Chemicals and materials are used in every processing step in the fabrication of silicon and gallium arsenide integrated circuits. Technological advances in Si and GaAs ICs have resulted in more stringent requirements in the purity and quality of processing chemicals and materials for cleaning, etching, and deposition. As linewidths decrease, the level and size of contaminants in both chemicals and the manufacturing cleanroom become increasingly important as it directly impacts device yield. Each new generation of IC processing requires higher levels of purity.
Front-end-of-line (FEOL) and back-end-of-line (BEOL) wet chemical cleaning processes are critical to the fabrication of semiconductor devices. As linewidths continue to shrink, maximizing the purity of chemicals used in wet cleans is a prerequisite for maintaining and improving chip yield. The incoming and in-process purity of chemicals used in wet cleaning greatly impacts the surface contamination of wafers. While incoming ultrapure chemicals have reduced ion levels, exposure to metallics has persisted during wet processing.
One way of effectively minimizing ionic contamination is to continuously purify the chemicals in use. In this approach, the metallic ions are removed by binding them to the complexing agents immobilized on membrane filters that can be plumbed in-line in the wet tools.
During the manufacture of microelectronic devices, silicon wafers are exposed to high-purity water more frequently than any other liquid chemicals, and can require >1100 gal of ultrapure rinse water to process a 200 mm wafer. However, it is difficult to maintain high purity below 1 ppt out of the central system during the distribution to points of use for wafer surface cleaning. The process of distributing high-purity DI water often introduces particles and trace ionic contamination that can leach out from the plumbing components and process equipment. The ITRS 2001 guidelines call for a total metal contamination level on the wafer surface of <7X109 atoms/cm2 for 130 nm devices.
Purification and filtration technologies have been developed to achieve the stringent purity levels required of liquid chemicals in semiconductor manufacturing. Although shrinking geometries continue to drive this innovation, other process-related needs that will provide the impetus for purification are:
The BEOL wet cleaning process has become increasingly important as the number of metal levels has increased with the shrinking feature sizes of the newer ICs. In fact, BEOL constitute up to 50% of all wet cleaning steps. BEOL cleaning steps begin at the end of FEOL after a metal layer is deposited on the wafer. The presence of a metal layer precludes the use of aggressive cleaning steps used in FEOL, as the metal layers would be attacked. The BEOL cleaning uses less reactive solvents (e.g. NMP - N-Methyl-2-Pyrrolidinone) for photoresist stripping, which are expensive to use and dispose of.
For residue stripping, after an ashing process, many less aggressive semi-aqueous cleaning chemistries have been introduced. To lower the high cost of cleaning and to reduce defect density, it has become critical to clean up and extend the life of chemical bath by point-of-use purification with optimized filtration.
Photoresist stripping involves removal of bulk photoresist; the chemicals used are primarily organic in nature, slightly to highly basic. Residue stripping removes particulate, organic and inorganic contamination after the photoresist has been removed by plasma ashing or after liquid photoresist stripping. The residue stripping chemicals are semiaqueous or aqueous-a very diverse mixtures of solvents, amines, and corrosion inhibitors.
Standard hydroxyl amine based chemistries have shown good polymer removal/cleaning performance, but require high temperatures and 15-45 min. process times. The new semi-aqueous fluoride based cleaning chemistries can be used at low or room temperature for wet benches, spray tools and the single wafer tools.
Ultrapure DI water rinsing process following the chemical cleaning step is very critical from the metal corrosion standpoint. Point-of-use purifier/filter devices for the removal of low level metal and particulate contamination from ultrapure water, organic solvents, and other chemicals used in microelectronics.
This report is offered for the purpose of assisting a user in evaluating the spectrum of products, packaging, and dispensing systems available for his use. It also suggests criteria for selecting a vendor as well as a chemical delivery and dispensing system that will serve his specific requirements.
The report also gives insights to suppliers for future user needs and should assist them in long-range planning, new product development and product improvement.
This report addresses the strategic issues impacting both the user and supplier of chemicals and materials and is written for: