Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
  • H01L31/02—Details
  • H01L31/0236—Special surface textures
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
  • C09K13/00—Etching, surface-brightening or pickling compositions
  • C09K13/02—Etching, surface-brightening or pickling compositions containing an alkali metal hydroxide
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
  • H01L31/02—Details
  • H01L31/0236—Special surface textures
  • H01L31/02363—Special surface textures of the semiconductor body itself, e.g. textured active layers

Definitions

• the invention concerns a product, its use as an additive or component of etching solutions and a process for producing it.
• etching materials When etching materials, the aim is frequently to obtain an etching result which is defined in terms of the type, position and/or extent of the etching. This is particularly the case when semiconductor materials are etched, for example in the manufacture of electronic components or solar cells.
• semiconductor material is silicon.
• monocrystalline or multicrystalline silicon is used as semiconductor material in the industrial manufacture of silicon solar cells.
• a defined etching of crystalline materials, in particular monocrystalline or multicrystalline silicon, is expensive, since the different types of grains and any crystal defects present are etched to varying degrees by most etching solu- tions. This is the case, for example, with alkali hydroxide- based alkaline etching solutions, which are used on an industrial scale in the etching and in particular in the texture etching of silicon wafers.
• the respective etching process must be precisely coordinated with the semiconductor material, for example silicon material, used in the individual case.
• Etching parameters such as etching time, composition of the etching solution and etching temperature can thereby be influ- enced, inter alia, by the type of crystallisation of the semiconductor material used, e.g. block-cast or edge-stabilised drawn multicrystalline silicon or monocrystalline silicon, the dopant type and dopant thickness thereof and also the type and density of the crystal defects.
• the result of this is that different etching parameters must be used in each case, even for the various silicon materials from a single manufacturer.
• the multiplicity of etching parameters increases still more when materials from various manufacturers are used.
• texture etchings such as those fre- quently carried out in the production of solar cells in order to form a surface structure for the purpose of increasing the injection of light
• the sensitivity of the texture etching processes with respect to the material used gives rise to a large number of different sets of etching parameters.
• DE 10 2008 056 086 discloses an additive for etching solutions which makes this possible.
• the production of this additive requires the separation of phases of various densities, which is accompanied by a certain expense.
• the present invention is therefore based on the problem of providing a product which enables the etching processes, espe- cially texture etching processes, to be simplified and can be produced at little expense.
• the product according to the invention is obtainable by mixing at least one polyethylene glycol with a base, forming a single-phase mixture, heating the single-phase mixture to a temperature of 80°C and allowing the single-phase mixture to rest in ambient air until the single-phase mixture changes colour.
• base in this case means, in principle, any compound and any element capable of forming hydroxide ions in aqueous solution.
• the base used is an alkali hydroxide or an ammonium hydroxide, especially preferably potassium hydroxide or sodium hydroxide.
• the mass fraction of the alkali hydroxide used, in the components mixed for the purpose of forming the single-phase mixture, for example tetraethylene glycol and potassium hydroxide, is 1 to 10 mass percent, preferably about 7 mass percent.
• Single-phase mixture means that the mixture, even after a long service life of several hours, does not separate into several phases of varying density.
• Ambient air in the present sense is a gas mixture, such as that usually found on the earth in ar ⁇ eas occupied by human beings.
• the term ⁇ allow to rest' in this case does not necessarily mean an absolute rest of the mix- ture.
• the mixture can also be moved.
• a colour change of the single-phase mixture takes place when the single-phase mixture changes its colour with respect to its original colour.
• there is a change of colour when a previously transparent single-phase mixture takes on a colour.
• the resting time until the change of colour depends on many parameters, in particular the mixed substances. In most cases, a resting period of about 15 minutes to 16 hours is required .
• the etching solution can be used for various types and qualities of a semiconductor material using the same etching parameters and with equivalent etching results, for example in the same way for p-doped as well as for n-doped silicon.
• the number of etching parameter sets required known as etching recipes, can therefore be significantly reduced. This reduction in the number of etching recipes required further simplifies, insofar as this may even be necessary, the adaptation of both the composition of the etching solution and the etching parameters to the semiconductor material to be etched. Moreover, an extended service life of the etching solution may result.
