Damage In Silicon Wafers Research Articles

Two-dimensional detection of subsurface damage in silicon wafers with polarized laser scattering

Abstract This study proposes a polarized laser scattering (PLS) method for detection of the two-dimensional distribution of the grinding-induced subsurface damage (SSD). This study also uses two destructive methods to observe the distribution of SSD in the ground silicon wafers by cross-sectional microscopy and by layer-by-layer microscopy. An experimental investigation is arranged for detecting the two-dimensional damage from diamond wheel grinding of silicon wafers through wafer sample preparation and SSD observations with the cross-sectional and layer-by-layer microcopy. It also includes PLS detection of the ground silicon wafers for SSD information. The results show that both the depth of SSD and the crack density contribute to the PLS detection signals. The study reveals the characteristics of the PLS detection, which illustrates the potential application of the PLS method to in-process detection.

A fracture mechanics approach to enhance product and process sustainability in diamond wire sawing of silicon wafers for solar cells through improved wire design

By decreasing the subsurface damage in silicon wafers produced by diamond wire sawing, the mechanical strength of wafers can be increased, and the amount of silicon to be etched in subsequent manufacturing steps can be minimised, enhancing both product and process sustainability. Apart from the sawing process parameters, the subsurface damage in as-sawn silicon wafers is influenced by the design of the diamond wire. We present a fracture mechanics approach for the design of fixed abrasive diamond wires used in wire sawing of silicon wafers for solar cells. Starting from an allowable damage (crack) depth, indentation fracture mechanics and contact analysis are used to determine the wire design parameters, namely the grit protrusion and peripheral distribution of diamond abrasives. The improved wire design can reduce subsurface damage and thereby improve the surface integrity (product sustainability), and reduce the processing time and chemicals used in the subsequent saw-damage removal step (process sustainability).

Crystalline damage in silicon wafers and 'rare event' failure introduced by low-energy mechanical impact

We used X-ray diffraction imaging to detect and characterize mechanical damage introduced to 300mm silicon wafers by low impact energy exerted on the wafer edge. Maps of crystalline damage show a correlation between the damage size, the magnitude of the impact energy and the location of the impact point. We demonstrate the existence of crystalline non-visual defects; crystalline defects that appear in the X-Ray diffraction images but not in optical microscopy or scanning electron microscope. We propose a mechanism of crystalline damage formation at low impact energies based on finite element analysis and high-resolution synchrotron white beam transmission X-ray topography. Finally, we propose the concept of 'rare-event' to described relatively low rate of occurrence of wafer failure by fracture within semiconductor manufacturing facilities.

Subsurface crack damage in silicon wafers induced by resin bonded diamond wire sawing

In order to optimize the process of wire sawing, this work studied the subsurface crack damage in silicon wafers induced by resin bonded diamond wire sawing using theoretical and experimental methods. A novel mathematical relationship between subsurface crack damage depth and processing parameters was established according to the indentation fracture mechanics. Sawing experiment using resin bonded diamond wire saw was performed on a wire saw machine. The validity of the proposed model was conducted by comparing with the experimental results. At last, the influences of processing parameters on subsurface damage depth were discussed. Results indicate that the median cracks are mainly oblique cracks which generate the subsurface crack damage. On the diamond wire saw cross section, the abrasives with the position angle 78° between abrasive position and vertical direction generate the largest subsurface damage depth. Furthermore, abrasives, generating the subsurface damage, tend away from the bottom of diamond wire with the increase of wire speed or decreases with the increase of feed rate. However, the wire speed and feed rate have opposite effects on the subsurface crack damage depth. In addition, the subsurface crack damage depth is unchanged when the ratio of feed rate and wire speed does not change.

Improvement in Surface Grinding Damage in Silicon Wafers by Chemical Spin Etching

Understanding damage caused by mechanical grinding is required for wafer thinning processes, because such damage significantly affects device performance in large-scale integrated circuits. Herein, in-depth analysis of damage caused by mechanical grinding was conducted by measuring minority carrier lifetime and by the photoacoustic displacement (PAD) technique, which are highly sensitive and quantitative methods for measuring damage. Previous low-sensitivity damage measurements indicate that grinding damage is distributed within a 5-μm-thick surface layer. However, although a 10-μm-thick surface layer is removed by chemical spin etching (CSE), the minority carrier lifetime remains low. This result suggests that significant damage still exists in layers deeper than 10 μm. After etching a 200-μm-thick layer, PAD measurements show that displacement at the surface recovers to 20 pm, which is the level of undamaged silicon. While minority carrier lifetime gradually increases with increased etching, this lifetime remains low after removing a 100-μm-thick strain layer. The minority carrier lifetime reaches that of defect-free silicon after removing a 300-μm-thick layer. These results clearly indicate that deep damage (i.e., depth of 200 μm) is caused at the silicon surface by conventional mechanical grinding. Additionally, we conclude that the CSE process is useful for thinning silicon wafers without inducing damage or strain.

