Ultrafiltration treatment for spent tungsten slurry generated by chemical polishing process in wafer fabrication industry for reuse / Nur Fatin Amalina Muhammad Sanusi
Proses pengilatan kimia diaplikasi secara meluas terutamanya dalam industri
mikro elektronik bertujuan untuk meratakan permukaan wafer. Proses ini melibatkan
mengilatkan permukaan bersalut logam oleh proses kimia dan diikuti pembuangan
lapisan logam yang telah terjejas oleh proses mekanikal untuk mencapai pengilatan
yang sempurna menggunakan buburan tungsten. Ia terdiri daripada campuran
komponen yang kompleks di mana sifat fizikal dan kimianya boleh berubah
bergantung kepada jenis dan keadaan rawatan yang diterima. Oleh itu, pencirian
kimia dan fizikal buburan tungsten terpakai merupakan maklumat penting dalam
usaha mempertimbangkan kaedah pemulihan yang sesuai. Penggunaan semula
butiran silika bersaiz nano diperkenalkan sebagai salah satu langkah untuk
mengurangkan kos pembuatan dan jumlah pengeluaran air sisa di mana ia memberi
kebaikan dari segi kos dan alam sekitar. Sistem ultrapenapisan aliran silang telah
dipilih sebagai kaedah untuk merawat dan kitar semula buburan tungsten terpakai
hasil daripada proses pengilatan kimia. Ujikaji membran ultrapenapisan telah
dijalankan menggunakan terhadap tiga jenis membran yang berbeza (polysulfone,
polyethersulfone and polyvinylidene fluoride) dengan MWCO yg berbeza iaitu 10,
30, 50 dan 100KDa. Kesan kesan tekanan dalaman (TMP) membran dan kadar aliran
fluks telah juga diuji. Analisis terhadap pemilihan, pengekalan butiran silica dan
pengubahsuaian nilai pH pada buburan tungsten terpakai telah dijalankan untuk
menentukkan prestasi kecekapan membran penapisan dan fenomena pengotoran.
Tekanan membran 1 bar memberikan kadar terbaik dan tahap kotor yang paling
rendah berbanding tekanan dalaman yang lain. Keputusan terbaik ditunjukkan oleh
membran PS 50KDa yang mempamerkan pencapaian 92% dalam pengekalan butiran
silika dan cuma 42% dalam pengekalan tungsten. Ia juga mencapai purata saiz paling
rendah di mana perbezaan purata saiz hanya pada tahap 0.5% berbanding purata saiz
asal butiran silika isitu 125 nm dalam retentate berbanding membran PVDF dengan
MWCO yang sama. Pemulihan buburan tungsten terpakai boleh ditingkatkan dengan
pengubahsuaian nilai pH 9 telah mencapai prestasi yang baik kerana mempunyai
nilai saiz purata 126 nm berbanding nilai saiz purata asal 125 nm dan memberi
pengekalan butiran silika terbesar sebanyak 42% dalam retentate. Ia juga mencapai
nilai negatif terbesar -40 mV dalam nilai zeta potensi yang menunjukkan kestabilannya. Secara kesimpulan, membran PS 50KDa menunjukkan potensi terbesar dalam penapisan dan pemekatan butiran silika hasil proses pengilatan kimia dengan keadaan nilai pH 9.
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Chemical Mechanical Polishing (CMP) is a widely used process to planarize
wafers for microelectronic applications. It involves the polishing of metallic surface
by chemical action followed by the removal of the modified layer by mechanical
action using tungsten slurry. It is a rather complex mixture that both physical and
chemical properties of the components in the slurry are expected to change
depending on the condition and type of treatments that they receive. As such,
characterization of the spent tungsten slurry and knowledge on its physical and
chemical properties are critical in order to consider suitable recovery methods.
Recycling of the abrasive slurry is one of the options to reduce the manufacturing
cost and to achieve environmental benefits that arise from the reduction of
wastewater volume. Crossflow ultrafiltration system was used as a method to recycle
the silica based slurry. It investigated using three membrane materials i.e.
polysulfone (PS), polyethersulfone (PES) and polyvinylidene fluoride (PVDF) with
different molecular weight cut off (MWCO) of 10, 30, 50 and 100KDa. Effects of
transmembrane pressure (TMP) on flux flow rate were characterized. Analyses of
selectivity, retention and pH adjustment of feed water were done to demonstrate the
membrane performance and fouling phenomena. A TMP of 1 bar gave the lowest
fouling result as compared to the other TMPs. The PS 50KDa membrane
demonstrated the best results with 92% retention of silica particles and only 42%
retention of tungsten. It also achieved the lowest mean size particle of 125nm in the
retentate or only 0.5% value difference compared to that of the original spent
tungsten slurry than those of other membranes especially PVDF membrane with the
same MWCO. The performance in spent tungsten slurry recovery could be improved
by adjusting the pH to 9 that gave the best performance in terms of having the lowest
mean size of 126 nm which was close to 125 nm of the original size of particles in
the spent tungsten slurry. It gave the highest retention of silica particles of 42% in the
retentate. It also had the largest negative value of -40mV in zeta potential to suggest
its stability. In conclusion, PS ultrafiltration with 50KDa of MWCO membrane
showed the highest potential in filtrating and concentrating the spent tungsten slurry
of CMP process with the best result achieved at a pH value of 9.
Ultrafiltration treatment for spent tungsten slurry generated by chemical polishing process in wafer fabrication industry for reuse / Nur Fatin Amalina Muhammad Sanusi
Ultrafiltration treatment for spent tungsten slurry generated by chemical polishing process in wafer fabrication industry for reuse_ Nur Fatin Amalina Muhammad Sanusi_K4_2017_MYMY