NL2008943C2

NL2008943C2 - Plasma jet etching device and method for removing an encapsulation portion of a sample via plasma jet etching.

Info

Publication number: NL2008943C2
Application number: NL2008943A
Authority: NL
Inventors: Cornelis Ignatius Maria Beenakker; Jiaqi Tang; Johannes Bernardus Jozef Schelen
Original assignee: Stichting Materials Innovation Inst M2I
Priority date: 2012-06-06
Filing date: 2012-06-06
Publication date: 2013-12-09
Also published as: WO2013184000A1; TW201403708A

Description

Plasma jet etching device and method for removing an encapsulation portion of a sample via plasma jet etching.

TECHNICAL FIELD

5 [0001] 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 semiconductor device or light emitting diode) via plasma jet etching. Furthermore, the invention relates to a computer program product with instructions to carry out the proposed method.

10

BACKGROUND ART

[0002] 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. The term “semiconductor device” refers 15 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.

[0003] 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, 20 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. Gold has been used as bond wire material for many years. Nowadays 25 however, the integrated circuit industry is switching from gold wire bonding to copper wire bonding. Conventional acid decapsulation methods using for example hot nitric acid (HNO3) and sulphuric acid (H2SO4) are not suitable for samples involving copper wire bonding. Although many methods of plasma etching in a vacuum chamber are known that are suitable for decapsulating semiconductor packages involving copper 30 wire bonds, these known methods require very long processing times in order to remove any silica filler in the moulding compounds.

[0004] In ref.[l], 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 2 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]). The considerable electric field amplitude 5 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 (MIP) 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) causes etching of the chip’s encapsulation, thereby 10 removing the plastic moulding and exposing the circuit die. 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) remains functional after the Beenakker cavity based plasma etching process has been 15 completed, and may subsequently be subjected to failure analysis.

[0005] Although the plasma jet from the discharge conduit of the known 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.

20

SUMMARY OF INVENTION

[0006] It would be desirable to provide a plasma etcher device with an improved etching accuracy.

[0007] According to a first aspect, there is provided a plasma etcher device for 25 generating a plasma jet and removing an encapsulation portion of a sample via etching, wherein 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 30 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 3 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 to confine the plasma jet 5 to an etching region on the sample surface.

[0008] The proposed device according to this aspect of the invention 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 10 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.

[0009] In the proposed device, there is provided a “mask generatof’, which refers herein to a means for applying a liquid masking layer at the sample surface and within 15 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 20 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. At this circular area or etching region, 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 25 the controllability of the plasma etching process.

[0010] In the absence of such a liquid mask, 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. By control of 30 the liquid masking layer, 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.

4

[0011] Depending on the type of liquid and the ambient temperature, 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 5 temperature locally raised by the plasma jet to a level that contributes to achieving a satisfactory etching rate.

[0012] In a plasma etching process using the proposed device, a typical plasma temperature for a plasma flow having a composition of 1400 seem argon (Ar), 20 seem oxygen gas (O2), and 10 seem carbontetrafluoride (CF4), (wherein “seem” stands for 10 standard cubic centimetre per minute, i.e. cubic centimetre per minute at 0°C and 1 atmospheric pressure) 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 15 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 p.m of moulding compound without causing thermal damage to the die.

[0013] By careful selection and/or control of the applied liquid masking layer in 20 the proposed plasma etcher device, various additional process control effects may be achieved.

[0014] 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.

25 [0015] Furthermore, 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.

30 [0016] Moreover, 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 5 required for the liquid to cause decomposition of the sample surface (e.g. by corroding or dissolving).

[0017] 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 5 having an encapsulation containing 50 mm3 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.

[0018] The proposed plasma etcher device according to this aspect of the invention 10 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.

[0019] In general, a masking liquid should be selected that is compatible with the sample characteristics, such that the plasma etcher device according to the invention 15 may be effectively employed for removing the encapsulation of various electronic packages.

[0020] 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.

