Device and method for continuous production of porous silicon layers

Patent metadata

Field	Value
Publication number	US-2016211154-A1
Application number	US-201415025362-A
Country	US
Kind code	A1
Filing date	Sep 29, 2014
Priority date	Oct 1, 2013
Publication date	Jul 21, 2016
Grant date	—

Abstract

The invention relates to a device and a method for continuous production of porous silicon layers (single or multiple layers) on workpieces made of silicon or workpieces with a silicon coating. The method according to the invention is thereby based on a one-sided etching method, the workpiece being guided horizontally, by means of a transport device, with the front side of the workpiece to be etched, past at least one etching chamber, comprising an electrolyte and a cathode. This method can be used in particular for the production of PV cells.

First claim

1 . Device for continuous production of porous silicon layers on workpieces made of silicon or on a workpiece with a silicon coating by means of one-sided etching, comprising:
at least one transport device for continuous transport of the workpiece, at least one etching chamber comprising an electrolyte and a cathode which is disposed such that only one surface of the workpiece to be etched can be made wet with the electrolyte, and also, an anode which is contacted electrically with the workpiece via a contact unit on a surface not to be etched,

2 . Device according to claim 1 ,
characterised in that the etching chamber is disposed below the workpiece.

3 . Device according to one of the claims,
characterised in that the cathode is selected from the group consisting of planar electrodes, electrode wire netting, individual electrode wires or combinations hereof, the material of the cathode consisting preferably of platinum, nickel alloys and/or glassy carbon.

4 . Device according to one of the preceding claims,
characterised in that the spacing of the at least one cathode relative to the surface of the workpiece to be etched is in the range of 1 to 500 mm, preferably 10 to 100 mm.

5 . Device according to one of the preceding claims,
characterised in that the at least one anode is configured as a sliding contact, rolling contact or rotating contact, the material of the at least one anode consisting preferably of platinum, nickel alloys, corrosion-resistant stainless steel, titanium, aluminium, graphite and/or glassy carbon.

6 . Device according to one of the preceding claims,
characterised in that the contact unit of the at least one anode is purged with protective gas, preferably with air or N 2 , so that the exposed contact material does not come in contact with electrolyte- or reaction vapours.

7 . Device according to one of the preceding claims,
characterised in that the device is coupled to further conditioning units or post-treatment units, in particular for surface treatment, for rinsing or for drying.

8 . Device according to one of the preceding claims,
characterised in that the device is coupled to a further unit for thermal reorganisation of the porous silicon layer, which preferably has a temperature- or power control for temperature-control of the workpiece and also a device for producing a controlled gas atmosphere at least on the heated parts of the front-side, preferably produced by air locks.

9 . Device according to one of the preceding claims,
characterised in that the unit for thermal reorganisation has planar or focused lamps for adjusting the temperature required for the reorganisation in the porous silicon layer, the lamps being preferably selected from the group of halogen lamps, LED lamps or semiconductor lasers.

10 . Device according to one of the preceding claims,
characterised in that the workpiece is a planar disc, in particular made of silicon, with a front-side and a rear-side and the transport device effects a horizontal transport of the planar disc, the surface to be etched being the front-side of the planar disc and the rear-side which is not in contact with the electrolyte being contacted electrically with the anode via the contact unit.

11 . Device according to the preceding claim,
characterised in that the at least one transport device is selected from the group consisting of roller transport, air-/fluid cushion transport or sliding transport.

12 . Device according to one of the claims 1 to 10 ,
characterised in that the workpiece is a cylinder, in particular a silicon ingot, and the transport device effects rotation of the cylinder, the surface to be etched being the outer surface area of the cylinder and the cylinder being contacted electrically with the anode via the contact unit on a surface not to be etched.

13 . Device according to claim 12 ,
characterised in that the cathode has a concave surface, the curvature of the concave surface of the cathode being adapted to the curvature of the outer surface area of the cylinder such that the cathode has a uniform spacing relative to the outer surface area of the cylinder.

14 . Method for continuous production of porous silicon layers on workpieces made of silicon or workpieces with a silicon coating by means of one-sided etching, in which at least one workpiece is guided, by means of at least one transport device, with the surface of the workpiece to be etched, past at least one etching chamber comprising an electrolyte and a cathode, only the surface to be etched being made wet with the electrolyte, and the workpiece being contacted electrically with an anode via a contact unit on a surface not to be etched, as a result of which electrochemical etching of the surface is made possible.

15 . Method according to claim 14 ,
characterised in that the etching chamber is disposed below the workpiece.

16 . Method according to one of the claim 14 or 15 ,
characterised in that the electrochemical etching is implemented with an etching current of 0.1 to 1,000 mA/cm 2 , preferably of 5 to 500 mA/cm 2 .

17 . Method according to one of the claims 14 to 16 ,
characterised in that the electrolyte comprises hydrofluoric acid and at least one alcohol or a surfactant, in particular ethanol, acetonitride, dimethylsulphoxide, dimethylacetamide, dimethylformamide, formamide, acetic acid, mixtures of surfactants, e.g. siloxanes and polyalkylene oxide copolymers.

18 . Method according to one of the claims 14 to 17 ,
characterised in that convection of the electrolyte is effected in order to avoid formation of bubbles.

19 . Method according to one of the claims 14 to 18 ,
characterised in that the the workpiece made of silicon or the workpiece with a silicon coating is radiated with light in order to produce electron defects (“holes”), the light having a wavelength between 200 nm and 1,200 nm, preferably between 400 nm and 1,100 nm.

20 . Method according to one of the claims 14 to 19 ,
characterised in that the workpiece is a planar disc, in particular a silicon disc with a thickness of 50 μm to 500 mm, with a front-side and a rear-side and transport of the planar disc is effected horizontally, the front-side of the planar disc being etched and the planar disc being contacted electrically with the anode via the contact unit in a region not to be etched.

21 . Method according to one of the claims 14 to 20 ,
characterised in that the workpiece is a cylinder, in particular a silicon ingot, and the transport device effects rotation of the cylinder, the surface to be etched being the outer surface area of the cylinder and the cylinder being contacted electrically with the anode via the contact unit on a surface not to be etched.

22 . Method according to one of the claims 14 to 21 ,
characterised in that a device according to one of the claims 1 to 11 is used.

23 . Use of the device according to one of the claims 1 to 13 for the production of PV cells or electrodes for Si—Li batteries or Si-air batteries.

Assignees

• Fraunhofer Ges Forschung
• Fraunhofer Ges Forschung

Inventors

• Reber Stefen
• Lindekugel Stefan
• Janz Stefan
• Pavlovic Regina

Classifications

• H10P72/3314

  Continuous loading and unloading into and out of a processing chamber, e.g. transporting belts within processing chambers · CPC title

• H10P72/0476

  comprising at least one plating chamber · CPC title

• H10P72/0436

  mainly by radiation · CPC title

• H10P72/0426 Primary

  with the semiconductor substrates being dipped in baths or vessels · CPC title

• C25F3/12

  of semiconducting materials · CPC title