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What is temporary bonding and why is it needed?

What makes it possible for our smartphones, tablets, gaming systems, networking devices, and everyday electronics to operate at faster speeds, process more information, and continue to shrink in size? Until now, the answer has included a number of advanced technologies and processes that have allowed the microelectronics industry to double the number of circuits in the same two-dimensional space, but the future relies on the emerging innovation of stacked memory and three-dimensional integrated circuits.

Topics: thin wafer handling, temporary bonding materials

Directed Self-Assembly

SPIEbannerimage Directed self-assembly (DSA) refers to the integration of block copolymer (BCP) materials that undergo phase separation with traditional manufacturing processes. With DSA, nanoscale dimensions are achieved at a drastically reduced cost by novel material designs without additional equipment upgrades.

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Automated dispense systems for small substrate applications

Many research laboratories and institutes use spin-coating technology to cost-effectively create thin-film coatings with precise thickness and uniformity control. In many cases, the most significant initial costs of development work are for the semiconductor-grade substrates. Consequently, many spin-on application projects may use irregularly shaped wafer pieces, microscope slides, and/or wafer die (1 cm × 1 cm) in early development work. Material deposition is typically performed with handheld syringes, manual pipettes, or more sophisticated digital repeater pipettes.

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Process methodologies for temporary thin wafer handling solutions

Use of temporary bonding/debonding as part of thin wafer handling processes is rapidly increasing. Users must determine which temporary bonding/debonding method is appropriate for a specific application. Some of the technologies that have been developed are chemical release, thermal slide separation, and ZoneBOND® debonding.

Topics: thin wafer handling, thermal slide debonding, temporary bonding materials, ZoneBOND

Thermal slide debonding for temporary bonding processes (Part 3 of 3)

Thermal slide debonding represents the next significant advancement in obtaining high-yield thin wafer results. Initial detection of anomalies and cracks usually occurs during debonding; however, many causes for this damage originate during upstream bonding material coating, curing, bonding, and thinning processes. Moreover, only thermal separation tools that are highly precise and highly accurate will consistently render desirable process yields. The bonded pair is subjected to many thermal and compressive forces during processing and debonding. The thinned device layers are often very sensitive to outside factors including temperature, vacuum, and mechanical compression and release.

Topics: spincoat, thin wafer handling, 3D packaging, debonder

Thermal slide debonding for temporary bonding processes (Part 2 of 3)

In addition to precisely controlling application of the materials that enable wafer bonding, a solvent-enriched sealed spin chamber contributes to process integrity. One of the most critical variables in achieving optimal uniformities at the desired target thickness is airflow dynamics. Ideal conditions are created in a sealed chamber with a prewet solvent nozzle, a backside rinse, a lid gasket, a splash ring (air-flow baffle), a programmable exhaust, and center-stream bonding material delivery. Radial and reverse-radial scanning dispense arms are not recommended because they require open bowl environments. Additionally, the scanning technique has not demonstrated significant advantages related to uniformity or material conservation.

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Thermal slide debonding for temporary bonding processes (Part 1 of 3)

The microelectronics industry is rapidly migrating to fabricating 3-D wafer stacking interconnects using through-silicon via (TSV) technology. Major market segments seeking to benefit from TSV technology include advanced packaging for memory/logic, light-emitting diodes (LEDs), and compound semiconductor (III-V) high-power radio-frequency (RF) devices. In this cutting-edge technology, fragile device substrates are bonded to carrier substrates with polymeric bonding materials for uniform support during backgrinding (thinning) processes. Device wafers containing various topographies, including etched topographies, high-aspect-ratio structures, trenches, and bored holes throughout the active component area, are first coated and planarized using spin-on bonding materials. Each coated device wafer is then mounted to a rigid carrier and thinned, usually to a thickness of less than100 µm, for further processing. The bonded pair, including the bonding material layer, will be subjected to a wide variety of thermo-mechanical stresses generated during backside processing to thin the device wafer and create electrical input/output redistribution layers (Figures 1 through 5). An effective temporary wafer bonding solution is expected to provide complete support, retain bond strength, and remain soluble for relatively low-temperature (>150°C) separation and cleaning. Temporary bonding process steps include the following:

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Programmable bake plates and electronic proximity lift-pins

 Since the dawn of the microelectronics industry, application engineers have required the ability to uniformly cure photosensitive materials. Particularly, curing wet-developable spin-applied films evenly across the substrate surface has presented a technical challenge. Such curing has become increasingly difficult with the introduction of large format substrates (200- to 300-mm) and the continual decrease in critical dimensions. Uniform baking across the substrate surface is critical to reduce over-curing, which causes "scumming," and under-baking, which causes undercut erosion and pattern collapse.

Topics: spin coat, bake plate, uniform baking across substrates, high-uniformity bake plates

Developer options for spin-on photosensitive materials

Developing photosensitive film layers to produce features of targeted sizes is a critical process step within any photolithography application. Application engineers have created several processes for performing this step with tank immersion (that is, a bath) and/or several adaptations of spin developing a single wafer to make patterns of features based on film areas of differing solubility. The use of immersion tank processes has steadily declined in MEMS fabrication and advanced lithography over the past decade due to excessive material consumption, non-uniform resolution, and poor clearing from high-aspect-ratio features due to insufficient agitation. Additionally, increased throughput requirements and smaller critical dimensions (CDs) have further shifted mainstream applications to single-wafer (track) spray/puddle process flows. 

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Automated dispense systems for applying high-viscosity materials

Process Engineers have explored several techniques for consistently dispensing high-viscosity resins for spin-on material applications. Manually pouring and/or using pre-filled syringes requires significant material consumption and excessive time and introduces microbubbles into the viscous material. Achieving consistently accurate dispense rates and volumes and controlled suck-back is a daunting challenge. Automatic dispense options provide a feasible solution, however, many variables must be considered when pursuing this option.

Topics: spincoat, spin coat

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