EP1228538A1 - Method and device for producing solar cells - Google Patents

Method and device for producing solar cells

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Publication number
EP1228538A1
EP1228538A1 EP00965843A EP00965843A EP1228538A1 EP 1228538 A1 EP1228538 A1 EP 1228538A1 EP 00965843 A EP00965843 A EP 00965843A EP 00965843 A EP00965843 A EP 00965843A EP 1228538 A1 EP1228538 A1 EP 1228538A1
Authority
EP
European Patent Office
Prior art keywords
hydrogen
plasma
solar cells
passivation
semiconductor
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
EP00965843A
Other languages
German (de)
French (fr)
Inventor
Peter Fath
Markus Spiegel
Thomas Pernau
Gernot Wandel
Rainer MÖLLER
Johann-Georg Reichart
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Universitaet Konstanz
Centrotherm Thermal Solutions GmbH and Co KG
Original Assignee
Centrotherm Elektrische Anlagen GmbH and Co
Universitaet Konstanz
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from DE19962896A external-priority patent/DE19962896A1/en
Application filed by Centrotherm Elektrische Anlagen GmbH and Co, Universitaet Konstanz filed Critical Centrotherm Elektrische Anlagen GmbH and Co
Publication of EP1228538A1 publication Critical patent/EP1228538A1/en
Ceased legal-status Critical Current

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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
    • H01L31/18—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof
    • H01L31/186—Particular post-treatment for the devices, e.g. annealing, impurity gettering, short-circuit elimination, recrystallisation
    • H01L31/1868—Passivation
    • 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
    • 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
    • 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
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S438/00—Semiconductor device manufacturing: process
    • Y10S438/958—Passivation layer

Definitions

  • the present invention relates to the preambles of the independent claims.
  • the present invention is concerned with the manufacture of photovoltaic solar cells.
  • a number of different techniques are known in the prior art by means of which the hydrogen passivation is to be achieved. It has been proposed to implant high-energy hydrogen ions in the surface area of a silicon wafer and then to drive them thermally into the interior of the volume. It has also been proposed to expose the silicon wafers to a hydrogen atmosphere at temperatures which are e.g. 700 ° C is chosen so high that the molecular hydrogen dissociates and can then diffuse into the wafer. It has also been proposed to expose the samples to a hydrogen plasma, which is generated capacitively or mechanically directly and directly on the silicon wafers. It has also been proposed to carry out the passivation in conjunction with an anti-reflective coating on the solar cell.
  • a hydrogen-containing silicon nitride layer can be deposited by PE-CVD; The hydrogen atoms contained in the superficial, hydrogen-containing silicon nitride layer then enter the solar cell volume in a subsequent processing step.
  • the object of the present invention is to provide something new for commercial use, and in particular, but not exclusively, to improve the possibilities of inexpensive production of solar cells with high efficiency and to extend the methods obtained there to other areas of semiconductor production.
  • the invention thus proposes a method for the treatment of semiconductors, in which material is deposited on a semiconductor and passivation is carried out with hydrogen plasma, the material being deposited by means of low-pressure CVD and the hydrogen passivation being carried out by supplying a hydrogen plasma induced remotely from the partially processed semiconductor.
  • Preferred semiconductors are silicon semiconductors or substantial portions of semiconductors containing silicon.
  • the method according to the invention is particularly preferred in the production of solar cells from inexpensive silicate substrates.
  • good improvements of the resulting solar cells are achieved, but also e.g. in the case of poorer qualltat and thus higher defect numbers as well as in thin-film solar cells, significant improvements are possible with emcrystalline silicon substrates.
  • the partially processed solar cells are at least temporarily irritated during the hydrogen passivation; this can be done by heat radiation from an IR light source and / or resistance heating.
  • Such active heating during the hydrogen passivation instead of a temperature which has remained unchanged since a previous step is preferred in order to enable the setting of the optimal process parameters.
  • the actual hydrogen passivation according to the invention can be shortened by means of remotely induced hydrogen plasma, which occurs at typically 30 mm at 350 ° C., by passivating both during the deposition and during the heating and / or cooling phase.
  • the response time for the passive tion step can be shortened if, after the LP-CVD (low-pressure CVD), a screen printing through-firing process and / or another contact-firing process takes place, since here too the hydrogen can diffuse deeper into the cell. Passivation is thus at least partially carried out during the temperature change required to carry out another or several other process steps, and moreover at least part of the hydrogen passivation is carried out simultaneously during at least one other treatment step.
  • the hydrogen plasma is preferably generated by means of microwave radiation, because this enables particularly good control and / or regulation of the radiation intensity.
  • the plasma can be generated in a manner known per se in the presence of a non-reactive, in particular noble gas, in particular helium. This in particular reduces self-reactions in the plasma from the location of the plasma induction to the location of the partially processed solar cells, so that the efficiency of the plasma treatment increases.
  • the hydrogen plasma comes into contact with the partially processed solar cells at least during part of the passivation phase in the presence of other gases brought.
  • the plasma chemically activates the gases used for the deposition, such as NH3, S1H4, SiH2Cl2, which increases the proportion of atomic hydrogen at the sample location and at the same time accelerates the deposition process for SiN, for example.
  • the solar cells can be continuous in small units, e.g. horizontally lying or vertically arranged in a hoarding order and processed in the process, but it is preferred if a batch-like process is carried out on a large number of simultaneously processed wafers, since the process conditions are particularly easy to control.
  • the invention further relates to a device for producing solar cells from a multicrystalline silicon substrate with a reaction space for processing the solar cells, a source for passivating hydrogen, in which the source for passivating hydrogen comprises a microwave generator for the microwave induction of plasma, which removes is arranged from the reaction space, and the reaction space is designed for the execution of a low-pressure CVD.
  • the system for the simultaneous treatment of a large number of wafers is elongated and the hydrogen injection takes place transversely to the longitudinal axis, a plurality of hydrogen plasma injection openings being provided transversely to the longitudinal axis, to which a plurality of hydrogen plasma-reducing microwave arrangements are preferably provided assigned.
  • the implementation of the method according to the invention can be at least substantially automated in such a system by means of a suitable process control. The invention is described below only by way of example with reference to the drawing. In this shows:
  • FIG. 1 shows a first exemplary embodiment of a solar cell production system according to the invention in
  • Page section; 2 shows a further exemplary embodiment of a solar cell manufacturing plant according to the invention in the
  • Page section; 3a shows a third exemplary embodiment of a solar cell production plant according to the invention in
  • FIG. 3b shows the third exemplary embodiment in cross section
  • 4a shows a fourth exemplary embodiment of a solar cell manufacturing plant according to the invention in FIG
  • a system 1, generally designated 1, for the batchwise production of solar cells comprises an elongated process tube 2 made of quartz glass. At one end of the elongated process tube 2 there is a closable opening 3 which is large enough to insert a silicon wafer carrier 4a with a plurality of standing wafers 4b made of multicrystalline silicon. At the opposite end of the process tube 2, a suction opening 5 is provided, which leads to a vacuum pump (not shown).
