WO2013184000A1 - Dispositif de gravure par jet de plasma et procédé permettant de supprimer une partie d'encapsulation d'un échantillon au moyen d'une gravure par jet de plasma - Google Patents

Dispositif de gravure par jet de plasma et procédé permettant de supprimer une partie d'encapsulation d'un échantillon au moyen d'une gravure par jet de plasma Download PDF

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Publication number
WO2013184000A1
WO2013184000A1 PCT/NL2013/050404 NL2013050404W WO2013184000A1 WO 2013184000 A1 WO2013184000 A1 WO 2013184000A1 NL 2013050404 W NL2013050404 W NL 2013050404W WO 2013184000 A1 WO2013184000 A1 WO 2013184000A1
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Prior art keywords
plasma
etching
gas
sample
plasma jet
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PCT/NL2013/050404
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English (en)
Inventor
Cornelis Ignatius Maria Beenakker
Jiaqi TANG
Johannes Bernardus Jozef Schelen
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Stichting Materials Innovation Institute (M2I)
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Publication of WO2013184000A1 publication Critical patent/WO2013184000A1/fr

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N1/00—Sampling; Preparing specimens for investigation
    • G01N1/28—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q
    • G01N1/32—Polishing; Etching
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
    • H01J37/32—Gas-filled discharge tubes
    • H01J37/32009—Arrangements for generation of plasma specially adapted for examination or treatment of objects, e.g. plasma sources
    • H01J37/32192—Microwave generated discharge
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
    • H01J37/32—Gas-filled discharge tubes
    • H01J37/32009—Arrangements for generation of plasma specially adapted for examination or treatment of objects, e.g. plasma sources
    • H01J37/32357—Generation remote from the workpiece, e.g. down-stream
    • H—ELECTRICITY
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    • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
    • H01J37/32—Gas-filled discharge tubes
    • H01J37/32009—Arrangements for generation of plasma specially adapted for examination or treatment of objects, e.g. plasma sources
    • H01J37/32366—Localised processing
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    • H01L2224/45144—Gold (Au) as principal constituent
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    • H01L2224/45147—Copper (Cu) as principal constituent
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    • H01L2224/48151—Connecting between a semiconductor or solid-state body and an item not being a semiconductor or solid-state body, e.g. chip-to-substrate, chip-to-passive
    • H01L2224/48221—Connecting between a semiconductor or solid-state body and an item not being a semiconductor or solid-state body, e.g. chip-to-substrate, chip-to-passive the body and the item being stacked
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    • H01L2924/181—Encapsulation

Definitions

  • Plasma jet etching device and method for removing an encapsulation portion of a sample via plasma jet etching are described herein.
  • the invention relates to a plasma etcher device and a method for removing an encapsulation portion of a sample (e.g. an integrated circuit, a discrete
  • the invention relates to a computer program product with instructions to carry out the proposed method.
  • Decapsulation of a plastic package of a semiconductor device is a process of removing the moulding compounds forming the encapsulation of the chip, in order to expose the chip's internal components.
  • semiconductor device refers herein to a broad class of functional devices including integrated circuits (complex circuit and functions), discrete electronic devices (e.g. single diode with simple functions), light emitting diodes (LED), microelectromechanical systems (MEMS), etc.
  • a typical composition of such a moulding compound is formed by epoxy (10 - 30 wt%), silica fillers (70 - 90 wt%), and small amounts of coupling agents, hardener, releasing agents, flame retardants, etc.
  • the decapsulation process should preferably keep the (silicon) circuit die, the metal bond wires and the (aluminium) bond pads intact, to allow the die to be subjected to further failure analysis, for example by means of optical microscopy, scanning electron microscopy (SEM), or photo emission microscopy.
  • SEM scanning electron microscopy
  • Gold has been used as bond wire material for many years.
  • the integrated circuit industry is switching from gold wire bonding to copper wire bonding.
  • Tang et al disclose a plasma etcher device that is suitable for etching away a plastic encapsulation of an integrated circuit with copper wire bonding on the basis of focused plasma jet etching.
  • This known plasma etcher comprises a source of electromagnetic (EM) microwave (MW) radiation, and a so-called Beenakker MW resonance cavity in which a standing wave pattern is formed which is induced by the EM MW radiation (elucidated in ref.[2]).
  • EM electromagnetic
  • MW microwave
  • Beenakker MW resonance cavity in which a standing wave pattern is formed which is induced by the EM MW radiation (elucidated in ref.[2]).
  • the considerable electric field amplitude of the standing MW generated inside the resonance cavity allows formation of a plasma gas from a gas mixture that is introduced at the centre of the resonance cavity.
  • This microwave induced plasma is ejected from the Beenakker cavity through a discharge conduit in a direction towards the semiconductor chip.
  • the ejected plasma gas i.e. plasma effluent or jet
  • the known Beenakker cavity based plasma etching device obviates the need for prior treatment of the circuit encapsulation via wet acid etching and/or laser ablation techniques.
  • the resulting decapsulated circuit i.e. the circuit die with its encapsulation stripped off
  • Beenakker cavity can be directed to selected areas of the sample surface (which is not possible in wet acid etching methods), the accuracy and reproducibility of the plasma jet etching method from using the known device is still lower than desired.
