Frequently Asked Questions (FAQ) about MaxMile EpiEL Technologies/systems
- What is EpiEL?
- Why is EpiEL useful?
- Can EpiEL system characterize EL of wafers with insulated substrate, such as GaN on sapphire substrate?
- Is there any difference between your EpiEL measurement and device test?
- The EpiEL mapping and device data show some similar patterns and some quite different results. Am I misinterpreting your maps?
- EL results will be different for different device structures, especially for different light extraction approach. Can EpiEL system reflect these differences?
- We have the similar system already, but it is not accuracy & right. Many parameters effect epi-wafer, such kind technology can not tell the truth.
- We can use device process to control quality. If the processed wafer is OK, the rest wafers of same batch would pass the quality control. This procedure is pretty reliable. Why do we need EpiEL system?
- How can you demonstrate the capability of your system? Do you provide on-site system demonstration?
- Do you provide wafer scanning service?
- If I send my samples, how is the turn-around time of your wafer characterization service?
- How about throughput/speed of your EpiEL system? Can it meet high throughput requirement?
- Is there any consumer goods need to prepare?
- What is the probe size?
- Can I use EpiEL probes alone and develop own system?
- Is there any competitive products? What is superiority of EpiEL?
- I have a PL mapper already, why do I need an EpiEL system?
- What is EpiEL/PL mapping wavelength range?
- Is there any contamination you expect during probing? I need to process the wafer after probing; do I need to do some surface pre-treatment after EpiEL probing?
- Will your tool damage the surface of wafer after EpiEL mapping measurement?
- I was wondering what the distance between two probes is and what kind of metal you use for the probe. Is it Pt or Cu?
- Please tell me any restrictions on materials for your EL mapping. As you know, it is hard to make a contact on p-GaN itself. How do you make p-contacts and n-contacts without fabricating device?
- Where can I find more information about EpiEL?
- What is lead/delivery time if place the order?
EpiEL is a technology developed by MaxMile,
which can be used for electroluminescence (EL) measurement
directly on epitaxial materials, such as LED epiwafers.
EL measurement is usually performed on the
finished devices (such as LEDs) since it needs a device structure
to inject current. Conventional electroluminescence evaluation
could not provide fast response for material development since the
fabrication of devices is usually time-consuming and costly.
MaxMile EpiEL mapping technology overcomes this limitation by
temporarily forming a well defined light emitting diode (LED)
inside the material. It characterizes the electroluminescence
behavior of light emitting material as the finished device
functions through electroluminescence.
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EpiEL is an unprecedented
characterization/simulation solution for optoelectronic industry.
It provides virtual LED device fabrication & characterization
system which can be used to measure LED device parameters directly
on epiwafers. Without any costly and
time-consuming device fabrication, yet as through a
finished device, EpiEL reveals not only the electro-luminescence
(EL) but also the electrical properties of the material. With such
unique capability, EpiEL can enable device-level quality control
at early stage and on every wafer, provide instant feedback for
material development, enable "fabless" LED material and CVD system
development. EpiEL is also a powerful
tool which can be used to simulate the different light extraction
approaches in different device structure. It can assemble any
device-level optical and electrical properties of the material in
a fabless manner which could significantly reduce the R&D time and
cost.
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Yes. EpiEL system uses proprietary electrode
contact technology which can be used to obtain EL from any type of
LED epi-wafers with insulated or conductive substrates.
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The correlation between EpiEL and device
depends on device structures and test conditions.
Generally speaking, the wavelength related
information, such as WLP, WLD, WLC, FWHM, provided by EpiEL will be the
same as those from device test if both test conditions are similar
(with same equivalent current).
Since the spectrum of LED will change as the driving current
changes, the wavelength-related information might be slightly
different between EpiEL and device results due to different device
size and driving current. This difference can be correlated
through the procedure called equivalent driving current.
