P. Roman

Mist deposition of thin photoresist films

This experiment is concerned with the development of mist deposition technology as an alternative to spin-on method of photoresist deposition in microelectronic manufacturing. A commercial 200 mm mist deposition tool is used in this study. The results obtained demonstrate effectiveness of mist deposition in resist processing. Basic parameters of resist mist deposition are determined. Deposition rate can be controlled within 10 to 50 nm/min range. Using a stepper and UV-5 photoresist 250 nm patterns were readily defined in 120 nm thick mist deposited resist. It is postulated that mist deposition offers advantages over spin-on process in the case of very thin resist technology as well as in the case of resist deposition on large, non-circular substrates.

Process monitoring using surface charge profiling (SCP) method

This paper is concerned with the method of surface charge profiling (SCP) developed for in-line monitoring of front- end processes in semiconductor manufacturing. In this study a commercial SCP system is used to monitor wafer cleans in terms of oxide/hydrogen coverage of Si surfaces following cleaning with emphasis on HF last cleaning sequences. Moreover, metal contamination of bare silicon surfaces and deactivation of boron dopant in the near-surface region of p-type Si wafers are monitored. Finally, the unique capability of SCP in monitoring time-dependent evolution of characteristics of Si surfaces exposed to various ambients is demonstrated.

Deep lateral anhydrous HF/methanol etching for MEMS release processes

As demonstrated earlier, gas-phase etching of sacrificial oxide with a vapor mixture of anhydrous HF (AHF) and methanol (CH3OH) offers a clean, stiction-free, effective etching technique for microelectromechanical systems (MEMS) release. The use of AHF/methanol process in MEMS release operations is explored in the deep lateral etching of patterned silicon-on-insulator (SOI) substrates using a 200 mm multiwafer commercial module, which assures adequate process throughput. It was determined that highly selective, with respect to both Si and Si3N4, etching of SiO2 can be accomplished by controlling pressure and wafer temperature. It was also observed that the vertical etch rates for both the AHF/methanol and the HF: H2O solution was higher than the rates of lateral etches in confined geometries. Furthermore, the AHF/methanol and 1:10 HF: H2O etch chemistries were directly compared in releasing silicon cantilevers up to 500 µm in length and a significantly faster, stiction-free process was observed in the former case. Adequate process reproducibility from wafer to wafer as well uniformity across the wafer was demonstrated.

Surface Charge Evolution during Early Stage of Thermal Oxidation of Silicon

A noncontact method which measures a density of electric charge on the semiconductor surface without bias, and hence, with no electric field in the oxide is used to monitor the evolution of surface charge during an early stage of thermal oxidation of silicon, i.e., from bare surface to oxide about 3 nm thick. It is shown that before positive charge associated with trivalent silicon in the SiO 2 /Si interface region is established, a surface charge is controlled by a negative charge most likely associated with nonbridging oxygen. A transition between these two regimes takes place in the oxide thickness range of about 1.5-2.5 nm. For oxide above 3 nm thick the surface charge is fully developed and remains constant with an increase of oxide thickness.

Current Advances in Anhydrous HF/Organic Solvent Processing of Semiconductor Surfaces

The process in which anhydrous HF (AHF) is mixed with the vapor of an organic solvent for the purpose of etching of native SiO2 on Si surfaces is well established (e.g [1-4]). The process was also explored as part of a dry-wet wafer cleaning sequence [5]. More recently, the same process has been successfully expanded into MEMS technology for the purpose of stiction-free releasing of structures by isotropic etching of sacrificial SiO2 [6,7]. The current strong push in advanced Si digital IC technology toward extremely fragile 3D geometries engraved on Si wafer surfaces, in which case conventional etch methods may not work properly [8], as well as needs with regard to native oxide etching in emerging Si-based technologies such as solar cell manufacturing has brought about renewed interest in AHF technology.

Electrical Studies on Metal /SrTa2O6 or TiO2/ Si Substrate Stack Systems

SrTa2O6 or TiO2 high-k gate dielectrics is observed to have significantly different dependence on the temperature and the frequency of a capacitance-voltage measurement than that of the conventional metal-oxide-Si (MOS) capacitors. It is shown that this is due to contributions from the, often, inadvertently grown, and relatively poorer quality interfacial dielectric between the high-k material stack and the Si substrate. Although it is generally accepted that NH3 or NO nitridation of pre-high k-deposition Si surface is able to suppress the thickness of the dielectric layer, we found out that it does not necessarily improve the effective oxide thickness value, reduce the leakage current density and the interface state density, or protect the silicon substrate from the deposition related electrically active bulk Si deep traps.

Gate dielectric monitoring using noncontact electrical characterization

Reduction of gate oxide thicknesses to the tunnelable range as well as the anticipated introduction of alternative gate dielectric materials create new challenges regarding monitoring of gate insulation processes. In this paper methodologies applied in gate oxide characterization are considered and advantages of non-contact methods are emphasized. More specifically, the Surface Charge Profiling (SCP) method, which is particularly well suited for this application is discussed. This method allows measurement of the charge density without any bias on the oxide, and hence, without any current flow across the oxide. Therefore, measurements of surface/oxide charge density as well surface recombination lifetime can be carried on oxides in which charge measurement using other methods would be prevented due to significant current. This capability of the SCP method is demonstrated using experimental results.