  • a resistance heater 6 is arranged along the circumference of the process tube 2, consisting of a heating wire winding ⁇ a and an insulation 6b against the outside. The resistance heater 6 is designed so that a temperature inside the process tube temperature of at least 770 ° C can be achieved under all process conditions. With thermocouples 7, the temperature inside the process tube 2 can be checked.
  • a gas inlet 8 is provided for process gases which are intended to effect low-pressure material deposition (LP-CVD) on the wafers made of multicrystalline silicon.
  • the gas inlet 8 is connected to suitable sources for process gases such as S1CI2H2 and NH3.
  • a further inlet opening 9 is provided, which leads to a microwave cavity 10 and through which a hydrogen / helium mixture n is fed to the process tube 2 from a suitable source. Microwave energy of a frequency and intensity which is sufficient to ignite a plasma is fed into the microwave cavity 10.
  • the first identical hydrogen plasma unit is provided near the suction opening 5. This injection unit also injects the hydrogen plasma generally perpendicular to the longitudinal axis of the process tube 2.
  • a controller (not shown) is provided in order to run a predetermined temperature characteristic with the resistance heater, to control the suction and the process gas supply in accordance with a predetermined, desired process course and to influence the passivation gas supply and excitation.
  • Plant 1 of the present invention can be used to manufacture solar cells, for example, as follows: The system is first ventilated and loaded with wafers made of multicrystalline silicon prepared in a conventional manner. It is then pumped off for 10 mm to a pressure below 30 mTorr at 500 ° C. in order to remove pest gases. Subsequently, a gas mixture of 90% He and 10% H2 is introduced from the loading side through the microwave resonator 10 until a pressure of 500 mTorr is reached. Then 200 W of microwave energy at 2.4 GHz m are fed into the cavity. The passivation takes place for 40 mm at 500 ° C; then the resistance heater 6 heats up to 750 ° C. at 10 ° C./min while plasma continues to be generated.
  • the temperature is increased at a reduced rate of rise from 2 ° C / mm to 770 ° C.
  • the plasma is switched off and the tube is briefly evacuated.
  • 1 mm NH3 ⁇ gas up to a pressure of 230 mTorr is introduced from the loading side.
  • a mixture of 37.5 sccm dichlorosilane and 150 Sccm NH3 is fed in on the loading side for 22 to 26 mm and a pressure of 250 mTorr is fed in.
  • NH3 ⁇ gas is spooled on the loading side for 1 mm and a pressure of
  • the hydrogen passivation is continued during a cooling phase at 7 ° C / mm from 770 ° C to 500 ° C.
  • the plasma is switched off and, after a brief evacuation, the tube is "vented to discharge".
  • Fig. 1 essentially identical, but undercut m in the number of hydrogen injection units and their arrival Order.
  • 2 shows an arrangement in which the hydrogen plasma is first conducted in a pipe 9b inside the process pipe, which increases the uniformity of the plasma deposition. Due to the multiple microwave cavities 10a, 10b, 10c and the respective feed lines 9a, 9b, 9c, particularly high plasma performances can be achieved. The throughput can also be increased in the arrangement of FIG. 3 with a number of microwave cavities 10. It is clear that the entire system can also be constructed in a modular manner in order to enable a correspondingly high throughput in production lines for very high numbers of pieces.
  • the F g. 4 show an exemplary embodiment of a system with which a quasi-continuous process of batchwise treatment of wafers of the present invention can be carried out.
  • the actual reaction space which in turn can be heated via a heater 6, is tubular and is connected to a suitable vacuum source.
  • the semiconductor wafers to be processed are fed in via a vacuum lock 3a, so that when a boat is fed with a number of wafers to be processed, there is no impairment of the pressure conditions and the gases present in the reaction space.
  • a vacuum removal lock 3b is also provided on the opposite exit side, which is sufficient to hold e boat together with the wafers contained therein. With a suitable design of the vacuum lock and the pump to be connected to it, a quasi-continuous supply of boats can take place, for example, every minute.
  • the boats loaded with wafers to be processed are activated by a so-called "Walkmg beam” through the reaction required by space.
  • a so-called "Walkmg beam” through the reaction required by space.
  • the solar cells obtained in this way are compared with solar cells obtained in the same system without hydrogen passivation.
  • only a rinse with N2 was carried out in the comparison process during the temperature change phases.
  • the deposition phases in particular are chosen to be as long as those in the case of hydrogen passivation and the temperatures used were identical.
  • Photocurrent disconnection curves were determined on the inventive and comparative samples. It was found that the process according to the invention, which combines a low-pressure deposition process (LP-CVD) with passivation by hydrogen plasma generated at a distance from the location of the solar cell processing, leads to substantial increases in the lifetime of the charge carrier.
  • the average lifespan of the method according to the invention could be increased from 1.74 ⁇ s to 6.94 ⁇ s. At the same time, the efficiency was increased by an average of 4% (relative).
  • the system structure and the wafer holder are simple and that the passivation before and after the cell metallization is possible, which enables particularly high flexibility.
  • the process parameters can easily be adapted for efficient bulk passivation, in order to adapt, for example, to foil silicon, crystalline thin layers and / or ingot-molded silicon. It is particularly advantageous that foil silicon can be used regardless of any ripple that may be present, e.g. problems with the PE-CVD process due to the flat support on an electrode.
  • a surface passivating layer can be applied on both sides with the LP-CVD process.
  • the maintenance intervals in the LP-CVD process are long and, due to the overall process, the requirements for the vacuum system are relatively low, since the lowest required pressures around 250 mTorr.
  • the overall process is also not very sensitive to temperature homogeneity and gas distribution.
  • thermocouples in the interior of the process tube 2 offers advantages, in particular with regard to the response times, but it may also be possible to arrange them outside the process tube 2, for example on its outer wall.

Abstract

The present invention relates to a method for producing a solar cell. Material is deposited on a multicrystalline silicon substrate. Passivation is carried out with hydrogen plasma. According to the invention, the material is deposited by means of low pressure CVD and the hydrogen passivation is carried out by supplying hydrogen plasma that is induced away from the partially processed solar cells. The invention also relates to a device for carrying out said method.

Description

Titel: Verfahren und Vorrichtung zur Herstellung von SolarzellenTitle: Method and device for producing solar cells
BescnreibungBescnreibung
Die vorliegende Erfindung betrifft die Oberbegriffe der unabhängigen Ansprüche. Damit befaßt sich die vorliegende Erfin- düng mit der Herstellung photovoltaischer Solarzellen.The present invention relates to the preambles of the independent claims. The present invention is concerned with the manufacture of photovoltaic solar cells.
