Development of a physical haze and microroughness standard

Microroughness, or haze, on wafer surfaces can mask the detection of particles by scanning surface inspection systems (SSIS). The ability of silicon dioxide or other films to function efficiently as insulators depends partially on the underlying microroughness of the silicon surface. For thin oxides, breakdown voltages are reduced commensurately with increased levels of microroughness. There are similar effects on film layers deposited in later processing steps, and an effect on bonding for silicon-on- insulator applications. The disk drive industry depends on a steady transfer rate of data from the recording medium. Imparted surface texture must be carefully controlled since it is in conflict with the desire to have the head in close proximity to the recording surface; however, too fine of a polish can lead to stick-slip or blocking. Additionally, the surface texture must be very uniform across the face of the recording media. The flat panel display industry, with their ubiquitous screens now so common in laptop computers, relies on an orientation layer with a precise amount of microroughness on the substrates. In these and numerous other applications, a well characterized surface is paramount to high production yields. And yet, the most often used of these measurements, rms microroughness, is grossly misunderstood. Surface roughness is not a unique number nor is it an intrinsic surface property. Roughness measurements depend on the parameters of the instrument used for measurement--whether that be an optical or mechanical profiler, a SSIS used for haze detection, or an atomic force microscope. Each of these instruments may give very different values from exactly the same surface. A novel approach to developing a practical haze standard has been employed by photolithographically etching features to as little as 1 nm deep into the surface of 150 mm silicon wafers. To prevent a wafer scanner from detecting these features as particles or other light scattering events, a high surface density (4 X 106 features/cm2) is produced such that the distance between features is much less than the spatial resolution of current instruments (typically 50 micrometers - 100 micrometers ). Once the wafers have been fabricated, the haze or microroughness level detected by a given scanning instrument may then be calculated from the Power Spectral Density function plots generated for each wafer by various techniques (such as angle resolved light scattering or atomic force microscopy). The amount of simulated haze produced by this method is a function of the depth of etch into the silicon surface.