S1160405 Effects of Residual Gases during Deposition on the Friction Properties of PECVD-DLC

At a Glance

Metadata	Details
Publication Date	2015-01-01
Journal	The Proceedings of Mechanical Engineering Congress Japan
Authors	Hotaka SHIBASAWA, Hiroyuki Kousaka, Noritsugu Umehara, Xinerui DENG
Institutions	Nagoya University
Analysis	Full AI Review Included

Technical Documentation & Analysis: S1160405

Effects of Residual Gases during Deposition on the Friction Properties of PECVD-DLC

This document analyzes the research findings regarding the stability and performance of Si-DLC films under varying PECVD conditions, translating the requirements for robust tribological coatings into specific material solutions offered by 6CCVD (6ccvd.com), a specialist in high-purity MPCVD diamond.

Executive Summary

The research investigates the impact of residual water vapor during PECVD deposition on the structural and mechanical properties of Si-DLC films, providing critical insights into process robustness for high-throughput coating applications.

Process Sensitivity: Increasing residual water content (simulating poor vacuum) significantly degraded the film properties, causing hardness to drop from 18.6 GPa to 10.8 GPa and increasing the degree of graphitization (ID/IG ratio).
Structural Changes: High residual water led to substantial increases in Si/C (0.37 to 0.76) and O/C (0.02 to 0.42) ratios, indicating oxygen incorporation and structural modification.
MVP Mitigation: The use of high-density MVP (Microwave sheath-Voltage combination Plasma) effectively suppressed these negative effects due to its high deposition rate (40.7 µm/h) and high gas flow, which diluted the residual water vapor.
Tribological Stability: Despite significant changes in film structure and hardness, the friction coefficient in PAO oil remained consistently low (0.08 to 0.1) across all specimens, suggesting that rough vacuum processing may be acceptable for certain oil-lubricated applications.
6CCVD Value Proposition: While Si-DLC offers good tribology, 6CCVD’s MPCVD Single Crystal Diamond (SCD) provides intrinsic hardness and wear resistance (up to 100 GPa) that are orders of magnitude superior, offering ultimate performance stability independent of minor CVD process fluctuations.

Technical Specifications

The following table summarizes the key quantitative results extracted from the study, highlighting the material degradation observed under high residual water conditions (Specimens B, C, B’, C’).

Parameter	Value Range	Unit	Context
Hardness (DC Plasma)	10.8 to 18.6	GPa	Decreased with increasing residual water
ID/IG Ratio (DC Plasma)	0.25 to 0.41	Dimensionless	Increased with increasing residual water (Graphitization)
Si/C Ratio	0.37 to 0.76	Dimensionless	Increased with increasing residual water
O/C Ratio	0.02 to 0.42	Dimensionless	Increased with increasing residual water (Oxygen incorporation)
DC Deposition Rate	4.7	µm/h	Low plasma density
MVP Deposition Rate	40.7	µm/h	High plasma density (8.5x faster)
Pre-Vacuum Pressure (High Vacuum)	4 x 10^-4	Pa	Baseline condition (A, A’)
Pre-Vacuum Pressure (Rough Vacuum)	1	Pa	Degraded condition (B, B’, C, C’)
H₂O Flow (Intentional Addition)	8 to 10	sccm	Condition C, C’
Friction Coefficient (PAO Oil)	0.08 to 0.1	Dimensionless	Consistent across all specimens
Normal Load (Tribology)	0.5	N	Ball-on-Disk Test (SUJ2 ball)
Sliding Speed (Tribology)	41.2	mm/s	Test condition in PAO oil

Key Methodologies

The experiment compared two PECVD methods (DC and MVP) under three distinct vacuum/residual gas conditions to deposit Si-containing Diamond-Like Carbon (Si-DLC) films on SUS304 substrates.

Substrate Preparation: Circular SUS304 disk specimens (Φ17 x t1 mm) were used for deposition.
Deposition Methods: Films were grown using both conventional DC Plasma and high-density MVP (Microwave sheath-Voltage combination Plasma).
Vacuum Conditions: Three conditions were tested to control residual water vapor:
- High Vacuum (A, A’): Evacuated to 4 x 10^-4 Pa using a turbo-molecular pump.
- Rough Vacuum (B, B’): Evacuated only to 1 Pa using a rotary pump.
- Water Added (C, C’): Evacuated to 1 Pa, followed by intentional introduction of 8-10 sccm of H₂O during deposition.
Gas Composition: The primary process gases were Ar, CH₄, and TMS (tetramethylsilane), with the CH₄/TMS ratio adjusted between DC and MVP methods to maintain a similar Si/C ratio in the baseline films.
- DC Plasma: Total gas flow 18.5 sccm. Bias Voltage: -600 V.
- MVP Plasma: Total gas flow 123 sccm. Microwave Power: 150 W (2.45 GHz). Bias Voltage: -300 V.
Characterization:
- Hardness: Measured using a micro-indentation tester with a 65° diamond indenter.
- Structure: Raman Spectroscopy was used to determine the carbon bonding state (ID/IG ratio).
- Composition: X-ray Photoelectron Spectroscopy (XPS) with 1 minute of Ar ion sputtering was used to determine Si/C and O/C elemental ratios.
- Tribology: Ball-on-disk friction tests were conducted in PAO oil against an SUJ2 counter ball (Φ8), under a 0.5 N load and 41.2 mm/s sliding speed.

