Pyrex Glass Wafer Research Articles

Defect-free wet etching through pyrex glass using Cr/Au mask

This paper reports the highest etch depth of annealed Pyrex glass achieved by wet etching in highly concentrated HF solution, using a low stress chromium–gold with assistance of photoresist as masking layer. The strategies to achieve that are: increasing the etch rate of glass and simultaneously increasing the resistance of Cr/Au mask in the etchant. By annealing the Pyrex glass and using a highly concentrated HF acid, a high etch rate can be obtained. Furthermore, a method to achieve a good resistance of the Cr/Au masking layer in the etching solution is to control the residual stress and to increase the thickness of Au deposition up to 1 μm. In addition, the presence of a hard baked photoresist can improve the etching performance. As a result, a 500-μm thick Pyrex glass wafer was etched through.

Capillary liquid chromatography–microchip atmospheric pressure chemical ionization–mass spectrometry

A miniaturized nebulizer chip for capillary liquid chromatography-atmospheric pressure chemical ionization-mass spectrometry (capillary LC-microchip APCI-MS) is presented. The APCI chip consists of two wafers, a silicon wafer and a Pyrex glass wafer. The silicon wafer has a DRIE etched through-wafer nebulizer gas inlet, an edge capillary insertion channel, a stopper, a vaporizer channel and a nozzle. The platinum heater electrode and pads for electrical connection were patterned on to the Pyrex glass wafer. The two wafers were joined by anodic bonding, creating a microchip version of an APCI-source. The sample inlet capillary from an LC column is directly connected to the vaporizer channel of the APCI chip. The etched nozzle in the microchip forms a narrow sample plume, which is ionized by an external corona needle, and the formed ions are analyzed by a mass spectrometer. The nebulizer chip enables for the first time the use of low flow rate separation techniques with APCI-MS. The performance of capillary LC-microchip APCI-MS was tested with selected neurosteroids. The capillary LC-microchip APCI-MS provides quantitative repeatability and good linearity. The limits of detection (LOD) with a signal-to-noise ratio (S/N) of 3 in MS/MS mode for the selected neurosteroids were 20-1000 fmol (10-500 nmol l(-1)). LODs (S/N = 3) with commercial macro APCI with the same compounds using the same MS were about 10 times higher. Fast heat transfer allows the use of the optimized temperature for each compound during an LC run. The microchip APCI-source provides a convenient and easy method to combine capillary LC to any API-MS equipped with an APCI source. The advantages and potentials of the microchip APCI also make it a very attractive interface in microfluidic APCI-MS.

Boiling nucleation and two-phase flow patterns in forced liquid flow in microchannels

Using microfabrication techniques, a microscale platinum heater was fabricated on a Pyrex glass wafer and located in a shallow, but nearly trapezoidal microchannel with a hydraulic diameter of D h = 56 microns fabricated on another glass wafer. Using a high-speed digital CCD video camera and microscope, the boiling nucleation temperature and two-phase flow patterns were observed and examined at different mass flow rates. The nucleation temperature was found to be reasonably close to the theoretical values as predicted by a 3D numerical heat transfer simulation with the measured bulk temperature of the microheater. The stability of the developed flow indicated three clearly distinguishable two-phase flow regimes: bubbly, wavy and annular. To avoid problems observed in the past, care was taken to ensure that the results were not influenced by the entrance and/or exit regions of the test section. The observed variations in the two-phase flow patterns were compared with the results of a model developed using a stability analysis of the liquid film.