20 [0021] According to an embodiment, 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.

[0022] In alternative embodiments, the MW source may not be an integral part of the plasma etcher device, but instead may have connection means for connecting to the

25 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.

[0023] According to an embodiment, the liquid mask generator comprises a mask controller for adjusting a thickness of the liquid mask layer in correlation with a change 30 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;

[0024] By means of the mask controller, the thickness of the liquid mask layer may be dynamically adjusted during etching, thereby regulating the size of the etching 6 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. By proper calibration of the proposed plasma etcher device including the mask generator, the etching region may be kept at a 5 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.

In addition, 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.

10 [0025] According to an embodiment, 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.

[0026] 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 15 flowing out through the discharge conduit and toward the sample surface.

[0027] This will result in regulation of the size of the etching region, which for an (approximately) circular etching region may be defined by an etching region diameter.

[0028] If, according to a further embodiment, the mask controller and the gas flow controller are provided in combination, then the mask controller may be configured to 20 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.

[0029] In alternative or further embodiments, the gas flow controller may be used for dynamically adjusting the composition of the gas. In this way, the ratios of the various gas components in the gas supplied from the gas source to the resonance cavity 25 may be altered, in order to change the composition and hence the etching rate of the generated plasma. For example, 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.

[0030] According to an embodiment, the mask generator comprises an ultrasonic 30 transducer arranged for generating ultrasound waves within the liquid mask layer during use.

[0031 ] The ultrasound waves generated within the masking layer by the ultrasonic transducer during a decapsulation process will yield cavitation forces that assist in 7 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 5 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.

[0032] According to an embodiment, the plasma etcher device comprises an optical monitoring unit arranged for monitoring the etching region.

10 [0033] 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. For example, 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 15 user and/or for any provided etching process control. Up until now, 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 20 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.

[0034] According to an embodiment, the plasma-etcher device comprises a controlled stage configured for dynamically repositioning the sample surface with 25 respect to the discharge conduit at least in a plane perpendicular to the flow trajectory of the plasma jet during etching.

[0035] 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 30 prevents the plasma jet from being focused at a particular sample etching area for too long. Furthermore, the controlled stage may be configured for carrying out a predetermined motion, enabling the sample to be automatically etched in a predetermined pattern, while still allowing for intermittent interventions, by the user of 8 via computer control. The scan route and speed can thus be specified and programmed so that precise localization control and high decapsulation reproducibility can be achieved

[0036] According to a further embodiment, the controlled stage is configured for 5 dynamically adjusting the perpendicular distance between the sample surface and the discharge conduit during etching.

[0037] 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 10 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.

[0038] According to an embodiment, the liquid mask generator is arranged for 15 generating a transparent liquid masking layer, preferably comprising water, more preferably distilled water.

[0039] The use of 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 20 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. In addition, a processing unit may be provided, configured with an automated visual inspection algorithm for monitoring and keeping track of the sample condition. Advantageously, the entire sample surface can be continuously be assessed and compared to the local 25 etching result of the exposed surface.

[0040] The use of (distilled) water as a masking layer is preferred in a 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.

30 [0041] According to an embodiment, 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.

9

[0042] In a further embodiment, the contrast liquid is formed by an opaque liquid masking layer comprising an opaque colloid of colloidal particles in water (e.g. milk).

In another further embodiment, the contrast liquid masking layer may be partially transparent, for example by addition of ink to the water.

5 [0043] In other further embodiments, the opacity or transmission characteristics of the liquid masking layer may be varied during an etching process by dynamically operating the mask controller.

[0044] By using an opaque liquid masking layer, it becomes possible to accurately identify the boundary region and etching region between the plasma jet, the exposed 10 sample surface, and the liquid masking layer. This allows a processing unit of the etching device provided with an automated visual inspection algorithm to monitor this boundary region and etching region, and to evaluate its size and position with respect to the sample surface. Prediction models may be used to dynamically assess and predict the etching efficiency resulting from such etching region during the etching process.

