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Andy Phillips, Lake Shore Cryotronics, Inc. The MRS Corporate Partner Program supports the Materials Research Society Foundation. H measurement systems are invaluable research tools for electronic materials and device characterization, providing quantitative data on carrier type, concentration, and mobility, as well as measurements related to resistivity, I–V curves, and other useful information. Understanding the underlying transport mechanisms of a material provides insights into its potential for use in new device applications. Sample preparation for Hall measurements can be a time-consuming process. Conventional Hall measurement techniques generally require a small, dedicated sample with hard-wired electrical connections. This typically entails destruction of at least part of the sample and prevents repeated measurement of the same structure at different stages of device fabrication. In addition, while Hall systems generally offer measurement at a range of temperatures, their sample environments may not be ideally suited to materials that react quickly in atmosphere. In these cases, a different measurement platform is indicated. Recognizing the need for non-destructive testing of wafer-scale materials, and with an eye toward providing improved environmental control for Hall measurements, Lake Shore has been working to integrate its vertical fi eld-equipped cryogenic probe station platform with its Hall measurement instrumentation. This type of confi guration makes for easier sample preparation and enables measuring of multiple structures in a single experimental session, as well as providing the ability to repeat measurements of Hall structures at progressive steps in the formation of devices co-located on the wafer. Since carrier densities and transport mechanisms change with temperature in very specifi c ways, a range of Hall measurements starting at cryogenic temperatures are typically taken. Cryogen-free refrigeration and advancements in thermally compliant cryogenic probe design now enable automated variable temperature measurement runs while ensuring consistent contact quality. The probe station’s tightly controlled vacuum environment accommodates materials that are reactive to air and those that require initial warming to drive out moisture. Finally, the probe station platform allows the researcher to easily reconfi gure the attached instrumentation in order to make any other (non-Hall) electrical measurements required while the sample is still in the environment. Easy sample handling In conventional Hall measurement systems, sample preparation usually involves dicing a wafer into appropriately sized pieces and attaching wires by soldering, wire bonding, or, if all else fails, conductive epoxies. Soldering and wire bonding can be especially tricky with high-bandgap materials like SiC, while sensitive materials like organics can be damaged in the process. The use of a probe station platform eliminates the need to attach wires to the sample, signifi cantly speeding sample prep and avoiding any damage to the sample. Instead, four or six micromanipulated probes are individually positioned as needed once the sample has been installed in the sample chamber. The probe station provides a large sample stage that can accommodate multiple individual samples and is ideal for handling wafer-scale samples (in the case of the Lake Shore system, up to 51 mm in diameter). In the typical case where the device developer has patterned a variety of different test structures on the same wafer, the repositionable probes can shift from measuring one Hall structure to the next without affecting the overall sample environment. Transport characteristics can be quickly confi rmed at the current stage of device development, and the wafer remains intact for subsequent processing steps (see Figure 1). NE S & ANALYSIS

White Paper: Non-destructive Hall measurement environment facilitates novel device R&D