  • a plasma etcher device for generating a plasma jet and removing an encapsulation portion of a sample via etching
  • the plasma-etcher device comprises: - a microwave resonance cavity, connectable to a microwave source, and arranged for inducing an electromagnetic standing wave via microwave radiation from the microwave source, and for retaining within the resonance cavity a gas received from a gas source, and for generating a plasma from the gas, wherein the resonance cavity comprises a plasma discharge conduit for discharging the plasma in the form of a plasma jet; - a sample holder, for retaining the sample at a sample distance from the discharge conduit with a sample surface directed towards the discharge conduit, so that during use, the plasma jet is directed along a predetermined flow trajectory toward the sample surface, so as to remove the encapsulation portion via etching; characterized in that the sample holder is provided with a mask generator, for applying a liquid masking layer at the sample surface and within the flow trajectory of the plasma jet, so as
  • the proposed device allows efficient decapsulation, i.e. eliminating the moulding compounds of an encapsulation, of an electronic or semiconductor device by means of plasma jet based etching.
  • the proposed device enables complete decapsulation of the sample in a non-destructive manner that keeps the circuit die, the bond wires, and the bond pads intact. This nondestructive decapsulation allows the die to be subjected to further failure analysis, e.g. to find structural or electrical defects.
  • a “mask generator” which refers herein to a means for applying a liquid masking layer at the sample surface and within the flow trajectory of the plasma jet during etching, to confine or focus the plasma jet to a reduced etching region on the sample surface. If such a liquid layer is applied on top of the sample surface, then the plasma gas flow impinging the surface will locally blow away the liquid, thereby forming a localized spherical hole or void in the liquid mask layer. At a sufficiently high outflow rate or flux of the plasma gas, the impinging plasma jet will be strong enough to make the spherical void penetrate the liquid mask and form a nearly circular interface (i.e. reduced etching region) with the sample surface.
  • the plasma gas is in direct contact with the sample surface, resulting in etching of the encapsulation.
  • the ability to focus the plasma jet in the etching region by means of the liquid masking layer greatly enhances the controllability of the plasma etching process.
  • the plasma gas stream exiting the discharge conduit and directed toward the sample surface will flow sideways after impinging on the sample surface, causing undesired etching of a relatively large neighbouring sample area at which the plasma gas is not directly targeted.
  • the plasma jet can be confined in a controllable manner, in such a way that the sample surface is only locally etched away within the reduced etching region by the confined plasma jet, while the remaining sample surface remains covered and effectively protected by the liquid mask.
  • the liquid mask may also act as a cooling agent to keep the bulk temperature of the sample (e.g. semiconductor package) relatively low, and avoid thermal damage to the sample die, while the sample surface portion that is subjected to plasma etching will have its temperature locally raised by the plasma jet to a level that contributes to achieving a satisfactory etching rate.
  • a typical plasma temperature for a plasma flow having a composition of 1400 seem argon (Ar), 20 seem oxygen gas (0 2 ), and 10 seem carbontetrafluoride (CF 4 ), may be in the range of 300° - 600° C, while, if a water mask is used, a typical resulting semiconductor package sample temperature may be kept in the range of 40 - 100° C.
  • the proposed plasma etching device is very effective in controlling the etching temperature, which can be kept below critical T throughout the complete etching process. This is contrasted to known laser ablation devices and methods in which the excessive heat generation prevents the process from being usable for removing the last 100 ⁇ of moulding compound without causing thermal damage to the die.
  • the liquid used for the masking layer may be transparent or opaque, any of which may provide distinct additional advantages in recognizing and/or characterizing the etching region.
  • the liquid used for the masking layer should preferably be non-inflammable, or should at least have an ignition temperature that is substantially higher than the temperature of the plasma jet during operation, "substantially higher” meaning here that even a typical fluctuation of the plasma jet temperature is insufficient for igniting the masking liquid.
  • the liquid used for the masking layer should preferably be essentially chemically inert with respect to the sample, "essentially inert” meaning here that the typical time scale for the etching process is significantly shorter than the time required for the liquid to cause decomposition of the sample surface (e.g. by corroding or dissolving).
  • a typical time scale or duration for the currently proposed plasma-etching device is in the order of 20 min, for a sample of size 20 mm by 7 mm by 2.5 mm, and having an encapsulation containing 50 mm 3 of material. If the above conditions for the selected masking liquid are not met during operation of the proposed device, then the risk of damaging the sample during the etching process is significantly increased, which is undesirable.
  • the proposed plasma etcher device according to this aspect of the invention may however also be used in combination with a chemically reactive masking liquid (e.g. an acid), for example for decapsulating a sample circuit with a virtually chemically inert die and bond wires.
  • a chemically reactive masking liquid e.g. an acid
  • a masking liquid should be selected that is compatible with the sample characteristics, such that the plasma etcher device according to the invention may be effectively employed for removing the encapsulation of various electronic packages.
  • the device according to this aspect may for example be used for removing the silicone lens on a LED die of a LED package, for removing the plastic casing of an integrated circuit, etc.
  • the MW source forms a part of the plasma etcher device. This MW source is arranged for generating the EM MW radiation that induces the standing wave pattern in the resonance cavity.
  • the MW source may not be an integral part of the plasma etcher device, but instead may have connection means for connecting to the resonance cavity and functioning as a MW guide for supplying the generated MW radiation to the resonance cavity. In any case, it is required during use that the plasma etcher device is in some way connected to the source of MW radiation.
  • the liquid mask generator comprises a mask controller for adjusting a thickness of the liquid mask layer in correlation with a change in at least one of: - a gas flow rate of gas from the gas source, and - a plasma flow rate of plasma from the plasma discharge conduit.
  • the thickness of the liquid mask layer may be dynamically adjusted during etching, thereby regulating the size of the etching region.
  • the mask controller may be configured for automatically adjusting the masking layer thickness in response to a changing plasma gas flow rate flowing out through the discharge conduit toward the sample surface.
