Deposition and characterization studies of boron carbon nitride (BCN) thin films prepared by dual target sputtering

At a Glance

Metadata	Details
Publication Date	2016-01-01
Journal	STARS (University of Central Florida)
Authors	Adithya Prakash
Citations	3
Analysis	Full AI Review Included

Technical Analysis: Boron Carbon Nitride (BCN) Thin Films for Advanced Dielectrics and UV Photonics

Executive Summary

This doctoral research analyzes the deposition and characterization of Boron Carbon Nitride (BCN) thin films, synthesized via dual target reactive sputtering, validating their potential for next-generation electronic and photonic applications.

BCN films synthesized via dual target reactive RF magnetron sputtering exhibit exceptional promise for next-generation ULSI Interlayer Dielectrics (ILDs).
Achieved ultra-low dielectric constants ranging from 1.9 to 2.1, meeting stringent requirements for reducing RC signal delay in advanced CMOS circuits.
Demonstrated highly tunable mechanical properties, with Young’s modulus up to ~285 GPa and hardness up to 40 GPa (attributable to B$_{4}$C rich phases).
Successfully engineered the optical bandgap (E_g) over a broad range (1.9 eV to 3.7 eV) by controlling the N$_{2}$/Ar gas flow ratio, confirming strong potential for UV photonics.
Validated BCN’s robustness as a Cu interconnect barrier, showing minimal copper diffusion even after annealing up to 400 °C, crucial for ILD reliability.
The optimal balance of high mechanical hardness, low dielectric constant, and chemical stability is achieved with approximately 20% nitrogen incorporation.
Prototype Metal-Insulator-Metal (MIM) UV photodetectors using BCN exhibited a photocurrent response two orders of magnitude higher than the dark current.

Technical Specifications

Parameter	Value	Unit	Context
Target Dielectric Constant ($\kappa$)	1.5 - 3.0	N/A	ILD requirement target (achieved 1.9-2.1)
Breakdown Strength	≥ 1	MV/cm	ILD requirement threshold
Bulk/Surface Resistivity	≥ 10¹⁵	$\Omega$cm	ILD requirement threshold
Young’s Modulus (E) (Max)	~285	GPa	For B- or C-rich films (low N content)
Hardness (H) (Max)	30 - 40	GPa	For B- or C-rich films (low N content)
Optical Band Gap (E$_{g}$) Range	1.9 to 3.7	eV	Tunable via N$_{2}$/Ar ratio and deposition temperature
Max Mass Density ($\rho$)	2.4 - 2.5	g/cm³	Sputtering in pure Ar (approaches theoretical B$_{4}$C density)
Lowest Mass Density ($\rho$)	2.0 - 2.1	g/cm³	Films with high N content (20-45%)
Maximum Photo Responsivity (R)	6	mA/W	Al-BCN-Au MIM device, 365 nm UV illumination, 3V bias
Highest Etch Rate	231.6	Å/min	RT deposited BCN film (N$_{2}$/Ar=0.25, 70°C wet etch temp)
Minimum Activation Energy (E$_{a}$)	0.375	eV	Wet etching of RT deposited BCN film (N$_{2}$/Ar=0.5)

Key Methodologies

The BCN thin films were synthesized primarily using dual target reactive RF magnetron sputtering techniques, allowing precise control over elemental incorporation and resulting phase formation.

Sputtering Technique: Dual target reactive RF magnetron sputtering was performed in an Ultra High Vacuum (UHV) system (base pressure $\sim$1 x 10^-7 Torr).
Target Materials: Two main configurations were used:
- B$_{4}$C target (3 inch, 99.5% purity) supplied with DC power.
- BN target supplied with constant RF power (200W or 250W).
Working Gas Control: Nitrogen (N$_{2}$) served as the reactive gas, mixed with Argon (Ar) as the inert sputtering gas.
Gas Flow Ratios: The total gas flow was maintained constant at 20 sccm. The N$_{2}$/Ar flow ratio was varied incrementally from 0.25 to 1.
Power Parameters: B$_{4}$C (DC) power was varied (e.g., 20W, 40W) while BN (RF) power was held constant, or vice-versa, to control composition.
Deposition Conditions: Films were deposited at various temperatures: Room Temperature (RT), 200°C, 300°C, 400°C, and 500°C.
Film Thickness: BCN film thicknesses ranged from 900 Å ($\sim$90 nm) to 2000 Å ($\sim$200 nm).
Etching Studies: Wet chemical etching feasibility was tested using a common aluminum etchant (H${3}$PO${4}$, HNO${3}$, CH${3}$COOH, DI water) at elevated temperatures (50°C, 60°C, 70°C).
Device Structure: Metal-Insulator-Metal (MIM) devices (Al-BCN-Al or Au-BCN-Al) were fabricated on glass substrates for electrical and optical characterization.

