Press Releases


December 2, 2009

Electrolyzed Sulfuric Acid Generator "Green Sulfaceed KD™",
A New Technology for Semiconductor Resist Removal, Dramatically Reduces the Environmental Impact of the Semiconductor Cleaning Process

Kurita Water Industries, Ltd. (headquarters: Shinjuku-ku, Tokyo; President: Hiroshi Saito) received the first order and completed the delivery of its electrolyzed sulfuric acid generator "Green Sulfaceed KD™" for resist removal in semiconductor manufacturing. The order was received from a leading U.S. semiconductor manufacturer.

The resist removal process traditionally uses a mixed solution of sulfuric acid and hydrogen peroxide (SPM) in semiconductor manufacturing; however, a need to minimize environmental impact and processing costs has led to a strong demand for reducing the consumption of processing liquids. This has led to our research into resist removal using an electrolyzed sulfuric acid solution and, in turn, the development of the electrolyzed sulfuric acid generator. This new technology allows semiconductor manufacturers to significantly reduce consumption of processing liquids while ensuring higher efficiency than the conventional SPM method.

This groundbreaking technology will be marketed to wafer and semiconductor manufacturers aiming to improve their semiconductor wet cleaning processes, reducing costs, and protecting the environment.

1. Background of development

(1) Need to improve semiconductor manufacturing processes

In recent years, semiconductor manufacturers have been continuously improving their manufacturing processes not only for micronization, but also for increasing productivity, reducing cost, and minimizing environmental impact. For the wet cleaning process, in particular, efforts have been made to reduce the consumption of processing liquids using functional cleaning water, and to ensure process stability by controlling processing liquid concentrations. The resist removal process is also in need of improvement.

(2) Technical problems with resist removal in conventional method

Resist, a resin used in semiconductor circuit production, is removed after formation of the circuit. Traditionally, resist removal has usually been achieved using the SPM method. Because it consumes large amounts of sulfuric acid and hydrogen peroxide,there has been a demand for the development of an alternative technology that meets the needs of minimizing environmental impact and reducing manufacturing cost.

2. Electrolyzed sulfuric acid generator "Green Sulfaceed KD™"

(1) Outline features

Sulfuric acid is electrolyzed to generate peroxosulfuric acid, which exhibits extremely high oxidizing power. The resulting peroxosulfuric acid is transferred to the cleaning machine, where resist on wafers is removed. The used peroxosulfuric acid then becomes sulfuric acid and is recovered for recycling; liquid waste volume is significantly reduced.
Compared with the conventional SPM method processing, this new system allows semiconductor manufacturers to significantly reduce the consumption of processing liquids and stabilize their cleaning processes while ensuring higher resist removal efficiency.

(2) Advantages over the conventional method

1)Minimizes environmental impact (waste volume reduction) and reduces costs.

  • -No aqueous hydrogen peroxide is used.
  • -Consumption of sulfuric acid can be reduced to about one-tenth of the conventional level by recycling sulfuric acid.

2)Ensures stable resist removal effect

  • -Because sulfuric acid is electrolyzed under control, there is no deterioration of processing liquids. This allows semiconductor manufacturers to maintain constant concentrations of sulfuric acid and peroxosulfuric acid, a key to successful resist removal; sustained resist removal effectiveness can be achieved irrespective of processing time.
  • *When using the conventional method, the resist removal effectiveness diminishes in two to three hours. The electrolyzed sulfuric acid generator ensures adequate resist removal effectiveness, even after 40 hours.

3)Obviates ashing

  • -Depending on the type of resist, ashing apparatus for resist removal in the dry process is no longer necessary (ashing-less process), thereby significantly improving productivity and reducing initial investments and running costs further.