Double-side Polished Wafer Research Articles

Wafer Level Vacuum Packaging of MEMS-Based Uncooled Infrared Sensors.

This paper introduces a cost-effective, high-performance approach to achieving wafer level vacuum packaging (WLVP) for MEMS-based uncooled infrared sensors. Reliable and hermetic packages for MEMS devices are achieved using a cap wafer that is formed using two silicon wafers, where one wafer has precise grating/moth-eye structures on both sides of a double-sided polished wafer for improved transmission of over 80% in the long-wave infrared (LWIR) wavelength region without the need for an AR coating, while the other wafer is used to form a cavity. The two wafers are bonded using Au-In transient liquid phase (TLP) bonding at low temperature to form the cap wafer, which is then bondelectrical and Electronics d to the sensor wafer using glass frit bonding at high temperature to activate the getter inside the cavity region. The bond quality is assessed using three methods, including He-leak tests, cap deflection, and Pirani vacuum gauges. Hermeticity is confirmed through He-leak tests according to MIL-STD 883, yielding values as low as 0.1 × 10-9 atm·cc/s. The average shear strength is measured as 23.38 MPa. The package pressure varies from 133-533 Pa without the getter usage to as low as 0.13 Pa with the getter usage.

Interferometry of double-sided polished wafer and error analysis

Interferometry of double-sided polished wafer and error analysis

Formation of Diagenetic Minerals in the Carboniferous Rock Complex from the Fore-Sudetic Monocline (SW Poland): Fluid Inclusion, Isotopic and Raman Constraints

The paper presents the latest state of knowledge on clastic sedimentary rocks from the Carboniferous complex in the SW part of the Polish Lowlands, studied to help determine their potential prospectivity for the occurrence of oil and/or gas deposits. Rocks were analyzed with respect to the petrographic-mineralogical characteristics of the Carboniferous deposits, their diagenesis, determinations of pressure-temperature conditions of mineral formation and the hydrocarbon occurrence. Analyses were carried out on samples from four selected boreholes in the Fore-Sudetic Monocline. After microscopic analysis of rocks and minerals in thin sections, the following techniques were used: luminescence analysis (UV, blue light), microthermometric analysis of fluid inclusions in double-sided polished wafers, cathodoluminescence analysis, electron scanning microscope studies, XRD analyses, stable isotopic analyses (carbon, oxygen) on calcite and dolomite-ankerite and Raman spectra of fluid inclusions. Orthochemical components, such as carbonates and authigenic quartz, that form cements or fill the veins cutting the sample material have been studied. Fluid inclusion data in quartz and carbonates result in homogenization temperatures of 74–233 °C. The Raman analysis gives temperature estimations for the organic matter of about 164 °C and 197 °C, depending on the borehole, which points to a low coalification degree. The post-sedimentary processes of compaction, cementation and diagenetic dissolution under eo- and meso-diagenetic conditions to temperatures of over 160 °C influenced the present character of the deposits. P-T conditions of brines and methane trapping have been estimated to be ~850–920 bars and 185–210 °C (vein calcite) and ~1140 bars and 220 °C (Fe-dolomite/ankerite). Therefore, locally, temperatures might have been higher (>200 °C), which may be a symptom of local regional metamorphism of a very low degree.

Double-sided and single-sided polished 6H-SiC wafers with subsurface damage layer studied by Mueller matrix ellipsometry

The complex optical constants and the subsurface damage layer of uniaxial doped 6H-SiC wafers are measured using Mueller matrix spectroscopic ellipsometry. A comparison is made between measurements on a single-sided polished wafer that can be treated as a semi-infinite substrate and on a double-sided polished wafer that is studied with the partial-wave theory. The refractive indices and extinction coefficients for ordinary and extraordinary directions are determined below the bandgap after point-by-point fitting of experimental Mueller matrices. The thickness of the subsurface damage layer caused by mechanical polishing and chemical mechanical polishing determined by ellipsometry is consistent with the result of transmission electron microscope. The ellipsometry results show that the analysis based on a double-sided polished wafer is more informative about the optical properties of 6H-SiC than that of the single-sided polished wafer as it renders information properties about the bulk properties of the material, for example, allowing the determination of the very weak absorption coefficient (k≈10−4) due to doping.

3D Printing for Low-Cost and Versatile Attenuated Total Reflection Infrared Spectroscopy.

