Your Environmental Monitoring System (EMS) is your first line of defense against contamination – and you should have the utmost trust in it. Here at LWS, we pave the way in clean air technology with over 40 years of expertise. We design our clean air technology around your needs, predicting what you need before you know you need it. Our goal is to make your life easier and your cleanroom safer.
The fundamentals of particle counters are relatively simple. You need to know how and why they work. If you have a basic grasp of these fundamentals, you’ll be on your way to better understanding particle counters.
An aerosol particle counter works on the principal of either light scattering or light blocking. An aerosol stream is drawn through a chamber with a light source (either Laser Based Light or White Light). When a particle is illuminated by this light beam, it is redirected or absorbed. Light scattered by a single particle in a specific direction in relation to the original direction has a unique signature which relates to the size of the particle. This allows for sizing and counting of individual particles.
A particle counter is made up of 4 components:
What is AMC?
Airborne Molecular Contamination (AMC) is chemical contamination in the form of vapors or aerosols that has a detrimental effect on a product or a process. These chemicals may be organic or inorganic in nature and includes acids, bases, polymer additives, organometallic compounds and dopants. The main sources for AMC are building and cleanroom construction materials, general environment, process chemicals and operating personnel.
What are the effects of AMC?
AMC can cause a multitude of adverse effects such as:
· Corrosion of metal surfaces on the wafer
· Degradation of HEPA/ULPA filter media
· Haze on wafers
· Haze on optics
· T Topping of chemically amplified photoresist
· Changes in contact resistance and voltage shifts
Who is monitoring AMC in my industry?
Almost all leading edge semiconductor companies are doing some type of AMC monitoring on a real time basis. This monitoring has been traditionally focused around the photolithographic area, but the area of coverage is now extending into other process locations.
My lab already does testing for AMC. Why should I use a monitoring system for AMC?
In general the testing done by most labs is static. This means the data cannot show actual trends over time, it can only show an average concentration level. The most common form of testing done by a lab is impinger testing. An impinger is put out into the environment to be tested for a fixed length of time. The sample collected is then analyzed for chemical concentration levels. The data provided from this type of testing only shows an average concentration level. Online monitoring gives you the ability to see AMC levels in real time. It can show you whether concentration in AMC is at normal background levels or is a specific contamination event, where the low and high phases are in the daily cycle.
What compounds do you monitor?
We are able to monitor all types of compounds. The most common chemicals that are monitored are as follows:
What are the minimum detection limits?
The minimum detection limits depend on the type of chemicals you want to sample and the technology you want to use. Some technologies can view chemical concentrations into the part per trillion level; others in the parts per million level. It is important to first understand what the requirements are for your process and then to determine what the appropriate detection limits should be.
How many points can I monitor?
The Lighthouse AMC Manifold can be configured to sample anywhere from only 1 location to as many as 64 locations. If more than 64 locations are needed, multiple Lighthouse AMC Manifolds can be combined into a single system with up to thousands of sampling locations.
How often can I get samples?
The frequency of sampling from each location is determined by 3 things: number of sample locations, purge time, and sample time. Together, these values determine the Total Cycle Time – which is the time it takes for the manifold to sample from all locations and return to the original location for another sample. The Total Cycle Time is determined as follows:
Number of Sample Locations x (Purge Time + Sample Time)
So, for example, if you have 12 sample locations, a Purge Time of 5 minutes, and a Sample Time of 1 minute, your Total Cycle Time will be:
12 * (5 min + 1 min) = 72 minutes
Number of Sample Locations:
Naturally, the more locations you sample, the longer it will take to cycle through all locations and take another sample at the original sample location.
However, the Lighthouse AMC Manifold also allows you to choose specific sample locations for higher priority sampling, allowing you to sample multiple times from specific locations during the course of a cycle.
For example, you could choose to sample from a few particularly sensitive locations 3 times for every 1 time you sample from all other locations. This allows you to expand your sampling system without sacrificing the speed at which you sample more sensitive locations.
Purge Time:
After the manifold changes to a new sampling location, it waits for some time to allow the air from the previous location to be replaced by the air from the new sample location. This is called the Purge Time.
The value of the Purge Time is dependent on the response time of the sensors used, not on the manifold. Sensors with slow response times require longer purge times – which in turn increases the Total Cycle Time, reducing the frequency with which you can sample each location.
Even with sensors that have fast response times, the minimum recommended Purge Time is 5 minutes; for sensors with slow response times, the Purge Time may need to be as long as 30 minutes. It’s for this reason that it is important to select sensors with fast response times.