  • the etching region may be kept at a desired size at all times during etching, even if the etching rate is increased or decreased by changing the flow rate, temperature, composition, etc. of the plasma jet.
  • the automatic adjustment may provide a measure for protecting the sample in case the gas outflow rate or similar parameter exceeds a predefined level for which damage to the sample can be expected.
  • the plasma-etcher device comprises a gas source provided with a gas flow controller for adjusting the gas flow rate and/or a gas composition supplied to the resonance cavity.
  • the gas flow controller may be used to adjust the flow rate (flux) of the gas supplied to the resonance cavity, and hence to adjust the flow rate of the plasma gas flowing out through the discharge conduit and toward the sample surface.
  • the mask controller may be configured to dynamically adjust the mask thickness, in response to a received input of the gas flow rate and/or plasma flow rate set by the gas flow controller.
  • the gas flow controller may be used for dynamically adjusting the composition of the gas.
  • the ratios of the various gas components in the gas supplied from the gas source to the resonance cavity may be altered, in order to change the composition and hence the etching rate of the generated plasma.
  • various stages of the plasma decapsulation process may require different gas compositions, as will be explained below with reference to the second aspect of the invention.
  • the mask generator comprises an ultrasonic transducer arranged for generating ultrasound waves within the liquid mask layer during use.
  • the ultrasound waves generated within the masking layer by the ultrasonic transducer during a decapsulation process will yield cavitation forces that assist in dissociating the silica filler in the moulding compound removed from the sample.
  • This removal of silica filler agglomerate from the sample surface increases the overall moulding removal rate, and reduces the time required for decapsulating the sample.
  • Ultrasound wave generation within the liquid masking layer may be selectively applied during distinct phases of the decapsulation process, which may additionally be combined with adjusting the gas composition, as will be explained below with reference to the second aspect of the invention.
  • the plasma etcher device comprises an optical monitoring unit arranged for monitoring the etching region.
  • the optical monitoring unit allows for continuous and real-time imaging of the etching process via visual inspection.
  • Real time imaging of the etching process allows for accurate layer-by-layer decapsulation of the sample.
  • the images from the optical monitoring unit may clearly show the bond wires and exposed die portion during plasma etching, which information may be used as feedback for the user and/or for any provided etching process control.
  • inspection of the decapsulation results was only achieved via imaging after completion of the etching process, for example via SEM imaging.
  • the real-time optical monitoring unit according to this embodiment may be efficiently implemented by means of a charged coupled device (CCD) camera having a viewing area and optical axis directed towards the etching region during use.
  • the optical axis should preferably be directed at an acute non-zero angle with respect to the plasma jet flow trajectory, in order to avoid blocking of the plasma jet or interfering with the etching process.
  • CCD charged coupled device
  • the plasma-etcher device comprises a controlled stage configured for dynamically repositioning the sample surface with respect to the discharge conduit at least in a plane perpendicular to the flow trajectory of the plasma jet during etching.
  • the controlled stage enables dynamic repositioning of the sample surface with respect to the discharge conduits in the perpendicular plane, so that the etching area in which etching of the sample surface takes place can be repositioned at will. This prevents the plasma jet from being focused at a particular sample etching area for too long.
  • the controlled stage may be configured for carrying out a predetermined motion, enabling the sample to be automatically etched in a
  • the scan route and speed can thus be specified and programmed so that precise localization control and high decapsulation reproducibility can be achieved
  • the controlled stage is configured for dynamically adjusting the perpendicular distance between the sample surface and the discharge conduit during etching.
  • Dynamic adjustment of the perpendicular distance between the sample surface and the discharge conduit via the controlled stage will result in a slight change in the focus of the plasma jet impinging the sample in the etching region. This will have a slight impact on the local temperature in the sample during etching, as well as on the size of the etching region. Dynamic perpendicular adjustment thus provides an additional degree of freedom for controlling the accuracy and non-destructive nature of the etching process.
  • the liquid mask generator is arranged for generating a transparent liquid masking layer, preferably comprising water, more preferably distilled water.
  • a transparent liquid masking layer enables monitoring of the entire sample surface during etching operation. Not only the etching region of the sample that is directly etched may be observed, but also the regions of the sample that remain covered by the liquid masking layer. This allows the user of the etcher device to keep track of the condition of the entire sample during etching.
  • a processing unit may be provided, configured with an automated visual inspection algorithm for monitoring and keeping track of the sample condition.
  • the entire sample surface can be continuously be assessed and compared to the local etching result of the exposed surface.
  • decapsulation application wherein chemical reaction with any constituents involved in the decapsulation process (e.g. oxygen, fluorine, a silicon die, aluminium bond pad, and/or copper bond wires) is to be avoided.
  • any constituents involved in the decapsulation process e.g. oxygen, fluorine, a silicon die, aluminium bond pad, and/or copper bond wires
  • the liquid mask generator is arranged for generating a contrast liquid masking layer, and wherein the optical monitoring unit is configured for registering the etching region and/or a boundary region between the plasma jet and the contrast liquid mask.
  • the contrast liquid is formed by an opaque liquid masking layer comprising an opaque colloid of colloidal particles in water (e.g. milk).
  • the contrast liquid masking layer may be partially transparent, for example by addition of ink to the water.
  • the opacity or transmission characteristics of the liquid masking layer may be varied during an etching process by dynamically operating the mask controller.
  • the plasma etcher device comprises a processing unit configured for automatically controlling the position of the sample with respect to the plasma discharge conduit, in response to a predetermined condition of the etching region or of a boundary region between the plasma jet and the liquid mask, registered by the optical monitoring unit.
