VPD-ICPMS vs TXRF

VPD-ICPMS vs TXRF

There is a bit of a battle in the analytical arena when it comes to the best method for measuring trace contaminants on the surface of a silicon wafer.  We described the analysis of trace metals on silicon wafers by Vapor Phase Decomposition – Inductively Coupled Plasma Mass Spectroscopy (VPD-ICPMS) in a previous blog post.  TXRF or Total Reflection X-Ray Fluorescence is another technique that is often used in semiconductor manufacturing to monitor contamination.  Where VPD-ICPMS collects the contaminants in a droplet that is then analyzed by mass spectroscopy, the TXRF instrument uses an x-ray beam to excite the wafer surface.   Elements fluoresce after being excited, the fluorescence is then measured to determine what elements are present and in what amounts.  There is considerable overlap between the two techniques, but each has its own unique features.

VPD-ICPMS on one hand is a very well-defined process and provides analysis of the top surface of the wafer, about 20 Angstroms.  Whereas TXRF is more versatile and can be used on different wafer surfaces.  Below is a comparison of the two techniques.

VPD-ICPMS TXRF
Contaminants from the entire wafer surface are collected and analyzed. Only the area excited by the X-Ray beam (~2cm spot) is analyzed.  To do the entire wafer multiple spots are required e.g., a 300 mm wafer will need 350 spot analyses to cover the full surface of the wafer.
Results are cumulative for the wafer surface, no spatial information is available. TXRF can produce maps showing the impurity distribution on the wafer surface.
10-100X greater sensitivity.
Detects light elements like Li, Na and Mg where TXRF cannot. Detects non-metals like Cl, and Ar where VPD-ICPMS cannot.
Considered destructive analysis Non-destructive analysis.
Wafer can only be analyzed 1x. Wafer can be reanalyzed as needed.
Analyzes ~20 Angstroms or thickness of oxide film. X-Ray beam penetrates ~ 500 Angstroms.
Can only analyze bare Si or Si with SiO2 films. Will analyze oxide and any amorphous or crystalline film beneath it.

VPD-ICPMS and TXRF use very different methods to analyze for contamination on wafer surfaces.  These different mechanisms however provide certain benefits for each.  In fact, chemists and engineers realized the advantages and now many semiconductor fabrication facilities use an integrated VPD-TXRF system to monitor contamination.

Frequently Asked Questions Regarding Vapor Phase Decomposition Inductively Coupled Mass Spectroscopy

Frequently Asked Questions Regarding Vapor Phase Decomposition Inductively Coupled Mass Spectroscopy

You’re an expert in your industry, but not the specifics and niche fields of all the science related to it. Nowhere is this more evident than when it comes to Vapor Phase Decomposition Inductively Coupled Mass Spectroscopy. If you’ve been wanting to learn a little more about it, Cerium Labs can answer all your questions! Not only can we tell you all about it, but we can also perform it for you too. Before we get more into exactly what services we can do for you, let’s go over all the details and answer the specific questions you have relating to Vapor Phase Decomposition Inductively Coupled Mass Spectroscopy. 

What does VPD-ICPMS stand for?

In the industry, Vapor Phase Decomposition Inductively Coupled Mass Spectroscopy is abbreviated to VPD-ICPMS. 

How do you prepare to begin the process?

It all starts with the vapor phase decomposition sample preparation technique. During this process, trace elements on the surface of a silicon wafer are collected into a liquid sample to be analyzed by HR-ICP-MS. The silicon wafer is exposed to hydrofluoric acid vapor in a sealed chilling chamber. The hydrofluoric acid vapor forms a condensate on the chilled wafer surface. 

What is the size of the silicon wafer?

The silicon wafer can be 150, 200, or 300 mm. 

Why are you looking for the condensate?

This condensate etches the oxide layer off of the wafer surface along with any trace metals that are present. These trace metals are exactly what we’re looking for, because they hold the answers to the questions you are asking. The condensate is then collected by rolling a drop of scan solution across the surface of the wafer. 

What scan solution do you use?

The scan solution is almost always a dilute mixture of hydrogen peroxide, nitric acid, and hydrofluoric acid. The drop is transferred from the wafer surface into a clean sample vial. 

What is this method capable of measuring?

The liquid sample is analyzed for trace metals using HR-ICP-MS. The VPD technique is capable of measuring metallic contaminants at concentrations ranging from 1E6 to 1E14 atoms/cm2. 

What elements are measured?

This is particularly useful in measuring light elements on bare silicon or in hydrofluoric acid soluble thin films. The most popular light elements that can be measured this way include lithium, beryllium, boron, sodium, magnesium, and aluminum.

What instrument is used?

Cerium Labs has the instruments, knowledge, and industry experts to do this job the right way. The specific instrument we use is a gemetec automated VPD prep tool. This is a special production tool for online monitoring of metal contamination on semiconductor wafers with ultra-low detection limits.

You can trust our processes, which means you can trust our results too. Do you have any further questions? Reach out to us today to learn more about what our scientists can do for you! Call us at (866) 770-7752 or email sales@ceriumlabs.com to get started.

