WO2009150556A1

WO2009150556A1 - A device for and a method of monitoring an etching procedure

Info

Publication number: WO2009150556A1
Application number: PCT/IB2009/052070
Authority: WO
Inventors: Sahel El Nadeim; Isak Venter
Original assignee: Nxp B.V.
Priority date: 2008-06-09
Filing date: 2009-05-19
Publication date: 2009-12-17

Abstract

A device (100) for monitoring an etching procedure comprising a detector unit (102) adapted for detecting etching of a substance of a substrate based on detecting a permittivity of a product (134) of the etching procedure, particularly an exhaust gas (134), generated upon etching the substance.

Description

A device for and a method of monitoring an etching procedure

FIELD OF THE INVENTION The invention relates to a device for monitoring an etching procedure.

Beyond this, the invention relates to a method of monitoring an etching procedure.

Moreover, the invention relates to a program element. Furthermore, the invention relates to a computer-readable medium.

BACKGROUND OF THE INVENTION

When an integrated circuit product is etched, it may be difficult to detect an endpoint of the etching of a specific layer before etching of the next layer starts. It may also be difficult to detect a starting point of the etching of a specific layer after etching of the previous layer is finished.

US 2003/0136425 Al discloses a method and an apparatus for determining an endpoint of a cleaning process running in a chamber. In particular, one embodiment is a method that includes steps of directing radiation absorbed by a byproduct of the cleaning process into an exhaust line of the chamber, detecting a measure of absorbance of the radiation by the byproduct, and determining the endpoint when the measure of absorbance falls within a predetermined window.

However, with such a complex procedure, it may be difficult to precisely detect an endpoint of an etching of a layer in a simple manner.

OBJECT AND SUMMARY OF THE INVENTION

It is an object of the invention to provide a system allowing an estimation of an endpoint of the etching of a structure with sufficient accuracy and in a simple manner.

In order to achieve the object defined above, a device for monitoring an etching procedure, and a method of monitoring an etching procedure according to the independent claims are provided.

According to an exemplary embodiment of the invention, a device for monitoring an etching procedure is provided comprising a detector unit adapted for detecting etching of a substance of a substrate (for instance a beginning or an end of such an etching) based on detecting a permittivity of a product of the etching procedure (that is a reaction product resulting from the etching of the substance), particularly an exhaust gas (or any other gaseous, liquid or solid product), generated upon etching the substance. The permittivity of a product of an etching procedure may change when the product changes, which - in turn - results from a change of the substance being etched. Thus, when a substance has been removed completely by etching, another substance of the substrate begins to be removed by etching, thereby changing the product and consequently the detected permittivity thereof. According to another exemplary embodiment of the invention, a method of monitoring an etching procedure is provided, the method comprising detecting etching of a substance of a substrate based on detecting a permittivity of a product of the etching procedure, particularly an exhaust gas, generated upon etching the substance.

According to still another exemplary embodiment of the invention, a program element (for instance a software routine, in source code or in executable code) is provided, which, when being executed by a processor, is adapted to control or carry out an etch monitoring method having the above mentioned features.

According to yet another exemplary embodiment of the invention, a computer- readable medium (for instance a CD, a DVD, a USB stick, a floppy disk or a harddisk) is provided, in which a computer program is stored which, when being executed by a processor, is adapted to control or carry out an etch monitoring method having the above mentioned features.

Electronic control for etch monitoring purposes that may be performed according to embodiments of the invention can be realized by a computer program, that is by software, or by using one or more special electronic optimization circuits, that is in hardware, or in hybrid form, that is by means of software components and hardware components. The term "etching procedure" may particularly denote any physical and/or chemical treatment of a substrate in which a specific portion or substance of the substrate is removed therefrom. In such a scenario, it may be desirable to detect a point of time or a stage of the procedure after which the substance has been completely removed from the substrate and an etching of a next substance starts. For instance, such a substance removal may be performed by applying a plasma and by further promoting etching by a suitable chemical such as a fluoro comprising chemical like HF (hydrofluoric acid).

The term "permittivity" or dielectric permittivity may particularly denote a physical quantity that describes how an electric field effects and is affected by a dielectric medium and is determined by the ability of a material to polarize in response to the electric field. Permittivity may be denoted as the ratio of the electric displacement in a medium to the electric field strength, and may also be denoted as the dielectric constant.

