WO2015198185A1

WO2015198185A1 - Electrochemical coating stress sensor, apparatus and method for accurately monitoring and controlling electrochemical reactions and material coating

Info

Publication number: WO2015198185A1
Application number: PCT/IB2015/054510
Authority: WO
Inventors: Terunobu Akiyama
Original assignee: Ecole Polytechnique Federale de Lausanne EPFL
Current assignee: Ecole Polytechnique Federale de Lausanne EPFL
Priority date: 2014-06-23
Filing date: 2015-06-15
Publication date: 2015-12-30
Anticipated expiration: 2016-12-23

Abstract

The present invention relates to an electrochemical coating stress sensor comprising a stress member for receiving an electrochemical coating layer; a support frame supporting the stress member; at least two bridging portions separating the stress member from the support frame and connecting the stress member to the support frame. The stress member includes an electrochemical coating zone comprising a metal or metal oxide layer for receiving the electrochemical coating layer.

Description

Electrochemical coating stress sensor, apparatus and method for accurately monitoring and controlling electrochemical reactions and material coating

CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of international application No. PCT/IB2014/062537 filed June 23^rd 2014, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD OF THE INVENTION

The present invention concerns a stress sensor and more particularly a surface stress sensor or an electrochemical coating stress sensor. The present invention also concerns a method for monitoring or measuring stress in a material coating or layer. The present invention furthermore concerns a material coating monitoring apparatus for measuring or monitoring stress in a material coating or layer. The application fields of this invention are, for example, electroplating, electroforming, electroless plating, electrochemical corrosion, etching, or others which employ electrochemical reactions to, for example, deposit and/or remove material on/from target objects.

BACKGROUND OF THE INVENTION

Plating techniques such as, for example, electroplating (sometimes called galvanic plating), electroforming, electroless plating, etc. have been widely used in industry to coat a workpiece with a metallic layer. Distortion of lattice structure due to metallurgical disparities in an electrodeposited or catalytically deposited metal may cause either tensile or compressive internal stress. If too much stress is accumulated in the deposited layer, undesired phenomena like a deformation of the target workpiece or a peeling off of the layer itself can occur.

The internal stress and/or surface roughness of the plated layer, both related to quality of coating, can be minimized by precisely optimizing the process conditions by changing, for example, deposition rate, agitation of the plating solution, or by adding chemicals, etc.

Today, many electroplating companies are still using "open-loop" systems. A typical plating procedure is following: The operators initially fix the deposition parameters like current flow, agitation and temperature of the plating solution, which are based on their experiences, and execute the process. Once the deposition process is started, none of the parameters is changed until the process is completed. Only after the process is finished, quality of the deposited coating is investigated. It often takes more than 10 hours to complete a process. After this long time of waiting, they sometimes find that the process parameters were not adequate. Under such a circumstance, a lot of "waste" is generated. Therefore, a compact and useful "in-situ" or "real time" stress monitor is highly demanded by the plating industry. A system which actively changes one of the plating process parameters according to the sensor signal representing the internal stress of the depositing layer, while the deposition is underway, is also demanded by the plating industry.

There have been attempts in the art to monitor the stress by instruments which measure micro-strain or deformation in a deformable receptor which is undergoing the deposition of a coating under similar conditions as the item of interest is being coated. For example, US4986130, EP0209302A2, US4986130 and US4086154.

Fig. 0 of the present application shows the disclosed sensor in US4986130.

Those sensors are bulky and relatively large. It is difficult to mount such sensors in between small workpiece such as, for example, watch parts or luxury pieces. In addition, the effective sensor area on which a metal layer is formed is often much larger than that of the workpiece. These sensors are not suitable for accurate real-time monitoring of the stress in the depositing layer on the workpiece.

Surface stress sensors disclosed in the prior art to monitor surface stress can be found, for example, in EP2579010A1 , KR20130028933A, WO201 1 148774, US20130133433, WO2013157581 and WO201 1 148774 A1.

This surface stress sensor needs a layer deposited on the flat member of the sensor, which generates surface stress. Primarily, the deposited layer is made of polymer which absorbs target molecules.

SUMMARY OF THE INVENTION

The objective of this present invention is to provide a sensor, apparatus and method for accurately monitoring physical or mechanical stress in a material layer, for example, in a depositing layer and controlling the plating process to have a better quality layer.

In particular, the present invention concerns an electrochemical coating stress sensor according to claim 1 , a method for monitoring stress in a material coating according to claim 16, a material coating monitoring apparatus according to claim 24, and a use of a stress sensor to monitor stress in a material coating according to claim 30.

