Silicon Surface Quality Research Articles

Improving monocrystalline silicon surface quality with chemical mechanical polishing using the slurry with the additive of isopropanol

Enhancing the silicon surface smoothness with chemical mechanical polishing (CMP) is crucial to achieve better beam quality in X-ray systems. The additive in CMP slurry is the key factor in determining the resulting surface morphology. This paper exploits the effect of isopropanol (IPA) additive on regulating the material removal process and resulting microscopical surface morphology through varying the IPA concentration and polishing pressure. The improvement of surface quality and a dropping material removal rate (MRR) are obtained by increasing the IPA concentration from 0.1 to 2.5 mol/L. When the polishing pressure increases from 0.25 to 0.48 psi, a better surface quality and enhanced MRR are observed. By using the optimal polishing pressure of 0.48 psi and IPA concentration of 2.5 mol/L, the root-mean-square roughness can be reduced to 0.10 nm under a measurement area of 1 µm × 1 µm with atomic force microscopy, more than 58.3% lower compared to surfaces polished without IPA. This work suggests an approach to obtain the ultra-smooth silicon mirrors, which has promising applications in the field of X-ray, aerospace, and photovoltaics.

Study on surface integrity and ductile cutting of PV polycrystalline silicon and wear mechanisms of electroplated diamond wire

This study aimed to evaluate and better understand the mechanical and crystalline responses of polycrystalline silicon sawn by diamond wire sawing. To simplify the multi-wire sawing kinematic, an endless wire saw with a single looped diamond wire welded was used. The wire cutting speed and feed rate were varied in order to evaluate the characteristics of surface morphology, surface roughness, and subsurface damage. The analysis of brittle-ductile transition and residual stress of the sawn surface and silicon chips were performed with Raman spectroscopy. The wear and failure mechanism of the diamond wire were analyzed. The results showed that sawn surface is composed of brittle and ductile regions and the predominance of one of these directly affected the surface roughness Ra. The ductile cutting mode induced the predominance of microgrooves and ploughing over the sawn surface and led to formation of an amorphous layer with residual compressive stress around of − 192.3 MPa. Micro-cracks in subsurface were identified and it reached a minimum depth of 7.2 ± 1.6 µm. Chip fragments and elongated chips were observed and latter is practically amorphous. The wire wear analysis indicated that during the cutting there is deformation of the Ni-layer, exposed grits, and grit pullout. The main wear mechanisms are Ni-matrix removal and abrasive wear of the diamond grit. A better surface quality of polycrystalline silicon was obtained on increasing wire cutting speed and decreasing feed rate. Thus, the looped diamond wire sawing allows to reach a high surface quality of the silicon wafer, since the material removal occurs more in ductile cutting mode, generating a smooth surface with shallow subsurface damage.Graphical abstract

Investigation of the effect of chemical pre-treatment on uniformity of the silicon wafer texturing for manufacturing a solar cell

The role of chemical pre-treatment on silicon surface quality and texturing uniformity was investigated. It was shown that for better uniformity of texturing the initial silicon surface of as-cut slurry sawed wafer should be treated to clean up from organic and metal contaminations followed by the organic solvent traces removing and saw damaged silicon layer etching. Additional measurements of photoluminescence decay confirmed high quality and uniformity of textured wafers passivated by a-Si:H.

Communication—In-Line Detection of Silicon Surface Quality Variation Using Surface Photovoltage and Room Temperature Photoluminescence Measurements

Occasionally, in volume device manufacturing, a large number of particles may be generated on cleaned Si wafers. Surface (ionic, organic and/or metallic) contamination is generally suspected. However, conventional chemical analysis techniques for contamination are generally not able to distinguish between Si wafers with good and poor particle performance. No suspicious chemicals and elements were detected from any wafers regardless of characterization techniques. Surface photovoltage (SPV) measurement barely showed the differences between wafers with good and poor particle performance. Multiwavelength room temperature photoluminescence (RTPL) showed significant differences in intensity between them, indicating the presence of surface quality variations.

