ELECTROCHEMICAL PROCESSING DEVICE EQUIPPED WITH A LIGHTING SYSTEM

Abstract

Electrochemical processing device (1), particularly for the manufacture of porous silicon substrates, comprising a frame (10) including a cavity (11) suitable for containing an electrolytic solution, at least one electrode (2, 3), a substrate holder (4), and a lighting system (5) including light sources (51), said at least one electrode, the substrate holder and the lighting system being arranged in parallel planes in the cavity and intended to be immersed in the electrolyte solution, characterized in that the lighting system (5) includes a rigid support structure (50) which has a first face (52A) intended to be opposite the substrate holder and on which the light sources (51) are arranged, the light sources (51) being distributed, preferably regularly distributed, over a surface corresponding at least to the surface of the substrate intended to be treated, and in that the support structure (50) is openwork.Figure to be published with the abbreviation: Fig. 2.

Description

Title of the invention: ELECTROCHEMICAL PROCESSING DEVICE WITH A LIGHTING SYSTEM

[0001] The invention relates to the field of electrochemical treatment of substrates for the purpose of etching or depositing material. It relates in particular to the field of manufacturing porous silicon wafers.

[0002] Electrochemical treatment is commonly used in the structuring of conductive or semiconductive surfaces for numerous applications, particularly in the field of microelectronics, or relating to sensors, electrodes, filter membranes, microdiffusers, optical or thermal reflectors, thermal or electrical insulation supports, etc.

[0003] In the context of semiconductors, the electrochemical texturing of silicon wafers may be mentioned. The invention will be more particularly described with regard to this application, without however being limited thereto.

[0004] A first known technique for carrying out an electrochemical treatment is to place the substrate to be treated in an electrolyte bath comprising an electrode placed at a distance from the substrate, the substrate being intended to constitute a second electrode.

[0005] A second technique consists of placing a wafer holder that holds the substrate (wafer) to be treated in an electrolyte. The wafer holder delimits two baths, in each of which an electrode is immersed at a distance from the substrate. The wafer holder has suitable sealing means that cooperate with the entire periphery of the substrate to seal the electrolyte baths from each other.

[0006] In the case of manufacturing porous silicon wafers, for the etching reaction to take place, the silicon must have a sufficient number of electron holes. This is generally the case for so-called P-type silicon, but conversely, is generally not the case for N-type silicon. Thus, for N-type silicon, it may be necessary to add electron holes. One such technique is photogeneration, which creates electron-hole pairs and consequently generates electron holes.

[0007] Furthermore, in the case of the second technique using two electrodes on either side of the silicon wafer, the electronic contact between the rear face of the silicon wafer and the facing electrode, which is ensured by the electrolyte, must be efficient in order to obtain the ad hoc treatment of the front face of the wafer. However, in order to guarantee this good electronic contact, it is sometimes necessary to dope the rear face (P or N type doping) of the wafer at concentrations higher than that of the wafer. Doping is generally carried out by expensive processes (implantation ionic or pre-deposition followed by high-temperature annealing). Recently, it has been shown that illumination of the back side of the wafer can advantageously replace this doping.

[0008] Consequently, the use of lighting in an electrochemical treatment device has various advantages.

[0009] Generally, the lighting is arranged outside the frame containing the electrolyte solution. It is preferably coupled to a system of lens(es) to focus the light onto a transparent window of the frame through which the light passes so as to illuminate one of the faces of the substrate (of the wafer) to be treated. However, this device is only suitable when the substrate constitutes one of the electrodes according to the first electrochemical etching technique mentioned above. Indeed, in the case of the second technique with two solid electrodes which are arranged on each side of the substrate, it is impossible to illuminate an entire face of the substrate from the outside, because each of the faces of the substrate is hidden by each of the electrodes.

[0010] Moreover, external lighting ultimately makes the entire electrochemical etching device cumbersome. Furthermore, since illuminance is inversely proportional to the square of the distance between the light source and the substrate to be illuminated, the further the light source is from the substrate, the more it will be necessary to increase the light intensity, which does not contribute to energy savings.