  • the predetermined condition for the etching region and/or boundary region may be one or more of a size, a shape property e.g. curvature, reflectivity, colour, etc.
  • the processing unit is in signal communication with at least one of the following device components: the gas flow controllers, the MW source, the optical monitoring unit, the mask generator with mask controller, the ultrasonic transducer, and the stage. Signal communication between processing unit and any of these device components allows the processing unit to automatically control the described functions of respective components, and/or to receive information from these components (e.g. measurement data, component settings, component status).
  • the processing unit is configured for optically recognizing the etching region and/or the boundary region, and for adjusting any one of the gas flow rate, the plasma flow rate, the mask thickness, and the perpendicular distance between the sample surface and the plasma discharge conduit.
  • the MW source is arranged for generating electromagnetic microwave radiation with a frequency in a range of 2.4 GHz - 2.5 GHz, and preferably of 2.45 GHz.
  • the indicated EM frequency band centred at 2.45 GHz has been made internationally available as a frequency range in which also non-communication based devices are free to operate and generate EM radiation.
  • Devices operating at this EM frequency band like magnetrons for MW ovens or similar sources of MW radiation, are relatively easy to obtain and to integrate with known MW resonance cavities that are suitable and optimized for use in the proposed device and method.
  • the MW resonance cavity preferably has optimized dimensions for enabling EM wave resonance centred on the specified frequency band. See for example the Beenakker cavity described in ref. [2].
  • the gas in the plasma etcher device comprises a noble gas, and preferably argon or helium, and wherein the MW resonance cavity is arranged for sustaining generation of a plasma gas from the gas under atmospheric conditions.
  • the MW resonance cavity is formed by a so-called Beenakker cavity, which is known from in the art (see ref. [2]), and which is very suitable for generating plasma as etching agent under atmospheric conditions. This suitability obviates the need for executing the etching process under vacuum conditions and for providing and controlling delicate vacuum setup components.
  • atmospheric pressure plasma sources may be used in the proposed etching device and method.
  • examples of such cavities are the so-called Surfatron and the Evenson cavity.
  • the MW field and plasma characteristics for the Beenakker cavity indicate that the use of this type of cavity will yield best results for the proposed decapsulation purposes.
  • a method for removing an encapsulation portion of a semiconductor device using a plasma etcher device comprising: - placing the semiconductor device in a holder of the plasma etcher device; - supplying gas from a gas source into a resonance cavity of the plasma etcher device; - inducing a standing microwave inside the resonance cavity, by means of microwave radiation from a microwave generator; - generating inside the resonance cavity a plasma from the gas; - directing a plasma jet through the plasma discharge conduit toward a package surface of the semiconductor device, so as to remove the encapsulation portion via etching; characterized by - applying a liquid masking layer on the package surface, by means of a mask generator provided by the plasma etcher device, so as to confine the plasma jet to an etching region on the sample surface, and - removing an encapsulation portion of the semiconductor device via
  • the proposed method provides a non-destructive process for removing the encapsulation of the semiconductor device.
  • the moulding compound of the sample encapsulation is thereby etched away and removed without damaging the functional parts or die of the semiconductor device, allowing for subsequent failure analysis of the still functional die.
  • the method comprises: - dynamically adjusting a thickness of the liquid masking layer in correlation with a change in at least one of: a gas flow rate of gas from the gas source, and a plasma flow rate of plasma from the plasma discharge conduit.
  • the method comprises: - optically monitoring the etching region and/or a boundary region between the plasma jet, the liquid mask, and the package surface; - dynamically adjusting at least one of a gas flow rate, the mask thickness of the liquid masking layer, and the sample distance between the semiconductor device and the discharge conduit, in response to a predetermined condition for the etching region and/or the boundary region.
  • the method comprises: - supplying gas with a first gas composition comprising Ar, 0 2 , and CF 4 from the gas source into the resonance cavity, to generate a first plasma jet, and - directing the first plasma jet toward the package surface of the semiconductor device to remove a first encapsulation portion with a first layer thickness via selective etching.
  • semiconductor package are epoxy (10 - 30 wt%) and silica fillers (70 - 90 wt%).
  • Oxygen radicals in the plasma jet react with epoxy, while fluorine radicals react with silica filler.
  • Oxygen plasma etching leaves a layer of silica agglomerate residue on the sample surface that cannot be easily removed. This silica layer blocks further etching of moulding compound by the plasma jet.
  • Carbontetrafluoride plasma only etches the silica filler, so moulding compound etching rate is extremely low. Only when both oxygen and carbontetrafluoride are added into the plasma can a high etching rate be achieved.
  • the epoxy in the sample moulding compound is completely etched while the silica filler is only etched on the surface so that the agglomerate structure becomes loose.
  • a percentage of CF 4 with respect to one unit (i.e. 100%) of O2/CF 4 etchant gas mixture is between 30 - 60% for CF 4 .
  • the plasma jet may be composed of an argon gas flow of 1400 seem and a total 0 2 /CF gas flow of 21 seem.
  • the moulding material is a composite, both epoxy and silica filler have to be etched simultaneously in order to achieve a high combined etching rate.
  • This preferred CF percentage range with respect to one unit of 0 2 /CF etchant gas mixture will yield an optimal moulding compound etching rate.
  • a deviation in the CF -percentage from this optimal range lowers the etching rate.
  • a low CF addition favours epoxy etching, while a high CF addition favours silica etching.
  • the effect that the addition of CF into 0 2 plasmas increases epoxy etching rate, and the addition of 0 2 into CF plasmas increases silicon dioxide etching rate also facilitates the moulding compound etching by the Ar/0 2 /CF mixture plasma.
