Noble Metal Shielding for Semiconductor Sensors in Harsh Media
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Solution Overview
Problem
Integrated semiconductor sensors face challenges in harsh media environments due to corrosion and stress issues, particularly with standard CMOS processing techniques that are not suitable for exposure to chemicals like sulfuric or fuming nitric acids or iodine, leading to potential sensor offset and corrosion of bondpad metals.
Innovation Solution
A sensor device and method utilizing a single noble metal layer, such as palladium or platinum, to create a shield for lowly doped diffusion areas, which provides a low ohmic contact and diffusion barrier, preventing modulation by surface charges and corrosion, while avoiding the use of sensitive metals like aluminum or copper.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If standard CMOS processing techniques are used with aluminum or copper bondpad metals, then cost-effective fabrication is achieved, but corrosion occurs when exposed to harsh media like sulfuric acid, fuming nitric acid, or iodine
Solution Approach 1:
The patent employs a composite metal layer structure consisting of a noble metal layer (such as platinum, palladium, or rhodium) combined with a diffusion barrier layer (such as titanium nitride or tungsten silicide). This composite structure provides both the electrical conductivity needed for bondpads and interconnects while offering superior corrosion resistance against harsh media like sulfuric acid, fuming nitric acid, and iodine, eliminating the need for additional protective passivation layers.
2Reliability
If a shield is placed over lowly doped diffusion areas to prevent modulation by surface charges, then sensor stability is improved, but stress is added to the stress-sensitive lowly doped diffusion area causing offset in measurements
Solution Approach 1:
The patent modifies the physical and mechanical parameters of the shield material by using a noble metal layer with specific properties: low stress characteristics, appropriate thickness (controlling mechanical impact), and suitable elastic modulus. By carefully selecting and controlling these parameters, the shield effectively prevents modulation of piezoresistive elements by surface charges while minimizing the addition of stress that would cause measurement offset.
Solution Approach 2:
The noble metal layer provides a uniform and homogeneous shielding effect across the sensor surface. The material's consistent electrical and mechanical properties ensure even distribution of the shielding function, preventing localized stress concentrations that could affect measurement precision while maintaining stable protection against surface charge modulation throughout the entire lowly doped diffusion area.
3Reliability
If additional passivation layers are added to protect against harsh media, then corrosion resistance is improved, but device complexity and fabrication steps increase
Solution Approach 1:
The noble metal layer serves multiple functions simultaneously: it acts as a corrosion-resistant protective layer against harsh media, provides electrical conductivity for bondpads and interconnects, offers a diffusion barrier to prevent metal migration, and functions as a shield to prevent modulation of piezoresistive elements by surface charges. This multi-functionality eliminates the need for separate passivation layers, reducing device complexity while maintaining comprehensive protection.
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 solution enables cost-effective fabrication of sensors with improved stability and resistance to harsh media, reducing sensor offset and corrosion risks, allowing for efficient operation in harsh environments without the need for additional passivation layers.
Implementation Method 1
The Ti layer may furthermore be exposed to nitrogen to form a titanium nitride (TiN) layer on top of the titanium. For example, during the titanium sputtering, e.g. halfway during the sputtering process, nitrogen can be introduced in the sputter chamber to incorporate nitrogen into the upper part of the titanium film. This TiN layer can form a diffusion barrier
Implementation Method 2
a contact layer contacting the silicon die, in which the contact layer comprises a refractory metal and an ohmic contact to the silicon die via a silicide of the refractory metal
Implementation Method 3
The noble metal layer is adapted for providing a shield for preventing modulation of the lowly doped region by surface charges
Implementation Method 4
bondpad metals, such as aluminium or copper, may corrode, e.g. due to oxidation, when exposed to such chemicals
Data Source
AI summary
A sensor device for use in harsh media, comprising a silicon die comprises a lowly doped region, and a contact layer, contacting the silicon die. The contact layer comprises a refractory metal and an ohmic contact to the silicon die via a silicide of the refractory metal. A noble metal layer is provided over the contact layer such that the contact layer is completely covered by the noble metal layer. The noble metal layer comprises palladium, platinum or a metal alloy of palladium and/or platinum. The noble metal layer is patterned to form an interconnect structure and a contact connecting via the contact layer to the ohmic contact. The noble metal layer is adapted for providing a shield to prevent modulation of the lowly doped region by surface charges. The noble metal layer may advantageously protect the contact layer against harsh media in an external environment of the sensor device.