Bulletin of the American Physical Society
74th Annual Gaseous Electronics Conference
Volume 66, Number 7
Monday–Friday, October 4–8, 2021;
Virtual: GEC Platform
Time Zone: Central Daylight Time, USA
Session PR22: Plasma Etch |
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Chair: Sebastian Wilczek, Ruhr-University Bochum, Germany Room: Virtual GEC platform |
Thursday, October 7, 2021 10:15AM - 10:45AM Not Participating |
PR22.00001: An In-house Rigorous Etching Model for Process Recipe Tuning Invited Speaker: Wei Tian As device critical dimensions (CDs) continue to shrink, plasma etching of Si structure, such as shallow trench isolation (STI), requires precise control of ion energy and angular spread. Sophiscated tuning parameters, such as multi-frequency pulsing and cyclic processes, has been introduced to meet the requirments. With the increasing complexity of the etching processes and the large number of process variables, a rigorous etching model becomes attractive as it can not only provide key insights into the fundamental etching and deposition mechanisms but also explore the parameters beyond the existing process window. |
Thursday, October 7, 2021 10:45AM - 11:00AM |
PR22.00002: In-plasma, vacuum ultraviolet photon-assisted etching of silicon Vincent Donnelly, Linfeng Du, Emilia Hirsch, Demetre J Economou, Paul Ruchhoeft In-plasma photo-assisted etching (PAE) of p-type Si (100) in a Cl2/Ar inductively-coupled plasma (ICP) was investigated. Experiments were carried out in a tandem reactor that allowed predominantly 104 and 106 nm Ar emission from the upper He/Ar ICP to enter the lower, main Cl2/Ar ICP through a mesh that prevented plasma transmission. With ion energies below the ion-assisted etching threshold in the Faraday-shielded main ICP, VUV photons are found to be remarkably efficient in promoting etching, with measured yields of over 100 Si atoms etched per photon. Masked samples were found to etch with no undercutting and smooth sidewalls with angles of 125o, corresponding to (111) planes. It was found that PAE in the main ICP was enhanced by up to 50% by simultaneous operation of both the upper and lower ICPs. When only the upper ICP VUV source was operated, irradiating the substrate in the lower chamber in the presence of Cl2, no etching occurred. Energetic ion bombardment obtained by rf-biasing the substrate in the main ICP suppressed PAE, as did the addition of trace O2. The PAE mechanism is believed to be due to the formation of hot holes (h) that photo-catalyze etching due to the hole-weakened Si-Si bonds. Ion bombardment creates e-h recombination centers and loss of holes, while O suppresses the formation of volatile products. |
Thursday, October 7, 2021 11:00AM - 11:15AM |
PR22.00003: Molecular dynamic simulation of glancing-angle scatterings on different materials in a high aspect ratio etching process Yao Du, Steven Shannon, Sang Ki Nam, Hoki Lee Forming high aspect ratio (HAR) hole structures is a common objective in plasma etching. Energetic ions interacting with side walls plays a key factor in HAR process, particularly with regard to profile shape, and can lead to faceting and bowing issues. Understanding how etching ions interact at near glancing angles with side walls helps in optimizing etching processes. |
Thursday, October 7, 2021 11:15AM - 11:30AM |
PR22.00004: Mitigating the effects of surface charging during high aspect ratio plasma etching using voltage waveform tailoring Florian Krüger, Hyunjae Lee, Sang Ki Nam, Mark J Kushner High aspect ratio (HAR) plasma etching of nanoscale features using halogen containing gas mixtures faces major challenges posed by shrinking features sizes, increased aspect ratio and less tolerance for feature distortion. Electrostatic charge effects and the resulting deflection of electrons and ions can be a major cause of feature distortion and etch rate reduction during the processing of non-conductive materials such as SiO2. The use of non-sinusoidal voltage waveforms as a means of power coupling has become an area of interest due to its potential to control electric field and charged particle dynamics in the sheath region. In this work the influence of tailored voltage waveforms on the distributions of surface incident electrons and ions in a capacitively coupled CF4 containing plasma, operated at 40 mTorr, was investigated using the Hybrid Plasma Equipment Model (HPEM). The applied waveform consists of 5 consecutive harmonics with a base frequency of 1 MHz and fixed relative amplitudes. Based on the energy and angularly resolved fluxes from the HPEM, a via etch through SiO2 was simulated using the Monte Carlo Feature Profile Model (MCFPM). The resulting features were evaluated with respect to surface charge distribution. feature deformation and etch rate. |
Thursday, October 7, 2021 11:30AM - 11:45AM |
