|
|
|
|
|
|
Harrick
Scientific's Plasma Cleaner models are low-cost tabletop inductively coupled
plasma devices that serve as excellent tools for surface cleaning, surface
preparation and surface modification. Plasma treatment may be applied to a
wide variety of materials, including metals, ceramics, composites, plastics,
polymers and biomaterials.
Our plasma cleaners may be employed in a
broad range of surface engineering applications, including surface cleaning,
surface sterilization, surface activation, surface energy alteration,
surface preparation for bonding and adhesion, modification of surface
chemistry, as well as the surface treatment of polymers and biomaterials
through activation, grafting and surface coating.
Our plasma cleaners are specifically
designed for laboratory, R&D and office use. They offer inexpensive, compact
functionality. Key applications areas include materials science, polymer
science, biomedical materials, sterilization of dental and medical implants
and instruments, optical cleaning and micro-fluidics.
Links to further information on plasma
surface cleaning and surface treatment with Harrick Scientific Plasma
Cleaner models are given below: |
|
General Plasma
Information
Physics of Plasma
— what plasma is, how it is generated
and sustained, and the basics of how it interacts with a material surface
Plasma Advantages
— the advantages of plasma surface
treatment for the surface itself, process flexibility and consistency,
low-cost, ease-of-use, and user and environmental safety
Plasma-Surface Interaction
— the fundamental modalities of
plasma-surface interaction: ablation, activation, crosslinking and
deposition
Plasma Process Gases
— a guide to the use of different plasma
process gases for chemical and mechanical contamination removal, oxidation,
activation, crosslinking and deposition
Plasma Cleaner
Information
Plasma Cleaner Features
— Plasma Cleaner product features, model
options, device requirements and applied power settings
Plasma Accessory Features
— product features of our PlasmaFlo gas
mixing/metering and vacuum pump accessories
Details of Operation
— basic principles of operation, details
of operational procedure and general guidance on surface cleaning and
modification
Ordering Information
— contact and ordering information for
our low-cost Plasma Cleaner models and PlasmaFlo gas mixing/metering and
vacuum pump accessories
Technical References
— a partial listing of technical
articles and patents that reference the use of our Plasma Cleaner models
Specific Plasma
Applications
Plasma Applications: Plasma Cleaning
— the advantages of plasma cleaning for
surface preparation prior to bonding and other applications; ATR
measurements demonstrating contaminant removal following plasma cleaning
Plasma Applications: Polymers
— surface cleaning and surface treatment
of polymers, surface restructuring through polymer crosslinking, chemical
surface modification through activation and grafting, and polymer surface
deposition
Plasma Applications: Biomaterials
— sterilization of medical instruments,
adhesion promotion of biomaterials, alteration of biomaterial wetting
properties, deposition of biomaterial coatings and plasma enhancement of
biocompatibility |
Expanded Plasma Cleaner |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Nature
of Plasma |
|
 |
A plasma is
a partially ionized gas consisting of electrons, ions and neutral atoms or
molecules |
|
|
The plasma
electrons are at a much higher temperatures than the neutral gas species,
typically around 104°K, although the plasma gas as a whole is at
near ambient temperature |
|
|
The plasma
electron density is typically around 1011 cm-3
|
|
|
Plasma
Formation |
|
|
An RF
oscillating electric field is generated in the gas region, either through
the use of capacitive plates or through magnetic induction |
|
|
At
sufficiently low pressures the combined effect of the electric field
acceleration of electrons and elastic scattering of the electrons with
