Tom Lii

Inductively coupled, point-of-use plasma abatement of perfluorinated compounds and hydrofluorinated compounds from etch processes utilizing O2 and H2O as additive gases

A current major environmental concern involves the emission of fluorinated compounds (FCs) used in semiconductor manufacturing for dielectric etching and plasma-assisted chamber cleaning processes in dielectric film chemical vapor deposition (CVD) systems. While progress has been made in reducing FC emissions from CVD tools using alternative chemistries and process optimization, the stringent demands of dielectric etch processes have limited emission reduction from this source. A promising strategy for reducing FC emissions from etch processes is point-of-use plasma abatement. In this approach, a high-density plasma is generated by a device installed downstream of the process chamber in the foreline that dissociates the FC effluent species and recombines the resulting fragments with additive gas fragments to create by-products that are either environmentally benign or scrubbable. In this work, the performance of an inductively coupled plasma abatement device is examined for the treatment of exhaust from a...

Selective etching of TiN over TaN and vice versa in chlorine-containing plasmas

Selectivity of etching between physical vapor-deposited TiN and TaN was studied in chlorine-containing plasmas, under isotropic etching conditions. Etching rates for blanket films were measured in-situ using optical emission of the N2 (C3Πu →B3Πg) bandhead at 337 nm to determine the etching time, and transmission electron microscopy to determine the starting film thickness. The etching selectivity in Cl2/He or HCl/He plasmas was poor (<2:1). There was a window of very high selectivity of etching TiN over TaN by adding small amounts (<1%) of O2 in the Cl2/He plasma. Reverse selectivity (10:1 of TaN etching over TiN) was observed when adding small amounts of O2 to the HCl/He plasma. Results are explained on the basis of the volatility of plausible reaction products.

Transition from precise to accurate critical dimension metrology

A new measurement system analysis (MSA) methodology has been developed at Texas Instruments (TI) to evaluate the status of the 65 nm technology critical dimension (CD) metrology and its readiness for production. Elements of the methodology were used in a previously reported scatterometry evaluation [1]. At every critical process level the precision, bias, linearity and total measurement uncertainty (TMU) were evaluated for metrology fleet over extended periods of time, and with the technology representative set of samples. The samples with variations that fully covered and often exceeded process space were pre-calibrated by CD atomic force microscope (AFM). CD AFM measurement precision was determined for every analyzed process level based on repeated measurements conducted over several days. The National Institute of Standards and Technologies (NIST) traceable standards were used to verify CD AFM line CD and scale calibrations. Therefore, for the first time the NIST traceability has been established for CD metrology at every critical process level for the entire technology. The data indicates an overall healthy status of the 65 nm CD metrology. Sub-nanometer accuracy has been established for gate CD metrology. The thorough CD metrology characterization and specifically absolute CD calibration were instrumental in seamless technology transfer from 200 mm to 300 mm fabs. The qualification of CD metrology also revealed several problems. Most of these are well-known from previous studies and should soon be addressed. CD scanning electron microscopy (SEM) has a systematic problem with bias of CD measurements. The problem is common for several front-end and back-end of line process levels. For most process levels, TMU of CD SEM is noticeably affected by sample modification inflicted by electron irradiation (shrinkage, charging, buildups, etc.). This causes problems, especially in the case of fleet TMU evaluation. An improved data collection methodology should be devised to minimize the impact of sample modification on fleet TMU measurements. The reported progress in semiconductor industrial CD metrology became possible after a recent breakthrough in line CD standard technology [2,3], recognition of CD AFM as an instrument for CD traceability [4,5] and development of the concept and mathematical tools for TMU analysis [6,7].

Differences in erosion mechanism and selectivity between Ti and TiN in fluorocarbon plasmas for dielectric etch

Metallic masking materials are promising candidates for plasma-based pattern transfer into low-k materials for fabricating integrated circuits. Improving etching selectivity (ES) between the low-k and hardmask material requires a fundamental understanding of material erosion in fluorocarbon (FC) plasmas. The authors have previously reported on the erosion mechanism and plasma parametric dependencies of Ti etch in FC discharges. The present work focuses on elucidating differences in the erosion behavior between Ti and TiN hardmasks. The authors studied erosion of Ti, TiN, and organosilicate glass (OSG), a reference low-k material, in CF4/Ar and C4F8/Ar plasmas. Changes in surface composition, FC surface reaction layer thicknesses, erosion rates, and corresponding ES were established by x-ray photoelectron spectroscopy and in situ ellipsometry. The authors found that the erosion stages and plasma parameter dependent surface compositions were similar for Ti and TiN. The previously established dependence of T...

Characterization of bending CD errors induced by resist trimming in 65 nm node and beyond

Resist trimming is a technique that is often used to close the gap between line widths which can be repeatedly printed with currently available lithography tools and the desired transistor gate length. For the 65-nm node, the resist line width delivered at pattern is between 60 to 70 nm while the final transistor gate length is usually targeted between 35 to 45 nm. The 15 to 35 nm critical dimension (CD) difference can be bridged by resist trimming. Due to the stringent gate CD budget, a resist trimming process should ideally have the following characteristics: i) no degradation in CD uniformity; ii) no damage in pattern fidelity; iii) controllable CD trim rate with good linearity; and iv) no degradation in line edge roughness (LER) or line width roughness (LWR). Unfortunately, a realistic resist trimming process is never perfect. In particular, resist consumption and the resultant internal stress build-up during resist trimming can lead to resist line bending. The effect of bent resist lines is a higher post-etch CD and significantly degraded local CD uniformity (LCDU). In order to reduce resist bending CD errors (defined as the difference between the post-etch CD and the design CD due to resist bending after trimming) several useful procedures either in layout or in processes are presented. These procedures include: i) symmetrically aligning gates to contact pads and field connecting poly in the circuit layout; ii) enlarging the distance between contact pad (or field connecting poly) to active area within the limits of the design rules (DR) and silicon real estate; iii) adding assist features to the layout within the DR limits; iv) minimizing resist thickness; and v) applying special plasma cure before resist trim.

Study of Ti etching and selectivity mechanism in fluorocarbon plasmas for dielectric etch

The authors studied the behavior of Ti hardmasks in CF4/Ar and C4F8/Ar discharges using conditions relevant to pattern transfer processes into organosilicate glass (OSG), a reference low-k material investigated in parallel. The authors examined various material erosion stages and determined the dependencies of etch rates (ERs) and etching selectivities (ESs) on the following plasma parameters: self-bias voltage (50–150 V), processing pressure (20–60 mTorr) and %CF4 (10–30 %) in CF4/Ar discharges, and O2 addition (0–10 %) and N2 addition (0–20 %) to C4F8/Ar discharges. Erosion behavior and ERs were characterized by real-time ellipsometric measurements and multilayer optical modeling. These measurements were complemented by x ray photoelectron spectroscopy to study the surface composition. The impact of plasma parameter changes were investigated by comparing ERs and corresponding ESs (OSG ER/Ti ER). During the erosion of Ti, the initially oxidized film surface was transformed into a TiFx layer (x ∼ 3) cover...