The term "exhaust gas" may particularly denote any gaseous product resulting from a physical and/or chemical reaction between a substance to be removed by etching and an etchant chemical. For example, when silicon material is removed and hydrofluoric acid is used as an etchant medium, the resultant medium may be SiF₄ (silicontetrafluoride). Since such a substance may be present in a gaseous state of matter, it may be denoted as an exhaust gas. According to an exemplary embodiment of the invention, the termination of an etching procedure of etching a specific material of a component may be detected by a sudden alteration of the generated etching product (for instance exhaust gas) which can be detected based on a change of the electrical permittivity in an environment of an etching chamber which can change the value of the capacitance of a capacitor used for monitoring the etching. Since exhaust gas generated during an etching procedure has the tendency to exhaust, leak or pass off in a specific manner (which can also be promoted by applying a vacuum pressure or the like), the proper arrangement of a capacitor is a cheap but efficient way of detecting the present constitution of the exhaust gas, thereby allowing to analyze which material is presently etched as a consequence of an analysis of a corresponding exhaust gas. A transition between an etching of different materials can be determined easily by monitoring a parameter indicative of the permittivity of the etch result.

According to a particularly preferred advantageous embodiment of the invention, the starting of a silicon etching after having previously removed (by etching) a package of a semiconductor product may be securely detected when a package semiconductor component shall be analyzed and therefore the package around the silicon chip is to be removed. In such an embodiment, the starting of the silicon etch can be accurately detected by the start of the generation Of SiF₄ (silicontetrafluoride) which is a fingerprint for the silicon etch removal. It may be sufficient to install a capacitor within or coupled to an etching chamber, which allows triggering to stop of the etching process when a product of the silicon etching is detected by a change of the capacity due to change of the electrical permittivity of the generated etching product in the progress of the etching procedure. Since silicontetrafluoride has a comparatively large permittivity, it can be sensed rapidly and clearly. In an embodiment, endpoint detection for package etching with a plasma etcher - A - may be performed. This may include a detection of silicon material laid open (end point) while etching the package, by detecting the change in permittivity of the exhaust gas, wherein a change in permittivity (for instance an increase) may indicate the presence of SiF₄ which is produced as soon as the silicon is laid open. Monitoring the permittivity of the exhaust gases using the exhaust gas as a dielectric of a capacitor may be used to determine when as end- point has been reached in plasma etching.

When decapsulating an integrated circuit in a plasma etcher, it is difficult to determine the exact endpoint, where for instance the packaging material of the integrated chip is removed and the silicon of the chip is laid open. According to an exemplary embodiment of the invention, a device for plasma etching is provided, comprising an etching chamber adapted for etching an etching sample to thereby generate exhaust gas, and a sensor arranged and adapted for sensing permittivity of the exhaust gas to thereby provide an etching stop signal based on a change of permittivity of the exhaust gas. Such an embodiment is much more facile and can be realised with a small number of mechanical parts, hence is much cheaper to establish. Such a system may be used for endpoint detecting when etching a package in plasma etcher.

In an embodiment, the exhaust gas may be led through a parallel-plate capacitor. In case of plasma etching a packaged Si-IC, the reaction product of etched silicon, SiF₄, can be detected by its high relative permittivity. Silicontetrafluoride (SiF₄) has a high relative permittivity, so the relative permittivity of the exhaust gas will rise too, when the silicon is laid open. The capacity of the parallel-plate capacitor rises, this can be used as an indicator for the achievement of the endpoint (and may trigger an etching stop signal). An embodiment provides a method for detection of silicon laid open while etching the package of an integrated circuit. The reaction product of etched silicon, SiF₄, can be detected by its high relative permittivity by implementing a capacitor, which uses the plasma etcher's exhaust gas as dielectric. A correspondingly operated capacitor may change its capacity value as soon as the silicon is laid open.

As soon as the silicon and/or a passivation of an integrated circuit is laid open, it will be involved in the plasma etch reaction. When this happens, silicontetrafluoride is produced and will be blown out of the reaction chamber with the exhaust gas. The exhaust gas has to be led through a parallel-plate capacitor. Silicontetrafluoride has a high relative permittivity, so the relative permittivity of the exhaust gas will rise too, when the silicon is laid open. The capacity of the parallel-plate capacitor rises, and this can be used as an indicator for the achievement of the endpoint.

