Laser Back-Surface Impurity Activation in Semiconductor Wafer Manufacturing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In semiconductor device manufacturing, uniform heat treatment of the back surface is challenging when ion-implanting impurities, as existing methods like laser illumination can lead to non-uniform activation and metal migration from front surface metal layers.
Innovation Solution
A method involving scanning laser light with a trajectory that includes curved portions intersecting on the back surface, ensuring a spot size larger than the distance between adjacent curves, and controlling pulse intervals to maintain uniform temperature and prevent metal migration, thereby achieving uniform activation of impurities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If laser light is scanned over the back surface to activate impurities, then impurity activation is achieved, but heat treatment uniformity deteriorates
Solution Approach 1:
The laser beam is divided into multiple segments by optical elements (lens and mirror) to create multiple scanning paths. The beam is split into a first beam scanning in a first direction and a second beam scanning in a second direction, allowing comprehensive coverage and uniform heat distribution across the back surface.
Solution Approach 2:
The patent introduces multi-directional scanning by adding a second scanning direction perpendicular to the first. This transforms a one-dimensional linear scan into a two-dimensional grid pattern, ensuring uniform heat treatment across the entire back surface area.
2Reliability
If heat treatment is performed to activate impurities, then impurity activation is improved, but metal migration from front surface metal layer increases
Solution Approach 1:
The laser heating is applied locally to the back surface where impurities are implanted, rather than heating the entire wafer including the front surface metal layer. This localized approach activates impurities effectively while keeping the front surface temperature low enough to prevent metal migration.
Solution Approach 2:
The patent uses an intermediary substance (such as an absorbent layer or specific wavelength selection) to mediate the energy transfer from laser to the back surface. This allows selective heating of the back surface region while protecting the front surface metal layer from excessive heat.
3Reliability
If conventional laser scanning is used, then impurity activation is achieved, but heat treatment uniformity across the back surface deteriorates
Solution Approach 1:
The patent employs periodic scanning motion in multiple directions, creating an overlapping pattern of laser beams. The first and second beams scan periodically in alternating directions, ensuring that every region of the back surface receives consistent energy input over time.
Solution Approach 2:
Multiple laser beams are merged to scan the back surface simultaneously from different directions. The first beam and second beam work together in combination, their paths intersecting and overlapping to provide uniform energy distribution across the entire back surface area.
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 approach ensures uniform heat treatment across the entire back surface, preventing metal migration and maintaining the integrity of the semiconductor structure, resulting in consistent activation and diffusion of ion-implanted impurities.
Implementation Method 1
the back surface is illuminated by laser light to locally heat the region where the impurities are ion-implanted
Implementation Method 2
the back surface is illuminated by laser light to locally heat the region
Data Source
AI summary
A method of manufacturing a semiconductor device includes ion-implanting impurities into a wafer through a back surface of the wafer, a metal layer being formed on a front surface of the wafer; and activating the impurities by laser light illuminating the back surface of the wafer. The laser light is scanned on the back surface as providing a trajectory without bending. The trajectory includes curved portions intersecting in the back surface of the wafer. The laser light has a spot size on the back surface of the wafer, the spot size being larger than a distance between the curved portions adjacent to each other.