Atmospheric Pressure Photoionization-Mass Spectrometry with a Microchip Heated Nebulizer

A novel, microfabricated heated nebulizer chip for atmospheric pressure photoionization-mass spectrometry (APPI-MS) is presented. The chip consists of fluidic and gas inlets, a mixer, and a nozzle etched onto silicon wafer that is anodically bonded to a Pyrex glass wafer, on which an aluminum heater is sputtered. A krypton discharge lamp is used as the source for 10-eV photons to initiate the photoionization process. Dopant, delivered as part of the sample solution, is used to achieve efficient ionization. The use of the microfabricated heated nebulizer with APPI in the analysis of four analytes is demonstrated, and the spectra are compared to those obtained with a conventional APPI source. Ionization in positive and negative ion modes was successfully achieved and the spectra were mainly similar to those obtained with conventional APPI, indicating that the ionization in microfabricated and conventional APPI sources takes place by the same mechanisms. The flow rates with conventional APPI are approximately 100 muL/min, whereas the microchip heated nebulizer allows the use of flow rates 0.05-5 muL/min, thus being compatible with microfluidic separation systems or micro- and nano-LC. A stable signal was demonstrated throughout a 5-h measurement, which proved the excellent stability of the micro-APPI. The same heated nebulizer chip can be used for weeks.

Effects of Wafer Cleaning and Annealing on Glass/Silicon Wafer Direct Bonding

We studied cleaning and annealing effects in glass/Si direct bonding using 4 inch Pyrex glass and silicon wafers. SPM cleaning (sulfuric-peroxide mixture, H2SO4:H2O2=4:1,120°C), RCA cleaning (NH4OH:H2O2:H2O=1:1:5,80°C), and combinations of these two methods were examined to investigate the wafer cleaning effect. When wafers were cleaned by RCA after SPM cleaning, maximal bonding quality at room temperature was gained. Surface roughness, as measured by AFM (atomic force microscope), was found to correspond with bonding quality at room temperature. Bonding strength increased as the annealing temperatures increased to 400°C, but debonding occurred at 450°C. The difference in thermal expansion coefficients of the glass and the Si wafer used led to this debonding. When wafers bonded at room temperature were annealed at 300 or 400°C, the bonding strength increased for 28 hours, and then it decreased with further annealing. The decrease in bonding strength caused by further annealing was due to sodium ion drift through the glass/Si interface.

A new masking technology for deep glass etching and its microfluidic application

A new masking technology for wet etching of glass, to a depth of more than 300 μm, is reported. Various mask materials, which can be patterned by standard photolithography and metal etching processes, were investigated for glass etching in concentrated hydrofluoric acid (HF). A multilayer of metal, Cr/Au/Cr/Au, in combination with thick SPR220-7 photoresist, was found to be ideal for this purpose. Through holes etched from both sides of a 500 μm thick Pyrex glass wafer were obtained. Pinholes, created in the glass by failure of simple metal masking when subjected to HF etching, were successfully eliminated using the new masking technology. In addition, the lateral undercutting of glass caused by the underetching of the Cr mask was minimized to 27% of the etching depth. With these advantages, this newly developed masking method was successfully applied to fabricate microfluidic components for a micro-peristaltic pump to be integrated in a micro polymerase chain reaction (PCR) device. These components include through holes for liquid accessing and electrical contacting and a 200 μm thick pump diaphragm. This new masking technology also adds to the methods available to fabricate the microfluidic devices in glass substrates.

Microfabrication and characterization of liquid core waveguide glass channels coated with teflon af

We report on the microfabrication and testing of liquid core waveguides (LCW) using Teflon AF for integration in microfabricated microanalysis systems. Teflon AF has an index of refraction less than that of water allowing it to function as a waveguide when used as a cladding layer surrounding an aqueous core. Straight microchannels (400-/spl mu/m width, 60-/spl mu/m depth) etched into Pyrex and soda-lime glass wafers were coated with Teflon AF and sealed with a Teflon AF coated capping wafer. Aqueous fluorescein solutions with varying concentrations were injected into the channels and were illuminated transversely using an ultraviolet light emitting diode. For studying the waveguide attenuation performance, light was focused to a point on the channel. Fluorescence generated in the channel was used to quantify the light collection and waveguide characteristics. The Teflon coating produces a significant enhancement in the amount of light collected in the channel, allowing light to be collected from the 16-mm length tested. This is compared to a control microchannel in glass (no coating), for which the fluorescence drops to the background level in an illumination-detection separation of <4 mm. For sensitivity performance, the entire channel was illuminated. The lower detection limit for spectroscopically resolved fluorescence was /spl sim/10 nMolar.

