Madhavi Chandrachood

Development of a production worthy copper CMP process

A chemical mechanical polishing (CMP) process for copper damascene structures has been developed and characterized on a second generation, multiple platen polishing tool. Several formulations of experimental copper slurries containing alumina abrasive particles were evaluated for their selectivity of copper to Ta, TaN and PETEOS films. The extent of copper dishing and oxide erosion of these slurries is investigated with various process parameters such as slurry flow rate, platen speed and wafer pressure. The amount of dishing and erosion is found to be largely dependent on process parameters as well as the slurry composition. It is shown that the extent of oxide erosion and copper dishing can be significantly reduced by using a two slurry copper polish process (one slurry to polish copper and another to polish barrier layers) in conjunction with an optical end-point detection system.

A novel process of etching EUV masks for future generation technology

Studies on pattern transfer of next generation lithographic (EUV) photomask were carried out. Based on current absorber layer material candidates, thermodynamic calculations were performed and plasma etch gas system and composition were investigated. The gas systems have the advantage of all etch products being in volatile condition. This is helpful to keep the etch process and etch chamber clean. For etch CD bias challenge in EUV photomask etch, self-mask concept was investigated, which makes anti-reflective (AR) sub-layer of the absorber layer function as a hard mask for the bulk absorber layer beneath. It significantly reduces etch CD bias and improves pattern transfer fidelity. For common candidates of EUV mask absorber layers such as TaBO/TaBN and TaSiON/TaSi, reactive gas systems were proposed according to thermodynamic calculations with all products volatile. AR sub-layers were etched in one gas composition with volatiles. Once the AR sub-layer is etched through, gas composition was changed so that the bulk absorber sub-layer beneath is etched selectively with volatile products. Excellent results in profiles, CD bias, CD uniformity, and underneath buffer/capping layer impact have been demonstrated.

Optimization of a 65-nm alternating phase-shift quartz etch process

As mask features advance to the 65 nm technology node, the ability to develop advanced phase shifting masks with reliable and repeatable processes is becoming increasingly important. Changes in process conditions (i.e. power, pressure, gases, etc.), play an important role in the reduction of RIE lag, micro-trenching, loading and the improvement of sidewall profiles. In this study, the effects of changing process conditions on the TetraTM II Photomask Etch System were investigated. Process development was conducted to screen for a quartz etch process regime with enhanced performance.

Photomask etch system and process for 10nm technology node and beyond

While the industry is making progress to offer EUV lithography schemes to attain ultimate critical dimensions down to 20 nm half pitch, an interim optical lithography solution to address an immediate need for resolution is offered by various integration schemes using advanced PSM (Phase Shift Mask) materials including thin e-beam resist and hard mask. Using the 193nm wavelength to produce 10nm or 7nm patterns requires a range of optimization techniques, including immersion and multiple patterning, which place a heavy demand on photomask technologies. Mask schemes with hard mask certainly help attain better selectivity and hence better resolution but pose integration challenges and defectivity issues. This paper presents a new photomask etch solution for attenuated phase shift masks that offers high selectivity (Cr:Resist > 1.5:1), tighter control on the CD uniformity with a 3sigma value approaching 1 nm and controllable CD bias (5-20 nm) with excellent CD linearity performance (<5 nm) down to the finer resolution. The new system has successfully demonstrated capability to meet the 10 nm node photomask CD requirements without the use of more complicated hard mask phase shift blanks. Significant improvement in post wet clean recovery performance was demonstrated by the use of advanced chamber materials. Examples of CD uniformity, linearity, and minimum feature size, and etch bias performance on 10 nm test site and production mask designs will be shown.

Model-based etch profile simulation of PSM films

For advanced binary and PSM mask etch, final profile control is critically important for achieving desired mask specifications. As an aid to attain profile control, an etch profile simulation method has been developed. The method starts with an initial photoresist profile and incorporates etch rate and directionality information to predict the final etch profile. In this paper, simulated results are compared to measured etch profiles for PSM substrates. The results highlight the importance and implications of incoming resist profile and etch selectivity on final profile.

