Showing papers on "Anodic bonding published in 1991"

Method for preparing a substrate for semiconductor devices

Abstract: In a method for preparing a substrate for semiconductor device, the substrate is prepared either by directly bonding a bonding wafer to a base wafer or by bonding the bonding wafer to the base wafer with an oxide film formed on at least the bonding surface of the bonding wafer or the bonding surface of the base wafer to make finished semiconductor devices with an SOI structure. Prior to the bonding operation, the bonding wafer and the base wafer are subjected to the steps of (1) making the diameter of the bonding wafer smaller than the diameter of the base wafer, (2) setting the beveling width of the back side (bonding side) of the bonding wafer at 50 microns or less, and (3) beveling the front side of said base wafer so that the bonding surface of the base wafer is equal in size to the bonding surface of the bonding wafer. When the bonding wafer, which has been bonded to the base wafer, is subjected to polishing into a thin film, the peripheral portions of the bonding wafer form a smooth surface of the base wafer. This prevents the peripheral portions from chipping off.

Electrode Phenomena during Anodic Bonding of Silicon to Sodium Borosilicate Glass

Abstract: Electrode phenomena during anodic bonding of silicon to sodium borosilicate glass are examined. The cathodic reaction, reduction of sodium, does not usually limit the reaction rate. The anodic reaction, oxidation of the silicon, requires very high electric fields in the anodic depletion layer and is the limiting electrode reaction. The ohmic drop in the glass determines the rate of establishment of the high interfacial fields. The transient current response under constant voltage conditions is modeled over the timescale of interest for bonding by a simple equivalent circuit. The current response model is also applicable to the initial transient during electrode polarization of glass at a blocking anode.

Silicon-to-silicon anodic bonding with a borosilicate glass layer

Abstract: Anodic bonding of silicon wafers by sputter deposited glass films, silicon-to-silicon anodic bonding, is presented as a promising sealing method in microengineering. A reliable process for wafer-to-wafer bonding is described and data concerning yield and bonding strength are given. Cathodic bonding is reported in a discussion about the bonding mechanism. Different sputter deposited and annealed Pyrex 7740 layers are evaluated as sealing material. Some advantages of silicon-to-silicon anodic bonding as a mounting method for micromechanical sensors are quantified.

Semiconductor chip bonding process

Abstract: A semiconductor chip bonding process is disclosed, and the process comprises the steps of forming a first Au ball using a wire ball bump bonding apparatus, stacking a second Au ball on the first Au ball, stacking a Pb ball on the second Au ball using the wire ball bump bonding apparatus, and bonding the chip to a substrate, wherein the conventional complicated BUMP manufacturing process is omitted due to the CHIP BONDING technique during the assembling process, so that the formation process is shortened and the defect rate during the chip bonding is minimized, thereby the manufacturing cost can be saved.

Interface phenomena and bonding mechanism of thermally-sprayed metal and ceramic composites

Abstract: Metal and ceramic materials were sprayed on polished steel and iron substrates using atmospheric arc (nickel, molybdenum) and plasma (Al 2 O 3 , ZrO 2 -7Y 2 O 3 ) spraying. The bonding quality at the substrate-coating interface depends on the size and depth of the contact zones. The chemical-metallurgical interactions (diffusion, reactions) between the sprayed particles and the metal substrate as a function of the properties of the sprayed materials, contact temperature and solidification time were analysed. Higher contact temperature and longer interaction time for spraying of metals result in better bonding. Moreover, oxidation of the metal substrate to a limited degree by spraying of oxides allows one to improve the bonding quality. It is possible to correlate the results of microscopical investigations of the interface phenomena with the results of quantitative measurement of the bonding tensile strength.

Silicon on insulator material by wafer bonding

Abstract: Thermal bonding of oxidized silicon wafers is used to obtain high-quality silicon on insulator (SOI) starting material for electronics and sensor applications. An overview of the technology is followed by a detailed description of the bonding technique and the ensuing wafer thinning processes for making SOI of various film thicknesses. Bonded pairs of wafers can be reproducibly produced free of contact voids. Thick-film SOI is produced using a simple bond and grind/polish technique. Thin-film SOI, suitable for CMOS applications, is produced using the bond and etch back (BE-SOI) process. A comparison of selective etch-back chemistry with different etchstop fabrication techniques is presented. These methods produce inexpensive, low-defect SOI, for integrated circuit applications, using materials and equipment common to silicon integrated circuit process lines.

