Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
  • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
  • H01L21/02104—Forming layers
  • H01L21/02365—Forming inorganic semiconducting materials on a substrate
  • H01L21/02612—Formation types
  • H01L21/02617—Deposition types
  • H01L21/0262—Reduction or decomposition of gaseous compounds, e.g. CVD
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
  • C23C16/22—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the deposition of inorganic material, other than metallic material
  • C23C16/24—Deposition of silicon only
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
  • C23C16/44—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating
  • C23C16/455—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating characterised by the method used for introducing gases into reaction chamber or for modifying gas flows in reaction chamber
  • C23C16/45557—Pulsed pressure or control pressure
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
  • C23C16/44—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating
  • C23C16/50—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating using electric discharges
  • C23C16/505—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating using electric discharges using radio frequency discharges
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
  • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
  • H01L21/02104—Forming layers
  • H01L21/02365—Forming inorganic semiconducting materials on a substrate
  • H01L21/02518—Deposited layers
  • H01L21/02521—Materials
  • H01L21/02524—Group 14 semiconducting materials
  • H01L21/02532—Silicon, silicon germanium, germanium
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
  • H10F71/00—Manufacture or treatment of devices covered by this subclass
  • H10F71/121—The active layers comprising only Group IV materials
  • H10F71/1224—The active layers comprising only Group IV materials comprising microcrystalline silicon
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E10/00—Energy generation through renewable energy sources
  • Y02E10/50—Photovoltaic [PV] energy
  • Y02E10/545—Microcrystalline silicon PV cells
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
  • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

• the invention relates to a method for the deposition of silicon layers, in particular a method for the deposition of microcrystalline silicon, in which only a little hydrogen is required.
• Microcrystalline silicon is a material that is used as an absorber material in particular in solar cells. In many laboratories today, it is manufactured from silane and hydrogen using the PECVD (plasma enhanced chemical vapor deposition) process. The addition of hydrogen, the so-called hydrogen dilution, is necessary to produce crystalline silicon at substrate temperatures below 500 ° C. These crystalline silicon layers consist of many microscopic crystallites - hence the name microcrystalline silicon.
• PECVD plasma enhanced chemical vapor deposition
• High-quality layers of microcrystalline silicon can be deposited in various deposition regimes.
• the hydrogen is needed to influence the layer growth. However, only a small part of the hydrogen used is built into the silicon layer produced, typically less than 10%. The remaining hydrogen is pumped out. For a later industrial Production, the high hydrogen consumption, especially when separating at 13.56 MHz, is a serious problem due to the high costs [1] .
• This investigated process runs cyclically (discontinuously) and essentially comprises two process steps.
• a small amount of the reactive process gas SiH 4 or a CH 4 / SiH 4 mixture
• This step serves to refresh the gas atmosphere after a process cycle.
• the plasma burns at low power (approx. 10 W), so that an ultra thin silicon layer is deposited.
• both the pumping power from the chamber and the gas supply into the chamber are interrupted.
• the deposit pressure is increased and the silane concentration is reduced to ⁇ 5%.
• the plasma continues to burn at approx. 60 W.
• the process gases are gradually decomposed and the separated layer continues to grow.
• an opposite effect occurs.
• the layer is etched by H radicals. The etching rate decreases due to the increasing proportion of hydrogen in the plasma until finally a balance between layer growth and etching is reached. Atoms that are weakly bonded are preferably etched, so that a network with stronger bonds is finally formed.
• the entire deposition process takes place as a constant sequence of these two steps (layer by layer) up to the desired layer thickness.
• a crystalline volume fraction of more than 90% is reported. Due to the cyclical change in the process conditions, this process is very complex. It differs fundamentally from the standard PECVD process and is not yet for the
• VHFGD very high frequency glow discharge
• the deposition Since the deposition is started with a pure silane plasma and hydrogen is only added later through the decomposition of the silane, the deposited layer has a pronounced amorphous incubation layer
• the object of the invention is to provide a method for producing microcrystalline silicon layers which, on the one hand, has an almost homogeneous microcrystalline structure in the direction of layer growth, i. H. has homogeneous structural properties and, on the other hand, only uses small amounts of hydrogen.
• homogeneous microcrystalline silicon layers in particular as a first layer on a substrate in a plasma deposition chamber, can only take place in the presence of corresponding amounts of hydrogen. This means that hydrogen must already be present at the beginning of a deposition so that crystalline growth can take place advantageously from the start.
• a method was developed in order to provide sufficient hydrogen from the beginning of the deposition with a low overall hydrogen consumption. Only small amounts of hydrogen are advantageously used in the continuous process.
• Static deposition conditions are advantageously set during the deposition process. This is done, among other things, by a controlled supply and discharge of the corresponding gases in and out of the plasma chamber.
• Silane is particularly suitable as a reactive, silicon-containing gas suitable for these processes.
• Higher silanes e.g. B. disilane (Si 2 H 6 ), chlorosilors and fluorosilanes, e.g. As SiCl 4 or SiF 4 , and their higher forms and mixed forms z.
• B. dichlorosilane (SiCl 2 H 2 ) are also conceivable.
• the excitation frequency for the plasma should advantageously be chosen to be less than 50 MHz, in particular less than 30 MHz.
