Polished Silicon Wafers Research Articles

Applications of Polishing Technology Using Polymer Particles to Silicon Wafers and Quartz Crystal Wafers

This paper deals with a novel polishing technology using polymer particles. It has been proposed and developed by the authors for the purpose of solving the problems associated with polishing pads such as pad deterioration, process inconsistency and poor accuracy. Single side polishing of silicon wafers and double side polishing of quartz crystal square wafers were performed to clarify the basic characteristics of the technology. The results showed that appropriate combination of tool plate with polymer particles could greatly improve polishing characteristics. In particular, the edge profiles can be controlled to have desirable shape as well as amplitudes.

연마 Recycling 시간에 따른 콜로이드 실리카 슬러리의 안정성 및 연마속도

The stability of slurry and removal rate during recycling of colloidal silica slurry was evaluated in silicon wafer polishing. The particle size distribution, pH, and zeta potential were measured to investigate the stability of colloidal silica. Large particles appeared as recycling time increased while average size of slurry did not change. Large particles were identified by EDS (energy dispersive spectrometer) as foreign substances from pad or abraded silicon flakes during polishing. As the recycling time increased, pH of slurry decreased and removal rate of silicon reduced but zeta potential decreased inversely. Hence, it could be mentioned that decrease of removal rate is related to consumption of OH? ions during recycling. Attention should be given to the control of pH of slurry during polishing.

Frequency selective IR-filter produced by using EB-lithography

This paper reports on the fabrication of Jerusalem cross diplexer by direct write electron beam (EB) lithography followed by reactive ion etching (RIE) on a phosphorus doped polished silicon wafer substrate. Such structures can be used as frequency selective components in visible, microwave and near infra-red wavelength region. Replication of the patterns is accomplished by micron or sub-micron order mould fabricated from the silicon (Si) master. Fourier transform infra-red reflectance (FT-IR) measurements were performed to characterize the structured patterns. The spectral reflectance from these patterns clearly show a reflection dip due to surface plasmon excitation in the near infra-red wavelength at about 1.42 and 2.5 μm, respectively. Potential applications such as antireflection surface (ARS) can be realized.

CMP Pad Break-in Time Reduction in Silicon Wafer Polishing

This paper investigated the correlation between the surface conditions of the polishing pad and the break-in phenomena during silicon wafer polishing. The break-in is defined as pad conditioning to insure first polishing is consistent with second and following wafer polishing. A piezoelectric force sensor and an infrared (IR) sensor were installed on a silicon wafer polisher. The signals for friction force and temperature of the pad surface were measured simultaneously for monitoring the break-in phenomena during the polishing process. As a result of monitoring, the pad surface condition had the most significant effect on the break-in phenomena than compared to the other polishing parameters. Therefore, the control of the surface condition of the pad ensures the reduction of the break-in time during silicon wafer polishing.

252 シリコンウエハの研磨に関する研究(切削・研削・研磨加工III)

252 シリコンウエハの研磨に関する研究(切削・研削・研磨加工III)

Comparative analysis of amorphous silicon and silicon nitride multilayer by spectroscopic ellipsometry and transmission electron microscopy

Amorphous silicon (a-Si) and silicon nitride (SiN) films were prepared on polished silicon wafers by radio frequency sputtering using silicon target in argon and nitrogen plasma. The process described here is simple and well suited for fabricating multilayer structures of films with different refractive indices. Optical models were developed to analyze the spectroscopic ellipsometry data measured on the multilayer structure. The dielectric functions of amorphous silicon and silicon nitride were modeled by the Tauc–Lorentz oscillator model and by the Cauchy dispersion model, respectively. A thick a-Si layer was prepared and measured to establish appropriate initial refractive index data for evaluation of measurements on multilayer stacks. The parameters of layers with identical materials in the layer stack were coupled to decrease the number of fitted model parameters. Refractive index spectra of a-Si and SiN as well as thicknesses of the multilayer structure were calculated from one measurement. The results of the ellipsometric analysis are in good agreement with transmission electron microscopy data.