  • the composition of a lens on a LED die is silicone, which contains organic groups chemically bonded with inorganic silicon elements.
  • a plasma etcher device used in the method comprises an ultrasonic transducer for generating ultrasound waves within the liquid mask layer, wherein in addition to: - supplying gas with a first gas composition comprising Ar, 0 2 , and CF 4 from the gas source into the resonance cavity to generate a first plasma jet, and - directing the first plasma jet toward the sample surface of the semiconductor device to remove a first encapsulation portion with a first layer thickness via selective etching; the method further comprises: - subsequently supplying gas with a second gas composition comprising Ar and 0 2 but excluding CF 4 from the gas source into the resonance cavity, so as to generate a second plasma jet; - directing the second plasma jet toward the surface of the semiconductor device to remove a second encapsulation portion with a second layer thickness via selective etching, and - generating ultrasound waves within the liquid mask layer using the ultrasonic transducer for dissociating a silica filler agglomerate layer from the surface.
  • the decapsulation method should be carried out in the following order:
  • gas with a first gas composition comprising Ar, 0 2 , as well as CF is used for plasma etching, to remove a first layer of moulding compound on top of the die.
  • the first layer thickness is relatively large, e.g. in the order of 300 ⁇ to 1 mm.
  • the proposed method should be stopped when the remaining moulding compound on top of the die has a second layer thickness of about 50 ⁇ .
  • a critical second layer thickness of moulding compound is found to be 30 ⁇ , and below this value Ar/0 2 /CF -plasma over-etching of the Si 3 N 4 passivation layer will occur.
  • gas with a second gas composition comprising Ar and 0 2 but excluding CF is used for plasma etching of the remaining moulding compound.
  • 0 2 plasma is used for etching, the epoxy in moulding compound is removed, but the silica filler (Si0 2 ) is left as an agglomerate layer, due to the lack of fluorine (F) atoms.
  • An improved plasma etching process by adding an 0 2 plasma etching followed by an ultrasonic cleaning step successfully avoids over-etching of Si 3 N 4 and Si.
  • a sample semiconductor package retains full electrical functionality after etching.
  • the actions of etching using the second plasma jet, and generating ultrasound waves may be alternated and repeated several times, or be executed simultaneously, until the desired decapsulation result is achieved.
  • the last action of ultrasonic cleaning is substituted by an action wherein the sample is first removed from the sample holder, and transferred to a separate sample holder that does not necessarily form part of the plasma-etcher device.
  • This separate sample holder comprises a container enclosing a liquid wherein the (partially) treated sample is immersed.
  • the second sample holder comprise a separate ultrasonic transducer for generating ultrasonic waves within the liquid layer of the separate sample holder, for dissociating the silica filler agglomerate layer from the circuit surface.
  • This alternative embodiment is considered inferior, for it requires repositioning of the sample between the sample holders. Integration of the ultrasound transducer with the liquid mask in the device and corresponding method is considered more efficient.
  • the plasma etcher device used in the method also comprises an optical monitoring unit for monitoring the etching region, and the method comprises observing the sample surface during the generation of the ultrasound waves, so as to monitor the dissociation of the silica filler agglomerate layer from the circuit surface.
  • the cleaning results for the sample can be evaluated in real-time during the decapsulation process, which improves the decapsulation rate and accuracy.
  • a computer program product configured to provide instructions to carry out a method according to the second aspect, when loaded on a computer arrangement.
  • a computer readable medium comprising a computer program product according to the third aspect.
  • the high etching rate and selectivity, low stray field, good localization control of the plasma jet, and real time imaging ability render these very suitable for efficient decapsulation of copper wire bonded semiconductor packages, for subsequent failure analysis and quality control.
  • a plasma etcher device for generating a plasma jet for etching a surface of a sample
  • the plasma-etcher device comprising: a sample holder for retaining the sample, so that during use, the plasma jet is directed along a predetermined flow trajectory toward the sample surface to etch the sample surface, characterized in that the sample holder is provided with a mask generator for applying a liquid masking layer at the sample surface and within the flow trajectory of the plasma jet, so as to confine the plasma jet to a focussed etching region on the sample surface.
  • This plasma etcher device may be further defined and/or augmented with any technical features as described herein above with respect to the device
  • a method for etching a surface of a sample using such a plasma etcher device comprising: - placing the sample in a holder of the plasma etcher device; - generating a plasma jet and directing the plasma jet toward the sample surface, so as to remove the encapsulation portion via etching; characterized by - applying a liquid masking layer on the sample surface by means of a mask generator, so as to confine the plasma jet to a focussed etching region on the sample surface, and to selectively etch the sample surface in this focussed etching region by the confined plasma jet.
  • This plasma etching method may also be further defined and/or augmented with any features and actions as described herein above with respect to the method embodiments according to the second aspect, to achieve similar effects.
  • FIG.1 schematically shows an embodiment of the plasma etcher device according to a first aspect
  • FIG.2 presents an enlarged partial side view of the embodiment shown in Fig. l;
  • FIG.3 schematically shows a side view of a sample for decapsulation with a device and method according to embodiments
  • Fig.1 shows a schematic side view of an embodiment of the plasma etcher device 1 according to the first aspect of the invention, for generating a plasma jet 44 and removing an encapsulation portion of a sample 46 via etching.
  • the shown plasma etcher device 1 comprises a source or generator 2 of electromagnetic (EM) microwave (MW) radiation, and a MW resonance cavity 6, which is connected to the MW source 2 by means of a MW guide 5 comprising a coaxial cable.
