FAQ's
Please find below a list of frequently asked questions. If there is a query that you have and is not found below please feel free to contact us.
- Technical Support
How long will the laser last?
Can I extend the warranty?
What support do I get?
Is there a warranty?
What does the warranty cover?
Generally -10,000 hours
Yes – Contact ORS Ltd for details
Unlimited telephone and email support – Other support packages are available. Contact ORS Ltd for a quote.
Yes - 12 months return to base warranty.
Failure of components not due to damage from misuse.
- Products
What products do ORS make?
Production Reflectometers, pyrometers, wafer curvature monitors and analysis software. Custom sensors to your specification and post growth wafer imaging systems.
- Installation and Setup
Is it easy to set-up?
Is installation included?
Yes – A full installation manual will be provided.
No – Installation is designed to be simple. However, we are happy to install if you need our support. Contact ORS Ltd for a quote.
- Software Packages
Do I get free upgrades to the software?
Will it export to word/excel?
How many licences can I have?
Will R-Fit work with other reflectometers?
What is better about R-Fit to competitors’ software?
What information does R-fit give me?
How will R-Fit LIVE help me make more wafers?
How live is R-Fit LIVE?
What are the benefits of R-Fit LIVE over R-Fit v4?
What is the difference between R-fit v4 and R-Fit LIVE?
Standard upgrades will be provided if you are an existing customer. Additional functionality may be charged.
Excel/Access/any CSV reader
As many as you like.
Yes – Subject to correct output of data.
We use a ‘matrix’ approach to the maths which has no approximations in it. They use the virtual interface approach. They use look up tables, we don’t, we calculate everything. We can cope with any number of layers of any thickness (from about 20 Å) upwards.
Both packages give you information on; • Growth rate • Thickness • Surface roughness • Run to run reproducibility • R-Fit v4.0 also gives you information on; • Refractive index.
It helps you improve your efficiency by flagging up any problem you are having very early on in the growth. It allows you to calibrate your reactor immediately before you start the structure thereby allowing you to correct the recipe and hence more of your wafers will be within specification. Because R-Fit LIVE provides real time information, then it can be used for closed-loop feedback control.
Within 0.25s of the layer going down you have the information.
Real time, instant results and information on which you can act. It will also give you information on which wafers in a multi-wafer reactor are growing on spec and which are not; this can be due to simple things like the wafer has not seated correctly in its pocket. R-Fit LIVE is for production whereas R-Fit v4 covers both production and research.
R-Fit LIVE requires the refractive index to be input, then it automatically fits the incoming data to provide rate and roughness. R-Fit v4 cannot provide data in real time, but does not need an accurate value of refractive index to be put in. Both have to have ranges of values for the rate and the roughness in order to work.
- Specifications
What wavelength are the lasers at?
What is the minimum radius of curvature of your wafer bow?
Typically; UV – 375nm Blue – 405nm, 445nm, 473nm, Red – 635nm, 650nm, 670nm, Green – 532nm IR – 780nm, 805nm, 850nm, 905nm, 950nm, 980nm, 1064nm, 1310nm and 1550nm.
100m – Changes of around a micron can be seen.
- Technical Background
How do I know it is always measuring the same point?
How do you overcome the ambient light affecting the data?
If the area was bigger would it not give me more data?
Over what area can it see the growth?
Will the laser affect the growth?
Why don’t you use white light and filter out the wavelength you are interested in?
I grow homo-epitaxial materials (GaAs on GaAs). Will it still work?
I grow the weirdest material in the world. Will it still work?
My growth rate is 500nm per second. Will it work?
I grow on a transparent material. Will it still work?
Do I need a different instrument for MOVCD & MBE and if so why?
What are the differences between MOCVD and MBE?
Why hasn’t everybody already got in-situ monitoring?
Why do I need in situ monitoring?
Can the pyrometer temperature go lower/higher? Why?
Why is it important to correct emissivity?
What is emissivity?
How does the pyrometer work?
Why are these standard wavelengths?
What if I don’t have any windows on my reactor?
What makes ORS solutions better than their competitors?
How do ORS’ reflectometers work?
What is the difference between a reflectometer and an interferometer?
The instrument is designed to make a reading at a specific time after it senses the homing pulse. Therefore, you are sure to be hitting the same spot at each rotation of your susceptor.
For reflectometry this is not a problem unless the heating is via IR lamps (even then we can introduce a narrow band pass filter to remove its effects). Our emissivity corrected pyrometry has been designed with special optics to be insensitive to such thing as Knudsen cells.
No, it would give you more averaged data; not necessarily a good thing. The spot size is keep small to allow the beam to pass into the reactor and come out again without hitting something you don’t want it to.
Over the area of the laser beam, roughly a circle of diameter about 2mm (so roughly 3 – 4 mm²) – It is possible to profile across a wafer so you are able to see more area if required.
Not normally due to the low intensity of our laser diodes and the fact that they are modulated so spend some of their time off. This can be an issue with some II-VI materials but not for III-V and group IV materials.
