Q1. What is Contamination ?
People often think of contamination as particles, dust, dirt or some type of chemical residue. Lighthouse looks at contamination per the Institute of Environmental Sciences and Technology (IEST) definition: “Any foreign material or energy that has a detrimental effect on product or process.”
Examples could be:
a. Air or liquid borne particles
b. Gas phase or airborne molecular contamination
c. Electrostatic charge or electrostatic discharge
d. Electromagnetic interference
e. Fluctuations of cleanroom or minienvironment differential pressure
f. Fluctuations of cleanroom temperature & relative humidity
h. Surface particles
i. Air changes
Q2. Why Real-time Monotoring ?
Why do I need to monitor the state of my cleanroom?
There are two main reasons why you would monitor your cleanroom. One is to verify that your process environment is performing at the required specifications. The other is to document historical data of the process environment. Cleanrooms are built to the specific requirements of the products to be built. Contamination has a negative effect on yield and quality of these products. The cleanroom environment is very dynamic with products and personnel moving and changing, thus contamination events can happen at any time. Monitoring will enable you to know when the environment is not safe for building the products at any time. The ability to recall historical data is a very valuable tool to have. Trend charts, and records of events can help define maintenance cycles of equipment and cleaning. In addition, post mortem analysis is simplified when referring to this data. These reports will serve as records that can be used to present supporting data to customers, government organizations, and regulatory committees.
Can’t I just hire some people to go around to each room once a day and measure the cleanliness of each area?
Historically most companies started out that way, but companies learned that determining the level of particles in a room is not as simple as taking one single reading. Particulate levels must be measured at multiple locations throughout the cleanroom wherever product is exposed. Cases where measurements have been taken near HEPA or ULPA filters may show low particle levels, and yet at the product level work surface particulate levels may be unacceptable, causing product defects and lowering yield. Cleanroom processes are dynamic. Particle shedding events are rarely predictable, and can happen at random times throughout the day. Monitoring this environment on a continuous automated basis will help to catch these types of issues before they get out of control or affect production. Millions of dollars worth of products can pass through a cleanroom on a daily basis depending on the type of facility. Finding out about a contamination problem a day or two late could be an expensive and/or catastrophic situation. In most cases, the Return of Investment (ROI) on the contamination monitoring equipment and the system can be achieved during the first few detected events.
How can I effectively monitor my cleanrooms?
First you have to identify what the risks are for your product and process. Also, you need to understand the design intention of the cleanroom. This is necessary, as you would want to choose the right instrument for the application. A class 10,000 (ISO Class 7) cleanroom would not be monitored effectively with a 0.1 micron. Using a 0.3 or 0.5 particle counter would be a better choice.
a. Determine critical locations (locations where contamination can have an effect on the product or a large number of products)
b. Determine busy locations (locations where the product is moving or being manufactured).
c. Make an assessment of the cleanroom particle data during the operational state. Collecting data in the operational state (when manufacturing is actually occurring) is important to determine the locations where you are at risk.
d. A contamination monitoring system will be able to track, record and alarm when out of control limits are reached and/or exceeded.
What size particles do I need to monitor for?
This is determined by your product or your process. Other factors such as coverage and budget come into play. The smallest size particle that could possibly affect your product or smaller is a good place to start. However budgets and coverage of the whole process must be taken into consideration as well. Keep an important factor in mind. Particle shedding events occur at more than one particle size. Having one particle sensor in a cleanroom with 0.1 micron or lower resolution vs. having ten particle sensors with 0.3 micron resolution in the same cleanroom may not be a better situation. You must look at what is going on and what the risks are. Sometimes, many less sensitive sensors are better than a few or one of the more sensitive sensors.
How do I determine the number of airborne particle sample points that I need to monitor in my cleanroom, and where should I locate them?
The location and number of monitoring points is primarily dictated by the requirements of the product and the production process as well as understanding how the system will be used. Please refer to the Tech Papers section on this website to download “Justifying a Continuous Contamination Monitoring System”.
How do I justify the expense of an Automated Monitoring System?
Please see our Tech Papers section on this website for “Justifying a Continuous Contamination Monitoring System.”
Why can’t I use my building automation or facility control system for monitoring my cleanroom?
Many customers of ours have asked this question, and from a technical standpoint, it is possible to do so. There are several reasons for not integrating solely to the building control system. The primary responsibility of a control
Q3. How Does a Particle Counter Work ?
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:
a. Light Source (Gas Based Laser, Solid State Laser Diode, High Intensity Light)
b. Photo Detection Electronics
c. Sample Flow System
d. Counting Electronics
Q4. How to Select a Particle Counter?
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)?
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.
Q5. What is Airborne Molecular Contamination?