  • EM electromagnetic
  • MW microwave
  • an antenna 4 is provided for coupling the MW radiation into the resonance chamber to generate standing wave EM fields.
  • the design of the antenna 4 is adapted to optimize the EM coupling efficiency by reduction of power reflection, as described in ref.[4].
  • the MW source 2 is arranged for generating EM MW radiation with a frequency in the range of 2.4 GHz - 2.5 GHz (2.45 GHz centre frequency).
  • a typical MW power provided by the MW source 2 to the MW antenna 4 is in the range of 40 - 200 W, in order to generate the EM MW radiation used for sustaining the plasma.
  • the MW resonance cavity 6 is formed by a Beenakker cavity 7 with an oblate cylindrical resonance chamber that is configured for inducing EM MW field resonance in the TM 0 io cylindrical transverse magnetic field mode at 2450 MHz (described in ref.[2]) from the MW radiation received from the MW source 2.
  • the cylindrical resonance chamber comprises a gas supply conduit 12 in a first centre region shown on an upper side in Fig.1. Inside the resonance cavity 7, a plasma will be generated from the gas.
  • the Beenakker cavity 7 allows sustained generation of the plasma from the gas under atmospheric conditions, obviating the need for vacuum creation components.
  • the Beenakker cavity 7 is provided with a plasma discharge conduit 14 for discharging the plasma in the form of a plasma jet 44.
  • the plasma jet 44 is directed toward the semiconductor package surface 52 along a predetermined flow trajectory F by means of the discharge conduit 14.
  • the gas supply conduit 12 and plasma discharge conduit 14 are integrally formed as a gas tube that extends through the centre of the Beenakker cavity 7.
  • This tube may for example comprise alumina or quartz, and may have an outer tube diameter 0o of 6 mm, and inner tube diameter 0i of 1.2 mm (shown in Fig.2).
  • a discharge tube length D3 of the plasma discharge tube portion 14 is about 14 mm, and a total tube length of the entire gas tube is about 10 cm (not shown).
  • the gas tube 12, 14 effectively isolates the gas flowing inside the Beenakker cavity 7 from the remaining void enclosed by the hollow structure forming the cavity's resonance chamber.
  • the gas supply conduit 12 is in fluid communication with a plurality of gas sources 8 via a plurality of gas conduits that join into the gas supply conduit 12.
  • the gas sources 8 are formed by containers for pressurized gasses of
  • the individual gas flow rates of the various gasses from the sources 8 are controllable via individual gas flow controllers 10 provided for each gas source 8.
  • the gas composition of the total gas flow Og that is supplied to the resonance cavity 6 and which results from mixing of the individual gas flows can be regulated by coordinated operation of the gas flow controllers 10.
  • the plasma etcher device 1 has a sample holder 16 positioned at a perpendicular distance Dl from the plasma discharge conduit 14.
  • the sample holder 16 provides a surface for holding the sample 46, shown here as an integrated circuit 54, at a perpendicular distance Dl from the discharge conduit 14 and with a sample surface 52 directed towards the discharge conduit 14.
  • the sample holder 16 forms a receptacle for retaining a liquid masking layer 58 in which the sample 46 is immersed.
  • the sample holder 16 has a mask generator 20 for applying the liquid masking layer 58 on top of the sample 46 and within the flow trajectory F of the plasma jet 44.
  • the mask generator 20 includes a mask controller 22 for regulating a thickness D2 of the masking layer 58 during etching processes.
  • the mask controller 22 is configured for adjusting the thickness D2 in correlation with a change in the gas flow rate Og of gas from the gas source 8, and/or in a plasma flow rate Op of plasma from the plasma discharge conduit 14.
  • the mask generator 20 is also provided with an ultrasonic transducer 26 arranged for generating ultrasound waves within the liquid mask layer 58 during execution of the plasma etching method.
  • the sample holder 16 is mounted on a controllable stage 24 that is configured for dynamically adjusting the position of the sample holder 16 holding the circuit 54, and thus for dynamically repositioning the sample surface 52 with respect to the discharge conduit 14 during execution of the plasma etching method.
  • the shown controllable stage 24 allows relative movement between the sample surface 52 and the discharge conduit 14 in all three dimensions, i.e. relative motion in a plane S perpendicular to the flow trajectory F of the plasma jet 44, and as well as variation of the perpendicular distance Dl between the sample surface 52 and the discharge conduit 14.
  • the plasma etcher device 1 comprises an optical monitoring unit 30 formed by a CCD, for real-time monitoring of the package surface 52 during the etching process.
  • the CCD 30 With the CCD 30, the etching region Ae between an exposed portion of the sample surface 52 and the plasma jet 44 can be imaged. Also, a truncated, semi- spherically shaped boundary region Ab between the plasma jet 44 and the liquid mask 58 can be imaged by the CCD 30.
  • the embodiment of the etcher device 1 shown in Fig.1 also comprises a processor unit 32 as part of a computer arrangement 33.
  • the processor unit 32 is in signal communication with the controlled stage 24, the gas flow controllers 10, the MW source 2, the CCD 30, the ultrasound transducer 26, and the mask generator 20 with mask controller 22.
  • the processing unit 32 is configured for automatically controlling the position of the sample 46 with respect to the plasma discharge conduit 14, in response to a predetermined condition of the etching region Ae and/or of the boundary region Ab observed by the optical monitoring unit 30.
  • the processing unit 32 is configured for optically recognizing the etching region Ae and/or the boundary region Ab, and for adjusting any one of the gas flow rate Og, the plasma flow rate ⁇ , the mask thickness D2, and the perpendicular distance Dl between the sample surface 52 and the plasma discharge conduit 14.