Understanding Vapor Phase Decomposition Inductively Coupled Mass Spectroscopy

Understanding Vapor Phase Decomposition Inductively Coupled Mass Spectroscopy

In the industry, Vapor Phase Decomposition Inductively Coupled Mass Spectroscopy is abbreviated to VPD-ICPMS. If you’ve been wanting to learn a little more about it, Cerium Labs is happy to help! Not only can we tell you all about Vapor Phase Decomposition Inductively Coupled Mass Spectroscopy but we can also perform the service for companies who need it professionally done as well. Before we get more into exactly what we can do for you, let’s go over the details of Vapor Phase Decomposition Inductively Coupled Mass Spectroscopy more specifically. 

It all starts with the vapor phase decomposition sample preparation technique. During this process, trace elements on the surface of a silicon wafer are collected into a liquid sample to be analyzed by HR-ICP-MS. The silicon wafer, which can be 150, 200, or 300 mm, is exposed to hydrofluoric acid vapor in a sealed chilling chamber. The hydrofluoric acid vapor forms a condensate on the chilled wafer surface. This condensate etches the oxide layer off of the wafer surface along with any trace metals that are present. These trace metals are exactly what we’re looking for, because they hold the answers to the questions you are asking.

After this step, the condensate is then collected by rolling a drop of scan solution across the surface of the wafer. The scan solution is almost always a dilute mixture of hydrogen peroxide, nitric acid, and hydrofluoric acid. It’s just a tiny drop, so don’t worry! The drop is transferred from the wafer surface into a clean sample vial. 

Lastly, the liquid sample is then analyzed for trace metals using HR-ICP-MS. The VPD technique is capable of measuring metallic contaminants at concentrations ranging from 1E6 to 1E14 atoms/cm2. It is particularly useful in measuring light elements on bare silicon or in hydrofluoric acid soluble thin films. The most popular light elements that can be measured this way include lithium, beryllium, boron, sodium, magnesium, and aluminum.

Even if you wanted to, this isn’t something you can do on your own. If nothing else, you probably don’t have a gemetec automated VPD prep tool needed to perform the procedure! That’s okay, because Cerium Labs has the instruments, knowledge, and industry experts to do this job the right way. You can trust our processes, which means you can trust our results too. 

We offer an extensive array of material analysis techniques including surface science, trace metal testing, electron imaging, mass spectroscopy, as well as chemical analysis. Our team solves problems for some of the world’s leading companies, including semiconductors, pharmaceuticals, medical devices, alternative energy manufacturers, and many more. Do you think we can help you? We do too! Reach out to us today to learn more about what our scientists can do for you! Call us at (866) 770-7752 or email sales@ceriumlabs.com to get started.

What’s in the water – analytical chemistry helps everyone

What’s in the water – analytical chemistry helps everyone

Analytical chemistry of water

What do you think of when you hear the term “Inductively Coupled Plasma Mass Spectroscopy”?  A CSI episode? College Chemistry? Or maybe nothing at all? Most likely you are not familiar with Inductively Coupled Plasma Mass Spectroscopy or ICPMS for short.  But one type of analysis performed with ICPMS is highly relevant to our health and safety and that is the analysis of metals in water.

While you may not have heard of ICPMS, you probably have heard of lead, the soft, malleable silvery gray metal.  Lead poisoning has been documented for centuries but not until the early 1970’s did the US government start to regulate lead to reduce its effect on the environment and wildlife.  In the last few decades regulations for cleaner gasoline, use of lead-free plumbing and paints and many other products have greatly reduced the problem, but not completely. This is because in many cases, old infrastructure is still in use, older buildings are being gentrified and antique items with the original lead-based paints are now chic. These are just some of the ways lead could be ingested or leak into the water supply.

Science tells us that even low-level lead exposure can cause neurological and cardiovascular disease, infertility, and decreased kidney function. Higher than healthy amounts of lead have been linked to learning and behavioral problems, lower IQ, and other health issues in young children. These adverse health effects can last a lifetime! This is why health experts agree that any level of lead in one’s blood, no matter how small, is cause for concern. This is where Inductively Coupled Plasma Mass Spectroscopy can help. ICPMS can measure lead at extremely low levels in water, soil, or other materials like paint.

The ICPMS technique can measure a long list of metallic contaminants in the part per trillion concentration range.  To visualize how minute this is, think of 1 drop of water in 10,000,000 gallons of water!  An Olympic size swimming pool holds 660,000 gallons of water so 1 part per trillion is 1 drop in about 15 full Olympic size pools.  Furthermore, some elements, Pb included, can be measured in the parts per quadrillion range!

You cannot taste, see, or smell low levels lead in the water, which makes it pretty scary.  But knowing that scientists have a method of “seeing” it should make us all feel a little safer.  With the help of a professional lab you can be sure your house, soil, child’s toy or grandma’s antique armoire are not sources of lead in your home.  Inductively Coupled Plasma Mass Spectroscopy is actually highly relevant to protecting ourselves and our children’s health!

