In the final stage of silicon wafer cleaning the silicon oxide layer has to be removed and the clean wafer dried without contamination. When wafers are removed from the HF etching process and transferred to a drying chamber, the extra handling increases the chances for wafers to pick up contaminating particles. Such particles cause errors in the further processing of the wafers and can result in final semiconductor products that are defective or of poor quality. Carrying out the final etching and the wafer drying in one chamber reduces the possibility of contamination and can result in better output quality. The latest field results from a customer using Modutek’s single chamber HF-last and IPA vapor dryer show a substantial reduction in particle counts on wafer substrates.
The Single Chamber Process
Modutek uses IPA vapor (Marangoni) drying in a free-standing unit with one drying chamber for DI water rinsing and drying. The IPA vapor is generated in a standard one gallon bottle and is introduced into the drying chamber through the top cover to ensure even distribution. IPA consumption is low but is still adequate to give surface tension drying across all wafers and substrates. The Marangoni drying technique results in wafers without any watermarks.
To allow single step etching and drying in one chamber, Modutek modified the IPA vapor dryer to include HF (hydrofluoric) acid injection before the start of the standard IPA vapor drying process. The HF acid injection is ratio controlled and provides an oxide etch down to bare silicon. Once etched, the wafers are rinsed to a controlled pH level. When the required pH level is reached, the IPA drying process begins without moving the wafers. The particle count on the wafers remains low.
Field Results
Modutek has supplied the new single chamber HF-last IPA dryer to customers and the first large scale results are now in. In the 0.3 to 5 micron range, fewer than 20 particles (adders) were added to the etched substrate after using the Modutek etching/drying combined system. These particle counts are substantially below those achieved using the previous process in this particular field trial. Semiconductor manufacturing facility managers and research center engineers can compare these results to particle counts resulting from their current process and may be able to achieve significant improvements using the Modutek equipment.
The number of microscopic particles on wafers is becoming more and more critical as micro-structures and electronic features become smaller. Where comparatively large conducting areas and physical structures can work well even when they contain a disruptive particle, particles in the way of smaller structures either result in defective semiconductor components or in components whose characteristics are not as specified.
Modutek’s single chamber technology lets semiconductor manufacturing facilities improve output performance and increase yield. The entire etching, rinsing and drying process took only about 15 to 20 minutes in this application. One customer is reviewing particle counts, yields and output quality throughout the entire operation because it is likely that the improved facility performance with the Modutek system can justify the cost of acquiring the new equipment.
How Modutek Can Help
Modutek has over 35 years of experience providing wet processing equipment to the semiconductor manufacturing industry. The company has the expertise to advise customers regarding their semiconductor processing needs and can customize their equipment to fit particular applications. Their state-of-the-art equipment has helped wet process facilities meet their production goals in the past and the new single chamber HF-last etch and IPA vapor dryer can now help customers improve overall production line performance and increase facility profitability.