Other advantageous features of the present invention can be found in the dependent claims. BRIEF DESCRIPTION OF THE FIGURES

The above object, features and other advantages of the present invention will be best understood from the following detailed description in conjunction with the accompanying drawings, in which:

Figure 0 shows a sensor of prior art document US4986130;

Figures 1A and 1 B show respectively a top view and a cross-sectional view of a sensor according to an embodiment of the present invention;

Figure 1 C shows a sensor similar to the sensor of Figures 1A and 1 B including solely two bridging sections;

Figure 2 shows a sensor according to a further embodiment of the present invention;

Figure 3 shows a sensor according to a further embodiment of the present invention;

Figure 4 shows four piezoresistors used to form a full Wheatstone bridge;

Figure 5 shows an electroplating apparatus;

Figure 6A shows a case of tensile stress inducing a deformation of a flat member of the sensor according to the present invention, and Figure 6B shows a case of compressive stress inducing a deformation of a flat member of the sensor according to the present invention;

Figures 7A and 7B show respectively a top view and a cross-sectional view of a sensor according to a further embodiment of the present invention;

Figure 7C shows a sensor similar to the sensor of Figures 7A and 7B including solely two bridging sections;

Figure 8 shows a sensor according to a further embodiment of the present invention; Figure 9 shows an electroless plating apparatus;

Figure 10 shows an electrochemical corrosion test apparatus;

Figure 1 1 shows an etching apparatus;

Figure 12 illustrates a feedback-controlled electroplating apparatus;

Figure 13 illustrates an advanced feedback-controlled electroplating apparatus;

Figure 14 shows a feedback-controlled electroless plating apparatus;

Figure 15 shows a sensor according to the present invention;

Figure 16 shows a cross-sectional view (lower view) and a top view (upper view) of a sensor according to the present invention;

Figure 17 illustrates another embodiment of the present invention in which the member includes two interdigitated portions;

Figure 18 shows a sensor according to a further embodiment of the present invention; Figure 19 shows a sensor according to a further embodiment of the present invention; Figures 20A and 20B show respectively a top view and a cross-sectional view of a sensor according to a further embodiment of the present invention;

Figure 21 shows a plan view of another embodiment of the present invention; Figures 22A and 22B show a possible configuration of the sensor shown in Figure 21 ; and

Figures 23A and 22B show a further possible configuration of the sensor shown in Figure 21.

DETAILED DESCRIPTION OF THE INVENTION

The sensor

Fig. 1A and 1 B respectively show a plan view and a cross-sectional view of a sensor 1 , according to one preferred embodiment of the present invention, for accurately monitoring physical or mechanical stress in a depositing layer or a layer from which material is being removed.

The sensor 1 (or surface stress sensor) is for example a sensor for measuring or detecting a stress induced or generated by a coating or deposited layer that is produced by an electrochemical coating process.

The sensor 1 includes a stress member 3 for receiving an electrochemical coating layer, a support frame 5 supporting the stress member 3, a plurality of bridging portions 7 separating the stress member 3 from the support frame 5. Each bridging portion 7 connects the stress member 3 to the support frame 5.

The stress member 3 includes an electrochemical coating zone 9 comprising a metal or metal oxide layer for receiving an electrochemical coating layer.

The sensor has a substantially flat member 3. An electrode 1 1 is disposed on the flat member 3. The flat member 3 is also preferably flexible, that is, made of a material permitting the member to deform or bend and/or has a thickness that permits the member to deform or bend.

The support frame or fixing member 5 is made of a material and/or has a thickness that renders it rigid relative to the member 3.

There are at least two narrow or bridging portions 7 in between the flat member 3 and the fixing member 5 for fixing the flat member 3 there around so as to form a bridge. Piezoresistors 15 are disposed on the narrow portions. Each bridging portion 7 includes a piezoresistor 15 in the embodiment illustrated in Figure 1. Preferably, at least one bridging portion 7 includes at least one piezoresistor 15.

Alternatively, only one bridging portion 7 of the sensor 1 includes a piezoresistor 15 (or only one piezoresistor 15). For example, the sensor 1 includes at least two or solely two bridging portions 7 and only one of the at least two bridging portions 7 includes a piezoresistor 15 (or only one piezoresistor 15), or only one of the sole two bridging portions 7 includes a piezoresistor 15 (or only one piezoresistor 15). Figure 1 C illustrates a sensor comprising only two bridging portions and only one of these two bridging portions includes a piezoresistor 15.

The electrochemical coating zone includes the electrode 1 1.

The electrode 1 1 can include or be a metal or metal oxide electrode, such as for example ITO (indium tin oxide) electrode. The electrode 1 1 can include or be for example a continuous metal or metal oxide film with small grains, for example, between 1 nm and 1 μηι, and preferably 100 nm. The electrode 1 1 can alternatively or additionally comprise metal-nano-particles, or metal-oxide-nano-particles, in each case with or without binders.

The sensor 1 comprises a separation zone 14 between the bridging portions 7 to permit movement of the member 3. The separation zone 14 is for example comprised of empty space.

The piezoresistor 15 can be covered with a protection for example a protection layer 17 (Fig. 2).

The electrode 1 1 can be disposed on an insulator or insulator layer 19 which is disposed on the flat member 3 (Fig. 3).

