Bulletin of the American Physical Society
64th Annual Gaseous Electronics Conference
Volume 56, Number 15
Monday–Friday, November 14–18, 2011; Salt Lake City, Utah
Session NR1: Plasma Etching |
Hide Abstracts |
Chair: Kouichi Ono, Kyoto University Room: 255D |
Thursday, November 17, 2011 9:30AM - 10:00AM |
NR1.00001: Mechanism of Si and metal etching based on sticking reaction model Invited Speaker: Plasma etching technique has been wildly used in the fabrication of LSI device. With shrinking the device size, it is required to reduce CD shift and under-cutting as well as to improve uniformity in etching process. In development of etching apparatus and process, it has been necessary to understand the mechanism of the cause of CD shift. The CD shift and etching rate is determined by the reaction of incident species (ions, radicals), and surface materials. However, their mechanisms of the surface reactions are not explained quantitatively, although a portion of them was understood clearly. We proposed the mechanism taking a sticking reaction model on a wafer surface because the reaction is one of the key factors to determine the etching rate and CD shift. Because the surface reaction depends on the surface condition and temperature, the sticking coefficient S is formulated approximately as a function of them, S=$\alpha $[1-{\{}1-(1-$\theta )$[1-(1-P$_{r})^{n/L}$]{\}}$^{L }$], where $\alpha $ is the trapping coefficients, n and L is the vibration times and migration times until desorbing from the trapping state (physical adsorption), P$_{r}$ is the chemical reaction probability from the state, and $\theta $ is the ratio of inactive site (coverage). n, L, P$_{r}$ are functions of the surface temperature and potential energy barrier. In addition this equation can be expanded to chemical reactions. CD shift $\delta $CD is also formulated by assuming the taper angle determined by the balance of deposition and ion etching, $\delta $CD=2h cot cos$^{-1}$(R$_{d}$/Y$\Gamma _{ion})$, where h is the film thickness, R$_{d}$ is the deposition rate, Y$\Gamma _{ion}$ is the sputtering rate of deposited film. By using these two equations, we have studied the mechanism of CD shift in Al etching and undercutting in Si etching. It was confirmed that temperature dependence of them are explained. In addition, by comparing the CD shift equation with another one based on the statistical analysis, it was found that RIE-lag was a factor of CD shift in gate etching. [Preview Abstract] |
Thursday, November 17, 2011 10:00AM - 10:15AM |
NR1.00002: Noninvasive sheath diagnostics in an inductively coupled plasma using a remote RF sensor Satoru Kobayashi, Shahid Rauf, ken Collins A commercial RF voltage/current (VI) sensor, mounted in the match circuit of an ICP chamber, is used to diagnose plasma density, sheath voltage and ion-energy distribution. The electrical measurements are related to plasma properties utilizing the algorithm proposed by Sobolewski (2000). This approach was previously confirmed by the authors in a commercial CCP chamber in which the VI probes were mounted on a surface close to the cathode surface, providing precise real-time RF VI signals. The VI sensor in the current work is mounted at the output of the match circuit with a complicated transmission line structure in-between. To transfer the RF voltage and current measurements at the match to the cathode surface, an ABCD matrix is calculated using the FDTD method for the specific cathode and chamber design. The resulting ABCD matrix well reflects the physical structure of the chamber, which allows one to approximate the ABCD matrix using simplified circuit concepts as well. The transformed voltages at 13.56 MHz are often 1.5 times larger than the measurement at the match, even though the total line-length is about 50 cm, which is attributed to the high characteristic impedances of some of the coaxial lines. The computed electron density is compared to measurements using a microwave resonant cavity probe and a Langmuir probe. The modeling shows good agreement with measurements. [Preview Abstract] |
Thursday, November 17, 2011 10:15AM - 10:30AM |
