电解水清洗用于半导体制造

A semiconductor cleaning technology has been based upon RCA cleaning which consumes vastThis technology hence gives rise to manyamnounts of chemicals and ultra pure water.e.vironmental issues, and some alternatives such as electrolyzed water are being studied. In thiswork, intentionally contaminated Si wafers were cleaned using the electrolyzed water.Theelectrolyzed waters were obtained in anode and cathode with oxidation reduction potentials and pH of-1050mV and 4.8,and -750mV and 10.0, respectively. The electrolyzed water deterioration wascorrelated with CO, concentration changes dissolved from air. Overflowing of electrolyzed waterduring cleaning particles resulted in the same cleanness as could be obtained with RCA clean.Theroughness of patterned wafer surfaces after EW clean maintained that of as-received wafers.RCAclean consumed about 91 chemicals, while electrolyzed water clean did only 400m HCl or 600mlNH,Cl to clean 8”wafers in this study. It was hence concluded that electrolyzed water cleaningtechnology would be very effective for releasing environment, safety, and health(ESH) issues in therext generation semiconductor manufacturing.

L.INTRODUCTION

Ultraclean wafer surface must be achieved for the next generation semiconductor processes.Many wet cleaning processes that aim to eliminate contaminants have been developed based on RCAcleaning. RCA cleaning is the several step process which consists of highly concentrated chemicalt-eatments at relatively high temperature.As the diameter of Si wafers increases and thesemiconductor devices shrinks, the number of cleaning process units increases so that the amount otchemicals and ultra pure water(UPW) consumed in RCA cleaning process increases drastically andcroduction cost increases as well. In order to resolve these issues, advanced cleaning methods haveceen studied applying functional water such as hydrogenated ultra pure water (H,-UPW), ozonized

water(O;-UPW)7-8and electrolyzed water(EW).9-1fIt is expected that application of EW would increase in semiconductor manufacturing because thecharacteristics of EW are able to be controlled more diversely and accurately than those of otherfanctional waters such as hydrogenated UPW or ozonized UPW. Hence, silicon wafer cleaning isstudied introducing EW in this work.

IILRESULTS AND DISCUSSION

In case of NHOH addition as an alkaline electrolyte, the pH/ORP for AW and CW weremeasured to be 6.3/+450 mV, and 9.8-10.0/-750 mV, respectively. It was observed that reductivealkaline solution was generated in cathode chamber with the NHOH electrolyte. In case of HCladdition as acid electrolyte, the pH/ORP for AW and CW were 4.7/+1000 mV and 6.3/-550 mV.respectively, and it was observed that oxidative acid solution was generated in anode chamber. Incase of NHCl electrolyte, the pH/ORP of AW and CW were measured to be 4.8/+1050 mV and 10.0/.750 mV, respectively. It was also observed that AW and CW were suddenly deteriorated afterelectrolyzed, but maintained their characteristics at least for more than 40 minutes. AW with highORP was expected to be applied to remove metallic contaminations because of its oxidativecharacteristic, while CW with low ORP for particle removal.CO2 concentration changes dissolved in EW were measured with FT-IR/ATR.COzconcentrations in EW increased as exposured time to air increased after EW generation. After 2-3hour exposure to air CO, concentration decreased gradually to the level that the normal water couldtake.It seemed that ORP deterioration could be correlated with temporal oversaturation of CO,Cleaning was carried out to evaluate metallic impurity removal capability of EW generated with NHClelectrolyte RCA cleaning was compared with EW cleaning, and it was realized that RCA cleaningshowed the best results so far.Metallic removal efficiency of AW was nearly as much as RCAcleaning, and therefore possible application of AW for metallic removal was confirmed, These

results could be reviewed with Pourbaix diagram.In this experiment, RCA and HPM cleaning were applied at 65C and comsumed about 9l and60 chemicals, respectively, while EW was applied at room temperature and included only 400ml HClelectrolyte or 600m NHCl electrolyte uses. The consumption of chemicals with EW is 1/22~1/10times less than that of RCA or HPM cleaning processes. By employing EW for metal removal in acleaning process, it was expected that not only saving chemicals but also obtaining a drastic reductionin the amount ofrinsing UPW could be achieved.