[0011] Patent application WO2012164485 discloses an electrochemical treatment device which comprises lighting which is not external but is immersed directly in the electrolytic solution, thus being close to the substrate. The lighting consists of light focused by one or more optical fibers whose illuminating end is pointed at the substrate to form a pore. However, the optical fiber(s) must be moved to reach a network of pores, while ensuring each time that the fiber is perfectly arranged at the desired location for the formation of a pore. This lighting system is long and complex to implement, and is in reality not at all suitable for the treatment of large surfaces, such as for silicon wafers with a diameter of 300 mm. Furthermore, there is no guarantee of obtaining homogeneous etching of the entire surface of the substrate, a substrate which may in particular have a diameter of 300 mm.

[0012] The invention therefore aims to provide an electrochemical treatment device equipped with lighting which does not have the aforementioned disadvantages, and in particular to make the implementation device compact without affecting the quality of the treatment.

[0013] According to the invention, the electrochemical processing device, particularly for the manufacture of porous silicon substrates, comprises a frame including a cavity suitable for containing an electrolytic solution, at least one electrode, a substrate holder, and a lighting system including light sources, said at minus one electrode, the substrate holder and the lighting system are arranged in parallel planes within the cavity and are intended to be immersed in the electrolytic solution. The lighting system is specifically arranged between the substrate holder and one electrode. The lighting system comprises a rigid support structure with a first face facing the substrate holder, on which the light sources are arranged. The light sources are distributed, preferably evenly distributed, over a surface at least equal to the surface area of ​​the substrate to be treated. The lighting system (support structure and light sources) is electrically insulating. Furthermore, the support structure is perforated (perforated), preferably forming a comb or grid pattern.

[0014] Thus, the electrochemical treatment device with such a lighting system integrated into the electrolytic solution provides a compact device.

[0015] Furthermore, the lighting system is extended in surface area opposite the entire surface of the substrate intended to be carried by the substrate holder, providing close, focused and homogeneous light over the entire surface of the substrate.

[0016] Moreover, surprisingly, although the rigid structure constitutes an obstacle in the electrolytic solution between the substrate and the electrode, and this over the entire surface of the substrate, it turns out that by being perforated, it does not disturb the current lines in the electrolytic solution, nor does it affect the electronic contact; the treatment obtained on the substrate is perfectly homogeneous.

[0017] Tests were carried out to manufacture porous silicon wafers, including leaving the rigid structure in place without turning on the light sources for a wafer not requiring photogeneration; the porosity proved to be perfectly homogeneous over the entire surface of the substrate.

[0018] In the following description, the terms "horizontal", "vertical", "upper", "lower", "top", "bottom" are understood to qualify elements of the electrochemical treatment device, within the framework of a normal installation of said electrochemical treatment device which would rest on a horizontal surface.

[0019] The rigid structure forms in particular a comb, the light sources being mounted aligned on the teeth of the comb. Alternatively, the rigid structure could be in the form of a grid, having spaced solid lines intersecting in a plane along the two directions of space, the light sources being arranged on these lines.

[0020] Preferably, the light sources are light-emitting diodes, in particular illuminating in the infrared. The proximity of the lighting to the substrate and the additional use of LEDs as light sources provides homogeneous lighting and greatly contributes to energy saving.

[0021] According to one feature, the load-bearing structure includes an external sealing coating, electrically insulating and chemically resistant to the electrolytic solution, in particular made of plastic, said coating being at least transparent with respect to light sources.

[0022] According to another feature, the light sources are fixed by gluing to the carrier structure (the body of the carrier structure), in particular are fixed by gluing using a thermally conductive adhesive while the carrier structure has a body made of a thermally conductive material, preferably copper.

[0023] According to an advantageous characteristic, the supporting structure comprises a heat exchange circuit capable of cooperating with the surface for arranging the light sources. This configuration makes it possible to evacuate the calories released by the light sources without heating the electrolytic solution, avoiding disturbing the electrochemical treatment, and therefore contributing to the proper functioning of the device.

