were of the order of one volt. This effect was attributed to the polarization induced in the depletion layer by the mechanical stress. On this basis a model was developed which accounts for the experimental results.

On the electrostatic contribution to the interfacial tension of semiconductor/gas and semiconductor/electrolyte interfaces

The concept of electrically charged surface states, which is well known in semiconductor surface physics, is connected with the thermodynamics of charged interfaces as developed in colloid chemistry and electrochemistry. Along these lines an interpretation is suggested of the phenomenon of the spontaneous bending of InSb wafers, discovered by Hanneman, Finn and Gatos. Experiments are described concerning contact angles of ionic solution droplets placed on etched Ge-surfaces, the droplets being provided with a Pt wire shaped electrode. The observations are interpreted in terms of slow states on these surface because the known relaxation times and state densities of slow states can easily be connected with the behaviour of the contact angles. Slow states are rather loosely defined as nonstable ionic, atomic and molecular configurations in which the chemical compounds which meet at the surface participate.