Extreme ultraviolet lithography mask etch study and overview

Abstract. An overview of extreme ultraviolet lithography (EUVL) mask etch is presented and a EUVL mask etch study was carried out. Today, EUVL implementation has three critical challenges that hinder its adoption: extreme ultraviolet (EUV) source power, resist resolution-line width roughness-sensitivity, and a qualified EUVL mask. The EUVL mask defect challenges result from defects generated during blank preparation, absorber and multilayer deposition processes, as well as patterning, etching and wet clean processes. Stringent control on several performance criteria including critical dimension (CD) uniformity, etch bias, micro-loading, profile control, defect control, and high etch selectivity requirement to capping layer is required during the resist pattern duplication on the underlying absorber layer. EUVL mask absorbers comprise of mainly tantalum-based materials rather than chrome- or MoSi-based materials used in standard optical masks. Compared to the conventional chrome-based absorbers and phase shift materials, tantalum-based absorbers need high ion energy to obtain moderate etch rates. However, high ion energy may lower resist selectivity, and could introduce defects. Current EUVL mask consists of an anti-reflective layer on top of the bulk absorber. Recent studies indicate that a native oxide layer would suffice as an anti-reflective coating layer during the electron beam inspection. The absorber thickness and the material properties are optimized based on optical density targets for the mask as well as electromagnetic field effects and optics requirements of the patterning tools. EUVL mask etch processes are modified according to the structure of the absorber, its material, and thickness. However, etch product volatility is the fundamental requirement. Overlapping lithographic exposure near chip border may require etching through the multilayer, resulting in challenges in profile control and etch selectivity. Optical proximity correction is applied to further enhance the resolution. Other resolution enhancement techniques, such as phase shifting, are also in consideration for EUVL. Phase-shifting will involve partial etching of the multilayer. The trend to use shorter EUV wavelength (e.g., 6.7 nm) for enhancing resolution will use new multilayer and absorber compositions, and will require new etch process development efforts. TaBO/TaBN absorber layers (features down to 40 nm) were etched with vertical profiles, low etch CD bias, and 1.7 nm etch CD uniformity (3σ). In the light shed application, Mo/Si multilayer etching yielded vertical profiles and high etch selectivity.

Photomask etch: addressing the resist challenges for advanced phase-shift and binary photomasks

As lithography requirements mandate ever-thinner resist thickness, the need for in-situ monitoring has become more urgent. In this paper we present an in-situ optical methodology-based system to determine residual photoresist thickness during advanced photomask etch with < 1000 Å photoresist. Several types of phase-shift masks and photoresists were examined. A series of masks were etched to demonstrate the performance of the system. Results show an average accuracy of better than 2%, with a maximum absolute range of all tests within 8%.

Dry etching performance of advanced EUV mask blanks

Mask defectivity is often highlighted as one of the barriers to a manufacturable EUV solution. As EUV lithography matures, other components of mask making also emerge as key focus areas in the industry: critical dimension (CD) control, film variability, selectivity, and profile tolerance. Mask materials and specifications continue to evolve to meet the unique challenges of EUV lithography, creating the need for etch capabilities that can keep pace with the latest developments. In this study, the performance of a new EUV mask etch system will be evaluated using a variety of mask blanks to determine the relative performance of each blank type. Etch contributions to mean to target (MTT), CDU, linearity, selectivity, capping layer uniformity, line edge roughness (LER), and profile quality will be characterized to determine tool performance. The new system will also be used to demonstrate multilayer etching capabilities, important for opaque frame and alternating phase shift applications. A comprehensive summary of the etch performance of various EUV films and the readiness for manufacturing applications will be provided.

Plasma characterization of Tetra III chrome etch system

Both Langmuir probe and spatial optical emission spectroscopy (OES) measurements have been used to characterize the TetraTM chrome etch chamber. Langmuir data was measured over a range of process pressures between 1.5mT and 10mT and source powers between 150W and 500W. At 350W, the data show electron and ion densities near 1 x 109 cm-3 for Ar and for Cl2/O2 etch plasmas. Ion density trends with pressure were observed to be opposite for the two plasmas. The effect of the third electrode designed in the chamber was demonstrated to reduce ion density by more than an order of magnitude for Ar plasma and still lower for Cl2/O2 plasma. Electron temperature and plasma potential are also reduced. Radial OES measurements are reported with a new apparatus that yields direct spatial emission data. Spatial scans of infrared emission from atomic Cl were measured under a range of several chamber conditions already measured with the Langmuir probe. The scans showed that the emission uniformity above the mask can be adjusted to a flat profile by selection of the process condition.

Chrome etch solutions for 45-nm and beyond

Requirements to meet the 45nm technology node place significant challenges on Mask makers. Resolution Enhancement Techniques (RET) employed to extend optical lithography in order to resolve sub-resolution features, have burdened mask processes margins. Also, Yield compromises loom with every nanometer of error incurred on the Mask and the Device platforms. RET techniques, such as Optical Proximity Correction (OPC), require the Mask Etcher to achieve exceptionally tight control of Critical Dimensions (CD). This ensures OPC feature integrity on the mask and resultant image fidelity of OPC structures, as well as, subsequently high and sustainable yields. This paper talks about 45 nm Chrome etch challenges and how Applied Materials next generation mask etcher provides solutions to these challenges.