[0024] In a particular embodiment, the supporting structure comprises supporting elements, preferably flat, which are regularly spaced and on which the light sources are arranged. Advantageously, the light sources are arranged on the same face of the supporting elements. In particular, the supporting elements are elongated elements which are spaced apart at the same spacing of between 3 mm and 150 mm, and are of a length at least equal to the largest dimension of the substrate to be treated. The openwork structure therefore comprises through passages or holes, which are for example obtained by arranging the supporting elements at a distance from each other. The spacing between the supporting elements provides the openwork (perforated) structure. The spacing is adapted so as to obtain homogeneous lighting extending over the entire surface of the substrate and to obtain homogeneous treatment of the surface of the substrate.For example, when spacing by a dimension of the order of 100 and 150 mm, it will nevertheless be necessary to ensure that the lighting can be uniform over the entire surface of the substrate, and when the spacing is minimal, in particular less than 10 mm, or even 5 mm, it will be necessary to ensure that a uniform treatment is maintained.

[0025] According to one feature, the supporting structure comprises spaced-apart supporting elements on which the light sources are arranged, the supporting elements being hollow and their interior being suitable for the circulation of a heat transfer fluid, the supporting elements being in particular manufactured from a thermally conductive material such as copper. In a preferred embodiment, each of the supporting elements comprises an internal partition which delimits a first circulation chamber and a second circulation chamber, the two circulation chambers communicating with each other at one of the distal ends of the supporting element (which corresponds to the lower end of the supporting structure), while at the opposite distal end At the top of the load-bearing element (the upper end of the structure), the first circulation chamber connects to an inlet manifold for receiving a heat transfer fluid, and the second circulation chamber connects to an outlet manifold for discharging the heated heat transfer fluid. Alternatively, each load-bearing element could have only one circulation chamber, which connects at its upper end to an inlet manifold for a heat transfer fluid, and at its lower end to a peripheral section of the load-bearing structure that connects to an outlet manifold.

[0026] According to the invention, the support device is in particular used to support a substrate, of the silicon wafer type, to be treated, in particular to be structured electrochemically on at least one of its flat faces. By way of non-limiting examples, mention may be made of monocrystalline or multi-crystalline wafers, or even mixed wafers of the insulating / semiconductor type, and with varied shapes and dimensions, such as circular from 2 to 12 inches (50 to 300 mm) in diameter and more, square or rectangular shapes, with or without rounded corners, for photovoltaic applications for example.

[0027] In a particular application, in particular for manufacturing a porous silicon substrate, the electrochemical treatment device comprises a first electrode and a second electrode between which is arranged the substrate holder which is designed to delimit in a sealed manner two compartments when a substrate is in place, the lighting system being arranged between one of the electrodes and the substrate holder and the light sources being capable of illuminating the substrate on the side of the (rear) face opposite the face intended to be treated (in particular being porous).

[0028] Advantageously, the lighting system is removable and / or adjustable in distance from the substrate holder.

[0029] Preferably, the electrochemical treatment device includes a cover that closes the entire device.

[0030] The invention also relates to a lighting system having the aforementioned characteristics and used for an electrochemical treatment device.

[0031] The present invention is now described using examples which are solely illustrative and in no way limitative of the scope of the invention, and from the attached illustrations, in which: - [Fig.1] or [Fig.1] represents a top perspective view of an example embodiment of the electrochemical treatment device according to the invention. - [Fig.2] or [Fig.2] illustrates a schematic cross-sectional view of the electrochemical treatment device of the [Fig.1] containing an electrolytic solution and being hooded. - [Fig.3] or [Fig.3] illustrates a schematic sectional view of a variant of the electrochemical treatment device of the invention, the substrate to be treated constituting one of the electrodes. - [Fig.4] or [Fig.4] is a front view of an example embodiment of the lighting system of the electrochemical treatment device of the invention. - [Fig.5] or [Fig.5] corresponds to the rear of the lighting system of [Fig.4]. - [Fig.6] or [Fig.6] is a schematic partial cross-sectional view according to the height of a supporting element of the light sources of the lighting system of [Fig.4].

[0032] The electrochemical treatment device 1 of the invention illustrated in figures 1 and 2 is intended to electro-chemically treat, in particular by electrolytic means, a substrate 1' such as a silicon wafer.

