Blank Wafer Research Articles

Repeatability and sensitivity of quartz crystal microbalance (QCM) sensor array modified with four sensitive materials

With continuous expansion of livestock and poultry breeding industry, the emission of harmful gases has inevitably increased which has also prompted the rapid development of research on harmful gases detection, such as quartz crystal microbalance(QCM)sensors. In this research, a gas-sensing system based on QCM sensor array modified with ethyl cellulose (EC), polyethyleneimine (PEI), tetramethylammonium fluoride tetrahydrate (TMAF), and polypyrrole (PPy) was established to detect three standard harmful gases, namely CO2, NH3, and H2S. It has been observed that the QCM sensors modified with four materials had a good repeatability and a significant response to the three standard harmful gases. Furthermore, the suitable concentrations of the sensitive materials were 20 mg/ml for EC, 10 mg/ml for TMAF, 35 mg/ml for PEI, and 7 mg/ml for PPy. The frequency shift resulted by modified mass of the sensors for the four materials with the best concentrations were 21,343.1 Hz for EC, 21,065.5 Hz for TMAF, 2736.9 Hz for PEI, and 5292.4 Hz for PPy. Additionally, there was a linear relationship between the frequency shift and the concentration of three sample gases in different ranges with a high linear fit coefficient (R2>0.92), except TMAF versus CO2. Moreover, R2 with blank quartz wafer compensation was slightly smaller than which one without compensation. Therefore, the gas-sensing system based on QCM sensor array has an ideal repeatability and recovery response to the three standard gases, and the sensitivity performance was good. This work provides basic information for the research on QCM sensor array in gas detection.

Selective etching of silicon nitride over silicon oxide using ClF3/H2 remote plasma

Precise and selective removal of silicon nitride (SiNx) over silicon oxide (SiOy) in a oxide/nitride stack is crucial for a current three dimensional NOT-AND type flash memory fabrication process. In this study, fast and selective isotropic etching of SiNx over SiOy has been investigated using a ClF3/H2 remote plasma in an inductively coupled plasma system. The SiNx etch rate over 80 nm/min with the etch selectivity (SiNx over SiOy) of ~ 130 was observed under a ClF3 remote plasma at a room temperature. Furthermore, the addition of H2 to the ClF3 resulted in an increase of etching selectivity over 200 while lowering the etch rate of both oxide and nitride due to the reduction of F radicals in the plasma. The time dependent-etch characteristics of ClF3, ClF3 & H2 remote plasma showed little loading effect during the etching of silicon nitride on oxide/nitride stack wafer with similar etch rate with that of blank nitride wafer.

Anodically Bonded Photoacoustic Transducer: An Approach towards Wafer-Level Optical Gas Sensors.

We present a concept for a wafer-level manufactured photoacoustic transducer, suitable to be used in consumer-grade gas sensors. The transducer consists of an anodically bonded two-layer stack of a blank silicon wafer and an 11 µm membrane, which was wet-etched from a borosilicate wafer. The membrane separates two cavities; one of which was hermetically sealed and filled with CO2 during the anodic bonding and acts as an infrared absorber. The second cavity was designed to be connected to a standard MEMS microphone on PCB-level forming an infrared-sensitive photoacoustic detector. CO2 sensors consisting of the detector and a MEMS infrared emitter were built up and characterized towards their sensitivity and noise levels at six different component distance ranging from 3.0 mm to 15.5 mm. The signal response for the sample with the longest absorption path ranged from a decrease of 8.3% at a CO2 concentration of 9400 ppm to a decrease of % at a concentration of 560 ppm. A standard deviation of the measured values of 18 ppm was determined when the sensor was exposed to 1000 ppm CO2.

Vertically Aligned n-Type Silicon Nanowire Array as a Free-Standing Anode for Lithium-Ion Batteries.