• a first embodiment of the method provides for a mixture of hydrogen and a reactive silicon-containing gas, in particular silane, to be initially presented as an initial condition within the deposition chamber. This can be done, for example, both by a) flowing through the plasma chamber continuously with a corresponding gas mixture of silane and hydrogen, or else b) by flooding the previously evacuated plasma chamber with a gas mixture. In case a), the hydrogen supply is then stopped simultaneously with the start of the plasma.
• a reactive silicon-containing gas in particular silane
• the silane dissociated by the plasma and consumed by the deposition process is replaced by continuous addition into the chamber.
• a corresponding amount of the gas mixture present there is accordingly removed from the chamber.
• the microcrystalline growth of the silicon layers on the substrate takes place from the start.
• the gas flows are each related to the substrate surface to be coated.
• the gas flows set for the reactive, silicon-containing gas after the plasma start are advantageously in the range between 0.5 and 20 sccm / 100 cm 2 coating area, in particular in the range between 0.5 and 5 sccm / 100 cm 2 coating area.
• a mixture of reactive, silicon-containing gas and hydrogen is fed continuously to the plasma chamber having the substrate. The plasma is started and the desired microcrystalline deposition of the silicon on the substrate takes place.
• a corresponding amount of the gas mixture present there is removed from the chamber in order to maintain the static pressure conditions within the chamber.
• Both the total gas flow and the ratio of reactive silicon-containing gas to hydrogen are advantageously kept constant during the entire deposition.
• Typical total flows are in the range below 20 sccm / 100 cm 2 coating area, in particular in the range below 6 sccm / 100 cm 2 coating area.
• the set ratio of reactive, silicon-containing gas and hydrogen is advantageously in the range above 15%, in particular above 19% (theoretically it is also conceivable to start with a pure H 2 plasma).
• a total gas flow of less than 10 sccm / 100 cm 2 coating area at a deposition rate> 1 ⁇ / s, of less than 50 sccm / 100 cm 2 coating area at a deposition rate> 5 ⁇ / s, of less than 100 sccm has proven to be particularly advantageous / 100 cm 2 coating area at a deposition rate> 10 ⁇ / s, and less than 200 sccm / 100 cm 2 coating area at a deposition rate> 20 ⁇ / s.
• the method according to the invention makes it possible in a simple manner to produce homogeneous, microcrystalline silicon layers which have proven to be particularly suitable for use as absorber layers in solar cells. Particular attention is paid to the possibility with this
• FIG. 1 The solar cell parameters a) efficiency ⁇ , b) fill factor FF, c) open circuit voltage V 0 c and d) Short-circuit current density J S c depending on the silane concentration [SiH 4 ] / [H 2 ].
• FIG. 1 explains the behavior of the solar cell parameters when the silane concentration is varied during the i-layer growth. With a certain silane concentration (here: ⁇ 0.9%) a maximum efficiency is achieved. This silane concentration is not only important for solar cells, but is also the highest silane concentration at which microcrystalline silicon with a high crystalline volume fraction can be produced under the given conditions.
• FIG. 2 shows the maximum silane flows at which certain hydrogen flows flow in a continuous process microcrystalline growth can take place and the resulting silane concentrations are applied.
• the optimization was carried out according to FIG. 1. With these combinations of silane and hydrogen flows, the homogeneous growth of microcrystalline silicon layers (with a high crystalline volume fraction) is possible at the specified pressure and the specified output.
• FIG. 3 shows the quantum efficiency of a solar cell in which no more hydrogen was added during the deposition.
• the high quantum efficiency in the long-wave (> 800 nm) spectral range shows that the i-layer has a high crystalline volume fraction.
• Both exemplary embodiments relate to a substrate area of 100 cm 2 .
• a mixture of hydrogen and silane (corresponding to standard process conditions, ie a silane-hydrogen mixture according to FIG. 2) is used in order to ensure defined initial conditions before the start of the deposition. Since hydrogen is present from the beginning, microcrystalline growth can also take place from the beginning. After the plasma has started, the hydrogen flow is switched off. The used silane is replaced by a low silane flow. There is hydrogen all the time, because on the one hand there is hydrogen only a small part of it was used up and pumped out at the beginning, and on the other hand, the deposition of silicon from silane constantly produces new hydrogen (SiH 4 -> Si (layer) + 2H 2 ). The pumping is regulated all the time so that the deposit pressure remains constant. The process is optimized through the selection of suitable initial conditions and the selection of the si- lan flow during the deposition.
• the process therefore consists of two steps: 1. Building up the deposition pressure with high hydrogen flow and low silane flow (without plasma). 2. Deposition under the exclusive flow of
• the plasma start 13.56 MHz plasma
• the silane flow set after the plasma start was 1 sccm.
• the silicon was deposited on the substrate at a power of 0.7 W / cm 2 .
• the thickness of the deposited layer was 1.8 ⁇ m with a deposition rate of 1.7 ⁇ / s.
• the completely microcrystalline layer produced using this method was successfully used in a solar cell.
• FIG. 3 shows the quantum efficiency of the solar cell produced.
• the high short-circuit current and the high quantum efficiency for wavelengths greater than 800 nm are an indication of the high crystalline volume fraction across the entire i-layer thickness. If one uses the used silane for this cell in relation to the hydrogen used for the pressure build-up, one comes to a ratio of 4: 3.

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