Focusing device for photo-exposure system

• US 4,441,808 A
• Filed: 11/15/1982
• Issued: 04/10/1984
• Est. Priority Date: 11/15/1982
• Status: Expired due to Term

• Current Assignee: Interserv Corporation
• Original Assignee: TRE Semiconductor Equipment Corporation
• Inventors: Giacomelli, Thomas P.
• Primary Examiner(s): Hayes, Monroe H.
• Application Number:
  US06/441,648
• Time in Patent Office: 512 Days
• Field of Search: 355/53, 355/73, 355/76
• US Class Current: 355/53
• CPC Class Codes: G03F 9/7026 Focusing

Abstract

A focusing apparatus for use in a step and repeat photo-exposure system is provided in which air jets are located immediately adjacent the exposure area of the exposure system. Back pressure of the air jets is sensed to determine the distance of the optical unit of the photo-exposure system to the surface of a semiconductor wafer being exposed. The average back-pressure is utilized to control movement of the optical system in order to achieve precise focusing. A map of the surface aberration of the wafer may be obtained by measuring the position of the camera at each die site after focusing has been achieved.

Claims

1. An apparatus useful in a step and repeat semiconductor wafer photo-exposure system of the type having a camera for sequentially exposing different areas on said wafer to produce semiconductor devices, said apparatus achieving spaced parallel alignment of the surface of said semiconductor wafer with a reference plane that is associated with the body of the camera of said system and is in spaced facing relationship with said wafer surface, comprising:

a platform for supporting said wafer;

a spherical air bearing mounting for said platform;

a plurality of first channels in said camera body for conducting gas under pressure to first openings in said camera body facing said wafer surface so as to form gas jets directed toward said semiconductor wafer;

first pressure sensors associated with each of sad channels to sense the gas back-pressure therewithin,

means for applying gas via said channels so that the force of said gas jets applied against said wafer will cause said wafer and said platform to move within said air bearing mounting until the back-pressure condition indicating that the distance from each of said openings to said wafer surface is equal, whereby said parallel alignment between said semiconductor wafer and the reference plane of said camera body is achieved;

vacuum clamping means for locking with said spherical air bearing mounting to prevent further movement of said platform therewithin, said vacuum clamping means being actuated upon detection by said sensors of said equal back-pressure condition;

a plurality of second channels in said camera body for conducting gas under pressure to second openings in the camera body facing said wafer surface so as to form gas jets directed toward said semiconductor wafer, wherein the second openings are located so that the gas jets strike the semiconductor wafer adjacent the exposure field of the camera;

second pressure sensors associated with each of said second channels to sense the gas back-pressure therewithin;

means for moving said camera body toward and away from said semiconductor wafer; and

focusing means for causing said moving means to move said body relative to said wafer until the average level of back-pressure sensed at all of the said second sensors is equal to a predetermined value, said value corresponding to a spacing between said body end and said wafer at which said camera is most accurately focused on said surface.

2. The apparatus of claim 1 wherein there are four second openings which are located on the camera body to form gas jets which surround the exposure field of the camera.

3. The apparatus of claim 1 including means for measuring the position of the camera body with respect to a reference position and means for storing a position measurement after the camera has been focused at each exposure location, whereby a record of the surface characteristics of the wafer is obtained.

4. The apparatus of claim 3 wherein the means for measuring comprises a linear voltage differential transducer attached to the camera body.