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.
The photomask industry is constantly reaching towards next-generation technology that can advance today's 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 today's and tomorrow's 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.
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.
Advances in photo mask etch technology are clearing the way for 65nm alternating phase shifting masks (alt-PSM) to be used as a principal component in a typical mask set. As wafer features shrink to ever smaller sizes, the specifications on the photo mask etch performance become more and more stringent. To meet the challenging demands of 65nm technology, alt-PSM’s are employed to help deliver a reliable and repeatable pattern transfer to the wafer. Hence, especially in the framework of quartz dry etch technology for the production of high-end alt-PSM’s ever tightening specifications generate various efforts of machine vendors and mask making industry to meet the demands 1. This paper covers data from a ten experiment two level three factorial Design of Experiment. Therein, the effects of changing quartz process conditions (i.e., ICP power, RIE power, and gas chemistry) on the Applied Materials TetraTM II Photomask Etch System were investigated. As for alt-PSM's the universally agreed upon number one priority is phase angle uniformity followed closely by RIE lag, sidewall angle (SWA), and micro-trenching this was also taken into account during the optimization process of the DoE findings. The results show phase angle uniformity of less than 2.0° relative to a 180° etch depth and acceptable performance for RIE lag, SWA, and micro-trenching. Trends and graphs of the DoE are presented and discussed in detail.
The Picosecond Laser-Electron Inter-Action for the Dynamic Evaluation of Structures (PLEIADES) facility, is a unique, novel, tunable (10-200 keV), ultrafast (ps-fs), hard x-ray source that greatly extends the parameter range reached by existing 3rd generation sources, both in terms of x-ray energy range, pulse duration, and peak brightness at high energies. First light was observed at 70 keV early in 2003, and the experimental data agrees with 3D codes developed at LLNL. The x-rays are generated by the interaction of a 50 fs Fourier-transform-limited laser pulse produced by the TW-class FALCON CPA laser and a highly focused, relativistic (20-100 MeV), high brightness (1 nC, 0.3-5 ps, 5 mm.mrad 0.2% energy spread) photo-electron bunch. The resulting x-ray brightness is expected to exceed 1020 ph/mm2/s/mrad2/0.1% BW. The beam is well-collimated (10 mrad divergence over the full spectrum, 1 mrad for a single color), and the source is a unique tool for time-resolved dynamic measurements in matter, including high-Z materials.
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.
The phase shift effect in Alternating Phase Shift Masks (AAPSMs) and chrome-less phase shift masks is created by etching trenches directly into the quartz substrate. Since the phase shift is critically dependent on the etch depth, the quartz etch process must be tightly controlled. In the absence of an etch stop for the process, an integrated metrology solution is desirable on the mask tech tool. Traditional methods for measuring etch depth or phase shift, such as interferometry, profilometry, AFM, and SEM, are expensive, slow, and/or destructive. In addition, traditional methods cannot measure quartz etch depth without removing the resist and in some cases the chrome mask, making them unsuitable for integration into the etch process. This paper will present measurements of trench depth and phase shift on quartz phase shift mask using the n&k Analyzer 1512-RT. The n&k Analyzer measures reflectance (R) and transmittance (T) from 190-1000nm, which is analyzed according to the Forouhi-Bloomer dispersion relations to simultaneously determine n, k, film thicknesses, trench depth, and phase shift. The measurement is non-destructive and fast, typically taking 2-3 seconds per measurement point. No special test structures are required for the measurement. In addition, the n&k Analyzer can measure quartz etch depth with the chrome mask, ARC layers, and resist still intact. The n&k Analyzer measurements show good correlation with 193nm interferometer measurements, and good repeatability. The small footprint, ease of use, measurement speed, and the ability to measure quartz depth in the presence of chrome and resist make the n&k Analyzer an ideal candidate for integrated metrology applications on mask etch tools for advanced proces control (APC). The Applied Materials' Tetra II phootmask etch system has the unique capability to accommodate integrated metrology modules through the factory interface. Applications of APC with integrated phase shift measurements will be discussed.
Accurate determination of endpoint is important for creating a repeatable process that maximizes sidewall profile angle and resist selectivity while maintaining a low etch bias. An Applied Materials EyeD (TM) spectrometer on the Tetra(TM) II photomask etch system is used to examine several endpoint methods to maximize flexibility and productivity. These methods include: slope changes to a single line, slope changes via a ratio of product and etchant species and slope changes of a linear combination of all slope changes. Endpoint identification is typically performed with a single spectral line. In addition, a method using neural networks, or principal component analysis (PCA) has also been created in order to fully optimize and characterize exact endpoint definition. Comparison between these methods will be discussed.
The Etec Systems TetraTM photomask etch system is currently used to etch attenuated phase shift photomasks. Currently, MoSiON is a common film used for phase shifting. Either chrome or re sist can be used as a mask for etching this film. Because the quartz substrate etches with the same chemistry commonly used to etch MoSiON, precise endpoint control is necessary to meet the phase targeting requirements to create this type of phase-shifting mask. This paper will address techniques used to obtain precise endpoint control ofthe MoSiON-quartz boundary. Endpoint control is required for the precise phase targeting of 1 800 ± 1 .5° needed for advanced subwavelength patterning technologies. In this paper, optical emission spectroscopy is used to characterize and monitor chrome etch processes on the Etec Systems TetraTM photomask etch chamber. Changes in process conditions have been captured by time-averaged optical emission traces. Using multi-wavelength optical emission spectroscopy data collected during MoSiON etching, a fingerprint ofthe plasma can be taken. The fingerprint is used to detect changes in emission lines during the etch and determine the best wavelength for endpoint detection. Secondly, this paper will examine numerical methods ofendpoint optimization, including averaging, smoothing and derivative techniques.