Bei photovoltaischen Solarzellen kommt es im Regelfall darauf an, eine bestimmte elektrische Leistung zu möglichst gunstigen Preisen zur Verfugung zu stellen. Dies erfordert einer- seits einen hohen Wirkungsgrad, andererseits möglichst niedrige Herstellungskosten. Einen wesentlichen Kostenbeitrag kann das Ausgangsmateπal darstellen. Es ist daher erwünscht, nach Möglichkeit ultikristallmes Silizium anstelle von hochreinem einkristallinen Czochralski-Silizium zu verwenden. Nachteilig bei der Verwendung von multikristallinem Silizium ist jedoch, daß dieses eine Vielzahl von den Wirkungsgrad verringernden Defekten aufweist. Hierzu zahlen sowohl geometrische Fehler im Aufbau des Kristallgitters wie Versetzungen und Korngrenzen als auch eingelagerte Fremdatome, die sich bevorzugt an den Korngrenzen ablagern.In the case of photovoltaic solar cells, it is usually a question of making a certain electrical output available at the lowest possible prices. On the one hand, this requires high efficiency, on the other hand, the lowest possible production costs. The source material can make a significant contribution to costs. It is therefore desirable, if possible, to use ultra-crystalline silicon instead of high-purity single-crystal Czochralski silicon. A disadvantage of using multicrystalline silicon, however, is that it has a large number of defects which reduce the efficiency. This includes both geometric errors in the structure of the crystal lattice, such as dislocations and grain boundaries, and embedded foreign atoms, which are preferentially deposited at the grain boundaries.
Um den negativen Einfluß solcher Fremdatome usw. zu verringern, ist vorgeschlagen worden, den nachteiligen Einfluß zumindest der elektronisch geladenen Defekte durch Einbringung von atomarem Wasserstoff zu neutralisieren. Wichtig ist dabei, daß der atomare Wasserstoff nicht an der Oberflache der herzustellenden Solarzelle verbleiben darf, sondern m das Volumeninnere eindringen muß, damit er m unmittelbare Nahe zu den zu passivierenden Defekten gelangen kann.In order to reduce the negative influence of such foreign atoms, etc., it has been proposed to neutralize the disadvantageous influence of at least the electronically charged defects by introducing atomic hydrogen. It is important that the atomic hydrogen must not remain on the surface of the solar cell to be manufactured, but rather that The interior of the volume must penetrate so that it can get close to the defects to be passivated.
Es sind im Stand der Technik eine Reihe von unterschiedlichen Techniken bekannt, mittels derer die Wasserstoffpassivierung erreicht werden soll. So wurde vorgeschlagen, hochenergetische Wasserstoffionen m den Oberflachenbereich eines Silizi- umwafers zu implantieren und anschließend thermisch in das Volumeninnere zu treiben. Weiter wurde vorgeschlagen, die Si- liziumwafer einer Wasserstoffatmosphare bei Temperaturen auszusetzen, die mit z.B. 700°C so hoch gewählt ist, daß der molekulare Wassserstoff dissoziiert und dann in den Wafer diffundieren kann. Es wurde auch vorgeschlagen, die Proben einem Wasserstoffplasma auszusetzen, welches kapazitiv oder mduk- tiv direkt und unmittelbar an den Siliziumwafern erzeugt wird. Weiter wurde vorgeschlagen, die Passivierung in Verbindung mit einer Antireflexbeschichtung der Solarzelle vorzunehmen. Hierbei kann eine wasserstofhaltige Siliziumnitπd- schicht durch PE-CVD abgeschieden werden; die in der ober- flachlichen, wasserstoffhaltigen Siliziumnitπdschicht enthaltenen Wasserstoffatome gelangen dann bei einem nachfolgenden Bearbeitungsschritt in das Solarzellenvolumen hinein.A number of different techniques are known in the prior art by means of which the hydrogen passivation is to be achieved. It has been proposed to implant high-energy hydrogen ions in the surface area of a silicon wafer and then to drive them thermally into the interior of the volume. It has also been proposed to expose the silicon wafers to a hydrogen atmosphere at temperatures which are e.g. 700 ° C is chosen so high that the molecular hydrogen dissociates and can then diffuse into the wafer. It has also been proposed to expose the samples to a hydrogen plasma, which is generated capacitively or mechanically directly and directly on the silicon wafers. It has also been proposed to carry out the passivation in conjunction with an anti-reflective coating on the solar cell. Here, a hydrogen-containing silicon nitride layer can be deposited by PE-CVD; The hydrogen atoms contained in the superficial, hydrogen-containing silicon nitride layer then enter the solar cell volume in a subsequent processing step.
Hingewiesen wird auch auf den Aufsatz „ Detailed Study on Microwave Induced Remote Hydrogen Plasma Passivation of Multicrystalline Silicon" von M. Spiegel, P. Fath, K. Peter, G. Willeke und E. Bucher m 13^h EC-PVSEC, Nizza, 1995, Seiten 421 ff. Dort wird vorgeschlagen, mittels Mikrowellenemstrah- lung ein Wasserstoffplasma entfernt vom Ort der zu prozessie- renden Solarzellen zu erzeugen und dann an die Solarzellen heranzufuhren. Die bekannten Techniken sind jedoch im Regelfall langsam, allenfalls mit hohem technischen Aufwand industriell ausfuhrbar und/oder inkompatibel mit typischen heutigen Herstellungsverfahren. Es ist daher mit dem Stand der Technik nur einge- schrankt möglich, eine Solarzelle mit hohem Wirkungsgrad kostengünstig herzustellen.Attention is also drawn to the article "Detailed Study on Microwave Induced Remote Hydrogen Plasma Passivation of Multicrystalline Silicon" by M. Spiegel, P. Fath, K. Peter, G. Willeke and E. Bucher m 13 ^ h EC-PVSEC, Nice, 1995, pages 421 ff. There it is proposed to use microwave radiation to generate a hydrogen plasma distant from the location of the solar cells to be processed and then to bring them to the solar cells. However, the known techniques are generally slow, at best with a high level of technical complexity, can be carried out industrially and / or are incompatible with typical production processes today. It is therefore only possible to a limited extent with the prior art to produce a solar cell with high efficiency at low cost.
Die Aufgabe der vorliegenden Erfindung besteht darin, Neues für die gewerbliche Anwendung bereitzustellen, und msbeson- dere, jedoch nicht ausschließlich, sowohl die Möglichkeiten einer kostengünstigen Herstellung von Solarzellen mit hohem Wirkungsgrad zu verbessern als auch die dort gewonnenen Verfahrensweisen auf andere Bereich der Halbleiterherstellung auszudehnen .The object of the present invention is to provide something new for commercial use, and in particular, but not exclusively, to improve the possibilities of inexpensive production of solar cells with high efficiency and to extend the methods obtained there to other areas of semiconductor production.
Die Losung dieser Aufgabe wird unabhängig beansprucht. Bevorzugte Ausfuhrungsformen finden sich m den Unteranspruchen.The solution to this task is claimed independently. Preferred embodiments are found in the subclaims.
Die Erfindung schlagt somit ein Verfahren zur Behandlung von Halbleitern, worin auf einem Halbleiter Material abgeschieden wird und eine Passivierung mit Wasserstoffplasma vorgenommen wird, wobei das Material mittels Niederdruck-CVD abgeschieden wird und die Wasserstoffpassivierung durch Zuleitung eines entfernt von dem teilprozessierten Halbleiter induzierten Wasserstoffplasmas erfolgt.The invention thus proposes a method for the treatment of semiconductors, in which material is deposited on a semiconductor and passivation is carried out with hydrogen plasma, the material being deposited by means of low-pressure CVD and the hydrogen passivation being carried out by supplying a hydrogen plasma induced remotely from the partially processed semiconductor.