• both monocrystalline and multicrystalline semiconductor materials in particular silicon wafers
• aqueous texture etching solutions which contain 0.5 to 6 wt . % in alkali hydroxides and 1 to 10% by volume of alcohols, mostly isopropyl alcohol (cf. e.g. US 3,998,659) are used as texture etching solutions.
• the texture etching usually takes place at a temperature of 70 to 90°C over a period of typically 20 to 75 minutes.
• the single-phase mixture is allowed to rest in ambient air until it takes on a colour which lies between orange and red-brown in the optical spectrum.
• the single-phase mixture is allowed to rest until it takes on a red-brown shade. It has emerged that the darker the shade to which the product according to the invention changes, the more effective it is. An especially strong effect results when the shade is red-brown. However, from a certain degree of colour change, the effect of the product reduces again. So when the single-phase mixture is dark brown or black, there is only a weak effect.
• One variant embodiment of the invention makes provision for the at least one polyethylene glycol to be mixed with the base and water to form the single-phase mixture.
• aqueous alkali hydroxide solution with the at least one polyethylene glycol.
• aqueous alkali hydroxide solutions with an alkali, hydroxide concentration of at least 20 mass percent have been proven for this.
• the water proportion must always be selected such that a single-phase mixture is formed and the mixture does not separate into several phases after a certain service life.
• a non-oxidising acid is admixed into the single-phase mixture, preferably hydrochloric acid or acetic acid.
• the product according to the invention is unstable over time with respect to its ef- feet.
• stability and therefore storage life can be improved.
• the product containing the non-oxidising acid can thus be stored for longer. It has proven advantageous to admix the non-oxidising acid in such a way that a pH value of less then 7, preferably less than 3, ensues.
• the non-oxidising acid is admixed after the single-phase mixture has changed colour.
• water and at least one alkali hydroxide preferably sodium hydroxide or potassium hydroxide
• an etching or texture etching solution can be made available which is advantageous in one of the ways described above.
• the proportion by volume of. the sin- gle-phase mixture in the mixture formed amounts to about 0.01 to 5%, preferably 0.01 to 1% and especially preferably 0.07 to 0.3%.
• alcohol in particular isopropyl alcohol
• the solution formed in the way de- scribed can in principle still be admixed with alcohol, in particular isopropyl alcohol.
• All variant embodiments of the product according to the invention can be used advantageously as additive in alkaline etch- ing solutions for semiconductor materials, preferably in alkaline etching solutions for inorganic semiconductor materials such as monocrystalline or multicrystalline silicon. In particular they have proven advantageous as additive in texture etching solutions.
• the product according to the invention can itself be used as texture etching solution for semiconductor materials, preferably for inorganic semiconductor materials and especially preferably for silicon materials such as monocrystalline or multicrystalline silicon wafers.
• a surface texturing with randomly oriented pyramids can be produced on silicon surfaces. This has proven , itself especially on monocrystalline silicon surfaces.
• the height of the pyramids in this case can be influenced by the ratio of the single-phase mixture to the texture etching solution used.
• At least one polyethylene glycol is mixed with a base to form a single-phase mixture and a change in colour of the single-phase mixture is awaited.
• base single-phase mixture and colour change are to be understood in the way explained above.
• the change of colour takes place, for example, when the single-phase mixture is exposed to ambient air during the waiting period. In principle, however, other ambient atmospheres are also possible, provided they enable the necessary change in colour of the single-phase mixture. It is also possible to pass ambient air or other gas mixtures into or through the single-phase mixture, thus reducing the waiting period.
• the at least one polyethylene glycol is mixed with the base and water to form the single-phase mixture.
• This is done preferably by mixing the at least one polyethylene glycol with an aqueous solution of the base, for example with an aqueous sodium hydroxide or potassium hydroxide solution.
• the proportion of water is, as described above, to be selected in such a way that the single-phase mixture does not separate into several phases.
• Alkali hydroxides, in particular sodium hydroxide or potassium hydroxide have proven themselves as base.
