- SEMI MF1618 - Practice for Determination of Uniformity of Thin Films on Silicon Wafers
This Standard was technically approved by the Silicon Wafer Global Technical Committee. This edition was approved for publication by the global Audits and Reviews Subcommittee on August 31, 2015. Available at www.semiviews.org and www.semi.org in November 2015; originally published by ASTM International as ASTM F1618-95; previously published November 2010.
The fabrication of semiconductor, dielectric, and metal thin films is a critical part of silicon integrated circuit production. The variation of film properties across the surface of a wafer can have significant impact on the further processing of the wafer and on the ultimate yield of acceptable chips from the wafer, as well as on their reliability.
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.
This Practice is intended for process control, research and development, and process equipment evaluation purposes. It is intended for the benefit of semiconductor device and equipment manufacturers alike so that acquisition, reduction, and communication of thin film data is consistent among various parties who may need to concur on interpretation of the results of a thin film fabrication-process step.
Measurement of the uniformity of one or more thin film properties such as thickness, sheet resistance, reflectivity, dielectric constant or index of refraction enables the monitoring of a critical aspect of the results of a given process step. This information can be used to determine the behavior of individual process steps; it can be used with similar information from earlier process steps to determine their interaction with respect to final product uniformity. Also, it can be used in conjunction with historical data from the same process step to determine loss of control of the piece of equipment or the process cycle being used with respect to producing product having a required level of uniformity. Further, it can be used to determine the adequacy of new or modified process cycles, materials or equipment for a given film deposition or film modification requirement.
It is common practice to monitor the value of a simple statistic, such as the standard deviation, that results from layer uniformity measurement data and to compare the current value of the statistic with historical values for the same layer formation process. An increase of the current value over historical values is taken as an indication of possible deterioration of the quality of the layer formation process. It is then common to convert the data into a contour or similar map of uniformity to aid in diagnosing changes in the process that caused the increase in standard deviation (or similar statistic). This practice does not treat the interpretation of the statistic resulting from data analysis, nor does it give procedures for converting the data to a uniformity map.
The nonuniformities of a film property on a given wafer are primarily systematic, not random, in their spatial shape or distribution and arise from spatially systematic variations in such process variables as temperature, gas flow, pressure, or electric field. As a result, the simple statistic standard deviation that is specified for analysis of data acquired with this Practice will not generally have the normal interpretation for the standard deviation of a sample from a random population. It is a figure of merit for comparing data sets of a similar type, but it cannot be used for computing confidence or tolerance intervals.
Referenced SEMI Standards
SEMI M1 — Specifications for Polished Single Crystal Silicon Wafers
SEMI M20 — Practice for Establishing a Wafer Coordinate System
SEMI M59 — Terminology for Silicon Technology
SEMI MF81 — Test Method for Measuring Radial Resistivity Variation on Silicon Wafers
SEMI MF374 — Test Method for Sheet Resistance of Silicon Epitaxial, Diffused, Polysilicon, and Ion-Implanted Layers Using an In-Line Four-Point Probe with the Single-Configuration Procedure
SEMI MF576 — Test Method for Measurement of Insulator Thickness and Refractive Index on Silicon Substrates by Ellipsometry
SEMI MF673 — Test Methods for Measuring Resistivity of Semiconductor Slices or Sheet Resistance of Semiconductor Films with a Noncontact Eddy-Current Gage
SEMI MF1392 — Test Method for Determining Net Carrier Density Profiles in Silicon Wafers by Capacitance-Voltage Measurements with a Mercury Probe
SEMI MF1393 (Withdrawn 0705) — Test Method for Determining Net Carrier Density in Silicon Wafers by Miller Feedback Profiler Measurements with a Mercury Probe
SEMI MF1529 — Test Method for Sheet Resistance Uniformity Evaluation by In-line Four-Point Probe with the Dual-Configuration Procedure