Douglas Keil

Oxide Dual Damascene Trench Etch Profile Control

A systematic study of trench profile evolution in a medium-density oxide etch reactor is presented. A Langmuir site balance model is developed in the limit of unity sticking coefficient which exhibits a flat etch front as is frequently required for dual damascene applications. The model indicates that it is desirable to operate in a neutral-limited ion-assisted etch regime Physical sputtering is also shown to be necessary, hut this etch contribution must be kept small with respect to the ion-assisted etch rate. The model also indicates how either microtrenching or bottom rounding may he controlled or avoided altogether. Model predictions are compared with experimental data obtained from a Lam Research 4520XLE medium density reactor. This work includes a study of the trenct bottom rounding dependencies upon pressure, etch time aspect ratio, and process gas flow for a fluorocarbon-based etch process. The model is shown to qualitatively capture experimentally observed process trends. In some regimes, good quantitative agreement with observed measurement is seen. It can thus serve as a useful guide for trench etch process development.

Plasma ignition in a grounded chamber connected to a capacitive discharge

A capacitive discharge connected through a dielectric or metal slot to a peripheral grounded region is a configuration of both theoretical and practical interest. The configuration is used in commercial dual frequency capacitive discharges, where a dielectric slot surrounding the substrate separates the main plasma from the peripheral grounded pumping region. Ignition of the peripheral plasma produces effects such as poor matching and relaxation oscillations that are detrimental to processing performance. Discharge models are developed for diffusion and plasma maintenance in the slot, and plasma maintenance in the periphery. The theoretical predictions of ignition conditions as a function of voltage and pressure are compared with experimental results for a driving frequency of 27.12 MHz and a gap spacing of 0.635 cm connecting the two regions, giving good agreement.

Multi frequency matching for voltage waveform tailoring

Customized voltage waveforms composed of a number of frequencies and used as the excitation of radio-frequency plasmas can control various plasma parameters such as energy distribution functions, homogeneity of the ionflux or ionization dynamics. So far this technology, while being extensively studied in academia, has yet to be established in applications. One reason for this is the lack of a suitable multi-frequency matching network that allows for maximum power absorption for each excitation frequency that is generated and transmitted via a single broadband amplifier. In this work, a method is introduced for designing such a network based on network theory and synthesis. Using this method, a circuit simulation is established that connects an exemplary matching network to an equivalent circuit plasma model of a capacitive radio-frequency discharge. It is found that for a range of gas pressures and number of excitation frequencies the matching conditions can be satisfied, which proves the functionality and feasibility of the proposed concept. Based on the proposed multi-frequency impedance matching, tailored voltage waveforms can be used at an industrial level.