There might be a time delay of, for instance, a few seconds, until the silicontetrafluoride can be sensed in the exhaust gas of the vacuum chamber. In this time, the etching process continues on the surface of the silicon chip. This detector can be implemented in a plasma etcher mainly used in opening plastic encapsulation. Conventionally, a way of checking if the silicon was already laid open was to stop the etching process, open the chamber and have a look at the device. So it was possible that the silicon was etched already for, for instance, a quarter hour.

According to an exemplary embodiment of the invention, an detector may be mounted in a connecting piece between an etch chamber and a vacuum pump and may be situated so that the sensitivity is maximized. With such a method it is possible to modify a simple plasma etcher without endpoint detection to make it able to detect at least the endpoint of a package etching, wherein such a modification is not very expensive.

According to an exemplary embodiment of the invention, the capacity measurement may be done as following: the sensor-capacity may be used as a frequency- defining element in an astable multivibrator. The frequency can be monitored by a microcontroller or any other control unit, which gives an alarm when the frequency changes, for instance in an expected way (for example frequency gets lower). This measurement can detect a relative change of the capacitance. It does not matter, which absolute value the capacitor has in the beginning, the only important thing is its change. This allows for a simple and robust detection.

According to an exemplary embodiment of the invention, a change of a resonance frequency of a capacitor comprising oscillator circuit may be detected as a result of a change of a dielectric between capacitor plates of the capacitor of the oscillator circuit. Next, further exemplary embodiments of the device for monitoring an etching procedure will be explained. However, these embodiments also apply to the method, to the program element and to the computer-readable medium.

The detector unit may be adapted for detecting an endpoint (in time) of the etching of the substance of the substrate or for detecting a starting point of the etching of the substance of the substrate based on detecting a change of permittivity of the product generated upon etching the substance. The sensing principle may be sensitive for any change of a substance presently removed by etching. When the etching of a first material has been finished and the etching of a second material begins, an educt of a chemical reaction involved in the etching procedure suddenly changes which may immediately result in a change of the products of the etching procedure. Thus, the material(s) generated during such a chemical reaction may be altered resulting in a change of a permittivity of such a (particularly gaseous) product. This change may also change a capacitance value of a capacitor when the product serves as a dielectric medium between capacitor electrodes of any desired geometry. Therefore, with a capacity measurement or the measurement of any capacity dependent electronic parameter, it is possible to immediately detect a change in a constitution of the etching products.

According to an exemplary embodiment, the detector unit is adapted for detecting an endpoint of the etching of a package of a packaged silicon chip or for detecting a starting point of the etching of silicon of a packaged silicon chip based on detecting a change of permittivity of the etching product generated upon etching the substance (for instance package or silicon). When a silicon chip or wafer is packaged (for instance with a plastic material) the change of carbon based etching products to silicon based products is a clear indicator that the package etching is terminated and the silicon etching starts. Thus, when it is desired to expose a silicon portion of a packaged silicon semiconductor product by removing package material by etching, the sudden generation of a silicon based exhaust product is an unambiguous indicator that the package etching is finished and the silicon etching is about to start. In such an embodiment, silicontetrafluoride (SiF₄) is suddenly generated which can be the trigger to terminate an etching procedure. Silicontetrafluoride is a gas which has the property to have a quite high value of the permittivity so that it can be clearly distinguished by a capacitance measurement from etching products of any previous etching procedure such as a package etching. For detection purposes, the detector unit may comprise one or more capacitor structures adapted for detecting etching of the substance of the substrate based on detecting a value of a capacitance of the capacitor structure influenced by the product in the capacitor structure. Such a capacitor structure may be arranged directly within an exhaust chamber (such as a plasma etching chamber) to thereby detect in direct spatial relation to the etching procedure the finishing point of time of a package etching. Alternatively, such a capacitor structure may be arranged outside of the etching chamber but in gas (or fluid) communication with the etching chamber so that exhaust gases may be guided from such an exhaust chamber to an etching probe in which the capacitor structure is arranged. Such a capacitor structure may comprise a parallel-plate capacitor having two planar plates between which the etching product can be accommodated as a dielectric medium. In accordance with the equation C = ε A / d, a change of ε (permittivity) of the dielectric medium results in a change of the capacitance C, wherein an area A of the capacitor plates and a distance d between the capacitor plates are constant geometric parameters.