15 The control parameters (i.e. gas flux, composition, mask thickness, sample distance) may be dynamically adjusted in response, to improve the etching result during the process.

[0045] According to an embodiment, the plasma etcher device comprises a processing unit configured for automatically controlling the position of the sample with 20 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.

[0046] 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.

25 According to further embodiments, 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 30 the described functions of respective components, and/or to receive information from these components (e.g. measurement data, component settings, component status).

[0047] According to a further embodiment, the processing unit is configured for optically recognizing the etching region and/or the boundary region, and for adjusting 10 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.

[0048] According to an embodiment, the MW source is arranged for generating electromagnetic microwave radiation with a frequency in a range of 2.4 GHz - 2.5 5 GHz, and preferably of 2.45 GHz.

[0049] 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, 10 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], 15 [0050] According to an embodiment, 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.

[0051] Selecting argon or helium as one of the main gas components for 20 generating plasma is preferred, due to its relatively low price and easiness to ignite a plasma.

[0052] According to an embodiment, 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 25 suitability obviates the need for executing the etching process under vacuum conditions and for providing and controlling delicate vacuum setup components. Other 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. Compared to other atmospheric pressure plasma jet sources, the MW field and plasma 30 characteristics for the Beenakker cavity indicate that the use this type of cavity will yield best results for the proposed decapsulation purposes.

[0053] According to a second aspect, and in accordance with the advantages and effects described herein above with respect to the plasma etcher device, there is 11 provided a method for removing an encapsulation portion of a semiconductor device using a plasma etcher device according to the first aspect, the method 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 5 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 10 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 selective etching by the confined plasma jet.

[0054] The proposed method provides a non-destructive process for removing the encapsulation of the semiconductor device. The moulding compound of the sample 15 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.

[0055] According to an embodiment and in accordance with advantages and effects described herein above, the method comprises: - dynamically adjusting a 20 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.

[0056] According to another embodiment, the method comprises: - optically monitoring the etching region and/or a boundary region between the plasma jet, the 25 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.

[0057] According to an embodiment, the method comprises: - supplying gas with a 30 first gas composition comprising Ar, O2, and CF4 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.

12

[0058] Two major constituents of the moulding compound of plastic 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 5 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 10 silica filler is only etched on the surface so that the agglomerate structure becomes loose. The impulse from the plasma jet will efficiently blow off the etched silica filler from the sample surface. According to a further embodiment, a percentage of CF4 with respect to one unit (i.e. 100%) of O2/CF4 etchant gas mixture (in a gas composition comprising Ar, O2, and CF4) is between 30 - 60% for CF4. For example, the plasma jet 15 may be composed of an argon gas flow of 1400 seem and a total O2/CF4 gas flow of 21 seem. As 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 CF4 percentage range with respect to one unit of O2/CF4 etchant gas mixture will yield an optimal moulding compound etching rate. A deviation in the CF4-percentage from 20 this optimal range lowers the etching rate. A low CF4 addition favours epoxy etching, while a high CF4 addition favours silica etching. The effect that the addition of CF4 into O2 plasmas increases epoxy etching rate, and the addition of O2 into CF4 plasmas increases silicon dioxide etching rate also facilitates the moulding compound etching by the Ar/02/CF4 mixture plasma. The composition of a lens on a LED die is silicone, 25 which contains organic groups chemically bonded with inorganic silicon elements. Similar to moulding compound etching, pure O2 plasma or pure CF4 plasma results in very low etching rate. Only when both O2 and CF4 are added into the plasma can a high etching rate be achieved. Optimal ratio of O2 and CF4 addition for silicone etching may vary due to the different composition in the certain silicone used.

30 [0059] According to a further embodiment, 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, O2, and CF4 from the gas source into the resonance cavity to generate a 13 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 O2 but excluding CF4 from the 5 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.