In this work, we present a fully 3D-printed module for attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy ready for use in commercial FTIR spectrometers. The developed setup stands out in terms of robustness and ease of sample application. Rapid prototyping paired with theoretical considerations were employed to design and fabricate the module. Cost-efficient commercial available silicon and germanium ATR crystals prepared from double-sided polished wafers were mounted in the setup. While low-noise levels and stability bear comparison with commercial systems, the multibounce ATR crystal's long interaction pathlengths as well as their interchangeability turns the presented ATR module into an even more sophisticated tool. The versatility of the proposed setup is demonstrated for various spectroscopic challenges: Curing of a cyanoacrylate and a two-component epoxy based adhesive was monitored by tracking polymerization processes at room and high temperatures. To emphasize potential applications of the disposable ATR module in life science studies exploring potential biohazardous samples, mid-IR spectra of Escherichia coli and bovine serum albumin were recorded. The total printing time of the ATR module is 10.5 h, enabling overnight fabrication at a total cost ranging from 150 to 613 €, making the high versatility of ATR spectroscopy accessible to a broader audience. This proves the potential of 3D printing to generate optical instruments tailored to the needs of individual analytical problems.

Single-Side Fabricated p+Si/Al Thermopile-Based Gas Flow Sensor for IC-Foundry-Compatible, High-Yield, and Low-Cost Volume Manufacturing

In this brief, a low-cost and high-yield bulk under thin-film (BUT) MEMS technique for the volume production of flow sensors is proposed and developed. The IC-foundry-compatible process is conducted only from the front side of (111) silicon wafers, without double-sided alignment exposure, wafer bonding, cavity silicon on insulator, and double-sided polished wafers needed. With the single-wafer-based BUT structure, the thermopile consisting of 21 pairs of single-crystalline Si/Al thermocouples that show significantly higher Seebeck coefficient and lower noise compared to the traditional poly-Si/Al thermocouples is employed to construct the gas flow sensor, and the fabricated sensor chip size is as small as 0.65 mm×0.65 mm that facilitates low-cost high-throughput IC-foundry batch fabrication. The fabricated sensor shows a high normalized sensitivity of 199 μV/(SLM)/mW for nitrogen gas flow, which is 1 order of magnitude higher than that of the reported thermopile-based gas flow sensor, and a short response time of 3.5 ms could be achieved. With the new technique, the proposed sensors are promising in automotive and process control system applications.

Wet-chemical Treatment for Improved Surface Passivation of Textured Silicon Heterojunction Solar Cells

Silicon heterojunction (SHJ) solar cells constantly gain more attention due to their low cost and relatively high efficiency. An important aspect of these solar cells is the incorporation of intrinsic hydrogenated amorphous silicon (a-Si:H) layers at each side of the c-Si wafer, which has increased the efficiency potential due to the excellent surface passivation. By applying a randomly textured instead of a double-side polished wafer, optical enhancement is achieved resulting in significant reflection reduction and high short-circuit current densities (Jsc). However, texturing-induced defects lead to an a-Si:H/c-Si interface with increased recombination, which limits the open circuit voltage (Voc) of the SHJ device after using the same cleaning treatment as for the flat wafer. Thus, a one-to-one transfer of process parameters from flat to textured c-Si substrate is not necessarily appropriate and a different wet-chemical treatment is needed. In this work, a chemical treatment is demonstrated, which leads to an improved surface passivation.

Mechanical Strength Characterization for Silicon-to-Silicon Direct Bonding

In this paper, silicon direct bonding was performed by two different cleaning processes, and the bonding quality was obtained by tensile test and IR test. For (100) P-type double side polished wafer, the optimum process condition was established with respect to the results of two different cleaning processes. The cleaning process of NH3•H2O/H2O2/H2O (Standard Cleaning 1, SC1) after the H2SO4/H2O2 (piranha solution) was found to be better suited for high bonding quality. The bonding strength of the SC1-cleaned samples is about 5.4 MPa with partially crack but no more than 0.7 MPa for the only piranha solution cleaned samples.