Due to its high theoretical specific capacity, a silicon anode is one of the candidates for realizing high energy density lithium-ion batteries (LIBs). However, problems related to bulk silicon (e.g., low intrinsic conductivity and massive volume expansion) limit the performance of silicon anodes. In this work, to improve the performance of silicon anodes, a vertically aligned n-type silicon nanowire array (n-SiNW) was fabricated using a well-controlled, top-down nano-machining technique by combining photolithography and inductively coupled plasma reactive ion etching (ICP-RIE) at a cryogenic temperature. The array of nanowires ~1 µm in diameter and with the aspect ratio of ~10 was successfully prepared from commercial n-type silicon wafer. The half-cell LIB with free-standing n-SiNW electrode exhibited an initial Coulombic efficiency of 91.1%, which was higher than the battery with a blank n-silicon wafer electrode (i.e., 67.5%). Upon 100 cycles of stability testing at 0.06 mA cm−2, the battery with the n-SiNW electrode retained 85.9% of its 0.50 mAh cm−2 capacity after the pre-lithiation step, whereas its counterpart, the blank n-silicon wafer electrode, only maintained 61.4% of 0.21 mAh cm−2 capacity. Furthermore, 76.7% capacity retention can be obtained at a current density of 0.2 mA cm−2, showing the potential of n-SiNW anodes for high current density applications. This work presents an alternative method for facile, high precision, and high throughput patterning on a wafer-scale to obtain a high aspect ratio n-SiNW, and its application in LIBs.

Investigation of Post-Bond Distortion in Direct Wafer Bonding

As device sizes continue to shrink, accurate alignment in semiconductor wafer bonding process becomes more important. In the case of two patterned wafers directly bonded together, proper alignment of the electrical connections between the two bonding surfaces is critical. Misalignment between the wafers during bonding may lead to degraded electrical performance or even device failure. In the case of a patterned wafer directly bonded onto a blank carrier wafer, the relative displacement along the bonded interface is important for subsequent steps. This relative displacement contributes to overlay error in lithography steps. Furthermore, as device density continues to increase, pre-bond wafer shapes become more complex while warp magnitude increases. The distortion contribution from pre-bond wafer shapes becomes more significant as a result. Therefore, it is important to understand the direct wafer bonding distortion mechanics to reduce the yield impact of the process.This paper develops a mechanics model to study wafer bonder performance. An axisymmetric solid mechanics model simulates the wafer bonding dynamics by using a rate-dependent adhesion model. This simulation model includes calibration parameters to tune against experimental results. Using the optimized calibration parameters, an extended 3D simulation model studies more complex phenomena. This paper will report the simulation results that include local variations in wafer properties, clamping and thermal fluctuation effects. Distortion impact due to pre-bond wafer shapes, such as the relative contributions from the pre-bond wafer pair, is also discussed.The results of this model can enable improved hardware optimization to address stricter distortion requirements. This model can optimize key hardware features in lieu of large number of wafer tests to minimize the cost of development. Using this model, target performance can be achieved with fewer hardware iterations and reduce development time. Bonder recipes can also be designed and optimized to account for pre-bond wafer characteristics.

Optimizing the Within Wafer Non-Uniformity at the Chemical Mechanical Planarization step in Interposers and RDL fabrication process for 3D IC stacking

Abstract Chemical Mechanical Planarization (CMP) is an integral step in fabrication processes of through silicon via based Interposer and Redistribution layer for routing. The key motivation in the CMP process is to achieve planarization with minimum recess and dishing on the metal routing sites. In this work we established the metrics for Within-wafer non-uniformity (WIWNU) and optimized the CMP parameters. Currently, there is no standard guideline for reporting the WIWNU during CMP and thus a better understanding and practice is needed to enhance post CMP uniformity across the wafer. The work reported in this article were conducted on 200 mm silicon wafers with either Copper or Tungsten to optimize the uniformity of removal rate with respect to polishing parameters, such as slurry flow, slurry composition, down force, relative velocity of wafer surface with pad, etc. With optimized CMP parameters for blank wafer, the WIWNU in patterned wafer were evaluated and analyzed for additional optimization in non-uniformity.