[0033] The electrochemical treatment device 1 forms a removable, single-unit assembly, ready for installation. It comprises a frame 10 defining a cavity 11 intended to be filled with an electrochemical treatment solution S (electrolyte or electrolytic solution), at least one electrode 2 independent of the substrate 1', in particular two electrodes 2 and 3, a substrate holder 4 for supporting the substrate 1', and a lighting system 5 for illuminating one face of the substrate 1'. The two electrodes 2 and 3, the substrate holder 4, and the lighting system 5 are arranged inside the cavity 11 and are intended to be immersed in the electrolytic solution S. Preferably, the electrochemical treatment device 1 includes a cover 12 ([Fig. 3]) for closing the assembly.

[0034] The substrate 1' has two opposite faces, the front face IA and the rear face IB. The front face IA is the face intended to be treated, for example to be made porous in the case of a silicon wafer.

[0035] In the case of two electrodes 2 and 3 (Figures 1 and 2), which respectively constitute a cathode and an anode, the substrate holder 4 with the substrate 1' is arranged between the two electrodes 2 and 3. Once the substrate 1' is positioned within it, the substrate holder is designed to delimit two compartments that are sealed from each other. The lighting system 5 is preferably arranged between the substrate holder 4 and the anode, illuminating the rear face IB of the substrate. Alternatively, the lighting system 5 can be arranged between the cathode and the substrate holder 4 to illuminate the front face IA of the substrate.

[0036] In yet another variant ([Fig.3]), the electrochemical treatment device 1 may comprise only one electrode 2 independent of the substrate 1', and immersed in the solution S, the substrate 1' then constituting the second electrode to ensure the treatment. The submerged lighting system 5 is arranged between the electrode 2 and the substrate holder 4, therefore between the electrode 2 which forms the cathode and the substrate 1' which forms the anode, illuminating the front face IA of the substrate.

[0037] The two electrodes 2 and 3 have a solid surface. The two electrodes 2 and 3 are capable of being adjustable in distance relative to the substrate-carrying support 4, via translation adjustment means 20 and 30 coupled to the respective electrodes 2 and 3. The electrical power supply inlets, known per se, of the electrodes 2 and 3 are not shown for the sake of simplification.

[0038] The substrate holder 4 comprises a frame 40, preferably equipped with a handle 41 for easily removing the support 4 from the cavity in order to mount and dismount the substrate. The frame 40 is adapted to the geometry of the substrate 1'. The frame 40 includes sealing means around its entire inner periphery for cooperation with the edge and the two opposing surfaces IA and IB of the substrate.

[0039] The lighting system 5 is designed to be waterproof, electrically insulating, and resistant to chemical attack from the electrolyte.

[0040] The lighting system 5 is capable of simultaneously illuminating the entire surface of one of the two faces of the substrate 1', while also forming a perforated surface. Unexpectedly, although constituting an electrically insulating barrier that should cause a disturbance of the current lines in the electrolyte, the resulting treatment of the substrate is perfectly homogeneous.

[0041] The lighting system 5 comprises a rigid structure 50 and a multiplicity of light sources 51 which are carried by the structure 50 and are distributed over a surface area at least equal to the surface area of ​​the substrate to be treated. The lighting system 5 with its multiplicity of light sources 51 form a single-piece assembly. The lighting system 5 may comprise translation adjustment means 5' (shown diagrammatically in [Fig. 2]) for adjusting its distance relative to the substrate-carrying support 4.

[0042] With reference to Figures 4 and 6, the structure 50 comprises supporting elements 52 on which the light sources 51 are arranged. The supporting elements 52 are rigid. The structure 50 is preferably in the form of a frame with the supporting elements 52 extending from the upper end of the frame to its lower end.

[0043] The load-bearing elements 52 are in the form of elongated elements (like bars). The load-bearing elements 52 are spaced apart, preferably at regular intervals. The load-bearing elements 52 form a hollow surface, like a grid, which does not disrupt the streamlines. Each load-bearing element 52 is, in particular, spaced from an immediately adjacent load-bearing element by a distance of approximately 15 mm. Preferably, the load-bearing elements 52 extend along a single direction, here the vertical direction. Alternatively, the grid could have a different shape. The load-bearing elements 52 could have a different geometry.

