AVS 46th International Symposium
    Manufacturing Science and Technology Group Wednesday Sessions
       Session MS-WeP

Paper MS-WeP3
Plasma Etch-Back Coupled to Chemical Mechanical Polishing for Sub 0.18 µm Shallow Trench Isolation Technology

Wednesday, October 27, 1999, 5:30 pm, Room 4C

Session: Poster Session
Presenter: A. Schiltz, France Telecom, CNET-CNS, France
Authors: A. Schiltz, France Telecom, CNET-CNS, France
L. Palatini, ESPEO - Orleans University, France
M. Paoli, France Telecom, CNET-CNS
M. Rivoire, France Telecom, CNET-CNS
A. Prola, France Telecom, CNET-CNS
Correspondent: Click to Email
This paper presents a new etch-back planarization technique with counter-masking to pre-planarize Shallow Trench Isolation substrates before Chemical Mechanical Polishing (CMP). A pre-planarization step is necessary since CMP alone cannot provide effective planarization for sub 0.18 technology due to dishing effect . The pre-planarization step uses the principle of Two Layer Planarization (TLP)@footnote 1@ technique which consists in spin-coating a first photoresist layer, using a counter-mask for the lithographic step, flowing and curing the resist blocks in STI topographies, spin-coating a second photoresist layer to planarize the residual topography and transferring the final flat surface into the substrate using plasma etch-back. In difference with previous techniques, we used a special mask with oversizing and exclusion of all STI critical dimensions smaller than 1.55 µm, the zones with the smaller STI dimensions being masked using a special narrow lines grid. Such a masking strategy avoids any misalignment problem, the resized first photoresist blocks are reflowed in STI topographies, leading to an easy planarization by the second resist layer. Additionally, the lithographic step is a non-critical step using conventional i-line resist. The final surface is transferred into the oxide substrate using (Ar/CF4/ O2) gas mixture in a LAM 4520 plasma etching equipment. To allow simultaneous etching of resist and oxide, various gas mixtures of Ar/x/O2 or Ar/x/y/O2 were tested, with x and y being chosen among following fluorine gas : CF4 - SF6 - C4F8 - CHF3. The (Ar/CF4/O2) gas mixture was observed to fulfill the etch back requirements with better performance. Equality of etch rate in resist and in oxide can be adjusted by the O2/CF4 gas ratio. A design of experiment (DOE) was used to determine the optimum conditions of plasma transfer of the planarized profile into the substrate. No ARDE (aspect ratio dependent etching) was observed, but loading effect was observed. Equality of etch rate in resist and in oxide during profile etch back transfer depends on oxide/resist surface ratio and therefore on the STI mask density. Then, equality of etch rate can be adjusted by the O2/CF4 gas ratio. Finally, the pre-planarized wafer is polished by CMP, resulting in an effectively planarized topography with residual topography smaller than 50 nm. The technique is a non-critical lithographic technique scaleable for technologies below 0.18 µm. @FootnoteText@ @footnote 1@ A. Schiltz and M. Pons, J. of the Electrochem. Soc., Vol. 133, 1, 178 (1986)