Semiconductor die sealing

Abstract: Integrated circuit bonding pads are sealed by a surface passivation coating. The bonding pads are first edge-sealed by means of a first applied passivation coating that overlaps the edges of the bonding pad while leaving the central area uncoated. Then, a sequence of metal layers applied to overlap the open central area of the bonding pad. The layer sequence includes an optional first adherence layer such as aluminum, a barrier metal layer such as titanium-tungsten alloy, and an outer noble metal layer such as gold. Then, a second passivation layer is applied so as to overlap and seal the edges of the sequence of metal layers so as to leave only the central portion of the noble metal layer exposed. Electrical contact to the IC is then made to the exposed noble metal in the conventional manner. With respect to the passivating coatings, either or both can be silicon dioxide overcoated with silicon nitride. Furthermore, the second passivating coating can include either low melting glass that is spun-on using a powdered-glass slurry or it can be an organic, such as a polyimide monomer, spun-on in liquid form.

Tensile strength characterization of low-temperature fusion-bonded silicon wafers

Abstract: Silicon fusion bonding was investigated with emphasis on the low temperature regime. For (100) p-type wafers with and without thermally oxidized surfaces the optimum process conditions with respect to surface preparation and gas ambient were established. H2SO4/H2O2 and hot HNO3 were found to be best suited for bonding blank/blank (without thermal oxide) and oxidized wafers, respectively. Direct measurements of bond tensile strength were made on a computer-controlled test machine. The temperature and time dependence of the bond tensile strength was determined. If the best possible clean-room conditions during processing are observed, wafers without thermal oxide, i.e. with only a chemical oxide of 25 AA thickness due to surface preparation, exhibit a measured bond tensile strength in excess of 240 kp cm-2 at a bonding temperature of only 200 degrees C and a bonding time of 4 h. This value cannot be improved by increasing the bonding temperature. If one or both surfaces are thermally oxidized the bond tensile strength is only 20% of this value. Bond tensile strength for oxidized surfaces, however, can be improved at higher temperatures to reach the high values as found for blank wafers.

Direct bonding of micromachined silicon wafers for laser diode heat exchanger applications

Abstract: A novel application of silicon direct-thermal-wafer bonding is demonstrated using micromachined wafers. Two (110) Si wafers are patterned and micromachined using wet chemistry. The prepared wafers are cleaned, leaving only native chemical oxides on the Si surfaces. After the cleaning steps, the wafers are thermally bonded without electrostatic pressure. The points of bonded contact are 410 mu m*25 mu m. Hydraulic pressure testing on the bonded wafers has substantiated a bond strength comparable to contiguous SiO2. The final structure is intended as a micromachined heat exchanger for cooling laser diodes.

Aligned wafer bonding: a key to three dimensional microstructures

Abstract: Successful fabrication of critically aligned three dimensional structures has been achieved by combining precision alignment procedures and techniques for direct silicon bonding. This produces three dimensional bonded layers that might include combinations of mechanical, electronic and/or optical elements formed in separate prefabricated layers. We call this techniquealigned wafer bonding. The precise aligned bonding of the features was done with an Optical AssociatesHyperline 400 Infrared Aligner. This machine can hold two imprinted wafers face to face while projecting an infrared image of the surfaces to a viewing screen. An array of alignment marks were etched into the surface of silicon wafers with hot potassium hydroxide. These V-grooves were then precisely aligned and the wafers were brought into contact for initial bonding. Subsequent high temperature annealing was used to strengthen and complete the chemical bonding. The instrumentation used in this work required alignment features with a vertical dimension of 30 micrometers to produce a suitable infrared image. We found that the apparent size of the images produced by the optical system limited the accuracy in precision alignment. However, with reduced wafer separation, we achieved wafer alignment with an accuracy of better than 5 micrometers. This technique would generally be used for the precision alignment and bonding of complementary micromechanical, electrical, or optical structures during the formation of three dimensional devices. The details of the aligned wafer bonding and its applications are presented.

Method of minimizing lateral shrinkage in a co-fired, ceramic-on-metal circuit board

Abstract: A method of fabricating a multi-layered, co-fired, ceramic-on-metal circuit board utilizes a bonding layer of glass. The glass has a coefficient of thermal expansion not greater than that of the metal base. The glass of the bonding layer has a softening point below that of the glass in the multi-layer ceramic so that the glass of the bonding layer flows and bonds to the metal to minimize the lateral shrinkage of the multi-layered ceramic.

