AVS1996 Session PS1-WeA: Oxide Etch II - Etch Stop

Wednesday, October 16, 1996 2:00 PM in Room 201C

Wednesday Afternoon

Start	Invited?	Item
2:00 PM	Invited	PS1-WeA-1 Development of 0.15\mu\m Contact Hole Etching Process for 1G-bit Era M. Sekine, H. Hayashi, H. Tamura, K. Kurihara (Toshiba Corporation, Japan) Fine width and high aspect oxide etching is indispensable process for the 1G-bit era. The critical issue for the oxide etching is the RIE-lag, especially 'etch stop' and selectivity to Si or Si\sub 3\N\sub 4\. Selectivity to Si\sub 3\N\sub 4\ shows trade-off relation to the etch stop. In order to establish a precise process, we studied the pattern size dependence and etching mechanism of high selectivity to Si\sub 3\N\sub 4\ in C\sub 4\F\sub 8\ + CO magnetron plasma. It was found that these etch rates can be characterized by aspect ratio, regardless of absolute pattern size. From ion current measurements through capillary plates (CP), it was deduced that etch rates decreased at high aspect ratio because of decreasing ion current. A small amount of O\sub 2\ addition to the C\sub 4\F\sub 8\ + CO broke the RIE-lag. It was found that oxygen plays two roles. First, oxygen reduced C-rich deposition species in the gas phase. Second, O\sub 2\ addition increased ion current density at the hole bottom. These phenomena clear the bottom surface of etch inhibiting fluorocarbon deposition. The mechanism of highly-selective etching of SiO\sub 2\ to Si\sub 3\N\sub 4\ was also investigated. Large amount of CO addition to C\sub 4\F\sub 8\ reduced the etch rate of Si\sub 3\N\sub 4\. According to the CO addition amount, C\super +\ ion in the plasma increased drastically. As a result, the C incorporation in Si\sub 3\N\sub 4\ enhances fluorocarbon deposition that protects the Si\sub 3\N\sub 4\. In fact, C implanted Si\sub 3\N\sub 4\ shows lower etch rate. Further investigation on carbon's role in the surface reaction is necessary to control selectivity.
2:40 PM	Invited	PS1-WeA-3 Oxide Etching in High Density Etch Tools K. Donohoe (Micron Technology, Inc.) High density etch tools provide oxide etch performance that is quite different from that obtained in conventional parallel plate etchers. The biggest advantages of these high density tools are the possibility of high throughputs from \> 2um\ /min etchrates in 0.5 \um\ features, good profile control, and relatively small aspect ratio dependent etchrate effects. Self-aligned contact etching which requires selectivity to sidewall nitride near the bottom of the etch feature is also simpler in these tools. The biggest problems with these tools are engineering issues, not fundamental process capability issues. Excellent results are relatively easy to obtain on small numbers of wafers but quite difficult to reproduce during multi- thousand wafer production runs. The problems include wear on chamber parts from both the etch and in-situ clean processes, the requirement for in-situ cleans after each wafer, and for some designs, poor process stability caused by insufficient control of the temperatures of the chamber surfaces. This paper will review some electrical characterization of these sources, the interaction of source (top) power and bias (wafer) power on etch results, and then discuss the performance of high density tools for conventional and self aligned contact etching in the context of the advantages and problems described above.
3:20 PM		PS1-WeA-5 High Density Plasma Tool Process Development using "Plasma Chemical State" Diagnostics H. Anderson, M. Splichal, J. Pender, J. Cecchi (University of New Mexico); J. Arnold (Motorola); E. Lu (Sematech) Diode laser spectroscopy and multi-point OES have been used to examine aspects of the plasma chemistry controlling reactor performance in an AMAT HDP5300 oxide etch tool. Due to low pressure, the oxide, photoresist and poly-Si etch rates in high density tools are affected by complex interactions of surface and gas phase reactions. In a process window suitable for contact etching, the relationships between gas phase measurements of reactive species and the surface concentration of these same species are in fact inverted or counter intuitive. For example, it is shown that oxide etch rates are positively correlated with increasing C\sub 2\ optical emission and CF absorption (the principle components for polymer deposition), while negatively correlated to increasing F and O atom optical emission (the principle etching species). Etch characteristics are shown to be dominated by transport and deposition of polymeric species to the reactor walls. Bias and flow appear to be the major factors controlling this response, while source power and wall temperature exert only a secondary influence. Etch stopping behavior in the tool is also shown to be related to bias. The effect of wall-plasma interactions on plasma chemistry is difficult to measure without advanced diagnostic techniques capable of accurately measuring the "plasma chemical state" during etching. The combination of these two techniques is shown to provide an invaluable aid to process development.
