ASTM F 1618 : 1996

1.1 This practice covers a set of site distribution patterns for measuring the uniformity of a property of a thin film on a silicon wafer, as well as simple procedures for analysing and reporting the results of those measurements. The purpose of this practice is to promote commonality of approach to the analysis of uniformity among all parties needing to generate or assess such information, including manufacturers of the basic test instrumentation to be used.

1.2 This practice is intended for use as a template for the evaluation of the uniformity of intrinsic film properties such as thickness or composition, and also film functional characteristics such as sheet resistance and reflectivity. The resulting information may be used to assess the uniformity of the film itself or of the layer formation process. This practice is not directly applicable to evaluating wafer-to-wafer or lot-to-lot variations.

1.3 This practice is intended for use with any thin film or layer type, or formation technique, for which basic measurement instrumentation and capability exists that is appropriate to the film parameter of interest. This practice is intended for layer growth and deposition techniques such as epitaxy, implantation, thermal and CVD oxidation, and metallization, as well as for layer modification such as various means of layer etching.

1.4 This practice can be used with any measurement method, procedure or instrumentation that can measure the needed film property or characteristic with sufficient precision and spatial resolution to reveal the needed information on spatial nonuniformity of the film. This practice does not itself contain details on performing any specific measurement.

1.4.2 Not all types of measurements that may need to be used for evaluation of the uniformity of a thin film have formal procedural standards. Test Methods F374, F576, F1392, F1393, and F1529 give details of measurement procedures that may be applied to evaluating the uniformity of thin film properties.

1.4.2 This practice does not deal with acquisition or analysis of uniformity data where it is desired to take more than one measurement per specified spatial cell such as is commonly done for wafer site flatness measurements.

1.5 This practice is written for evaluation of planar or blanket films, but it may be applied to patterned films if the pattern size, shape and distribution do not interfere with the spatial resolution of the selected measurement technique and the specified measurement site selection. If either of these interferences occur, the user may adapt the principles of the method to the needed application but the interpretation of the results may change.

1.6 This practice makes no recommendations regarding the interpretation of the statistics that result from analysis of the data acquired with regard to the goodness or badness of given values of the test statistic, nor does it make recommendations regarding decisions about the process cycle or equipment used to produce the thin film that was measured.

1.7 The principles of this practice may be adapted to determine the uniformity of bulk silicon wafer properties such as interstitial oxygen content and resistivity, but depending on the desired property and the chosen measurement technique, depth dependent variations may be misinterpreted as lateral variations.

1.8 The principles of the practice may be adapted to other semiconductor material systems, such as gallium arsenide, but particular concerns with those other materials may not be addressed adequately in this practice.