Semiconductor device having improved electrode pad structure

Abstract: In a semiconductor device in which copper or copper alloy bonding wire is bonded to an electrode pad on a semiconductor element, the electrode pad is formed of a first metal layer ohmically contacting the semiconductor element, a second metal layer hard enough not to be deformed at wire bonding step, and a third metal layer for bonding a copper wire, to suppress variation in the electric characteristics of a bonding portion and the production of stain in the semiconductor element at wire bonding step

Apparatus for ultrasonic bonding

Abstract: An ultrasonic transducer, bonding tool and method of bonding gold or gold plated leads to gold or gold plated bonding pads located on unheated substrates is disclosed. More particularly, the transducer of the present invention incorporates a modified transducer/tool interface which provides for increased durability as well as increased excursion control of any bonding tool placed therein. The bonding tool of the present invention includes a modified end having a raised pattern used to form an impression in the lead to be bonded to enhance gripping of the lead during bonding. The preferred methods include using the modified transducer and bonding tool to perform gold-to-gold bonding on unheated substrates while providing increased vertical clearance for bonding between structures.

Silicon wafer bonding techniques for assembly of micromechanical elements

Abstract: Different bonding techniques under development for assembly of micromechanical elements are reviewed. A versatile wafer-to-wafer bonding process using silicon-to-silicon anodic bonding with sputtered Pyrex 7740 borosilicate thin film has been developed. The method gives sealings with a bonding strength of approximately 2.5*10/sup 6/N/m/sup 2/ and excellent thermal matching, resulting in minimized thermally induced stress in micromechanical components. The anodic bonding is performed at temperatures well below the aluminum/silicon eutectic temperature, making the process suitable also for metallized wafers. The large electrostatic force obtained during bonding is crucial for a high-yield wafer-to-wafer bonding process. High bonding strength and complete bonding of 3-in wafers were obtained. This technique was used for a silicon pressure sensor application, giving excellent thermal and long term stability for this sensor. The results are supported by finite-element calculations. >

Method for making a magnetic head having surface-reinforced glass

Abstract: Glass is surface reinforced by providing a surface layer which contains an oxide component, typically silicon oxide in more excess than the underlying base glass, the oxide component exhibiting higher chemical or mechanical durability than the base glass itself. A surface of glass is tailored by a dry process, typically by exposure to UV radiation in the presence of ozone such that the oxide component is present more at the surface than in the underlying glass while a heavy metal such as Pb is driven out. A magnetic head having such a surface-reinforced sealing glass for bonding a core block to a slider is highly reliable.

Wafer fusion bonding and its application to silicon-on-insulator fabrication

Abstract: The principles of the wafer fusion bonding technique at room temperature and with thermal treatment are described. Experiments using plain and patterned silicon wafers coated with different surface materials are presented. Results obtained for different thermal annealing conditions are discussed in terms of homogeneity and strength of the bond. Thinning of the bonded wafers is performed by grinding and polishing or with preferential etch techniques using p+ etchstops. Uniform silicon-on-insulator (SOI) films with thicknesses 1 mu m-30 mu m have been obtained.

Method of forming bonding bumps by punching a metal ribbon

Abstract: Disclosed is a method of forming bonding metal bumps on electrodes of a submount for use with an optical device array. Small bonding metal pieces are arranged on a transfer piece resting substrate so as to be aligned with the electrodes of the submount. Next, the bonding metal pieces thus arranged are transferred onto respective electrodes of the submount. In one embodiment, bonding metal pieces are preferably formed by punching a ribbon-shaped bonding metal and respectively fixed by a force of the punching operation directly onto the electrodes of the submount.

A bonding technique for thin GaAs dice with via holes using gold-tin composites

Abstract: 100 mu m thin 2-mm-by-3-mm GaAs dice with via holes have been successfully bonded on alumina substrates using the technique of gold-tin multilayer composite. The bondings are near perfect, as confirmed by a scanning acoustic microscope. Scanning electron microscope images of cross sections reveal that the bonding layers are very uniform and the thickness is 1.5 mu m. EDX analysis shows that the composition of the bonding layer is nearly gold-tin eutectic. No die crackings were observed after the bonding. The specimens underwent 40 cycles of thermal shock test between -196 degrees C and 160 degrees C without incurring bonding degradation and die cracking. >

Low-temperature glass bonding for sensor application using boron oxide thin films

Abstract: Low-temperature glass bonding of silicon, silicon dioxide and silicon nitride is described. Boron oxide was used as the intermediate glass layer at a bonding temperature of 450 degrees C. First experiments indicate that due to reflow and deformation of the molten glass layer bonding over metal patterns is possible, e.g. aluminium or chromium/gold. No voids are observed by examination of cleaved cross sections using optical microscopy or by IR transmission of bonded wafers. Scanning acoustic tomography, however, revealed regions of good, as well as regions of bad bonding quality. Bonding at low temperatures, with less critical demands for surface flatness, and the possibility of metalized electrical feedthrough will offer more process flexibility in the fabrication of sensors and actuators.

