Characterization of an ultra-thick positive photoresist for electroplating applications

Flack, Warren W.; Nguyen, Ha-Ai; Capsuto, Elliott Sean

doi:10.1117/12.483748

Cited by 10 publications

(9 citation statements)

References 9 publications

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“…For example, an electroplating process is very sensitive to sidewall angles and footing in a photoresist [8]. This suggests that what appears to be a cosmetic defect on the wafer could be a reliability problem due to lower shear stress or uneven bump heights.…”

Section: Introductionmentioning

confidence: 96%

Defect printability for high-exposure dose advanced packaging applications

et al. 2003

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Pellicles are used in semiconductor lithography to minimize printable defects and reduce reticle cleaning frequency. However, there are a growing number of microlithography applications, such as advanced packaging and nanotechnology, where it is not clear that pellicles always offer a significant benefit. These applications have relatively large critical dimensions and require ultra thick photoresists with extremely high exposure doses. Given that the lithography is performed in Class 100 cleanroom conditions, it is possible that the risk of defects from contamination is sufficiently low that pellicles would not be required on certain process layer reticles. The elimination of the pellicle requirement would provide a cost reduction by saving the original pellicle cost and eliminating future pellicle replacement and repair costs.This study examines the imaging potential of defects with reticle patterns and processes typical for gold-bump and solder-bump advanced packaging lithography. The test reticle consists of 30 to 90 µm octagonal contact patterns representative of advanced packaging reticles. Programmed defects are added that represent the range of particle sizes (3 to 30 µm) normally protected by the pellicle and that are typical of advanced packaging lithography cleanrooms. The reticle is exposed using an Ultratech Saturn Spectrum 300e 2 1X stepper on wafers coated with a variety of ultra thick (30 to 100 µm) positive and negative-acting photoresists commonly used in advanced packaging.The experimental results show that in many cases smaller particles continue to be yield issues for the feature size and density typical of advanced packaging processes. For the two negative photoresists studied it appears that a pellicle is not required for protection from defects smaller than 10 to 15 µm depending on the photoresist thickness. Thus the decision on pellicle usage for these materials would need to be made based on the device fabrication process and the cleanliness of a the fabrication facility. For the two positive photoresists studied it appears that a pellicle is required to protect from defects down to 3 µm defects depending on the photoresist thickness. This suggests that a pellicle should always be used for these materials. Since a typical fabrication facility would use both positive and negative photoresists it may be advantageous to use pellicles on all reticles simply to avoid confusion. The cost savings of not using a pellicle could easily be outweighed by the yield benefits of using one.

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Section: Introductionmentioning

confidence: 96%

Defect printability for high-exposure dose advanced packaging applications

et al. 2003

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“…With chemical amplification, during exposure one photon can trigger the reaction of hundreds (if not thousands) of acidcatalyzed deprotection reactions, rather than one proton to decompose one photoactive compound molecule system used for DNQ/Novolak systems [2]. These resists are also transparent enough to allow photons to penetrate throughout the depth of the mask and generate the reactions [3].…”

Section: Introductionmentioning

confidence: 99%

Wet Chemical Processing with Megasonics Assist for the Removal of Bumping Process Photomasks

Seong¹,

Tracy²

2014

Additional Conferences (Device Packaging, HiTEC, HiTEN, and CICMT)