Angesichts der Unterschiede bei den Prozeßbedingungen von PE- CVD und Niederdruck-CVD war es trotz der bekannten Passivierung von im PE-CVD-Verfahren hergestellten Solarzellen für den Fachmann überraschend, daß eine Passivierung mit entfernt vom Ort der teilprozessierten Solarzellen mikrowelleniduzier- tem Wasserstoff auch bei Niederdruck-Verfahren zu einer si- gnifikanten Verbesserung des Wirkungsgrades fuhrt, ohne jedoch den Prozeß wesentlich zu verteuern.In view of the differences in the process conditions of PE-CVD and low-pressure CVD, it was surprising to the person skilled in the art, in spite of the known passivation of solar cells produced in the PE-CVD process, that passivation with hydrogen which is microwave-induced away from the location of the partially processed solar cells also Low pressure process to a si- significant improvement in efficiency, but without making the process significantly more expensive.
Als Halbleiter kommen bevorzugt Siliziumhalbleiter bzw. we- sentlich Anteile Silizium entnaltende Halbleiter in Betracht. Das erfindungsgemaße Verfahren ist dabei besonders bevorzugt bei der Herstellung von Solarzellen aus preiswerten Silizim- substraten. Insbesondere bei multikristallinen Siliziumsub- straten werden gute Verbesserungen der resultierenden Solar- zellen erzielt, aber auch z.B. bei emkristallinen Silizium- substraten schlechterer Qualltat und damit höheren Defektzahlen sowie bei Dunnschichtsolarzellen sind signifikante Verbesserungen möglich.Preferred semiconductors are silicon semiconductors or substantial portions of semiconductors containing silicon. The method according to the invention is particularly preferred in the production of solar cells from inexpensive silicate substrates. In particular with multicrystalline silicon substrates, good improvements of the resulting solar cells are achieved, but also e.g. in the case of poorer qualltat and thus higher defect numbers as well as in thin-film solar cells, significant improvements are possible with emcrystalline silicon substrates.
Es ist möglich, daß die teilprozessierten Solarzellen wahrend der Wasserstoffpassivierung zumindest zeitweise geneizt werden; dies kann durch Wärmestrahlung aus einer IR-Lichtquelle und/oder einer Widerstandsheizung geschehen. Eine derartige aktive Aufheizung wahrend der Wasserstoffpassivierung anstel- le einer seit einem vorhergehenden Schritt unverändert gehaltenen Temperatur ist bevorzugt, um die Einstellung der optimalen Prozeßparameter zu ermöglichen.It is possible that the partially processed solar cells are at least temporarily irritated during the hydrogen passivation; this can be done by heat radiation from an IR light source and / or resistance heating. Such active heating during the hydrogen passivation instead of a temperature which has remained unchanged since a previous step is preferred in order to enable the setting of the optimal process parameters.
Die Niederdruck-CVD, mit welcher die erfindungsgemaße Wasser- stoffpassivierung verknüpft ist, wird m einer bevorzugtenThe low-pressure CVD with which the hydrogen passivation according to the invention is linked is preferred
Ausfuhrung zur Abscheidung von Siliziumnitrid erfolgen. Diese Abscheide-Reaktion findet typisch bei etwa 750°C statt. Hier kann die eigentliche erfindungsgemaße Wasserstoffpassivierung mittels entfernt induziertem Wasserstoffplasma, die bei ty- pisch wahrend z.B. 30 mm be 350 °C erfolgt, dadurch verkürzt werden, daß sowohl wahrend des Abscheidens als auch wahrend der Aufheiz- und/oder Abkuhlphase eine Passivierung erfolgt. Noch weiter kann die Reaktionszeit für den Passivie- rungsschritt an sich verkürzt werden, wenn nach dem LP-CVD (Niederdruck-CVD) ein Siebdruckdurchfeuerprozeß und/oder ein anderer Kontaktfeuerprozeß erfolgt, da auch hierbei der Wasserstoff tiefer in die Zelle diffundieren kann. Damit wird also eine Passivierung zumindest partiell wahrend der zur Durchfuhrung eines anderen bzw. mehrerer anderer Prozess- Schritte erforderlichen Temperaturanderung vorgenommen und überdies wird zumindest ein Teil der Wasserstoffpassivierung gleichzeitig wahrend wenigstens eines anderen Behandlungs- Schrittes vorgenommen.Execution for the deposition of silicon nitride. This separation reaction typically takes place at around 750 ° C. Here, the actual hydrogen passivation according to the invention can be shortened by means of remotely induced hydrogen plasma, which occurs at typically 30 mm at 350 ° C., by passivating both during the deposition and during the heating and / or cooling phase. The response time for the passive tion step can be shortened if, after the LP-CVD (low-pressure CVD), a screen printing through-firing process and / or another contact-firing process takes place, since here too the hydrogen can diffuse deeper into the cell. Passivation is thus at least partially carried out during the temperature change required to carry out another or several other process steps, and moreover at least part of the hydrogen passivation is carried out simultaneously during at least one other treatment step.
Es wird hier im wesentlichen möglich, die Volumen- Passivierung αurch entfernt induziertes Wasserstoffplasma ohne Solarzellenprozeßzeitverlangerung vorzunehmen. Die Mehrko- sten des erfmdungsgemaßen Solarzellenprozesses sind damit nur noch durch die Anlagen- und zusätzlichen Betriebskosten bedingt, die durch das Wasserstoffgas bzw. -gasgemisch und den zur Plasmamduktion erforderlichen Energieaufwand hervorgerufen werden.It essentially becomes possible here to carry out the volume passivation by means of hydrogen plasma which is induced remotely without lengthening the solar cell process time. The additional costs of the solar cell process according to the invention are therefore only due to the system and additional operating costs which are caused by the hydrogen gas or gas mixture and the energy expenditure required for plasma reduction.
Das Wasserstoffplasma wird bevorzugt mittels Mikrowellenem- strahlung erzeugt, weil dies eine besonders gute Steuerung und/oder Regulierung der E strahlungs-Intensitat ermöglicht. Die Plasmaerzeugung kann in per se bekannter Weise in Gegen- wart von einem nichtreaktiven, insbesondere Edelgas, insbesondere Helium durchgeführt werden. Damit werden insbesondere Selbstreaktionen im Plasma vom Ort der Plasmamduktion bis zum Ort der teilprozessierten Solarzellen verringert, so daß die Effizienz der Plasmabehandlung steigt.The hydrogen plasma is preferably generated by means of microwave radiation, because this enables particularly good control and / or regulation of the radiation intensity. The plasma can be generated in a manner known per se in the presence of a non-reactive, in particular noble gas, in particular helium. This in particular reduces self-reactions in the plasma from the location of the plasma induction to the location of the partially processed solar cells, so that the efficiency of the plasma treatment increases.