Biodegradable wafers releasing Temozolomide and Carmustine for the treatment of brain cancer

Glioblastoma multiforme (GBM) has few clinically approved therapeutic regimens. One of these therapeutic options includes placing biodegradable wafers releasing BCNU (Gliadel®) into the tumor bed at the time of surgical removal of the tumor. Due to the significant benefit this polymer technology has had clinically, we have prepared wafers releasing Temozolomide (TMZ), an anticancer drug used systemically for treating GBM. TMZ delivered via polymer wafer could be used as a complementary treatment with or as an alternative to Gliadel®. TMZ is an alkylating agent which is water soluble. To remain comparable with the preclinical studies that led to Gliadel® the same size of wafers were formulated with TMZ. Wafers were loaded with 50% w/w TMZ in poly(lactic acid-glycolic acid) (PLGA) and showed reliable release of high dose TMZ for a period of 4 weeks. To achieve this 30-day release of the highly water soluble drug, we developed an encapsulation method, where the drug powder was first coated with the polymer to form core-shell particles in which the coating shell served as a rate controlling membrane for the drug particles. Wafers were also made with a co-loading of TMZ and BCNU. All wafers were tested in vivo by treating an intracranial 9 L gliosarcoma model in F344 rats. Rats that were either untreated or treated with blank wafer died within 11 days while the median survival for rats treated with systemic TMZ was 18 days. The group that received the BCNU alone wafer had a median survival of 15 days, the group that received the TMZ wafer alone had a median survival of 19 days, and the group treated with the BCNU-TMZ wafer had a median survival of 28 days with 25% of the animals living long term (p < .0038 vs. Control; p < .001 vs. Blank Polymer). These findings demonstrate the potential of this newly designed wafer for treating GBM. Moreover, this concept, can pave the way for other drug combinations that may improve the clinical application of numerous agents to treat solid tumors.

Re-installation of the total reflection X-ray fluorescence spectrometer ATOMIKA 8300W for Si wafer surface inspection at Atominstitut

Total reflection X-ray fluorescence (TXRF) is ideally suited for the inspection of silicon wafer surfaces in the ultra trace regime. Detection limits in the range of 1010 atoms⋅ cm−2 for metals are achievable by straight TXRF. The determination of surface contaminations on silicon wafers is of great importance to the semiconductor industry as the purity of the wafers has a direct impact on the quality and yield of the end product. The ATOMIKA 8300W spectrometer can perform a position sensitive analysis and thus provide data which can be used to track down the source of the contamination and possibly improve the manufacturing process. The quantification procedure uses an external standard technique and is described in detail.To bring the spectrometer back into operation, the functionality of its components had to be checked and most importantly a new reference wafer had to be prepared and validated. This was done by intentionally contaminating a blank wafer with a known amount of a certified nickel standard. The new reference wafer was then validated by using it to analyze and quantify blank wafers contaminated with a known quantity of the CRM NIST 1640. The achieved detection limit for nickel is comparable to results previously recorded using the ATOMIKA 8030W spectrometer. The 8300 W spectrometer was successfully put into operation and shows satisfactory reproducibility data, allowing the use in an accredited laboratory.

Surface modification of silicon wafer by grafting zwitterionic polymers to improve its antifouling property

Silicon (111) wafer was modified by triethoxyvinylsilane containing double bond as an intermedium, and then P4VP (polymer 4-vinyl pyridine) brush was “grafted” onto the surface of silicon wafer containing reactive double bonds by adopting the “grafting from” way and Si-P4VP substrate (silicon wafer grafted by P4VP) was obtained. Finally, P4VP brush of Si-P4VP substrate was modified by 1,3-propanesulfonate fully to obtain P4VP-psl brush (zwitterionic polypyridinium salt) and the functional Si-P4VP-psl substrate (silicon wafer grafted by zwitterionic polypyridinium salt based on polymer 4-vinyl pyridine) was obtained successfully. The antifouling property of the silicon wafer, the Si-P4VP substrate and the Si-P4VP-psl substrate was investigated by using bovine serum albumin, mononuclear macrophages (RAW 264.7) and Escherichia coli (E. coli) ATTC25922 as model bacterium. The results showed that compared with the blank sample-silicon wafer, the Si-P4VP-psl substrate had excellent anti-adhesion ability against bovine serum albumin, cells and bacterium, due to zwitterionic P4VP-psl brush (polymer 4-vinyl pyridine salt) having special functionality like antifouling ability on biomaterial field.