Study of multi-cutting by WEDM for specific crystallographic planes of monocrystalline silicon

In this study, multi-cutting technology by wire electrical discharge machining (WEDM) for metal material processing is applied to cut semiconductor monocrystalline silicon with specific crystal orientation, which is to improve the surface quality and machining accuracy of single-crystal silicon with specific crystal orientation. First, the deterioration layer thickness of silicon wafer surface and the discharge gap under different discharge energy values are analyzed to determine the reasonable trim cutting values of multiple cutting. The effects of multiple cutting on the surface quality of silicon and crystal orientation accuracy are also studied. Results show that multi-cutting technology by WEDM can significantly improve the surface quality of silicon, with few surface cracks and low deterioration layer thickness. Processing the same quality surface under experimental conditions, multiple cutting obtained sixfold efficiency of single cutting. Furthermore, this technology can significantly reduce the orientation error band and error fluctuations as well as improve surface crystallographic orientation precision of silicon wafer when cutting silicon wafers with high thickness.

Strong opto-electro-mechanical coupling in a silicon photonic crystal cavity.

We fabricate and characterize a microscale silicon opto-electromechanical system whose mechanical motion is coupled capacitively to an electrical circuit and optically via radiation pressure to a photonic crystal cavity. To achieve large electromechanical interaction strength, we implement an inverse shadow mask fabrication scheme which obtains capacitor gaps as small as 30 nm while maintaining a silicon surface quality necessary for minimizing optical loss. Using the sensitive optical read-out of the photonic crystal cavity, we characterize the linear and nonlinear capacitive coupling to the fundamental ω(m)/2π = 63 MHz in-plane flexural motion of the structure, showing that the large electromechanical coupling in such devices may be suitable for realizing efficient microwave-to-optical signal conversion.

Solar Cell Fabrication by Wet Etching Combined with Ultrasonic Vibration for Multicrystalline Silicon

With the development of economy and society, more and more energy is needed to meet the requirement of industries and social life. It is necessary to find new types of energy that is clear, high effective and non-polluted. Although wet etching is widely used in industries to prepare the silicon surface texture, the etching process is stochastic and the influence light trapping. Many efforts have been made such as adjusting the proportion of different acids, to improve the quality of silicon surface by wet etching, the result does not meet the ideal requirement by now. In this paper, a new approach is presented to prepare the surface texturing. By combining wet etching and ultrasonic vibration, the sodium or acid molecular motion can be controlled, and the pyramid structure in silicon surface can be made regular.

Solar Cell Surface Texturing Combined Wet Etching and Ultrasonic Vibration

With the development of economy and society, more and more energy is needed to meet the requirement of industries and social life. It is necessary to find new types of energy that is clear, high effective and non-polluted. Although wet etching is widely used in industries to prepare the silicon surface texture, the etching process is stochastic and the influence light is trapping. Many efforts have been made, such as adjusting the proportion of different acids, to improve the quality of silicon surface by wet etching, the effectiveness is still limited. In this paper, a new approach is presented to prepare the surface texturing. By combining wet etching and ultrasonic vibration, the sodium or acid molecular motion can be controlled, and the pyramid structure in silicon surface can be made regular.

Application of Surfactant in Si CMP Processing

With the rapidly developing of ULSI fabrication technique to high integration and low cost, the key technology is how to ensure the higher flattening, lower roughness and lower cost. The chemical mechanical polishing (CMP) method is the best one for global planarization. In this paper, the CMP mechanism process of silicon wafer was analyzed, and it was pointed that chemical reaction was the kinetics control process. The influence of surfactant on silicon surface quality during CMP process was also discussed, and the contrast experiments were processed. SiO2 was selected as abrasive, which particle size was 40nm. And the polishing temperature was 25°. At the end of silicon CMP, the water polishing was processed using de-ionized water with surfactant, and the optimal surface was gotten, and the surface roughness was 0.5nm.

