Multi-layer Sputtered Metal Seed for Solar Cell Contacts
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Solution Overview
Problem
The challenge in solar cell manufacturing is to prevent nickel (Ni) from penetrating to the wafer surface during the formation of conductive contacts, which can reduce rear surface reflectivity and cell efficiency, while maintaining the integrity of the metal seed layers and preventing inter-diffusion between aluminum and nickel layers.
Innovation Solution
A multi-layer sputtered metal seed stack using Aluminum/Silicon (AlSi) and Nickel/Vanadium (NiV) layers is implemented, where the Ni preferentially alloys with the upper Al layer, stopping at an interface between aluminum layers, and multiple aluminum targets are used to ensure complete deposition and prevent Ni penetration, with a crystalline interface formed between the layers to inhibit Ni penetration into the first conductive seed layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single-layer metal seed is used for conductive contact formation, then the manufacturing process is simpler, but nickel penetrates to the wafer surface reducing rear surface reflectivity and cell efficiency
Solution Approach 1:
The single-layer metal seed is segmented into multiple layers: a first aluminum layer deposited on the semiconductor region, and a second aluminum layer deposited on the first aluminum layer. The nickel layer is positioned between these two aluminum layers, creating a segmented structure that prevents nickel penetration while maintaining manufacturing feasibility through sequential deposition processes
Solution Approach 2:
The first aluminum layer acts as an intermediary barrier between the nickel layer and the semiconductor wafer surface. This intermediate aluminum layer prevents direct contact and penetration of nickel into the wafer, thereby protecting the rear surface reflectivity and maintaining cell efficiency
2Reliability
If the metal seed layer is made thinner to improve efficiency, then rear surface reflectivity is maintained, but the integrity and barrier function of the layer is compromised
Solution Approach 1:
The metal seed structure is segmented into multiple thinner layers (first aluminum layer, nickel layer, second aluminum layer) rather than using a single thick layer. Each layer is sufficiently thin to maintain overall efficiency and reflectivity, yet collectively they provide the necessary structural integrity and barrier function through their combined multi-layer configuration
Solution Approach 2:
The metal seed uses a composite multi-layer structure combining aluminum and nickel layers with different properties. The aluminum layers provide barrier and reflective functions, while the nickel layer provides conductive properties, creating a composite structure that achieves both thinness for efficiency and sufficient integrity for structural stability
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 effectively prevents Ni from reaching the wafer surface, maintaining high efficiency and reducing the risk of lowering short-circuit current density, while allowing for a thinner metal thickness and adjustable Si percentage in the outer layer, thereby enhancing solar cell performance.
Implementation Method 1
sputtering a first conductive seed layer on a semiconductor region disposed in or above a substrate, the first conductive seed layer including a majority of a first metal species. The method also involves sputtering a second conductive seed layer on the first conductive seed layer
Implementation Method 2
annealing the first, second, and third conductive seed layers, wherein the annealing drives the second metal species from the third conductive seed layer into the second conductive seed layer
Data Source
AI summary
Multi-layer sputtered metal seed for solar cell conductive contacts and methods of forming solar cell conductive contacts are described. In an example, a solar cell includes a substrate. A semiconductor region is disposed in or above the substrate. A conductive contact is disposed on the semiconductor region and includes a seed material stack in contact with the semiconductor region. The seed material stack includes a first aluminum layer having a first crystallinity and disposed on the semiconductor layer, and a second aluminum layer having a second crystallinity and disposed on and having an interface with the first aluminum layer. The first crystallinity is different from the second crystallinity.