Similar equations exist or can be derived for a parallel-cylinder capacitor having two concentrically arranged electrically conductive cylindrical shells having different radii, with a parallel-spheres capacitor having two concentrically arranged electrically conductive sphere shells having different radii, or any other desired capacitor geometry. For instance, two capacitor plates may also be adapted as coupled meander structures or as interdigitating finger electrodes. Also the use of more than two capacitor electrodes is possible.

The detector unit may comprise an oscillation unit adapted for generating or triggering an electromagnetic oscillation of the capacitor structure. In such an embodiment, the detector unit may be adapted for detecting a change of the etching of the substance of the substrate based on a change of a frequency of the oscillation of the capacitor structure, since the frequency of such a circuit may depend with high sensitivity on the dielectric of the capacitor. When an electric signal is applied to the capacitor structure forcing the capacitor structure to oscillate, the oscillation frequency is characteristically influenced by the permittivity of a medium between the capacitance elements such as capacitor plates. A change of the permittivity due to a change of the etching products (for instance due to the sudden inclusion of a silicon based reaction product) results in a clearly measurable change of the characteristic frequency. Detecting such a change in the characteristic frequency in an electronic manner (for instance by sampling a signal of the capacitor for the purpose of frequency detection) allows to clearly determine a point of time at which a first etching procedure removing a first material is finished and a second etching procedure removing a second material (differing from the first material) starts.

The oscillation unit may be adapted as an astable multivibrator. Such an embodiment allows to detect a change of the frequency with high accuracy. A multivibrator may be an electronic circuit used to implement a variety of simple two-state systems such as oscillators, timers or flip-flops. It may be characterized by two amplifying devices (transistors, electron tubes or other devices) cross-coupled by resistors and capacitors. An astable multivibrator may be a multivibrator in which the circuit is not stable in either state so that it continuously oscillates from one state to the other. The device may comprise a casing (or a housing) for accommodating the detector unit, the casing comprising an inlet to be coupled to an etching section and comprising an outlet to be coupled to a suction pump for sucking the product from the etching section, through the casing, and towards the suction pump. Such an embodiment allows for a specifically precise detection of a point of time of a change of an etching procedure, since a suction pump such as a vacuum pump may suck an exhaust gas or another exhaust fluid or even a solid etch product from the etching section such as an etching chamber through the detector unit. Thus, specific provisions may be taken to promote a desired streaming path of the exhaust gas. The inlet may comprise a horn (or a funnel or a hopper, more generally a fluid focussing element) for focussing exhaust gas from the etching section towards the detector unit in the casing. For instance, a conically tapering portion may allow to increase the concentration of the exhaust gas at the position of the detector unit, thereby further refining the accuracy of the etch sensor. The device may comprise an etching section (such as a plasma etching chamber) for etching the substance of the substrate to thereby generate the product, wherein the etching section may be in gas communication with the detector unit when the product is an etching gas. When the product is a liquid, the etching section may be in liquid communication with the detector unit. In any case, the exhaust product may be transported from the etching section towards a detector unit.

The device may comprise an etch control unit adapted for (at least temporarily) deactivating the etching section upon detection, by the detector unit, an endpoint of the etching of a substance of a substrate or a starting point of the etching of a substance of a substrate. The device may be adapted for monitoring a plasma etching procedure. Plasma etching may be denoted as a form of plasma processing used to fabricate integrated circuits. It may involve a high-speed stream of glow discharge (plasma) of an appropriate gas mixture being shot (in pulses) at a sample. The plasma source, known as etch species, can be either charged (ions) or neutral (atoms and radicals). During the process, the plasma may generate volatile etch products from the chemical reactions between the elements of the material etched and the reactive species generated by the plasma.

However, in other embodiments, other etching procedures may be monitored, for instance dry etching or wet etching procedures. Exposing an integrated circuit (for instance a passivation layer made of silicon nitride, a suicide structure, or a silicon portion) may be desired for error analysis of an IC product. Such an analysis may require a surface analysis of the silicon chip. This may also support a quality control entity. The aspects defined above and further aspects of the invention are apparent from the examples of embodiment to be described hereinafter and are explained with reference to these examples of embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be described in more detail hereinafter with reference to examples of embodiment but to which the invention is not limited.