[0044] The carrier elements 52 extend over a surface area which is greater than the surface area of ​​the substrate 1' to be treated. They extend over a surface area at least equivalent to the surface area of ​​the nearest electrode. The carrier elements 52, extending in the vertical direction, have a length greater than the largest dimension of the substrate 1' to be treated. They have a length corresponding to the length of the nearest electrode.

[0045] The load-bearing elements 52 are preferably flat ([Fig. 6]). They have two opposite faces 52A and 52B. Only one of the faces 52A carries the light sources 51. The illuminating face 52A is intended to be placed opposite the substrate 1'. The opposite face 52B ([Fig. 5]) is without light sources.

[0046] The light sources 51 are arranged in lines on the structure 50. They are positioned on and along one of the faces of the supporting elements 52. The light sources 51 are distributed over a surface area that corresponds at least to the cross-sectional area of ​​the substrate 1' to be treated. Preferably, the light sources 51 are distributed over a surface area substantially larger than the cross-sectional area of ​​the substrate, but not excessively so, in order to optimize the manufacturing cost of the lighting system and avoid unnecessary consumption of electrical energy. For example, the light sources are distributed over a diameter of 330 or 335 mm to treat a substrate 1' with a cross-sectional area of ​​300 mm² or less.

[0047] The light sources 51 are light-emitting diodes (LEDs). The LEDs preferably illuminate in the infrared.

[0048] The LEDs are attached to a support which is directly a printed circuit board. The printed circuit board is directly fixed to the body of the support structure 4, in particular to each support element 52. The fixing is achieved by bonding, preferably with an adhesive 51' ([Fig.6]) which is thermally conductive such as epoxy glue.

[0049] The LEDs 51 are spaced regularly according to the length of their printed circuit board. The number of LEDs and their spacing depend, in particular, on the beam angle. Preferably, the LEDs have a beam angle of 120°. For example, they are spaced approximately 30 mm apart.

[0050] The assembly of the carrier elements 52 and the light sources 51 is trapped in at least one encapsulating material 53 ([Fig.6]) which is waterproof, electrically insulating and chemically resistant to the electrolytic solution. The waterproof and electrically insulating encapsulating material 53 covers the light sources 51 and their printed circuit board, and is transparent at least opposite the sources of light 51. The waterproof, electrically insulating, and chemically resistant material is, in particular, made of plastic, for example, a fluoropolymer. For example, it is a transparent plastic sleeve that was fitted during the manufacture of the lighting system 5, by covering each load-bearing element 52 and the light sources 51, and securing it to the assembly by heat shrinking. A cover, preferably made of plastic, may have been fitted prior to the waterproof sleeve 53 to cover and render invisible at least the printed circuit board of the light sources 51, while also having cut-out windows around the light sources 51 to allow light to pass through.

[0051] The load-bearing elements 52 are of small thickness. They have a thickness in particular of the order of 10 to 15 mm. By being thus flat, the volume occupied by the structure 50 is minimized so as not to affect the size of the electrochemical treatment device 1, and to allow adaptation to existing devices.

[0052] The carrier elements 52 are made of a constituent material which is preferably thermally conductive, such as copper.

[0053] The supporting elements 52 are preferably hollow in order to allow the internal passage of a heat transfer fluid. Indeed, the structure 50 of the lighting system 5 advantageously comprises a heat exchange circuit 54 which comprises, on the one hand, an inlet manifold 55 and an outlet manifold 56 arranged at the upper end of the structure 50 (upper part of the frame of the structure), and on the other hand, at least the hollow interior of the supporting elements 52. The peripheral part of the frame of the structure 50 (vertical side and lower end) can also be part of the heat exchange circuit 54.

[0054] The thermally conductive material carrier elements 52 (and the thermally conductive adhesive 51') serve as a heat exchange surface between the light sources 51 and the heat transfer fluid circulating inside the carrier elements 52.

[0055] The inlet 54 and outlet 55 collectors of the structure 50 are intended to be connected to a cooling circuit with a pump and a heat transfer fluid which is injected at a temperature of the order of 10°C.

