SiCN Direct Wafer Bonding for Low-Temperature High Bond Strength
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Solution Overview
Problem
Current direct bonding techniques for semiconductor substrates face challenges in achieving high bond strength at lower temperatures while preventing metal diffusion in hybrid wafer bonding, which increases thermal budget and can lead to leakage or shorting.
Innovation Solution
A method involving the deposition of a dielectric layer followed by Chemical Mechanical Polishing (CMP) to achieve a roughness of less than 0.2nm RMS, then a silicon carbon nitride (SiCN) layer with a thickness between 10nm and 150nm is deposited and polished to a roughness of less than 0.1nm RMS. The substrates undergo pre-bond and post-bond annealing at temperatures of less than or equal to 250°C.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional direct bonding techniques are used to achieve high bond strength, then bonding force is improved, but annealing temperature must be increased above 400°C which increases thermal budget
Solution Approach 1:
The invention changes the material parameter of the bonding layer from conventional dielectric materials to silicon carbon nitride (SiCN), which has different chemical and physical properties. This material substitution enables strong chemical bonding at lower temperatures (≤250°C) by forming Si-O-Si bonds between the SiCN layers, resolving the contradiction between achieving high bond strength and maintaining low annealing temperature
Solution Approach 2:
The invention uses a composite structure consisting of a dielectric layer combined with a silicon carbon nitride (SiCN) bonding layer. This composite material approach combines the advantages of both materials: the dielectric layer provides electrical isolation while the SiCN layer provides strong bonding capability at low temperatures, thus achieving both high bond strength and low thermal budget
2Reliability
If hybrid wafer bonding with metal areas is used to achieve electrical contacts, then electrical connectivity is improved, but metal diffusion into dielectric layer occurs causing leakage or shorting
Solution Approach 1:
The SiCN bonding layer acts as an intermediary barrier between the metal interconnect areas and the underlying dielectric layer. This intermediate layer prevents direct contact and diffusion pathways for metal atoms, thereby blocking metal diffusion into the dielectric while still allowing electrical connectivity through the metal contact areas
Solution Approach 2:
The invention changes the chemical composition and bonding characteristics of the bonding layer to SiCN, which has different diffusion barrier properties compared to conventional dielectric materials. This material parameter change creates a more effective barrier against metal diffusion, preventing leakage and shorting while maintaining electrical connectivity
3Object-generated harmful factors
If SiCN is used as bonding layer to prevent metal diffusion, then diffusion barrier is improved, but achieving high bonding force becomes more difficult
Solution Approach 1:
The invention optimizes the composition parameters of the SiCN bonding layer, specifically controlling the Si:C:N ratio and the amount of nitrogen content. By adjusting these parameters, the SiCN layer achieves optimal properties: sufficient diffusion barrier capability while maintaining high bonding strength through Si-O-Si bond formation during low-temperature annealing
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 achieves excellent bond strength even at lower annealing temperatures, reducing the thermal budget and preventing metal diffusion, thus enhancing the reliability of semiconductor bonding processes.
Implementation Method 1
both substrates are subjected to the following steps, prior to bonding: deposition of a dielectric layer on the surface of the substrate, subjecting the dielectric layer to a CMP step to reduce the roughness of said dielectric layer, deposition of a silicon carbon nitride layer with a thickness between 10nm and 150nm on the surface of the dielectric layer, subjecting the substrate to a pre-bond annealing step, subjecting the SiCN layer to a CMP step to reduce the roughness of said SiCN layer
Implementation Method 2
Direct bonding on wafer level, commonly referred to as 'wafer to wafer' bonding, involves the alignment and contacting at room temperature of two semiconductor wafers, usually silicon wafers, followed by an annealing step, during which step chemical bonds are formed between the materials on at least a portion of the contacted wafer surfaces
Implementation Method 3
followed by an annealing step, during which step chemical bonds are formed between the materials on at least a portion of the contacted wafer surfaces
Data Source
Figure 1a~1c
Figure 1d~1e
Figure 1f
AI summary
The present invention is related to a method for bonding a first semiconductor substrate to a second semiconductor substrate by direct bonding, wherein the substrates are both provided on their contact surfaces with a dielectric layer, followed by a CMP step for reducing the roughness of the dielectric layer. Preferably, the dielectric layer after CMP has an roughness of less than 0.2nm RMS. Then a layer of SiCN is deposited onto the dielectric layer, followed by a CMP step which reduces the roughness of the SiCN layer to the order of 1 tenth of a nanometre. Preferably the RMS value after CMP is less than 0.1nm. Then the substrates are subjected to a pre-bond annealing step. The substrates are then bonded by direct bonding, possibly preceded by one or more pre-treatments of the contact surfaces, and followed by a post-bond annealing step, at a temperature of less than or equal to 250°C, preferably between 200°C and 250°C. It has been found that the bond strength is excellent, even at the above named annealing temperatures, which are lower than presently known in the art.