SO3 Cleaning

Consulting

Contact Us

No Plasma Charging or Radiation Damage
The SO3 gas-phase process is free of the charging and radiation damage characteristic of dry, plasma-ashing methods.  In most applications, the process requires only exposure to sulfur trioxide gas followed by a simple water rinse; no plasma exposure of any kind is required.  Only in some very difficult applications, where a photoresist crust forms during processing, such as high-dose ion implant > e13 and some post-oxide etch applications, is a short, low-temperature, plasma-based pre-treatment required to break through the hardened photoresist crust in preparation for exposure to sulfur trioxide gas.   Thus, in all commonly used semiconductor manufacturing applications, the SO3 process offers a plasma-damage-free method to remove photoresist, improving product yield and reliability for semiconductor manufacturers.
 

Improved Gate-Oxide Integrity
The simple, sulfur trioxide and water process eliminates or greatly reduces the use of damaging plasma and the halogen gases often used in combination with plasma.  Elimination or reduction of  plasma and halogen damage improves gate-oxide integrity, which has been identified by the Semiconductor Industry Association (SIA) as one of the top 5 wafer fabrication process challenges which must be solved before 2005.
 

Control Over Metal Corrosion
In the absence of water, sulfur trioxide is capable of modifying organic films and photoresist residues through sulfonation, sulfamation and sulfation reactions without damaging or corroding underlying metal surfaces.  By integrating a prompt, DI-water flushing step immediately after SO3 exposure, organic films can be removed without corrosion, thus offering an improved capability for cleaning photoresist on wafers with exposed metal films.  Conventional wet strip/clean processes have limitations due to the corrosive nature of the acids employed, often forcing the use of toxic organic solvents for strip/clean.
 

Faster Stripping Times
The SO3 stripping process provides much faster photoresist stripping and cycle times by replacing, with one tool, the conventional two-tool set now used for removing photoresist (i.e. plasma ashing followed by a post-ash residue clean in liquid chemicals). 
 

Removal of Side-wall Polymers, Via Veils, Metal Fences
The SO3 process has demonstrated a capability to completely strip photoresist without leaving side-wall polymer residues, "via veils", "metal fences" and other photoresist residues which often remain after dry-plasma ashing.  No  fluorine-containing plasmas, no ozone gas, no acids, no organic solvents or other wet chemistries are needed to do this.  By keeping  substrate temperatures well below 120ºC during stripping and cleaning, the SO3 process avoids baking and hardening these residues on to the substrate.  In fact, in many applications SO3 processing temperatures are very low, never rising above 80ºC.  Conventional plasma-ashing processes, on the other hand, operate at temperatures over 200ºC in order to remove bulk photoresist, thus baking and hardening these residues, making them more difficult to remove.

For example, typical post-metal etch structures and post-oxide etch structures, cleaned with the SO3 process (and using no halogen gases, no ozone, no acids and no organic solvents) do not leave "metal fences".  While plasma-ashing stripping techniques typically  require a post-ash, wet-chemical clean to achieve this same degree of residue removal. 
 

Low-Temperature Stripping
The SO3 gas method of stripping has been demonstrated to be effective at temperatures as low as 40ºC for photoresist which has not been process-hardened.  And unlike plasma-ashing stripping methods which operate at temperatures over 200ºC, more difficult, process-hardened photoresist can still be thoroughly removed without exceeding stripping temperatures of about 120ºC.
 

Reduced Waste Stream & Improved Environmental Safety
By eliminating the post-ash wet-clean operation typically required by conventional cleaning methods for complete residue removal, the SO3 process results in very large reductions in the volume of the hazardous and toxic operating chemicals which must be purchased, managed and disposed of in the user's waste stream.  The user can thus anticipate dramatic savings in operating costs arising from the elimination of no-longer-required, post-ash wet-clean operations.
 

Uniform Stripping and End-Point Detection
Because the sulfur trioxide process is a self-limiting process in which the sulfur-chemistry reactions stop when all organic material has been processed, end-point detection is not required for most applications.  Rather, the sulfur chemistry reactions are allowed to continue until all reactions have completed before the substrate is removed from the exposure chamber for flushing with water.  Thus, for those applications involving inorganic substrates such as polysilicon, SiO2 and metal alloys, 100% uniformity of strip is possible across each wafer, between wafers in the same process batch, and between wafers in different process batches.

In some applications where an organic substrate is involved, end-point detection may be used to terminate the sulfur-chemistry reactions at an optimum point. 
 

Smaller Footprint
With no requirements to generate energetic plasmas or high vacuums, and requiring a process chamber only slightly larger than the substrate itself, the stripping tool can be very small.  With a significantly smaller footprint than is now required for the conventional stripping technology tool set, the SO3 process tool offers a substantially lower cost of ownership in expensive IC manufacturing facilities.
 

Scalability Upward to Larger Substrates and Batch Processing
Because the SO3 process is a dry-gas exposure process, it is relatively easy to scale the process upward to handle both larger substrate sizes and batch processing.  This is a particular advantage over dry-ashing technology, where it is necessary to either maintain a uniform plasma over a large area, or to sacrifice stripping effectiveness and through-put with a single-wafer, down-stream asher.
 

Lower Maintenance and Operating Costs
The relatively simple process, the small footprint of the equipment, the breadth of applicability of the process, and the absence of plasma generators and high vacuum systems offers both low-maintenance and low operating costs to the user.