6CCVD Solutions & Capabilities

This research demonstrates the immediate engineering relevance of boron-carbon-nitrogen compounds for advanced interconnects and harsh environment optics. 6CCVD, an expert in high-purity CVD diamond materials, is uniquely positioned to supply the foundational and complementary materials required to replicate, optimize, and scale this research.

Application Requirement (from Paper)	6CCVD Solution & Capability
Foundation for BCN Composites	The BCN films are derived directly from boron carbide (B$_{4}$C) and BN phases. We supply High Purity Polycrystalline Diamond (PCD) wafers up to 125mm size, providing the high-quality carbon matrix needed for further development of BCN films. For Boron-rich studies, our Heavy Boron-Doped Diamond (BDD) wafers offer excellent platforms for investigating electrically insulating and semiconducting properties.
Hardness and Mechanical Stability	The highest hardness achieved (40 GPa) is critical for ILD reliability. Our Single Crystal Diamond (SCD) materials provide the industry benchmark for ultimate hardness and mechanical stability, serving as ideal base substrates or comparison materials for BCN mechanical characterization.
Precise Film Thickness & Uniformity	The research focuses on thin films (0.1µm to 0.2µm). 6CCVD specializes in CVD diamond films with thickness control ranging from 0.1 µm up to 500 µm for both SCD and PCD, ensuring direct compatibility for ILD/ULSI structures.
Custom Device Prototyping (MIM)	The successful Al-BCN-Au MIM UV detector prototype requires advanced metalization. 6CCVD offers in-house custom metalization services, including the deposition of Au, Ti, Pt, W, and Cu layers, enabling rapid turnaround for complex multilayer device structures used in photodetector or interconnect research.
Surface Finish for Integration	CMOS interconnect fabrication demands ultra-flat surfaces for subsequent patterning (CMP). Our polished SCD material achieves surface roughness of Ra < 1 nm, while inch-size PCD achieves Ra < 5 nm, directly addressing the planarization needs identified in the ILD processing challenges.
Advanced Etching & Cleaning Support	The paper details etching using common aluminum etchant chemistry. 6CCVD offers expert engineering support from our in-house PhD team to assist researchers in optimizing material selection and post-processing protocols for UV detector and Inter-Dielectric Layer projects.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly. We ship globally (DDU default, DDP available).

View Original Abstract

As complementary metal-oxide semiconductor (CMOS) devices shrink to smaller size, the problems related to circuit performance such as critical path signal delay are becoming a pressing issue. These delays are a result of resistance and capacitance product (RC time constant) of the interconnect circuit. A novel material with reduced dielectric constants may compromise both the thermal and mechanical properties that can lead to die cracking during package and other reliability issues. Boron carbon nitride (BCN) compounds have been expected to combine the excellent properties of boron carbide (B4C), boron nitride (BN) and carbon nitride (C3N4), with their properties adjustable, depending on composition and structure. BCN thin film is a good candidate for being hard, dense, pore-free, low-k dielectric with values in the range of 1.9 to 2.1. Excellent mechanical properties such as adhesion, high hardness and good wear resistance have been reported in the case of sputtered BCN thin films. Problems posed by high hardness materials such as diamonds in high cutting applications and the comparatively lower hardness of c-BN gave rise to the idea of a mixed phase that can overcome these problems with a minimum compromise in its properties. A hybrid between semi-metallic graphite and insulating h-BN may show adjusted semiconductor properties. BCN exhibits the potential to control optical bandgap (band gap engineering) by atomic composition, hence making it a good candidate for electronic and photonic devices. Due to tremendous bandgap engineering capability and refractive index variability in BCN thin film, it is feasible to develop filters and mirrors for use in ultra violet (UV) wavelength region. It is of prime importance to understand process integration challenges like deposition rates, curing, and etching, cleaning and polishing during characterization of low-k films. The sputtering technique provides unique advantages over other techniques such as freedom to choose the substrate material and a uniform deposition over relatively large area. BCN films are prepared by dual target reactive magnetron sputtering from a B4C and BN targets using DC and RF powers respectively. In this work, an investigation of mechanical, optical, chemical, surface and device characterizations is undertaken. These holistic and thorough studies, will provide the insight into the capability of BCN being a hard, chemically inert, low-k, wideband gap material, as a potential leader in semiconductor and optics industry.

Tech Support

Original Source

DOI: None