High speed alignment method for wafer stepper

• US 4,550,374 A
• Filed: 11/15/1982
• Issued: 10/29/1985
• Est. Priority Date: 11/15/1982
• Status: Expired due to Term

• Current Assignee: Interserv Corporation
• Original Assignee: TRE Semiconductor Equipment Corporation
• Inventors: Kerekes, Thomas A., Green, Lawrence S., Karlinsky, David, Meshman, Boris
• Primary Examiner(s): Wise, Edward J.
• Application Number:
  US06/441,413
• Time in Patent Office: 1,079 Days
• Field of Search: 364/488, 364/489, 364/491, 364/490, 364/525, 364/571, 364/559, 356/401, 358/101
• US Class Current: 716/53
• CPC Class Codes: G06T 1/0014 Image feed-back for automatic industrial control, e.g. robot with camera robots B25J19/023

Abstract

A step-and-repeat exposure system incorporates a method for achieving die-by-die alignment at high speed in order to increase the throughput of the system. In order to align circuit patterns which are to be exposed onto a semiconductor wafer in an overlapping fashion, the wafer is initially moved to a target position in order to view an alignment target previously formed on the wafer, and is subsequently moved to an exposure position. The movement to the exposure position is controlled as a function of the calculated position of the alignment target. The method involves initiating the video scan to view the alignment target prior to the stage coming to a complete rest at the target position. The characteristics of the stage motion are determined and the acquisition of the video data is initiated as soon as the oscillation of the stage has subsided by an acceptable amount. By initiating the video scan at an early point, a significant decrease in the alignment time at each die site is achieved.

Claims

1. In an exposure system in which a plurality of overlapping patterns are exposed onto a semiconductor wafer in a step-and-repeat fashion, wherein each pattern formed during an initial step-and-repeat operation includes an associated alignment target and subsequent patterns are aligned with the initial patterns by viewing the alignment targets, a method for increasing the throughput of the system comprising the steps of:

stepping the wafer toward a predetermined target position while monitoring the position of the wafer;

viewing an area on the wafer which includes the target, wherein the viewing is intiated after the wafer has arrived at the target position but prior to the wafer coming to acomplete stop at the target position;

moving the wafer toward an expected exposure position immediately upon completion of the viewing of the wafer;

calculating, as a function of the position of the target when the wafer is at the target position, the offset of the initially exposed pattern with respect to its desired position, wherein said calculating is done while the wafer is being moved;

moving the wafer toward a corrected exposure position in response to the offset calculation; and

exposing a subsequent pattern onto the wafer after it has arrived at the corrected exposure position.

2. The method of claim 1 wherein the step of viewing includes the step of scanning the area of the wafer with a video camera.

3. The method of claim 2 wherein the step of viewing includes the steps of continuously scanning with the camera and storing the results of a scan taken when the wafer is at the target position, wherein the stored results are used to calculate the offset of the patterns.

4. The method of claim 2 wherein the step of viewing is done with a high speed camera and is done immediately upon arrival of the wafer at the target position and wherein the velocity of the wafer as it passes the target position is maintained constant.

5. The method of claim 2 wherein the wafer is brought to a stop at the target position.

6. In an exposure system in which a semiconductor wafer is stepped and repeated to repeatedly expose a pattern onto a semiconductor wafer and additional patterns are exposed over initial patterns in an overlapping relationship, wherein the initial patterns include an alignment target which is viewed with a scanning video camera to determine alignment between initial and subsequent patterns, wherein alignment is achieved by initially moving the wafer to a predetermined target position and determining the offset of the alignment target with respect to its expected position and subsequently moving the wafer to an exposure position which is determined as a function of said offset, the improvement for increasing the throughput of said system, comprising the steps of:

stepping the wafer toward a target position;

initiating the acquiring of data from a video scan after the wafer has arrived at the target position and has begun to stop but prior to the wafer coming to a complete stop;

starting to move toward an expected exposure position immediately upon the acquisition of data for a complete video scan;

calculating, as a function of the acquired data, a corrected exposure position; and

moving the wafer to the corrected exposure position and exposing a pattern on the wafer.

7. In an exposure system in which a plurality of overlapping patterns are exposed onto a semiconductor wafer in a step-and-repeat fashion, wherein each pattern formed during an initial step-and-repeat operation includes an associated alignment target and subsequent patterns are aligned with the initial patterns by viewing the alignment targets, a method for increasing the throughput of the system comprising the steps of:

stepping the wafer toward a predetermined target position while monitoring the position of the wafer;

viewing an area on the wafer which includes the target to thereby determine the actual position of the target when the wafer is at said predetermined target position, wherein the viewing is initiated after the wafer has arrived at said predetermined target position but prior to the wafer coming to a complete stop at said predetermined target position;

moving the wafer toward an expected exposure position which is a predetermined distance from said predetermined target position immediately upon completion of the viewing of the wafer;

correcting the movement of said wafer toward said expected exposure position in accordance with the determined actual position of the target when the wafer is at said predetermined target position, wherein the correcting is performed while the wafer is being moved; and

exposing a subsequent pattern onto the wafer after it has arrived at the corrected exposure position.

8. In an exposure system in which a plurality of overlapping patterns are exposed onto a semiconductor wafer in a step-and-repeat fashion, wherein each pattern formed during an initial step-and-repeat operation includes an associated alignment target and subsequent patterns are aligned with the initial patterns by viewing the alignment targets, wherein the wafer is carried on a stage, a method for increasing the throughput of the system comprising the steps of:

stepping the stage toward a predetermined target position while monitoring the position of the stage;

viewing an area on the wafer which includes the target, wherein the viewing is initiated after the stage has arrived at the predetermined target position but prior to the cessation of motion of the stage to determine the offset of the actual target position with respect to said predetermined target position;

moving the stage toward an expected exposure position which is a predetermined distance from said predetermined target position immediately upon completion of the viewing of the wafer;

correcting said movement of said stage toward said expected exposure position in accordance with said offset determined from said viewing, wherein said correcting is done while the wafer is being moved; and

exposing a subsequent pattern onto the wafer after the stage has arrived at the corrected exposure position.