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1 - What is the "Hall effect" and what results do you obtain with the measurements ?
The "Hall effect" was discovered by Mr. Hall, a professor of Johnnes Hopkins university in USA. If a magnetic flux is imposed on a leading wire containing electric current, it creates an electronic stress which can be measured by a voltage called "Hall voltage".
Measuring the Hall effect permits analysis and characterization of various basic characteristics of semiconductors, mobility, carrier density, resistivity, conductivity & Magnetoresistance…
LThe Hall effect measurements systems are being part of the productrange offered by MW. They are particularly dedicated to materials research and are used in the labs, in the universities in application research or educational, within the industrials in applications monitoring of layers… Several models are available.
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2 - I need to measure a "very high" sheet resistivity, what would you suggest ?
We would suggest to use a classical Four point probe method. Our range of 4PP is proposed in several models allowing measurement of a wide range of resistivity. The base model 280 will measure up to 8E5 (800kohm/square), the model 280DI can go up to 8E9 and a further option allows 8E11 for very resistive materials like amorphous silicon.
In the case where the resistivity is too high to be measured by 4PP, our model CVMap is a mercury 4 point probe and can measure higher values of materials close to isolent and other substrates. Typically a description of the material and/or a sample submitted will confirm the capabilitiy of the proposed equipment to fullfill the characterization need.
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3 - What is the budget price for a simple Four Point Probe ?
Simple for us means no automation, no software, one point at a time, the sample loading is obviously manual as well as the X-Y positioning. A simple 4 Point Probe stand with its Probehead is below 3k€, adding the instrumentation (sourcemeter), the software and an optional mapping feature< can be made on site for a cost which is less than 14k€. A complete system capable of measuring automatically on 1 or 5 points, upgradeable to a full mapping version will require around 34k€.
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4 - Is it possible to measure the resistivity of some materials while heating up the sample ?
Absolutely, some materials actually can't be measured without temperature, otherwise they are too much resistive at ambient. We do have a specific Four Point Probe serie that can be used in conjunction with a hot chuck (temp. up to 500°C) and specific high temp. probehead. Another option is to use a Probe station equipped with a hot chuck and a special micropositionner holding the 4 Point Probehead.
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5 - What are the advantages/disadvantages of using a C-V station with Mercury contact ?
Typically the C-V station is composed of a standard probe station (contact is made thru the needles to a metal pad). That probe station is linked to some instruments (Agilent, Anritsu, Keithley…) which will input the necessary signals including the sine wave signals at variable frequency used to excitate the electrons onto the layer and measure the capacitance at different voltage. The C-V station is relatively complex as linking several instruments manufactured by different companies and not purposely made for being stacked together in order to offer the smallest footprint.
Within these configurations, still widely used by the characterization labs, MW does offer a few things, various models of probe stations, meters…Our close relation with instrumentation manufacturers allows us to provide a complete turn-key solution.
Talking of Mercury probe is a different subject and actually easier in the sense that the mercure itself does create the contact on the measured layer. There is no need to metallize and add the metal pads which are used only for the contact.
The mercury is a soft, elastic metal and it can contact directly onto the oxide or other layers, epitaxial, implanted, fragile layers…The mercury is the only material that can efficiently measure Ultra-shallow Junctions (USJ) found in the latest semiconductors technologies C90, C65, C45…
The safety aspect of the Mercury is also obviously a key factor of the C-V mercury probe systems As well, the systems integrate the electronic hardware and software resulting in a small footprint totally integrated system for all substrates sizes. To complement these significant advantages, one can mention adaptability to a large range of materials (including SOI, III-V compounds…), choice of a manual system (no mapping) or automatic system with multiple measurements sites, variety of mercury probehead simple point, guarding, double-rings…
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6 - What is the purpose of this process ?
