Alan R. Stivers

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 ...

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.

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.

EUV mask absorber characterization and selection

In this paper, we will present our research work in EUVL mask absorber characterization and selection. The EUV mask patterning process development depends on the choice of EUVL mask absorber material, which has direct impact on the mask quality such as critical dimension (CD) control, and registration. EUVL mask absorber material selection consideration involves many aspects of material properties and processes. These include film absorption at EUV wavelength, film emissivity, film stress, mask CD and defect control, defect inspection contrast, absorber repair selectivity to the buffer layer, etc. The selection of the best candidate is non-trivial since no material is found to be superior in all aspects. In an effort of searching the best absorber materials and processes, we evaluated Al-Cu, Ti, TiN, Ta, TaN, and Cr absorbers. The comparison of material intrinsic properties and process properties allowed us to focus on the most promising absorbers and to further develop the corresponding processes to meet EUVL requirement.

EUV substrate and blank inspection with confocal microscopy

One of the key challenges for the successful implementation of EUV Lithography (EUVL) is the supply of defect free mask blanks. Obviously a reliable defect inspection is a prerequisite to achieve this goal. We report results from a EUVL blank inspection tool developed by Lasertec. The inspection principle of this tool is based on confocal microscopy at 488nm inspection wavelength. On quartz substrates a sensitivity of 60nm is demonstrated. On buried defects in the multilayer stack a reasonable capture rate down to approximately 25nm defect height has been measured. We compare these results to previously reported data on the wafer version (M350) of the current M1350.

EUV mask patterning approaches

In the last two years, we have developed tow Extreme UV (EUV) mask fabrication process flows, namely the substractive metal and the damascene process flows, utilizing silicon wafer process tools. Both types of EUV mask have been tested in a 10X reduction EUV exposure system. Dense lines less than 100 nm in width have been printed using both 0.6 micrometers thick top surface imaging resists and ultra-thin DUV resist. The EUV masks used in EUV lithography development work have been routinely made by using the current wafer process tools. The two EUV mask processes that we have developed both have some advantages and disadvantages. The simpler subtractive metal process is compatible with the current reticle defect repair methodologies. On the other hand, the more complex damascene process facilitates mask cleaning and particle inspection.

Characterization of defect detection sensitivity in inspection of mask substrates and blanks for extreme ultraviolet lithography

Defect detection sensitivity of a multi-beam confocal inspection system operating at a wavelength of 488 nm is characterized using experiments and image modeling. Experimental data on defect sensitivity are reported for programmed defects on mask substrates and blanks that are being developed for extreme ultraviolet lithography. The effects of sample surface roughness on the detection sensitivity and signal-to-noise levels are quantified. Theoretical analysis of confocal imaging of defects is in excellent agreement with measured defect images. Modeling is used to predict inspection sensitivity for defects commonly found on mask blanks.

E-beam mask repair: fundamental capability and applications

We have installed the industrys first commercial electron beam mask repair tool in Intels mask shop. In this paper we describe our on-going efforts of developing e-beam repair processes for binary, phase-shifting and EUVL masks. We present a complete characterization of fundamental capabilities of e-beam repair and make general comparisons with other technologies, in terms of repair resolutions, substrate damage, edge placement, removal selectivity, and process margin. Among many applications, results from quartz etch with excellent resolution and vertical profile are described.

Evaluation of the Capability of a Multibeam Confocal Inspection System for Inspection of EUVL Mask Blanks

Extreme ultraviolet (EUV) multilayer defects (phase defects) are a defect type unique to extreme ultraviolet lithography (EUVL) masks. A manufacturable inspection capability for these defects is key to the success of EUV lithography. Simulations of EUV scattering from multilayer defects suggest that defect printability is related to the phase error induced by the defect, which is in turn strongly coupled to the size of a multilayer surface protrusion or intrusion. We can adopt a strategy of measuring the multilayer surface to detect phase defects. During the past year a working group composed of members of Intel Corporation, Lawrence Berkeley and Lawrence Livermore National Laboratories, and International Sematech searched for a commercial tool for EUVL mask substrate and blank inspection. This working group established the tool requirements, methodologies for tool evaluation, collected data and recommended a supplier for further development with International Sematech. We collected data from several vendors and found that a multibeam confocal inspection (MCI) system had a capability significantly better than the tools used today. We will present our strategy, requirements, methodologies and results. We will discuss in detail our unique programmed substrate and multilayer defect masks used to support the tool selection, including their actinic characterization. We will present data that quantifies the inspection capability of the MCI system.