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A new generation of negative tone resists by TOK, JSR, and Dow Chemical is gaining momentum in advanced packaging applications. Resist thickness requirements are actually increasing to the 50-100 um range as Cu pillars are adopted to accommodate the tighter pitches required in advanced packaging. In order to form pillars the resist must be thicker to contain the entire bump structure. Thick, negative tone resists are more transparent to exposure light wavelengths than positive tone resists and can be exposed by the lithography process much faster (~1 x 104 cross-linking chemical events are driven by 1 photochemical event vs. 100 – 1000 for positive tone resist).1 Therefore exposure times can be shorter, post-exposure bake steps can be shorter, and delay before or after exposure is not necessary, saving photolithography time and CoO. And, due to more complete cross-linking throughout the resist, the resist mask profiles are truer (from Flack et.al, “A Comparison of New Thick Photoresists for Solder Bumping”, SPIE 2005).1 The major drawback to negative tone resists is that the solvent strip times of the highly cross-linked resist masks are much longer than for positive tone. Flack et.al. noted resist strip times of 5 minutes for two positive resists used in their experiments vs. 50 minutes for the AZ-100nXT negative tone resist, using AZ400T at 80°C (most likely in an immersion tool). Long strip times or special stripping requirements are noted on the data sheets of the other majority suppliers of negative resists as well. Akrion engineers have developed a novel, single-wafer, negative PR strip processes using organic solvents plus Goldfinger megasonics, to provide 30 - 70% reductions in process times and the associated chemical consumption when compared to processes that do not utilize a megasonics assist. The multi-step process can be accomplished in a single process chamber, with each step optimized for time and temperature based on the resist thickness and solvent stripping chemistry used. In the Akrion process, a period of solvent exposure at low wafer spin speed is used initially to begin swelling and dissolving the thick photoresist layer. This is followed by a second solvent exposure step using aggressive frontside megasonic energy to promote polymer chain scission throughout the bulk of the photoresist layer. Following this step A DI water rinse and spin dry step are sufficient to completely remove the solvent, dissolved photoresist and any polymer residues. This paper reviews the development of the Akrion process and several examples of improvement in stripping time and results from work with customers.

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“…Today there is a rapid increase in the pin counts of most solder bump applications. The necessary corresponding reduction in bump pitch makes conventional "mushroom" type over plating impractical in high bump count devices [2,3,4,5]. Elimination of the umbrella requires even thicker photoresist layers since the entire solder volume is contained by the photoresist mold.…”

Section: Introductionmentioning

confidence: 99%

“…Elimination of the umbrella requires even thicker photoresist layers since the entire solder volume is contained by the photoresist mold. Typical thicknesses for mushroom free processes are in the 60 to 100 μm range [3]. Extending the microlithographic processes into these rapidly growing areas is placing new demands on both the photosensitive materials and the lithography equipment.…”

Section: Introductionmentioning

confidence: 99%

Characterization of a high-photospeed positive thick photoresist for lead-free solder electroplating

Flack¹,

Nguyen²,

Washio³

et al. 2007

Proceedings of SPIE

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The introduction of lead free solder (SnAg) electroplating for advanced packaging applications has created new challenges for thick photoresist processes. Dry film laminate photoresist materials do not provide sufficient resolution or process control for the smaller bump diameters used with advanced design rules. The traditional positive tone DNQ-Novolak photoresists require large exposure doses and long processing times that are unacceptable for the total cost of ownership (COO) of the lithography cell in a manufacturing environment. Standard chemically amplified positive photoresists have interactions between the PAG and Cu or Cu 2 O at the soft bake step which makes it impossible to obtain sufficient pattern fidelity for electroplating lead free solder on copper seed layer substrates. This study will characterize a novel positive tone, chemically amplified photoresist (TOK PC-0059B PM) that can be double coated up to 100 μm thick for lead free solder electroplating. The PAG in the photoresist has been formulated to prevent any interaction with Cu or Cu 2 O. This photoresist exhibits extremely high photospeed, excellent pattern resolution and ease of stripability after electroplating. The lithographic performance of the thick positive photoresist will be optimized on 300mm wafers using a broad band, low numerical stepper. Enhanced process latitude and very high photospeeds will be demonstrated for thicknesses up to 100 μm. Cross sectional SEM analysis, process linearity, and electroplating performance are used to establish the lithographic capabilities.

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Characterization of an ultra-thick positive photoresist for electroplating applications

Cited by 10 publications

References 9 publications

Defect printability for high-exposure dose advanced packaging applications

Defect printability for high-exposure dose advanced packaging applications

Wet Chemical Processing with Megasonics Assist for the Removal of Bumping Process Photomasks

Characterization of a high-photospeed positive thick photoresist for lead-free solder electroplating

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