IES20010601A2 - Control of high speed laser machining - Google Patents

Abstract

A laser beam is scanned in X and Y directions by a scanner. A scanning laser beam is directed by a telecentric lens to ensure that is perpendicular to the surface. A sensor is placed at the Scheimpflug angle so that the laser scanned area is in the depth of field of the sensor over the entire field of view.

Description

The invention relates to a process for inspecting and measuring laser micro-machined features in two and three dimensions for real time control and analysis of high speed laser micro machining processes.

Statements of Invention According to the invention, there is provided an apparatus for inspecting and measuring location and depth of laser etch patterns on a substrate during a process of laser machining of substrates, the apparatus comprising:15 means for directing a machining laser to the substrate through an optical scanner for scanning the beam in X and in Y directions, a scanning laser operable at a wavelength in which a sensor has a response directed to the substrate through the optical scanner, a telecentric scan lens comprising means for ensuring that the beam travelling to the surface is perpendicular to the surface at all scan angles, a camera for 2 D registration of fiducial locations, and a sensor, placed at the Scheimpflug angle to the scanning laser beam such that the laser scanned area is in the depth of field of the sensor over the entire field of view.

OPEN TO PUBLIC INSPECTION UNDER SECTION 28 AND RULE 23 JNL No. 1°» -OF 2¾ Me V IE010601 -2In one embodiment, the camera has an exposure time greater than the time required to scan the full inspection area.

In another embodiment, the sensor has sufficient responsivity to sense the scanned laser over the exposure time.

In one embodiment, the laser is sufficiently intense to provide a response from the sensor over the entire exposure time.

In one embodiment, the scanning laser is the machining laser.

According to another aspect, there is provided a method for measuring the amount of material removed in a laser machining process based on a measured amount of light generated during the machining process.

In one embodiment, the optical emission spectrum generated during the cut process is used to monitor the material that is being machined, wherein in the case of multilayer structures this spectrum is compared to a previous spectrum so that the laser parameters can be controlled and modified to achieve effective machining in each layer of material.

Description of the Invention The invention will be more clearly understood from the following description of some embodiments thereof, given by way of example only with reference to the accompanying drawings in which:Fig. 1 is a diagram showing a machining apparatus; Fig. 2 is an image diagram; and IE010601 -3Fig. 3 is a process flow chart.

The invention provides control information on the process of laser micro-machining throughout the laser micro-machining cut process.

As shown in Fig. 1, the machining system consists of a telecentric XY scanning galvanometer beam delivery head. The telecentric scan lens is designed to allow for the telecentric projection of more than one wavelength of light such that the second wavelength of light may be used to perform 3D inspection of the area previously machined by the first wavelength of light. The 3D inspection is performed by triangulation using an imaging camera placed at the Scheimpflug angle. Alternatively, where the machining wavelength falls within the sensitivity range of the sensor , this wavelength may be used as the scanning beam.

The exposure time of the camera and the scan time is such that a complete scan of the area will provide complete 3D information on the object area.

This same sensor may be used in a second exposure configuration which monitors the intensity and/or spectrum of light generated during the machining process at the first wavelength, yielding information on material removal rates and material type.

A second sensor is used for registration purposes and this camera is placed on the galvo line. Alternatively, this camera may be used at a fixed offset to the 3D camera.

In one embodiment the imaging system is used to monitor and control a laser machining process for machining through holes. The through hole laser machining process is performed through consecutive etching of layers from the surface downwards. Typically, laser scanners can show positional drift. Also, scan lenses can show variation of laser transmission as a function of scan angle resulting in IE010601 -4variation of depth across a single etch profile across the field of view. By scanning a laser and imaging through a camera at an angle alpha which is corrected by the Scheimpflug angle, the full field of view may be imaged. Using triangulation principles, 3D information may be obtained as the etch depth is modified.

The 3D data obtained as described above is used to provide feedback to a positioning system such that the laser parameters can be reset to allow correction of defective machining.

In a second embodiment the inspection system as described may be used to inspect and measure chipping at the laser cut edges.

In a third embodiment of the invention the sensor at the angle alpha is used to measure the amount of light generated during the machining process. The amount of light generated is proportional to the amount of material removed. By measuring the intensity of the emission, quantitative information on the material removal rates may be determined.

In a fourth embodiment the sensor is a spectrometer. The spectrometer is used to record information on the wavelength and wavelength range of the emission so that information on the material that is being etched can be gathered throughout the process.

The spectral information gathered this way is used to control the laser machining parameters. For example in a multiplayer structure the spectral emission will change significantly between layers. As the spectrum changes it is usually necessary to change the machining parameters. Therefore by monitoring the spectrum the laser machining parameters can be modified “on the fly”.

IE010601 -5High speed inspection in each embodiment may be enabled by ensuring that the incident intensity is sufficient and sensor exposure time is longer than the time taken to scan over the object field of interest.

In another embodiment the process is a laser based process for dicing semiconductor wafers or substrates and performing in situ inspection of the resulting machined profiles.

In another embodiment, the inspection may be performed on craters created by individual pulses in the case of a pulsed laser machining process at various points in the field of view.

The invention is not limited to the embodiments described but may be varied in construction and detail.

Claims (5)

1. An apparatus for inspecting and measuring location and depth of laser etch patterns on a substrate during a process of laser machining of substrates, the apparatus comprising:means for directing a machining laser to the substrate through an optical scanner for scanning the beam in X and in Y directions, a scanning laser operable at a wavelength in which a sensor has a response directed to the substrate through the optical scanner, a telecentric scan lens comprising means for ensuring that the beam travelling to the surface is perpendicular to the surface at all scan angles, a camera for 2 D registration of fiducial locations, and a sensor, placed at the Scheimpflug angle to the scanning laser beam such that the laser scanned area is in the depth of field of the sensor over the entire field of view.

2. An apparatus as claimed in claim 1, wherein the camera has an exposure time greater than the time required to scan the full inspection area; and wherein the sensor has sufficient responsivity to sense the scanned laser over the exposure time; and wherein the laser is sufficiently intense to provide a response from the sensor over the entire exposure time.

3. An apparatus as claimed in any preceding claim, wherein the scanning laser is the machining laser. IE010601 -74. An apparatus substantially as described with reference to the drawings.

4.

5. A method for measuring the amount of material removed in a laser machining process based on a measured amount of light generated during the 5 machining process; and wherein the optical emission spectrum generated during the cut process is used to monitor the material that is being machined, wherein in the case of multilayer structures this spectrum is compared to a previous spectrum so that the laser parameters can be controlled and modified to achieve effective machining in each layer of material.