10 [0060] In order to prevent over-etching on any part on the die, and in particular of over-etching of an Si3N4 passivation layer that is often provided on a top surface of the die, the decapsulation method should be carried out in the following order: In an initial action of this method embodiment, gas with a first gas composition comprising Ar, O2, as well as CF4 is used for plasma etching, to remove a first layer of moulding 15 compound on top of the die. Preferably, the first layer thickness is relatively large, e.g. in the order of 300 pm to 1 mm. Preferably, the proposed method should be stopped when the remaining moulding compound on top of the die has a second layer thickness of about 50 pm. A critical second layer thickness of moulding compound is found to be 30 pm, and below this value Ar/02/CF4-plasma over-etching of the Si3N4 passivation 20 layer will occur. In a subsequent action, gas with a second gas composition comprising Ar and O2 but excluding CF4 is used for plasma etching of the remaining moulding compound. As only O2 plasma is used for etching, the epoxy in moulding compound is removed, but the silica filler (SiCF) is left as an agglomerate layer, due to the lack of fluorine (F) atoms. An improved plasma etching process by adding an O2 plasma 25 etching followed by an ultrasonic cleaning step successfully avoids over-etching of Si3N4 and Si. As a result, 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.

30 [0061] According to an alternative embodiment, 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 14 container enclosing a liquid wherein the (partially) treated sample is immersed. Here, 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 5 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.

[0062] According to a further embodiment, the plasma etcher device used in the method also comprises an optical monitoring unit for monitoring the etching region, 10 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.

[0063] By monitoring the sample surface during the action of ultrasound wave generation, the cleaning results for the sample can be evaluated in real-time during the 15 decapsulation process, which improves the decapsulation rate and accuracy.

[0064] According to a third aspect, there is provided a computer program product configured to provide instructions to carry out a method according to the second aspect, when loaded on a computer arrangement.

[0065] Furthermore, according to a fourth aspect, there is provided a computer 20 readable medium, comprising a computer program product according to the third aspect.

[0066] In general, the high etching rate and selectivity, low stray field, good localization control of the plasma jet, and real time imaging ability provided by the proposed plasma etcher device and method, render these very suitable for efficient 25 decapsulation of copper wire bonded semiconductor packages, for subsequent failure analysis and quality control.

[0067] The ability to focus the plasma jet by using the liquid masking layer is considered an inventive concept on its own. So according to an aspect that may be subject of a divisional application, there is provided a plasma etcher device for 30 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 15 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.

[0068] This plasma etcher device may be further defined and/or augmented with 5 any technical features as described herein above with respect to the device embodiments according to the first aspect, to achieve similar effects.

[0069] Similarly, according to another aspect that may be subject of a divisional application, there is provided a method for etching a surface of a sample using such a plasma etcher device, the method comprising: - placing the sample in a holder of the 10 plasma etcher device; - generating a plasma j et 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 15 plasma jet.

[0070] 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.

20 BRIEF DESCRIPTION OF DRAWINGS

[0071] Embodiments will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which:

[0072] Fig. 1 schematically shows an embodiment of the plasma etcher device 25 according to a first aspect;

[0073] Fig.2 presents an enlarged partial side view of the embodiment shown in

Fig-1;

[0074] Fig.3 schematically shows a side view of a sample for decapsulation with a device and method according to embodiments; 30 [0075] The figures are meant for illustrative purposes only, and do not serve as restriction of the scope or the protection as laid down by the claims.

16

DESCRIPTION OF EMBODIMENTS

[0076] 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 5 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. Inside the MW resonance cavity 6, 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 10 to optimize the EM coupling efficiency by reduction of power reflection, as described in ref.[4], In this embodiment, 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 15 sustaining the plasma.

[0077] 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 TM0io cylindrical transverse magnetic field mode at 2450 MHz (described in ref. [2]) from the MW radiation received from the MW source 2. The 20 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. At an opposite (lower) centre region, the Beenakker cavity 7 is 25 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. In the shown embodiment, 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 30 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 17 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. In 5 Fig. 1, the gas sources 8 are formed by containers for pressurized gasses of predetermined composition (e.g. Ar, 02, CF4). 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 10 flows can be regulated by coordinated operation of the gas flow controllers 10.