PR22.00005: Computational study of plasma dynamics and reactive chemistry in a low-pressure inductively coupled CF4/O2 plasma Dmitry Levko, Chandrashekar Shukla, Rochan Upadhyay, Laxminarayan L Raja Plasma etching continues to play the central role in microelectronics manufacturing. As the semiconductor industry continues to shrink critical feature sizes and improve device performance, etch challenges continue to increase due to the requirement of processing smaller features along with new device structures. With their high density and high-aspect ratio features, these structures are challenging to manufacture and have required innovation in multiple areas of wafer processing. Innovations in this technology are increasingly reliant on comprehensive physical and chemical models of plasma etch processes. In the present paper, we develop a new mechanism of plasma chemical reactions for a low-pressure CF4/O2 plasma. We validate this mechanism against available experimental data using the self-consistent axisymmetric fluid model of inductively coupled plasma discharge. We show that this mechanism is in reasonable agreement with the results of experiments both quantitively and qualitatively. Using this mechanism, we analyze the influence of oxygen fraction in the feed gas mixture on the kinetics of the ion species, and the fluorine and oxygen atom yield. |
Thursday, October 7, 2021 11:45AM - 12:00PM |
PR22.00006: E-H Transitions in Ar/O2 Inductively Coupled Plasmas for Varying Antenna Aspect Ratio - Experiment Walter N Gekelman, Patrick Pribyl, Yuchen Qian, Alex Paterson, Tugba Piskin, Mark J Kushner Electronegative pulsed inductively coupled plasmas (ICPs) are used in the microelectronics industry for etching, and passivation. Pulsing is a primary control strategy to optimize conditions. Pulsed ICPs are prone to repetitive mode transitions from the capacitive (E mode) to the inductive (H mode) at the beginning of each power pulse due to the decrease in electron density in attaching gas mixtures during the interpulse afterglow. The E-H transitions are sensitive to circuit and reactor configurations, in particular the geometry of the antenna. In this work, we report on measurements of E-H transitions in pulsed ICPs (tens of mTorr) sustained in Ar/O2 mixtures for different antenna aspect ratios (i.e., the height vs width of individual windings of a stovetop style coil) and duty cycle. A 3D probe drive system was used to measure changing magnetic fields throughout the plasma volume. These results are used to compute volumetric current and azimuthal electric field, from which we calculate inductive power dissipated in the plasma as a function of time. Antenna power is carefully measured, with the difference attributed to capacitive coupling. In addition, capacitive probes measure the induced voltage inside the ceramic window just underneath the antenna. Results are reported for varying ratios of Argon to Oxygen flow rate. Results are compared to the results from 2-dimensional modeling. |
Thursday, October 7, 2021 12:00PM - 12:15PM |
PR22.00007: Consequences of photodetachment in pulsed Ar/O2 and Ar/Cl2 inductively coupled plasmas Tugba Piskin, Yunchen Qian, Patrick Pribyl, Walter N Gekelman, Mark J Kushner Pulsed electronegative inductively coupled plasma (ICPs) are now used for high volume manufacturing (HVM) microelectronics fabrication. Pulsed ICPs in electronegative gases typically undergo a mode transition from the capacitive (E-mode) to the inductive (H-mode) at the beginning of each power pulse due to the decrease in electron density in the attaching gas mixture during the interpulse afterglow. The E-H transition produces plasma waves and high energy ion bombardment of the window under the antenna which leads to process variability and erosion of the window. Methods to control the E-H transition (e.g., duty cycle, gas mixture) are somewhat limited due to their effect on other aspects of the process such as etch selectivity. In this work, we discuss results from a computational investigation of photo-detachment of electrons from negative ions as a means to control E-H transitions. The electrons produced by photo-detachment contribute to plasma conductivity which accelerates the onset of the H-mode. This investigation was performed using the Hybrid Plasma Equipment Model (HPEM) with Ar/O2 and Ar/Cl2 gas mixtures at tens of mTorr with a pulsed laser producing photodetachment from the O- or Cl- negative ions. Comparisons are made to experimental measurements of plasma properties in similar ICPs using pulsed lasers to produce photo-detachment |
Thursday, October 7, 2021 12:15PM - 12:30PM |
PR22.00008: Evaluation of charge density at hole bottom of capillary plates in a pulsed dual-frequency capacitively coupled plasma Haruka Suzuki, Makoto Moriyama, Naoya Nakahara, Hirotaka Toyoda In recent years, high-aspect-ratio hole etching by reactive ion etching (RIE) using pulsed dual-frequency capacitively coupled plasma (CCP) has become difficult in the fabrication of 3D NAND memory devices. In particular, the anomalous profile caused by ion orbit deflection due to positive charge-up inside the hole pattern has become a major problem. In order to solve the problem, it is important to understand the behavior of ions inside the hole and the mechanism of charge-up. In this study, the absolute density of the positive charge accumulated at the hole bottom is evaluated by measuring the high-frequency voltages around the hole pattern on a CCP cathode electrode using high-voltage probes. As a model of the hole pattern, lead-glass capillary plates with electrodes at the bottom are placed on the cathode through an insulated alumina plate. The charge density is evaluated from a one-dimensional equivalent circuit model using the measured voltage, plasma potential, and plate capacitance. The aspect ratio of the hole strongly affects the amount of positive and negative charged particles that reach the hole bottom. It is also confirmed that more negative charges reach the hole bottom by applying a low-frequency bias i.e. driving at dual frequency. |
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