Bulletin of the American Physical Society
75th Annual Gaseous Electronics Conference
Volume 67, Number 9
Monday–Friday, October 3–7, 2022;
Sendai International Center, Sendai, Japan
The session times in this program are intended for Japan Standard Time zone in Tokyo, Japan (GMT+9)
Session ER2: Plasma Etching |
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Chair: Hirotaka Toyoda Room: Sendai International Center Hagi |
Thursday, October 6, 2022 10:00AM - 10:15AM |
ER2.00001: Low Bias Frequencies for High Aspect Ratio Plasma Etching Evan Litch, Hyunjae Lee, Sang Ki Nam, Mark J Kushner Semiconductor processing employs inductively plasmas (ICPs) and capacitively coupled plasmas (CCPs) with large substrate biases to fabricate features with high aspect ratios (HAR) for the production of high-density memory. To maintain critical dimensions of these HAR structures, ion energy and angular distributions (IEADs) must have increasingly high energies and narrow angular distributions. To achieve these goals, substrate biases with progressively lower frequencies are being used. Since lower frequencies are not efficient at heating electrons and plasma production, these systems are typically multi-frequency CCPs (a higher frequency sustains the plasma) or an ICP (where the wave heating sustains the plasma). The trend towards lower frequencies is intended to extend the maximum ion energy to fully that of the sum of the RF amplitude and dc bias, while narrowing the IEAD. However, these lower frequencies also produce nearly quasi-steady state conditions, which affects sheath thickness and flux uniformity, and charging of adjacent surfaces. |
Thursday, October 6, 2022 10:15AM - 10:30AM Author not Attending |
ER2.00002: Effects of the focus ring on uniformity in capacitively coupled plasma etching reactors Fang-Fang Ma, Quan-Zhi Zhang, Jing-Yu Sun, You-Nian Wang In the fabrication of modern microelectronic devices, the uniformity of the wafer processing has been a critical problem in plasma etching. The non-uniformity is usually the most pronounced at the edge, due to different electrical properties at the wafer edge, resulting in sheath bending and ion trajectories distorting. In etching reactors, the wafer terminating structure, which is often called a focus ring, modifies the sheath structure around the edge of the wafer to enable uniform ion fluxes. However, the focus ring is a consumable component that is easily eroded by the plasma. It is expected that the ion energy bombarding the focus ring should be as small as possible. In this paper, the ion angle onto the wafer and the ion energy onto the focus ring with the variations of the wafer-focus ring gap, the focus ring height, and the dielectric constant of the focus ring are discussed by using a 2D3V particle-in-cell/ Monte Carlo collision model. Horizontal electric fields appear in opposite directions at the edge of the wafer and the inner edge of the focus ring. The ion angle onto the wafer edge can be improved by adjusting the material and geometry of the focus ring. In addition, lower ion energy at the focus ring can also be achieved by using a larger gap between the wafer and focus ring, or using a higher height/smaller dielectric constant of the focus ring. *This work was financially supported by the National Natural Science Foundation of China (NSFC) (Grant Nos. 11935005, 12105035), the Fundamental Research Funds for the Central Universities (No. DUT21TD104). |
Thursday, October 6, 2022 10:30AM - 11:00AM |
ER2.00003: Development of validated fluorocarbon plasma chemistry for multi-dimensional modeling of semiconductor plasma etch processes Invited Speaker: Dmitry Levko In this presentation, recent progress in the development and understanding of fluorocarbon plasma chemical mechanisms will be discussed. The mechanisms include the perfluorocyclobutane (c-C4F8) and tetrafluoromethane (CF4), two important gases in plasma etching applications. The self-consistent plasma fluid simulation model coupled with a comprehensive finite-rate chemical reaction mechanism is used for the mechanism development and validation. First, the deficiencies of the existing mechanisms of plasma chemical reactions found in the literature will be discussed and the approach to improve these mechanisms will be presented. Second, the results of self-consistent simulations of inductively coupled plasmas in pure c-C4F8 and CF4 with the experimental data available in the literature will be compared. Finally, the influence of various model parameters such as the surface reactions mechanism, gas pressure, discharge power, and electron stochastic heating length scale on the plasma parameters will be analyzed. The influence of these parameters on the kinetics of the dominant plasma species will be presented. |
Thursday, October 6, 2022 11:00AM - 11:15AM |
ER2.00004: Development of virtual metrology using plasma information to predict mask shape in HAR etch process Jaemin Song, Namjae Bae, Jihoon Park, Taejun Park, Ji-Won Kwon, Sangwon Ryu, Ingyu Lee, Gon-Ho Kim The mask pattern erosion transferring ions and neutrals to high aspect ratio etching profile is studied. For a facet on mask edge and sidewall, it has been previously demonstrated that several facet angles were defined by equilibrium between angle dependent etching by reactive directional ions and isotropic passivation by deposited neutrals. On facet planes of the mask, energetic ions incoming through sheath are reflected in deeper profile with spread angle distribution. Modified energetic ions directing sidewall of inner profile can make worse profile distortion such as bowing. In this study, mask shape variables determining entering ions characteristics were predicted with a linear combination of plasma information(PI) variables representing ion-inhibited etching reaction in fluorocarbon gas-based plasma. For mask etching species, O ion density correlated with O atom density was measured with OES actinometry. Ion energies were defined by 2 variables with low and high region from voltage-current sensor assuming bi-modal energy distribution. Results show that linear combination of high energy oxygen ion flux and its ratio to CF2 neutral flux variables expected well mask etched area. Facets were determined by surface positions, edge corner and sidewall of mask. The angle of the 1st facet on edge was predicted with low energy O ion flux and its ratio to CF2 neutrals, although the angle of the 2nd facet on sidewall was dominantly estimated with etch byproduct resulted from etching on the 1st facet. Furthermore, by using phenomenologically devised PI variable of reflected high energy ion flux with spread angle on 2nd facet, bowing on mask sidewall was well explained. |