Microstructure studies of the grinding damage in monocrystalline silicon wafers

Abstract The depth and nature of the subsurface damage in a silicon wafer will limit the performance of IC components. Damage microstructures of the silicon wafers ground by the #325, #600, and #2000 grinding wheels was analyzed. The results show that many microcracks, fractures, and dislocation rosettes appear in the surface and subsurface of the wafer ground by the #325 grinding wheel. No obvious microstructure change exists. The amorphous layer with a thickness of about 100 nm, microcracks, high density dislocations, and polycrystalline silicon are observed in the subsurface of the wafer ground by the #600 grinding wheel. For the wafer ground by the #2000 grinding wheel, an amorphous layer of about 30 nm thickness, a polycrystalline silicon layer, a few dislocations, and an elastic deformation layer exist. In general, with the decrease in grit size, the material removal mode changes from micro-fracture mode to ductile mode gradually.

Non-destructive evaluation methods for subsurface damage in silicon wafers: a literature review

The Subsurface Damage (SSD) in silicon wafers induced by any mechanical material-removal processes has to be removed by subsequent processes. Therefore, the measurement of SSD is critically important for cost-effective manufacturing of silicon wafers. This review paper presents several Non-Destructive Evaluation (NDE) methods for SSD in silicon wafers, including X-ray diffraction, micro-Raman spectroscopy, photoluminescence and laser scattering.

Analysis of Ion Implantation Damage in Silicon Wafers by a Contactless Microwave Diagnostic

AbstractRapid thermal annealing (RTA) of lattice damage created by heavy ion implantation damage is required to maintain the integrity of semiconductor material used for submicron-integrated circuit devices. A quick, efficient, and contactless diagnostic of the implantation damage is highly desirable in both research and production environments. A contactless measurement technique has been recently applied to this problem that uses a deeply penetrating low-frequency microwave probe frequency operating at 420 MHz. Here, we will demonstrate the use of this high frequency resonance-coupled photoconductive decay (RCPCD) technique, which, when combined with a tunable optical excitation source, enables us to map the radiation damage in boron and arsenic-implanted silicon wafers. We quantify the damage by mapping the minority-carrier lifetime as a function of optical penetration depth. In this work, we quickly and efficiently compared the effectiveness of various RTA processes by the RCPCD diagnostic.

Characterization of mechanical damage on structural and electrical properties of silicon wafers

The effect of artificial mechanical damage in Czochralski silicon wafers was studied by measuring the structural and electrical characteristics of the wafers. A liquid honing method was used to induce mechanical damage and the damage grade was varied by controlling process parameters. Surface microroughness of the damaged sample was analyzed using an atomic force microscope (AFM). The wet oxidation/preferential etch method, photo-acoustic displacement (PAD) method and the minority carrier lifetime with a laser excitation/microwave reflection photoconductance decay technique were used to characterize the intensity of mechanical damage in silicon wafers. As the degree of mechanical damage increases, the density of oxygen induced stacking faults (OISF) is increased, while the depth of OISF generation is almost independent of damage grade. The minority carrier lifetime is inversely proportional to the mechanical damage grade, while the PAD values are proportionally increased. Other experimental results are discussed from a viewpoint of a structure–property relationship.

Investigation On Subsurface Damage In Silicon Wafers

AbstractMicro-Raman spectroscopy and chemical etching were applied to determine the depth of subsurface damage in silicon wafers undergoing different machining processes: cutting, grinding, polishing and lapping. In comparison with the Raman spectrum of perfect single crystal silicon, both the shape and intensity at the shoulder (500 cm−1) and the subpeak (300 cm−1) spectral regions were changed in all the machined wafers. The intensities at shoulder and subpeak gradually decreased and finally resumed to normal, as the depth of the investigated layer increased. According to the chemical etch rate, the depth of the subsurface damage was thus evaluated for the different wafers. TEM observations further confirmed the obtained results.