[0078] The plasma etcher device 1 has a sample holder 16 positioned at a perpendicular distance D1 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 D1 from the discharge conduit 14 and with a sample surface 15 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. This liquid masking layer 58 serves to confine the plasma jet 44 in such a manner that only a relatively 20 small interface between the plasma jet 44 and the sample surface 52 is established, which is referred to as the etching region Ae. 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 25 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.

[0079] The sample holder 16 is mounted on a controllable stage 24 that is 30 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 18 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 D1 between the sample surface 52 and the discharge conduit 14.

5 [0080] 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. 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 10 58 can be imaged by the CCD 30.

[0081] 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 15 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. In addition, the processing unit 32 is configured for optically recognizing the etching region Ae and/or the boundary 20 region Ab, and for adjusting any one of the gas flow rate Og, the plasma flow rate Op, the mask thickness D2, and the perpendicular distance D1 between the sample surface 52 and the plasma discharge conduit 14.

[0082] A computer program can be loaded on the computer arrangement 33 to provide instructions for carrying out a method as described herein below. This 25 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.

[0083] In an embodiment of a method for removing an encapsulation portion 50 of an integrated circuit 46 or LED, a plasma etcher device 1 as described above is used.

30 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 19 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 5 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 etching by the confined plasma jet.

[0084] 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 10 from the gas source 8, or - a plasma flow rate Op 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 15 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. In general, a thicker liquid mask 58 requires a larger gas flow rate Og to obtain a similar etching region diameter 0e. For a discharge tube inner diameter 0i of 1.2 mm, a discharge tube length D3 of 14 mm, a sample distance D1 of 6 mm, a liquid mask layer 58 consisting of 20 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: D2 = 1.10 mm: 0e = 0.12 • (Og - 400); D2 = 2.15 mm: 0e = 0.028 (Og - 1000); 25 D2 = 2.70 mm: 0e = 0.018 (Og - 1020);

[0085] 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 30 D1 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.

[0086] 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 20 executed: - supplying gas with a first gas composition comprising Ar, O2, and CF4 from the gas source 8 into the resonance cavity 6, so as to generate a first plasma jet 44; -directing the first plasma jet 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 5 selective etching; - subsequently supplying gas with a second gas composition comprising Ar and O2 but excluding CF4 from the gas source 8 into the resonance cavity 6, so as to generate a second plasma jet 44’; - directing the second plasma jet 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 -10 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.

[0087] 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 15 Argon plasma generates atomic oxygen that efficiently reacts with organic materials like photo resist and epoxy. CF4 gas added to the Argon plasma generates atomic fluorine that reacts with silicon containing materials forming volatile SiF4 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 CF4 with respect to one 20 unit (i.e. 100%) of 02/CF4 etchant gas mixture (in a gas composition comprising Ar, O2, and CF4) is selected from a range between 30% and 60%. Here, the plasma jet may be composed of an argon gas flow of 1400 seem and a total C>2/CF4 gas flow of 21 seem.

[0088] A further plasma etching method embodiment is used to avoid etching of 25 the Si3N4 passivation layer 57. In initial method actions, Ar/02/CF4 mixture plasma is used to quickly remove thick moulding compound layer with a first layer thickness D4 of about 300 pm 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 pm acts 30 as a protection layer to the underlying Si3N4 passivation layer 57. In further actions of the further method embodiment, an Ar/C>2 mixture plasma is used to selectively etch away the epoxy in the remaining moulding compound, which may take approximately 2 minutes. Because no fluorine containing gas is used, Si3N4 and SiC>2 are not etched, 21 resulting in undamaged die 54 and passivation layer 57 covered by a silica layer. The residual silica filler left after the epoxy has been removed from the moulding compound does not appear in powder form, but instead forms an agglomerate layer that cannot be easily be removed by the impulse of the plasma jet 44. The remaining action 5 of the further method embodiment involves a safe and clean way of removing the remaining layer of silica agglomerate by ultrasonic cleaning in the liquid layer, which may take approximately 10 seconds. The cavitations generated in the liquid layer 58 are capable of dissociating the silica agglomerate into powder efficiently, leaving a clean surface of die 54 and bond wires 56. The silicon die 54, Si3N4 passivation layer 57, and 10 copper bond wires 56 remain undamaged after decapsulation, and are in excellent condition for further failure analysis. The surface of the copper wires 56 after the improved plasma etching process is smooth.