Fig. 1 illustrates a device for monitoring an etching procedure according to an exemplary embodiment of the invention.

Fig. 2 illustrates a system of monitoring an etching procedure according to an exemplary embodiment.

Fig. 3 illustrates a circuitry for monitoring an etching procedure according to an exemplary embodiment.

Fig. 4 illustrates an alternative geometry for monitoring an etching procedure according to an exemplary embodiment of the invention. Fig. 5 illustrates a system for monitoring an etching procedure according to an exemplary embodiment.

Fig. 6 illustrates a diagram showing a characteristic curve measured by a system for monitoring an etching procedure and allowing to detect a point of time at which an etching procedure is finished.

DESCRIPTION OF EMBODIMENTS

The illustration in the drawing is schematical. In different drawings, similar or identical elements are provided with the same reference signs.

In the following, referring to Fig. 1, a device 100 for monitoring a plasma etching procedure according to an exemplary embodiment of the invention will be explained.

The device 100 comprises a detector section 102 adapted for detecting etching of silicon material of a packaged silicon product based on detecting an electric permittivity (ε_r) of silicontetrafluoride (SiF₄) as an exhaust gas generated during a plasma etching procedure involving a silicon etch, and resulting from a chemical reaction between an exposed silicon surface of the (previously packaged) silicon product and an etchant used during a plasma etching process. After having removed a (for instance carbon-based plastic) package of the packaged semiconductor chip on the one hand, silicon is exposed and participates at the further etching procedure. The generated exhaust gas 134 is supplied to the detector probe 102 from an etching chamber such as a plasma chamber of a plasma etcher which is not shown in Fig. 1. When the package removal is finished and the silicon removal starts, the chemical constitution of the exhaust gas 134 suddenly changes, which can be detected by the detector probe 102 as will be explained below in more detail. The detector unit 102 comprises a capacitor structure 104, which is arranged within an accommodation chamber 106 of a T-piece 108. An electronic control unit 110 such as a CPU (central processing unit) or a microprocessor is electrically coupled with the capacitor structure 104 to trigger or excite an electronic oscillation of the capacitor structure 104 with a characteristic frequency and for detecting a change of the etching products based on a change of a chemical composition of the exhaust gas 104 which results in a change of a characteristic frequency of an oscillation of the capacitor structure 104 due to a changed permittivity in hollow spaces 112 between the various capacitor plates of the capacitor structure 104. The circuitry of the control unit 110 comprises an astable multivibrator circuitry. The T-piece 108 serves as a casing for accommodating the capacitor structure

104 and comprises an inlet flange 114 to be coupled to an etching section (not shown in Fig. 1) and comprises an outlet flange 116 to be coupled to a suction pump 118 such as a vacuum pump. Thus, the exhaust gas 134 is sucked by a sucking force generated by the vacuum pump 118, from the etching section, through the inlet flange 114, is focused by a horn or funnel 120 onto the capacitor structure 104 and is then removed from the accommodation chamber 106 towards the vacuum pump 118 via the outlet flange 116.

When the control unit 110 has detected a change of the constitution of the exhaust gas 134, particularly has detected a sudden increase of the permittivity and therefore a sudden change of the characteristic frequency, this event may be correlated with the termination of the removal of a package of a semiconductor product in the etching chamber and the start of the removal of silicon material from the silicon chip. When such an event is detected, a control signal may be supplied from the control unit 110 via a wired (or wireless) communication connection 122 towards an etch control unit 124 of a plasma etching apparatus, thereby allowing the etch control unit 124 to terminate an etching procedure.

Subsequently, an exposed silicon chip freed of the surrounding package may be analyzed.

The device 100 further comprises an input/output interface 140 bidirectionally coupled with the control unit 110 and allowing a user to input control commands to the control unit 110. A user may be informed about a progress of an etching procedure via the input/output interface 140. The input/output unit 140 may comprise input elements such as a button, a joystick, a keypad, etc., and may comprise a display unit such as an LCD display.

