3D microscope and methods of measuring patterned substrates
A three-dimensional (3D) microscope for patterned substrate measurement can include an objective lens, a reflected illuminator, a transmitted illuminator, a focusing adjustment device, an optical sensor, and a processor. The focusing adjustment device can automatically adjust the objective lens focus at a plurality of Z steps. The optical sensor can be capable of acquiring images at each of these Z steps. The processor can control the reflected illuminator, the transmitted illuminator, the focusing adjustment device, and the optical sensor. The processor can be configured to capture first and second images at multiple Z steps, the first image with the pattern using the reflected illuminator and the second image without the pattern using one of the reflected illuminator and the transmitted illuminator.
1. A method of measuring a patterned substrate sample, the patterned substrate sample including a plurality of patterned substrate features, the method comprising:
varying a relative distance between the patterned substrate sample and an objective lens at predetermined steps;
at one or more of the predetermined steps:
projecting an image of a patterned article onto a focal plane of the objective lens;
capturing a first image with a pattern associated with the patterned article and the patterned substrate sample, and storing the first image in a first image array; and
capturing a second image of the patterned substrate sample without the pattern associated with the patterned article, and storing the second image in a second image array;
using the second image array to roughly estimate a bottom position of the patterned substrate features;
using the roughly estimated bottom position and the second image array to identify first locations of the patterned substrate sample that do not include the plurality of patterned substrate features;
using the first image array and the first locations to accurately determine the bottom position of the patterned surface features;
using the accurately determined bottom position and the second image array to identify second locations of the patterned substrate sample that include the plurality of patterned substrate features;
determining a top of each patterned substrate feature based on the second locations and one of the first image array and the second image array; and
calculating geometric parameters of patterned substrate features using the second locations, the accurately determined bottom position, and the top of each patterned substrate feature.
2. The method of claim 1 , wherein capturing the second image includes using one of a reflected illuminator and a transmitted illuminator.
3. The method of claim 2 , wherein the transmitted illuminator is a light emitting diode (LED) and one of a lens and a lens group.
4. The method of claim 1 , further comprising calculating a histogram spread for the second image array to roughly estimate the bottom position of the patterned substrate features.
5. The method of claim 1 , wherein using the first image array and the first locations to accurately determine the bottom position of the patterned surface features includes: performing a contrast calculation using only portions of the first image array associated with the first locations.
6. The method of claim 5 , wherein the accurately determined bottom position is based on a maximum contrast value of the contrast calculation.
7. The method of claim 1 , wherein the second locations of the patterned substrate are determined using a threshold method.
8. The method of claim 1 , wherein the geometric parameters include size, pitch, height, space, and top size of the patterned substrate features.
9. The method of claim 1 , wherein varying the relative distance between the patterned substrate sample and the objective lens at predetermined steps is performed automatically using an autofocus technique.
10. The method of claim 9 , wherein the auto-focus technique includes a first auto-focus technique and a second auto-focus technique.
11. The method of claim 10 , wherein the first auto-focus technique includes a conditional early exit.
12. The method of claim 11 , wherein the conditional early exit includes determining whether more than a threshold scan range is done.
13. The method of claim 11 , wherein the first auto-focus technique includes capturing images while varying the relative distance between the patterned substrate sample and the objective lens.
14. The method of claim 11 , wherein the second auto-focus technique has a step size smaller than that of the first auto-focus technique.
15. The method of claim 14 , wherein the second auto-focus technique includes detecting a falling contrast pattern.