Diane Stewart

Gas-assisted etching with focused ion beam technology

Abstract The role of focused ion beam (FIB) systems in device failure analysis has been well documented 1 . FIB etching is used to cross-section features and to prepare TEM samples with better than 0.1 micron (μm) accuracy 2 , to open probe holes for mechanical and electron beam probing of circuitry, and to rewire circuits by cutting or adding connections. FIB is used to image cross sections with either secondary ions or secondary electrons, to measure metal grain size distributions through channeling contrast, and to measure process control parameters. System limitations include a relatively slow removal rate by beam sputtering of large volumes of material. Also, redeposition of sputtered material on the sidewalls of holes limits the achievable sidewall angle, and thus limits the aspect ratios of holes to approximately 6:1. With decreasing geometry sizes and multiple planarized metal layers, device modifications require cuts and interconnect holes of up to 10:1 aspect ratio, which up to now have been difficult with FIB. We will discuss recent progress in using gas-assisted etching (GAE) to enhance the FIB etching, to sharpen the etch profile, and to etch high aspect ratio holes. The hardware and GAE process will be briefly described. We will discuss the relative etch rates and selectivity of GAE with typical device materials, such as aluminum (Al), tungsten (W), silicon dioxide (SiO 2 ) and silicon (Si), using two halogen-based etchant gases, xenon difluoride (XeF 2 ) and chlorine (Cl 2 ). Images of sidewall profiles with and without GAE will be compared, and we will demonstrate several applications of GAE for e-beam and optical analysis.

Ion-beam-induced insulator deposition for chip circuit modification

Abstract As semiconductor manufacturing technologies become more complex and the number of metallization levels increases, the complexity of chip circuit modification using focused ion beam technology has also increased. The fabrication of an insulating film in a localized region to protect exposed metal greatly enhances the modification capability. It is often necessary to remove a portion of an overlying metal line to gain access to an underlying area of interest. To maintain functionality, this overlying metal line must be reconnected without shorting to underlying metallurgy. We have developed an ion-beam-induced process for circuit modification which uses an oxygen and siloxane precursor. Test structures were fabricated to evaluate the electrical integrity of these films. Results indicating sufficient dielectric strength for both memory and logic applications and the material analysis of this insulator film, are presented.

Gas flow modeling for focused ion beam (FIB) repair processes

Focused Ion Beam (FIB) systems can be used to repair photomasks by accurately depositing and/or removing absorber material at the nanometer-scale. These repairs are enabled or enhanced by process gases delivered to the area of ion beam impact on the sample. To optimize gas delivery, three-dimensional computational fluid dynamics (CFD) models of selected gas delivery systems for FIB tools have been developed. The models were verified through an experiment in which water vapor was dispensed onto a cryogenically-cooled substrate. Water vapor hitting the sample surface immediately freezes. The height of the deposited ice on the sample surface is proportional to the product of the local gas flux and the exposure time. The gas flux predicted by the CFD model was found to be in good agreement with the experimental measurement. The CFD models were used to predict the mass flux of process gas and the pressure distribution at the sample surface for various gas delivery system designs. The mass flux and pressure relate directly to the amount of reactants that are available for the FIB repair processes. Parametric studies of key gas dispense system geometric parameters are presented and used to optimize the gas dispense system geometry.

Application of mask simulation to mask repair

The repair of an opaque defect by focused ion beam milling is compromised by non-idealities of the repair process, which include an error in the placement of the repaired edge, over-etching and implantation of gallium into the quartz substrate, and the re-deposition of sputtered material. Through the application of the mask simulation software SOLID-CM (Sigma-C GmbH), the relative influence of these repair artifacts upon the aerial image of a line array after the removal of a line-edge defect on a binary mask was simulated under conditions commensurate with the 100-nm lithography node. From these simulations, we conclude that the repair process would benefit most from an enhancement in the repeatability of edge-placement and from a reduction in the Ga stain. Additional modeling was performed on the tradeoff between the improvement in transmission afforded by the removal of the Ga-stained quartz versus the reduction in light as a consequence of increased scattering by the addition of quartz damage. For the feature size investigated, the aerial image was not improved through the substitution of stained quartz with air. In summary, the simulation of the aerial image after the repair of an opaque defect can greatly aid and guide process development.

Focused ion beams for x-ray mask repair

To ensure production of functional devices based on X-ray lithography, the masks must be defect free. We have developed a repair process integrated with a focused ion beam (FIB) system such that proximity print X-ray masks with features as small as 0.25 micrometers can be repaired to industry specifications. Inspection data is transferred to the tool, and defects on masks are repaired using this data. We will review the primary technical concerns associated with repair of X-ray masks, and we will discuss design elements of the FIB system which are vital to machine performance. Examples of the inspection-repair cycle will be shown. Finally, we address the ability of the tool to place repairs accurately and reproducibly so that manufacturing specifications can be achieved on proximity print X-ray masks.