The Plasma Etching of Polysilicon with CF 3Cl / Argon Discharges: III . Modeling of Etching Rate and Directionality

375

181

We report the experimentally obtained response surfaces of silicon etching rate, aspect ratio dependent etching (ARDE), photoresist etching rate, and anisotropy parameter in a time multiplexed inductively coupled plasma etcher. The data were collected while varying eight etching variables. The relevance of electrode power, pressure, and gas flow rates is presented and has been found to agree with observations reported in the literature. The observed behavior presented in this report serves as a tool to locate and optimize operating conditions to etch high aspect ratio structures. The performance of this deep reactive ion etcher allows the tailoring of silicon etching rates in excess of 4 m/min with anisotropic profiles, nonuniformities of less than 4% across the wafer, and ARDE control with a depth variation of less than 1 m for trenches of dissimilar width. Furthermore it is possible to prescribe the slope of etched trenches from positive to reentrant.

Section: Resultsmentioning

confidence: 99%

Characterization of a Time Multiplexed Inductively Coupled Plasma Etcher

Ayón

Braff

Lin

et al. 1999

375

181

“…As the reaction rate is the number of Si atoms reacted per area and time, the rate constant is proportional to the product of the number density and the refreshing frequency of the activators, i.e., the incident flux of ions, ⌫ i . 8,[26][27][28] According to the collision cascade theory, 29 ions with high kinetic energy transfer their momentum to the surface species more effectively than ions with low energy.…”

Section: Resultsmentioning

confidence: 99%

Expression of the Si Etch Rate in a CF 4 Plasma with Four Internal Process Variables

Cho

Hwang

Kim

et al. 1999

Prediction of the Si etch rate in a fluorocarbon plasma is important in finding the optimal process condition for highly selective SiO 2 etching over Si which is essential for ultralarge-scale integration (ULSI) fabrication. [1][2][3][4] The best tool in making such a prediction is the etch-rate equation with the rate expressed as a function of the process variables. However, the relations between the etch rate and the external process variables such as total pressure, power density, and gas flow rate are strongly dependent on the hardware configuration of the etching system and do not guarantee run-to-run reproducibility in different etchers. The internal process variables such as the partial pressures of radicals, the sheath bias voltage, and the ion current density, which are set in response to the external variables, eventually determine the etching characteristics independent of the etcher configuration. 5 Therefore, they are more useful than the external variables for etch-rate prediction. The internal variables in the etch rate equation are not necessarily independent of each other but should be measurable in the process with proper diagnostic tools.Several research groups have expressed the Si etch rate in a fluorine-based plasma with the internal process variables. [6][7][8][9][10][11] The F concentration is the most important because F atoms are the main etchant species in the system. Ninomiya et al. 6 observed that the Si etch rate increased linearly with the F concentration. Flamm et al., 7 who expressed the etch rate as a function of the F concentration and the substrate temperature, also reported that the rate was proportional to the F concentration. However, these two groups excluded the influence of reactive ions in their experiments by locating the Si substrate outside the F 2 plasma. Therefore, these equations represent the thermal etch rate due to F atoms but not the rate in the ion-enhanced plasma etching where the thermal rate is relatively small.The mechanisms of the ion-enhanced etching are still debated but are summarized into four categories: chemical sputtering, 12 chemically enhanced physical sputtering, 13 damage-enhanced chemical reaction, 14 and increased spontaneous etching. 15 Enhancement of the etch rate by ions is related to two internal variables: the sheath bias voltage and the ion current density. The former represents the kinetic energy of incident ions and the latter the number flux of ions. Although the ionic kinetic energy is determined by the difference between the plasma and the electrode potentials, it is usually dependent on the electrode potential only, because the plasma potential is relatively small enough to be neglected. 16 Mayer and Barker 17 observed that the Si etch yield, the etch rate per incident ion, increased with the kinetic energy of the ions in their study with reactive ion beam etching (RIBE) apparatus. Moreover, Steinbrüchel 18 reported that the ionenhanced chemical etch yield increased linearly with the square root of the ion energy. A few groups, in...

“…Two etchers, a research etcher and a commercial etcher, were used in the current study. The main etcher used in this work was a parallel-plate single-wafer research etcher, which has been previously described (12,13) and is shown in Fig. 1.…”

Section: Methodsmentioning

confidence: 99%

Effects of O 2 Feed Gas Impurity on Cl2 Based Plasma Etching of Polysilicon

Zau

Sawin

1992

The effect of low level, between 0.001 and 10%, O2 addition on C12 based plasma etching of polysilicon in a parallelplate etcher was investigated. Three strong effects on the etching rate of unmasked polysilicon were observed. Low level O2 addition, 0.1-2%, enhanced the etching rate up to 4 times that of the pristine system. High level 02 addition, >-6%, stopped the etching altogether. Pure C12 plasma etching rates were enhanced by previous runs with 02 addition; a hysteresis effect. The hysteresis was reduced by subsequent system plasma exposure. Running a CF4 plasma after 02 addition runs cleaned the system and returned it to its pristine state. The stopping of etching at high O2 levels was attributed to plasma oxidation of the polysilicon surface; since C12 plasmas are very selective with respect to oxide, the etching is stopped by the surface oxide. Both the low level 02 etching rate enhancement and the hysteresis effect can be attributed to the deposition of an oxychloride film on the etcher surfaces. The oxychloride film, formed by reaction between the etching products and the added O=, passivates the interior etcher surfaces against C1 surface recombination, and, therefore, reduces the major C1 loss mechanism. The gas-phase C1 concentration increases, which in turn increases the polysilicon etching rate. These results demonstrate the importance of etcher surface condition and of the etching product deposition. Photoresist masked polysilicon films etched in the same configuration showed similar 02 addition dependencies as unmasked polysilicon films. The main difference is that the 02 addition effect thresholds are higher with the photoresist mask due to the consumption of the added 02 by photoresist etching. Unmasked polysilicon film etched in a commercial etcher, Applied Materials Precision 5000, under magnetically enhanced reactive ion etching configuration, exhibited the same trends as in the parallel-plate research etcher. This indicates that results obtained from the parallel-plate research etcher can be generalized to other configurations.