Sodium contamination of SiO2 caused by anodic bonding

In this paper we present an investigation of sodium contamination of SiO2 (oxide) during anodic bonding. Sodium contamination can be deleterious to the electrical properties of silicon structures. Silicon wafers with metal–oxide semiconductor (MOS) capacitors were bonded to Corning 7740 (Pyrex) glass wafers. The concentration of mobile ions was measured on capacitors outside and within glass cavities using the triangular voltage sweep method. Using secondary ion mass spectrometry analysis, it was confirmed that the ions were sodium. We found an increase in sodium concentration Nm between 1010 and 1013 cm−2, depending on the oxide location and the geometry of the glass cavity. The gate aluminium of the MOS capacitor was found to partly shield the oxide from contamination, causing a two to five times smaller increase in Nm. Reducing the bonding voltage from 800 to 500 V did not affect the increase in Nm significantly. In contrast, changing the ambient in the bonding chamber from vacuum to 1020 mbar air, reduced the contamination of capacitors situated outside the glass. A plasma-enhanced chemical vapour deposited Si3N4 film was found to be very beneficial in protecting the capacitors. The Si3N4 prevented sodium contamination of the capacitors situated within the glass cavities, and radically reduced the contamination of the capacitors situated outside the glass. The results suggest that the contaminating sodium originated from the bulk glass.

Endpoint detectable plating through femtosecond laser drilled glass wafers for electrical interconnections

An endpoint detectable plating process to avoid over-electroplating was proposed and performed in this work. The technology was developed for fabrication of Pyrex glass wafer with electrical feed-throughs. Thin film of gold was deposited on the glass wafer prior to the femtosecond laser drilling. When the growing metal in the through-holes was contacted to the metal, a resistance between the opposite two electrodes decreases suddenly. Thus, the endpoint detection was realized by in situ monitoring of applied voltage at constant current mode. After the endpoint detection, periodic reverse plating was applied to fill the through-holes uniformly. Finally, uniform copper deposition in the through-holes up to 12 aspect ratios was realized by this method. This technology was also applicable to the fabrication of microstructure based on electroforming.

A micro-cavity fluidic dye laser

We have successfully fabricated and characterized a micro-cavity fluidic dye laser with metallic mirrors, which can be integrated with other microfluidic systems without adding further process steps. A laser dye solution is pumped through a microfluidic channel containing the laser cavity. The microfluidic channel structure, which is formed in SU-8 photoresist, is sandwiched between Pyrex glass wafers, bonded together at low temperature by means of SU-8. The laser was characterized using Rhodamine 6G laser dye dissolved in ethanol as the active medium, and optically pumped by a frequency doubled Nd:YAG laser. The dye solution was optimized, and lasing was observed at a wavelength of 570 nm with a full width half maximum linewidth of 5.7 nm and the optical pumping power density threshold for lasing was 34 mW cm−2.

Fabrication of high-density electrical feed-throughs by deep-reactive-ion etching of Pyrex glass

This paper describes the fabrication technology for high-density electrical feed-throughs in Pyrex glass wafers. Small through holes (40-80 /spl mu/m in diameter) in Pyrex glass wafers have been fabricated using deep-reactive-ion etching (DRIE) in a sulfur hexafluoride (SF/sub 6/) plasma. The maximum aspect ratios obtained were between 5 and 7 for a hole pattern and 10 for a trench pattern. Through the wafer etching of a hole pattern of 50 /spl mu/m diameter was carried out using 150-/spl mu/m-thick Pyrex glass wafers. The electrical feed-throughs in the wafers were fabricated by filling the through-holes with electroplated nickel. We were able to successfully bond the glass wafer to silicon by anodic bonding after removing the electroplated nickel on the surface of the wafer by chemical-mechanical polishing (CMP). The electric resistance of the feed-through was estimated by a 4 point wire sensing method to be about 40 m/spl Omega/ per hole. The heat cycles test shows that the resistance changes were within 3% after 100 cycles. The fabrication of high density electrical feed-throughs is one of the key processes in the field of MEMS. Probable applications of this technology are in electrical feed-throughs between logic elements and microprobe arrays for high-density data storage and for packaged devices.