Thursday, October 6, 2022 11:15AM - 11:30AM Author not Attending |
ER2.00005: Electron-assisted photoresist etching in an inductively coupled oxygen plasma via low-energy electron beam Jiwon Jung, Chin-Wook Chung An electron-assisted photoresist etching (as known as ashing) was proceeded in an inductively coupled plasma (ICP) with grid system. The low-energy electron beam (< 40 eV) was generated in oxygen plasma by using the grid, and beam energy was controlled by varying the DC grid voltage. As DC voltage increase from 0 V to 40 V, PR etch rate decreases and then increases. This etch rate variation is related with the thickness of the sheath on the grid. When the grid is open due to thin sheath, source plasma can diffuse freely to the electron beam extraction region, so that plasma potential become high (≈25 V). Therefore, the main mechanism of PR etching in this case is ion-assisted etching due to high ion bombardment energy. However, since the effect of ion decreases because sheath becomes thicker as increasing DC voltage, PR etch rate also decreases and have a minimum value. When the grid is fully closed, electron beam starts to be generated and the PR etch rate increases due to increment of electron beam energy by increasing DC voltage. This relation between the sheath and the PR etch rate was discussed in detailed by measuring electron energy distribution function (EEDF). The electron-assisted PR etching was clarified by measuring the ion bombardment energy and the optical emission spectroscopy. Since the relative O radical density is nearly constant and the ion bombardment energy decreases as increasing DC voltage, the effect of O radical and ion can be neglected. Further, PR etching was proceeded as decreasing DC voltage from 40 V to 0 V to prevent thermal effect on the PR etch rate. Therefore, the increment of PR etch rate is regarded as the result of electron-assisted PR etching. |
Thursday, October 6, 2022 11:30AM - 11:45AM |
ER2.00006: Ar plasma nanostructuring of PTFE for the wettability transition from hydrophobic to superhydrophobic and hydrophilic surfaces Vivek Pachchigar, Umesh K Gaur, Sooraj K. P., Sukriti Hans, Mukesh Ranjan Plasma processing of polymer surfaces like polytetrafluoroethylene (PTFE) has been extensively studied to achieve unique functional properties such as surface activation, desired wettability, surface adhesion, bonding, etc. Naturally, PTFE is hydrophobic with a water contact angle (WCA) of 105°. Hence, continuous efforts have been carried out to either increase or decrease the wettability of PTFE surfaces. However, as per the literature, the production of superhydrophobic PTFE by radiofrequency (RF) Ar plasma processing is challenging as it leads to defluorination and results in a hydrophilic surface. In the present study, the influence of RF power, plasma treatment time, impurities, and surface temperature on Ar plasma-treated PTFE was investigated. A single electrode-based arrangement with a sacrificial PTFE disc behind the sample was used for plasma discharge to avoid impurity and temperature effects. After 5 min treatment at 100 W, the surface became superhydrophobic (WCA=156°) due to the formation of nanostructures on the surface. However, 30 min of plasma treatment caused chemical changes and defluorination which resulted in a hydrophilic surface (WCA=14°). A yellowish layer was formed on the surface due to crosslinking, redeposition of fluorocarbon species, and iron impurities as confirmed by XPS analysis. Application of such surfaces for self-cleaning application will also be presented. |
Thursday, October 6, 2022 11:45AM - 12:00PM |
ER2.00007: Achieving selective etching of SiN and SiO2 over amorphous carbon during CF4/H2 by controlling substrate temperature Shih-Nan Hsiao, Thi-Thuy-Nga Nguyen, Takayoshi Tsutsumi, Kenji Ishikawa, Makoto Sekine, Masaru Hori The effects of substrate temperature (Ts, from 50 to –20 oC) on the etch rates (ER) of the PECVD-prepared SiN and SiO2, and their selectivity were investigated with a CF4/H2 plasma. The chemical composition and physical properties of the films were analyzed with a RBS and XRR. The ERs for the SiN at all Ts were higher than that for the SiO2 films. As Ts was decreased from 50 to –20 oC, the ER for the SiN decreased. Contrarily, the ER of the SiO2 films increased. The etch selectivity of SiN over SiO2 reached to near unity when the Ts was –20 oC. Simultaneously, the polymer deposition for the amorphous carbon (a-C) irrespective of Ts was found, suggesting the process which is applicable to the etching of 3D NAND structure composed of alternatively multilayered structure of SiN/SiO2. The angular-resolved XPS results revealed that fluorocarbon (FC) thickness was thicker for the SiO2 films than that of the SiN. The lower ER for the SiO2 was therefore attributed to the thicker FC layer and resultant etching mechanism. As the Ts was decreased, the FC thickness on the both series of films decreased. This led to the fact that the ER of the SiO2 slightly increased. On the contrary, the decrease of ER for the SiN at the low temperature was likely due to the formation of N–H bonding layer. |
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