Es ist überdies bevorzugt, wenn das Wasserstoffplasma zumindest wahrend eines Teils der Passivierungsphase in Gegenwart anderer Gase mit den teilprozessierten Solarzellen in Kontakt gebracht wird. Das Plasma aktiviert hierbei die zur Abscheidung verwendeten Gase wie NH3, S1H4, SiH2Cl2 chemisch, was den Anteil atomaren Wasserstoffs am Probenort erhöht und zugleich den Abscheidungsprozeß für z.B. SiN beschleunigt.It is also preferred if the hydrogen plasma comes into contact with the partially processed solar cells at least during part of the passivation phase in the presence of other gases brought. The plasma chemically activates the gases used for the deposition, such as NH3, S1H4, SiH2Cl2, which increases the proportion of atomic hydrogen at the sample location and at the same time accelerates the deposition process for SiN, for example.
Die Solarzellen können zwar in kleinen Einheiten kontinuierlich, z.B. horizontal liegend oder m Horten senkrecht stehend angeordnet durch eine Anlage befordert und dabei prozessiert werden, bevorzugt ist aber, wenn ein batchartiger Pro- zeß an einer Vielzahl von simultan bearbeiteten Wafern vorgenommen wird, da so die Prozeßbedingungen besonders gut kontrollierbar sind.The solar cells can be continuous in small units, e.g. horizontally lying or vertically arranged in a hoarding order and processed in the process, but it is preferred if a batch-like process is carried out on a large number of simultaneously processed wafers, since the process conditions are particularly easy to control.
Gegenstand der Erfindung ist weiter eine Vorrichtung zur Her- Stellung von Solarzellen aus einem multikristallmen Siliziumsubstrat mit einem Reaktionsraum zur Prozessierung der Solarzellen, einer Quelle für passivierenden Wasserstoff, bei welcher die Quelle für passivierenden Wasserstoff einen Mikrowellengenerator zur Mikrowelleninduktion von Plasma um- faßt, der entfernt vom Reaktionsraum angeordnet ist, und der Reaktionsraum für die Ausfuhrung einer Niederdruck-CVD ausgelegt ist. Es kann dabei insbesondere vorgesehen sein, daß die Anlage zur gleichzeitigen Behandlung einer Vielzahl von Wafern langgestreckt ist und die Wasserstoffin ektion quer zur Langsachse erfolgt, wobei quer zur Langsachse eine Mehrzahl von Wasserstoffplasma-Injektionsoffnungen vorgesehen sind, denen vorzugsweise eine Mehrzahl von Wasserstoffplasma- mduzierenden Mikrowellenanordnungen zugeordnet ist. Mittels einer geeigneten Prozeßsteuerung kann in einer solchen Anlage die Durchfuhrung des erfmdungsgemaßen Verfahrens zumindest im wesentlichen automatisiert werden. Die Erfindung wird im folgenden nur beispielsweise anhand der Zeichnung beschrieben. In dieser zeigt:The invention further relates to a device for producing solar cells from a multicrystalline silicon substrate with a reaction space for processing the solar cells, a source for passivating hydrogen, in which the source for passivating hydrogen comprises a microwave generator for the microwave induction of plasma, which removes is arranged from the reaction space, and the reaction space is designed for the execution of a low-pressure CVD. In particular, it can be provided that the system for the simultaneous treatment of a large number of wafers is elongated and the hydrogen injection takes place transversely to the longitudinal axis, a plurality of hydrogen plasma injection openings being provided transversely to the longitudinal axis, to which a plurality of hydrogen plasma-reducing microwave arrangements are preferably provided assigned. The implementation of the method according to the invention can be at least substantially automated in such a system by means of a suitable process control. The invention is described below only by way of example with reference to the drawing. In this shows:
Fig. 1 ein erstes Ausfuhrungsbeispiel einer erfin- dungsgemaßen Solarzellen-Herstellungsanlage im1 shows a first exemplary embodiment of a solar cell production system according to the invention in
Seitenschnitt; Fig. 2 ein weiteres Ausfuhrungsbeispiel einer erfin- dungsgemaßen Solarzellen-Herstellungsanlage imPage section; 2 shows a further exemplary embodiment of a solar cell manufacturing plant according to the invention in the
Seitenschnitt; Fig.3a ein drittes Ausfuhrungsbeispiel einer erfm- dungsgemaßen Solarzellen-Herstellungsanlage imPage section; 3a shows a third exemplary embodiment of a solar cell production plant according to the invention in
Seitenschnitt ; Fig.3b das dritte Ausfuhrungsbeispiel im Querschnitt; Fig. 4a ein viertes Ausfuhrungsbeispiel einer erfm- dungsgemaßen Solarzellen-Herstellungsanlage imSide cut; 3b shows the third exemplary embodiment in cross section; 4a shows a fourth exemplary embodiment of a solar cell manufacturing plant according to the invention in FIG
Seitenschnitt für die quasi kontinuierlicheSide cut for the quasi continuous
Prozessierung; Fig. 4b das vierte Ausfuhrungsbeispiel im Querschnitt.processing; Fig. 4b, the fourth exemplary embodiment in cross section.
Nach Fig. 1 umfaßt eine allgemein mit 1 bezeichnete Anlage 1 zur batchweisen Herstellung von Solarzellen ein langgestrecktes Prozeßrohr 2 aus Quarzglas. Am einen Ende des langgestrecktes Prozeßrohres 2 ist eine verschließbare Öffnung 3 vorgesehen, welche groß genug ist, um einen Siliziumwafertrager 4a mit einer Vielzahl von stehenden Wafern 4b aus multikristallinem Silizium einzuschieben. Am gegenüberliegenden Ende des Prozeßrohres 2 ist eine Absaugoffnung 5 vorgesehen, die zu einer Vakuumpumpe (nicht gezeigt) fuhrt. Längs des Um- fanges des Prozeßrohres 2 ist eine Widerstandsheizung 6 angeordnet, bestehend aus einer Heizdrahtwicklung βa und einer Isolierung 6b gegen die Außenseite. Die Widerstandsheizung 6 ist so ausgelegt, daß im Inneren des Prozeßrohres eine Tempe- ratur von wenigstens 770 °C unter allen Prozeßbedingungen erreicht werden kann. Mir Thermoelementen 7 kann die Temperatur im Inneren des Prozeßrohres 2 kontrolliert werden.According to FIG. 1, a system 1, generally designated 1, for the batchwise production of solar cells comprises an elongated process tube 2 made of quartz glass. At one end of the elongated process tube 2 there is a closable opening 3 which is large enough to insert a silicon wafer carrier 4a with a plurality of standing wafers 4b made of multicrystalline silicon. At the opposite end of the process tube 2, a suction opening 5 is provided, which leads to a vacuum pump (not shown). A resistance heater 6 is arranged along the circumference of the process tube 2, consisting of a heating wire winding βa and an insulation 6b against the outside. The resistance heater 6 is designed so that a temperature inside the process tube temperature of at least 770 ° C can be achieved under all process conditions. With thermocouples 7, the temperature inside the process tube 2 can be checked.