Performance of an integrated microoptical system for fluorescence detection in microfluidic systems.

This article presents a new integrated microfluidic/microoptic device designed for basic biochemical analysis. The microfluidic network is wet-etched in a Borofloat 33 (Pyrex) glass wafer and sealed by means of a second wafer. Unlike other similar microfluidic systems, elements of the detection system are realized with the help of microfabrication techniques and directly deposited on both sides of the microchemical chip. The detection system is composed of the combination of refractive circular or elliptical microlens arrays and chromium aperture arrays. The microfluidic channels are 60 microm wide and 25 microm deep. The elliptical microlenses have a major axis of 400 microm and a minor axis of 350 microm. The circular microlens diameters range from 280 microm to 350 microm. The apertures deposited on the outer chip surfaces are etched in a 3000-A-thick chromium layer. The overall thickness of this microchemical system is < 1.6 mm. A limit of detection of 3.3 nM for a Cy5 solution in phosphate buffer (pH 7.4) was demonstrated. The cross-talk signal measured between two adjacent microchannels with 1 mm pitch was < 1:5600, meaning that < or = 1.8 x 10(-4)% of the fluorescence light power emitted from one microchannel filled with a 50 microM Cy5 solution reaches the photodetector at the adjacent microchannel. This performance compares very well with that obtainable in microchemical chips using confocal fluorescence systems, taking differences in parameters, such as excitation power into microchannels, data acquisition rates, and signal filtering into account.

유리/실리콘 기판 직접 접합에서의 세정과 열처리 효과

We have investigated the effects of various wafers cleaning on glass/Si bonding using 4 inch Pyrex glass wafers and 4 inch silicon wafers. The various wafer cleaning methods were examined; SPM(sulfuric-peroxide mixture, <TEX>$H_2SO_4:H_2O_2$</TEX> = 4 : 1, <TEX>$120^{\circ}C$</TEX>), RCA(company name, <TEX>$NH_4OH:H_2O_2:H_2O$</TEX> = 1 : 1 : 5, <TEX>$80^{\circ}C$</TEX>), and combinations of those. The best room temperature bonding result was achieved when wafers were cleaned by SPM followed by RCA cleaning. The minimum increase in surface roughness measured by AFM(atomic force microscope) confirmed such results. During successive heat treatments, the bonding strength was improved with increased annealing temperatures up to <TEX>$400^{\circ}C$</TEX>, but debonding was observed at <TEX>$450^{\circ}C$</TEX>. The difference in thermal expansion coefficients between glass and Si wafer led debonding. When annealed at fixed temperatures(300 and <TEX>$400^{\circ}C$</TEX>), bonding strength was enhanced until 28 hours, but then decreased for further anneal. To find the cause of decrease in bonding strength in excessively long annealing time, the ion distribution at Si surface was investigated using SIMS(secondary ion mass spectrometry). tons such as sodium, which had been existed only in glass before annealing, were found at Si surface for long annealed samples. Decrease in bonding strength can be caused by the diffused sodium ions to pass the glass/si interface. Therefore, maximum bonding strength can be achieved when the cleaning procedure and the ion concentrations at interface are optimized in glass/Si wafer direct bonding.

