Abstract:
Disclosed is a method of determining an overlay error between two layers of a multiple layer sample. For a plurality of periodic targets that each have a first structure formed from a first layer and a second structure formed from a second layer of the sample, an optical system is employed to thereby measure an optical signal from each of the periodic targets. There are predefined offsets between the first and second structures. An overlay error is determined between the first and second structures by analyzing the measured optical signals from the periodic targets using a scatterometry overlay technique based on the predefined offsets. The optical system comprises any one or more of the following apparatuses: a reflectometric, a ellipsomertic, imaging, interferometric, and/ or scanning angle system.
Abstract:
Disclosed are techniques, apparatus, and targets for determining overlay error between two layers of a sample. In one embodiment, a method for determining overlay between a plurality of first structures in a first layer of a sample and a plurality of second structures in a second layer of the sample is disclosed. Targets A, B, C and D that each include a portion of the first and second structures are provided. Target A is designed to have an offset Xa between its first and second structures portions; target B is designed to have an offset Xb between its first and second structures portions; target C is designed to have an offset Xc between its first and second structures portions; and target D is designed to have an offset Xd between its first and second structures portions. Each of the offsets Xa, Xb, Xc and Xd is preferably different from zero; Xa is an opposite sign and differ from Xb; and Xc is an opposite sign and differs from Xd. The targets A, B, C and D are illuminated with electromagnetic radiation to obtain spectra SA, SB, SC, and SD from targets A, B, C, and D, respectively. Any overlay error between the first structures and the second structures is then determined using a linear approximation based on the obtained spectra SA, SB, SC, and SD.
Abstract:
Various systems for measurement or analysis of a specimen are provided. One system includes a first optical subsystem, which is disposed within a purged environment. The purged environment may be provided by a differential purging subsystem. The first optical subsystem performs measurements using vacuum ultraviolet light. This system also includes a second optical subsystem, which is disposed within a non-purged environment. The second optical subsystem performs measurements using non-vacuum ultraviolet light. Another system includes two or more optical subsystems configured to perform measurements of a specimen using vacuum ultraviolet light. The system also includes a purging subsystem configured to maintain a purged environment around the two or more optical subsystems. The purging subsystem is also configured to maintain the same level of purging in both optical subsystems. Some systems also include a cleaning subsystem configured to remove contaminants from a portion of a specimen prior to measurements at vacuum ultraviolet wavelengths.