Burning conditions of non-thermal Ar-plasma at continuous and pulsed mode

A new capacitively coupling system has been developed for the plasma treatment and film coating of planar substrates. The system with a bottom rotary electrode and an upper grounded shower-type electrode can be evacuated to the basic vacuum of 10−6 Pa using a turbomolecular pump. A side load lock can be used to feed the bottom electrode by six substrates (double-side polished silicon wafer 10×10×0.6mm3) using a magnetic drive. The reactor was equipped by an RF power supply of 1 000W (13.56 MHz) operated in continuous and pulsed mode. The distance between both the electrodes can be positioned from 20mm to 60 mm. Discharge conditions of Ar-plasma have been determined with respect to the argon flow-rate (2 ÷ 50 sccm), pressure (0:5 ÷ 50Pa) and RF power of continuous (1 ÷ 300W) and pulsed (0:1 ÷ 300W) mode for two distances of the electrodes (30 and 60 mm). Processing chart pressure vs. power has been constructed in order to found out conditions for stable Ar-plasma. The stability of glow discharge was observed by phototransistor, sensitive in the range 300 ÷ 850 nm. The self-bias of the bottom electrode was monitored as a function of the RF power, flow-rate and pressure as well.

Quick-response film photodetector of high-power laser radiation based on the optical rectification effect

The efficiency of conversion of high-power laser radiation to an electric signal based on the optical rectification effect in nanographite films is studied experimentally. The amplitude of the signal is found to significantly depend on the size of the film, as well as on the length and arrangement of measuring electrodes. The maximal sensitivity of the photodetector (above 500 mV/MW at a wavelength of 1064 nm) consisting of the film with electrodes and operating without an external power supply and add-on components is shown to be achieved when the size of the film is comparable to the laser beam diameter. The sensitivity of the photodetector is studied under the condition when a nanosecond beam from a pulsed laser scans the surface of the film in two mutually perpendicular directions. The local sensitivity increases near the free ends of the photodetector. It is shown that the nanographite detector and a similar photodetector made of a polished silicon wafer have radically different parameters.

Design, modeling, fabrication and testing of a high aspect ratio electrostatic torsional MEMS micromirror

As an essential part of an optical imager project, there was the need for a very high aspect ratio MEMS optical scanning mirror (5 mm × 150 µm clear aperture), capable of a ±2° sweep at 1 kHz with an applied voltage less than 200 V. This paper reports on the design, fabrication, modeling and testing of such an electrostatically actuated MEMS mirror. Fabrication involves using a ⟨1 0 0⟩ n-type double side polished silicon wafer, along with surface and bulk micromachining techniques, to produce a mirror with nickel torsion springs and nickel electrostatic actuators. There were 8 masks and 20 processing steps required. The performance of these devices was measured and found to be within the required specifications. Analysis involved developing models to predict the dynamic behavior of these MEMS micromirrors. A basic parallel plate capacitor model was adjusted with finite element analysis to account for fringing fields. Young's modulus of the electroplated nickel was determined to be 110 GPa from a comparison of the model with the results of dynamic testing, and the residual strain test structures led to a value of 0.0029 for the residual strain. Each of these values is within the rather wide range of published values. Once these values were determined, the model agreed very well with the measurements of the dynamic angular response of the mirror.

Annealing Effects on Silicon Oxynitride Layer Synthesized by N Plasma Immersion Ion Implantation

A silicon oxynitride layer was obtained on a polished silicon wafer surface by nitrogen plasma immersion ion implantation. Oxygen is provided by the residual gas in the implantation chamber (base pressure of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$3 times 10^-5 hboxmbar$</tex> ) and is also implanted as the main impurity. As-implanted Si samples were analyzed by high-resolution Auger electron spectroscopy (AES), which indicated the formation of a <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$hboxSiO_ xhboxN_ y$</tex> layer of about 30 nm with varying <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$x$</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$y$</tex> , along the depth of the treatment layer. AES also provided concentration profiles of the implanted elements at the as-implanted stage. Annealing of samples from a batch of such oxynitrided Si samples was carried out at different temperatures ranging from 200 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$^circhboxC$</tex> to 1060 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$^circhboxC$</tex> . The AES analysis of these annealed samples indicated a significant escape of the implanted nitrogen atoms (starting already at 200 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$^circhboxC$</tex> ), but even at 1060 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$^circhboxC$</tex> , there was a very thin (about 12 nm) remaining layer of the silicon oxynitride, which is probably in crystalline form. Results from high-resolution X-ray diffraction measurements also corroborate the aforementioned results.