Due to a variety of device structures, the
correlation of EL intensity-related information, such as emissive
intensity, peak intensity, external quantum efficiency, between
EpiEL measurement and device results will be strongly related to
their corresponding light extraction approaches. The
intensity-related information revealed by EpiEL and device test
will be similar if both light extraction methods are similar.
EpiEL system can be configured to best simulate the specific device
structure.
The
EpiEL voltage will be related to probe device size and
contact resistance. For nitride-based application, electrical
information provided EpiEL is strongly related to p-layer
activation condition; and some wafers might
indicate larger values due to improper p-activation. If the size
of device is similar, usually
the driving voltage at small driving current (including turn-on
voltage) provided by EpiEL will be similar to that from real
device, while driving voltage at high driving current will be
slightly higher than those in real device.
MaxMile latest EpiEL technology gives out device Vf estimation which is close to real device value.
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In order to correlate EpiEL results with device
data, please pay attention to the following factors:
-
Wafer orientation.
-
Color encoding system: different color
encoding in EpiEL and device test could cause misunderstanding.
MaxMile EpiEL system has the capability to customize its color
encoding system. MaxMile also offers the service to generate the
color-encoded mapping from customers' device data.
-
Test condition: different test conditions
could lead to different results. For more information, please
check the question "Is there any difference between your EpiEL
measurement and device test?" in this FAQ.
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There
is a way for EpiEL technology to correlate its test results with
specific device structure. EpiEL system (EpiEL-700) can be configured to best
simulate the corresponding device structure.
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EL
measurement provided by MaxMile EpiEL system is pretty accurate and
reliable. To our knowledge, currently there is no
other similar system which has same performance level (device-level
EL measurement directly on epiwafer).
There are a couple
of quick tests which have been used by the LED industry. One of them
uses indium dots
temporarily soldered on wafer surface, the other one uses simple
metal probes. The EL measurement provided by these techniques may not
be accurate and reliable, and corresponding formation
of contacts could damage wafers.
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It is a matter of efficiency and cost
effectiveness. The device process "destroys" control wafer, and it
is costly and takes much longer time. MaxMile EpiEL system provides
the device level results just as device process does. The rapid and
nondestructive nature of EpiEL system enable the manufacturer to
perform "device test" on each wafer (100% quality control), and
provide instantly feedback for material development. Furthermore,
EpiEL can use a near identical device test condition, it will
provide an improved wafer evaluation for quality control.
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Currently MaxMile offers free sample
characterization service to demonstrate the capability of EpiEL
system. Samples will be returned right after EpiEL scanning.
Customer can evaluate MaxMile EpiEL system through correlating EpiEL
mapping results with their device test results.
MaxMile can arrange for on-site system
demonstration if the customer is serious in purchasing EpiEL system.
MaxMile suggests customer to evaluate EpiEL systems through free
sample characterization first.
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Yes. MaxMile does provide wafer scanning
service. First couple samples will be free for each customer to
evaluate the effectiveness of EpiEL system. There will be a service
charge for characterizing more wafers. MaxMile offers favorable rate
service if customer signs a contract for routine wafer
characterization service.
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For
small amount samples (<10), we can finish the EpiEL test and send
you the report within a day or two. For the first time of
characterizing your sample, we usually fully characterize your
sample and might take a little more time than regular EpiEL test.
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Yes. EpiEL is a rather flexible system which
can meet requirements spanning from comprehensive research and
development to rapid quality control.
Usually EpiEL measure 32 points full LIV for
5-10 minute in a 2-inch wafer, depending on test configuration. For rapid
quality control, EpiEL could take only a couple minutes to determine
the quality of the wafer.
MaxMile also provides a high throughput version
of EpiEL to meet a demanding application need.
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No. EpiEL is rather simple to use. Customer
just needs to load epiwafers (right after growth) into system and
select the corresponding characterization purpose, the system will
finish the rest.
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It depends on specific application and test
purpose. EpiEL uses different probe sizes to meet different
application requirements.