Sample Time:
Lighthouse recommends that the Sample Time is set for 60 seconds. This gives the sensors enough time to get a valid sample, and gives the Lighthouse AMC Manifold enough time to accurately determine the stability of the sample (regardless of the sensor used).
What is required to maintain the system (calibration, gases, etc…)?
There are two parts to this question.
1. First for the sampling system, the unit requires very little maintenance. The vacuum pumps will need to be maintained on a quarterly basis.
2. The maintenance requirements for the analyzers will be dependent on the type of analyzer used and the gases being monitored. Different analyzers will have different calibration requirements. Calibration frequency is often dependent on the desired accuracy of the sensor. Some sensors come with on board calibration systems while others require external hardware and standard gases to calibrate them.
Where should we install the sample points?
Sample points should be installed as close to critical processes as possible without interfering with the processes. It is common to install points both inside and out side of a process so if an increase in AMC does occur, it can be determined whether the increase came from the ambient environment or from within the tool itself. It is also common to install sample points up and down stream from the chemical filters. This will help to understand the removal efficiency of the chemical filters.
How much does a system like this cost?
The cost is dependent on what chemicals you want to monitor and how many locations you want to sample from. Prices can range from a low at $3,000 for a single sensor to $400,000 for an entire system sampling multiple locations.
Why do a I need to monitor AMC?
Monitoring for any type of contamination is an important aspect of contamination control. Monitoring specifically for AMC is important in industries where AMC can directly affect the product or process. Even the newest state of the art facilities are not immune from AMC related incidents. Incidents such as spills or contamination episodes result from tool or equipment failures and associated maintenance. Chemical filtration is affected by the environment; changes in the environment may result in performance changes in chemical filtration. Only continuous AMC monitoring can provide assurance that the facility is performing properly and can alert personnel when an incident has occurred. This type of monitoring allows for rapid responses to incidents that can be carried out immediately instead of days or weeks after the facility has been contaminated.
What sensors do you recommend we use?
AMC monitoring is very specific for the application; therefore, the sensor used should be based on the application. When picking a sensor you should consider the following:
Can I send my data to our existing data management system?
Yes. The Lighthouse AMC manifold reads the data from multiple sensors, using different protocols and signals but provides all the data via a single interface, using the industry-standard Modbus protocol. Almost every commercial automation and control system on the market – including most legacy systems – can read data using the Modbus protocol.
Do your instruments have any radioactive materials in them?
Lighthouse does not make AMC analyzers. We integrate various analyzers from different instrument suppliers into the sampling manifold. This allows us to match different techniques to provide a broad range of AMC monitoring.
Some instruments use a radioactive source to ionize the sample. This is found most commonly in sensors utilizing Ion Mobility Spectroscopy as an analysis technique. We recommend that you ask each instrument supplier this question.
How long can the tubing runs be from manifold to sample point?
The runs can be as long as you like, however, the longer the distance, the greater the chance for contaminating or diluting the sample. Contamination of the sample can come from leaks in the sample tubing. Dilution will come from part of the sample being absorbed by the sample tubing material. We recommend not running sample tubing any longer then 80 meters. At longer distances, it is a good idea to use a booster pump to maintain adequate sample flow.
What materials are used for the tubing?
The most commonly used sample tubing is teflon. Stainless steel can also be used, but it tends to be more expensive and is not compatible with all chemicals.
How frequently should we calibrate the sensors?
Frequency of calibration will depend on three factors.
1. The Zero Drift of the sensor per day – this is the amount of drift the sensor will experience from zero in a set period of time, normally a day or week.
2. The Span Drift – this is the amount of drift the sensor will experience from a fixed concentration amount over a day or week period of time.
3. What is the target level of detection you are looking for? The lower the level, the more frequently you will need to calibrate to keep the zero and span drift from growing larger than the minimum detection limit you want to achieve.
Why doesn’t the data collected match our impinger sample?
There are two parts to this answer.
1. Different analysis techniques will tend to produce slightly different results. Some techniques are more prone to interference and thus can show drastically different results.
2. An impinger sample is taken over a set period of time, normally 2 – 24 hours. Thus impinger data will only show an average concentration over the period of time the sample was taken. Real-time instruments will give a continuous readout and are designed to show trends in AMC levels.
What do you recommend to monitor in my process?
This is dependent on what type of manufacturing process you have.
Semiconductor industry:
Hard Disk Drive manufacturing:
How many manifolds do I need?
A single Lighthouse AMC Manifold can monitor up to 64 sampling locations and can collect data from up to 10 different sensors, all at the same time, depending on the types of sensors used and their output signal. Please contact your Lighthouse sales representative for details of how to integrate your specific sensors into the Lighthouse AMC Manifold system.