Diamond-like carbon films with End-Hall ion source enhanced chemical vapour deposition

A custom-designed End-Hall ion source was used to deposit diamond-like carbon (DLC) films in a plasma enhanced chemical vapour deposition (PECVD) mode. The deposition system was characterised and optimised for infrared transmission enhancement applications and large area deposition onto silicon or germanium substrates. Ion bombardment energy (in eV) on substrate was found to scale about 60% of the discharge voltage. Uniformity was about 2.5% and 5% for substrate diameters of 20 cm and 40 cm respectively. For the infrared enhancement applications the optimised ion bombardment energy was about 54 eV with a high deposition rate approximate 30 nm/min. Coating the DLC onto a single side of double-sided polished silicon wafers resulted in a transmission of 69.5% in the wavelength of about 4 μm, very close to the ideal value. Mechanical and reliability properties of the DLC films on silicon wafers were analysed at different environmental conditions. It was found that the DLC films produced in the ion source PECVD deposition system were satisfied with the requirements for the infrared transmission enhancement applications.

Study on the Mechanism of the Continuous Composite Electroplating Polishing for Silicon Wafer

The pad is one of the key factors in the chemical-mechanical planarization (CMP) process. To ensure the machining capability and the quality of workpieces, the pad must be conditioned in the process. It will cause the pad thiner, and be replaced by a new one for losing the machining capability finally. For this reason, a new method of CMP by using the continuous composite electroplating on the polishing disc is introduced. In this process, the machining ability of the pad can be ensured due to the continuous Sn-SiO2 composite electroplating. The effect of cathode current density and time of plating on the characteristics of composite coating and silica wafer are investigated. The experiment indicates that the continuous composite electroplating polishing (CCEP) is an efficiency method for polishing silicon wafer, and the surface roughness of the silicon wafer is 0.005μm

Unique commercial applications of the sol-gel process in Japan

Two unique commercial applications of the sol-gel process in Japan are presented. One application involves alkoxide-derived nanometer-sized silica particles used in the final polishing of silicon wafers for the fabrication of integrated circuits. The particles are cocoon-like in shape and have almost replaced conventional abrasives because of the advantages over spherical particles of similar size in terms of obtaining high polishing efficiency for good surface finish. The other application concerns the treatment of paper with an alkoxide solution for water repellent and oil resistance properties, which leads to new products for disposable tableware or cooking ware for microwave oven use.

Analysis of the Tribological Mechanisms Arising in the Chemical Mechanical Polishing of Copper-Film Wafers When Using a Pad With Concentric Grooves

An average Reynolds equation considering the effects of a pad’s annular grooves and surface roughness is developed in this study to examine mixed lubrication in the chemical mechanical polishing (CMP) of a copper-film silicon wafer. This equation is obtained on the basis of the principle that the pressure gradients and volume flow rates in the direction normal to the border of a groove and a plateau as well as on two sides of the border must be equal. The continuities of volume flow rates and hydrodynamic pressure on two sides of the border as well as in the direction normal to the border of a groove and a plateau are satisfied in order to develop this Reynolds equation. The removal rate model is obtained by taking the concentration of active abrasives in the slurry and the pad grooves into account. Theoretical results are also shown in order to investigate the effects of changing the groove depth and width on the removal rate and the nonuniformity of a copper-film wafer. The application of concentric grooves in general can lower the suction pressure (negative pressure) formed between the pad and the wafer, elevate the wear rate, and reduce the nonuniformity. However, the influences of the groove depth on wear rate and nonuniformity become insignificant when the depth is excessively large. The removal rate is reduced by increasing the groove width such that it finally approaches to the result of a nongrooved pad.

Effects of Suspending Abrasives on the Lubrication Properties of Slurry in Chemical Mechanical Polishing of Silicon Wafer

The lubrication properties of the slurry between the silicon wafer and the pad in chemical mechanical polishing (CMP) are critical to the planarity of the silicon wafer. Moreover, the suspending abrasives, which are contained in the slurry, have an extremely important influence on the lubrication properties of the slurry. In the CMP process of the large-sized silicon wafers, the influence of suspending abrasives on the slurry becomes more prominent. In order to explore the effects of suspending abrasives on the lubrication properties of the slurry under the light load conditions, a three-dimensional lubrication model based on the micro-polar fluid theory is developed. The effects of suspending abrasives on the fluid pressure acting on the wafer and the distribution of the slurry film between the silicon wafer and the pad are discussed.

