Method and system for precisely positioning a waist of a material-processing laser beam to process microstructures within a laser-processing site

• US 20020125231A1
• Filed: 11/02/2001
• Published: 09/12/2002
• Est. Priority Date: 05/16/2000
• Status: Active Grant

• Current Assignee: Electro Scientific Industries Incorporated (MKS Instruments Incorporated)
• Original Assignee: General Scanning, Inc. (KOCH Industries Incorporated)
• Inventors: Hunter, Bradley L., Ehrmann, Jonathan S., Plotkin, Michael, Cahill, Steven P.
• Granted Patent: US 6,573,473 B2
• Time in Patent Office: Days
• US Class Current: 219/121.69
• CPC Class Codes: B23K 2101/40 Semiconductor devices
• CPC Class Codes: B23K 26/02 Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
• CPC Class Codes: B23K 26/04 Automatically aligning, aiming or focusing the laser beam, e.g. using the back-scattered light
• CPC Class Codes: B23K 26/043 along the beam path, i.e. alignment of laser beam axis relative to laser beam apparatus
• CPC Class Codes: B23K 26/046 Automatically focusing the laser beam
• CPC Class Codes: B23K 26/0853 Devices involving movement of the workpiece in at least in two axial directions, e.g. in a plane
• CPC Class Codes: G03F 7/70041 by pulsed sources, e.g. multiplexing, pulse duration, interval control or intensity control
• CPC Class Codes: G03F 7/70725 control

Abstract

A high-speed method and system for precisely positioning a waist of a material-processing laser beam to dynamically compensate for local variations in height of microstructures located on a plurality of objects spaced apart within a laser-processing site are provided. In the preferred embodiment, the microstructures are a plurality of conductive lines formed on a plurality of memory dice of a semiconductor wafer. The system includes a focusing lens subsystem for focusing a laser beam along an optical axis substantially orthogonal to a plane, an x-y stage for moving the wafer in the plane, and a first air bearing sled for moving the focusing lens subsystem along the optical axis. The system also includes a first controller for controlling the x-y stage based on reference data which represents 3-D locations of microstructures to be processed within the site, a second controller, and a first voice coil coupled to the second controller for positioning the first air bearing sled along the optical axis also based on the reference data. The reference data is generated by the system which includes a modulator for reducing power of the material-processing laser beam to obtain a probe laser beam to measure height of the semiconductor wafer at a plurality of locations about the site to obtain reference height data. A computer computes a reference surface based on the reference height data. A trajectory planner generates trajectories for the wafer and the waist of the laser beam based on the reference surface. The x-y stage and the first air bearing sled controllably move the wafer and the focusing lens subsystem, respectively, to precisely position the waist of the laser beam so that the waist substantially coincides with the 3-D locations of the microstructures within the site. The system also includes a spot size lens subsystem for controlling size of the waist of the laser beam, a second air bearing sled for moving the spot size lens subsystem along the optical axis, a third controller for controlling the second air bearing sled, and a second voice coil coupled to the third controller for positioning the second air bearing sled along the optical axis.

Claims

1. A method for precisely positioning a waist of a material-processing laser beam to dynamically compensate for local variations in height of microstructures located on a plurality of objects spaced apart within a laser-processing site, the method comprising:

providing reference data which represents 3-D locations of microstructures to be processed within the site;

positioning the waist of the laser beam along an optical axis based on the reference data; and

positioning the objects in a plane based on the reference data so that the waist of the laser beam substantially coincides with the 3-D locations of the microstructures within the site.

2. The method as claimed in claim 1 wherein the objects are dice of a semiconductor wafer.

3. The method as claimed in claim 2 wherein the microstructures are conductive lines of the dice.

4. The method as claimed in claim 3 wherein the conductive lines are metal lines.

5. The method as claimed in claim 1 wherein the objects are semiconductor devices.

6. The method as claimed in claim 5 wherein the semiconductor devices are semiconductor memory devices.

7. The method as claimed in claim 2 wherein the dice are semiconductor dice.

8. The method as claimed in claim 2 wherein the step of providing includes the step of measuring height of the semiconductor wafer at a plurality of locations about the site to obtain reference height data.

9. The method as claimed in claim 8 wherein the step of providing further includes the steps of computing a reference surface based on the reference height data and generating trajectories for the wafer and the waist of the laser beam based on the reference surface.

10. The method as claimed in claim 9 wherein the reference surface is non-planar.

11. The method as claimed in claim 1 further comprising varying size of the waist of the laser beam along the optical axis.

12. The method as claimed in claim 8 wherein the step of providing includes the steps of reducing power of the material-processing laser beam to obtain a probe laser beam and utilizing the probe laser beam to perform the step of measuring.

14. The system as claimed in claim 13 further comprising a support for supporting the second actuator and the focusing lens subsystem for movement along the optical axis.

15. The system as claimed in claim 14 further comprising;

a spot size lens subsystem for controlling size of the waist of the laser beam;

a third actuator for moving the spot size lens subsystem wherein the support supports the spot lens subsystem and the third actuator for movement along the optical axis; and

a third controller for controlling the third actuator.

16. The system as claimed in claim 13 wherein the first actuator is an x-y stage.

17. The system as claimed in claim 14 wherein the second actuator is an air bearing sled for supporting the focusing lens subsystem and mounted for sliding movement on the support.

18. The system as claimed in claim 15 wherein the third actuator is an air bearing sled for supporting the spot size lens subsystem and mounted for sliding movement on the support.

19. The system as claimed in claim 17 further comprising a voice coil coupled to the second controller for positioning the air bearing sled along the optical axis.

20. The system as claimed in claim 13 further comprising a position sensor for sensing position of the focusing lens subsystem and providing a position feedback signal to the second controller.

21. The system as claimed in claim 20 wherein the position sensor is a capacitive feedback sensor.

22. The system as claimed in claim 13 wherein the laser beam is a Gaussian laser beam.

23. The system as claimed in claim 13 wherein the objects are dice of a semiconductor wafer.

24. The system as claimed in claim 23 further comprising a trajectory planner coupled to the first and second controllers for generating trajectories for the wafer and the waist of the laser beam.

25. The system as claimed in claim 24 wherein at least one of the trajectories has an acceleration/deceleration profile.

26. The system as claimed in claim 24 further comprising a modulator for reducing power of the material-processing laser beam to obtain a probe laser beam to measure height of the semiconductor wafer at a plurality of locations about the site to obtain reference height data.

27. The system as claimed in claim 26 further comprising a computer for computing a reference surface based on the reference height data and wherein the trajectory planner generates the trajectories based on the reference surface.

28. The system as claimed in claim 27 wherein the reference surface is non-planar.

13. A system for precisely positioning a waist of a material-processing laser beam to dynamically compensate for local variations in height of microstructures located on a plurality of objects spaced apart within a laser-processing site, the system comprising:

a focusing lens subsystem for focusing a laser beam along an optical axis;

a first actuator for moving the objects in a plane;

a second actuator for moving the focusing lens subsystem along the optical axis;

a first controller for controlling the first actuator based on reference data which represents 3-D locations of microstructures to be processed within the site; and

a second controller for controlling of the second actuator also based on the reference data wherein the first and second actuators controllably move the objects and the focusing lens subsystem, respectively, to precisely position the waist of the laser beam and the objects so that the waist substantially coincides with the 3-D locations of the microstructures within the site.