Alternative Wafer Cleaning Using HF-H2O ProcessingEPA Grant Number: R826737
Title: Alternative Wafer Cleaning Using HF-H2O Processing
Investigators: Sawin, Herbert H.
Institution: Massachusetts Institute of Technology
EPA Project Officer: Richards, April
Project Period: January 1, 1999 through December 31, 2001 (Extended to December 31, 2002)
Project Amount: $340,000
RFA: Technology for a Sustainable Environment (1999) RFA Text | Recipients Lists
Research Category: Sustainability , Pollution Prevention/Sustainable Development
A novel HF/water vapor process for in situ dry cleaning of microelectronic wafers is being studied 1) to understand its surface kinetics and 2) to develop it as a replacement for current wet cleaning processes. The successful development of such a dry cleaning process could greatly reduce the number of wet cleaning processes needed in microelectronics manufacturing, thereby reducing the deionized water needed for rinsing; reducing the amount of acids, bases, and solvents consumed and disposed; and improving worker safety.
The use of HF, other acids, bases, and solvents in the cleaning of wafers between process steps is problematic for the microelectronics industry in terms of environmental impact, material costs, safety, productivity, and disposal costs. The avoidance of aqueous baths that inherently risk worker exposure would both increase safety, as well as reduce the facility floor area associated with cleaning processes. In a state-of-the-art fab a list of the primary chemical usage in cleaning is approximately as follows:
|Deionized water (>750,000 gallons/day)||>23,000,000 gal/month|
|Concentrated sulfuric acid||10,000 gal/month|
|Concentrated hydrogen peroxide||13,000 gal/month|
|Concentrated HF||3,500 gal/month|
|Concentrated ammonia hydroxide||4,000 gal/month|
|Concentrated BOE (buffered oxide etch)||2,500 gal/month|
All of the above chemicals must be disposed after use with the exception of the deionized water that is partially recycled. The disposal products vary from concentrated solutions such as piranha (4:1 H2SO4/H2O2) to dilute HF (200:1).
The HF-H2O process for the removal of silicon oxides, other oxides, and alkali metals has been found which operates in a parameter space that has not been reported in the literature and is different from the HF vapor process practiced industrially. Its incorporation could greatly reduce the need for water and cleaning chemicals by the microelectronics industry.
The following potential process benefits could also be obtained using the proposed process:
- The etching rates are ~5 nm/minute, which allows good control of the cleaning process.
- The selectivity of undensified TEOS oxide and thermal oxide etching is approximately 2-3:1, which allows the cleaning of layered oxides.
- Wafers can be pre-cleaned avoiding solvents, acids, or bases. No other preconditioning of the surface is needed for repeatable oxide removal.
- The surface after etching is not roughened.
- The etching rate promotion by patterned wafer surfaces can be avoided.
The implementation of this process would greatly reduce the use and disposal of chemicals used in the cleaning of wafers during the manufacture of microelectronics.