Scatterometer and method of scatterometry using acoustic radiation

A scatterometer comprising:

• a first acoustic transceiver comprising:
• a first acoustic source configured to project first acoustic radiation at a first angle of incidence onto a target formed on a substrate to produce a first acoustic diffraction order;
• and
• a first acoustic detector configured to detect the first acoustic diffraction order while discriminating from spectral reflection and to produce a first detection signal;
• and
• a second acoustic transceiver comprising:
• a second acoustic source configured to project second acoustic radiation at a second angle of incidence onto the target to produce a second acoustic diffraction order;
• and
• a second acoustic detector configured to detect the second acoustic diffraction order while discriminating from spectral reflection and to produce a second detection signal,
• wherein the scatterometer is configured to determine a property of the substrate based on the first and second detection signals, and
• wherein the first and second acoustic transceivers are configured to project the first and second acoustic radiation at different times and with the first and second angles of incidence selected such that the first and second acoustic transceivers are configured to separately detect the first and second acoustic diffraction orders.

A scatterometer comprising:

• an acoustic transceiver comprising:
• an acoustic source configured to project first acoustic radiation at a first angle of incidence onto a target formed on a substrate to produce a first acoustic diffraction order, and configured to project second acoustic radiation at a second angle of incidence onto the target to produce a second acoustic diffraction order;
• and
• an acoustic detector configured to detect the first acoustic diffraction order while discriminating from spectral reflection and to produce a first detection signal, and configured to detect the second acoustic diffraction order while discriminating from spectral reflection and to produce a second detection signal,
• wherein the scatterometer is configured to determine a property of the substrate based on the first and second detection signals, and
• wherein the acoustic transceiver is configured to project the first and second acoustic radiation at different times and with the first and second angles of incidence selected such that the acoustic transceiver is configured to separately detect the first and second acoustic diffraction orders.