Bei der Öffnung 3 ist ein Gaseinlaß 8 für Prozeßgase vorgesehen, die eine Niederdruck-Mateπalabscheidung (LP-CVD) auf den Wafern aus multikristallinem Silizium bewirken sollen. Dazu ist der Gaseinlaß 8 mit geeigneten Quellen für Prozeßgase wie S1CI2H2 und NH3 verbunden.At the opening 3, a gas inlet 8 is provided for process gases which are intended to effect low-pressure material deposition (LP-CVD) on the wafers made of multicrystalline silicon. For this purpose, the gas inlet 8 is connected to suitable sources for process gases such as S1CI2H2 and NH3.
Diametral gegenüberliegend zum Gaseinlaß 8 und senkrecht zur Achse des Prozeßrohres 2 ist eine weitere Einlaßöffnung 9 vorgesehen, die zu einer Mikrowellenkavitat 10 fuhrt und durch welche aus einer geeigneten Quelle ein Wasserstoff- / Heliumgemisch n das Prozeßrohr 2 gefuhrt wird. In die Mikrowellenkavitat 10 wird Mikrowellenenergie einer Frequenz und Intensität eingespeist, die ausreicht, um ein Plasma zu zünden.Diametrically opposite the gas inlet 8 and perpendicular to the axis of the process tube 2, a further inlet opening 9 is provided, which leads to a microwave cavity 10 and through which a hydrogen / helium mixture n is fed to the process tube 2 from a suitable source. Microwave energy of a frequency and intensity which is sufficient to ignite a plasma is fed into the microwave cavity 10.
Eine weitere, der ersten identische Wasserstoffplasammj ekti- onsemheit ist nahe der Absaugoffnung 5 vorgesehen. Diese Injektionseinheit injiziert das Wasserstoffplasma gleichfalls allgemein senkrecht zur Langsachse des Prozeßrohres 2.Another, the first identical hydrogen plasma unit is provided near the suction opening 5. This injection unit also injects the hydrogen plasma generally perpendicular to the longitudinal axis of the process tube 2.
Eine Steuerung (nicht gezeigt) ist vorgesehen, um mit der Wi- derstandsheizung eine vorgegebene Temperaturkennlinie abzufahren, die Absaugung und die Prozeßgaszufuhr entsprechend einem vorgegebenen, gewünschten Prozeßverlauf zu steuern und die Passivierungsgas-Zufuhr und -anregung zu beeinflussen.A controller (not shown) is provided in order to run a predetermined temperature characteristic with the resistance heater, to control the suction and the process gas supply in accordance with a predetermined, desired process course and to influence the passivation gas supply and excitation.
Die Anlage 1 der vorliegenden Erfindung kann zur Herstellung von Solarzellen beispielsweise verwendet werden wie folgt: Zunächst wird die Anlage belüftet und mit in herkömmlicher Weise vorbereiteten Wafern aus multikristallinem Silizium beladen. Dann wird für 10 mm abgepumpt auf einen Druck unter 30 mTorr bei 500°C, um Pestgase zu entfernen. Anschließend wird em Gasgemisch aus 90% He und 10% H2 von der Beladeseite ner durch den Mikrowellenresonator 10 eingeleitet, bis em Druck von 500 mTorr erreicht ist. Dann werden 200 W Mikrowel- lenenergie mit 2,4 GHz m die Kavitat eingespeist. Die Passivierung erfolgt für 40 mm bei 500°C; dann wird mittels der Widerstandsheizung 6 mit 10°C/mιn auf 750°C hochgeheizt, wahrend weiter Plasma erzeugt wird. Nach Erreichen von 750°C wird mit verringerter Temperatur-Anstiegsgeschwindigkeit von 2°C/mm bis auf 770°C weitergeheizt. Bei dieser Temperatur wird das Plasma ausgeschaltet und das Rohr kurz evakuiert. Dann wird für 1 mm NH3~Gas bis zu einem Druck von 230 mTorr von der Beladeseite her eingeleitet. Anschließend wird, je nachdem ob partielle oder vollständige Beladung des Prozeßrohres vorliegt, für 22 bis 26 mm em Gemisch aus 37,5 sccm Dichlorsilan und 150 Sccm NH3 beladeseitig her eingespeist und em Druck von 250 mTorr eingespeist. Danach wird für 1 mm beladeseitig mit NH3~Gas gespult und dabei ein Druck vonPlant 1 of the present invention can be used to manufacture solar cells, for example, as follows: The system is first ventilated and loaded with wafers made of multicrystalline silicon prepared in a conventional manner. It is then pumped off for 10 mm to a pressure below 30 mTorr at 500 ° C. in order to remove pest gases. Subsequently, a gas mixture of 90% He and 10% H2 is introduced from the loading side through the microwave resonator 10 until a pressure of 500 mTorr is reached. Then 200 W of microwave energy at 2.4 GHz m are fed into the cavity. The passivation takes place for 40 mm at 500 ° C; then the resistance heater 6 heats up to 750 ° C. at 10 ° C./min while plasma continues to be generated. After reaching 750 ° C, the temperature is increased at a reduced rate of rise from 2 ° C / mm to 770 ° C. At this temperature the plasma is switched off and the tube is briefly evacuated. Then for 1 mm NH3 ~ gas up to a pressure of 230 mTorr is introduced from the loading side. Then, depending on whether the process tube is partially or fully loaded, a mixture of 37.5 sccm dichlorosilane and 150 Sccm NH3 is fed in on the loading side for 22 to 26 mm and a pressure of 250 mTorr is fed in. Thereafter, NH3 ~ gas is spooled on the loading side for 1 mm and a pressure of
230 mTorr eingestellt. Es wird dann wiederum ein Gasgemisch aus 90% He und 10% H2 in das Prozeßrohr eingespeist und das230 mTorr set. A gas mixture of 90% He and 10% H2 is then again fed into the process tube and that
Plasma durch Einspeisung von 200 W Mikrowellenenergie mit 2,4 GHz in die Kavitat gezündet. Die Wasserstoffpassivierung wird wahrend einer Abkuhlphase mit 7°C /mm von 770°C auf 500°C fortgesetzt. Dann wird das Plasma ausgeschaltet und das Rohr nach kurzem Evakuiere" zum Entladen belüftet.Plasma ignited by feeding 200 W microwave energy at 2.4 GHz into the cavity. The hydrogen passivation is continued during a cooling phase at 7 ° C / mm from 770 ° C to 500 ° C. Then the plasma is switched off and, after a brief evacuation, the tube is "vented to discharge".
Die Anordnungen in Fig.2 und Fig. 3 sind dem Beispiel vonThe arrangements in Fig. 2 and Fig. 3 are the example of
Fig. 1 im wesentlichen identisch, unterscneiden sich aber m der Anzahl der WasserstoffInjektionseinheiten und deren An- Ordnung. Fig. 2 zeigt dabei eine Anordnung, bei der das Wasserstoffplasma zunächst in einer Rohrleitung 9b im Inneren des Prozeßrohres gefuhrt wird, was die Gleichmäßigkeit der Plasmaabscheidung erhöht. Durch die mehrfach vorhandenen Mi- krowellenkavitaten 10a, 10b, 10c und die jeweiligen Zuleitungen 9a, 9b, 9c sind überdies besonders hone Plasmaleistungen erzielbar. Auch bei der Anordnung von Fig. 3 mit einer Reihe von Mikrowellenkavitaten 10 kann die Durchsatzleistung erhöht werden. Es ist einsichtig, daß die Gesamtanlage auch modular aufgebaut werden kann, um bei Fertigungsstraßen für sehr hohe Stuckzahlen einen entsprechend hohen Durchsatz zu ermöglichen .Fig. 1 essentially identical, but undercut m in the number of hydrogen injection units and their arrival Order. 2 shows an arrangement in which the hydrogen plasma is first conducted in a pipe 9b inside the process pipe, which increases the uniformity of the plasma deposition. Due to the multiple microwave cavities 10a, 10b, 10c and the respective feed lines 9a, 9b, 9c, particularly high plasma performances can be achieved. The throughput can also be increased in the arrangement of FIG. 3 with a number of microwave cavities 10. It is clear that the entire system can also be constructed in a modular manner in order to enable a correspondingly high throughput in production lines for very high numbers of pieces.