neutral atoms or field lines leads to heating of the electrons |
|
|
When
electrons gain kinetic energy in excess of the first ionization threshold in
the neutral gas species, electron-neutral collisions lead to further
ionization, yielding additional free electrons that are heated in turn
|
|
|
Plasma-Surface Interaction |
|
|
The energy
of plasma electrons and ions is sufficient to ionize neutral atoms, break
molecules apart to form reactive radical species, generate excited states in
atoms or molecules, and locally heat the surface |
|
|
Depending on
the process gases and parameters, plasmas are capable of both mechanical
work, through the ablative effect of kinetic transfer of electrons and ions
with the surface, and chemical work, through the interaction of reactive
radical species with the surface |
|
|
In general,
plasmas can interact with and modify a surface through several mechanisms:
ablation, activation, deposition, cross-linking and grafting - see
Plasma-Surface Interaction |
|
|
|
|
|
|
|
Surface Interaction |
|
|
Plasma
treatment only affects the near surface of a material; it does not change
bulk material properties |
|
|
Plasma
cleaning leaves no organic residue, unlike many wet cleaning processes;
under proper conditions, it can achieve complete contamination removal,
resulting in an "atomically clean" surface |
|
|
Plasma has
no surface tension constraints, unlike aqueous cleaning solutions; it can
clean rough, porous or uneven surfaces |
|
|
Plasma
treatment occurs at near-ambient temperature, minimizing the risk of damage
to heat-sensitive materials |
|
|
Process Flexibility & Consistency |
|
|
Depending on
process gases and usage configuration, plasma treatment can be used for
cleaning, activation, sterilization and general alteration of surface
characteristics |
|
|
Plasma will
react with a wide variety of materials; as such, plasma can also treat
assemblies made of different materials |
|
|
Plasma
cleaning can treat odd-shaped parts with difficult surface geometries |
|
|
Plasma
treatment is highly reproducible; it is typically characterized by a greater
consistency than chemical or mechanical processes |
|
|
Low
Cost / Ease of Use |
|
|
Plasma
processing is highly efficient, with short processing times, no drying stage
and little energy consumed |
|
|
Plasma
treatment helps to avoid process yield loss due to heat or solvent damage |
|
|
Plasma
processing is easier to use and maintain than chemical or mechanical
processes; in addition, it requires no complicated chemical analysis or
maintenance |
|
|
Plasma
treatment frequently eliminates the need for solvents, along with their
ongoing purchase and disposal costs |
|
|
User &
Environmental Safety |
|
|
Plasma
treatment eliminates safety risks associated with worker exposure to
dangerous chemicals |
|
|
Plasma
processing is contained within a vacuum chamber, with little or no direct
worker exposure |
|
|
Plasma
processing operates at near-ambient temperatures with no risk of heat
exposure |
|
|
Plasma
treatment uses no harmful chlorinated fluorocarbons, solvents, or acid
cleaning chemicals |
|
|
The EPA has
classified most plasma processes as "green" environmentally friendly
processes |
|
|
|
|
|
|
|
Ablation |
|
|
Plasma
ablation involves the mechanical removal of surface contaminants by
energetic electron and ion bombardment |
|
|
Surface
contamination layers (e.g. cutting oils, skin oils, mold releases) are
typically comprised of weak C-H bonds |
|
|
Ablation
breaks down weak covalent bonds in polymeric contaminants through mechanical
bombardment |
|
|
Surface
contaminants undergo repetitive chain scission until their molecular weight
is sufficiently low for them to boil away in the vacuum |
|
|
Ablation
affects only the contaminant layers and the outermost molecular layers of
the substrate material |
|
|
Argon is
often used for ablation; high ablation efficiency, no chemical reactivity
with the surface material |
|
|
Activation |
|
|
Plasma
surface activation involves the creation of surface chemical functional
