Systems and methods of characterizing process-induced wafer shape for process control using CGS interferometry
Systems and methods of characterizing wafer shape using coherent gradient sensing (CGS) interferometry are disclosed. The method includes measuring at least 3×10 6 data points on a wafer surface using a CGS system to obtain a topography map of the wafer surface. The data are collected on a wafer for pre-processing and post-processing of the wafer, and the difference calculated to obtain a measurement of the effect of the process on wafer surface shape. The process steps for processing the same wafer or subsequent wafers are controlled based on measured process-induced change in the wafer surface shape in order to improve the quality of the wafer processing.
1. A method of determining an in-plane displacement on a front-side of a first wafer having a back-side spaced from the front-side and subject to one or more semiconductor manufacturing process steps, comprising:
a) prior to performing the one or more semiconductor manufacturing process steps, performing a first measurement of a first shape of at least one of the front-side and back-side surfaces of the first wafer according to a wafer-shape sampling plan;
b) performing at least one of the one or more semiconductor manufacturing process steps on at least one of the front-side and the back-side of the first wafer;
c) performing a second measurement of a second shape of at least one of the front-side and back-side surfaces of the first wafer after carrying out step b) using the same wafer-shape sampling plan of step a);
d) determining a process-induced change in the first shape of the first wafer by comparing the first and second measurements; and
e) determining the in-plane displacement as a function of the process-induced change in the first shape and as a function of a displacement calculation that varies based on which one or more of the front-side and the back-side is stressed by the one or more semiconductor manufacturing process steps so as to cause the process-induced change in the first shape.
2. The method according to claim 1 , further comprising:
processing a second wafer using the one or more semiconductor manufacturing processing steps; and
altering at least one of the one or more semiconductor manufacturing process steps based on the determined process-induced change in a shape of the second wafer when processing the second wafer.
3. The method according to claim 1 , further comprising:
adjusting at least one of the one or more semiconductor manufacturing process steps that have not yet been applied to the first wafer based on the determined process-induced change in the first shape of the first wafer; and
processing the first wafer using the adjusted one or more semiconductor manufacturing processes steps.
4. The method according to claim 1 , further comprising:
making surface displacement measurements using alignment marks on at least one of the front-side and back-side of the first wafer, and using the surface displacement measurements in step d) of determining the process-induced change in the first shape of the first wafer.
5. The method according to claim 1 , wherein the first wafer includes front-side alignment marks on the front-side of the first wafer and back-side alignment marks on the back-side of the first wafer, and further comprising:
making first measurements of a surface displacement on the front-side of the first wafer using the front-side alignment marks after performing a front-side process step;
making second measurements of a surface displacement on the back-side of the first wafer using the back-side alignment marks after performing a back-side process step; and
using the first and second measurements of the surface displacement to identify respective contributions of the front-side and back-side process steps to the process-induced change in the first shape of the first wafer of step d).
6. The method according to claim 1 , wherein the first wafer includes front-side alignment marks on the front-side of the first wafer and back-side alignment marks on the back-side of the first wafer, and further comprising:
making an overlay measurement using the front-side and back-side alignment marks to identify respective contributions of front-side and back-side process steps to the process-induced change in the first shape of the first wafer of step d).
7. The method according to claim 1 , further comprising:
making a first stress measurement on the front-side of the first wafer after performing a front-side process step;
making a second stress measurement on the back-side of the first wafer after performing a back-side process step; and
using the first and second stress measurements to identify respective contributions of the front-side and back-side process steps to the process-induced change in first shape of the first wafer of step d).
8. The method according to claim 1 , wherein the first and second measurements each include front-side and back-side measurements.
9. The method according to claim 1 , wherein the first and second measurements each include only front-side measurements.
10. The method according to claim 1 , wherein the first and second measurements each include only back-side measurements.
11. The method according to claim 1 , wherein the at least one of the one or more semiconductor manufacturing process steps carried out in step b) includes multiple ones of the semiconductor manufacturing process steps carried out on a single lithography tool.
12. The method according to claim 1 , wherein the at least one of the one or more semiconductor manufacturing process steps carried out in step b) includes multiple ones of the semiconductor manufacturing process steps carried out on different lithography tools.
13. The method according to claim 1 , wherein step b) includes forming a semiconductor structure on at least one of the front-side and back-side of the first wafer.
14. The method according to claim 1 , wherein step b) includes processing an existing semiconductor structure on at least one of the front-side and back-side of the first wafer.
15. The method according to claim 1 , wherein the first and second measurements each includes at least 10 6 data points.
16. The method according to claim 1 , wherein the first and second measurements each includes between 1×10 5 data points and 5×10 6 data points.
17. The method according to claim 1 , further comprising developing the wafer-shape sampling plan based at least in part on whether the one or more semiconductor manufacturing process steps are all front-side process steps, are all back-side process steps, or are a mix of front-side process steps and back-side process steps.
18. The method according to claim 1 , further comprising developing the wafer-shape sampling plan based at least in part on whether or not multiple insertion points are required to isolate contribution of one or more front-side process steps to the process-induced change in the first shape from contribution of one or more back-side process steps to the process-induced change in the first shape.
19. The method according to claim 18 , wherein, when multiple insertion points are not required, the developing of the wafer-shape sampling plan includes performing the first measurement and the second measurement once each.
20. The method according to claim 18 , wherein:
when multiple insertion points are required, the developing of the wafer-shape sampling plan includes performing the first measurement and the second measurement multiple times in alternating series to obtain multiple sets of measurements; and
step e) further includes determining the in-plane displacement further as a function of the multiple sets of measurements.
21. The method according to claim 18 , wherein, when multiple insertion points are required, the method developing of the wafer-shape sampling plan further includes determining whether or not multiple insertion points are possible or practical.
22. The method according to claim 21 , wherein multiple insertion points are neither possible nor practical, and step e) further includes determining the in-plane displacement further as a function of complementary data.
23. The method according to claim 1 , wherein each of the first and second measurements is a coherent gradient sensing interferometric measurement.