Piezoelectric tone generator and a process for producing it

Abstract: To produce a piezoelectric tone generator, a layer of filler-free bonding agent whose dynamic viscosity is 800 to 18,000 mPa·s is applied between a metallized carrier plate and a piezoceramic wafer. The package composed of carrier plate, bonding layer and ceramic plate is pressed together, the quantity of bonding agent being chosen to be so large that during pressing a bead covering the edge of the ceramic wafer is formed. The bonding layer is cured thereafter, firstly catalytically or thermally and then by UV irradiation.

Development of laser bonding as a manufacturing process for inner-lead bonding

Abstract: The conventional thermo-compression bonding processes for bonding tape-automated-bonding (TAB) leadframes to silicon die has inherent reliability drawbacks due to the high pressures and temperatures necessary to produce a good metallurgical joint. Whether tin- or gold-plated tape is used, the bonding process can cause damage to the underlying structure of the device which results in device failures. The use of a laser source for inner lead bonding (ILB) has the advantage of providing a very localized temperature input to the bonding site with minimal contact force. The resulting mechanical stresses on the device are consequently low and the overall temperature extreme to which the device is subjected is similarly low. Advanced Micro Devices, Inc., has undertaken a program to qualify a gold/tin laser bonded ILB process as a viable manufacturing alternative to thermo-compression bonding. The initial evaluation has defined thresholds for laser input energy necessary to produce a good fillet around the TAB beam and a void-free interface. This is the first necessary step to provide the degree of gold/tin alloying necessary to prevent Kirkendall voiding during subsequent high temperature storage. Among the parameters critical to the bonding process is the wafer bump surface topography. The quality of the bonding process has been monitored using bond strength data and visual examination before and after high temperature storage and temperature cycling tests. The test samples used were 154 and 160 lead production TAB tape and device designs with approximately equals 200 (mu) lead pitch and a 410 lead experimental tape with 102 (mu) lead pitch.

Capacity type acceleration sensor

Abstract: PURPOSE: To obtain a capacity type acceleration sensor which can detect a failure correctly. CONSTITUTION: A silicon substrate 20 and a glass substrate 30 are bonded through anodic bonding in a capacity type acceleration sensor 10. The acceleration is measured by the change of the capacitance between a movable electrode 21 and a fixed electrode 31 formed on the substrates 20 and 30. A stopper 41 comprised of a conductive thin film 41a and an insulating thin film 41b is formed on the surface of the movable electrode 21. At the time of the anodic bonding, the conductive thin film 41a does not show polarization, whereas the insulating thin film 41b assumes considerably weak polarization. Before measurement, generally, a voltage is applied between the movable electrode 21 working also as a diagnostic electrode and a diagnostic electrode 32. The change of the output due to the change of the capacitance between the movable electrode 21 and the fixed electrode 31 is subsequently measured. Since a minute gap between the diagnostic electrodes is set to be small, the sensitivity at the checking time of failures is improved. Moreover, since a polarization is hardly brought about, the shifting amount between the electrodes in response to the application of the voltage for the purpose of checking failures is increased, thereby making it possible to detect a failure correctly. COPYRIGHT: (C)1993,JPO&Japio

Articles including thermosetting-powder surface-coatings

Abstract: Manufacture of an article incorporating a thermosetting-powder surface-coating includes bonding a component of the article to the coating by contacting the melted powder with the component before curing takes place, and maintaining it in contact through curing. In a glass architectural panel, an aluminium foil is bonded in this way to a polyester/triglycidyl-isocyanurate powder coating on the silane-primed back of the facing glass; the metal foil is backed by a plastics or rubber open-cell material to enhance resistance of the glass to impact, and also, together with the foil, resistance to thermal shock. The coating includes pigmentation to give the effect of colored glass, or is clear to allow the contact-surface of the metal to show through; further decorative effect is obtained by pigmentation variation in the coating and/or partial metallization of the glass back-surface. The technique is also applied to bonding fittings to the powder-coated face of a door; of decals of cured powder-coating material to, or within, powder-coatings; of glass over apertures in metal walls; and of glass to glass in building up a laminate.

