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

• US 20050184036A1
• Filed: 04/26/2005
• Published: 08/25/2005
• Est. Priority Date: 05/16/2000
• Status: Active Grant

• Current Assignee: Electro Scientific Industries Incorporated (MKS Instruments Incorporated)
• Original Assignee: GSI Lumonics Corporation (Novanta Inc.)
• Inventors: Hunter, Bradley L., Ehrmann, Jonathan S., Plotkin, Michael, Cahill, Steven P.
• Granted Patent: US 7,176,407 B2
• Time in Patent Office: Days
• US Class Current: 219/121.690
• 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

1-28. -28. (canceled)

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

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.

30. The system as claimed in claim 29 further comprising a support for supporting the second actuator and the focusing lens subsystem for movement along the optical axis.

31. The system as claimed in claim 30 further comprising;

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

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;

the controller controlling the third actuator.

32. The system as claimed in claim 29 wherein the first actuator is an x-y stage.

33. The system as claimed in claim 30 wherein the second actuator is an air bearing sled for supporting the focusing lens subsystem and mounted for sliding movement on the support.

34. The system as claimed in claim 31 wherein the third actuator is an air bearing sled for supporting the spot size lens subsystem and mounted for sliding movement on the support.

35. The system as claimed in claim 33 further comprising a voice coil coupled to the controller for positioning the air bearing sled along the optical axis.

36. The system as claimed in claim 29 further comprising a position sensor for sensing position of the focusing lens subsystem and providing a position feedback signal to the controller.

37. The system as claimed in claim 36 wherein the position sensor is a capacitive feedback sensor.

38. The system as claimed in claim 29 wherein the laser beam is a Gaussian laser beam.

39. The system as claimed in claim 29 wherein the objects are dice of a semiconductor wafer.

40. The system as claimed in claim 39 further comprising a trajectory planner coupled to the controllers for generating trajectories for the wafer and the waist of the laser beam.

41. The system as claimed in claim 40 wherein at least one of the trajectories has an acceleration/deceleration profile.

42. The system as claimed in claim 40 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.

43. The system as claimed in claim 42 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.

44. The system as claimed in claim 43 wherein the reference surface is non-planar.

45. A system for precisely positioning a waist of a material-processing laser beam to dynamically compensate for local variations in height of microstructures spaced apart within a laser-processing site, the microstructure lying on a surface which is substantially orthogonal to an optical axis, the system comprising:

a first optical component for focusing the laser beam along the optical axis;

a first actuator for moving the axis of the laser beam relative to the microstructures;

a second actuator for moving the first optical component along the optical axis;

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

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

46. The system of claim 45 wherein the bandwidth of the focusing lens positioning sub-system is about 150 hz or greater.

47. The system of claim 45 where the response of the second actuator results in controllable movement of the beam waist within about 0.03 msec or less.

48. The system of claim 45 wherein movement of the focusing lens is controllable within the depth of focus of the laser beam.

49. The system as claimed in claim 45 wherein the first optical component is a focusing lens.

50. The system as claimed in claim 49 further comprising:

a second optical component for controlling size of the waist of the laser beam; and

a third actuator for moving the second optical component along the optical axis;

the controller controlling the third actuator.

51. The system as claimed in claim 45 wherein the first actuator is an x-y stage.

52. The system as claimed in claim 49 wherein the second actuator is an air bearing sled.

53. The system as claimed in claim 50 wherein the third actuator is an air bearing sled.

54. The system as claimed in claim 52 wherein the controller includes a voice coil operatively connected to the air bearing sled.

55. The system as claimed in claim 45 further comprising a position sensor for sensing position of the second actuator and providing a position feedback signal to the controller.

56. The system as claimed in claim 55 wherein the position sensor is capacitive feedback sensor.

57. The system as claimed in claim 45 wherein the laser beam is a Gaussian laser beam.

58. The system as claimed in claim 45 wherein the objects are dice of a semiconductor wafer.

59. The system as claimed in claim 58 further comprising a trajectory planner coupled to the controller for generating trajectories for the wafer and the waist of the laser beam.

60. The system as claimed in claim 59 wherein at least one of the trajectories has an acceleration/deceleration profile.

61. The system as claimed in claim 59 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.

62. The system as claimed in claim 61 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.

63. The system as claimed in claim 62 wherein the reference surface is non-planar.

64. The system as claimed in claim 45 wherein movement of the focusing lens is controllable within one-half of the depth of focus of the laser beam.

65. The system as claimed in claim 45 wherein movement of the focusing lens is controllable within 1/10 of the depth of focus of the laser beam.