Temporary Bond Research Articles

Temporary Wafer Bonding Materials and Processes

Temporary wafer bonding has been used for many years to provide mechanical support to device wafers during thinning processes. However, the advent of 2.5D and 3D integration is placing significantly higher demands on the performance of temporary bonding materials as more fabrication processes are required on progressively thinner wafers. In response, materials providers have recently developed several different types of temporary bonding solutions that seek to provide a robust carrier with a simple debond process. Typical 2.5D or 3D integration process flows will require more types of processes than just backgrinding and CMP to be done on the backside of thinned wafers. RIE, PECVD oxide deposition, lithography, and electroplating are some of the process steps that will be needed to complete the TSV interconnects. Each of these steps, and the order in which they are done, will impose certain requirements on the temporary bond material. This presentation will examine the different categories of available temporary wafer bonding solutions with regard to their bonding and debonding methods as well as their resistance to and compatibility with various BEOL processing steps. In addition, ongoing work at RTI to evaluate temporary bond materials for silicon interposer and 3D-IC applications will be presented. This work has been focusing on the interaction between these materials and the processing requirements of several photoimageable dielectrics.

Impact of adhesive rheology on stress-distortion of bonded plastic substrates for flexible electronics applications

For fabrication of flexible electronics using standard microelectronics toolsets, a temporary bond–debond method has been developed that requires minimization of the distortion of bonded flexible substrate and bow of bonded system (flexible substrate-adhesive-carrier) during processing. To elucidate the critical parameters of the adhesive used in the bonding that control the stress (bow) and distortion, adhesives with different viscoelastic properties are examined systematically. By blending a high modulus adhesive into a low modulus adhesive, the storage modulus, loss modulus and loss factor of the adhesive can be tuned by orders of magnitude. Detailed examination of the impact of these three rheological parameters on the stress and distortion of bonded system reveals that the relative viscoelastic flow properties of the bonding adhesive to that of the bonded flexible substrate are directly correlated to bow and distortion. When the loss factor of the adhesive is less than that for the plastic substrate, precise registration of layers during photolithography is observed. These results provide insight into the rheological parameters critical to the adhesive formulations for the temporary bond–debond method in the fabrication of flexible electronics.

Temporary bond—debond technology for high‐performance transistors on flexible substrates

Abstract— A processing technology based upon a temporary bond—debond approach has been developed that enables direct fabrication of high‐performance electronic devices on flexible substrates. This technique facilitates processing of flexible plastic and metal‐foil substrates through automated standard semiconductor and flat‐panel tool sets without tool modification. The key to processing with these tool sets is rigidifying the flexible substrates through temporary bonding to carriers that can be handled in a similar manner as silicon wafers or glass substrates in conventional electronics manufacturing. To demonstrate the power of this processing technology, amorphous‐silicon thin‐film‐transistor (a‐Si:H TFT) backplanes designed for electrophoretic displays (EPDs) were fabricated using a low‐temperature process (180°C) on bonded‐plastic and metal‐foil substrates. The electrical characteristics of the TFTs fabricated on flexible substrates are found to be consistent with those processed with identical conditions on rigid silicon wafers. These TFTs on plastic exhibit a field‐effect mobility of 0.77 cm2/V‐sec, on/off current ratio >109 at Vds = 10 V, sub‐threshold swing of 365 mV/dec, threshold voltage of 0.49 V, and leakage current lower than 2 pA/μm gate width. After full TFT‐array fabrication on the bonded substrate and subsequent debonding, the flexible substrate retains its original flexibility; this enables bending of the EPD display without loss in performance.

