JOURNALOF MATERIALS SCIENCE: MATERIALS IN ELECTRONICS 14 (2003) 507±510 Microstructure and microchemistry of silicon particles formed during electrical-discharge machining LILIAN P. DAVILA, VALERIE J. LEPPERT, SUBHASH H. RISBUD Department of Chemical Engineering and Materials Science University of California, Davis 95616, USA Thestructureandmorphologyofparticlesrepresentingthebyproductofelectrical-discharge machining (EDM) were analyzed using transmission electron microscopy (TEM). The EDM process involved high-ef®ciency and high-accuracy ®ne boring of a single-crystal silicon ingot by high-frequency electrical spark discharges. As the silver electrode advanced, spark- discharge-melted or vaporized small particles of the silicon workpiece were produced and the particles were ¯ushed away and collected in deionized water. Standard TEM and analytical electron microscopy (AEM) observations were carried out. Bright-®eld (BF) images, diffraction, and energy-dispersive X-ray spectrometry (EDXS) data were obtained to completely characterize the EDM particles. BF images indicated the presence of large silicon particles decorated by smaller silver particles originating from the electrode as the byproducts of the EDM processing. Analysis of the particle-size distribution resulted in an average silicon particle size of about 500nm decorated by smaller silver particles of an average size of about 65nm. EDXS spectra depicted individual silicon and silver particles with characteristic peaks that identify the elements present. Selected-area electron diffraction(SAED)patterncon®rmedthepresenceofcrystallinesilicon.Finally,asetofSAED patterns, EDXS pro®les, and TEM images is included that fully describe the particles' chemistry, structure, and morphology, respectively. # 2003 Kluwer Academic Publishers 1. Introduction Single-crystal silicon boules, usually grown from the melt by Czochralski or Bridgman crystal growth techniques, are almost always subsequently processed by diamond saw slicing, machining, or grinding that leaves residual debris or particles of different shapes and chemistries. Some of the key steps in silicon integrated circuit manufacturing include slicing wafers from single- crystal boules, growth of silicon dioxide by oxidation, etching (chemical or plasma) of the silicon dioxide, and machining of ®ne holes by boring (drilling) with diamond grinding tools. Conventional machining methods are notoriously lacking in precision, often leaving tracks of the brittle fracture characteristics inherent in these approaches. We have recently reported [1] high-ef®ciency ®ne boring of silicon ingots by electrical-discharge machining (EDM) with the attendant advantages of higher material removal rate, small electrode wear, low contamination, and use of minimal machining force. As described in detail in [1], silicon ingots (approximately 5 mm in thickness) were sand- wiched between two silver plates for the EDM experiments. Silver electrodes used in the EDM process were in the form of a rotating pipe (1 mm outer diameter) with a tip to discharge the machining ¯uid. Typical discharge current varied from 2 to 15 A and the pulse duration from 4 to 28 ms. Viewed from a different perspective, the EDM process can be an interesting way of generating small particles of silicon and other machinable materials. The debris and residue collected in the machining ¯uid after the ®ne holes have been drilled were characterized in the present work for size, chemical composition, and structure. Transmission electron microscopy (TEM), electron diffraction, and energy-dispersive X-ray analysis were the principal techniques used in the investigation [2±5]. 2. Experimental procedure The nanoparticles were collected during the EDM process that involved high-frequency electrical-spark discharges from a silicon ingot. As the electrode advanced, spark-dischage-melted or vaporized small particles were produced. The particles were quickly ¯ushed away and collected in deionized water. Samples were prepared by sonicating the particles in their own deionized water solution (machining ¯uid) prior to transferring to 200-mesh Cu lacey carbon-coated TEM grids. First, a glass test tube containing the machining ¯uid was sonicated for 30 min in both 0957±4522 # 2003 Kluwer Academic Publishers 507