Die F g. 4 zeigen em Ausfuhrungsbeispiel einer Anlage, mit der em quasi kontinuierlicher Prozeß batchweiser Behandlung von Wafern der vorliegenden Erfindung vorgenommen werden kann. Der eigentliche Reaktionsraum, der wiederum über eine Heizung 6 erwärmt werden kann, ist rohrformig gestaltet, und mit einer geeigneter Vakuumquelle verbunden. Die zu prozes- sierenden Halbleiterwafer werden über eine Vakuumschleuse 3a zugeführt, so daß bei Zufuhrung eines Bootes mit einer Anzahl zu prozessierenden Wafer keine Beeinträchtigung der Druckverhaltnisse und der im Reaktionsraum vorhandenen Gase erfolgt. Weiter ist auf der gegenüberliegenden Austrittsseite gleich- falls eine Vakuumentnahmeschleuse 3b vorgesehen, die ausreicht, um jeweils e Boot samt der damit enthaltenen Wafer aufzunehmen. Unter geeigneter Auslegung der Vakuumschleuse und der damit zu verbindenden Pumpe kann eine quasi kontinuierliche Zufuhrung von Booten beispielsweise im Minutentakt erfolgen.The F g. 4 show an exemplary embodiment of a system with which a quasi-continuous process of batchwise treatment of wafers of the present invention can be carried out. The actual reaction space, which in turn can be heated via a heater 6, is tubular and is connected to a suitable vacuum source. The semiconductor wafers to be processed are fed in via a vacuum lock 3a, so that when a boat is fed with a number of wafers to be processed, there is no impairment of the pressure conditions and the gases present in the reaction space. Furthermore, a vacuum removal lock 3b is also provided on the opposite exit side, which is sufficient to hold e boat together with the wafers contained therein. With a suitable design of the vacuum lock and the pump to be connected to it, a quasi-continuous supply of boats can take place, for example, every minute.
Die mit zu prozessierenden Wafern beladenen Boote werden durch einen sogenannten „Walkmg-Beam" durch den Reaktions- räum motorisch gefordert. Durch αie Anordnung mehrerer Mikro- wellenkavitaten 10 an verschiedenen Anlagepositionen wird eine hohe Gesamtdurchsatzleistung erzielt mit einer homogenen Verteilung des atomaren Wasserstoffs über die Gesamtanlagen- lange.The boats loaded with wafers to be processed are activated by a so-called "Walkmg beam" through the reaction required by space. By arranging a plurality of microwaves cavities 10 at different plant positions, a high overall throughput is achieved with a homogeneous distribution of the atomic hydrogen over the entire plant length.
Die so erhaltenen Solarzellen werden verglichen mit Solarzellen, die der selben Anlage erhalten werden, ohne daß eine Wasserstoffpassivierung erfolgte. Dazu wurde im Vergleich- sprozeß wahrend der Temperaturveranderungsphasen lediglich eine Spulung mit N2 vorgenommen. Im Vergleich werden insbesondere die Abscheidephasen genauso lang gewählt wie jene im Fall der Wasserstoffpassivierung und die verwendeten Temperaturen waren identisch.The solar cells obtained in this way are compared with solar cells obtained in the same system without hydrogen passivation. For this purpose, only a rinse with N2 was carried out in the comparison process during the temperature change phases. In comparison, the deposition phases in particular are chosen to be as long as those in the case of hydrogen passivation and the temperatures used were identical.
An den erfmdungsgemaßen und Vergleichsproben wurden Photo- strom-Abklmgkurven bestimmt. Dabei zeigte sich, daß der er- findungsgemaße Prozeß, der e Niederdruck-Abscheideverfahren (LP-CVD) mit Passivierung durch entfernt vom Ort der Solar- zellenprozessierung erzeugtem Wasserstoffplasma verknüpft, zu wesentlichen Steigerungen der Mmoritatsladungstragerlebens- dauern fuhrt. So konnte die durchschnittliche Lebensdauer mit dem erfmdungsgemaßen Verfahren von 1,74 μs auf 6,94 μs gesteigert werden. Zugleich wurde der Wirkungsgrad um durch- schnittlich 4% (relativ) gesteigert .Photocurrent disconnection curves were determined on the inventive and comparative samples. It was found that the process according to the invention, which combines a low-pressure deposition process (LP-CVD) with passivation by hydrogen plasma generated at a distance from the location of the solar cell processing, leads to substantial increases in the lifetime of the charge carrier. The average lifespan of the method according to the invention could be increased from 1.74 μs to 6.94 μs. At the same time, the efficiency was increased by an average of 4% (relative).
Es sei erwähnt, daß das Vertauschen der Gasflußrichtung beim Übergang des H-Plasma-Prozesses zum LP-CVD-Verfahren Vorteile bietet. So kann in der Anlage von Fig.2 Wasserstoff auch über die entfernt vom Einlaß angeordneten Einlaßöffnungen 9b, 9c induziert und über die (dann gegebenenfalls von einem Mikrowellengenerator freien) Leitung 9a abgepumpt werden. Die Si- bzw. N-haltigen Prozeßgase konnten hingegen weiterhin am Ga- semlaß 8 m das Prozeßrohr eingelassen und an der Öffnung 5 abgesaugt werden. Diese Anordnung hat den Vorteil, daß die Mikrowellengeneratoren 10 dann ausschließlich an der leichter zugänglichen Stelle anzuordnen sind.It should be noted that the exchange of the gas flow direction offers advantages when the H plasma process is switched to the LP-CVD process. 2, hydrogen can also be induced via the inlet openings 9b, 9c arranged at a distance from the inlet and pumped out via the line 9a (then possibly free of a microwave generator). The process gases containing Si and N, on the other hand, were still able to semlaß 8 m let the process pipe and sucked off at the opening 5. This arrangement has the advantage that the microwave generators 10 can then only be arranged at the more easily accessible location.
