Papers by Author: Naohito Yamada

Abstract: Aluminum Nitride (AlN) ceramics are used as wafer heating plates and wafer holding electrostatic chucks in semiconductor fabrication equipments. For tailoring the electrical resistivity to satisfy the requirements of each component, several kinds of approaches were investigated for hot-pressed AlN ceramics. Three techniques to control the electrical resistivity of AlN ceramics were adopted: (1) AlN intragranular control, (2) intergranular phase control and (3) incorporation of electrically conductive second phase particles. In this paper, we introduce examples of each technique. The first one is addition of a small amount of Y2O3. The resistivity varied from 1015 Ωcm to 1010 Ωcm with the Y2O3 amount. The second one is addition of Sm2O3. The resistivity also varied from 1015 Ωcm to 1010 Ωcm with the Sm2O3 amount. The third one is incorporation of in-situ synthesized Boron Carbonitride (B-C-N). Networking of B-C-N platelets drastically decreased the resistivity to the range less than 102 Ωcm. By these techniques, it was possible to control the resistivity of AlN ceramics in a wide range with a small amount of additives.

Abstract: Electrically conductive AlN ceramics were fabricated by the addition of a small amount of B4C and sintering aid, and hot-press sintering in a nitrogen atmosphere. The electrical resistivity of AlN ceramics decreased remarkably from 1014
cm to the range of 100 to 102
cm by a minimum of 2.3 wt% of B4C addition. This resistivity decrease was caused by forming three-dimensional networks composed of boron carbonitride (B-C-N) platelets synthesized during sintering. To produce the networks of B-C-N platelets, two-step sintering with a heat-treatment step at 1600°C before the densification step at 2000°C was needed.

Abstract: Grain boundary microcracking in sliding test using a silicon pin was evaluated on several kinds of AlN to investigate the behavior of damage generation and the influence of material properties on it. The grain boundary fracture toughness (KIC gb ) was estimated from a percentage of the intergranular fracture as a grain boundary property for each specimen. KIC gb was greatly influensed by an amount and kinds of additives. After the sliding test, silicon debris accumulation and grain boundary microcracking of AlN were observed at the wear traces on the surface of AlN. The density of grain boundary microcracks increased linearly with increasing the contact load. Empirical relationship indicated that its density depended on KIC gb and the AlN grain size, and decreased mainly with increasing KIC gb. The density of grain boundary microcracks greatly degreased at the KIC gbvalue above 1.9 (MPa·m1/2).