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EpiEL probes are specially developed for
MaxMile EpiEL mapping systems which uses proprietary
instant-device-formation technique to obtain device-level EL
measurement directly on LED epiwafers without any device
fabrication. EpiEL probes alone could not work.
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To our knowledge, currently there is no similar
system provided by competitors. PL mapping, device test and some
quick tests (such as indium dot) have been used for quality control
in LED industry. EpiEL is developed to provide a better solution:
-
Compared to device process, EpiEL provides
improved quality control with identical test condition, and enables
100% quality control (“device test" on every wafer)
-
Compared to PL mapping, EpiEL enables true EL
test directly on epi-wafer.
-
Compared to quick tests, EpiEL provides
reliable and wafer-level mapping results.
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The photoluminescence (PL) is mainly determined by the optical
properties of the material, while the electroluminescence is
determined by a number of factors such as the optical properties and
physical structures of the optically active layers, the electrical
properties of two conductive regions which are used for cathode and
anode contacts, and the properties of the electrical contacts
through which the electrical current injected.
It is well known that photoluminescence is not equivalent to
electroluminescence. High photo-luminescence efficiency is necessary
but not sufficient for good light-emitting materials or wafers. A
wafer with high photoluminescence efficiency may or may not exhibit
high electroluminescence efficiency and hence good light emitting
diodes (LEDs). As indicated in green LED application, the different
emission mechanism between PL and EL could also result in different
emission wavelength/intensity. From quality control of view, PL
mapping could not provide sufficient information for epiwafer quality control.
Compared PL, EpiEL system enables device-level
EL measurement directly on epiwafers. As a finished device, EpiEL
reveals not only the electroluminescence, but also the electrical
properties of the material. The characterization performed by EpiEL
is rapid, nondestructive. The powerfulness and low-cost nature of
EpiEL provides an excellent balance between quality control and
cost-effectiveness for LED industry. EpiEL makes it possible to
perform "device test" on every wafer (100% quality control).
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Standard EpiEL/PL wavelength will be one of the
following options. We can also customize the system to meet specific
needs.
-
UV: 200-400nm / 200-450nm / 200-600nm
-
VIS: 350-700nm / 380-760nm / 400-800nm
-
VIS/NIR: 650-1050nm / 550-1050nm / 350-1050nm
-
UV/VIS: 200-700nm / 300-800nm / 200-850nm
-
UV/VIS/NIR: 200-950nm / 300-1050nm /
200-1050nm
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There is no contamination after EpiEL
measurement. It has been proven at least for nitride-based
applications that wafers with EpiEL test can be used for device
fabrication as those without EpiEL test.
If your wafers were tested through our sample
service, you might need to clean the wafer using regular
semiconductor cleaning process to remove the dust, etc., since our
EL mapping service is not performed under cleaning room environment.
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EpiEL must use some mechanism to touch wafer in
order to inject the current into the wader to light up EL emission.
For most applications, this contact is instant and nondestructive under recommended test condition.
If your samples are very sensitive in any contact, we suggest you to
validate the EpiEL measurement first through our free sample service.
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MaxMile EpiEL system uses a special and
proprietary LED probe technology to measure the electroluminescent
and electrical properties of unprocessed epiwafer.
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EpiEL works best on nitride LED material. There
is no restriction on materials for EpiEL measurement. Any kind of
LED epiwafers can be evaluated by EpiEL, though the level of information provided by EpiEL might be different for different materials. EpiEL uses a special and
proprietary LED probe technology which can instantly and
nondestructively form both anode and cathode contacts directly on
epiwafer.
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MaxMile home page (http://www.maxmiletech.com/)
is the best place to find the information about EpiEL. In order to
stimulate and foster relevant researches and technology innovations,
MaxMile Technologies shares most of its findings and technological
advances with industrial peers through journals and technical
conferences. It also develops these findings and advances into
practical application notes via its own website. MaxMile
Technologies believes that these publications will help customers to
use its service and technologies more effectively.
If you could not find information for which you
are looking, please contact MaxMile at
Info@MaxMileTech.com.
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Normally two months.
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