Fabrication and Characterization of Uniform Quantum Size Porous Silicon

Porous silicon layer microstructure is sensitive to many parameters which need to be controlled during etching. These include not only anodization time, current density and applied potential but also electrolyte composition. Careful control these parameters will yield excellent reproducibility from run to run. In this paper we outline the advances in porous silicon surface quality and uniformity by recent techniques that have made the production of uniformly sized silicon nanocrystallites possible. In this work we used the oxidant H2O2 in the wet etching bath, with a high etching current. The resulting technique greatly improves the uniformity of the porous surface, producing a very thin layer of porous silicon. This is a significant improvement to the previous method. The result of a combined study of FTIR spectra and photoluminescence show that both quantum confinement and surface passivation are responsible of blue shift of the luminescence peak.

Investigation of electrodischarge micromachining controllable factors on machined silicon surface quality

Electrodischarge micromachining (micro-EDM) is a prospective technology for the micromachining of conductive and even semi-conductive materials. However, there remain a number of application problems, particularly in relation to the understanding and control of the effect of micro-EDM controllable factor interaction on surface integrity in machining silicon. This study investigates the effect of the interaction of micro-EDM parameters, such as the rotary action of the tool electrode and discharge energy levels, on the surface integrity of a p-type boron-doped silicon wafer. Empirical models are formulated that adequately describe the effects of discharge energy on the average surface roughness and the area fraction voids. Subsequently, the nature and causes of micro-EDM surface and subsurface characteristics are discussed on the basis of scanning electron microscope and X-ray energy dispersive spectrometer analysis. This provides useful information for controlling the input process parameters to obtain smooth finished surfaces.

Monitoring and Optimization of Silicon Surface Quality

We have used contactless photoconductance decay measurements to monitor cleaning processes, surface contamination, and surface roughness. Changes in surface chemistry are evidenced by a degradation (increase) in the surface recombination velocity (decrease in measured decay time). We have applied the tool to monitor cleaning effectiveness, surface cleanliness, and roughness during cell processing. Iodine in methanol achieves a superior passivation of Si than H in 48%. The measured minority carrier lifetime in this solution is higher than in 48% . We illustrate that I‐terminated silicon surfaces are more stable than H‐terminated surfaces. We confirm that deionized water is responsible for the roughening of silicon surfaces. We show that is a superior alternate clean to dilute .

X-ray photoelectron spectroscopy studies of contamination and cleaning of surfaces exposed to a fluorocarbon plasma

A reactive ion etching (RIE) with a mixture of fluorocarbon gases is used to etch selectively SiO2 patterns on Si wafer. X-ray photoelectron spectroscopy (XPS) measurements were carried out to determine the walls contamination of the reactor with different cathode coatings like Al, Si, and photoresist. The contamination of different wafers (SiO2, Si with and without resist) following RIE processes was also studied in order to understand the mechanism of the selective etching. Then different cleaning processes, in particularly NF3 and O2 plasmas followed or not by a hydrophilic treatment, were also qualified by XPS. For every sample, the Al(2p) or Si(2p), C(1s), O(1s), and F(1s) photoelectron lines were monitored and concentrations determined as usual by integration of these lines. F(1s) and C(1s) were decomposed into several components corresponding to different chemical bonds. The results show that the contamination of the reactor walls by fluoropolymers is due to the presence of Si or of the photoresist on the cathode; there is no polymer formation with an Al cathode coating. The polymer contamination on the reactor walls is cleaned off by an O2 plasma and the residual fluorine forms a passivative layer with the Al of the reactor walls. During the plasma etching of a SiO2 film, there is formation of C–Si, C–C, O–Si–F, F–Si bonds but it is only when there is no oxygen left that CFx bonds are formed. These polymer layers stop the etching process on silicon. They are cleaned by O2 or NF3 plasma, but the latter removes the polymers without increasing the oxygen, fluorine or nitrogen contamination and appears to be most appropriate for improving the surface quality of silicon after fluorocarbon plasma etching.

Surface damage and the optical reflectance of single-crystal silicon

The reflectance of silicon measured at 4.3 eV can be used to determine the surface quality of silicon. Crystallographic damage, which occurs with abrasive polishing, and texture, which occurs with epitaxial film growth, can be detected. The effect of surface damage on the optical reflectance of silicon measured at 4.3 eV is reported. The reflectance measurement is nondestructive, simple, fast (on the order of seconds), and sensitive. The technique is readily adaptable to quality control inspection in silicon device manufacturing facilities.