Wafer Laser Processing In-Situ Crack Verification
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Solution Overview
Problem
The existing method for processing wafers using laser irradiation from the back surface to form a modified layer for division is inefficient due to the need for manual inspection of the front surface, requiring significant man-hours to verify if the crack has properly extended from the modified layer to the front surface, which affects the yield of device chips.
Innovation Solution
A processing method that includes forming a modified layer inside the wafer using a first laser beam, followed by an observation step using a second laser beam with controlled output power and wavelength, where the reflected light is imaged to determine the presence and state of the crack without moving the wafer from the processing apparatus, allowing for in-situ verification of the processing state.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the front surface of the wafer is observed by a microscope to check whether the crack properly progresses from the modified layer, then the processing state can be verified, but the wafer needs to be taken out from the laser processing apparatus and carried to the microscope with the wafer turned upside down, requiring significant man-hours
Solution Approach 1:
The patent merges the laser processing function and the inspection function into a single integrated apparatus. The laser processing apparatus includes both the laser beam irradiation unit for forming the modified layer and an imaging unit for observing the crack formation, eliminating the need to transfer the wafer to a separate microscope and thereby reducing inspection time while maintaining verification capability
Solution Approach 2:
The patent introduces a imaging unit as an intermediary component within the laser processing apparatus that enables direct observation of the crack formation process. This intermediary imaging system allows real-time verification of processing quality without requiring manual intervention or wafer manipulation, thus resolving the time loss associated with traditional inspection methods
2Ease of manufacture
If the wafer is irradiated with a laser beam from the back surface to form a modified layer for division, then the wafer can be divided along planned dividing lines, but the processing conditions must be precisely controlled to ensure proper crack extension, affecting the yield of device chips
Solution Approach 1:
The patent implements a feedback mechanism where the imaging unit continuously monitors the crack formation process in real-time. The obtained images are analyzed to determine whether the crack has properly extended from the modified layer to the front surface, providing feedback on processing quality. This allows for immediate detection of improper crack formation and enables adjustment of processing conditions to improve yield
Solution Approach 2:
The patent performs preliminary observation and analysis of the crack formation process during the laser irradiation itself, before completing the entire processing sequence. By using the imaging unit to capture images of the crack extension in real-time, the system can preliminarily assess whether the processing conditions are appropriate and make necessary adjustments before finalizing the division process, thereby improving reliability
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method enables efficient and accurate determination of the processing state, reducing man-hours and improving the yield of device chips by allowing real-time verification of crack formation and quality without manual intervention.
Implementation Method 1
a modified layer forming step of positioning a focal point of a first laser beam with a wavelength having transmissibility with respect to the wafer to the inside of the wafer and executing irradiation with the first laser beam along the planned dividing lines from the side of a back surface of the wafer while relatively moving a laser beam irradiation unit and the chuck table in a direction along the planned dividing line, to form the modified layer inside the wafer
Implementation Method 2
an observation laser beam irradiation step of positioning a focal point of a second laser beam with output power that does not exceed a processing threshold of the wafer and with a wavelength having transmissibility with respect to the wafer to the inside or the front surface of the wafer and executing irradiation with the second laser beam from the side of the back surface of the wafer after the modified layer forming step
Implementation Method 3
an imaging step of imaging reflected light of the second laser beam with which the irradiation is executed in the observation laser beam irradiation step by an imaging unit
Data Source
AI summary
A processing method of a wafer in which a modified layer is formed inside the wafer. In the processing method, irradiation with a first laser beam is executed from a back surface side of the wafer and the modified layer is formed inside the wafer. Then, irradiation with a second laser beam is executed with the focal point thereof positioned to the inside or the front surface of the wafer and reflected light is imaged by an imaging unit. Furthermore, a processing state of the wafer is determined on the basis of a taken image. The second laser beam is shaped in such a manner that a sectional shape thereof in a surface perpendicular to a traveling direction thereof becomes asymmetric across the modified layer.