Ted Liang

Advanced photolithographic mask repair using electron beams

Mask repair plays an important role in yielding advanced masks that support the lithography roadmap. It is also one of the more challenging parts of mask fabrication. Electron beam induced deposition and etching have shown great potential for mask repair applications. Our work has demonstrated that e-beam mask repair provides the superior resolution and damage-free process that is needed to support mask generations for the 32nm technology node and beyond. This article describes an installed e-beam mask repair tool at Intel Mask Operation and discusses the capabilities of this enabling technology based on results obtained from repairing masks with “defects” intentionally inserted into the design (programmed defect masks). Specifically, results are presented for quartz etch repair of alternating phase shift masks and TaBN absorber etch of extreme ultraviolet masks, two of the most difficult types of mask to repair using conventional methods.

Progress in extreme ultraviolet mask repair using a focused ion beam

The key challenge in extreme ultraviolet (EUV) mask defect repair is to avoid or limit the damage to the sensitive reflective multilayer (ML) stacks on the mask substrate and repair <55 nm mask defects. Our EUV mask design employs an oxide buffer layer between the ML and the absorber to protect the ML during repair. We have developed both opaque and clear EUV mask defect repair processes using focus ion beam (FIB) based gas-assisted etching (GAE) and ion-induced deposition. The process has been successfully demonstrated on our TiN baseline mask by 10× EUV print tests of 100 nm resist lines/spaces. More importantly we have assessed the current FIB tool performance capability and compared it with the general requirements for repairing the EUV mask for the 70 nm lithography node. The characterization includes minimum “effective” beam size, etch selectivity, and edge placement precision. We discussed the required improvements and future directions in repair tool research and development in order for the mask ...

Inhibiting spontaneous etching of nanoscale electron beam induced etching features: Solutions for nanoscale repair of extreme ultraviolet lithography masks

Electron beam induced etching (EBIE) is an important technique for repairing nanoscale defects on extreme ultraviolet (EUV) lithography masks as it provides excellent spatial resolution and etch selectivity while minimizing collateral damage to the mask. While EBIE itself is a complex process, a current problem with EBIE of the TaN EUV mask absorber layer using XeF2 is the spontaneous etching of repaired features during subsequent edits of the mask. This work explores three passivation techniques for controlling the spontaneous etching after an EBIE repair is made. An oxygen plasma was used to attempt to oxidize the TaN sidewalls, but it was not successful at stopping the spontaneous etching. An active electron beam induced passivation using water was successful at stopping the spontaneous etching. Also, simple adsorption of water molecules on the TaN sidewalls was successful at inhibiting spontaneous etching. The successful passivation strategies are affected by subsequent scanning electron beam imaging....

Damage-free mask repair using electron beam induced chemical reactions

Substrate damage from Ga ions is a fundamental problem of using focused ion beam (FIB) for mask defect repair. One way to avoid substrate damage from repair is to replace Ga ions with electrons. In this paper, we describe our efforts and present some promising results that demonstrate the feasibility of using e-beam induced processes for mask repair. We employ e-beam induced chemical etching for opaque defect removal and metal deposition for clear defect repair. The examples will include Pt deposition, quartz etch for phase-shift mask and TaN etch for EUV mask. High-resolution electron beam technology is relatively mature, so the infrastructure for building an e-beam system suitable for mask repair exists today. This makes the development of an e-beam based damage-free repair technology attractive. E-beam also offers superior spatial resolution for high edge placement precision and image quality for small defects on ever shrinking mask features.

Chemical Effect of Dry and Wet Cleaning of the Ru Protective Layer of the Extreme ultraviolet (EUV) Lithography Reflector

Chemical Effect of Dry and Wet Cleaning of the Ru Protective Layer of the Extreme Ultraviolet (EUV) Lithography Reflector Leonid Belau 1 , Jeong Y. Park 2 , Ted Liang 3 , Hyungtak Seo 1 , and Gabor A. Somorjai 1,2,* Department of Chemistry, University of California, Berkeley, California 94720 Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA Components Research, Technology and Manufacturing Group, Intel Corporation, Santa Clara, CA 95054 Abstract We report the chemical influence of cleaning of the Ru capping layer on the extreme ultraviolet (EUV) reflector surface. The cleaning of EUV reflector to remove the contamination particles has two requirements; to prevent corrosion and etching of the reflector surface and to maintain the reflectivity functionality of the reflector after the corrosive cleaning processes. Two main approaches for EUV reflector cleaning: wet chemical treatments (sulfuric acid and hydrogen peroxide mixture (SPM), ozonated water, and ozonated hydrogen peroxide) and dry cleaning (oxygen plasma and UV/ozone treatment) were tested. The change of surface morphology and roughness were characterized using scanning electron microscopy (SEM) and atomic force microscopy (AFM), while the surface etching and change of oxidation states were probed with X-ray photoelectron spectroscopy (XPS). Significant surface oxidation of the Ru capping layer was observed after oxygen plasma and UV/ozone treatment, while the oxidation is unnoticeable after SPM treatment. Based on these surface studies, we found that SPM treatment exhibits the minimal corrosive interactions with Ru capping layer. We address

