Shih-Ked Lee

The effect of HF vapor pre-treatment on the cobalt salicide process

The effect of HF vapor pre-treatment prior to Co deposition on the sheet resistance of cobalt silicide and gate oxide integrity has been investigated. During the HF cleaning, it was found that a significant amount of fluorine (F) atoms was diffused toward the polycrystalline silicon substrate with a large amount of segregation near the surface. Presence of F at the surface retarded interaction between Co and Si, hence formed non-uniform cobalt silicide. A low-energy sputter cleaning after HF vapor treatment successfully removed the F segregated layer and uniform cobalt silicide was achievable. In addition, gate oxide integrity such as charge-to-break down and leakage current was improved because the pre-existing F atoms block the diffusion of Co and stabilize the gate oxide.

Contact hole size-reducing methods by using water-soluble organic over-coating material (WASOOM) as a barrier layer toward 0.15-μm contact hole: resist flow technique I

In our experiment for 0.15 micrometer contact hole, we used Water-soluble organic overcoating material (WASOOM) as a barrier layer. Since WASOOM is water soluble, after baking for resist flow, water rinse will remove it completely. The key point of resist flow technique is to reduce overhang, in other words, reducing thermal stress at the top and bottom of resist pattern by WASOOM can lead to well-controlled DICD. Since WASOOM is water soluble and very compatible with resist, during resist flow, it is assumed that it will be acting as a barrier layer so that overhang should be reduced. In this paper we will describe below 0.2 micrometer contact hole pattern without overhang profile, well controlled DICD and fine etch profile. And also 0.15 micrometer contact hole patterning method will be described with half tone + resist flow by WASOOM. And also we will describe the application of SOG (Spin On Glass) for removing top flare after resist baking.

SiON as a panacea for KrF photolithography? Study on process optimization, substrate dependency, and delay time stability on silicon nitride and BPTEOS film

Silicon oxynitride film on Silicon Nitride film as an inorganic ARC has been investigated for the tighter critical dimension control. Use of SiON film as an inorganic ARC on silicon nitride film led to the better CD uniformity control reducing substrate dependency issue. Resist profiles on SiON have also been investigated on BPTEOS and on silicon nitride films. Footing on BPTEOS was removed completely by adding SiON film. It is found that SiON showed storage time limit after deposition. Five days after deposition, it showed footing profile. There must be some unknown chemistry to explain that phenomenon. Oxygen plasma applied onto the 5 dayed SiON film showed foot free profile. In the paper we will describe the CD control on Nitride by using SiON as an inorganic ARC, substrate dependence and storage time limit of SiON film.

Capping layers, cleaning method, and rapid thermal processing temperature on cobalt silicide formation

The effect of some key variables such as rapid thermal processing (RTP) temperature, substrate cleaning method and capping layers, on cobalt silicide formation has been investigated. The in-situ RF sputter etch is found to give a post RTP2 Rsh that is equivalent to a wet cleaned wafer. The temperature transformation curve of cobalt films, analyzed with Rsh data and XRD, reveal the formation of Co2Si-CoSi-CoSi2 phases in that order. The transformation curves of TiN capped films match those of blanket cobalt but the Ti capped films show the CoSi phase to be stable over a broader temperature range. There is no effect of dopants on the final cobalt disilicide Rsh values for either the single of polycrystalline substrates. Controlled oxygen leak studies in the RTP ambient reveal that the Rsh after RTP1 is degraded if a capping layer is not present. Electrical test results confirm the need for capping layers. This is indicated by lower Rsh and Rc values on both n+ and p+ junctions and poly structures. Furthermore the electrical results are comparable for Ti and TiN layers used as the cap films although the Rsh/Rc values are in general lower for the TiN capped films. Poly gate length vs Rsh plots show the extendibility of the capped cobalt silicide process to the 0.18 um node.

Properties of ultrathin gate oxides grown in N2O-based oxidation ambients by rapid thermal processing

Ultra-thin gate oxides grown by rapid thermal processing in N2O-based oxidation ambients were evaluated. Gate oxide integrity was improved by incorporating more nitrogen in the thin gate oxides and by diluting oxidation ambients in inert gases.