This question is obviously asked by persons not being in the semiconductor manufacturing world or in different manufacturing areas. Long time ago, semiconductor companies used to train their engineers on almost all aspects of the manufacturing chain, from the bare Silicon at the very beginning of what is called "Front-end" up to the dicing & packaging typically called "back-end" before final tests and shipping. Nowadays the engineers are more specializing in their specific technical areas and people from the "final test" department do not always know what the "front-end" is exactly as they have not passed thru.
The globalization also acts as the wafers can well be manufactured in one part of the world and packaged and tested in another different part. This is the nice feature of the Semi world, meeting all different people and cultures but catching in detail the steps of the worldwide manufacturing process is not easy then.
The back-grinding or back-thinning arises at the end of the front-end process, after having manufactured the complete wafer with all the dies but before dicing and packaging. The goal is to handle bigger and bigger wafers (300mm nowadays and 450mm to come…) with a specific thickness in order to guarantee a certain mechanical rigidity during the process steps. Then thinning those wafers depending on the projected applications. Chips for mobile applications are requesting thin wafers, or smartcards industry…
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7 - What products does the BG process imply and what does MW propose ?
Two technics are used in the back-grindind, one is mechanical, the other is chemical. In the mechanical grinding, the most important as it consists of thinning wafers from around 800µm to 200 or 300µm, the wafers are protected by an adhesive tape. Is is an ultra-clean adhesive tape (the protection is concerning the active side of the wafers, where the chips are) and the adhesive is either standard or UV sensitive
The grinding (or back-grinding as being done on the back of the wafer) is accomplished by diamond grinding wheels in two passes, rough or coarse, and fine. The lamination of the tapes on the wafers is made by automatic equipment in production areas. The small lots or engineering applications can be responded with manual or semi-automatic equipment The UV sensitive tapes need then to be cured so that the film can be removed with no residue.
The chemical thinning is more recent and uses specific polishing powders.
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8 - There are many microscopes and optical products, some of them very known as there are used within all research labs and production areas. How do you make a difference with your product offering ?
This is true, the offer on microscopes is large and concern a lot of different industrial and research sectors. We do not position ourselves as supplier of microscopes for all industries. It would be difficult to be expert in all technical areas using microscopes. In fact our probe stations for semiconductor materials testing are generally equipped with microscopes.
There can be simple and relatively low magnification (Stereozoom with binocular or trinocular head) or very performing as the PSM serie that we offer. There exists also a serie of mono-objective microscope with electronic magnification which offers a fixed working distance and are therefore very interesting for probing. The microscope and accessories supply are complementary products to our range and we have been often requested by our customers to offer them.
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9 - How about cameras to be used with ?
A microscope with a trinocular head can accept directly a camera and the camera can stay permanently while keeping the visual view through the eypepieces. We offer a choice of cameras analogical or numeric with CCD sensors at all prices and sophistication levels. They mount directly onto the microscope and connect to a PC or a monitor. Some cameras can be mounted onto the eyepiece for those who have simple binocular microscopes.
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10 - Concerning objectives, you offer in addition to your own models some of known brand, such as Mitutoyo or others. These objectives can be purchased directly from the manufacturers ?
Of course, as well it is possible to purchase some of the products that we offer from the manufacturing countries, USA or Asia or elsewhere. However we have a "added value" in the fact that we offer at same price with technical support.
Actually Mw can be considered as an "Integrator", which means some of the products will fit inside or around bigger equipment. In such case our purchase is evidently below the normal end-user price, which allows us offering the product at the same price with technical support added. Otherwise it could not work, especially in the very "global" semiconductors world.
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11 - Our wafers/substrates are ranging from 2" to 8" diameter, they can be square or round partial. We would like to characterize some internal devices and contact with needles. The size of the contact pads is 80x80µm, in some cases it could be smaller ?
