Apparatus and method for aligning and measuring misregistration

• US 5,696,835 A
• Filed: 02/16/1996
• Issued: 12/09/1997
• Est. Priority Date: 01/21/1994
• Status: Expired due to Term

• Current Assignee: Rudolph Technologies Incorporated (Onto Innovation Inc.)
• Original Assignee: Texas Instruments, Inc., Texas Tech University (Texas Tech University System)
• Inventors: Wong, Wan Sang, Hahn, Kwang-Soo, Demoor, Stephen J., Cleavelin, C. Rinn, Hennessey, A. Kathleen, Lin, YouLing
• Primary Examiner(s): Couso, Jose L.
• Assistant Examiner(s): Do, Anh Hong
• Application Number:
  US08/603,026
• Time in Patent Office: 662 Days
• Field of Search: 382/151, 382/141, 382/218, 364/491, 348/86, 348/87, 348/94, 348/95
• US Class Current: 382/141
• CPC Class Codes: G06T 2207/30148 Semiconductor; IC; Wafer
• CPC Class Codes: G06T 7/74 involving reference images or patches
• CPC Class Codes: H01L 21/681 using optical controlling means

Abstract

A method is provided for aligning a silicon wafer (20) in a fabrication tool (37) having a stage (22) involving the steps of producing a digital image of a portion of wafer (20) in a scope-of-view window (48), converting the digital image to image primitives, comparing the image primitives to grammar template primitives to locate a known intersection on wafer (20); and moving the stage (22) to align wafer (20). A method and apparatus are disclosed for determining the misregistration of two layers of a wafer (20) by converting targets (158, 160) to primitives and determining the relative displacement in symbolic space. The misregistration apparatus involves a camera (34), a video-to-digital converter (32), a computer (28), and a stage adjuster (24).

Claims

1. A method for aligning a wafer in a fabrication tool with a template, comprising the steps of:

placing the wafer on a moveable stage of the tool;

positioning the wafer so that a camera on the tool can capture a scope-of-view window at a specified location;

capturing a video image with the camera;

converting the video image to a digital image;

converting the digital image to image primitives where each image primitive defines a line segment trace of said video image along an intensity level by one or more points and a magnitude;

said step of converting the digital image to image primitives comprises locating horizontal line segments by;

(i) passing a kernel vertically until a gradient with a magnitude greater than a gradient threshold is located;

(ii) passing the kernel approximately horizontally to track the horizontal gradient;

(iii) saving at least two points along the line and the magnitude of the gradient; and

(iv) repeating steps (i) through (iii) for the scope-of-view window;

comparing the image primitives to grammar template primitives where each grammar template primitive defines a line segment trace of a reference image along an intensity level by one or more points and a magnitude;

determining the displacement of the video image from the template by determining the displacement of the image primitives from the template primitives;

developing correction signals from the difference in displacement; and

aligning the wafer in response to the correction signals.

2. A method for aligning a wafer in a fabrication tool with a template, comprising the steps of:

placing the wafer on a moveable stage of the tool;

positioning the wafer so that a camera on the tool can capture a scope-of-view window at a specified location;

capturing a video image with the camera;

converting the video image to a digital image;

converting the digital image to image primitives where each image primitive defines a line segment trace of said video image along an intensity level by one or more points and a magnitude;

said step of converting the digital image to image primitives comprises locating the vertical line segments by;

(i) passing a kernel horizontally until a gradient with a magnitude greater than a gradient threshold is located;

(ii) passing the kernel approximately vertically to track the vertical gradient;

(iii) saving at least two points along the line and the magnitude of the gradient; and

(iv) repeating steps (i) through (iii) for the scope-of-view window;

comparing the image primitives to grammar template primitives where each grammar template primitive defines a line segment trace of a reference image along an intensity level by one or more points and a magnitude;

determining the displacement of the video image from the template by determining the displacement of the image primitives from the template primitives;

developing correction signals from the difference in displacement; and

aligning the wafer in response to the correction signals.

3. A method for aligning a wafer in a fabrication tool with a template, comprising the steps of:

placing the wafer on a moveable stage of the tool;

positioning the wafer so that a camera on the tool can capture a scope-of-view window at a specified location;

capturing a video image with the camera;

converting the video image to a digital image;

converting the digital image to orthogonal image primitives where each image primitive defines a line segment trace of said video image along an intensity level by one or more points and a magnitude;

said step of converting the digital image to image primitives comprises;

(a) locating horizontal line segments by;

(i) passing a kernel vertically until a gradient with a magnitude greater than a gradient threshold is located;

(ii) passing the kernel approximately horizontally to track the gradient;

(iii) performing linear regression for the points along the line segment;

(iv) saving at least two points along the line and the magnitude of the gradient; and

(v) repeating steps (i) through (iv) of (a) for the scope-of-view window; and

(b) locating the vertical line segments by;

(i) passing a kernel horizontally until a gradient with a magnitude greater than a gradient threshold is located;

(ii) passing the kernel approximately vertically to track the gradient;

(iii) performing linear regression for the points along the line segment;

(iv) saving at least two points along the line and the magnitude of the gradient; and

(v) repeating steps (i) through (iv) of (b) for the scope-of-view window;

comparing the orthogonal image primitives to orthogonal grammar template primitives where each grammar template primitive defines a line segment trace of a reference image along an intensity level by one or more points and a magnitude;

determining the displacement of the video image from the template by determining the displacement of the orthogonal image primitives from the orthogonal template primitives;

developing correction signals from the difference in displacement; and

aligning the wafer in response to the correction signals.