Both the protection and the insulator can be employed on a device.

The flat member 3, the narrow portions 7 and the fixing member 5, all of them or one or more of them, can be made of insulator (or non-conductive material), more practically for example made with a thin insulator film, so that the electrode 1 1 and/or the piezoresistor 15 can be directly disposed on this insulator portion(s) (Fig. 18).

In such a case, it is preferred that the fixing member 5 is mechanically reinforced with one or more additional member(s) 21 to render it rigid relative to the member 3. The reinforcement can be done by attaching, or fixing, a separately fabricated member 21 on the fixing member 5 (Fig. 22), or by clamping it with plural members 21 (Fig. 23).

The piezoresistor 15 can be covered with a protection for example protection layer 17 (Fig. 19).

The narrow portion 7 can be four in number so that four piezoresistors 15 are disposed on a sensor 1. The four piezoresistors 15 are used to form a full Wheatstone bridge (Fig. 1 A, Fig. 1 B and Fig. 3), as for example illustrated in Figure 4.

Fig. 7A and 7B show a plan view and a cross-sectional view of another embodiment, respectively. The electrode 1 1 disposed on the flat member 3 can have a portion or extension arm 23 which is extended to the fixing member 5 (Fig. 7A and 7B). The extension arm 23 extends across the bridging portion 7 to the support frame 5. The extension arm 23 permits, for example, deposition of a material layer or coating on the flat member 3 and more particularly the electrochemical coating zone 9.

Each bridging portion 7 includes a piezoresistor 15 in the embodiment illustrated in Figure 7. Preferably, at least one bridging portion 7 includes at least one piezoresistor 15.

Alternatively, only one bridging portion 7 of the sensor 1 includes a piezoresistor 15 (or only one piezoresistor 15). For example, the sensor 1 includes at least two or solely two bridging portions 7 and only one of the at least two bridging portions 7 or only one of the sole two bridging portions 7 includes a piezoresistor 15 (or only one piezoresistor 15). Preferably, bridging portion 7 including the extended portion 23 is piezoresistor-less, that is, there is no piezoresistor 15 located in this bridging portion 7. Figure 7C illustrates a sensor comprising only two bridging portions and only one of these two bridging portions includes a piezoresistor 15.

The electrode 1 1 having the extended portion 23 can be disposed on an insulator 19 which is disposed on both flat member 3 and fixing member 5 (Fig. 8).

In another embodiment, the flat member 3, the narrow portions 7 and the fixing member 5, all of them or one or more of them, are made of insulator (non-conductive material), so that the electrode 1 1 with the extended portion 23 can be directly disposed on the insulator (Fig. 20A and 20B).

It is preferred that all those portions are made of the same material, but it is not indispensable. The portions can be made of different materials.

In the embodiment shown in Fig. 20A and 20B, there are three narrow portions 7. Two piezoresistors 15 are disposed on two of them. The extended portion 23 of the electrode is disposed on the third narrow portion 7 but the third narrow portion 7 does not include a piezoresistor 15.

Sensor operations

Electrochemical reactions, like deposition, etching, oxidation, reduction, etc. can occur on a surface of electrode 1 1 , for example a metal electrode, which has contact with an electrochemical medium such as electrolyte and plating solution.

An electrochemical reaction can cause to apply a mechanical stress to the reacting electrode. For example, electroplating is a process that uses electrical current to reduce dissolved metal cations so that they form a coherent metal coating on an electrode. Distortion of lattice structure due to metallurgical disparities in an electrodeposited layer may cause either tensile or compressive internal stress. Consequently, the stress is applied on the reacting electrode.

Electroplating

Fig. 5 shows an electroplating apparatus and the following is a method using the apparatus.

For example, the sensor 1 shown in Fig. 1A and 1 B is immersed in a plating solution. The electrode 1 1 of the sensor 1 is connected to the negative side of a current supply and is used as cathode. The positive side of the current supply is connected to an electrode immersed in the bath. This is anode. The piezoresistors 15 (or the sole piezoresistor 15) of the sensor 1 are connected to a sensor monitor 25 which is configured to measure and indicate changes in resistance of the piezoresistors 15.

Upon applying electric current through the anode and the cathode, a deposition of material occurs on the cathode, which is the electrode 1 1 formed on the flat member 3 of the sensor 1.

If the electrodeposited layer 27 has tensile or compressive internal stress, the stress induces a deformation of the flat member 3. For example, Fig. 6A shows a case of tensile stress and Fig. 6B is a case of compressive stress. Since the flat member 3 is supported with the narrow portions 7, the deformation of the flat member 3 yields bending of the narrow portions 7 (Fig. 6A and 6B). Consequently, the piezoresistors 15 formed on the narrow portions 7 change their resistances and the sensor monitor measures and indicates a relative amount of stress existing in the electrodeposited layer 27.

By operating the sensor 1 during the deposition process being underway, the sensor 1 can monitor accumulating stress in the depositing layer in real time.

