Helmuth Treichel

Substrate cleaning using ultrasonics/megasonics

The adhesion and detachment forces acting on spherical particles attached to a substrate is investigated. It is found that alumina particles larger than 50 nm and glass particles larger than 10 nm can be successfully dislodged by acoustic waves in an ultrasonic tank. Inspection of detachment forces reveals that the dominant detachment force is acoustic cavitation force for particles larger than 35 nm (f = 950 kHz).

Low-Temperature Deposition of Silicon Dioxide and Silicon Nitride for Dual Spacer Application

Advanced sub 65 nm spacer applications require high quality conformal silicon dioxide and silicon nitride deposition processes at low thermal budgets. In this paper, we report on a study where these films were deposited using a novel Si precursor material that enables high deposition rates at temperatures typically around 250degC using a production-proven single wafer chemical vapor deposition (CVD) system (Planar 300trade) from Aviza Technology. Films are deposited with excellent non-uniformities, step coverage over challenging device structures and low particle counts. The reported silicon dioxide process is a purely thermal CVD process, whereas the silicon nitride process uses an RF plasma to initiate ammonia reactivity. The use of a single platform and single C- and Cl-free Si precursor enables sequential processing of C- and CI- free SiO2 and SiN dual spacer layers at processing temperatures (< 400degC) compatible with advanced devices.

Low Temperature Silicon Dioxide Deposition and Characterization

Although much effort has been expended toward developing alternate dielectrics for use in fabricating ULSI circuits, there is still a need for high quality SiO 2 films. In particular, process temperature restrictions have increased the demand for high quality, low temperature SiO 2 films.[1] Such films have multiple applications in microelectronics, including use as passivation coatings, interlevel dielectrics, gate dielectrics in metal oxide semiconductor field effect transistors (MOSFETs), thin film transistors, and in devices using dual spacers.[2] Advanced devices at the 65-nm node and beyond are typically fabricated with nickel silicided electrodes—which enable lower junction silicon consumption, lower sheet resistance, and reduced agglomeration, but require subsequent process temperatures to be below 550°C. Also, to prevent movement of the ultra shallow junctions (USJs) during a subsequent thermal cycle, the temperatures for process steps after USJ formation must be kept below 600°C. To meet these needs, we have developed a low temperature ( 2 process that results in excellent dielectric quality. This paper presents results on high-quality chemical vapor deposition (CVD) SiO 2 films deposited at temperatures from 200°C to 450°C using a novel proprietary and versatile silicon precursor using oxygen as the oxidizer. Composition, film stress, deposition rate, leakage current density, and step coverage results are presented.

Derivation of Rate Constants for the Batch Furnace Radical Oxidation of Silicon Wafers via Hydrogen Combustion

Oxidation of silicon wafers via atomic oxygen radicals is becoming increasingly desirable and has already supplanted conventional wet or dry thermal oxidation for some applications. Growth rates for radical oxidation depend much less on crystal orientation than for thermal dry or wet oxidation, a vital characteristic for threedimensional transistor designs 1,2 and shallow-trench isolation STI liner oxides, for which the lack of sufficient corner rounding from thermal oxidation is a liability. 3 Radical-based oxide films have been shown to have superior breakdown voltages and leakage properties compared to thermal oxides. 4 At low temperatures, oxide growth rates from oxygen radicals are much higher than thermal oxidation rates. Radicals even enable wafer processing at temperatures below 400°C, a temperature range otherwise only accessible with plasmas. Various methods have long been explored to produce high-quality silicon dioxide at reduced temperatures. Examples include ozone oxidation, UV-assisted oxidation, and plasma oxidation. One single-wafer-based radical oxidation system, known as in situ steam generation ISSG, utilizes oxygen and hydroxyl radicals created through chemical reactions of hydrogen and oxygen. Its success relies on two critical conditions. First, the process must be run at low pressures to achieve a sufficiently long radical lifetime. Second, a high volume of oxygen and hydrogen must be used to reduce the chemical residence time. 5,6 The reactants are premixed at relatively low temperatures, e.g., 100°C, and flow over a heated silicon wafer. The reactants are heated by the wafer within the thermal boundary layer. Due to the low operating pressure and high mass flow rate, reactants flow over the wafer at high speeds. The silicon wafer has to be heated and maintained at a sufficiently high temperature to initiate and sustain the gas-phase combustion process. This raises the minimum temperature at which combustion-based radical oxidation can be performed, compared to a hotwall reactor, for example. The challenge for producers of capital equipment for semiconductor manufacturing has been to design radical oxidation systems that are not cost prohibitive, have high throughput, and produce wafers with superior oxide properties e.g., thickness uniformity. With these targets in mind, it becomes important to understand the nature of the radical-based oxidation, that is, to identify the ratelimiting factors, factors that have been long understood for thermal oxidation. Recently a model for the oxidation kinetics in two combustion-based systems was proposed in which an initial radicalbased oxidation regime dominates for thin oxides and is supplanted by wet oxidation for thicker oxides. 7 But what is still lacking is insight into the energetics of the system, activation energies for the oxidation reaction and the oxidant diffusion, that can be used to identify the oxidizing species through phenomena more directly based on the physics and chemistry of silicon oxidation. Silicon thermal oxidation via reaction with H2O wet oxidation or O2 dry oxidation is typically discussed in context with the Deal–Grove model DG, 8 which describes diffusion of an oxidant through an overlying oxide to the silicon–oxygen interface where the oxidant reacts with silicon and produces more oxide. The DG model is useful to identify oxidation regimes in which oxidation rate is limited by either the silicon reaction rate or the oxidant diffusion rate through the oxide, corresponding to thin or thick oxides where the growth rates are linear or parabolic, respectively. Comparison of the thermal activation energies for these rate-limiting factors for both wet and dry oxidation also provides insight into the microscopic mechanism responsible. The DG theory for wet and dry oxidation allows the derivation of a generalized expression for oxide thickness x as a function of time t and three adjustable parameters