groups through the use of plasma gases - such as oxygen, hydrogen, nitrogen
and ammonia - which dissociate and react with the surface |
|
|
In the case
of polymers, surface activation involves the replacement of surface polymer
groups with chemical groups from the plasma gas |
|
|
The plasma
breaks down weak surface bonds in the polymer and replaces them with highly
reactive carbonyl, carboxyl, and hydroxyl groups |
|
|
Such
activation alters the chemical activity and characteristics of the surface,
such as wetting and adhesion, yielding greatly enhanced adhesive strength
and permanency |
|
|
Crosslinking |
|
|
Cross-linking is the setting up of chemical links between the molecular
chains of polymers |
|
|
Plasma
processing with inert gases can be used to cross-link polymers and produce a
stronger and harder substrate microsurface |
|
|
Under
certain circumstances, crosslinking through plasma treatment can also lend
additional wear or chemical resistance to a material |
|
|
Deposition |
|
|
Plasma
deposition involves the formation of a thin polymer coating at the substrate
surface through polymerization of the process gas |
|
|
The
deposited thin coatings can possess various properties or physical
characteristics, depending on the specific gas and process parameters
selected |
|
|
Such
coatings exhibit a higher degree of crosslinking and much stronger adherence
to the substrate in comparison to films derived from conventional
polymerization |
|
|
|
|
|
|
|
Gas
Sources for Plasma Surface Cleaning and Modification |
|
|
Air |
|
|
Contamination Removal (chemical) |
|
|
Oxidation
Process |
|
|
Surface
Activation |
|
O2 |
|
|
Contamination Removal (chemical) |
|
|
Oxidation
Process |
|
|
Surface
Activation (wetting & adhesion) |
|
|
Etch
(organics) |
|
|
Deposition
(glass (w/ Si))
Note: a special 'oxygen service' vacuum
pump must be used in conjunction with O2 process gas in order to avoid risk
of possible injury; inquire with Harrick Scientific for details |
|
N2 |
|
|
Surface
Activation |
|
|
Deposition
(silicon nitride (w/ Si), metal nitride (w/ M)) |
|
Ar |
|
|
Contamination Removal (ablation) |
|
|
Crosslinking |
|
H2 |
|
|
Contamination Removal (chemical) |
|
|
Surface
Modification (curing) |
|
|
Reduction
Process (metal oxide) |
|
|
Deposition
(metals (w/ M))
Note: Extreme caution must be exercised
when working with H2 process gas in order to minimize the risk of
possible injury. |
|
|
|
|
|
|
|
Features |
|
|
Compact,
tabletop unit |
|
|
Adjustable
RF power |
|
|
Low, Medium,
and High power settings |
|
|
Two Plasma
Cleaner models available: |
|
|
 |
PDC-32G
(110V); PDC-32G-2 (220V) |
|
|
|
 |
Basic model
with a 3" diameter by 7" long chamber and a removable cover |
|
|
|
|
Applies a
maximum of 18W to the RF coil, with no RF emission |
|
|
|
|
Size: 8"H x
10"W x 8"D |
|
|
|
PDC-001(110V); PDC-002 (220V) |
|
|
|
|
Expanded
model with a 6" diameter by 6" long chamber and an integral switch for a
vacuum pump |
|
|
|
|
Its hinged
cover features a magnetic closure and a viewing window |
|
|
|
|
Applies a
maximum of 30W to the RF coil, with no RF emission |
|
|
|
|
Size: 11"H x
18"W x 9"D |
|
|
Optional
quartz Plasma Cleaner chamber |
|
|
Optional
flow mixer allows individually metered intakes for up to two different gases
and monitors the pressure in the chamber |
|
|
Compatible
vacuum pump available |
|
|
Requires |
|
|
A vacuum
pump with a minimum pumping speed of 1.4 m3/hr and a maximum
ultimate total pressure of 200 mtorr |
|
|
Includes |
|
|
1/8" NPT
needle valve to admit gases and control the pressure |
|
|
Pyrex Plasma
Cleaner chamber |
|
|
Power
Settings |
| Description |
PDC-32G or
PDC-32G-2 |
PDC-001 or
PDC-002 |
| Input Power |
100W |
200W |
|
Applied to the RF
Coil |
| Low Setting |
680V DC |
10 mA DC |
6.8W |
716V DC |
10 mA DC |
7.16W |
| Medium Setting |
700V DC |
15 mA DC |
10.5W |
720V DC |
15 mA DC |
10.15W |
| High Setting |
720V DC |
25 mA DC |
18W |
740V DC |
40 mA DC |
29.6W |
|
|
|
|
|
|
|
| Note: A