[0089] If the thickness of the blocking layer of moulding compound after the initial Ar/(VCF4 etching action becomes less than 30 pm, then the fluorine radicals will 15 penetrate through the moulding compound layer and reach the underlying Si3N4 passivation. During Ar/02/CF4 plasma etching, 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 Si3N4 even though a layer of loose-structured moulding 20 compound is still left on top of the die. After approximately 6 minutes of plasma etching, the Si3N4 passivation layer 57, Si die 54, 23 pm copper wire bonds 56 (and aluminium bond pads) are exposed without damage.

[0090] The descriptions above are intended to be illustrative, not limiting. It will be apparent to the person skilled in the art that alternative and equivalent embodiments 25 of the invention can be conceived and reduced to practice, without departing from the scope of the claims set out below.

[0091] In addition, according to one of alternative aspects that may be the subject of a divisional application, there is provided a plasma-etcher device 1, for generating a plasma jet 44 and removing an encapsulation portion of a sample 46 via etching, 30 wherein 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 22 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 D1 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 5 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-etcher device 1 comprises a controlled stage 24 configured for dynamically repositioning the sample surface 52 with respect to the discharge conduit 14 at least in a plane S perpendicular to the flow trajectory F of the plasma jet 44 during etching, and 10 comprises an optical monitoring unit 30 arranged for monitoring an etching region Ae between the plasma jet 44 and the sample surface 52 during use.

[0092] Advantageously, by augmenting the known Beenakker cavity based plasma-etching device with the optical monitoring unit 30 and the controlled stage 24, the process control for the plasma etching method achieved with the proposed plasma 15 etcher device is greatly enhanced. By introducing 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 20 occurrence of failures during etching can be immediately detected, over-etching of the sample 46 (e g. causing damage to functional sample components like a semiconductor die 54) is greatly reduced, the etched area is much more uniform, and reproducibility of the etching process is significantly improved. With the plasma etcher device 1 according to this alternative aspect, it becomes possible to etch away the complete top 25 surface of the encapsulation of the circuit via a single accurately controlled process, without damaging the die, and without needing any further etching equipment like a laser ablation device or an acid etching device. All of the technical features provided as described herein above with reference to embodiments of the plasma etcher device according to the first aspect may also be present in this alternative aspect to achieve the 30 same effects. As an example, the plasma etcher device according to this alternative aspect 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 23 trajectory of the plasma jet 44, so as to confine the plasma jet to a reduced etching region Ae on the sample surface 52.

5 CITATION LIST

[1] TANG J. et al, “Plasma Decapsulation of Plastic IC Packages with Copper Wire Bonds for Failure Analysis”, Proc 12th Int. Conf. on Electronic Packaging Technology and High Density Packaging, Shanghai, China, 2011, pp. 888-892.

10 [2] BEENAKKER C.I.M., “A cavity for microwave-induced plasmas operated in helium and argon at atmospheric pressure”, Spectrochimica Acta, vol.31B, pp.483-486, 1976.

[3] LI Q. et al, “A Novel Decapsulation Technique for Failure Analysis of Integrated 15 Circuits” , Proc 7th Int. Conf. on Electronic Packaging Technology, Shanghai, China, pp. 1-5, 2006 [4] TANG J. et al, “Optimization of the Microwave Induced Plasma System for Failure Analysis in Integrated Circuit Packaging”, Proc 11th Int. Conf. on Electronic 20 Packaging Technology and High Density Packaging, 2010, pp. 1034-1038.