For this application, it is preferred that the piezoresistor 15 is covered with a protection 17 like the drawing in Fig. 2. It is also preferred that the electrode 1 1 is formed on an insulator 19 disposed on the flat member 3 like the drawing in Fig. 3.

To facilitate an electrical contact to an external instrument, it is preferred that the electrode 1 1 formed on the flat member 3 has a portion 23 extend to the fixing member 5 (Fig. 7A, 7B, 20A and 20B). For example, a pad can be formed at the end of the extended portion 23 to facilitate a connection with a macro wire. Furthermore, it is preferred that the electrode 1 1 with the extended portion 23 is formed on an insulator like the figure in Fig. 8. Electroless plating

Fig. 9 shows an electroless plating apparatus and the following is a method using the apparatus.

Electroless plating, for example electroless nickel plating, is an auto-catalytic chemical technique used to deposit a layer on a solid workpiece, such as metal or plastic. The process relies on the presence of a reducing agent which reacts with the metal ions to deposit metal.

For example, an appropriate electrode 1 1 for electroless plating is formed on the flat member 3 of the sensor 1 shown in Fig. 1 A and 1 B (or a sensor according to any one of the other embodiments). The sensor 1 is immersed in an electroless plating bath. A deposition of material occurs on the electrode. The deposition process can be monitored in real time base on the principle mentioned above.

Electrochemical corrosion

Fig. 10 shows an electrochemical corrosion test apparatus and the following is a method using the apparatus.

Most metal corrosion occurs via electrochemical reactions at the interface between the metal and an electrolyte solution. It is an electrochemical process of oxidation and reduction reactions. As corrosion occurs, electrons are released by the metal (oxidation) and gained by elements (reduction) in the corroding solution. Because there is a flow of electrons (current) in the corrosion reaction, it can be measured and controlled electronically.

A typical experimental setup uses a potentiostat 29 connecting with three electrodes: working electrode, reference electrode, and counter electrode(s). Those electrodes are immersed in an electrolyte solution. The metal sample of interest is connected as the working electrode.

Electrochemical corrosion experiments measure and/or control the potential and current of the oxidation/reduction reactions. Several types of experiments are possible by manipulating and measuring these two variables.

Using the sensor 1 in this invention, not only the electrochemical aspects of a corrosion, but also physical or mechanical aspect of the corrosion can be investigated. Fig. 10 shows a typical measurement setup. The metal sample of interest is initially formed on the flat member 3 of the sensor 1 and connected to a potentiostat 29 as working electrode. While various measurements and/or controls are being executed, physical or mechanical status of the metal sample can be monitored in real time. Etching

Fig. 1 1 shows an etching apparatus and the following is a method using the apparatus.

The sensor 1 in this invention is useful to analyze stress distribution in a thin film.

There is, for example, a metal thin film deposited on a substrate by thermal evaporation with a changing condition in time. For example, two different deposition rates are employed at the first half and the latter half of the deposition process. Usually, such a film has a stress distributed along with the thickness direction. The stress distribution of the film can be measured in the following method.

Firstly, a thin film of interest is formed on the flat member 3 of the sensor 1. Then, the deposited thin film is slowly etched in etchant or electrolyte solution, while the sensor 1 is being operated (Fig. 1 1 ). A gradual removal of the material from the top of the thin film causes a change in total amount of stress being applied to the flat member 3. Evolution of the sensor output as a function of time can be referred as the stress distribution of the thin film.

Feedback-controlled electroplating and electroless plating apparatus

Fig. 12 shows a feedback-controlled electroplating apparatus and the following is a method using the apparatus.

Two different power supplies, which can actively change the current outputs according to external signals, are prepared. One power supply is connected to the electrode 1 1 of the senor 1 and an anode electrode. The other one is connected to workpiece and the same anode electrode. Both power supplies are controlled by micro controller which communicates with a computer. A program or algorithm is running on the computer to control the apparatus components. The micro controller receives the signal from the sensor monitor 25. It is an option that a reference electrode is connected with the micro controller. The reference electrode, the anode electrodes, the sensor and the workpiece are in the same bath filled with plating solution.

In this embodiment, the sensor 1 is used as an "in-situ" or a "real time" stress monitor. It measures stress in the deposited layer on the flat member, which represents the accumulating stress in the deposited layer on the workpiece. During operation, the computer receives the signal from the sensor 1 and actively controls the currents going to the sensor electrode and the workpiece. Consequently, the deposition rate is changed according to the sensor signal, which allows minimizing the internal stress in the deposited film owing to the feedback control. Fig. 13 shows an advanced feedback-controlled electroplating apparatus and the following is a method using the apparatus.

In general, the internal stress of the electroplated layer can be minimized by precisely optimizing the process conditions by changing, for example, deposition rate, agitation of the plating solution, or by adding chemicals, etc.

