This invention pertains in general to the field of electrochemical pattern replication. More particularly the invention relates to a method for filling an ECPR chamber, and a chuck adapted therefore.
Electroplating/electroetching is used for microelectronics in a wide range of applications, such as interconnects, components, waveguides, inductors, contact pads etc.
In the field of microelectronics electroplating/electroetching is suitable for applications involving production of micro and nano structures in single or multiple layers, fabrication of PWB (printed wiring boards), PCB (printed circuit boards), MEMS (micro electro mechanical systems), IC (integrated circuit) interconnects, above IC interconnects, sensors, flat panel displays, magnetic and optical storage devices, solar cells and other electronic devices. It can also be used for different types of structures in conductive polymers, structures in semiconductors, structures in metals, and others. Even 3D-structures in silicon, such as by formation of porous silicon, are possible.
Chemical vapour deposition and physical vapour deposition are processes that may also be used for metallization, but electroplating/electroetching is often preferred since it is generally less expensive than other metallization processes and it can take place at ambient temperatures and at ambient pressures.
Electroplating/electroetching of a work piece takes place in a reactor containing an electrolyte. An anode, carrying the metal to be plated, is connected to a positive voltage. In some cases, the anode is inert and the metal to be plated comes from the ions in the electrolyte. The conductivity of the work piece, such as a semiconductor substrate, is generally too low to allow the structures to be plated to be connected through the substrate to backside contacts. Therefore, the structures to be plated first have to be provided with a conductive layer, such as a seed layer. Leads connect the pattern to finger contacts on the front side. The finger contacts are in turn connected to a negative voltage. The electroplating step is an electrolytic process where the metal is transferred from the anode, or from the ions in the electrolyte, to the conductive pattern (cathode) by the electrolyte and the applied electric field between the anode and the conductive layer on the work piece, which forms the cathode.
The ever-increasing demand for smaller, faster and less expensive microelectronic and micro-electromechanical systems requires corresponding development of efficient and suitable manufacturing techniques, which has resulted in the development of electrochemical pattern replication (ECPR).
In ECPR plating/etching cells or cavities are formed between a master electrode and the substrate, said cavities being defined by a conductive surface on the master electrode, an insulating material, defining the pattern to be plated/etched, and the conductive surface of the substrate. During plating, a predeposited anode material has been arranged, normally through electrochemical plating, in the cavities. The master electrode and the substrate are put in close contact with each other in the presence of an electrolyte, suitable for the intended purpose, such that the electrolyte is "trapped" in the ECPR plating/etching cavities.
During an ECPR process the ECPR chamber has to be filled with electrolyte before plating in manner such that all the plating/etching cavities are filled. When introducing electrolyte into the ECPR chamber, the possibilities are somewhat reduced, due the positioning of the substrate and the master electrode, and there is a risk of entrapping gas volumes in the interspace between the master electrode and the substrate, resulting in inferior ECPR printing. Also, since complete covering of the master electrode must be assured, more electrolyte than needed is often injected into the ECPR chamber, but still there is no guarantee of filling the cavities or trenches completely, and a lot of electrolyte goes to waste.
Accordingly, the present invention preferably seeks to mitigate, alleviate or eliminate one or more of the above-identified deficiencies in the art and disadvantages singly or in any combination, by providing a chuck for holding a substrate or master electrode in an ECPR process, said chuck comprising an interaction surface for holding a master electrode or a substrate; a buffer surface circumferentially of the interaction surface; wherein the interaction surface and the buffer surface extend in substantially the same plane; at least one electrolyte injection mouth arranged in the buffer surface and adjacent the interaction surface; and a method of filling an ECPR chamber, said ECPR chamber comprising a master electrode and a substrate facing each other, said method comprising injecting an electrolyte adjacent the master electrode or substrate, from one side of the master electrode or substrate to the other side of the master electrode or substrate.
Further advantageous embodiments will be apparent from the appended dependent claims.
These and other aspects, features and advantages of which the invention is capable of will be apparent and elucidated from the following description of embodiments of the present invention, reference being made to the accompanying drawings, in which
The following description focuses on embodiments of the present invention applicable to a method for filling an ECPR chamber during an ECPR process, and chucks and chuck assemblies therefore. However, it will be appreciated that the invention is not limited to this application but may be applied to many other replication, patterning or bonding processes within the field of micro electronics and/or mechanics where filling of a process chamber or portions thereof with a fluid is desired, including for example wafer bonding, various lithographic processes, dry or wet etching processes, etc.