detailed User's Manual is provided with all Harrick Scientific Plasma
Cleaner models. |
|
|
Principles of Operation |
|
|
The sample
is placed in the plasma vacuum chamber |
|
|
Process
gas(es) are admitted to the chamber at low flow rates (1-2 SCFH) using
either a needle valve or the PlasmaFlo accessory and are kept at low
pressure (~200-600 mTorr) through vacuum pumping |
|
|
The gases
are subject to induced RF magnetic and electric fields generated by a
solenoidal coil current |
|
|
Plasma is
generated through the subsequent RF/collisional heating of the electrons in
the gas |
|
|
Details of Operation |
|
|
The plasma
vacuum chamber door has an o-ring quick disconnect seal for easy access to
the chamber |
|
|
The vacuum
pump is connected to an outlet at the back of the reaction chamber |
|
|
The needle
valve can be used to break the vacuum gently, to control the pressure or to
admit a special gas for plasma processing |
|
|
The RF power
level can be adjusted by means of a three-way selector switch |
|
|
The plasma
will emit a characteristic glow, which visibly indicates the successful
generation of the plasma state |
|
|
The
temperature change of a substrate during plasma treatment is minimal |
|
|
Surface Cleaning / Modification |
|
|
The
interaction between the plasma and the surface is determined by: |
|
|
|
The nature
of the substrate and surface contaminant layers |
|
|
|
The process
gases used |
|
|
|
The pressure
and flow rate of the gases |
|
|
|
The RF power
level & length of sample exposure |
|
|
For surface
cleaning, a few seconds exposure, following pump down of the chamber and
formation of plasma, is often adequate |
|
|
Surface
cleanliness can be tested most easily by observing the wettability of the
sample: on a clean surface, water drops will not bead, but will spread out
in a uniform film |
|
|
|
|
|
|
|
Plasma
Cleaning |
|
|
Conventional
cleaning methods often fail to completely remove surface films, leaving a
thin contamination layer; additionally, solvent cleaning typically leaves a
surface residue |
|
|
Plasma
cleaner use exposes the surface to a gas plasma discharge, gently and
thoroughly scrubbing the surface |
|
|
Plasma
cleaning will remove non-visible oil films, microscopic rust or other
contaminants that typically form on surfaces as a result of handling,
exposure or previous manufacturing or cleaning processes; additionally,
plasma cleaning does not leave a surface residue |
|
|
A plasma
cleaner can treat both a wide variety of materials - including plastics,
metals and ceramics - as well as complex surface geometries |
|
|
A plasma
cleaner is most commonly used prior to adhesive bonding both to clean away
loosely held contaminant residues and to activate the surface for increased
bonding strength |
|
| Figures 1
and 2 below show the ATR spectra, respectively, of Ge and Si substrates
prior to and following surface contaminant removal via plasma cleaning. |
|
| Figure 1. ATR spectra
(qave=45°, N=20) of a Ge surface before and after plasma cleaning
with a Harrick plasma cleaner. The lower trace shows Ge coated with
a thick (about I micron) film of photoresist (AZ111). The upper
trace shows same surface after fifteen minutes of plasma cleaning
with 02, indicating Ge is restored to its original
organic free condition with the photoresist stripped off the
surface. |
|
|
|
| Figure 2. Harrick
plasma cleaner hydrocarbon removal from the surface of a silicon ATR
plate (60 reflections, q = 45°). The C-H band (bottom trace),
representing 10% absorption, is completely eliminated (top trace)
after one minute exposure to an air plasma. |
|
|
|
|
|
|
|
|
|
Surface Cleaning of Polymers |
|
|
Plasma
ablation mechanically removes contaminant layers through energetic electron
and ion bombardment of the surface - see Ablation |
|
|
Plasma
surface cleaning removes surface contaminants, unwanted surface finish from
polymers and weak boundary layers which may be present in certain processed
polymers |
|
|
Surface Restructuring of Polymers |