Temporary Corrosion Protection and Bond of Prestressing Steel

This study investigates the performance of different temporary corrosion protection methods for prestressing steel. Four types of laboratory corrosion tests with three emulsifiable oil products in three concentrations resulted in the selection of one product that showed by far the best corrosion protection behavior. Field tests during the winter on 16 transverse deck post-tensioning tendons of 2 road bridges demonstrate the practical suitability of the selected product. Using this product, a pullout test with a long embedment length was performed on a post-tensioned seven-strand tendon with a plastic duct and compared with a reference test using untreated strands. A bond shear stress reduction by a factor of approximately 2.5 was observed compared with the untreated strands. This reduction does not appear to significantly influence the load-deformation response of post-tensioned concrete members and suggests that the emulsifiable oil does not need to be removed before grouting of the tendons. However, since the bond reduction caused by emulsifiable oils in grouted tendons may lead to a somewhat soft load-deformation response of post-tensioned concrete members in the decompressed state, a lower-bound estimate of the corresponding stiffness can be obtained if necessary by assuming a completely unbonded behavior of the post-tensioning tendons.

Appendix: 105-S06 Temporary Corrosion Protection and Bond of Prestressing Steel

Appendix: 105-S06 Temporary Corrosion Protection and Bond of Prestressing Steel

Double-flip transfer of indium phosphide layers via adhesive wafer bonding and ion-cutting process

A twice-transferred layer of indium phosphide (InP) onto a host substrate by means of ion cutting and adhesive wafer bonding was demonstrated to be suitable for device integration. A thin layer was first transferred onto a glass handle through the ion-cutting process by hydrogen implantation and adhesive bonding. The InP/adhesive/glass structure was then bonded to a host substrate using benzocyclobutene, followed by thermal separation of the temporary bond. The surface of the resulting InP layer is that of the original substrate, demonstrating the feasibility of prefabricated device layer transfer without etching sacrificial donors. The electrical properties of the transferred layer are also presented.

Silicon Layer Stacking Enabled by Wafer Bonding

ABSTRACTThree-dimensional integrated circuits (3-D ICs), in the form of a vertical stack of several interconnected device layers, have many performance, form factor, and integration advantages. The main objective of this work is to develop reliable process technology to enable the fabrication of a vertically interconnected silicon multi-layer stack.Low temperature wafer bonding processes, both copper thermo-compression bonding and silicon dioxide fusion bonding, are studied extensively as key enabling technology. Cu thermo-compression bonding is studied for its feasibility as a permanent bond between active layers in a multi-layer stack. Silicon dioxide wafer bonding, on the other hand, is used as a temporary bond to attach a donor wafer to a handle wafer during donor wafer thinning and subsequent layer transfer. Sufficiently high bond strength is obtained with careful surface preparation and activation prior to bonding.Silicon layer can be stacked either in a “face down” or “face up” orientation. Using a combination of wafer bonding and thinning, double-layer stacks in both orientations are fabricated. By repeating these steps on two “face down” double-layer stacks, a four-layer stack is successful demonstrated.

Exploration of the Scaling Limits of 3D Integration

ABSTRACTThree dimensional (3D) wafer bonding is an emerging technology that may be used to increase transistor densities by stacking devices over devices. The alignment of the wafers and the devices on them is a function of the mechanical capability of the wafer to wafer alignment tool and the thermal conditions of each wafer when bonded. However, as bonded wafers are thinned to 1% or less of their starting thickness the processes of bonding and thinning as well as previous process history affect wafer planarity and silicon stress. The drive to vertically interconnect circuit blocks at the sub-micron scale requires a high density of vertical interconnects and thinning a wafer to less than 5 μm enables through wafer via processing at a scale found in the first layers of the interconnect stack. In this paper the measurement of wafer to wafer alignment was done by comparing a metal pattern on a face down bonded silicon on insulator (SOI) wafer to a complementary metal pattern on the bulk wafer to which it was bonded. The effect of aggressive thinning is evaluated using thinned back to face bonded SOI wafers with functional devices and face down bonded non-patterned SOI wafers thinned after bonding. The face up bonded SOI wafers with functional devices were temporarily bonded face down to a Si-wafer I, thinned to the buried oxide (BOX), face up bonded with benzocyclobutene (BCB) on a Si-wafer II, followed by release of the temporary bond and electrical test. Raman and XRD stress measurements of the non-patterned SOI wafer silicon 70 nm and 110 nm thick SOI Si were taken before and after thinning, and the radius of curvature of the SOI wafers and the bulk wafer substrates was monitored. Thermo-mechanical models of SOI Si stress and bonded wafer curvature are compared to the measured results.

