Materials Case Study
provide wider process latitudes than those supported by 100 percent organic chemistries such as HA-based products.
The team theorized that one reason for the improved yields was that the HA- based chemistry, when used at higher temperatures (i.e. 85 C), can cause excessive etching pitting of metal layers, as can be seen in this SEM image.
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treatment) — one that fully satisfies the manufacturers yield and total cost of ownership goals.
The New Model: Cooperative Efforts Lead to Higher Yields
As a framework for advancing this collaborative model, a recent project to assess alternatives to hydroxyl-amine (HA)-based post-etch ash residue removal chemistries that Avantor Performance Materials pursued with the Singapore-based foundry, SSMC, Inc., suggests that increased levels of openness and collaboration can yield significant benefits. Avantor, formerly Mallinckrodt Baker, Inc., has supplied innovative, high-purity, high- performance surface cleaning chemistries and other products for photoresist stripping, residue removal and other surface modification applications to the semiconductor industry for more than 25 years. SSMC Inc. provides foundry services
processing 200mm wafers in the 0.25 down to 0.14 µm technology node. Seeking to control costs and achieve better process control, the company approached Avantor to investigate alternatives to its existing post-etch ash residue removal chemistry.
In the past, a foundry like SSMC would have
requested proposals from multiple chemistry suppliers, focusing almost exclusively on reducing unit costs compared to its existing process-of-record chemistry, while seeking comparable process performance. In this case, SSMC partnered exclusively with Avantor to fully investigate and test at both lab and pilot line level the potential value of Avantor’s BAKER ALEG-380 post-etch ash residue removal product. ALEG-380 residue remover is an engineered blend of organic solvents and semi- aqueous components suitable for bulk photoresist and post-etch ash residue and sidewall polymer removal. It is designed to
Cost Control Surprises Although cost control was the initial reason SSMC chose to collaborate with Avantor, the technical expertise and insight into wafer surface treatment chemistries and processes Avantor supplied help create an effective collaborative process. Avantor applications engineers worked with SSMC process engineers to conduct multiple comparison analyses on test wafers to assess ALEG-380’s viability and compare its performance with the existing POR chemistry. After a first detailed round of lab testing, ALEG- 380 was placed on one of the eight lines at the SSMC’s foundry in Singapore. Test wafers were sent through the standard manufacturing steps. The test results were better than expected: via and metal line yields were better for the Avantor performance chemistry compared to the existing HA-based chemistry, when SSMC was only expecting to achieve comparable yields. In addition, bath process temperature latitude was broader, and further testing and SEM imaging determined that ALEG-380 demonstrated much lower etch rates on both metal lines (Al and Cu) and on substrate materials.
Pilot Awareness Based on these test results, SSMC worked with Avantor to conduct a pilot run of ALEG-380 under full process conditions. The pilot production run validated the test results, and SSMC determined that it could achieve a 2-3 percent improvement in yield, and a corresponding 25-30 percent cost reduction in their post-etch ash residue removal process using ALEG-380. This led SSMC to change its process of record (POR) and implement use of ALEG-380 on all eight production lines.[1] The collaboration was a success because SSMC communicated to Avantor the key chemistry performance requirements, such as broader process latitude and reductions in metal and substrate etch, as well as cost-reduction goals, and engaged Avantor fully in the process of wafer testing, pilot production run and full implementation of the new chemistry. This enabled Avantor applications engineers, working alongside SSMC’s fab engineers, to contribute significant insight into optimization steps and methodologies for effectively comparing ALEG-380 with the HA-
www.euroasiasemiconductor.com Issue III 2011
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