Scatterometry based methods and systems for measurement of strain in semiconductor structures
Methods and systems for measuring optical properties of transistor channel structures and linking the optical properties to the state of strain are presented herein. Optical scatterometry measurements of strain are performed on metrology targets that closely mimic partially manufactured, real device structures. In one aspect, optical scatterometry is employed to measure uniaxial strain in a semiconductor channel based on differences in measured spectra along and across the semiconductor channel. In a further aspect, the effect of strain on measured spectra is decorrelated from other contributors, such as the geometry and material properties of structures captured in the measurement. In another aspect, measurements are performed on a metrology target pair including a strained metrology target and a corresponding unstrained metrology target to resolve the geometry of the metrology target under measurement and to provide a reference for the estimation of the absolute value of strain.
1. A metrology target pair, comprising:
a first periodic array of strained metrology target structures disposed on a wafer, each of the strained metrology target structures of the first periodic array having source, drain, and channel structures, wherein the dimensions of the source, drain, and channel structures of each of the strained metrology target structures of the first periodic array are the same dimensions as source, drain, and channel structures of a corresponding real transistor device structure further manufactured into a functioning electronic device, and wherein each of the strained metrology target structures of the first periodic array have a strained channel structure; and
a second periodic array of unstrained metrology target structures disposed on the wafer, each of the unstrained metrology target structures of the second array having at least a channel structure, wherein a dimension of the channel structure of each of the unstrained metrology target structures of the second periodic array is the same dimension as the channel structure of the corresponding real transistor device structure, and wherein each of the unstrained metrology target structures of the second periodic array have an unstrained channel structure.
2. The metrology target pair of claim 1 , wherein the real transistor device structure is a Fin Field Effect Transistor (FINFET) devices.
3. The metrology target pair of claim 1 , wherein each of the unstrained metrology target structures of the second periodic array include a channel structure without an epitaxial source structure and an epitaxial drain structure fabricated at either end of the channel structure.
4. The metrology target pair of claim 1 , wherein each of the unstrained metrology target structures of the second periodic array include an epitaxial source structure and an epitaxial drain structure at either end of the channel structure fabricated from the same material as the channel structure.
5. The metrology target pair of claim 1 , wherein the channel structure of each of the strained metrology target structures of the first periodic array is fabricated with Silicon.
6. The metrology target pair of claim 5 , wherein the source and drain structures of each of the strained metrology target structures of the first periodic array is fabricated with Silicon doped with Germanium, Phosphorous, Carbide, or any combination thereof.
7. The metrology target pair of claim 5 , wherein the channel structure of each of the unstrained metrology target structures of the second periodic array is fabricated with Silicon doped with Germanium, Phosphorous, Carbide, or any combination thereof.