Study of a silicon/glass bonded structure with a UV-curable adhesive for temporary bonding applications

This paper concerns the study of a temporary bonding process: 3MTM Wafer Support System. This process is dedicated to the handling of thin silicon wafers with a glass carrier bonded with a UV curable polymer. The dismounting process is achieved after a laser treatment. Firstly, the 300mm bonding process leads to a very homogeneous bonded structure without any bonding defects. The morphology of the bonded structure is mainly dependent of the morphology of the glass. Secondly this process is also compatible with a back – grinding process and the thinned silicon structure can be processed up to 250°C. When using a blank silicon wafer, the 3MTM dismounting process (laser and peeling) leads to a silicon thin wafer without any cracks, chippings or adhesive traces. Finally the laser process can be removed from the debonding steps and a single mechanical dismounting process can be used.

Comprehensive understanding of chamber conditioning effects on plasma characteristics in an advanced capacitively coupled plasma etcher

An advanced capacitively coupled plasma etcher with two frequencies and additional direct current is characterized with complementary sensors. Due to the restrictive boundary conditions of the manufacturing environment, which the authors had to take into account, applicable plasma sensors are limited. Thus, the plasma parameters depending on the center, wall, sheath, and cathode regions are extracted separately based on the tool parameters, optical emission spectroscopy, and self-excited electron spectroscopy. One main target of this investigation is a cross verification of complementary sensor data and a deeper understanding. Due to the complex chamber setup, the authors use a chemically simple system of an Ar plasma with a blank Si wafer as the substrate. It is found that the removal of SiO2 and sputtering Si from the cathode and wafer changes the chamber condition and thus causes changes in the plasma characteristics. The established plasma process model comprises a change in secondary electron emission caused by changing the surface condition and a subsequent change in collisionless electron heating, in particular, in the case of applied low frequency power. Current electron heating models and conditioning models are used for cross verification of the plasma process model. It indicates that both chemical and electrical aspects to chamber conditioning should be considered in multiple frequency driven plasma etchers. The results presented in this paper are expected to contribute to the understanding of the interaction of the chamber conditioning effects and plasma parameters in advanced plasma etchers for sub-20 nm devices.

Enhancing re-detection efficacy of defects on blank wafers using stealth fiducial markers

To qualify tools of semiconductor manufacturing, particles unintentionally deposited in these tools are characterized using blank wafers. With fast optical inspection tools one can quickly localize these particle defects. An example is TNO's Rapid Nano, which operates in optical dark field. The next step is defect review for further defect characterization. When the blank wafers are transferred to another tool, e.g. a SEM or an AFM the absolute defect position information is lost. Therefore, the re-detection of the defects in the review tool is time consuming. To enhance the re-detection speed, a fiducial marker system can be used that couples the coordinates of the fast inspection tool to the coordinates of the characterization (review) tool.In this work such a fiducial marker system was designed and validated. The influences of the height and the composition of the fiducial markers on the performance of the marker system were investigated using finite element analysis (by COMSOL) and experiments. The optimized fiducial markers are very visible in optical bright field and in SEM, while almost invisible (“stealth”) in optical dark field. These properties make the markers both easily visible and accurately localizable in the characterization tools. The stealth fiducial marker system was fabricated and validated by re-detecting programmed test defects on a blank wafer. The experimental results are compared to a Monte Carlo simulation that takes into account the uncertainties in the coordinate transformation and localization of the test defects.Our results show that a fiducial marker system greatly enhances the re-detection efficacy of defects on blank wafers. Using the fiducial marker system, 100% of the test defects were re-detected in SEM and AFM. A single 7×7μm2 SEM image suffices to meet the ITRS requirement for particles as small as 70nm in diameter.