In the previous embodiment in Fig. 12, only the deposition rate is changed by controlling the current. In this embodiment, agitation of the plating solution, temperature of the plating solution and adding chemicals are additionally under control of the micro controller and are employed as means to minimize the internal stress of the deposited layer. A temperature gauge is used to monitor the plating solution. There may be other means which are not described here, but can be employed for the same purpose. All the active means are executed by the program according to the sensor signal.

Fig. 14 shows a feedback-controlled electroless plating apparatus and the following is a method using the apparatus.

In case of electroless plating, no electrical control of the deposition is possible, meaning that the electrode of the sensor and the workpiece are not electrically connected to any instruments. Hence, the means to minimize the internal stress of the deposited layer are limited. In this embodiment, agitation of the plating solution, temperature of the plating solution and adding chemicals are the means under control of the micro controller. There may be other means which are not described here, but can be employed for the same purpose.

The present invention concerns a method for monitoring stress in a material coating layer wherein a stress sensor 1 according to any one of the embodiments described herein is used to measure stress in the material coating layer, and changes in resistance of at least one piezoresistor 15 are measured to determine the presence of stress in a depositing material coating layer or a deposited material coating layer, or to monitor the evolution of stress in a material coating layer.

The deposition of the material coating layer can be stopped when a value representing the stress in the depositing layer reaches a predetermined threshold, or the removal of the material coating layer is stopped when a value representing a stress distribution in the coating layer reaches a predetermined threshold. The material coating layer deposition conditions can be controlled based on the determined value representing the stress in the coating layer to minimize the internal stress of the coating layer. The material coating layer deposition conditions can be controlled by changing a material deposition rate.

The material coating layer deposition conditions can be controlled by one of or any combination of the following: changing a material deposition rate, agitation of a deposition solution, adding chemicals to the deposition solution or changing the temperature of the deposition solution.

The material coating layer is deposited by electrochemical reaction, electroplating, electroforming or electroless plating.

The material coating layer is removed by etching or electrochemical corrosion.

The present invention also concerns an apparatus for monitoring a material coating or layer comprising a stress sensor 1 according to any one of the embodiments described herein, and the stress sensor monitor device 25 for measuring changes in resistance of at least one piezoresistor 15 (or the sole piezoresistor 15) to determine the presence of stress in a depositing material coating layer or a deposited material coating layer, or to monitor the evolution of stress in a material coating layer. The apparatus according further comprises a controller (see for example Figures 12 to 14) configured to stop the deposition of the material coating layer when a value representing the stress in the depositing layer reaches a predetermined threshold, or stopping removal of the material coating layer when a value representing a stress distribution in the coating layer reaches a predetermined threshold.

The controller is further configured to control the material coating layer deposition conditions based on the determined value representing the stress in the coating layer to minimize the internal stress of the coating layer. The controller is additionally configured to change a material deposition rate.

The apparatus can include a heater, a chemical dispenser, an agitator and the controller is configured to change the material coating layer deposition conditions by one of or any combination of the following: changing a material deposition rate, agitation of a deposition solution, adding chemicals to the deposition solution or changing the temperature of the deposition solution.

The apparatus can further include a heater, a chemical dispenser, an agitator and the controller is configured to change the material coating layer deposition conditions by one of or any combination of the following: agitation of a deposition solution, adding chemicals to the deposition solution or changing the temperature of the deposition solution.

Microfabricated sensor

Fig. 15 shows an embodiment of the sensor 1 in this invention. The flat member 3 has a diameter of 300 μηι and a thickness of 2 μηι in this case. The diameter can be 50 μηι to several cm and the thickness can be 1 μηι to several mm. The flat member 3 is a film of a n-type silicon single crystal, and a surface of the film is a (100) plane of the single crystal.

There are four narrow portions and, hence, four piezoresistors 15 are formed on the sensor 1. One of the two piezoresistor pairs is disposed in a [1 10] direction of the single crystal, and the other pair is disposed in 90 degrees to the former pair. The piezoresistors are p-type diffusions.

The electrode 1 1 on the flat member 3 is a 100 nm gold layer.

Fabrication of sensor

The sensor 1 of this invention can for example be manufactured in the following way. Description will be made with reference to a cross-sectional view (lower view) and a plan view (upper view) in Fig. 16.

Silicon-on-insulator (SOI) wafer of 4 inches, having an n-type device layer 1 1 1 (thickness of about 3 μηι and about 10 Ω-cm) on a handling layer 1 12 (thickness of about 350 μηι and about 10 Ω-cm) is prepared.