NR1.00003: Mechanism for Plasma Etching of Shallow Trench Isolation Features in an Inductively Coupled Plasma Ankur Agarwal, Shahid Rauf, Jim He, Jinhan Choi, Ken Collins Plasma etching for microelectronics fabrication is facing extreme challenges as processes are developed for advanced technological nodes. As device sizes shrink, control of shallow trench isolation (STI) features become more important in both logic and memory devices. Halogen-based inductively coupled plasmas in a pressure range of 20 -- 60 mTorr are typically used to etch STI features. The need for improved performance and shorter development cycles are placing greater emphasis on understanding the underlying mechanisms to meet process specifications. In this work, a surface mechanism for STI etch process will be discussed that couples a fundamental plasma model to experimental etch process measurements. This model utilizes ion/neutral fluxes and energy distributions calculated using the Hybrid Plasma Equipment Model. Experiments are for blanket Si wafers in a Cl$_{2}$/HBr/O$_{2}$/N$_{2}$ plasma over a range of pressures, bias powers, and flow rates of feedstock gases. We found that kinetic treatment of electron transport was critical to achieve good agreement with experiments. The calibrated plasma model is then coupled to a string-based feature scale model to quantify the effect of varying process parameters on the etch profile. We found that the operating parameters strongly influence critical dimensions but have only a subtle impact on the etch depths. [Preview Abstract] |
Thursday, November 17, 2011 10:30AM - 10:45AM |
NR1.00004: Deposition Step in MEMS Time Multiplexed Etch Lawrence Overzet, Iqbal Saraf, Matthew Goeckner The deposition step of the Bosch process is examined by first forming standard trenches using a Plasma-Therm DSE-II and then depositing on those for an extended time. The deposition profiles at the bottom and sidewalls of trenches provide useful insights into the physical processes driving deposition process. SEMs reveal a dense film at the top and bottom of the trench as expected; however, it has an isolated fiber structure (like blades of grass) along sidewalls. This sidewall ``film'' structure is independent of the reactor used to deposit, is not caused by the original sidewall scallops, and is not affected by an air break between trench formation and deposition. It is critically dependent upon the ion flux and energy. Our model shows that neutral flux alone cannot form such a deposit inside trenches. This indicates that the deposition step can be highly ion-enhanced and suggests that one reduce the ion flux during Bosch deposition steps to limit the deposition rate at the bottom of the trench/via and thereby increase the etch rate as well as prevent feature closing. [Preview Abstract] |
Thursday, November 17, 2011 10:45AM - 11:00AM |
NR1.00005: Study on modification process of photoresist by fluorocarbon ions and radicals Takuya Takeuchi, Shinpei Amasaki, Keigo Takeda, Kenji Ishikawa, Hiroki Kondo, Makoto Sekine, Masaru Hori Etching processes for fabricating high-aspect ratio patterns with nano-scale accuracy are desired in such as a contract hole etching for the silicon dioxide that is used as a dielectric passivation layer over MOSFETs. Photoresists (PR) are indispensable for pattern formation by lithography and for masking of pattern-transfer etching processes. However, the ArF PR have poor tolerability against the process plasma and they may often be deformed to cause line edge roughness, striation, and twisting for the etched features. To overcome these problems and realize sophisticated etching process, we had investigated the reaction of ArF PR with mass-separated fluorocarbon ions, i.e. CF$_{x}^{+}$ (x=1$\sim $3). In this research, we employed a plasma beam system to ArF PR to expose active species, i.e. ions and radicals, produced in the inductively coupled plasma of fluorocarbon gases. The ion species are accelerated to specific bombardment energy. The plasma beam chamber is connected to analysis chamber of x-ray photoelectron spectroscopy, and the modified surface layer of ArF PR by the plasma beam produced was analyzed with in-situ analysis. From the XPS results, we found the modified layer after CF$_{4}$ plasma beam exposure was fluorinated more than that of C$_{4}$F$_{8}$. [Preview Abstract] |
Thursday, November 17, 2011 11:00AM - 11:15AM |