During ECPR an electrolyte is injected into an ECPR chamber, preferably a sealed ECPR chamber, such that a space between a master electrode and a substrate is filled with an electrolyte. Thereafter the substrate and the master electrode are compressed, and plating/etching is performed in the cavities formed between the conductive surface of the substrate, the isolating structure on the master electrode, and the conductive surface on the master electrode.
Circumferentially of the interaction surface 101 a buffer surface 102 is arranged. The buffer surface 102 act as an area/surface to collect the abundant electrolyte injected before ECPR printing and as an area/surface for injecting electrolyte before ECPR printing. The interaction surface 101 and the buffer surface 102 extend in substantially the same plane, to accomplish the collection of abundant electrolyte while simultaneously allowing for effective (with respect to volume, direction, control, etc.) injection of electrolyte.
In the buffer surface 102 electrolyte injection mouths 103 are arranged. The injection mouths 103 may be positioned adjacent the interaction surface 101. The injection mouths 103 may be directed upwards. Also the injection mouths 103 may be directed upwards and medially. This may be accomplished by positioning fins (not shown) in the injection mouths 103, said fins slanting upwards and inwards (medially). In this way the injected electrolyte may be directed towards the interaction surface 101 and a master electrode or substrate positioned there on.
In one embodiment, a seal is arranged on the top chuck or ECPR machine members adjacent the top chuck. The seal may be arranged on a hoisting member, said hoisting member being regulating the vertical position of the seal, such that it may be brought into contact with the bottom chuck or lifted upwards to be liberated from contact with the bottom chuck. The hoisting member may for instance comprise a pneumatic actuator. During printing the master electrode and the substrate are in contact with each other, whereby the hoisting member and the seal is in a first position with respect to the top chuck and creating a seal with an area on the bottom chuck. When separating the master electrode and substrate, by moving the top chuck and bottom chuck away from each other in vertical direction, the hoisting member and seal are moved to a second position with respect to the top chuck so that its relative vertical position to the bottom chuck is maintained, and the seal against the bottom chuck is kept.
For extra protection against leaks during filling of the ECPR chamber, said chamber may comprise a splash ring (not shown). The splash ring may be arranged circumferentially of the seal on the top chuck or ECPR machine members adjacent the top chuck. The splash ring may be arranged on a hoisting member, said hoisting member being regulating the vertical position of the splash ring, such that it may be positioned circumferentially of the seal. The hoisting member may for instance comprise a pneumatic actuator.The buffer surface 102 may be hydrophobic. The hydrophobic materials of said buffer surface 102 may be materials that act hydrophobic against electrolytes, such as hydrophobic polymeric materials, such as PTFE, or non-oxidizing metals, such as gold or platinum.
From the injection mouths 103, hydrophilic bridges (not shown) may be arranged towards the interaction surface 101. The hydrophilic bridges may be of polar dialectic materials, such as oxides of metals or semi-conductive materials, for example titanium, or silicon dioxide, silicon nitride, or glass material having a hydrophilic behavior in the electrolyte being used.
When the materials being used for the buffer surface 102 and the bridges are inert in the electrolyte being used, oxidation may be avoided.
The injection mouths 103 are distributed such that injected electrolyte will sweep across the master electrode or substrate positioned on the interaction surface 101. For this purpose the injection mouths 103 are distributed on one side of the interaction surface only. In case of multiple injection mouths 103, the array of injection mouths 103 is distributed along a curvature adjacent to and circumventing the interaction surface, wherein the angle a between the first of the injection mouths 103 in said array to a centre point 104 of the interaction surface 101 to the last of the injection mouths in said array creates an angle 270degrees or less. In this way, opposing flow directions of electrolyte is avoided, such opposing flows of electrolyte, risking to trap gas between the master electrode or substrate, such that a front is created that flows towards the other side of the wafer, thereby pushing out the volume of air that was previously existing between the master electrode and the substrate. By regulating the relative flow rates between several injection mouths the shape and propagation of the electrolyte filling front can be controlled, in order to deliver an optimized fill cycle with a short filling time and a fill front propagation ensuring that the volume of air that was previously existing between the master electrode and the substrate is not entrapped between the master electrode and the substrate. In one embodiment having at least three injection mouths forming an array distributed along a curvature adjacent to and circumventing the interaction surface, the flow rates are controlled such that the injection mouths oriented furthest out in the array have a lower flow rate than at least one of the other injection mouths in the array. Thus, when filling the ECPR chamber the electrolyte is injected through the mouths 103. The electrolyte may be degassed before entering the ECPR chamber through the mouths 103. The degassing of the electrolyte may be performed in an external or internal degassing system. Also, wetting agents may be added to the electrolyte before injection into the ECPR chamber. When entering the ECPR chamber, the electrolyte will build up on the buffer surface 102 in the vicinity of the mouths 103, because of the hydrophobic nature of the buffer surface 102. Then, the electrolyte will come into contact with the master electrode or substrate positioned on the interaction surface 101. When the electrolyte comes into contact with the master electrode or the substrate, the hydrophilic characteristics of master electrode or substrate will suck the electrolyte over the surface thereof. To facilitate the connection between the electrolyte and the master electrode or substrate the hydrophilic bridges may be arranged in between the interaction surface 101 and the mouths 103. Due to the arrangement of the mouths 103 along only one side of the interaction surface 101, the electrolyte will sweep from one side of the master electrode or substrate over to the other, without meeting opposing flows of electrolyte. Thus, entrapment of gas on the master electrode or substrate may be avoided.