|
|
The breaking
of polymer surface bonds by plasma ablation using an inert gas leads to the
creation of polymeric surface free radicals |
|
|
A surface
free radical can rebond in its original polymeric structure, it can bond
with an adjoining free radical on the same polymeric chain, or it can bond
with a nearby free radical on a different polymeric chain - see
Crosslinking |
|
|
Such polymer
surface restructuring can improve surface hardness, as well as tribological
and chemical resistance |
|
|
Surface Alteration of Polymers |
|
|
The breaking
of polymer surface bonds by plasma ablation leads to the creation of
polymeric surface free radicals |
|
|
The bonding
of these surface free radicals with atoms or chemical groups from the plasma
leads to the replacement of surface polymer functional groups with new
functional groups, based upon the chemistry of the plasma process gas - see
Activation |
|
|
Typical
polymer functional groups formed through plasma surface activation and
grafting include: amine amino-carboxyl, carboxyl hydroxyl and fluorination
carbonyl |
|
|
Such polymer
surface alteration can modify the chemical properties of the surface while
leaving the bulk properties unchanged |
|
|
Surface Deposition of Polymers |
|
|
Plasma
deposition involves the formation of a thin polymer coating on the substrate
surface through polymerization of the process gas |
|
|
If a process
gas comprised of more complex molecules, such as methane or carbon
tetrafluoride, is employed, these may undergo fragmentation in the plasma,
forming free radical monomers; these in turn bind to the surface and
recombine into deposited polymeric layers |
|
|
These
polymer thin-film coatings can dramatically alter the permeation and
tribological properties of the surface - see Deposition |
|
|
|
|
|
|
|
Sterilization |
|
|
Plasma
sterilization treatment is gaining growing acceptance for disinfecting and
sterilizing medical devices |
|
|
Plasma
treatment offers the potential for simultaneous cleaning and sterilization
of medical instruments |
|
|
Plasma
sterilization is particularly appropriate for medical or dental implants and
devices that are sensitive to the high temperature, chemical or irradiative
environments associated with autoclaving, EtO or gamma sterilization,
respectively |
|
|
Adhesion Promotion |
|
|
Many
biomaterials have a low to medium surface energy, making it difficult to
effectively apply adhesives or coatings |
|
|
Plasma
surface activation leads to the formation of surface functional groups that
increase surface energy and improve interfacial adhesion for biomaterial
bonding |
|
|
Wetting Properties |
|
|
Most
untreated biomaterials have poor wettability (hydrophilicity) |
|
|
Plasma
surface treatment has been used to enhance or decrease the wetting
characteristics on a wide variety of biomaterials |
|
|
Surfaces may
be rendered hydrophilic through plasma activation, and may be rendered
hydrophobic through plasma deposition of thin films |
|
|
Low-Friction & Barrier Coatings |
|
|
Some
silicones and polymers such as polyurethanes have a typically high
coefficient of friction against other surfaces |
|
|
Plasma
coating deposition of a lower coefficient of friction polymer coating yields
a more lubricious surface for biomaterials applications |
|
|
Plasma
coating deposition can also be used to form thin, dense barrier coatings
that decrease permeability to liquids or vapors for biomaterials
applications |
|
|
Biocompatibility |
|
|
Biomaterials
that come in contact with blood or protein require special surface
treatments to enhance biocompatibility |
|
|
Plasma
activation of biomaterial surfaces prepares them for cell growth or protein
bonding; additionally, biomaterial surfaces may also be modified to decrease
the bonding of proteins |
|
|
Biomaterials
with modified surfaces exhibit improved "biocompatibility", including
enhanced cell adhesion, improved cell culture surfaces, non-fouling surfaces
and promotion of selective protein adsorption |