• the alkali hydroxide used or the mixture of several alkali hydroxides used is dosed in such a way that its mass fraction in the components mixed to form the single-phase mixture amounts to 1% to 10%, preferably about 7%.
• a change of colour of the single-phase mixture is awaited, into a shade which lies between orange and red-brown in the optical spectrum.
• the shade taken on by the single-phase mixture has an influence on its effect. Therefore it is preferable to wait for a change of colour into a red-brown shade, since a single-phase mixture which has changed colour in this way exhibits an espe- cially strong effect.
• One advantageous variant embodiment of the process according to the invention provides that the single-phase mixture is heated to a temperature of at least 40°C, preferably to a tem- perature of between 40°C and 120°C and especially preferably to a temperature of between 75°C and 85°C.
• a heating device used to heat the single-phase mixture is preferably turned off after the target temperature is reached, but can in principle also remain switched on while awaiting the colour change.
• One refinement of the invention makes provision that a non- oxidising acid is admixed into the single-phase mixture, preferably hydrochloric acid or acetic acid.
• a non- oxidising acid is admixed into the single-phase mixture, preferably hydrochloric acid or acetic acid.
• the product which is unstable over time with respect to its effect can be stabilised and hence its storage life improved.
• the admixture of acid takes place after the change of colour of the single-phase mixture. It has proven advantageous to ad ⁇ mix the acid in a concentration and quantity such that a pH value of the single-phase mixture of less than 7, preferably less than 3, ensues.
• DE 10 2008 056 086 can likewise be stabilised by the admixture of a non-oxidising acid.
• a product obtainable by mixing at least one polyethylene glycol with a base, allowing the mixture to rest in ambient air and at a temperature of about 25°C until two phases form and separating the less dense phase representing the product can thus be stabilised with respect to its effect by admixing a non-oxidising acid into the separated less dense phase, preferably hydrochloric acid or acetic acid.
• the acid is preferably admixed in such a way that a pH value of the product of less than 7, preferably less than 3, ensues.
• This described stabilisation by the admixture of a non- oxidising acid such as hydrochloric acid or acetic acid is compatible with all the refinements and variant embodiments of the product described in DE 10 2008 056 086, as well as with the production processes of the product and its application described therein and has proven to be advantageous. It has proven particularly advantageous in conjunction with the use of an alkali hydroxide, preferably sodium hydroxide or potas ⁇ sium hydroxide, as base, the use of tetraethylene glycol as at least one polyethylene glycol or the admixture of water into the mixture described in said application.
• an alkali hydroxide preferably sodium hydroxide or potas ⁇ sium hydroxide
• the admixture of a non-oxidising acid has also proven to be advantageous when water and alkali hydroxides, preferably sodium hydroxide or potassium hydroxide, are admixed into the separated less dense phase, in order thus to form a texture etching solution.
• alkali hydroxides preferably sodium hydroxide or potassium hydroxide
• the additional admixture of alcohol, pref ⁇ erably isopropyl alcohol, is compatible with the described admixture of non-oxidising acid.
• such an admixture of alcohols is omitted, in order to avoid the associated disadvantages.
• DE 10 2008 056 086 provides that at least one polyethylene glycol is mixed with a base, and after forming two phases in the resulting mixture, the less dense phase representing the product is separated and a non-oxidising acid, preferably hy ⁇ drochloric acid or acetic acid, is admixed into the separated phase.
• a non-oxidising acid preferably hy ⁇ drochloric acid or acetic acid
• a change of colour of the separated less dense phase into a shade which lies between orange and red-brown in the optical spectrum, for example an orange shade or a red- brown shade, is awaited.
• the non-oxidising acid in this case is preferably admixed following the change of colour of the less dense phase.
• Figure 1 Schematic view of the production of one embodiment of the product according to the invention
• Figure 2 Schematic view of one embodiment of the process ac ⁇ cording to the invention
• Figure 3 Illustration of individual steps of the embodiments from Figures 1 and 2
• FIG. 1 shows the production of one embodiment of the product according to the invention in schematic view.