3:40 PM		PS1-WeA-6 Optical Emission Diagnostics used in Contact Etching S. McNevin, M. Cerullo, K. Cheung (Bell Laboratories) This talk will present recent optical emission diagnostic work used to study the contact and via etch processes in a commercial HDP reactor. The optical emission signals of C\sub 2\ (516 nm) and SiF (440 nm) are measured under a variety of experimental conditions. Endpoint results for ~2% open area wafers will be presented, which are obtained by digitally filtering the raw data. The time dependence of these optical emission signals will be shown to correlate with observed drifts in "etch stop" over the course of the cassette. This diagnostic method can monitor changes in chamber deposition and their dependence on the duration of the Oxygen post etch treatment. The optical emission of O (844 nm) during the Oxygen post etch treatment was used to determine the photoresist etch rate, and this was shown to correlate with these changes in the chamber deposition due to varying durations of Oxygen post etch treatment. The optical emission of CN (388 nm) was used to determine the TiN etch rate in via structures. The results in this talk will demonstrate that optical emission appears to be a viable real time diagnostic for monitoring contact and via etch.
4:00 PM		PS1-WeA-7 The Effects of CH\sub3\F Addition to Carbon-rich Chemistry on Nitride Barrier SAC Etching for 1G DRAM and Beyond J. Kim, J. Ryu, J. Kim, K. Baik (Hyundai Electronics Ind., Co., Korea); C. Yang, M. Chang (Applied Materials) The limitation of optical lithography makes it difficult to define contact windows below 0.25 (m size without electrical short for 1G DRAM and beyond. One method to delineate contact hole is the Self-Aligned Contact (SAC) process by using nitride barrier. But it is very difficult to get the high selectivity of oxide to nitride without etch stop or nitride punch through from the Nitride Barrier SAC (NBSAC) process. In this study, we have evaluated the NBSAC process which shows the high selectivity to nitride enough to implement into real device using just only C\sub3\Fsub8\ or C\sub4\F\sub8\ chemistry with CH\sub3\F gas in inductively Coupled Plasma oxide etcher. The NBSAC process uses just only C\sub3\F\sub8\ or C\sub4\F\sub8\ chemistry induced etch stop or nitride punch through. But the addition of CH\sub3\F to these chemistries changed the compositions of polymer and induced higher selectivity of oxide to nitride than 50 without etch stop even if it generates thicker carbon-rich polymer. The analysis of polymer by Hydrogen Forwardscattering Spectroscopy/Rutherford Backscattering Spectroscopy and X-ray Photoelectron Spectroscopy showed thicker carbon-rich polymer containing more hydrogen due to CH\sub3\F addition, which had a weak bonding structure with C and H. The results of Optical Emission Spectroscopy showed H peak and stronger C\sub 2\ peak and Mass Spectroscopy showed that CF\sub 2\ & CF\sub 3\ contents decreased due to the scavenging effect of H had made more CF contents with CH\ sub 3\F and so more carbon-rich polymer could be induced. Our NBSAC process for sub-quarter micron beyond 1G DRAM exhibits the best contact etching results without etch stop or nitride loss. In addition, the electrical characteristics are a better than normal contact process.
4:20 PM		PS1-WeA-8 Electron Cyclotron Resonance Plasma Etching of SiO\sub 2\ with C\sub 4\F\sub 8\/O\sub 2\ K. Nishikawa, T. Oomori, H. Ootera (Mitsubishi Electric Corporation, Japan) Low-pressure, high-density plasma sources such as an electron cyclotron resonance (ECR) plasma source have been proposed for etching process of contact hole in the fabrication of semiconductor devices with high aspect ratio structures. In fluorocarbon plasma etching of SiO\sub 2\, it is necessary to investigate mechanisms of SiO\sub 2\ etching and deposition of fluorocarbon film at the bottom of the contact hole, because both processes occur simultaneously during SiO\sub 2\ etching. In this paper, we present results of our investigation on SiO\sub 2\ etching in ECR C\sub 4\F\sub 8\/O\sub 2\ plasmas, together with measurement of plasma parameters. The selectivities of SiO\sub 2\ to Si and resist increased in the case of C\sub 4\F\sub 8\ plasmas as the same condition of operating discharge with C\sub 4\F\sub 8\/O\sub 2\, and reactive ion etching (RIE) lag effect was remarkably observed. However, in C\sub 4\F\sub 8\/O\sub 2\ plasmas, RIE lag effect was suppressed in comparison with the case of C\sub 4\F\sub 8\ plasmas, due to reduction of deposition rate of fluorocarbon film by adding O\sub 2\; the ratio of the etch rate at 0.18 \mu\m hole size to that at 0.5 \mu\m hole size was about 95%. Optical emission with rare gas actinometry, mass spectrometry and in situ Fourier transform infrared spectroscopy were used to estimate the behavior of CF\sub x\ radicals in C\sub 4\F\sub 8\/O\sub 2\ plasmas. It is expected that CF radical was a dominant polymer precursor in C\sub 4\F\sub 8\ plasmas. Furthermore, the ion species incident onto the rf-powered electrode will be measured, and the etching mechanism at the bottom of contact hole will be discussed.