Frequently asked questions

1. The zero count filter aka purge filter is used to two reasons.
   • To establish that your instrument can count zeros so you are assured that you are starting with a precision base line.
   • To purge clean a contaminated sensor.

Lighthouse particle counters count the stated particle size and the between sizes up to the next larger size while in differential mode.  In Cumulative mode your instrument will count from the stated size along with all larger particles.  

The touch screen needs to be aligned. Refer to the operating manual to align the touch screen.

No, the SOLAIR Particle Counter cannot be directly connected to an external printer. In order print to an external printer, connect the Solair to the PC with the supplied patch. Use LMS XChange or LMS Express (Free Version) to down the collected data from the SOLAIR into the PC. After data is downloaded, save it as a MS Excel file. Open MS Excel and print the saved data file.

Yes, use LMS XChange or LMS Express (Free Version) and go to “setup my location” to name locations then upload location names to your Hand Held.

(Applies to all Lighthouse Portable Particle Counters)

Connect the Hand Held to the PC with the supplied patch cord (RJ45 to USB cable). Use LMS XChange or LMS Express (Free Version) to download the collected data from the Hand Held into the PC. After data is downloaded, it can be saved as a MS Excel file.

No, all Remote P particle counters communicate via Modbus RS485, RS232, and Modbus TCP (Ethernet).

An Administrator to the software must log in and re-enable your account.

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.

A Building Management System (BMS) also known as a building automation system (BAS) is a computer-based control system installed in buildings that controls and monitors the building’s mechanical and electrical equipment such as ventilation, lighting, power systems, fire systems, and security systems.

The Lighthouse Monitoring System (LMS) provides a single point of configuration and data analysis. It offers the capability to view graphs, charts, maps, SPC, system status, sensor status, and more. Each of these can be customized and displayed simultaneously. The LMS provides superior data collection reliability by providing redundant data collection engines, redundant data storage and data viewing. The LMS system can monitor Particle, Temperature/Relative Humidity, Differential Pressure, CO2, and many other environmental sensors related to your cleanroom environment.

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:

• Ammonia 
• NMP 
• Total Amines 
• Total Acids 
• Total Sulfur 
• H2S 
• HF 
• HCL

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:

• Target chemical 
• Detection limits 
• Dynamic range 
• Response time 
• Zero and span drift 
• Potential interference 
• Portable or online use 
• Heat up times 
• Calibration method and frequency 
• 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 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: 

• Photo lithography 
• Metals 
• Etch 
• Copper Process Areas 
• Photomask Manufacturing

Hard Disk Drive manufacturing: 

• Wafer Operations 
• HGA/HSA Operations 
• Final Drive Assembly 
• Media

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.

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:

1. Light Source (Gas Based Laser, Solid State Laser Diode, High Intensity Light)
2. Photo Detection Electronics
3. Sample Flow System
4. Counting Electronics

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.

• Determine critical locations (locations where contamination can have an effect on the product or a large number of products)
• Determine busy locations (locations where the product is moving or being manufactured).
• 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.
• 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 system is to keep the facility running between a given set of parameters. Data inside the control limits is often not recorded. The facility group’s primary responsibility is to keep the facility running within the set-points, by maintaining and repairing utilities. Contamination monitoring is more of a primary function of a quality, engineering or contamination control group. Sensing points are placed with a different intent for the data.

Often we will integrate our LMS system to a building control system (BCS), in fact we encourage our customers to do so. Integrating this data (either uni-directional or bi-directional) to and from a BCS will increase the number of monitoring points on both systems giving the customer a better perspective of what is going on in the controlled environment.

What is the difference between a control system and monitoring system?

The main differences between these systems are the architecture and principles for which they serve. The building control system is designed and installed with the critical parameters of the facility in mind. The sensors for that system are installed and provide feedback allowing for automatic compensation for out-of-spec events. A monitoring system is geared toward monitoring the process and product level of information. The two systems may share some overlap in the general environment, but both are very necessary for tuning your process. Without the process level of monitoring, you will not be able to detect changes in process environment due to factors contributing from personnel, or equipment.

When or where should I use a discrete based particle counter system vs. a manifold type?

Both systems have their place and usefulness. A discrete based or remote particle counter system gives great resolution without missing any data. The cost per point is more expensive than a manifold system, but has a better chance to catch intermittent particle excursions. A manifold sampling system is much more cost efficient, but sacrifices resolution due to the time it takes to rotate one complete revolution on the manifold. The more manifold points you add to the manifold, the longer it takes to complete one cycle, and it is possible to miss events while sampling other locations.

When evaluating your process to determine whether a discrete sensor or manifold system should be used consider the following things:

• How many points do you want to monitor?
• What is your budget?
• What is the longest duration that you can have without information at that location?
• Is there a cycle time on the tool that you’re concerned about capturing? (Automation, process or cleaning cycles)
• Is this a critical location in your process?
• Are there considerable product volumes at this location?
• Who do you have to report this data to?

In short, if the maximum time of one complete sampling cycle on your manifold exceeds your maximum duration you can have without data from a single point you should try to use a discrete sensor for that location. In many cases, Lighthouse will recommend a hybrid of systems, or both a manifold and discrete system working together. The manifold system for non-critical, or lesser critical locations, and discrete sensors for more critical parts of the process. This will allow excellent coverage and data, and still be cost effective. Please see our Tech Papers section on this website “Continuous Particle Monitoring: An Evaluation of Real-time Versus Sequential Sampling Particle Monitoring Systems.”

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:

• Air or liquid borne particles
• Gas phase or airborne molecular contamination
• Electrostatic charge or electrostatic discharge
• Electromagnetic interference
• Fluctuations of cleanroom or minienvironment differential pressure
• Fluctuations of cleanroom temperature & relative humidity
• Vibration
• Surface particles
• Air changes

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