The analysis of warpage in wafer-level compression molding

Advanced 3D MEMS packaging technologies involving the encapsulation of devices at wafer-level are being developed in order to achieve further minimization and cost reduction of consumer electronic devices. Compression molding using epoxy molding compounds is one technique being considered for wafer-level encapsulation. Excessive out-of-plane deformation has been reported in wafer-level compression molding trials using blank wafers which would negatively impact device reliability and the implementation of successive processes to the molded wafer. This paper presents finite element models of the molded wafer, with and without embedded dies which simulate the observed multi-state warpage characteristics. Molded wafer warpage measurements were also carried out in order to verify the applicability of the small and large deformation theories for layered plates and to verify the finite element model of the molded blank wafer. Possible factors (non-planar mold layer thickness and anisotropic wafer elastic properties) leading to asymmetric warpage in molded blank wafers were also investigated. From the molded wafer model with embedded dies the effects of flip-chip die dimensions and wafer thickness on the out-of-plane deformation together with possible reliability issues were analyzed.

Fabrication of novel hybrid antireflection structures for solar cells

In solar cell technology, surface texturing is essential for reducing the reflectance of cell surfaces and increasing their efficiency. This study employs photo-assisted electrochemical etching (PAECE) to fabricate a hybrid structure comprising a reversed pyramid structure and a high aspect ratio macro-pore on the silicon wafer surface, to reduce cell surface reflectance. The experimental results show that the etching depth of the fabricated macro-pore array structure was approximately 67.1μm and its diameter was approximately 5μm on the 525-μm-thick sample, such that the aspect ratio of the pore was approximately 13.4:1. The mean reflectance of a blank silicon wafer is 37.4% in the wavelength range of 280–800nm; however, the reversed pyramid created using a 120-min PAECE process and 25-min RIE can reduce the mean reflectance to 0.7% on the 380-μm-thick sample. The novel fabrication process developed in this study is low cost and the hybrid structure can be applied to antireflection structures in single crystalline silicon solar cells.

Chemical mechanical planarization of Ge2Sb2Te5 using IC1010 and Politex reg pads in acidic slurry

In the paper, chemical mechanical planarization (CMP) of Ge2Sb2Te5 (GST) is investigated using IC1010 and Politex reg pads in acidic slurry. For the CMP with blank wafer, it is found that the removal rate (RR) of GST increases with the increase of pressure for both pads, but the RR of GST polished using IC1010 is far more than that of Politex reg. To check the surface defects, GST film is observed with an optical microscope (OM) and scanning electron microscope (SEM). For the CMP with Politex reg, many spots are observed on the surface of the blank wafer with OM, but no obvious spots are observed with SEM. With regard to the patterned wafer, a few stains are observed on the GST cell, but many residues are found on other area with OM. However, from SEM results, a few residues are observed on the GST cell, more dielectric loss is revealed about the trench structure. For the CMP with IC1010, the surface of the polished blank wafer suffers serious scratches found with both OM and SEM, which may result from a low hardness of GST, compared with those of IC1010 and abrasives. With regard to the patterned wafer, it can achieve a clean surface and almost no scratches are observed with OM, which may result from the high-hardness SiO2 film on the surface, not from the soft GST film across the whole wafer. From the SEM results, a clean interface and no residues are observed on the GST surface, and less dielectric loss is revealed. Compared with Politex reg, the patterned wafer can achieve a good performance after CMP using IC1010.

Dummy Poly Removal Impact Factors and Improvement in Hkmg Last Process

For 20/16nm HK-last and MG-last process, Dummy poly is removed by Wet process. This paper studies the factors impacting the dummy poly removal process, and presents some models to explain the impacting factors. Implant process is one of main factors influencing dummy poly removal capability because the differences of implant ions and doping amount into dummy poly induce difference of poly removal rate by wet process. We also study poly surface single clean, multiple clean and thermal process. Based on the model, we plan N-type doping poly and P-type doping poly with different ion doping amounts on blank wafer and 20nm structure wafers to evaluate dummy poly removal. We find dummy poly removal rate is different between N-type doping poly and P-type doping poly, and receive different dummy poly removal trend by ion amount on N-type doping poly and P-type doping poly. The model can help to improve dummy poly removal process control.