NR1.00006: Mechanism of Highly Selective SiO$_{2}$ Etching over Si using New Alternative Gas, C$_{5}$HF$_{7}$ Yudai Miyawaki, Keigo Takeda, Hiroki Kondo, Kenji Ishikawa, Makoto Sekine, Masaru Hori, Atsuyo Yamazaki, Azumi Ito, Hirokazu Matsumoto Highly selective etching of oxide for a high aspect ratio contact hole formation is important technologies of IC fabrications. To realize an extreme high etch performances for the future devices, it is important to control the plasma chemistry based on the feedstock gas selection and internal parameters of the plasma. We achieved that highly selective etching of SiO$_{2}$ against Si using a newly-designed gas, C$_{5}$HF$_{7}$, O$_{2}$, and Ar gas mixture employed a dual frequency capacitively coupled plasma (CCP). For the conventional C$_{5}$F$_{8}$/O$_{2}$/Ar plasma, the SiO$_{2}$ etch rate and maximum selectivity were 453 nm/min and 9.4. In contrast, for the newly developed C$_{5}$HF$_{7}$/O$_{2}$/Ar plasma, the maximum selectivity of 57.3 with the etch rate of 445 nm/min was obtained. Gas phase diagnostics were conducted for understanding the plasma chemistries. It was found the density of F radical (Si etchant) in C$_{5}$HF$_{7}$ plasma was lower than that of C$_{5}$F$_{8}$ plasma and appreciable amount of H containing species exist in C$_{5}$HF$_{7}$ plasma. It is considered F content in the CF film on Si was reduced by the H containing species and lower F radical supply, and then the Si etching was prevented. Consequently, C$_{5}$HF$_{7}$/O$_{2}$/Ar chemistry has a great potential for highly selective SiO$_{2}$ etching over Si. [Preview Abstract] |
Thursday, November 17, 2011 11:15AM - 11:30AM |
NR1.00007: Exploring High AR 2$\mu $m TSV (25:1) Maarten Kostermans, Ulrich Baier, Werner Boullart, Mohand Brouri, Johan Vertommen, Arnaud Pageau 3D integration allows for reduction of the system size, both in area and volume. It improves performance since 3D interconnects are shorter than traditional interconnects in a 2D configuration, enabling a higher operation speed and smaller power consumption. In order to ensure a reliable pattern transfer, a basic requirement for the etch mechanism is to provide anisotropy. Traditionally, through-silicon vias (TSVs) are achieved by means of the Bosch process, where anisotropic etch occurs via cycles of deposition and etch steps. This work investigates the etch process for 2 $\mu $m diameter vias with an aspect ratio up to 25:1, by means of an industrial ICP etch chamber with pulsed low frequency bias and ramping of different parameters like gasflows, bias voltage and separate etch and deposition step times. In order to reduce bowing while maintaining acceptable top/bottom CDs and reduce sidewall roughness, mechanisms of sidewall passivation have been studied by changing bias power duty cycle, modifying gas flow ramps, and O2 addition. Finally, scaling rules have been established that allow to predict etch time for various TSV diameters and A/R. [Preview Abstract] |
Thursday, November 17, 2011 11:30AM - 11:45AM |
NR1.00008: 2D etch rate uniformity improvement in a parallel turn ICP system: numerical modeling and experiment Junghoon Joo 2D uniformity at moderately high etch rate is a very important issue as well as under layer selectivity and upright profile. A multi parallel turn ICP has been developed and used as an efficient tool which can control plasma density profile by controlling the antenna coil currents independently in coupled with gas flow design. Fluid based numerical modeling is used to find out the effect of current ratio and gas flow profile. The calculated results are compared with Langmuir probe data. The measured ion saturation current profile is in good agreement with the modeling results. After optimization of the coil current ratio, 3.9 {\%} of wafer scale etch rate non-uniformity was obtained for SiO$_{2}$ etch by using Ar+CF$_{4}$ in experiment. While the effect of gas injection scheme, horizontal and vertical gas flow rate control, has little effect on the etch rate uniformity at 150 mm gap distance between the wafer and the antenna dielectric window. At lowest operational pressure of 3 mTorr, the best etch rate uniformity was obtained in experiment. [Preview Abstract] |
Thursday, November 17, 2011 11:45AM - 12:00PM |