Measurement of subsurface damage in silicon wafers

This article presents new experimental results on the measurement of surface and subsurface damage with a focus on the residual stress state of machined silicon single crystals. The x-ray diffraction technique is widely applied as a nondestructive method to determine residual stresses from the lattice deformations of the crystal. To obtain a higher resolution of x-ray diffraction, a modified diffractometer with a multicrystal monochromator was used. An optical technique that is useful for the measurement of stress-depth profiles is micro-Raman spectroscopy. With the low penetration depth of the laser, light stresses close to the surface were detected quantitatively.

Study of ion implantation and annealing effects in silicon wafers using high‐frequency phonon scattering

AbstractFor the first time, high‐frequency phonon scattering has been used to study ion implantation damage in silicon wafers. Diffusive scattering of reflected heat pulses was found to be greatly increased by self implantation at a dose of 1015 cm−2, which is known to produce an amorphous layer. Subsequent low‐temperature (250°C) annealing produced a reduction in scattering which could be attributed to smoothing of the amorphous–crystalline (a–c) interface, i.e. to a reduction in the short‐wavelength components of the interface roughness.

A Study of Postannealing and in situ Annealing of Silicon Wafers Implanted with a High Dose of Oxygen

The effects of postannealing and in situ annealing on the reduction of oxygen ion implantation damage in silicon wafers were investigated by means of scanning electron microscopy, Rutherford backscattering spectrometry, and transmission electron microscopy. The results of this study, which utilized an etch‐pit technique in conjunction with the SEM, showed that a high postannealing temperature (>1000°C) was needed to effectively lower the imperfection density in the top surface region of silicon wafers. A postannealing time of 2h at a high temperature (>1000°C) was sufficient to significantly reduce the implantation damage in the top silicon surface region. Finally, in situ annealing by wafer substrate heating during oxygen ion implantation was found to be more effective than postannealing at 1000°C. A 10 μm epitaxial layer containing a low density of dislocations (about ) was able to be grown onto thein situ annealed wafers.

Relaxation of ion implant damage in silicon wafers at room temperature measured by thermal waves and double implant sheet resistance

We have detected and measured the room-temperature relaxation of ion implant damage in silicon wafers. Measured with thermal wave modulated reflectance and with double implant (i.e., damage dependent) sheet resistance the duration of the relaxation varies from as short as a few hours to as long as a few days, depending on dose and species. For dose monitoring techniques which rely on the effects of implant damage and which do not correct the relaxation effect, large errors in the measured dose values may result. We describe the thermal wave method for automatic measurement and correction for the relaxation effect, thus preserving the ability to make real-time, post-implant dose measurements with thermal wave techniques.

Nondestructive measurement of subsurface structural defects in polished single-crystal silicon

Acorrelation has been found between scattering levels measured by a new photon backscattering technique and lattice damage revealed by etching polished and ion-implanted silicon wafers. The surfaces of the wafers appeared featureless when observed by Nomarski microscopy and no roughness differences could be measured by diamond stylus profilometry before etching. Photon backscattering thus appears to provide a nondestructive method for inspecting for subsurface damage in silicon wafers. A byproduct of the study was the finding that etched, ion-implanted silicon wafers which clearly showed the imprint of the mask used for the ion implantation did not have steps or height differences between ion-implanted and untreated areas. This result indicates that the etch rate was the same for ion-implanted and untreated areas, but that the optical constants of the material appear to have changed in the implanted regions.

Nondestructive measurement of subsurface structural defects in polished single-crystal silicon

Acorrelation has been found between scattering levels measured by a new photon backscattering technique and lattice damage revealed by etching polished and ion-implanted silicon wafers. The surfaces of the wafers appeared featureless when observed by Nomarski microscopy and no roughness differences could be measured by diamond stylus profilometry before etching. Photon backscattering thus appears to provide a nondestructive method for inspecting for subsurface damage in silicon wafers. A byproduct of the study was the finding that etched, ion-implanted silicon wafers which clearly showed the imprint of the mask used for the ion implantation did not have steps or height differences between ion-implanted and untreated areas. This result indicates that the etch rate was the same for ion-implanted and untreated areas, but that the optical constants of the material appear to have changed in the implanted regions.

A New Approach to Lattice Damage Gettering

We have successfully used a Nd:YAG laser to introduce controlled amounts of lattice damage in silicon wafers. The resultant damage was found to be an effective getter for metallic impurities when applied prior to an emitter diffusion in a bipolar integrated circuit fabrication process.

The Effect of a Prior Sirtl Etch on Subsequent Thermally Induced Processing Damage in Silicon Wafers

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