Often the selection of a particle counter for use in a cleanroom is done based upon the specifications and cost of the instrument.
Before getting into the details of the specifications it is important to look at what the instrument will be used for, the environments it will be used in, and who will be using the instrument. Without this information taken into consideration, a less then optimal choice of particle counter for the application could be made. Here are some items to consider prior to selecting a particle counter:
What type of environment will the particle counter be used in? Will it be used in an ISO Class 3 Cleanroom for routine particle counting or will it be used for verifying a flow bench is operating prior to a critical process?
What type of data is the particle counter expected to collect? Will this information be recorded as simple pass/fail or will the information have to be logged into a spreadsheet or database?
Will the operator be carrying the particle counter around and placing it on a critical work surface or will it be cart mounted?
Will this particle counter be used to certify cleanrooms and travel from location to location?
Will the particle counter be used to monitor the cleanroom on a continuous basis? Is the particle counter intended to interface with a Facility Monitoring System (FMS)?
Specifications:
Though all manufacturers use the same principle, the details of the design are what set one manufacturer apart from the rest. Things like sample flow rate, sensitivity, size range and number of counting channels, durability of the laser or laser diode, lifetime of the light source, the ability to hold calibration all are important factors to consider.
Sensitivity: The smallest size particle that can be detected.
Zero Count Level or False Count Rate: The number of falsely reported particles using filtered air at the optimum flow rate for a given amount of time. The correct reporting of this is number of particles per 5 minutes. (Expected Zero Count rate should be less then 1 count per 5 minutes)
Counting Efficiency: The ratio of the measured particle concentration to the true particle concentration. The true particle concentration is measured with a more sensitive instrument that has a counting efficiency of 100% at the minimum particle size of the instrument under test. A properly designed instrument should have a 50% counting efficiency.
Channels: This is the number of “bins” the particles are placed in based upon the respective size of each particle counted. Channels are represented in microns. For example, you may have a particle counter with 4 channels. This means that the particles can be counted and binned in 4 different channels. Examples of channels are: 0.1 µm , 0.2 µm , 0.3 µm, 0.5 µm , 1.0 µm , 5.0 µm .
Flow Rate: This is the amount of air that passes through the particle counter. This is typically represented in cubic feet per minute. Common flow rates are 1.0 cfm and 0.1cfm. The greater the flow rate, the larger the pump to pull the air and the bigger the particle counter.
All too often minimum size is chosen over the other criteria. Though this is an important consideration, other parameters should also be considered.
Typically the more sensitive instrument, the higher the initial investment, and the higher the maintenance cost. If the instrument is used in environments with extremely high concentration of particles, it may require frequent cleanings by service technicians.
By understanding the intended use of the particle counter and the specifications, a more educated decision can be made when selecting a particle counter.
Liquid particle counters are important tools used in various industries to measure and monitor the concentration and size distribution of particles in liquid samples. These particles can be contaminants or impurities that can affect the quality of the product or the efficiency of the manufacturing process. Liquid particle counters can be used in industries such as pharmaceuticals, biotechnology, food and beverage, semiconductor, and water treatment.
The importance of liquid particle counters lies in their ability to provide accurate and reliable measurements of particle size and concentration in liquid samples. This information is critical for quality control, process optimization, and troubleshooting in manufacturing processes. Liquid particle counters can help identify potential problems early on, reducing the risk of product recalls, equipment failures, and costly downtime.
To choose the best liquid particle counter, you should consider several factors such as the size range of particles you need to measure, the concentration of particles in your sample, the type of liquid you are testing, the required sensitivity and accuracy of the instrument, and the level of automation and ease of use. You should also consider the cost of the instrument, maintenance requirements, and the level of technical support provided by the manufacturer.
Some key features to look for when selecting a liquid particle counter include:
Particle size range and detection limit: ensure that the instrument can detect the size range of particles you need to measure, and that it has a low enough detection limit to accurately measure the concentration of particles in your sample.
Sample volume and flow rate: make sure the instrument can handle the volume and flow rate of your sample, and that it can provide accurate measurements over the entire sample volume.
Instrument sensitivity and accuracy: choose an instrument with high sensitivity and accuracy to ensure reliable and consistent measurements.
Automation and ease of use: look for an instrument that is easy to use and provides automated features such as self-cleaning, data storage, and report generation.
Maintenance requirements and technical support: consider the cost and frequency of maintenance required, and the level of technical support provided by the manufacturer.
Overall, choosing the best liquid particle counter depends on your specific needs and requirements. It is important to carefully evaluate different options and consult with experts to ensure you select an instrument that will provide reliable and accurate measurements for your application.
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