[0056] In a preferred embodiment ([Fig. 6]), each load-bearing element 52 has, within its hollow interior, a partition 52' which is open at its lower end to delimit a first and a second circulation chamber 54A and 54B respectively, communicating at their lower ends. The two circulation chambers 54A and 54B communicate at their upper ends, respectively, with the inlet manifold 55 and the outlet manifold 56. The first circulation chamber 54A, into which the heat transfer fluid first arrives, cooperates with the surface supporting the light sources 51; the outer wall of said first chamber circulation chamber 54A constitutes the external surface which carries the light sources 51. Schematically shown by the direction of the arrows in [Fig.6], the cold fluid arrives from the inlet manifold 55, travels in the first circulation chamber 52A which is contiguous to the light sources 51, providing a heat exchanger; the calories generated by the light sources 51 are evacuated by heating the fluid which continues its path through the second circulation chamber 52B to the outlet manifold 56. In this way, the LEDs are maintained at an operating temperature within their permissible temperature range. In addition, the electrolytic solution S is not heated by the evacuation of the calories generated by the LEDs, preventing any risk of disruption of the chemical treatment.

Claims

Claims

1. Electrochemical treatment device (1), in particular for the manufacture of porous silicon substrates, comprising a frame (10) comprising a cavity (11) capable of containing an electrolytic solution, at least one electrode (2, 3), a substrate holder (4), and a lighting system (5) comprising light sources (51), said at least one electrode, the substrate holder and the lighting system being arranged in parallel planes in the cavity and intended to be immersed in the electrolytic solution, the lighting system (5) comprising a rigid supporting structure (50) which has a first face (52A) intended to be opposite the substrate holder and on which the light sources (51) are arranged, the light sources (51) being distributed, preferably regularly distributed, over a surface corresponding at least to the surface of the substrate intended to be treated, and the supporting structure (50) being perforated,preferably the supporting structure forming a comb or a grid characterized in that the supporting structure (50) comprises a heat exchange circuit (54, 55, 56) capable of cooperating with the arrangement surface on which the light sources (51) are arranged.,

2. Electrochemical treatment device according to claim 1, characterized in that the light sources (51) are light-emitting diodes, in particular illuminating in the infrared.

3. Electrochemical treatment device according to claim 1 or 2, characterized in that the supporting structure (50) comprises an outer coating (53) which is electrically insulating and capable of chemically resisting the electrolytic solution, in particular made of plastic, said outer coating (53) being at least transparent with respect to the light sources (51).

4. Electrochemical treatment device according to any one of the preceding claims, characterized in that the light sources (51) are fixed by gluing to the supporting structure (50), in particular are fixed by gluing using a thermally conductive adhesive (51') while the supporting structure (50) has a body made of a thermally conductive material, preferably copper.

5. Electrochemical treatment device according to any one of the preceding claims, characterized in that the supporting structure (50) comprises supporting elements (52), preferably flat, which are regularly spaced and on which the light sources are arranged, in particular the supporting elements (52) being spaced at the same spacing which is between 3 mm and 150 mm, and being of length at least equal to the largest dimension of the substrate to be treated.

6. Electrochemical treatment device according to any one of the preceding claims, characterized in that the supporting structure (50) comprises supporting elements (52) on which the light sources are arranged, the supporting elements being hollow and their interior being suitable for the circulation of a heat transfer fluid, said supporting elements (52) being in particular manufactured from a thermally conductive material.

7. Electrochemical treatment device according to any one of the preceding claims, characterized in that it comprises a first electrode (2) and a second electrode (3) between which is arranged the substrate holder (4) which is designed to delimit in a sealed manner two compartments when a substrate (1') is in place in said substrate holder, the lighting system (5) being arranged between one of the electrodes (3) and the substrate holder (4) and the light sources being capable of illuminating the substrate (1') on the side of the face opposite the face intended to be treated.

8. Electrochemical treatment device according to any one of the preceding claims, characterized in that the lighting system (5) is removable and / or adjustable in distance relative to the substrate holder.

Images