ANALYTICAL AND EXPERIMENTAL STUDY ON PDC DRILL BITS QUALITY
Under geological extreme conditions, polycrystalline diamond compact bits (PDC) are a relevant choice because of their interesting drilling performances. In this way, the quality of innovating PDC bits materials has to be determined with accuracy by measuring cutting efficiency and wear rate, both related to the overall mechanical properties. A lathe-type test device was used to proceed to the first experiments. During these tests, cutters have been worn over an abrasion length greater than 15 km, with a mean normal load range from 3000 to 5000 N, a cutting speed about 1:8 m/ s and a penetration depth close to 2 mm. Analyses are based on models establishing coupled relations between cutting and friction stresses related to the drag bits excavation mechanism. In this work, models are implemented in order to evaluate cutting efficiency and to estimate the life time of the diamond insert. A variety of cutters was characterized by wear rates ranged from 9.4•10^(-15) to 1.1•10^(-13) mm^3/(Nm) (Archard’s model) and cutting efficiencies at 10 km evaluated between 31 and 55%. From here, an original approach is developed to describe the overall cutter quality by defining a ratio between efficiency and wear. The reference samples during preliminary tests clearly revealed various mechanical behaviors due to changes in the material composition and distinct manufacturing production methods. These changes are detected at several levels: coatings, grain sizes, surface roughness, etc.
Effects of Design and Processing Parameters on Performance of PDC Drag Cutters for Hard-Rock Drilling
Sandia National Laboratories and U S Synthetic Corporation have jointly conducted a multifaceted, baseline experimental study to support the development of improved drag cutters for advanced drill bits. This study, which involved the production and laboratory testing of different nonstandard cutter lots, evaluated the influence of variations in selected design and processing parameters on cutter loads, wear, and durability in hard-rock environments. The focus was on drag-bit cutters that incorporated ultrahard PDC (Polycrystalline Diamond Compact) overlays (i.e., diamond tables) on tungsten carbide substrates. Parameter variations selected for the test cutters included changes in cutter geometry, material composition, and processing conditions. Geometric variables were the diamond-table thickness, the chamfer design for the cutter edge, and the diamond-table/substrate interface configuration. Material and processing variables for the diamond table were, respectively, the nominal diamond particle size and the pressure that was applied during cutter production. Complementary drop-impact, granite-log abrasion, linear cutting-force, and rotary drilling tests examined the response of cutters from each lot. A wide range of behavior was observed from lot to lot, and analyses of the test results assessed the relative merits of these lots, allowing identification of features contributing to improved cutter performance in hard-rock (e.g., geothermal) drilling applications.
Bevel RIE application to reduce defectivity in copper BEOL processing
Bevel etch used during wafer fabrication for semiconductor devices is discussed. In this case, the bevel etch process was utilized in middle of the line processing (MOL) to reduce back end of line (BEOL) defectivity. Tungsten and titanium nitride films, from the formation of contacts to the transistors, extend into the bevel region of the wafer and have been shown to initiate arcing. This can spread foreign material defects on the front side of the wafer in various BEOL post processing steps including subsequent reactive ion etching, SEM metrology and film depositions. The bevel etch tool confines a plasma etch to the outer edge of the front side of the wafer (which can be individually adjusted) and can remove dielectric, organic and Ti/TiN/W films using a fluorine based chemistry.