6CCVD Solutions & Capabilities

This research demonstrates the challenges of maintaining consistent material properties in high-rate CVD processes when environmental control (residual gas) is compromised. For engineers requiring the highest level of material stability, hardness, and tribological performance, 6CCVD provides MPCVD diamond solutions that inherently surpass the performance envelope of Si-DLC films.

Applicable Materials

To replicate or extend this research into applications demanding extreme wear resistance and chemical inertness, 6CCVD recommends the following materials:

6CCVD Material	Application Focus	Key Advantage over Si-DLC
Optical Grade SCD	High-precision tribology, high-power optics, heat spreaders.	Intrinsic hardness & thermal conductivity are orders of magnitude higher. Ra < 1 nm polishing available.
High-Quality PCD	Large-area wear plates, robust tooling, high-pressure seals.	Available in large formats (up to 125 mm diameter) with superior hardness (50-70 GPa) compared to the 10-18 GPa DLC films studied.
Boron-Doped Diamond (BDD)	Electrochemical sensors, high-wear electrodes.	Offers the hardness of diamond combined with tunable electrical conductivity, ideal for harsh environments.

Customization Potential

The study highlights the importance of substrate and interface engineering (Si-DLC on SUS304). 6CCVD offers comprehensive customization capabilities to support advanced tribological and coating research:

Custom Dimensions: We supply SCD and PCD plates/wafers in custom shapes and sizes, up to 125 mm diameter for PCD, and thicknesses ranging from 0.1 µm to 500 µm.
Advanced Polishing: For critical tribological interfaces, 6CCVD guarantees ultra-low surface roughness: Ra < 1 nm for SCD and Ra < 5 nm for inch-size PCD.
Metalization Services: If the research requires patterned contacts or specific bonding layers (e.g., Ti/Pt/Au used in related diamond studies), 6CCVD provides in-house metalization capabilities, including Au, Pt, Pd, Ti, W, and Cu.
Substrate Integration: We can supply high-purity diamond substrates (up to 10 mm thick) for subsequent coating or integration into complex mechanical systems, ensuring a stable, high-performance foundation.

Engineering Support

The findings regarding the sensitivity of CVD processes to residual gases underscore the need for expert material selection. 6CCVD’s in-house PhD team specializes in the physics and chemistry of MPCVD growth and can assist researchers in:

Material Selection: Guiding the choice between SCD and PCD based on required hardness, thermal management, and cost targets for similar Tribological Coating projects.
Process Optimization: Consulting on the integration of diamond materials into existing high-vacuum or high-pressure systems, leveraging our expertise in high-purity CVD environments.
Global Logistics: Ensuring reliable, fast global shipping (DDU default, DDP available) for time-sensitive research projects.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

DLC (Diamond-Like Carbon) has excellent mechanical properties such as high hardness, low friction and high wear resistance. One of the main coating methods of DLC is PECVD, which enables ultra-high-speed coating at larger than 100 μm/h if combined with an appropriate high-density plasma represented by MVP (Microwave sheath-Voltage combination Plasma). For practically achieving high-throughput in DLC coating by MVP, not only coating time but also evacuation time should be shortened. If vacuum condition including not negligible amount of residual gases is allowed during coating, it leads to shorten the evacuation time before coating. Thus, in this research, in order to understand the effect of a residual gas, or water, during coating on Si-containing DLC (Si-DLC) deposited, we compared 3 Si-DLCs deposited under different 3 vacuum conditions; 1) evacuated down to 4×10^<-4> Pa with turbo-molecular pump, 2) evacuated down to 1 Pa only with rotary pump, and 3) water was added to the vacuum condition. Deposition of 3 Si-DLCs under the 3 vacuum conditions was conducted with not only MVP but also conventional DC plasma for comparison. As a result, it was observed in DC that 1) hardness decreased from 18.6 GPa to 10.8 GPa, 2) ID/IG increased from 0.25 to 0.41, 3) Si/C increased from 0.37 to 0.76, and 4) O/C increased from 0.02 to 0.42, with increasing of residual water during coating. Similar results were obtained in MVP, however, the increased/decreased ranges of the 4 parameters were decreased; in other words; the effect of residual water was suppressed by employing MVP instead of DC plasma. In spite of thus changes in films, friction coefficient in PAO oil was almost the same value from 0.08 to 0.1 in all specimens.

Tech Support

Original Source

DOI: https://doi.org/10.1299/jsmemecj.2015._s1160405-