Firstly, the wafer is cleaned. An oxide film 1 13 of 700 nm is formed by thermal oxidation. After photolithography, areas to form highly Boron doped p-type diffusions 1 14 are opened in the oxide film 1 13 by etching in buffered hydro fluoric acid (BHF). The wafer is again oxidized and an oxide film of 50 nm is formed in the opened areas. Then, Boron is doped by implantation at 45 keV with a dose of 5E+15 /cm². Activation and diffusion of the dopants are performed at 1000°C for 30 min. After photolithography, the oxide film is partially opened by BHF etching. The wafer is oxidized and an oxide film 1 15 of 50 nm is formed on the exposed Si areas. This step was done at 950°C by wet oxidation. After photolithography, Boron is doped to form a shallow p-type diffusion 1 16. It was done by implantation at 45 keV with a dose of 2.5E+14 /cm², with the patterned photoresist as mask. Activation of the doped Boron was performed by rapid thermal annealing at 1000°C for 10 sec. This step does not allow the doped Boron to further diffuse into silicon and consequently a shallow p-type diffusion is formed. Using low pressure chemical vapor deposition (LPCVD), a silicon nitride film 1 17 of 50 nm is formed on the entire wafer surface. After the photolithography, a contact hole 1 18 is opened by plasma and BHF etchings. A platinum film of 150 nm with tantalum adhesion layer is deposited on the device side and the metal line 119 is formed by lift-off technique. In order to protect the metal line 1 19, a silicon nitride film 120 of 100 nm is deposited by LPCVD and patterned by plasma etching with photoresist mask. Next, an opening on a rear surface of the wafer for KOH etching is formed. The wafer is mounted on a mechanical chuck and is dipped in KOH of 40 weight % at 60° C to form a large opening from the rear surface. Etching is automatically stops at a buried oxide film (BOX) 121. The BOX is etched in BHF to form a membrane 122 and a narrow bridge 123. Finally, a gold electrode 124 of 100 nm in thickness with titanium or chromium adhesion layer is formed on the membrane 122 by thermal evaporation and lift-off technique.

In the device configuration described above, the shallow p-type diffusion 1 16 is the piezoresistive sensing element 15. The highly Boron doped p-type diffusions 1 14 are used (i) to have good ohmic contact between the metal line 1 19 and the shallow p-type diffusion 1 16, which is much less Boron doped and has a higher sheet resistance, and (ii) to avoid negative sensing effect.

In Fig. 16, the piezoresistor is folded and has a U-shape. The directions of electric current going through the two shallow diffusions 1 16 are nearly parallel the direction of stress to be applied due to a deformation of the membrane 122. However, the bottom part of the U-shape has a current direction nearly perpendicular to the stress direction and yields a negative sensing effect. Since the piezoresistive coefficient of the highly Boron doped diffusion 1 14 is much lower than that of the shallow diffusions 1 16, it is placed at the bottom part of the U-shape so as not to lose sensitivity.

Figure 17 illustrates another embodiment of the present invention in which the member 3 includes two interdigitated portions 31. Each interdigitated portion 31 includes an extension portion 33 extending across a narrow portion 7 to the fixing member 5. Although Figure 17 illustrates two interdigitated portions 31 , three, four or more interdigitated portions 31 can be employed. This configuration can improve, for example, homogeneity of a depositing layer by applying current on one of them at a time and alternating the active electrode 1 1. The electrode disposed on the member 3 can be two or more in number. For example, two electrodes in an interdigitated pattern can be employed. Microfabricated sensor with non-semiconductor materials

A sensor 1 with non-semiconductor materials in this present invention can be manufactured with existing PCB (Printed circuit board) and/or screen printing technologies.

Fig. 21 shows a plan view of another embodiment of the present invention in which the flat member 3, the narrow portions 7 and the fixing member 5, all of these or one or more of them, are made out of insulator (insulator material). This is a similar case as the embodiments shown in Fig. 18, Fig. 19, Fig. 20A and Fig. 20B.

Fig. 22A and Fig. 22B show a possible layer configuration of the sensor 1 shown in Fig. 21. A reinforcement member 21 is attached, or fixed on the fixing member 5 with for example glue to render it rigid relative to the member 3.

The insulator material can be for example PI (Polyimide), PMMA (Poly Methyl Methacrylate), PE (Poly Ethylene), PET (Polyethylene terephthalate), PEEK (Polyether ether ketone), polyester, etc.

The thickness of the insulator material is for example 100 μητ The flat member 3 and/or the narrow portions 7 and/or the fixing member 5 thus has a thickness for example of 100 μητ The flat member 3 is for example 1 cm in diameter. The reinforcement member 21 can be made of plastic for example acrylic resin, or of FR4 which is used as substrate material for PCB. The thickness T of the reinforcement member 21 is for example 500 μηι, or thicker.

The reinforcement member 21 attaches to a section 51 of the support frame 5 that extends out substantially parallel from the bridging portions 7. The section 51 includes upper and lower substantially flat surfaces for receiving a reinforcement member 21. The attached reinforcement member 21 , for example, extends out from the section 51 substantially perpendicularly.

Fig. 23A and Fig. 23B show another possible layer configuration of the sensor 1 shown in Fig. 21 and Fig.22. Two members 21 clamp, or sandwich, the fixing member 5 (section 51 ) to increase its rigidity. The parts are assembled for example with screws 53so that only the sensor layer 1 can be exchanged or replaced after the sensor has been used. The dimensions and sizes of the components can be approximately the same as the case in Fig. 22A and Fig. 22B.