Exemplary embodiments of the invention may serve as a monitor for monitoring a plasma etching procedure, which may be applied for removing a plastic housing of a monolithically integrated semiconductor circuit. A purpose of such an etching procedure may be to further analyze the semiconductor or silicon chip in more detail. It is possible to use tetrafluoromethane (CF₄) as an etching gas, wherein oxygen may be used as an accelerator. These gases may be blown in a vacuum chamber in which also the packaged IC may be located. By means of microwaves, plasma ionizing the gases may be generated in this chamber. The individual ions may interact with the integrated circuit so that material may be removed by etching. As soon as the silicon chip is exposed from the package to be removed during the etching procedure, the etching procedure is to be stopped. A time for such an etching procedure may be several hours. According to an exemplary embodiment of the invention, the endpoint may be indicated by an alarm such as an acoustical or optical or a haptic alarm.

To generate such an alarm signal, embodiments of the invention use the chemical recognition that when silicon material is etched with the above-mentioned etching gases, silicontetrafluoride (SiF₄) is generated. The detection of silicontetrafluoride may allow deriving unambiguously that the silicon is now exposed within the etching chamber. The etching chamber should remain sealed due to the microwave application. In order to allow the attachment of a sensor to such an arrangement, this can be integrated within the etching chamber or may be mounted in a gas drain line of the etching chamber.

Fig. 2 illustrates a block diagram of a corresponding architecture of a system 200 for analyzing an etching procedure according to an exemplary embodiment of the invention.

A gas flow 134 from an etching chamber 202 is guided to a sensor 102 which is coupled with a vacuum pump 118 to suck the exhaust gas 134 through the sensor 102. A sensor signal may be supplied from the sensor 102 to the control unit 110, more particularly to a measurement circuitry 204 thereof. The measurement circuitry 204 of the endpoint detector unit 110 is coupled with a microprocessor 206, which is in turn coupled with an alert signal generator 208 such as an acoustical noise generator or an LED. Using the capacitor 104 employing the surrounding exhaust gas as a dielectric medium between the capacitor plates, it is possible to detect within an exhaust gas line 210 whether a plasma etching reaction presently removes silicon. This can be detected by a capacitance measurement, since silicontetrafluoride has a high dielectric constant and can therefore be detected even in small amounts. When the exposed amount is sufficient to sufficiently influence the capacity of the capacitor 104, endpoint detection may be performed.

The detection of such a change of capacity is possible using an astable multivibrator. The variable capacitor 104 may be used for frequency generation. As soon as the value of the capacity is increased, the generated frequency may be decreased. Such a change can be detected by the microcontroller 206 performing a frequency calculation in a timer/CCU (capture compare unit).

An advantage of such a measurement principle is the cheap construction of the detector unit 102. The measurement procedure is very simple as well. In order to suppress artefacts due to parasitic capacitances of such an apparatus, it is possible to properly shield a measurement line so that parasitic capacitances may be maintained constant and may therefore be prevented from influencing the accuracy of the measurement, which may rely on a detection of changes rather than detecting absolute values.

Fig. 3 illustrates a circuitry 300 which may be used for detecting a change of capacitance.

An integrated circuit 302 may be operated to drive an astable multivibrator having, as a frequency determining element, a capacitance 104 which may serve as a measurement sensor. An effective capacitance of the sensing system of Fig. 3 may be the sum of the capacitor capacitance and a (parasitic) cable capacitance.

A detailed image 310 of Fig. 3 further shows that an arrangement with a Zener diode 312 may be used for maintaining a supply voltage constant. A resistance 314 may serve for current limitation purposes.

Since silicontetrafluoride has a permittivity of about 6, the generation of silicontetrafluoride due to the etching of silicon in an etching chamber results in a change of the characteristic frequency of the circuit 300. As can be taken from Fig. 1, the capacitor 104 may be formed by connecting a plurality of (for instance ten) capacitor plates to one another. Individual capacitor plates of the capacitor 104 may be free from a direct contact to one another. However, in an alternating sequence of the capacitor plates of the capacitor 104, even plates may be connected to one another and odd plates may be connected to one another.

Fig. 4 shows an etch detector 400 according to another exemplary embodiment.

Again, exhaust gas 134 can be concentrated or focused, using a horn 120, onto an arrangement of parallel sensor capacitance plates 402. As a spacer between the individual metal plates of the capacitor 402 a plastic housing 404 may be used.

Fig. 5 shows a measurement circuitry 500 according to an exemplary embodiment of the invention. An oscilloscope 502 or any other kind of frequency monitor may be implemented as well.