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:
a. Corrosion of metal surfaces on the wafer
b. Degradation of HEPA/ULPA filter media
c. Haze on wafers
d. Haze on optics
e. Topping of chemically amplified photoresist
f. 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:
c. Total Amines
d. Total Acids
e. Total Sulfur
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.
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.
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.
First for the sampling system, the unit requires very little maintenance. The vacuum pumps will need to be maintained on a quarterly basis.
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 outside 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:
a. Target chemical
b. Detection limits
c. Dynamic range
d. Response time
e. Zero and span drift
f. Potential interference
g. Portable or online use
h. Heat up times
i. Calibration method and frequency
j. Operation cost
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 than 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.
a. 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.
b. 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.
c. 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.
a. Different analysis techniques will tend to produce slightly different results. Some techniques are more prone to interference and thus can show drastically different results.
b. 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.
a. Semiconductor industry:
- Photo lithography
- Copper Process Areas
- Photo-mask Manufacturing
b. Hard Disk Drive manufacturing:
- Wafer Operations
- HGA/HSA Operations
- Final Drive Assembly
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.
Q6. Why Lighthouse?
We regard our customers as business partners. Working in close partnership with our customers, we have arrived at systems and solutions that have revolutionized the approach, concepts, and results of the monitoring industry. Together, we have reengineered the industry, driving our suppliers and competitors to continually improve.
Lighthouse has grown to be an integral part of our customers’ manufacturing process. We are on a quest to improve yields by providing state-of-the-art technology. We have learned that Lighthouse and our customers all benefit from one another.
Lighthouse Worldwide Solutions truly is worldwide. We have performed hundreds of installations around the globe, servicing industries ranging from semiconductors and disk drive manufacture to aerospace and pharmaceuticals. Lighthouse customers include: Western Digital, Seagate, Applied Materials, Fujitsu, Hewlett-Packard, Hitachi, Hyundai, IBM, Komag, Lockheed Martin, Los Alamos National Laboratories, LSI, MEMC, Motorola, National/Panasonic, Quantum, Raytheon, Samsung, Sharp, Texas Instruments, TSMC, USC, VLSI, Xerox and many, many more…
Lighthouse Direct Offices
Lighthouse is committed to providing local offices in each of the regions where our customers do business. Direct sales, service, installation, and project management allow our customers to have a direct connection with the Lighthouse Team. We now have offices in California, Singapore, Taiwan, Philippines, Thailand, two in Malaysia, two in China, and most recently, we have added an office in Holland. Our strategy of establishing close regional contacts has proven very successful for Lighthouse and our customers over the years. Maintaining and expanding those contacts will remain a crucial part of our corporate strategy for success.
The Lighthouse Installation Team provides quality installations and system expansions. Our skilled professionals include project managers and installation crews worldwide, who make the installation of a Lighthouse system as seamless as possible. We provide the best quality installations in the industry. Our quality work, attention to detail, efficiency, and creativity to adapt to your needs are proven.
a. The Lighthouse project managers work with all internal departments, including sales, purchasing, manufacturing, engineering and upper management. The focus and hard work of a project manager begins when we receive the purchase order and continues to the end of the project.
b. Lighthouse provides a complete specification of our customer’s installation. Our project managers work with the customer every step of the way to answer questions and address concerns.
c. Lighthouse works with our customers on sensor locations, sensor naming, system configuration, and layout.
d. The Lighthouse project management team makes every installation a great success.
e. Lighthouse provides neat, clean, and organized cable/tubing installations.
f. The Lighthouse installation teams are skilled in the installation of a wide variety of sensors, including environmental, gas, liquid, etc.
g. Our installation teams have high standards of quality and craftsmanship. We strive to make each installation a showcase for our customers.
All Lighthouse installations undergo a rigorous data validation, quality, and system integrity check.
Lighthouse Service Team
The Lighthouse Service Team provides the best resources and expertise available. We are constantly receiving letters of praise from our customers thanking us for meeting and exceeding their needs.
Lighthouse has tailored a preventive maintenance program to maintain and extend the life of our system. This program includes the following:
a. All sensors and sensing points are manually inspected to ensure that each sensor is operating properly.
b. All nodes and data collection devices are manually inspected to ensure performance and operation of hardware.
c. All vacuum pumps are manually inspected to verify their condition.
d. Key data collection devices are checked for viruses, disk fragmentation and disk surface defects.
e. System backups are provided and data archived.
f. Performance is maximized through a cleanup of all files and a system integrity test.
g. All data collected is validated.
h. A Lighthouse Monitoring System Health Report is completed, including:
i. Locations of all devices
ii. Calibration due dates for all devices and sensors on the system
iii. Conditions of the vacuum pumps
iv. Suggestions for all concerns, problems, and expansion ideas