NR1.00009: Simulation study of SF6 plasma etching in the GEC reference cell Sergio Lopez-Lopez, Brent Walker, James Munro, Jonathan Tennyson Sulphur hexafluoride (SF$_{6}$) plasmas are used extensively for dry etching of silicon and silicon dioxide. The performance and efficiency of different processes vary widely, and simulations can provide important insights for optimization. Work is done at the plasma/surface boundary and radicals from the surface will enter the gas phase and take part in the plasma and surface reactions, so simulations must incorporate the surface material and chemistry associated with etch products. We present 2D simulations of a silicon etching process performed by an SF$_{6}$ plasma in an inductively driven version of the Gaseous Electronics Conference (GEC) reference cell. We use \textit{Quantemol-D}, a plasma simulation system built on the Hybrid Plasma Equipment Model (HPEM) code, which addresses coupling of bulk and surface processes. Pressure and power trends are obtained, along with chamber-wide gas-phase species concentrations, reactive fluxes to the surface, and surface species coverages. We find good agreement with experimental results for e.g.~the fluxes onto the wafer, and the electron and negative ion densities in the center of the chamber. The electron density increases roughly linearly with power as has been seen for a number of other gases in the GEC cell. Maximum concentrations are reached close to centre of the chamber, indicating that dissociation of SF$_6$ is taking place over the wafer. [Preview Abstract] |
Thursday, November 17, 2011 12:00PM - 12:15PM |
NR1.00010: Fourier Transform Infrared Absorption Spectroscopy of Gas-Phase and Surface Reaction Products during Si Etching in Inductively Coupled Cl$_{2}$ Plasmas Hiroki Miyata, Hirotaka Tsuda, Daisuke Fukushima, Yoshinori Takao, Koji Eriguchi, Kouichi Ono A better understanding of plasma-surface interactions is indispensable during etching, including the behavior of reaction or etch products, because the products on surfaces and in the plasma are important in passivation layer formation through their redeposition on surfaces. In practice, the nanometer-scale control of plasma etching would still rely largely on such passivation layer formation as well as ion-enhanced etching on feature surfaces. This paper presents \textit{in situ} Fourier transform infrared (FTIR) absorption spectroscopy of gas-phase and surface reaction products during inductively coupled plasma (ICP) etching of Si in Cl$_{2}$. The observation was made in the gas phase by transmission absorption spectroscopy (TAS), and also on the substrate surface by reflection absorption spectroscopy (RAS). The quantum chemical calculation was also made of the vibrational frequency of silicon chloride molecules. The deconvolution of the TAS spectrum revealed absorption features of Si$_{2}$Cl$_{6}$ and SiCl$_{x}$ ($x$=1-3) as well as SiCl$_{4}$, while that of the RAS spectrum revealed relatively increased absorption features of unsaturated silicon chlorides. A different behavior was also observed in bias power dependence between the TAS and RAS spectra. [Preview Abstract] |
Thursday, November 17, 2011 12:15PM - 12:30PM |
NR1.00011: Molecular Dynamics Analysis of Ion Incident Energy and Angle Dependences of Si etching with Cl, Br, and HBr beams Nobuya Nakazaki, Hirotaka Tsuda, Yoshinori Takao, Koji Eriguchi, Kouichi Ono Profile anomalies and surface roughness are now critical issues to be resolved in the plasma etching of nanometer-scale microelectronic devices, which in turn requires a better understanding of the effects of the ion incident angle on surface reaction kinetics. For example, the line edge and line width roughness of feature sidewalls and the roughness of bottom surfaces of the feature are assumed to be caused by the angular distribution of incident ions onto feature surfaces. This paper presents a classical molecular dynamics (MD) simulation of Si(100) etching by Cl$^{+}$, Br$^{+}$, and HBr$^{+}$ ion beams with different incident energies ($E_{i}$ = 20-300 eV) and angles (\textit{$\theta $} = 0$^{\circ}$- 90$^{\circ}$), where an improved Stillinger--Weber interatomic potential model is used for Si/halogen interactions. The results indicated that the surface reaction kinetics exhibit a characteristic of the ion-enhanced etching at lower energies, where the etch yield is maximum at normal incidence, while a characteristics of the physical sputtering at higher energies, where the yield is maximum at off-normal incidence. [Preview Abstract] |
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