Laser Dicing Solar Cell Stacks via Bottom-Up Trenching

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Solution Overview

Problem

Existing dicing methods for separating wafers with solar cell stacks face challenges due to the hardness of the cover glass and adhesive layer, making mechanical separation difficult and prone to damage, especially when dealing with different optical and thermal properties.

Innovation Solution

A dicing method using laser ablation to create a separating trench from the bottom of the wafer through the adhesive and cover glass layer, allowing precise separation without unnecessary damage, where the trench acts as an aperture to reduce back-scattering and facilitate the laser beam's focus up to the cover glass layer, enabling efficient separation of the composite wafer, adhesive, and cover glass.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If mechanical separation is used to divide the wafer, adhesive layer, and cover glass layer, then the separation process is simple, but the hardness of the glass and adhesive causes damage and deposits on the cutting blade

Engineering Contradiction:

Improveseparation process simplicityVSAvoiddamage to adhesive layer and blade deposits

Core Design Contradiction:

Ease of manufactureVSObject-affected harmful factors

Solution Approach 1:

The patent replaces the mechanical cutting system with a laser-based system. The laser beam creates a separating trench through laser ablation, eliminating the need for physical contact between a cutting blade and the workpiece. This substitution resolves the contradiction by maintaining process simplicity while avoiding mechanical damage and blade deposits.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the physical state and properties of materials through laser heating. By controlling laser parameters (power, pulse duration, wavelength), the adhesive layer transitions from a bonded state to a vaporized or ablated state, enabling separation without mechanical force. This parameter change allows clean separation without damage to surrounding areas.

Inventive Principle:

Principle #35Parameter changes

2Manufacturing precision

If laser ablation is used to create a separating trench through the entire wafer and adhesive layer, then separation precision is improved, but unnecessary damage occurs to the adhesive layer

Engineering Contradiction:

Improveseparation trench precisionVSAvoiddamage to adhesive layer

Core Design Contradiction:

Manufacturing precisionVSObject-generated harmful factors

Solution Approach 1:

The patent performs preliminary separation by creating the trench only up to the bottom of the cover glass layer or the area directly adjacent to it, rather than through the entire adhesive layer. This preliminary action achieves sufficient separation precision for the cover glass to be divided along the trench, while preventing unnecessary damage to the adhesive layer that would occur with complete penetration.

Inventive Principle:

Principle #10Preliminary action

3Measurement precision

If the separating trench is made wide enough to focus the laser beam to sufficient depth, then laser focusing is improved, but back-scattering from the cover glass layer increases

Engineering Contradiction:

Improvelaser beam focus depthVSAvoidback-scattering into active layers

Core Design Contradiction:

Measurement precisionVSObject-generated harmful factors

Solution Approach 1:

The patent creates a separating trench with specific local geometry - sufficiently wide at the entrance to allow laser beam focusing to the required depth, but controlled in width and depth to act as an aperture. This local quality modification enables the trench to simultaneously provide adequate laser focus and reduce back-scattering from the cover glass layer into the wafer's active layers.

Inventive Principle:

Principle #3Local quality

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 allows for effective separation of the wafer composite without damaging the adhesive layer, ensuring the cover glass protects the wafer from environmental influences and simplifies the breaking process, while minimizing damage and optimizing the separation process by adjusting the laser energy input and focal plane.

Implementation Method 1

creating a separating trench along the parting line by means of laser ablation, which extends from a bottom of the wafer through the wafer and through the adhesive layer at least up to a bottom of the cover glass layer

Methodology Applied

Scientific EffectLaser ablation: Laser Ablation

Implementation Method 2

the separating trench in the wafer acts as an aperture and reduces back-scattering from the cover glass layer into active layers of the wafer

Methodology Applied

Scientific EffectBack-scattering reduction: Scattering

Data Source

PatentUS11380814B2Dicing method for separating wafers comprising a plurality of solar cell stacks

Publication Date: 2022.07.05 AZUR SPACE SOLAR POWER

AI summary

A dicing method for separating a wafer comprising a plurality of solar cells stack along at least one parting line, at least having the steps of: providing the wafer with a top, a bottom, an adhesive layer which is integrally bonded with the top and a cover glass layer which is integrally bonded with the adhesive layer, wherein the wafer includes a plurality of solar cell stacks, each having a germanium substrate layer forming the bottom of the wafer, a germanium sub-cell and at least two III-V sub-cells; creating a separating trench along the parting line by means of laser ablation, which extends from a bottom of the wafer through the wafer and the adhesive layer at least up to a top of the cover glass layer; and dividing the cover glass layer along the separating trench.