A first reinforcement member 21 a attaches to the upper surface of the section 51 and a second reinforcement member 21 b attaches to the lower surface of the section 51. The attached reinforcement members 21 a, 21 b, for example, extends out from the section 51 substantially perpendicularly. The reinforcement members 21 a, 21 b and the section 51 include attachment means for fixing the reinforcement members 21 a, 21 b and the section 51 together. For example, the reinforcement members 21 a, 21 b and the section 51 include threaded bores 55 that receive screws 53.

The piezoresistor 15 can be for example a metallic strain gauge made of for example a constantan alloy, which is employed in the majority of commercially available strain gauges. However, other strain sensors made of other materials like for example (semi-) conductive polymer, (semi-)conductive ceramic, carbon nano-structure materials, or different metal alloys, etc. can be employed.

The electrode on the flat member 3 can be a thin gold alloy plated on Nikkei or Copper. Other metals can also be employed.

The diameter of the flat member 3 can be 100 μηι to several cm and the thickness can be 10 μηι to several mm.

Fabrication techniques like, formation of metallic lines on an insulator film, selectively attaching reinforcement materials (thickness of PCB can be partially increased), and covering the conductive lines with insulating material, are often employed in manufacturing of flexible PCB. Compared to the semiconductor version of the sensor described above, the fabrication of this embodiment of the present invention is less- complex and one can advantageously expect a large mass production of the sensor at a relatively low cost.

The flexible stress member 3 according to any of the previously described embodiments has a thickness between 1 μηι and 10mm, or preferably between 5μηι and 5mm, or more preferably between 10μηι and 5mm.

Having described now the preferred embodiments of this invention, it will be apparent to one of skill in the art that other embodiments incorporating its concept may be used. This invention should not be limited to the disclosed embodiments, but rather should be limited only by the scope of the appended claims.

Claims

1. Electrochemical coating stress sensor (1 ) comprising:

- a stress member(3) for receiving an electrochemical coating layer;

- a support frame (5) supporting the stress member (3);

- at least two bridging portions (7) separating the stress member (3) from the support frame (5) and connecting the stress member (3) to the support frame (5);

wherein the stress member (3) includes an electrochemical coating zone (9) comprising a metal or metal oxide layer for receiving the electrochemical coating layer.

2. Electrochemical coating stress sensor (1 ) according to claim 1 , wherein at least one bridging portion, or the at least two or each bridging portion (7) includes a piezoresistor

(15).

3. Electrochemical coating stress sensor (1 ) according to claim 2, wherein each bridging portion (7) further includes a protection layer (17) covering the piezoresistor (15).

4. Electrochemical coating stress sensor (1 ) according to any previous claim, wherein the stress member (3) further includes an insulator layer (19) disposed under the metal or metal oxide layer to insulate the electrochemical coating zone (9) from the support frame (5).

5. Electrochemical coating stress sensor (1 ) according to any previous claim, wherein the electrochemical coating zone (9) includes at least one extension arm (23) extending across at least one bridging portion (7) to the support frame (5) for permitting deposition of a material coating layer.

6. Electrochemical coating stress sensor (1 ) according to the previous claim, wherein the sensor (1 ) further includes an insulator layer (19) disposed under the extension arm (23) to insulate the extension arm (23) from the support frame (5).

7. Electrochemical coating stress sensor (1 ) according to any previous claim, wherein the metal layer includes gold and/or titanium and/or chromium.

8. Electrochemical coating stress sensor (1 ) according to any previous claim, wherein the electrochemical coating zone (9) includes at least two interdigitated portions (31 ).

9. Electrochemical coating stress sensor (1 ) according to the previous claim, wherein each interdigitated portion (31 ) includes an extension arm (33) extending across at least one bridging portion (7) to the support frame (5).

10. Electrochemical coating stress sensor (1 ) according to any previous claim, wherein the stress member (3) and/or each bridging portion (7) and/or the support frame (5) includes or consists of an insulating material.

1 1. Electrochemical coating stress sensor (1 ) according to the previous claim, wherein the insulating material is one or more of the following group: PI (Polyimide), PMMA

(Poly Methyl Methacrylate), PE (Poly Ethylene), PET (Polyethylene terephthalate), PEEK (Polyether ether ketone), polyester.

12. Electrochemical coating stress sensor (1 ) according to any previous claim, including solely three bridging portions (7) wherein two of the bridging portions (7) each include a piezoresistor (15) and the remaining bridging portion (7) is piezoresistor-less and includes an extension arm (23) extending across said bridging portion (7) to the support frame (5) for permitting deposition of a material coating layer.

13. Electrochemical coating stress sensor (1 ) according to any one of previous claims 10 to 12, wherein the support frame (5) includes an attachment section (51 ) and at least one reinforcement member (21 ) attached thereto.