EAVESDROPPING AND DEFENSIVE AUDITORY MASKING IN AN AUSTRALIAN BUSHCRICKET, CAEDICIA (PHANEROPTERINAE: TETTIGONIIDAE: ORTHOPTERA)

We investigated the potential for a novel alternative male tactic in Caedicia, an Australian genus of duetting phaneropterine bushcrickets (Orthoptera: Tettigoniidae: Phaneropterinae). Males listen to and track females as they reply to the calls of other males, using both the male call and the female reply to initiate their own searching behaviour. We describe this behaviour as eavesdropping. Calling males produce a high intensity chirp following their calling song, which has no apparent effect on female responsiveness. We test the possibility that this loud chirp acts to defend the temporary pair bond, established between the calling male and the duetting female, by preventing other males from hearing the female reply. We suggest means by which the calling male may be able to hear the female reply whilst producing the masking chirp. This behaviour may be considered a form of pre-copulatory acoustic mate guarding.

Effects of GABA and picrotoxin on temporary bonds in neuronal populations of the motor cortex

The paired stimulations of some brain structures (the medial lemniscus, the reticular nucleus of the midbrain tectum, and the pyramidal tract) resulted in the formation of temporary bonds in the neuronal populations of the motor cortex of the non-immobilized awake rabbits. The changes in the neuronal impulsation observed in the absence of the supporting stimuli were used as the criteria of establishment of the temporary bond. The changes consisted of the elements reproducing an initial response pattern and generation of impulse sequences that appeared later and differed in their configuration from the responses evoked by the real stimuli. The application of GABA directly to the site from which the neuronal activity was recorded blocked the former changes and significantly facilitated the latter ones. Picrotoxin antagonized the GABA effect only in relation to the late rearrangements of the impulse activity (generation of the sequences that differed from the responses evoked by stimulation).

Bacteriostatic effect of tetracycline in a temporary cement

Temporary crowns with subgingival margins can result in gingival inflammation. This inflammation is the result of plaque accumulating at the restoration-tooth interface and a change in the nature of that plaque to one associated with periodontitis. It was postulated that tetracycline incorporated in a slightly soluble cement would be released in the sulcus and decrease the amount, and improve the quality, of the subgingival microflora. The unknown was whether tetracycline is inactivated by any of the components of the temporary cement Temp Bond. To determine this concern, disks of Temp Bond cement with and without varying concentrations of tetracycline were anaerobically incubated in cultures of Bacteroides gingivalis. Results showed that tetracycline incorporated in Temp Bond at 10% by weight is highly bacteriostatic while retaining typical working properties of the cement.

Calculating the process of removing bond from insulator castings

In designing apparatus for removing the temporary bond it is necessary to possess data on the process kinetics in order to establish the time needed. Carrying out the appropriate experiments, considering a sufficiently wide range of insulators for sparkplugs, is connected with certain difficulties. Therefore it is of interest to develop a method of calculating the duration of this process which will be common for the most typical dimensions of the sparkplug insulators, and taking into account the mass-conducting properties of the ceramics in relation to the process parameters.

Renewing the link between communications and educational technology

William H. Allen (1971) recently reviewed long-term trends in instructional media concluding that the broad field of communication research, in which social psychology played a key role, 'never became integrated with the mainstream of instructional media and to this day these two related disciplines are taking different routes (pp. 6-7). Perhaps it was the temporary bond of common commitment to research in educational television that brought the two areas somewhat closer in the mid-fifties to mid-sixties than they are today. In the early sixties, programed instruction had a major impact on educational technology, but did not similarly influence the general communications area. The current trends and emphases in instructional media research cited by Allen seem to be evolutionary and interrelated spin-offs from