Polishing of ILD and STI by the LHA pad

This paper examines whether a polishing pad with abrasive grain can be adapted for oxide CMP (ILD CMP and STI CMP), which is currently performed by free abrasive polishing. Using the Loosely Held Abrasive (LHA) pad that is effective in the polishing of silicon wafers, silicon oxide and silicon nitride films are polished, and the polishing selectivity and performance are investigated. In the CMP of a silicon oxide film, it is revealed that the removal rate using the combination of the LHA pad and water is 1.6 times more than that using slurry and is compatible in the almost equivalent non-uniformity within a wafer. In free abrasive polishing, the polishing selectivity of a silicon oxide film is 1.4 times that of a silicon nitride film; however, in the case of the LHA pad, it was revealed that the polishing selectivity is 10 times or more. The LHA pad, which is a polishing pad with abrasive grain, can be adapted for ILD CMP and STI CMP, and the polishing selectivity and performance is better than free abrasive polishing.

Nanofabrication of planar split ring resonators for negative refractive index metamaterials in the infrared range

Experimental nanofabrication of planar structures for one-dimensional metamaterials designed to achieve a negative effective refractive index in the mid-infrared range (5-10 micrometers) was performed. Double split ring and complementary double split ring resonators (SRR and CSRR) with square and circular geometries, were chosen to be fabricated since these are the basic building blocks to achieve a negative effective dielectric permittivity and magnetic permeability. Scanning probe nanolithography with z-scanner movement was used to fabricate straight-line and curvilinear segments with a line width of 80-120 nm. The geometries were delineated in 20 nm thin silver layers sputter-deposited on a positive photoresist substrate spin-coated on polished single crystal silicon wafers, as well as on polycarbonate slabs. The morphology of the structures was characterized by atomic force microscopy. The feature repeatibility was 60-150 nm, depending on the process conditions and the feature complexity. The nanolithographic groove depth in different samples ranged from 4 nm to 80 nm.

Precise Polishing of Silicon Wafer Using Dilute NaCl Electrolytically Reduced Water

This paper describe precision polishing of the silicon wafer using dilute NaCl electrolytically reduced water, instead of conventional polishing with slurry which is environmental load increase and cost overrun. First, by the comparative experiment about the etching operation of electrolytically reduced water, NaOH solution and pure water to the surface of silicon wafer, it clarified the etching performance of electrolytically reduced water. Next, it experimented in the polish about the wafer which has oxide film (SiO2) and the wafer which removed oxide film (SiO2) by HF. It clarified the polishing characteristic of silicon wafer when using electrolytically reduced water by the experimental results. Moreover, when using electrolytically reduced water as polish solution, it clarified relation between the removal rate and polishing condition of the silicon wafer. It proved that electrolytically reduced water didn't have a bad influence on the polish pad last. By the result of this research, it proved that dilute NaCl electrolytically reduced water had an enough performance as the polishing solution of the silicon wafer.

Development of an Evanescent Light Measurement System for Si Wafer Microdefect Detection

In order to reduce and control yield loss in the fabrication process of next generation ULSI devices, nano-defects inspection technique for polished Silicon (Si) wafer surface becomes more essential. This paper discusses a new optical nano-defects detection method, which is applicable to silicon wafer surface inspection for next-generation semiconductors. In our proposed method, the evanescent light is emerged on the wafer surface with total internal reflection (TIR) of infrared (IR) laser at the Si-air interface. By scanning the surface where the evanescent light is emerging with a very shaped fiber probe, it enables to detect nanometer scale defects in the vicinity of Si wafer surface without diffraction limit to resolution. To experimentally verify the feasibility of this method, an evanescent light measurement system was developed and several fundamental experiments were performed. The results show that the proposed Si wafer microdefects detection method can detect the microdefect with 10nm scale on and beneath the surface based on evanescent light distribution.

Effect of emitter deposition temperature on surface passivation in hot-wire chemical vapor deposited silicon heterojunction solar cells

Low substrate temperature (< 150 °C) during initiation of amorphous silicon emitter deposition by hot-wire chemical vapor deposition is found to be crucial for reaching high open-circuit voltage ( V oc) in an amorphous/crystalline silicon (a-Si/c-Si) heterojunction solar cell. Low-temperature results in immediate a-Si deposition and a smooth interface to the c-Si substrate. The smooth heterojunction leads to effective passivation of the c-Si surface by the a-Si intrinsic layer through a much-reduced interface recombination velocity, and V oc is consistently above 620 mV. We obtain a V oc above 640 mV and a fill factor of 80% on Al-backed p-type Czochralski wafers with emitters deposited at temperatures below 135 °C. Energy conversion efficiencies of 14.8% and 15.7% are obtained on a polished p-type Czochralski silicon wafer and a polished p-type float-zone silicon wafer, respectively.