• tetraethylene glycol is used as the at least one poly- ethylene glycol and potassium hydroxide (KOH) is used as base.
• KOH potassium hydroxide
• These components are mixed 10 to form a single-phase mixture.
• the single-phase mixture in this case is heated 12 to 80°C.
• the single-phase mixture is allowed to rest 14 until it has changed colour to a red-brown shade, i.e. has taken on a red-brown shade.
• the single- phase mixture is allowed to rest in ambient air 14.
• the heat supply in the present embodiment is stopped once the target temperature of 80°C is reached, so the single-phase mixture cools down during the resting period 14.
• a change of colour of the single-phase mixture into a red-brown shade occurs after
• FIG. 2 shows a schematic embodiment of the process according to the invention.
• the starting point of the process in Figure 2 is tetraethylene glycol and an aqueous sodium hydroxide solution (NaOH solution) , which are firstly mixed together 20 to form a single-phase mixture.
• the resulting mixture is heated to a temperature of at least 40°C 22, preferably to a temperature of between 40°C and 120°C and especially preferably to a temperature of between 75°C and 85°C.
• a change of colour of the single-phase mixture to a red-brown shade is awaited 24. This typically takes place during a waiting period of 15 minutes to 16 hours.
• Figure 3 is a schematic illustration of individual steps of the embodiments in Figure 1 and in Figure 2. So Figure 3 shows the single-phase mixture 52 arranged in a container 50 being heated 12 or 22 using a heating device 54.
• the single-phase mixture 52 in the embodiments in Figures 1 and 2 is at first transparent, but after being left to rest 14, or waiting 24, it takes on a colour, in particular the red-brown shade known from Figures 1 and 2, so that a single-phase mixture 56 which has changed colour is present.
• hydrochloric acid is admixed 26 into the single-phase mixture from Figure 1 or Figure 2, after being left to rest 14, or after awaiting the change of colour 24.
• the stability of the product produced can be improved, so that it can be stored for longer.
• Figure 5 shows a further refinement option for the embodiments from Figures 1 and 2 and also from Figure 4 in schematic view. According to this, the process steps in Figures 1, 2 or 4 are followed by an additional step of the admixture 28 of at least one alkali hydroxide and water to the single-phase mixture.
• the resulting product can be used as etching solution, in particular as a texture etching solution, and has proven itself in texture etchings of silicon materials.
• An etching solution of this type has been especially proven in the texture etching of monocrystalline silicon wafers.
• NaOH or KOH are used as the at least one alkali hydroxide, in which case the at least one alkali hydroxide can be selected independently of the base used in the single-phase mixture 52.
• a proportion by volume of 0.01% to 5% of the single- phase mixture to the mixture formed has proven itself.
• this proportion by volume of the single-phase mixture amounts to 0.01 to 1% and especially preferably 0.07 to 0.3%.

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• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Organic Chemistry (AREA)
• Physics & Mathematics (AREA)
• Condensed Matter Physics & Semiconductors (AREA)
• Electromagnetism (AREA)
• General Physics & Mathematics (AREA)
• Computer Hardware Design (AREA)
• Microelectronics & Electronic Packaging (AREA)
• Power Engineering (AREA)
• Weting (AREA)
• Photovoltaic Devices (AREA)
• Cleaning Or Drying Semiconductors (AREA)

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• 2010
  • 2010-04-30 DE DE102010019079A patent/DE102010019079A1/de not_active Ceased
• 2011
  • 2011-04-25 TW TW100114245A patent/TWI467054B/zh not_active IP Right Cessation
  • 2011-04-27 CN CN201180004300.1A patent/CN102695778B/zh not_active Expired - Fee Related
  • 2011-04-27 KR KR1020127028184A patent/KR101478892B1/ko active IP Right Grant
  • 2011-04-27 EP EP11727757A patent/EP2470619A1/en not_active Withdrawn
  • 2011-04-27 JP JP2013506772A patent/JP5632533B2/ja not_active Expired - Fee Related
  • 2011-04-27 WO PCT/IB2011/000900 patent/WO2011135435A1/en active Application Filing

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