Fabrication of multilayer systems combining microfluidic and microoptical elements for fluorescence detection

This paper presents the fabrication of a microchemical chip for the detection of fluorescence species in microfluidics. The microfluidic network is wet-etched in a Borofloat 33 (Pyrex) glass wafer and sealed by means of a second wafer. Unlike other similar chemical systems, the detection system is realized with the help of microfabrication techniques and directly deposited on both sides of the microchemical chip. The detection system is composed of the combination of refractive microlens arrays and chromium aperture arrays. The microfluidic channels are 60 /spl mu/m wide and 25 /spl mu/m deep. The utilization of elliptical microlens arrays to reduce aberration effects and the integration of an intermediate (between the two bonded wafers) aluminum aperture array are also presented. The elliptical microlenses have a major axis of 400 /spl mu/m and a minor axis of 350 /spl mu/m. The circular microlens diameters range from 280 to 300 /spl mu/m. The apertures deposited on the outer chip surfaces are etched in a 3000-/spl Aring/-thick chromium layer, whereas the intermediate aperture layer is etched in a 1000-/spl Aring/-thick aluminum layer. The overall thickness of this microchemical system is less than 1.6 mm. The wet-etching process and new bonding procedures are discussed. Moreover, we present the successful detection of a 10-nM Cy5 solution with a signal-to-noise ratio (SNR) of 21 dB by means of this system.

Packaging of closed chamber PCR‐chips for DNA amplification

Reports the design, fabrication and packaging of a micromachined silicon/Pyrex based chip for the polymerase chain reaction (PCR). The anodic bonding method is used for sealing the chambers of 1μl volume with a Pyrex glass wafer. Platinum resistors on the back of the wafer are used as heaters and temperature sensors. The chip is externally cooled by forced air to achieve rapid temperature cycling. The transparency of the Pyrex makes it possible for using optical readout methods. The packaging is especially designed for easy handling, filling, power connection, temperature regulation and optical readout. The mass production of such silicon reactors could make single‐shot throwaway devices economically viable.

Photoluminescence spectroscopy of direct bonded silica based wafers

We report results of an original photoinduced luminescence spectroscopy application to determine the process of direct bonding of silica wafers. This application is based upon laser induced visible fluorescence of the defects created during the bonding process and can also be used in the cases when neither electron microscopy nor optical near field analysis permit a junction observation. The results are related to two different assemblies: first we consider two pyrex glass wafers assembled by direct wafer bonding technology and second we applied the same technology to two ion-exchanged wafers to obtain buried planar waveguide. The bonding process induces for both assemblies on the one hand an enhancement of emitting defects at 570 nm which are present in the blank wafer material and create on the other hand new defects emitting at 525 nm.

Bulk micromachining of Si by lithography and reactive ion etching (LIRIE) : I. W. Rangelow, P. Hudek and F. Shi. Vacuum, 46 (12), 1361 (December 1995).

This paper reports on the development of a technology which will offer the potential to manufacture micro-engines, micro-turbines, micro-sensors, micro-actuators and electronic circuits onto a single silicon chip. This technology is based on the highly anisotropic and selective dry etching of Si-monocrystals. Axes or stators (non-moving pans) are etched into the initial Si-wafer. The movable parts (rotors, beams, etc.) are prepared from electro-chemically etched Si-membranes with defined thicknesses. Both sides of the Si-membrane are covered with a 1.5 μm SiNxOy layer by a low stress (< 10 MP) PECVD-process. After that, all movable parts are created lithographically on the SiNxOy surface. This is followed by dry etching the mono-crystalline Si-membrane down to the SiNxOy sacrificial layer on the reverse side of the membrane by an RIE-process. This fixes the movable parts to the SiNxOy-layer. The wafer with the movable parts is flipped onto the wafer with the already etched axis and then positioned and centred. The SiNxOy-sacrificial layer is then dissolved by a chemical wet or vapour etch process. Subsequent bonding with a Pyrex glass wafer seals the parts.

