Substrate Cleaning Methods for Fabricating OLEDs and Its Effect on Current Leakage Defect Formation

Various methods for cleaning the large glass substrates (300 times 400 mm) used in organic light-emitting diode (OLED) fabrication processes were investigated. Horizontal roller-bed cleaning methods using a shower-rinse with megasonic (MS)-irradiation, or brush-scrubbing, were investigated for use with anode sputtering processes. Substrates were contaminated with particulate contaminants (0.3-0.5 particles/cm
²
) generated from anode sputtering targets. Large particles ( ges 5 mum) were easily removed with the MS irradiation (efficiency ges 95% ). Small particles (<3 mum) were harder to remove. The brush-scrubbing cleaning removed them with 80 - 90% efficiency, while the MS-irradiation cleaning had an efficiency of 60%-70%. spin-rinse-dry cleaning methods using ozonized or electrolyzed cathode water were investigated for use with pre-organic deposition processes. Glass substrates were intentionally contaminated by exposing them to a clean room atmosphere for either 24 or 100 hours. The number of particles was reduced from around 0.4 to 0.03/cm
²
and from around 1.7 to 0.08/cm
²
by the MS-irradiation cleaning using de-ionized water alone, respectively. The effect of the ozonized water treatment was evident for the longer exposure substrates: it reduced the number of particles to 0.03. The electrolyzed-cathode water cleaning was successful in removing submicrometer size particles. We also investigated the effect of particulate contaminants on the current leakage defect formation.