  • a computer program can be loaded on the computer arrangement 33 to provide instructions for carrying out a method as described herein below.
  • This computer program may be stored on a computer readable medium 36.
  • the processor unit may also send and/or receive further information or instructions via a data network 38, and/or via connected input/output devices 34.
  • a plasma etcher device 1 as described above is used.
  • the method comprises the following actions: - placing the integrated circuit 46 in a holder 16 of the plasma etcher device; - supplying gas from a gas source 8 into a resonance cavity 6 of the plasma etcher device 1; - inducing a standing MW inside the resonance cavity 6, by means of MW radiation from a MW generator 2; - generating inside the resonance cavity a plasma from the gas; - directing a plasma jet 44 through the plasma discharge conduit 14 along a predetermined flow trajectory F toward the package surface 52, so as to remove the encapsulation portion via etching; - applying a liquid masking layer 58 on the package surface 52, by means of a mask generator 20 provided by the plasma etcher device 1, so as to confine the plasma jet 44 to an etching region Ae on the package surface 52, and - removing an encapsulation portion of the integrated circuit via selective
  • the method embodiment further comprises: - adjusting a thickness D2 of the liquid masking layer 58 in correlation with a change in: - a gas flow rate Og of gas from the gas source 8, or - a plasma flow rate ⁇ of plasma from the plasma discharge conduit 14. If the sample surface 52 is oriented perpendicular to the flow trajectory F of the plasma jet 44, then the etching region Ae will be circular (at least in absence of sample obstructions) and can be described by an etching region diameter 0e. If the mask thickness D2 is kept constant, for example by proper setting of the mask controller 22, then an increase in the gas flow rate Og is expected to result in an (approximately) linear increase of the etching region diameter 0e.
  • a thicker liquid mask 58 requires a larger gas flow rate Og to obtain a similar etching region diameter 0e.
  • a discharge tube inner diameter 0i of 1.2 mm, a discharge tube length D3 of 14 mm, a sample distance Dl of 6 mm, a liquid mask layer 58 consisting of water, and argon as main constituent of the gas flow Og the following approximated linear relations between the etching region diameter 0e (in mm), the water layer thickness D2 (in mm) and the gas flow Og (in seem) are found:
  • the method embodiment further comprises: - optically monitoring the etching region Ae and/or a boundary region Ab between the plasma jet 44, the liquid mask 58, and the sample surface 52; - dynamically adjusting at least one of a gas flow rate Og, the mask thickness D2 of the liquid masking layer 58, and the sample distance Dl between the integrated circuit 46 and the discharge conduit 14, in response to a predetermined condition for the etching region Ae and/or the boundary region Ab.
  • the ultrasonic transducer 26 provided in the sample holder 16 of the plasma etcher device 1 is used in this method embodiment.
  • the following actions are executed: - supplying gas with a first gas composition comprising Ar, 0 2 , and CF 4 from the gas source 8 into the resonance cavity 6, so as to generate a first plasmajet 44; - directing the first plasmajet 44 toward the package surface 52 of the integrated circuit 46, so as to remove a first encapsulation portion 50 with a predetermined thickness via selective etching; - subsequently supplying gas with a second gas composition comprising Ar and 0 2 but excluding CF 4 from the gas source 8 into the resonance cavity 6, so as to generate a second plasmajet 44'; - directing the second plasmajet 44' toward the package surface 52 of the integrated circuit 46, so as to remove a second encapsulation portion 50' with a remaining thickness via selective etching, and - generating ultrasound waves within the liquid mask layer 58 using the ultrasonic transducer 26, for dissociating a silica filler agglomerate layer from the sample surface 52.
  • Two major constituents of the moulding compound of plastic IC package are epoxy (10 - 30 wt%) and silica fillers (70 - 90 wt%).
  • Oxygen gas added into the Argon plasma generates atomic oxygen that efficiently reacts with organic materials like photo resist and epoxy.
  • CF 4 gas added to the Argon plasma generates atomic fluorine that reacts with silicon containing materials forming volatile SiF allowing the removal of silica filler. Only when both oxygen and carbontetrafluoride are added into the plasma can a high etching rate be achieved.
  • the ratio of CF with respect to one unit i.e.
  • 0 2 /CF etchant gas mixture in a gas composition comprising Ar, 0 2 , and CF
  • the plasmajet may be composed of an argon gas flow of 1400 seem and a total 0 2 /CF gas flow of 21 seem.
  • a further plasma etching method embodiment is used to avoid etching of the Si 3 N 4 passivation layer 57.
  • Ar/0 2 /CF mixture plasma is used to quickly remove thick moulding compound layer with a first layer thickness D4 of about 300 ⁇ on top of the die 54, which may take approximately 4 minutes.
  • the bond wires 56 are exposed after this action, but the die 54 is not exposed.
  • the remaining moulding compound with a second layer thickness D5 of about 50 ⁇ acts as a protection layer to the underlying Si 3 N 4 passivation layer 57.
  • an Ar/0 2 mixture plasma is used to selectively etch away the epoxy in the remaining moulding compound, which may take approximately 2 minutes.
  • the fluorine radicals will penetrate through the moulding compound layer and reach the underlying S13N4 passivation.
  • the surface moulding compound layer is porous as epoxy is partly removed by oxygen radicals while the silica fillers are slower to remove and are left on the surface.
  • the fluorine radicals flow through these pores and cause over-etching of S13N4 even though a layer of loose-structured moulding compound is still left on top of the die.
