Study of fixed abrasive polishing and characterization of diamondlike carbon film as a low-k material

Shallow Trench Isolation is the preferred method of isolation for devices with feature size less than 0.25μM. With its excellent selectivity to topography, fixed abrasive polishing is an excellent alternative to conventional CMP processes for the STI CMP step. The polishing mechanism in a fixed abrasive CMP process is studied in great detail by polishing some STI test wafers with different pattern densities for different times. The pattern density effects in fixed abrasive CMP have also been investigated in this project by polishing various masks, to end-point, and analyzing their pattern density distribution in relation with their polishing characteristics.; Polishing the test wafers and studying the results obtained from those experiments suggested that the lower pattern densities polish faster than the higher pattern densities. Also, it was apparent that the structures having a lower pattern density had an effect on the polishing characteristics of structures having higher pattern density. It was found that the recessed regions (‘DOWN’ areas) did not show any removal of the oxide till the step height reached 100Å. At this step height there was a dramatic increase in the polish rate of the ‘DOWN’ areas, till planarity was achieved. From this point on, oxide was removed from the wafer at a very low rate. An empirical model has been proposed based on the results obtained here. Analysis of material removal from various sections of the STI test wafers suggested that there is minimal effect of pitch on the removal rate for features greater than 10μm wide. Submicron features, however, exhibited a much higher removal rate for the same pattern density. Comparison of the pattern density distribution of various masks to their polishing characteristics suggested that the presence of a certain amount of structures having low pattern density is essential to effect any removal of material from the wafer. This behavior is ascribed to the fact that the low pattern density structures activate the pad more effectively than the higher pattern density structures, thereby resulting in a faster removal of material from the wafer.; Also as a part of this project diamondlike carbon (DLC) and fluorocarbon films were characterized for use as inter-layer dielectric materials. In addition to measuring the dielectric constant of these films, they were also tested for their moisture retention, thermal stability and CMP compatibility. The dielectric constant of the DLC films was measured to be between 2.8 and 3.2 depending on the deposition conditions. It was found that the dielectric constant of the DLC films increases after thermal treatment. The moisture retention of the DLC films was measured to be less than 0.8 μg/cm2. It was also proved by electrochemical measurements that the DLC films are stable in highly acidic environments. CMP experiments of the DLC films with various abrasive particles in the presence and absence of any chemistry did not show any appreciable removal rate of these films.