Single-Side Fabricated Pressure Sensors for IC-Foundry-Compatible, High-Yield, and Low-Cost Volume Production

In this letter, a new low-cost and high-yield manufacturing technique for volume production of pressure sensors is proposed and developed. The IC-foundry-compatible process is conducted only from the front side of (111) silicon wafers, without double-sided alignment exposure, wafer bonding, and double-sided polished wafers needed. With the single-wafer-based single-side bulk-micromachining technique, the sensor chip size is as small as 0.6 mm × 0.6 mm that facilitates low-cost high-throughput IC-foundry batch fabrication. Compared with the conventional double-sided micromachining approach where the pressure-sensing diaphragm thickness is determined by back-side deep etching, the front-side micromachining scheme uses front-side shallow etching that provides more precise and uniform control to the thickness for higher yield. 0.087-mV/kPa sensitivity and ±0.09%FS nonlinearity are measured for the fabricated 750-kPa range sensor, and the temperature coefficient of offset ( TCO) is as low as -0.032%/ °C ·FS. With the new technique, the sensors are promising in automotive and consumer electronics applications.

Development of a double sided stitching interferometer for wafer characterization

A pre-prototype measurement machine for measuring the geometry of double side polished wafers has been developed. The measurement principle is based on a scanning double sided Fizeau interferometer with which the front side and the back side flatness of a wafer are measured simultaneously. Both flatness maps are used to derive the wafer thickness variation. Field distortion of the optical system, alignment errors and the thickness variations of the reference cavity are compensated by self-calibrating techniques in order to achieve a measurement uncertainty in the order of several nanometers.

Silicon wafer thickness variation measurements using the National Institute of Standards and Technology infrared interferometer

Decreasing depths of focus, coupled with increasing silicon wafer diameters, place greater restrictions on chucked wafer flatness in photolithography processes. A measurement device is described that measures thickness variation of double-sided polished wafers using an IR source and vidicon detector. Various possible instrument configura- tions are described with the focus on a setup that uses a collimated wavefront to produce interference fringes between the front and back surfaces of the plane parallel wafer. Experimental results are presented. These tests include (1) a drift test; (2) comparisons between measure- ments performed using different collimators and, subsequently, wave- fronts; (3) an exploration of the impact of phase change on reflection due to the wafer clamping method; and (4) an intercomparison with thickness measurements recorded by a capacitance gage-based instrument and surface measurements obtained using a separate visible wavelength interferometer. © 2003 Society of Photo-Optical Instrumentation Engineers.

High sensitivity acoustic transducers with thin p+ membranes and gold back-plate

High sensitivity acoustic transducers (microphones) have been fabricated on 5″ wafers in a production environment and the experimental results are presented. One of the main advantage of this microphone design is that it can be fabricated on a single wafer eliminating the need for the multiple wafers and subsequent wafers bonding steps as in conventional designs. The devices use thin (∼3 μm) p+ silicon membranes as the active movable element and a thick perforated plated gold back plate. The p+ membranes are fabricated using an optimized boron solid source diffusion at 1150°C. Ethylene–Diamine–Pyro-Catecol (EDP) etching at 100°C was performed from the backside of double-sided polished wafers to release the thin silicon membranes. The zero-bias capacitance with the air gap was 2.2 pF and it increased to 2.4 pF at 9 V. The frequency response was measured and the measured sensitivity of 5.28 mV/Pa at 5 V and 10.77 mV/Pa at 9 V at 1 kHz are among the highest reported in literature for micro-machined acoustic transducers.

Influence of temperature and backside roughness on the emissivity of Si wafers during rapid thermal processing

The influence of temperature and roughness on the backside emissivity of Si wafers was studied. In situ measurements were done in two commercial rapid thermal processing systems. An experimental setup was built for in situ emissivity measurements of wafers with a polished or nonpolished backside. The emissivity of double-side polished wafers was measured for temperatures ranging from 300 to 700 °C and at wavelengths of 1.7 and 3.4 μm. It was found that the absorption coefficient α of lightly doped silicon is described by the equation α=4.15×10−5λ1.51T2.95 exp(−7000/T) cm−1, for wavelengths λ ranging from 1.5 to 5 μm and temperatures T ranging from 673 to 973 K (λ in μm, T in K). The backside emissivity of Si wafers with different roughnesses was measured. At temperatures above 600–700 °C the wafers are opaque and the emissivity is only slightly dependent on backside roughness. At lower temperatures the wafers are partially transparent and the emissivity is strongly dependent on the backside roughness of the wafer due to light trapping in the bulk of the wafer. For the latter case a new model was developed to simulate the emissivity of wafers with a rough backside at low temperatures.