Micromachined semi-encapsulated spiral inductors for microelectromechanical systems (MEMS) applications

Semi-encapsulated spiral inductors for microelectromechanical systems (MEMS) applications have been designed, fabricated, and characterized using micromachining and electroplating techniques. The inductors are fabricated on a Pyrex glass wafer using a simple three mask process and have an area of 4 mm by 4 mm. Devices consist of electroplated copper conductor lines with width 50 /spl mu/m, thickness 25 /spl mu/m, and spacing 30 /spl mu/m; they are semi-encapsulated with an electroplated Ni-Fe (81%/19%) magnetic core. At the low frequency of 10 kHz, the inductance of the devices was measured as 1.5 /spl mu/H, while they exhibited a low resistance of only 3 ohms. Their low resistance and reasonably high inductance makes them ideal in MEMS applications as either sensors or actuators.

Etching processes for High Aspect Ratio Micro Systems Technology (HARMST)

This paper reports on the development of a dry etching based HARMS-Technology which will offer the potential to manufacture micro-engines, micro-turbines, micro-sensors, micro-actuators, and electronic circuits onto a single silicon IC chip. This technology is based on the highly anisotropic and selective dry etching of Si-monocrystals. The suitability of reactive ion etching for the fabrication of micro electro mechanical systems (MEMS) has been evaluated by characterising the change of lateral dimensions vs. depth in etching deep structures in silicon. Fluorine, chlorine and bromine containing gases have provided the basis for this investigation. A conventional planar RIE (Reactive Ion Etching) reactor has been used, in some cases with magnetic field enhancement or ICP (Inductive Coupled Plasma) Source and low substrate temperature. For reactive ion etching based on Cl2 or Cl2/HBr plasma a slightly “positive” (top wider than bottom) slope is achieved when etching structures with a depth of several 10 μm, whereas a “negative” slope is obtained when etching with an SF6/CCl2F2 based plasma. Pattern transfer with vertical walls is obtained for reactive ion etching based on SF6 (with O2 added) when maintaining the substrate at low temperature (in range ≈−100 °C). Further optimisation of plasma chemistries and reactive ion etching procedures should result in runouts in the order or 0.1 μm/100 μm depth in Si as well as in organic materials. Etching processes for HARMST is demonstrated in the realisation in Si microturbine. Axes or stators (nonmoving parts) are etched into the initial Si-wafer. The movable parts (rotors, beams, etc.) are prepared from electro-chemically etched Si-membranes with defined thicknesses that, all movable parts are created lithographically on the SiNxOy surface. This is followed by dry etching the mono-crystalline Si-membrane down to the SiNxOy sacrificial layer on the back side of the membrane by an RIE-process. The wafer with the movable parts is flipped onto the wafer with the already etched axis and then positioned and centred. The SiNxOy-sacrificial layer is then dissolved by a chemical wet or vapour etch process. Subsequent bonding with a Pyrex glass wafer seals the parts.

Bulk micromachining of Si by Lithography and Reactive Ion Etching (LIRIE)

This paper reports on the development of a technology which will offer the potential to manufacture micro-engines, micro-turbines, micro-sensors, micro-actuators and electronic circuits onto a single silicon chip. This technology is based on the highly anisotropic and selective dry etching of Si-monocrystals. Axes or stators (non-moving pans) are etched into the initial Si-wafer. The movable parts (rotors, beams, etc.) are prepared from electro-chemically etched Si-membranes with defined thicknesses. Both sides of the Si-membrane are covered with a 1.5 μm SiN xO y layer by a low stress (< 10 MP) PECVD-process. After that, all movable parts are created lithographically on the SiN xO y surface. This is followed by dry etching the mono-crystalline Si-membrane down to the SiN xO y sacrificial layer on the reverse side of the membrane by an RIE-process. This fixes the movable parts to the SiN xO y-layer. The wafer with the movable parts is flipped onto the wafer with the already etched axis and then positioned and centred. The SiN xO y-sacrificial layer is then dissolved by a chemical wet or vapour etch process. Subsequent bonding with a Pyrex glass wafer seals the parts.