Fig. 6 shows a diagram 600 having an abscissa 602 along which a measurement time is plotted. Along an ordinate 604, a measured capacitance value can be seen. After a signal artefact 606 which is presently believed to be generated by the application of an under pressure to an etching chamber, a package of a package semiconductor chip is removed by etching which results in a curvature which is slightly decreasing. After 3 hours and 15 minutes, an endpoint 608 is achieved which can be detected as a minimum of the measurement curve. This may be the trigger for the termination of the etching procedure, since silicon is now exposed resulting in a subsequent sudden increase of the capacitance due to the generation of silicontetrafluoride .

Finally, it should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be capable of designing many alternative embodiments without departing from the scope of the invention as defined by the appended claims. In the claims, any reference signs placed in parentheses shall not be construed as limiting the claims. The word "comprising" and "comprises", and the like, does not exclude the presence of elements or steps other than those listed in any claim or the specification as a whole. The singular reference of an element does not exclude the plural reference of such elements and vice-versa. In a device claim enumerating several means, several of these means may be embodied by one and the same item of software or hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

CLAIMS:

1. A device (100) for monitoring an etching procedure, the device (100) comprising a detector unit (102) adapted for detecting etching of a substance of a substrate based on detecting a permittivity of a product (134) of the etching procedure, particularly an exhaust gas (134), generated upon etching the substance.

2. The device (100) according to claim 1, wherein the detector unit (102) is adapted for detecting an endpoint or for detecting a starting point of the etching of the substance of the substrate based on detecting a change of permittivity of a product (134) generated upon etching a substance.

3. The device (100) according to claim 1, wherein the detector unit (102) is adapted for detecting an endpoint of the etching of a package of a packaged silicon chip or for detecting a starting point of the etching of silicon of a packaged silicon chip based on detecting a change of permittivity of a product (134) generated upon etching a substance.

4. The device (100) according to claim 1, wherein the detector unit (102) is adapted for detecting silicontetrafluoride as the exhaust gas (134).

5. The device (100) according to claim 1, wherein the detector unit (102) comprises a capacitor structure (104) adapted for detecting etching of the substance of the substrate based on detecting a parameter indicative of a value of a capacitance of the capacitor structure (104) influenced by the product (134) within the capacitor structure (104).

6. The device (100) according to claim 5, wherein the capacitor structure (104) comprises at least one of the group consisting of a parallel-plate capacitor, a parallel-cylinder capacitor, and a parallel-spheres capacitor.

7. The device (100) according to claim 5, wherein the detector unit (102) comprises an oscillation unit (110) adapted for generating an oscillation of the capacitor structure (104), and wherein the detector unit (102) is adapted for detecting a change of the etching of the substance of the substrate based on a change of a frequency of the oscillation of the capacitor structure (104).

8. The device (100) according to claim 7, wherein the oscillation unit (110) is adapted as an astable multivibrator.

9. The device (100) according to claim 1, comprising a casing (108) for accommodating a permittivity sensing portion of the detector unit (102), the casing (108) comprising an inlet (114) to be coupled to an etching section and comprising an outlet (116) to be coupled to a suction pump (118) for sucking the product (134) from the etching section, through the casing (108), and towards the suction pump (118).

10. The device (100) according to claim 9, wherein the inlet (114) comprises a horn (120) for focussing the exhaust gas (134) from the etching section towards the sensing portion of the detector unit (102) in the casing (108).

11. The device (100) according to claim 1, comprising an etching section for etching the substance of the substrate to thereby generate the product (134), wherein the etching section is in gas communication with the detector unit (102).

12. The device (100) according to claim 11, comprising an etch control unit (124) adapted for terminating etching by the etching section upon detection, by the detector unit (102), an endpoint of the etching of a substance of a substrate or a starting point of the etching of a substance of a substrate.

13. The device (100) according to claim 1, adapted for monitoring a plasma etching procedure.

14. A method of monitoring an etching procedure, the method comprising detecting etching of a substance of a substrate based on detecting a permittivity of a product (134) of the etching procedure, particularly an exhaust gas (134), generated upon etching the substance.

15. A computer-readable medium, in which a computer program of monitoring an etching procedure is stored, which computer program, when being executed by a processor (HO), is adapted to carry out or control a method according to claim 14.

16. A program element of monitoring an etching procedure, which program element, when being executed by a processor (110), is adapted to carry out or control a method according to claim 14.