24

REFERENCE SIGNS LIST

1 plasma-etcher device 2 microwave source (MW generator) 4 microwave antenna 5 5 microwave guide (coaxial cable) 6 microwave resonance cavity 7 Beenakker cavity 8 gas source 10 gas flow controller 10 12 gas supply conduit 14 plasma discharge conduit 16 sample holder 20 mask generator 22 mask controller 15 24 controlled stage 26 ultrasonic transducer 28 ultrasound waves 30 optical monitoring unit (CCD) 32 processor unit 20 33 computer arrangement 34 input/output device 36 computer readable medium 38 data network 44 plasma jet 25 46 sample 48 encapsulation (mould) 50 first encapsulation portion 51 second encapsulation portion 52 sample surface 30 53 lead frame 54 semiconductor die 55 lead finger 56 bond wire (copper) 25 57 passivation layer 58 liquid masking layer D1 sample distance D2 mask thickness 5 D3 discharge tube length D4 first layer thickness D5 second layer thickness S perpendicular plane F flow trajectory 10 O optical axis

Ab boundary region Ae etching region

Og gas flow rate (flux)

Op plasma flow rate (flux) 15 0e etching region diameter 0i inner tube diameter 0o outer tube diameter

Claims

A plasma etcher device (1) for generating a plasma stream (44) and removing an envelope portion of a sample (46) by means of 5 etchings, the plasma etcher device comprising: a microwave cavity (6) connectable to a microwave source (2), and adapted to generate an electromagnetic standing wave by means of microwave radiation from the microwave source, and to hold a gas received from the gas source (8) in the cavity, and to generate a plasma from the gas, wherein the cavity comprises a plasma discharge line (14) for discharging the plasma in the form of a plasma stream (44); - a sample holder (16), for holding the sample (46) at a sampling distance (D1) from the discharge line, with a sample surface (52) facing the discharge line, so that during use, the plasma flow along a predetermined flow path ( F) is directed towards the stamp surface (52) to remove an envelope portion via etching; characterized in that the sample holder (16) is provided with a mask generator (20), for applying a liquid mask layer (58) to the sample surface and in the flow path of the plasma flow, in order to limit the plasma flow to an etching area (Ae) on the sample surface.

2. Plasma etcher device (1) according to one of the preceding claims, wherein the liquid mask generator (20) comprises a mask regulator (22) for adjusting a thickness (D2) of the liquid mask layer (58) in connection with a change in the at least one of: - a gas flow rate (Og) of gas from the gas source (8), and - a plasma flow rate (Op) of plasma from the plasma discharge line (14);

The plasma etching device (1) according to claim 1 or 2, wherein the mask generator (20) comprises an ultrasound transducer (26) adapted to generate ultrasound waves within the liquid mask layer (58) during use.

A plasma etching device (1) according to any one of the preceding claims, comprising an optical monitoring unit (30) adapted to monitor the etching area (Ae).

The plasma etcher device (1) according to any of the preceding claims, comprising a controlled object table (24) configured to dynamically reposition the sample surface (52) during etching with respect to the discharge line (14) at least in one plane (S ) perpendicular to the flow path (F) of the plasma flow (44). 10

The plasma etching device (1) according to claim 5, wherein at the controlled object table (24) is configured to dynamically adjust the perpendicular distance (D1) between the sample surface (52) and the discharge line (14) during etching. 15

The plasma etcher device according to any of the preceding claims, wherein the liquid mask generator (20) is adapted to generate a transparent liquid mask layer, preferably comprising water, and in particular distilled water. 20

The plasma etching device according to any of claims 4-6, wherein the liquid mask generator (20) is adapted to generate a contrasting liquid mask layer, and wherein the optical monitor unit (30) is configured to detect the etching area (Ae) and / or a boundary region (Ab) between the plasma stream and the contrasting liquid mask.

