M. Ibrahim

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.

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.

Chrome etch challenges 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 Tetra IITM etcher provides solutions to these challenges.

Photomask etch challenges for future technology nodes

Requirements to meet the 45nm technology node place many challenges on photomask 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 rise with every nanometer of error incurred on the photomask (and device) platforms. As photomask costs rise, strict performance control is required for all photomask varieties utilized in the mask shop. Mask etching for future technology nodes, requires a system-level data and diagnostics strategy. This necessity stems from the need to control the performance of the mask etcher at increasingly stringent and diverse requirements of the photomask production environment. From etch applications perspective, alternating phase-shift masks (APSMs) and OPC masks pose key challenges. Specifically, the etcher needs to provide highly uniform CD performance across the entire active area of the photomask - for various feature sizes and load distributions, with no degradation to profiles. It is challenging to strike this balance, yet maintain adequate process window. Future etch systems require sensitive controls and knobs to provide this high precision and repeatable performance. Additionally, incoming variation in plate characteristics and quality necessitate tuning knobs capable of targeting the optimum performance across a diversity of applications.

Quartz etch solutions for 45-nm phase-shift masks

One means of extending the limits and lifetime of current lithography platforms for 45nm and beyond is the development of resolution enhancement techniques (RET) in the form of optical phase-shifting masks (PSM). By employing optical interference from 180° shifted lithography emission, PSM masks are able to enhance feature resolution at the wafer. This is particularly important for sub-wavelength features (i.e., features with critical dimensions less than the lithography wavelength) where line resolution can be severely degraded without such techniques. For these PSMs, the challenge is to provide highly uniform quartz etch performance across the entire active area of the mask for various feature sizes and local loads. Micro-loading (a.k.a. RIE lag or reactive ion etch lag) and phase angle range are key performance parameters to control. As the demands for these parameters tighten and mask costs rise, strict performance control is required for all PSM mask varieties utilized in the mask shop. In this paper we will discuss process results using Applied Materials next generation mask etch system in the area of APSM etch application. In particular, the discussion will focus on recent process results in phase uniformity and RIE lag for Quartz etch process. Feature profiles are also discussed with examples showing near vertical sidewalls and no micro-trenching.

Quartz etch challenges for 45 nm phase-shift masks

One means of extending the limits and lifetime of current lithography platforms for 45nm and beyond is the development of resolution enhancement techniques (RET) in the form of optical phase-shifting masks (PSM). By employing optical interference from 180° shifted lithography emission, PSM masks are able to enhance feature resolution at the wafer. This is particularly important for sub-wavelength features (i.e., features with critical dimensions less than the lithography wavelength) where line resolution can be severely degraded without such techniques. For these PSMs, the challenge is to provide highly uniform quartz etch performance across the entire active area of the mask for various feature sizes and local loads. Micro-loading (a.k.a. RIE lag or reactive ion etch lag) and phase angle range are key performance parameters to control. As the demands for these parameters tighten and mask costs rise, strict performance control is required for all PSM mask varieties utilized in the mask shop. In this paper we will discuss process improvements for the Applied Materials Tetra IITM chromeless phase lithography (CPL) etch application. In particular, the discussion will focus on recent process improvements in phase uniformity and RIE lag for our chrome hard mask CPL etch process. Results from modifications to the etch process are presented. Feature profiles are also discussed with examples showing near vertical sidewalls and no micro-trenching.

Mask etcher data strategy for 45nm and beyond

Mask Etching for the 45nm technology node and beyond requires a system-level data and diagnostics strategy. This necessity stems from the need to control the performance of the mask etcher to increasingly stringent and diverse requirements of the mask production environment. Increasing mask costs and the capability to acquire and consolidate a wealth of data within the mask etch platform are primary motivators towards harnessing data mines for feedback into the mask etching optimization. There are offline and real-time possibilities and scenarios. Here, we discuss the data architecture, acquisition, and strategies of the Applied Materials Tetra IITM Mask Etch System.

Evaluation of quartz dry etching performance for next generation phase-shift mask applications

The photomask industry is constantly reaching towards next-generation technology that can advance todays semi-conductor applications. One of the most successful and widely used techniques for advancing the current lithography capability and meeting many of the next-generation requirements is through the use of phase-shifting photomasks (PSM). Resolution enhancements techniques implemented through the use of PSMs can be a powerful tool in meeting both todays and tomorrows demanding lithographic requirements. For this work, effects of changing etch process parameters on the quartz dry-etching process performance is investigated. Considerations are given to phase depth uniformity, sidewall profile and reactive ion etch lag in the analysis of the quartz etch performance.

Photomask etch and profile control of 65nm chromeless phase lithography masks using scanning probe metrology

The demands on photomask pattern transfer become tighter with every advancing technology node. Transferring patterns with feature sizes below 200nm threaten to limit lithography capabilities and prohibit the extension of current 248nm and 193nm lithography techniques. One demand that jeopardizes the current technology is the degradation of line resolution at the smaller features sizes. Transferring patterns smaller than the lithography wavelength can distort the image at the wafer. One of the resolution enhancement techniques (RET) for improving this performance and extending the lifetime of current lithography methodology is chromeless phase lithography (CPL). In this work chromeless phase lithography masks have been etched using the Tetra II Photomask Etch System. Process development of the CPL etch process is discussed with emphasis on etch depth uniformity and CD profile. Effects of varying process parameters on etch performance are discussed for a typical low load patterned mask showing excellent etch uniformity range and reactive ion etch (RIE) lag. The requirements for uniformity range and RIE lag performance (both typically < 1%) require Z-depth precision on the order of the 0.25nm provided by the SNP. Non destructive CD profiling capability of the SNP is used to show the vertical sidewall etch performance. The ability to eliminate micro-trenching while maintaining excellent phase range and RIE lag is demonstrated. The capability of the Tetra II Photomask etch system to undercut the chrome hard mask during quartz etch is also demonstrated.