The intensity will be very low compared to a laser. This means the noise will be high and so there will be considerable uncertainty in the results. It is also more difficult to focus a white light beam (so a problem for MBE) and more difficult to control the stability of the light (so noise again becomes an issue). Extracting accurate reflectance data at sufficiently narrow wavelength bandwidth can also be a problem, leading to errors in the analysis of growth rate and thickness.
No – As there is no difference in refractive index between the substrate and the deposited material - unless you dope your materials
Provided the material is transparent to al least one of the laser wavelengths we use, then yes. As an example, it is possible to monitor thin layers of gold or other metals (thin is less than about 200-300Å).
It depends on other factors too; if you are growing on a single wafer which is under the EpiEYE at all times, then yes; if you are growing on a multi-wafer system with the wafers passing under the EpiEYE then it depends on the rotation speed; if the speed is slow, then no, if it is fast then yes. If it is slow then you just won’t be able to record enough data.
Yes, although you have to be careful if your substrates are polished on both sides as this can lead to unwanted thermal fringes.
The technique doesn’t matter, but the geometry does and it is this that determines what type of optical head you need.
In essence, the various techniques are the same and involve the controlled deposition of tiny particles onto the surface in question as depicted in the above diagram. There are several methods that have evolved over the years: a) Molecular Beam Epitaxy (MBE) in which the particles are atoms or molecules e.g. As2 or Si evaporated from the solid under ultra-high vacuum conditions. b) Metal Organic Vapour Phase Epitaxy (MOVPE, also known as Metal Organic Chemical Vapour Deposition MOCVD) where the particles are organic molecules containing a metal atom. The molecule ‘cracks’ on the surface to leave the metal atom behind, the organic part being volatile moves away from the surface. c) Ion Beam Sputtering involves nano / micron size globules of the element being formed and directed at the surface under high vacuum condition. Irrespective of the deposition technique, it is possible to monitor the development of the thin film as it is being deposited using optical techniques.
Several reasons; • They don’t have optical access • They have got along so far without it since the specifications they are working too we slack enough to allow them proceed. • Culturally they don’t understand what it’ll do for them. • It’s perceived as a nice to have and not an essential (this is true for some materials but for nitrides and others this is certainly not the case) • It is perceived to be expensive: However, the return of investment is typically less than 6 months if used correctly
If you want to know; • What you’ve deposited. • How much you’ve deposited. • What is the surface quality? • How fast you are depositing the layer? • The uniformity across an individual wafer. • The uniformity wafer to wafer. • The composition of the layer. • The temperature of the substrate and layer. • The degree of bend induced in the wafer during growth. It is also important to be able to perform accurate statistical process controls on what has been grown.
It can go as low as 400°C but no lower. This is because ‘warm’ objects don’t give off enough light for the photo-detector to detect. It can go up to very high temperatures; the problem then becomes saturating the photo-detector; it has a finite range and as bodies get hotter they give off more and more light.
The theory used for converting the measured light from a hot object into a temperature assumes that the objects surface is a ‘perfect transmitter of light’; the so called ‘black body’. No bodies are black bodies so we have to measure the emissivity and correct for it. Furthermore, as a thin film is being deposited, the emerging light will be subject to interferometry fringes. This is why its important to use a laser or diode to measure the fringes and then correct for them in the pyrometry, hence the name; Emissivity Corrected Pyrometry (ECP).
A property of all materials; it determines how efficient a surface is at allowing light to pass through
It is basically a photo-diode that just looks for light that any hot body gives off (as in wow! that poker is red hot!). The hotter an object, the more light it gives off and it is this that a pyrometer measures. In the instrument, you have to select a narrow wavelength range at which to make the measurement.
The red is convenient – you can see it so lining up is a lot easier. The IR is needed for pyrometry. The blue is required in some instances for monitoring from nitrides and when used in combination, it is possible to compute composition. See specification section for wavelengths.
Then you need to get some – if you can’t get light in then you can’t get it out and there’s nothing to see.
We have gone to a lot of trouble to make ours stable, we are able to trigger ours at a set time or angle relative to a homing pulse and we can make multiple measurements per rotation in a rotating (multi-wafer) reactor. Ours is also automatically back-ground corrected so the measured signal is ‘absolute intensity’ allowing for real-time fitting of the data. Ours converts data into information straight away. Ours can be fitted onto any make or model of reactor. We have a very large optical access so even if the return reflected beam does not share the same optical path as the transmitted beam, we can still capture it; particularly useful in MBE reactors. Also, because we can synchronise the capture of the beam to the rotation of the platen, we can all but eliminate intensity variations due to wafer wobble (precession; something 95% of reactors suffer from, particularly MBE). It is better because we designed it that way in response to the very large number of customers we have dealt with over the years, all with different reactor platforms.
Basic operation is described in answer 1; laser mounted above a cube beam splitter with a photo-detector to one side. Laser beam passes through cube, hits target, is reflected back into cube which directs beam into photo-detector. Photo-detector converts light to a current which is recorded.
An interferometer is a device for measuring very small changes in thickness, a reflectometer measures changes in reflectance. We sell a reflectometer which measures changes in reflected light intensity, the changes are due to the thin film causing interference fringes; the thin film is the interferometer.
Site Map | © Optical Reference Systems 2012