9. Plasma etcher device as claimed in any of the foregoing claims, comprising a processing unit (32) configured to automatically control the position of the sample (46) relative to the plasma discharge line (14) in response to a predetermined condition for the etching area (Ae) or of a boundary area (b) between the plasma stream and the liquid mask observed by the optical monitor unit (30).

The plasma etcher device according to claim 9, wherein the processing unit (32) is configured to optically recognize the etching area (Ae) and / or the boundary area (Ab), and to adjust one of the gas flow rate ((Dg) , the plasma flow rate (Op), the mask thickness (D2), and the perpendicular distance (D1) between the sample surface (52) and the plasma discharge line (14).

11. Plasma etcher device (1) according to one of the preceding claims, wherein the microwave source (2) is adapted to generate electromagnetic microwave radiation with a frequency in a range of 2.4 GHz - 2.5 GHz, and preferably of 2.45 GHz.

12. Plasma etcher device (1) as claimed in any of the foregoing claims, wherein the gas comprises a noble gas, preferably Argon or Helium, and wherein the microwave vibratory cavity (6) is adapted for the continuous generation of a plasma gas from atmospheric conditions from the gas.

A method of removing a casing portion from a semiconductor device (46) using a plasma etcher device (1) according to any of claims 1-12, the method comprising: 20. placing the semiconductor device (46) in a holder (16) of the plasma etcher device; - supplying gas from a gas source (8) to a cavity (6) of the plasma-etching device (1); - inducing a standing microwave within the cavity (6), by means of microwave radiation from a microwave generator (2); - generating a plasma from the gas within the cavity; - directing a plasma stream (44) through a plasma drain line (14) towards a component surface (52) of the semiconductor device (46), to remove the envelope portion by etching; Characterized by - applying a liquid mask layer (58) to the component surface (52), with the help of a mask generator (20) provided by the plasma etcher device, to limit the plasma flow to an etching area (Ae) on the circuit surface, and - removing the envelope portion (50) from the semiconductor device by selective etching with the limited plasma current. 5

A method according to claim 13, comprising: - dynamically adjusting a thickness (D2) of the liquid mask layer (58) in conjunction with a change in at least one of: - a gas flow rate (Og) of gas from the gas source (8) and 10. a plasma flow rate (Op) of plasma from the plasma discharge line (14).

Method according to claim 13 or 14, comprising: - optically monitoring the etching area (Ae) and / or a boundary area (Ab) between the plasma stream (44), the liquid mask (58), and the envelope surface 15 (52) ; - dynamically adjusting at least one of a gas flow rate (Og), the mask thickness (D2) of the liquid mask layer (58), and the sampling distance (D1) between the semiconductor device (46) and the discharge line (14), in response to a predetermined condition for the etching area (Ae) and / or the border area (Ab). 20

A method according to any of claims 13-15, wherein the plasma etcher device (1) used comprises an ultrasound transducer (26) adapted to generate ultrasound waves within the liquid mask layer (58) according to claim 3, wherein the method comprises: 25. supplying gas with a first gas composition comprising Ar, O2, and CF4 from the gas source (8) to the cavity (6), to generate a first plasma stream (44); - directing the first plasma stream (44) towards the component surface (52) of the semiconductor device (46) to remove a first envelope portion (50) with a first layer thickness (D4) via selective etching; - subsequently supplying gas with a second gas composition comprising Ar and O2 but without CF4 from the gas source (8) to the cavity (6), to generate a second plasma flow (44 "); - directing the second plasma stream (44 ') toward the component surface (52) of the semiconductor device (46) to remove a second sheath portion (51) with a second layer thickness (D5) via selective etching, and - generating ultrasound waves within the liquid mask layer (58) with the ultrasound transducer (26), for separating a silicate filler agglomeration layer from the envelope surface (52).

A computer program product configured to provide instructions for performing a method according to any of claims 13-16 when loaded on a computer device (33).

A computer readable medium (36) comprising a computer program product according to claim 17. 15