Laser Via Drilling with Plasma Wavelength Detection
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Solution Overview
Problem
In semiconductor device fabrication, forming via holes in a semiconductor wafer using a pulsed laser beam is challenging due to the difficulty in accurately stopping the laser application at the bonding pads, which can lead to melting and perforation of the pads.
Innovation Solution
A laser processing apparatus with plasma detecting means that uses a beam splitter and bandpass filters to differentiate between plasma light from the substrate and the bonding pads, allowing precise control of the laser beam application to prevent overheating and perforation of the pads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a pulsed laser beam is applied to the substrate from the back side to form via holes reaching the bonding pads, then the productivity is improved and the holes can be efficiently formed, but the bonding pads may be melted and perforated because it is difficult to stop the laser application at the precise moment the hole reaches the pad
Solution Approach 1:
The patent employs plasma emission detection as a feedback mechanism to monitor the laser drilling process in real-time. By detecting the plasma light emitted when the laser beam reaches the bonding pad, the system provides immediate feedback to control the laser application, enabling precise termination of the drilling process and preventing pad melting while maintaining high productivity
Solution Approach 2:
The patent utilizes the color (wavelength) changes of plasma light emitted during laser drilling to determine the drilling depth and detect when the hole reaches the bonding pad. Different materials emit plasma at different wavelengths, allowing optical detection to distinguish between substrate material and bonding pad material, thereby enabling precise control of hole depth
2Manufacturing precision
If the laser beam application is continued to ensure the hole reaches the bonding pad, then the manufacturing precision is improved, but the bonding pads may be melted due to excessive laser energy
Solution Approach 1:
The plasma detection system provides real-time feedback on the drilling process by monitoring plasma emission intensity and characteristics. When the plasma signal indicates that the hole has reached the bonding pad, the system immediately terminates laser application, preventing overheating and melting of the pad while ensuring accurate hole depth
Solution Approach 2:
The patent uses a threshold-based control approach where laser application is stopped as soon as the plasma detection signal indicates the hole has reached the bonding pad, rather than applying a fixed excessive amount of energy. This partial action approach ensures sufficient penetration while avoiding the harmful effects of over-exposure
3Object-affected harmful factors
If the laser beam is stopped early to prevent bonding pad melting, then the harmful factors are reduced, but the via holes may not reach the bonding pads
Solution Approach 1:
The plasma detection system continuously monitors the drilling process and provides feedback signals that indicate when the hole has successfully reached the bonding pad. This feedback mechanism ensures that the laser is stopped at the precise moment of pad contact, guaranteeing both sufficient hole depth and prevention of pad melting
Solution Approach 2:
The patent replaces mechanical depth measurement methods with optical plasma detection to determine hole depth and pad contact. This substitution enables non-contact, real-time monitoring of the drilling process, providing more accurate and responsive control compared to mechanical approaches
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
The apparatus efficiently forms laser processed holes extending from the substrate to the bonding pads without melting them, enhancing the precision and productivity of the hole formation process.
Implementation Method 1
a beam splitter for separating the plasma light into a first optical path and a second optical path
Implementation Method 2
a first bandpass filter provided on the first optical path for passing only the wavelength of plasma light generated from the first material; a second bandpass filter provided on the second optical path for passing only the wavelength of plasma light generated from the second material
Implementation Method 3
a first photodetector for detecting the light passed through the first bandpass filter and outputting a light intensity signal to the control means; a second photodetector for detecting the light passed through the second bandpass filter and outputting a light intensity signal to the control means
Implementation Method 4
plasma detecting means for detecting the wavelength of plasma light generated by applying the pulsed laser beam from the laser beam applying means to the workpiece
Data Source
AI summary
A laser processing method for forming a laser processed hole in a workpiece having a first member including a first material and a second member including a second material, the laser processed hole extending from the first member to the second member, the laser processing method including: applying a pulsed laser beam to the workpiece; using a plasma detecting means to detect the wavelength of plasma light generated by applying the pulsed laser beam to the workpiece; controlling, via a controller, a laser beam applying means according to a detection signal from the plasma detecting means; and stopping the application of the pulsed laser beam when both: (i) the light intensity detected by a first photodetector is decreased, and (ii) the light intensity detected by a second photodetector is increased to a peak value and next decreased to a given value that is slightly less than the peak value.