Helium ion microscope invasiveness and imaging study for semiconductor applications

The helium ion gas field ion source is a novel charged particle source technology with potentially greater capabilities than electron beam based tools for imaging and nanomachining [Ward et al., J. Vac. Sci. Technol. B (to be published); Morgan et al., Microscopy Today 14, 24 (2006); V. N. Tondare, J. Vac. Sci. Technol. A 23, 1498 (2005)]. Potential strengths of He ions over electrons (scanning electron microscopy) are improved thin film surface sensitivity, material contrast, IBIC voltage contrast, Rutherford backscattering material contrast, and the ability to utilize in situ electron charge neutralization on floating substrates which have enhanced charging properties (e.g., masks, photoresist). In this article, the authors will discuss and illustrate examples highlighting several of these attributes. Helium ions, unlike electrons, induce collision events in the material lattice. A critical area to understand is the operating conditions and sample types for which the advantages of helium ion imaging can...

EUV progress toward HVM readiness

This past year has witnessed a sharp increase in EUV lithography progress spanning production tools, source and infrastructure to better position the technology for HVM readiness. While the exposure source remains the largest contributor to downtime and availability, significant strides in demonstrated source power have bolstered confidence in the viability of EUVL for insertion into HVM production. The ongoing development of an EUV pellicle solution alleviates industry concern about one significant source of line-yield risk. In addition to continued expected improvements in EUV source power and availability, the ability to deliver predictable yield remains an ultimate gate to HVM insertion. Ensuring predictable yield requires significant emphasis on reticles. This includes continued pellicle development to enable the readiness and supply of a robust pellicle solution in advance of 250W source power, as well as improvements in mask blank defectivity and techniques to detect and mitigate reticle blank and pattern defects.

EUVL defect printability at the 32-nm node

The printability of both amplitude and phase defects has been investigated in proximity to absorber lines with widths corresponding to the 45 nm and 32 nm nodes. The single surface approximation was used to simulate defects within the multilayer coating. The printability of Gaussian phase defects was simulated versus width and height and location with respect to the absorber line. For narrow defects the worst location was found to be next to the absorber line, while wide defects had the greatest effect when centered under the absorber. A uniform flare was found to have little effect on the critical defect size. The results of these simulations are aimed at defining the critical defects for EUVL masks designed for the 32 nm node.

TaN EUVL mask fabrication and characterization

The EUV mask patterning process development depends on the choice of EUV mask absorber material, which has direct impact on the mask quality or performance such as CD control, defect control, and registration. In the past, several EUV mask absorber material candidates that include Al-Cu, Ti, TiN, Ta, TaN, and Cr have been evaluated. Our research indicated that TaN and Cr are the better candidates among the others evaluated. Cr absorber has been used for many optical lithography generations. Further extending Cr mask absorber to EUV lithography presents minimum impact to the currently mask technology infrastructure. TaN is a new film that has not been used in the currently mask technology. However, Ta based metal compound has been studied previously in x-ray mask technology. Its performance in EUV mask fabrication and printing was found compatible and comparable in many process steps and performance aspects to that of Cr absorber. In this paper, we will present our research and development work on TaN absorber EUV mask fabrication and characterization. The studies include material deposition study, etch development, cleaning compatibility evaluation, and mask printing test. The TaN absorber etch was able to achieve good etch profile and high etch selectivity to the buffer oxide layer. The cleaning benchmarking results showed that TaN absorber is compatible to the currently acid based Cr cleaning procedures and solution. No material damage or loss was found in the case of extreme harsh cleaning conditions used. The TaN thin absorber mask was successfully fabricated and printed in 10x microstepper at Sandia National Lab. Minimum feature of 70nm L/S were obtained.

Growth and printability of multilayer phase defects on extreme ultraviolet mask blanks

The ability to fabricate defect-free reflective Mo–Si multilayer (ML) blanks is a well-recognized challenge in enabling extreme ultraviolet (EUV) lithography for semiconductor manufacturing. Both the specification and reduction of defects necessitate the understanding of their printability and how they are generated and grow during ML deposition. A ML phase defect can be depicted by its topographical profile on the surface as either a bump or pit, which is then characterized by height or depth and width. These phase defects are complex in nature and their impact to resist printing. The authors developed an effective way to study phase defects with programmed defect mask (PDM) as “model” test vehicle. The defects are produced with tuned ML deposition process and placed in varying proximity to absorber patterns on the mask. This article describes the recent study of ML phase defect printability from exposures of a ML PDM on the EUV microexposure tool with annular, monopole, and dipole illuminations.