Method for monitoring focus on an integrated wafer
First Claim
1. A method of monitoring focus during photolithography on a wafer comprising the steps of:
- loading a wafer and a patterned reticle into a step-and-scan wafer imaging photolithography exposure system;
exposing the reticle using the step-and-scan system using a same dose but a varying focus for each exposure field of the reticle pattern on the wafer;
measuring the critical dimensions of two different features in two different regions in each exposure field, the features and regions being the same in each exposure field, the two different regions being positioned in each exposure field so that the step-and-scan wafer imaging photolithography exposure system cannot expose both of them at best focus;
plotting Bossung curves of critical dimension versus focus for the two different features in the two different regions;
determining a first best focus for the first of the two different features and a second best focus for the second of the two different features;
correlating the first and second best focuses with each other to determine their intersection point which comprises a best focus of the exposure field;
plotting the critical dimension difference between the Bossung curves for the two different features in the two different regions versus focus shift using data from the Bossung curves of the two different features and the best focus of the exposure field to obtain a sloped plot;
determining if the difference plot has sufficient sensitivity to be used as a focus monitor by determining whether the sloped plot has a desired minimum slope needed for the sloped plot to be used as the focus monitor, and if the sloped plot does not have the desired minimum slope to meet sufficient sensitivity, choosing new features in two different regions and repeating the measuring, best focus determination, correlating and plotting steps until sufficient sensitivity for use as a focus monitor is achieved;
determining focus instruction values based on the difference plot focus monitor;
scanning and exposing a new wafer based on the determined focus instruction values.
6 Assignments
0 Petitions
Accused Products
Abstract
A method and apparatus are provided for improving the focusing of a substrate such as a wafer during the photolithography imaging procedure of a semiconductor manufacturing process. The invention is particularly useful for step-and-scan system and the CD of two features in each exposure field are measured in fields exposed at varying focus to form at least two Bossung curves. Exposure focus instructions are calculated based on the intersection point of the curves and the wafer is then scanned and imaged based on the calculated exposure focus instructions. In another aspect of the invention, when multiple wafers are being processed operational variances may cause a drift in the focus. The focus drift can be easily corrected by measuring the critical dimension of each of the features and comparing the difference to determine if any focus offset is needed to return the focus to the original calculated focus value.
-
Citations
21 Claims
-
1. A method of monitoring focus during photolithography on a wafer comprising the steps of:
-
loading a wafer and a patterned reticle into a step-and-scan wafer imaging photolithography exposure system; exposing the reticle using the step-and-scan system using a same dose but a varying focus for each exposure field of the reticle pattern on the wafer; measuring the critical dimensions of two different features in two different regions in each exposure field, the features and regions being the same in each exposure field, the two different regions being positioned in each exposure field so that the step-and-scan wafer imaging photolithography exposure system cannot expose both of them at best focus; plotting Bossung curves of critical dimension versus focus for the two different features in the two different regions; determining a first best focus for the first of the two different features and a second best focus for the second of the two different features; correlating the first and second best focuses with each other to determine their intersection point which comprises a best focus of the exposure field; plotting the critical dimension difference between the Bossung curves for the two different features in the two different regions versus focus shift using data from the Bossung curves of the two different features and the best focus of the exposure field to obtain a sloped plot; determining if the difference plot has sufficient sensitivity to be used as a focus monitor by determining whether the sloped plot has a desired minimum slope needed for the sloped plot to be used as the focus monitor, and if the sloped plot does not have the desired minimum slope to meet sufficient sensitivity, choosing new features in two different regions and repeating the measuring, best focus determination, correlating and plotting steps until sufficient sensitivity for use as a focus monitor is achieved; determining focus instruction values based on the difference plot focus monitor; scanning and exposing a new wafer based on the determined focus instruction values. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 20)
-
-
14. An apparatus for making an integrated circuit device comprising a wafer wherein photolithography means are used to image the wafer during the making of the integrated circuit device comprising:
-
a loading apparatus for loading a wafer and a patterned reticle into a step-and-scan wafer imaging photolithography exposure system;
the photolithography exposure system including an exposure apparatus to expose the reticle using a same dose but a varying focus exposure field for each reticle pattern on the wafer;a measuring apparatus to measure the critical dimension of a feature in two different regions in each exposure field, the features and regions being the same in each exposure field, the two different regions being positioned in each exposure field so that the step-and-scan wafer imaging photolithography exposure system cannot expose both of them at best focus; a plotting apparatus to plot a Bossung curve of critical dimension versus focus for the two different features in the two different regions; a best focus determining and correlating apparatus to determine a best focus for each of the two different features, and to correlate these best focuses of the two different features with each other to determine their intersection point which comprises a best focus of the exposure field; a plotting apparatus for plotting the critical dimension difference between the critical dimension for the two different features in the two different regions regions versus focus shift using data from the Bossung curves of the two different features and the best focus of the exposure field to obtain a sloped plot; a difference plot sensitivity apparatus for determining if the difference plot has sufficient sensitivity to be used as a focus monitor by determining whether the sloped plot has a desired minimum slope needed for the sloped plot to be used as the focus monitor, and if the sloped plot does not have the desired minimum slope to meet sufficient sensitivity, choosing new features in two different regions and repeating the measuring, best focus determination, correlating and plotting steps until sufficient sensitivity for use as a focus monitor is achieved; a focus determination apparatus to determine a focus instruction value for the exposure fields based on the above plots; a scanning and imaging apparatus for scanning and imaging the wafer based on the determined focus instruction value; and a release apparatus for releasing the wafer and unloading the wafer from the exposure system. - View Dependent Claims (15, 16, 17, 18, 19)
-
-
21. A method of monitoring focus during photolithography on a wafer comprising the steps of:
-
loading a wafer and a patterned reticle into a photolithography exposure system; using the photolithography exposure system exposing the various exposure fields across the reticle pattern at a best focus of the photolithography exposure system; measuring critical dimensions of two different features in two different regions in each exposure field; plotting Bossung curves of critical dimension versus focus for the two different features in the two different regions; providing a best focus of the exposure field by determining best focus for each of the two different features followed by correlating these best focuses to obtain their intersection point which comprises the best focus of the exposure field; plotting a difference plot of the critical dimension difference between the Bossung curves versus focus shift of the best focus of the exposure field to obtain a sloped plot; and determining whether the sloped plot has a desired minimum slope of the sloped plot which indicates that the best focus of the exposure field has sufficient sensitivity to be used as a focus monitor, and if not, choosing new features in two different regions and repeating the measuring, best focus determination, correlating and plotting steps until sufficient sensitivity for use as a focus monitor is achieved.
-
Specification