  • the S13N4 passivation layer 57, Si die 54, 23 ⁇ copper wire bonds 56 (and aluminium bond pads) are exposed without damage.
  • a plasma-etcher device 1 for generating a plasma jet 44 and removing an encapsulation portion of a sample 46 via etching
  • the plasma-etcher device 1 comprises: - a MW resonance cavity 6, connectable to a MW source 2 for inducing an EM standing wave from MW radiation within the resonance cavity, and wherein the resonance cavity is arranged for holding a gas received from a gas source 8, and for generating a plasma from the gas, wherein the resonance cavity comprises a plasma discharge conduit 14 for discharging the plasma jet 44; - a sample holder 16, for retaining the sample 46 at a perpendicular distance Dl between the sample surface 52 and the discharge conduit 14, and with a sample surface 52 directed towards the discharge conduit 14, so that during use, the plasma jet is directed along a predetermined flow trajectory F toward the sample surface, so as to remove the encapsulation portion 50 via etching, characterized in that the plasma
  • the process control for the plasma etching method achieved with the proposed plasma etcher device is greatly enhanced.
  • the optical monitoring unit 30 and the controlled stage 24 it becomes possible to visually inspect the etching process continuously and in real-time, and to dynamically reposition the sample surface 52 at will if a predetermined etching criterion detected via visual inspection has been met, or to directly adjust or stop the process if an imminent failure is detected. In this way, the occurrence of failures during etching can be immediately detected, over-etching of the sample 46 (e.g.
  • the plasma etcher device may comprise a sample holder 16 that is provided with a mask generator 20, for applying a liquid masking layer 58 at the sample surface 52 and within the flow trajectory of the plasma jet 44, so as to confine the plasma jet to a reduced etching region Ae on the sample surface 52.

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Abstract

La présente invention a trait à un appareil de gravure par plasma (1) et à un procédé correspondant de désencapsulation (à savoir, de retrait de l'encapsulation ou du boîtier d'un) un échantillon semi-conducteur ou électronique (46), au moyen d'une gravure basée sur le jet de plasma induit par résonance à micro-ondes (44). Le jet de plasma est généré dans une cavité de résonance à micro-ondes (6) et éjecté vers l'échantillon (46). Le dispositif et le procédé selon la présente invention emploient une couche de masquage liquide (58) au-dessus de l'échantillon (46), de manière à confiner le jet de plasma (44) et à améliorer la précision de la gravure.
PCT/NL2013/050404 2012-06-06 2013-06-06 Dispositif de gravure par jet de plasma et procédé permettant de supprimer une partie d'encapsulation d'un échantillon au moyen d'une gravure par jet de plasma WO2013184000A1 (fr)

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NL2008943 2012-06-06
NL2008943A NL2008943C2 (en) 2012-06-06 2012-06-06 Plasma jet etching device and method for removing an encapsulation portion of a sample via plasma jet etching.

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WO2016144159A1 (fr) * 2015-03-06 2016-09-15 Jiaco Instruments Holding B.V. Système et procédé de décapsulation de conditionnements plastiques de circuits intégrés
WO2018016957A1 (fr) 2016-07-20 2018-01-25 Jiaco Instruments Holding B.V. Décapsulation de dispositifs électroniques
WO2018047241A1 (fr) * 2016-09-06 2018-03-15 日本サイエンティフィック株式会社 Dispositif de génération d'aiguille à plasma à pression atmosphérique, et dispositif et procédé d'ouverture d'un boîtier de circuit intégré à semi-conducteur à l'aide d'une aiguille à plasma à pression atmosphérique
CN111639464A (zh) * 2020-06-03 2020-09-08 国网重庆市电力公司电力科学研究院 等离子体射流发生器参数优化方法、装置及存储介质
CN112366127A (zh) * 2020-10-09 2021-02-12 上海交通大学 固态掩膜聚焦的大气压低温等离子体射流加工方法及应用

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WO2016144159A1 (fr) * 2015-03-06 2016-09-15 Jiaco Instruments Holding B.V. Système et procédé de décapsulation de conditionnements plastiques de circuits intégrés
NL2014415B1 (en) * 2015-03-06 2016-10-13 Jiaco Instr Holding B V System and method for decapsulation of plastic integrated circuit packages.
US11295968B2 (en) 2015-03-06 2022-04-05 Jiaco Instruments Holding B.V. System and method for decapsulation of plastic integrated circuit packages
KR20190039956A (ko) * 2016-07-20 2019-04-16 지아코 인스트루먼츠 홀딩 비.브이. 전자 디바이스들의 디캡
CN109643664A (zh) * 2016-07-20 2019-04-16 佳科仪器控股有限责任公司 电子设备的解封装
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KR102329407B1 (ko) * 2016-07-20 2021-11-23 지아코 인스트루먼츠 홀딩 비.브이. 전자 디바이스들의 디캡
WO2018016957A1 (fr) 2016-07-20 2018-01-25 Jiaco Instruments Holding B.V. Décapsulation de dispositifs électroniques
CN109643664B (zh) * 2016-07-20 2023-05-30 佳科仪器控股有限责任公司 电子设备的解封装
WO2018047241A1 (fr) * 2016-09-06 2018-03-15 日本サイエンティフィック株式会社 Dispositif de génération d'aiguille à plasma à pression atmosphérique, et dispositif et procédé d'ouverture d'un boîtier de circuit intégré à semi-conducteur à l'aide d'une aiguille à plasma à pression atmosphérique
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CN112366127B (zh) * 2020-10-09 2021-07-23 上海交通大学 固态掩膜聚焦的大气压低温等离子体射流加工方法及应用

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