1730 IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 37, NO. 9, SEPTEMBER 2009 Inductively Coupled Pulsed Plasmas in the Presence of Synchronous Pulsed Substrate Bias for Robust, Reliable, and Fine Conductor Etching Samer Banna, Ankur Agarwal, Ken Tokashiki, Hong Cho, Shahid Rauf, Senior Member, IEEE, Valentin Todorow, Kartik Ramaswamy, Ken Collins, Phillip Stout, Jeong-Yun Lee, Junho Yoon, Kyoungsub Shin, Sang-Jun Choi, Han-Soo Cho, Hyun-Joong Kim, Changhun Lee, and Dimitris Lymberopoulos Abstract—Inductively coupled pulsed plasmas in the presence of synchronous pulsed substrate bias are characterized in a com- mercial plasma etching reactor for conductor etching. The syn- chronous pulsed plasma characteristics are evaluated through the following: 1) Ar-based Langmuir probe diagnostics; 2) Ar/Cl 2 plasma modeling utilizing the hybrid plasma equipment model and the Monte Carlo feature model for the investigation of fea- ture profile evolutions; 3) basic etching characteristics such as average etch rate and uniformity; 4) sub-50-nm Dynamic Random Access Memory (DRAM) basic etching performance and profile control; and 5) charge damage evaluation. It is demonstrated that one can control the etching uniformity and profile in advanced gate etching, and reduce the leakage current by varying the syn- chronous pulsed plasma parameters. Moreover, it is shown that synchronous pulsing has the promise of significantly reducing the electron shading effects compared with source pulsing mode and continuous-wave mode. The synchronous pulsed plasma paves the way to a wider window of operating conditions, which allows new plasma etching processes to address the large number of challenges emerging in the 45-nm and below technologies. Index Terms—Inductively coupled plasma (ICP), plasma con- trol, plasma-induced damage (PID), plasma material-processing applications, synchronous pulse-time-modulated plasma. I. I NTRODUCTION F OLLOWING Moore’s law, the pace at which the micro- electronic technology is moving these days might highly be challenging with conventional device architecture. Several intrinsic limitations have triggered an extensive research ac- tivity seeking new materials to be implemented in the next generation of integrated circuits (e.g., [1]–[3]). Moreover, the more stringent and conflicting requirements in microelectron- Manuscript received December 19, 2008; revised June 30, 2009. Current version published September 10, 2009. This work was supported in part by the Etch Division, Applied Materials, Inc., and in part by the Semiconductor R&D Center, Samsung Electronics. S. Banna, A. Agarwal, S. Rauf, V. Todorow, K. Ramaswamy, K. Collins, and P. Stout are with the RF and Plasma Technology Group, Etch Division, Applied Materials, Inc., Sunnyvale, CA 94085 USA (e-mail: samer_banna@amat.com). K. Tokashiki, H. Cho, J.-Y. Lee, J. Yoon, and K. Shin are with the Semi- conductor R&D Center, Samsung Electronics Company Ltd., Hwasung City 445-701, Korea. S.-J. Choi, H.-S. Cho, H.-J. Kim, C. Lee, and D. Lymberopoulos are with the Etch Product Business Group, Etch Division, Applied Materials, Inc., Sunnyvale, CA 94085 USA. Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TPS.2009.2028071 ics for damage-free plasma etching processes with improved uniformity, higher selectivity, better anisotropy, and enhanced process throughput have stimulated an intensive research effort among academic and industrial communities in search of novel approaches and methods for the design and control of the next generation of plasma processing reactors. Hence, there is a vital need for wider and more flexible ranges of plasma operating conditions aiming to improve the etch processes for finer features. Typically, plasma reactors use an RF power source with con- stant average power or voltage to excite the plasma in a vacuum chamber. Such mode of operation is known as continuous-wave (CW) RF mode. For the last two decades, several researchers have demonstrated through numerical modeling and experi- mental studies that pulsing the RF power input, i.e., pulsed RF mode, has the promise to increase the flexibility of plasma processing by enlarging the range of operating conditions [4]– [42]. Two main parameters characterize the RF pulse: 1) pulse frequency, i.e., the frequency at which the RF power is turned on and off per second, and 2) pulse duty cycle. The latter is de- fined as the ratio between the pulse ON time and the total pulse duration. By varying the pulse frequency and the duty cycle, pulsed plasmas provide additional “control knobs” in which pri- mary plasma properties, such as ion/electron densities, electron temperature, ion/neutral flux ratio, and plasma potential, can be controlled. Hence, transitions from electron–ion plasma to ion–ion plasma during the after-glow phase (power-off period) might occur for electronegative plasmas [5]–[7], [28]. Further- more, for gate patterning applications, it was demonstrated that the pulsed plasma exhibits highly selective, highly anisotropic, notch-free, and charge-build-up damage-free polycrystalline silicon etching [8]–[14], [39], [40]. Undesirable profile distor- tions, such as microtrenching, bowing, and local side etching (notching), which are thought to be due to differential charging in features (electron shading), may be mitigated by using a pulsed plasma if the negative ions can be injected into the feature to neutralize the charge deposited by positive ions [4]– [20]. In addition, the pulsed RF mode is capable of reducing the ultraviolet radiation damage in plasma processing using high-density plasmas and plasma-induced charge damage (PID) [22]–[27], [45]–[51]. Moreover, pulsed plasmas have gained recognition as a means to control the plasma deposition envi- ronment (e.g., [31] and [37]). 0093-3813/$26.00 © 2009 IEEE Authorized licensed use limited to: Applied Materials via the e-Library. Downloaded on October 12, 2009 at 13:42 from IEEE Xplore. Restrictions apply.