A New Thinning Method for Obtaining Less than 100-nm-Thick Si Film on Wafer Bonding

Abstract: This paper proposes a new wafer thinning method in bonding silicon-on-insulator (SOI) technology. With this new method, thermal oxidation is performed on thin boron-doped Si films after highly selective back-etching to reduce the boron concentration in the film. The boron concentration in the silicon layer on oxide can be decreased more than 2 figures under proper thermal oxidation conditions. A 90-nm-thick silicon layer with 4×1017/cm3 boron concentration was formed on an insulator by this method. Transmission electron microscope (TEM) observation shows that the silicon layer has a highly crystalline quality. It is also found that the reflow of borophosphosilicate glass (BPSG) can effectively fill in the small surface gaps during wafer bonding.

Method for laminating and bonding flat electrodes

Abstract: According to the bonding method of flat electrodes of the present invention, a crystal glass material (5a) is arranged between electrodes (2, 3), headed, and melted while the flat electrodes are pressured, and the melted crystal glass material is fused and re-crystallized to the surface of each flat electrode, so that the flat electrodes can be bonded with strong bonding force. Since a plate-like spacer or an application glass of a low melting point is not used in the method, disadvantages resulting from the spacer or the glass can be removed.

Void elimination by lateral gap diffusion in silicon direct bonding (SDB) technology

Abstract: Voids at bonding seams caused by trapped air pockets during room temperature contacting can be eliminated by lateral gap diffusion. The optimised bonding temperature has been found to be around 1000 o C to realise void-free bonding interfaces

Magnetic head having core parts joined by low-melting point crystallized glass with composite gap

Abstract: A head core includes a pair of core parts made of a magnetic metallic material and bonded together by (1) a gap material which is a low-melting-point crystallized glass which serves as the bonding material and (2) non-magnetic material layers provided between the glass and the gap surfaces of the core parts. The non-magnetic material layers effectively prevent reaction between the low-melting-point crystallized glass and the metallic magnetic material of the core during the bonding heat treatment. The strength of the magnetic gap, as well as dimensional precision of the same, is enhanced as compared with the conventional arrangement of the same gap size in which bonding is accomplished by a low-melting-point non-crystallizable glass, even when the bonding is executed at the same temperature. The invention remarkably improves magnetic head production yields and reliability.

Stability and common mode sensitivity of piezoresistive silicon pressure sensors made by different mounting methods

Abstract: Mechanical stress introduced in a silicon diaphragm chip from the support chip or the substrate affects the performance of silicon pressure sensors. The influence of this effect on long-term stability, thermal zero shift, and common mode pressure sensitivity has been evaluated on differential piezoresistive sensors. The following different structures have been tested and compared: (1) unmounted diaphragm chips as reference; (2) silicon support chips sealed to diaphragm chips by silicon-to-silicon anodic bonding; (3) silicon support chips sealed to diaphragm chips with screen printed solder glass; and (4) Pyrex 7740 borosilicate glass substrates sealed to diaphragm chips by anodic bonding. The results from these tests show that all these methods can be used for high-performance piezoresistive pressure sensors. Silicon-to-silicon anodic bonding is shown to be the best method with respect to thermal zero stability and common mode pressure stability. >

Anodic bonding of insulating and conductive discs to sandwich - involves using two hot plates for heating and applying pressure to minimise distortion and allow more than two discs to be bonded

Abstract: In anodic bonding of an insulating disc to a conductive disc, the discs are sandwiched and heated under pressure on a hot plate and an electrical potential is applied to the sandwich. The novelty is that another hot plate is used for heating and applying pressure. The hot plates consist of stainless steel, pref. coated with a metal resistant to bases. A second insulating disc is used, with the conductive disc sandwiched between the two insulating discs, and the polarity of the potential applied to the hot plates is reversed once during bonding and/or the potential is applied to the insulating disc and one of the hot plates. Additional conductive disc(s) may be pressed onto the outside of the insulating disc(s). USE/ADVANTAGE - Useful for bonding discs of metal or semiconductor, e.g., Si, Ge, GaAs, InP or SiGe wafers, to insulating discs, e.g., of glass. Use of the second hot plate minimises distortion and makes it possible to bond more than 2 discs.

Method for making surface-reinforced glass

Abstract: Glass is surface reinforced by providing a surface layer which contains an oxide component, typically silicon oxide in more excess than the underlying base glass, the oxide component exhibiting higher chemical or mechanical durability than the base glass itself. A surface of glass is tailored by a dry process, typically by exposure to UV radiation in the presence of ozone such that the oxide component is present more at the surface than in the underlying glass while a heavy metal such as Pb is driven out. A magnetic head having such a surface-reinforced sealing glass for bonding a core block to a slider is highly reliable.