Necessity of Using VPD-ICPMS Technique in Semiconductor manufacturing

Necessity of Using VPD-ICPMS Technique in Semiconductor manufacturing

Implementing smaller device dimensions requires cleaner chemicals and, more importantly, cleaner production processes.  One example of a potential contamination source is polymeric seals often found in process chambers.  Over time, in aggressive environments such as plasmas, these materials can break down and release metals that can become incorporated in the product processed in that chamber.  Low levels of metals such as Na, K, Li, Cu, Zn, Fe, and Ti, can alter the electrical characteristics and affect long term reliability of semiconductor devices.  Here at Cerium Labs, we regularly use a technique called Vapor Phase Decomposition Inductively Coupled Plasma Mass Spectroscopy (VPD-ICPMS) to measure the trace metals on silicon wafers and identify the source of contamination.

The 3 process steps are:

Step 1: Vapor phase decomposition

Step 2: Wafer surface impurity collection using a scanning solution

Step 3: Analysis by ICP-MS

The procedure starts with the vapor phase decomposition sample preparation technique, by which trace metals on the surface of a silicon wafer are released so that they can be collected. The silicon wafer (from 75 up to 300 mm) is exposed to hydrofluoric acid vapor in a sealed chilling chamber. The hydrofluoric acid vapor forms a condensate on the chilled wafer surface. This condensate etches the surface silicon dioxide layer on the wafer surface along with any metals that are present.

After this, the condensate is collected by carefully scanning the entire wafer surface with a droplet of ultra-pure scanning solution.  This solution is typically a dilute mixture of hydrogen peroxide, nitric acid, and hydrofluoric acid. The scanning process is done by either our automated scanning system or manually by a certified chemist. The droplet is then transferred from the wafer surface into a clean sample vial. Once the droplet is collected, it is diluted and analyzed on the ICPMS.

Our VPD-ICPMS technique is capable of measuring metallic contaminants at concentrations ranging from 1E6 to 1E14 atoms/cm2.  It is particularly useful in measuring light elements on bare silicon or in hydrofluoric acid soluble thin films where TXRF analysis falls short.

The advantages of using this procedure are numerous in semiconductor manufacturing. Metal contamination comes from numerous sources and can lead to catastrophic failures and loss.  VPD-ICPMS and Cerium Laboratories can help you identify the source and improve your wafer yield.

What is Gas Chromatography-Mass Spectrometry (GC-MS)?

What is Gas Chromatography-Mass Spectrometry (GC-MS)?

Analyzing small and volatile molecules is made not only possible but simple with Gas chromatography-Mass Spectrometry (GC-MS). GC-MS is the separation technique of choice for smaller volatile and semi-volatile organic molecules such as hydrocarbons, alcohols, and aromatics, as well as pesticides, steroids, fatty acids, and hormones. When GC is combined with the detection power of mass spectrometry (MS), the process can be used to separate complex mixtures, quantify analytes, identify unknown peaks, and determine trace levels of contamination.

This technique can detect picogram quantities of material. Automated Thermal Desorption (ATD) GC-MS is a powerful tool for identifying organic contaminants. These may be present as an adsorbed film on silicon wafers, as airborne vapors in the manufacturing environment, as dissolved components in ultrapure water or process chemicals, or as vapors that outgas from plastics, coatings, garments, o-rings, and similar materials.

GC-MS can be used to study liquid, gas, or solid samples. How does it all work? Well, tell you! It all begins with the gas chromatograph. It is here that the sample is effectively vaporized into the gas phase and separated into its various components using a capillary column coated with a stationary, solid, or liquid, phase. The compounds are then propelled by an inert carrier gas. This is typically nitrogen, helium, or hydrogen. As components of the mixture are separated, each compound elutes from the column at a different time based on its boiling point and polarity.

The time of this elution is referred to as a compound retention time. Once the components leave the GC column, they are ionized and fragmented by the mass spectrometer. This is done using electron or chemical ionization sources. These molecules and fragments, now ionized, are accelerated through the instrument’s mass analyzer. This is most often a quadrupole or ion trap, but not always. Here, the ions are separated based on their different mass-to-charge (m/z) ratios. This type of data acquisition can be performed in either full scan mode, to cover either a wide range of m/z ratios, or selected ion monitoring (SIM) mode. A second option is to gather data for specific masses of interest.

The process is nearly complete! The final steps of the GC-MS process involve ion detection and analysis, with fragmented ions appearing as a function of their m/z ratios. These peak areas are proportional to the quantity of the corresponding compound. When a complex sample is separated by GC-MS, it will produce many different peaks in the gas chromatogram and each peak generates a unique mass spectrum used for compound identification. Thankfully, there are extensive commercially available libraries of mass spectra available to scientists across the world. Using this great resource, unknown compounds and target analytes can be identified and quantified.

This method has the capacity to resolve complex mixtures or sample extracts containing hundreds of compounds. Wow! If you need AFM, Cerium Labs is here to help! We have experts in Gas Chromatography-Mass Spectrometry (GC-MS) here in-house, ready to get to work for you and your project!