14. Electrochemical coating stress sensor (1 ) according to any previous claim, wherein the stress member (3) has a thickness between 1 μηι and 10mm, or between 5μηι and 5mm, or between 10μηι and 5mm.

15. Electrochemical coating stress sensor according to any previous claim, wherein the piezoresistor (15) includes at least one shallow acceptor or donor doped portion interconnecting at least two higher amount of acceptor or donor doped portions respectively.

16. Method for monitoring stress in a material coating layer comprising the steps of:

- providing a stress sensor (1 ) to measure stress in the material coating layer, the surface stress sensor including a stress member (3), a support frame (5) supporting the stress member (3) and at least two bridging portions (7) separating the stress member (3) from the support frame (5) and connecting the flexible stress member (3) to the support frame (5), at least one bridging portion (7), or the at least two or each bridging portion (7) including a piezoresistor (15); and

- measuring changes in resistance of at least one piezoresistor(15) to determine the presence of stress in a depositing material coating layer or a deposited material coating layer, or to monitor the evolution of stress in a material coating layer.

17. Method for monitoring stress in a material coating layer according to claim 16, further including the step of: - stopping the deposition of the material coating layer when a value representing the stress in the depositing layer reaches a predetermined threshold, or stopping removal of the material coating layer when a value representing a stress distribution in the coating layer reaches a predetermined threshold.

18. Method for monitoring stress in a material coating layer according to any one of previous claims 16 to 17, further including the step of:

- controlling the material coating layer deposition conditions based on the determined value representing the stress in the coating layer to minimize the internal stress of the coating layer.

19. Method for monitoring stress in a material coating layer according to the previous claim, wherein controlling the material coating layer deposition conditions is carried out by changing a material deposition rate.

20. Method for monitoring stress in a material coating layer according to previous claim 18, wherein controlling the material coating layer deposition conditions is carried out by one of or any combination of the following: changing a material deposition rate, agitation of a deposition solution, adding chemicals to the deposition solution or changing the temperature of the deposition solution.

21. Method for monitoring stress in a material coating layer according to any one of previous claims 16 to 20, wherein the material coating layer is deposited by electrochemical reaction.

22. Method for monitoring stress in a material coating layer according to any one of previous claims 16 to 21 , wherein the material coating layer is deposited by electroplating, electroforming or electroless plating.

23. Method for monitoring stress in a material coating layer according to any previous claim, wherein the material coating layer is removed by etching or electrochemical corrosion.

24. Material coating monitoring apparatus comprising:

- a stress sensor (1 ) for measuring stress in a material coating layer, the stress sensor (1 ) including a stress member (3), a support frame (5) for supporting the stress member (5) and at least two bridging portions (7) separating the stress member (3) from the support frame (5) and connecting the stress member (3) to the support frame (5), at least one bridging portion (7), or the at least two or each bridging portion (7) including a piezoresistor (15); and - a stress sensor monitor device (25) for measuring changes in resistance of at least one piezoresistor (15) to determine the presence of stress in a depositing material coating layer or a deposited material coating layer, or to monitor the evolution of stress in a material coating layer.

25. Material coating monitoring apparatus according to the previous claim, further comprising:

- a controller configured to stop the deposition of the material coating layer when a value representing the stress in the depositing layer reaches a predetermined threshold, or stopping removal of the material coating layer when a value representing a stress distribution in the coating layer reaches a predetermined threshold.

26. Material coating monitoring apparatus according to the previous claim 24, further comprising:

- a controller configured to control the material coating layer deposition conditions based on the determined value representing the stress in the coating layer to minimize the internal stress of the coating layer.

27. Material coating monitoring apparatus according to the previous claim, wherein the controller is configured to change a material deposition rate.

28. Material coating monitoring apparatus according to the previous claim, further including a heater, a chemical dispenser, an agitator and wherein the controller is configured to change the material coating layer deposition conditions by one of or any combination of the following: changing a material deposition rate, agitation of a deposition solution, adding chemicals to the deposition solution or changing the temperature of the deposition solution.

29. Material coating monitoring apparatus according to the claim 26, further including a heater, a chemical dispenser, an agitator and wherein the controller is configured to change the material coating layer deposition conditions by one of or any combination of the following: agitation of a deposition solution, adding chemicals to the deposition solution or changing the temperature of the deposition solution.

30. Use of a stress sensor (1 ) to monitor stress in a material coating layer, the stress sensor (1 ) including a stress member (3), a support frame (5) supporting the stress member (3) and at least two bridging portions (7) separating the stress member (3) from the support frame (5) and connecting the stress member (3) to the support frame (5), at least one bridging portion (7), or the at least two or each bridging potion (7) including a piezoresistor (15).

31. Use of a stress sensor (1 ) according to the previous claim wherein the stress monitoring is carried out during deposition of the material coating layer, or during removal of a deposited material coating layer.