In one embodiment, the pressure in the ECPR chamber is lowered by applying a vacuum in the ECPR chamber before injecting the electrolyte into the ECPR chamber. In this way the volume of gas, such as air, in the ECPR chamber may be lowered, thus minimizing the risk of gas entrapment. Also, a low pressure in the ECPR chamber speeds up the movement of the electrolyte across the master electrode or substrate. Thus, a low pressure nozzle (not shown) may be in communication with the ECPR chamber. Also, a small amount of ultrasonic energy may be added to the electrolyte before, during, or after being injected into the ECPR chamber. When applying ultrasonic energy, bubbles that have been trapped in the electrolyte or on the master electrode or substrate may be removed. The ultrasonic energy may be added through the chuck surface. Also, convection may be used, by pumping electrolyte in pumping patterns through the mouths 103, for removing entrapped gas bubbles in the same manner.
In one embodiment the substrate and the master electrode are positioned close to each other, such that the capillary force of the electrolyte may be used to suck the electrolyte over the interface, thus sweeping gas away from said interface.
Adjacent the interaction surface 101 electrolyte recycling outlets 105 are arranged. The recycling outlets 105 may be evenly distributed circumferentially of the interaction surface 101. The recycling outlets 105 are distributed around the entire interaction surface, to maximize electrolyte recycling. When the electrolyte has filled the space between master electrode and the substrate, and the master electrode and the substrate have been squeezed together, the excess of electrolyte will gather along the edge of the master electrode or substrate, due to the hydrophilic nature of the master electrode or the substrate. During normal filling procedures, a majority of the injected electrolyte may be pushed out towards the circumference of the master electrode and the substrate, and can gather along the edges thereof. Then, typically before printing, the excessive amount of electrolyte can be pumped out of the ECPR chamber through the recycling outlets 105 into a recycling tank (not shown).
Since the excess of electrolyte not has been part of a printing step, this electrolyte is chemically unchanged, and can be reused. Thus, the electrolyte in the recycling tank is filtered and transported into a supply tank (not shown), from which supply tank electrolyte is injected into the ECPR chamber again, during a subsequent filling step. For manufacturability or economical reasons, the electrolyte may be alternatively transported, possibly through a filter, directly to the supply tank.
When performing the recycling step, i.e. pumping electrolyte out from the ECPR chamber through the recycling outlets 105, typically the volume just outside the ECPR chamber may be ventilated to atmosphere, to facilitate the pumping of the electrolyte into the recycling tank.
In one embodiment the same holes are used as mouths 103 and outlets 105. In this embodiment there is a valve in the conduit leading to the holes on the buffer surface. Thus, at least one of the holes will act as inlet mouth(s) during filling of the ECPR chamber, in accordance with the criterions disclosed above. After filling and pressing the master electrode and the substrate together, valves in the conduits leading to this/these holes are switched, such that also these holes, as well as other holes arranged adjacent and circumferentially of the interaction surface 102, will act as recycling outlets.
It is readily understood that all references to lower/upper are merely for illustrative purposes, without any limiting effect on the scope of protection. Moreover, it should be realized that equivalent setups to those described may include setups having a substrate arranged on a lower chuck while the master electrode is mounted on an upper chuck, as well as setups in which the positions of the lower and upper chuck are switched.
In the claims, the term "comprises/comprising" does not exclude the presence of other elements or steps. Furthermore, although individually listed, a plurality of means, elements or method steps may be implemented by e.g. a single unit or processor. Additionally, although individual features may be included in different claims, these may possibly advantageously be combined, and the inclusion in different claims does not imply that a combination of features is not feasible and/or advantageous. In addition, singular references do not exclude a plurality. The terms "a", "an", "first", "second" etc do not preclude a plurality. Reference signs in the claims are provided merely as a clarifying example and shall not be construed as limiting the scope of the claims in any way.
This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.