Fabrication of Perforated Micro/Nanopore Membranes via a Combination of Nanoimprint Lithography and Pressed Self-Perfection Process for Size Reduction

Artificial membranes with perforated nanopores in defined locations provide an important biomimicking platform for sensing and analysis of biomolecules. This study presents a simple and flexible method to fabricate a freestanding polymer membrane with perforated micro- and nanopores using a combination of nanoimprint lithography (NIL) and pressed self-perfection (PSP) process. NIL was used to define initial pores of a few micrometers in diameter in the SU-8 membrane layer, which was followed by the PSP process where the patterned SU-8 membrane is pressed with a blank silicon wafer at an elevated temperature. This PSP process results in a lateral flow of the SU-8 resist and consequently reduces the pore size in the membrane. With this method, we have demonstrated fabrication of a SU-8 membrane with perforated pores down to approximately 300 nm in diameter. The results indicate that by employing a pore reduction process nanopore membranes can be manufactured without requirements of having a stamp with nanoscale structures and high aspect ratio imprinting with the stamp.

Impact of the phase defect structure on an actinic dark-field blank inspection signal and wafer printability

In extreme ultraviolet lithography, reducing the number of phase defects (PDs) on mask blanks is a critical issue because the PDs cause degradation of the printed pattern quality. To minimize the number of printable PDs, covering PDs beneath an absorber pattern is an effective way of addressing the problem. Therefore it becomes necessary to detect the PDs and pinpoint their locations by a blank inspector. In this work, a three-dimensional analysis of PDs has revealed that some PDs can grow and propagate in an angular direction away from the normal to the substrate surface. The impact of the inclination angle on the printing performance was evaluated by calculating printed pattern images using a simulator. A PD with an inclination angle of 1 deg corresponds to a 1-nanometer positional shift compared with a position defined as surface topography of a defect as observed by an atomic force microscope or by some nonactinic defect inspector. However, an actinic blank inspection (ABI) tool with high-magnification optics can pinpoint the actual location of the PDs. Covering a PD under an absorber pattern, by a shifting of the pattern based on the information of the PD’s location obtained by the ABI tool, works quite well.

Wafer Bonding for Backside Illuminated Image Sensors

Backside illuminated image sensors combine small pixel area with high signal-to-noise ratio. Wafer bonding is a key enabling process step for manufacturing of backside illuminated image sensors. The fully CMOS processed image sensor wafer is bonded to a blank silicon carrier wafer and then back thinned to reveal the photodiodes. As a result the photodiodes are on top of the metal interconnects thereby eliminating any shading of the photosensitive area. Plasma activated fusion wafer bonding enables a room temperature wafer bonding with highest wafer-to-wafer alignment accuracy.

Active Area Width and Topography Effects on Sub 45nm Poly Gate CD

Gate critical dimension (CD) is an important parameter in determining the CMOS device performance. During the process of aggressive feature size shrinking in 45nm node and beyond, aside from the recognized topographical impact on the wafer-to-wafer CD variation, the active area (AA) width has to be taken into consideration for the thorough analysis and the rigid control of within-wafer gate CD variation. Roughly 5%~8% within-wafer CD difference was observed on six gate structures (the same defined gate with different AA widths) right after the gate etch. Both topography wafer and blank wafer (deposited merely with gate oxide plus poly-Si) were utilized to identify the potential key contributors to such within-wafer CD variation. Results demonstrate that the shallow trench isolation (STI) step height, one of notorious topography factors, heavily relies on the local AA width. This leads to the instability of poly-Si film thickness, therefore resulting in the inconsistency of gate bottom profile. Despite, the optical proximity correction (OPC) based on the post-gate etch CD could be utilized to assuage the AA width related CD difference to some extent, the dependence of step height on AA width from the synergetic action of CMP and WET process should be solved for the fundamental solution to such within-wafer gate CD variation.