This is a good question for us as it does correspond to our expertise since more than 15 years. You could use a manual prober with a chuck accepting up to 8" substrates and a stability which allows landing on pads of the mentioned sizes. This is a pretty basic model for a budget cost with microscope less than 15k€. A number of accessories can be added depending on the needs for temperature characterization, level of current, protection from light & Radiation... The micro-positionners and the probe tips must be selected in function of the current to measure. For ultra-low current (fA), the triaxial package can be used.
In term of evolution & upgradeability of the system, and depending on the future requirements, it may be necessary to look for a more stable, more sophisticated, submicron prober, with possible options such as automatic movements of the X-Y tables, the microscope, the need of tri-temperature testing (ambient, hot, cold)…The range covers from the simple manual low-cost up to the semi-automatic totally "hands-off" probing.
There is available too a RF probers range, from 10GHz to >200GHz, they request specific positionners and RF probe tips.
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12 - What is the particularity & recommended applications of the adhesive tapes for dicing with ultraviolet sensitive adhesive ?
These tapes are typically used in the operations of wafer or substrate dicing (or in the wafer backgrinding). They are combining 2 properties which are very important for the process and normally opposite. First a high adhesion during dicing so as to avoid the "flying dies" due to the coolant pressure and the movement created by the spindle rotation, secondly after dicing the adhesion should become low so that the dies can be gently picked up without stress. This is particularly important in the case of fragile and thin dies.
The UV tape has an acrylic adhesive which is sensitive to UV rays. After exposure to a UV source (typically 254 or 365nm wavelenght ), the adhesive properties change and the force of adhesion become much lower than before UV, typically around 5% of the initial adhesion.
The disavantage of the UV tapes is however a higher cost and a shorter lifetime compared to standard non UV films. They must be used when the cost of the individual die or substrate is such that nothing can be lost or damaged by the dicing process.
The UV tapes are also used sometimes in the operations of back-grinding (back-thinning) when the final thickness is low and make the wafer very fragile.
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13 - How long should a resin dicing blade last ?
This is one of the toughest questions asked of any dicing blade manufacturer. Each material type, throughput requirements, and operating parameters all have major effects on blade life.
The resin bonded blade wears and is self sharpening.
Lhe slower the blade wears, the longer the life. Blade life in ceramic cutting is very dependent on the grain particle size that makes up the ceramic material. A 2-inch diameter blade may lose .001" on its radius for every 150 linear inches of cut in one ceramic type and only exhibit 20 linear inches of cut in another denser ceramic material. Many times in glass or crystal cutting where quality is of prime concern, the blade doesn’t wear fast enough to self sharpen, and poor cutting results occur.
Resin bonded dicing blades offered from MW are made up of quality abrasives throughout the blade from O.D. to I.D. Flanges in vast variety of diameters are available to allow the customer to utilize the entire dicing blade, resulting in a very efficient and low cost dicing operation.
We welcome your materials for establishing the best blade and dicing parameters for your projects.
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14 - I am looking for a specific burn in and test socket for my package, what do you propose, is there a MOQ (minimum ordering quantity) ?
Our range of standard burn in and test socket is composed of thousands of references and sockets for the most recent packages are being developed daily, QFN, BGA, µBGA Typically a simple drawing of your package is sufficient to determine if a standard existing socket can be proposed.
If not the wide range will most probably allow the selection of a similar socket that can be personalized to your packages with minor modifications. It is also possible to develop a custom socket for any package.
We do offer also some specific high performance & RF sockets On each socket type, there is a minimum quantity of order which depends on the model. The MOQ is always indicated in our quote and the delivery is typically 4 weeks or sooner (standard sockets).
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15 - What is the difference between antistatic bags and moisture barrier bags ?
The antistatic bags are typically protecting the devices, boards…from static charges carried outside in the air. They do not protect from the humidity. The humidity is kept away for the products by using the moisture barrier bags.
The moisture barrier bags are usually hermetically sealed by vacuum to insure an efficient protection against the humidity.
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Electrical characterization of semiconductor layers