Es sei erwähnt, daß der Anlagenaufbau wie auch die Waferhal- terung einfach sind und daß die Passivierung vor und nach der Zellmetallisierung möglich ist, wodurch eine besonders hohe Flexibilität ermöglicht wird. Weiter sei erwähnt, daß die Prozeßparameter ohne weiteres für effiziente Bulkpassivierung anpaßbar sind, um sich etwa Foliensilizium, kristallinen Dunnschichten und/oder blockgegossenem Silizium anzupassen. Besonders vorteilhaft ist, daß Foliensilizium ungeachet einer evtl. vorhandenn Welligkeit verwendet werden kann, welche z.B. beim PE-CVD-Verfahren aufgrund der flächigen Auflage an eine Elektrode Probleme bereitet. Zusatzlich kann mit dem LP- CVD-Verfahren eine oberflachenpassivierende Schicht beidseits aufgebracht werden.It should be mentioned that the system structure and the wafer holder are simple and that the passivation before and after the cell metallization is possible, which enables particularly high flexibility. It should also be mentioned that the process parameters can easily be adapted for efficient bulk passivation, in order to adapt, for example, to foil silicon, crystalline thin layers and / or ingot-molded silicon. It is particularly advantageous that foil silicon can be used regardless of any ripple that may be present, e.g. problems with the PE-CVD process due to the flat support on an electrode. In addition, a surface passivating layer can be applied on both sides with the LP-CVD process.
Überdies sind aufgrund der Vermeidung von Schichtabscheidun- gen an Elektroden, wie sie beim PE-CVD-Verfahren auftreten, die Wartungsintervalle beim LP-CVD-Verfahren lang und aufgrund des Gesamtverfahrens die Anforderungen an das Vakuumsystem relativ niedrig, da die niedrigsten erforderlichen Druk- ke um ca. 250 mTorr liegen. Der Gesamtprozeß ist zudem wenig sensibel auf Temperatunnhomogenitaten und die Gasverteilung.In addition, due to the avoidance of layer deposition on electrodes, as occurs in the PE-CVD process, the maintenance intervals in the LP-CVD process are long and, due to the overall process, the requirements for the vacuum system are relatively low, since the lowest required pressures around 250 mTorr. The overall process is also not very sensitive to temperature homogeneity and gas distribution.
Es sei erwähnt, daß die Anordnung der Thermoelemente im Inneren des Prozeßrohres 2 zwar insbesondere im Hinblick auf die Ansprechzeiten Vorteile bietet, aber gegebenenfalls auch deren Anordnung außerhalb des Prozeßrohres 2, etwa auf dessen Außenwandung, möglich ist. It should be mentioned that the arrangement of the thermocouples in the interior of the process tube 2 offers advantages, in particular with regard to the response times, but it may also be possible to arrange them outside the process tube 2, for example on its outer wall.

Claims

Patentansprüche Patent claims
1. Verfahren zur Behandlung von Halbleitern, worin auf ei- nem Halbleiter Material abgeschieden wird und eine Passivierung mit Wasserstoffplasma vorgenommen wird, dadurch gekennzeichnet, daß das Material mittels Niederdruck-CVD abgeschieden wird und die Wasserstoffpassivierung durch Zuleitung eines entfernt von den teilprozes- sierten Solarzellen induzierten Wasserstoffplasmas erfolgt.1. Process for the treatment of semiconductors, in which material is deposited on a semiconductor and passivation is carried out with hydrogen plasma, characterized in that the material is deposited using low-pressure CVD and the hydrogen passivation is carried out by supplying a solar cell that has been partially processed remotely induced hydrogen plasma takes place.
2. Verfahren nach dem vorhergehenden Anspruch, dadurch gekennzeichnet, daß als Halbleiter em Siliziumhalbleiter bzw. em wesentliche Anteile Silizium enthaltender Halbleiter behandelt wird.2. The method according to the preceding claim, characterized in that a silicon semiconductor or a substantial proportion of silicon-containing semiconductors is treated as the semiconductor.
3. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß als Halbleiter em Silizium- Substrat, insbesondere Siliziumwafer behandelt wird.3. Method according to one of the preceding claims, characterized in that a silicon substrate, in particular a silicon wafer, is treated as a semiconductor.
4. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß als Halbleiter em multikristallines Silizumsubstrat , insbesondere em multikπ- stallmer Siliziumwafer behandelt wird.4. The method according to any one of the preceding claims, characterized in that a multicrystalline silicon substrate, in particular a multicrystalline silicon wafer, is treated as a semiconductor.
5. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß es bei der Herstellung einer Solarzelle verwendet wird.5. Method according to one of the preceding claims, characterized in that it is used in the production of a solar cell.
6. Verfahren nach dem vorhergehenden Anspruch, dadurch gekennzeichnet, daß die teilprozessierten Solarzellen wah- rend der Wasserstoffpassivierung zumindest zeitweise geheizt werden.6. Method according to the preceding claim, characterized in that the partially processed solar cells are be heated at least temporarily during hydrogen passivation.
7. Verfahren nach einem der vorhergehenden Anspr che, da- durch gekennzeichnet, daß die Niederdruck-CVD zur Abscheidung von Siliziumnitπd erfolgt.7. Method according to one of the preceding claims, characterized in that the low-pressure CVD is carried out to deposit silicon nitride.
8. Verfahren nach dem vorhergehenden Anspruch, dadurch gekennzeichnet, daß durch Wärmestrahlung aus einer IR- Lichtquelle und/oder einer Widerstandsheizung aufgeheizt wird.8. The method according to the preceding claim, characterized in that heating is carried out by thermal radiation from an IR light source and / or a resistance heater.
9. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß die teilprozessierten Solar- Zeilen wahrend der Wasserstoffpassivierung eine Temperatur von zwischen 250 und 850 °C, insbesondere von app . 350°C erreichen.9. The method according to any one of the preceding claims, characterized in that the partially processed solar cells have a temperature of between 250 and 850 ° C, in particular of app. Reach 350°C.
10. Verfahren nach einem der vorhergehenden Ansprüche, da- durch gekennzeichnet, daß die Passivierung zumindest partiell wahrend der zur Durchfuhrung eines anderen Pro- zess-Schrittes erforderlichen Temperaturanderung vorgenommen wird.10. The method according to one of the preceding claims, characterized in that the passivation is carried out at least partially during the temperature change required to carry out another process step.
11. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß wahrend zumindest eines Teils der Wasserstoffpassivierung wenigstens em anderer Be- handlungsschπtt gleichzeitig vorgenommen wird.11. The method according to any one of the preceding claims, characterized in that during at least part of the hydrogen passivation, at least one other treatment step is carried out simultaneously.
12. Verfahren nach dem vorhergehenden Anspruch, dadurch gekennzeichnet, daß der andere Schritt ein Abscheideprozeß und/oder Siebdruckfeuerprozeßschritt ist. 12. The method according to the preceding claim, characterized in that the other step is a deposition process and / or screen printing firing process step.
13. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß das Wasserstoffplasma mittels Mikrowelleneinstrahlung erzeugt wird.13. The method according to any one of the preceding claims, characterized in that the hydrogen plasma is generated by means of microwave radiation.
1 . Verfahren nach dem vorhergehenden Anspruch, dadurch gekennzeichnet, daß das Wasserstoffplasma in Gegenwart von einem nichtreaktiven, insbesondere Edelgas, insbesondere Helium durchgeführt wird.1 . Method according to the preceding claim, characterized in that the hydrogen plasma is carried out in the presence of a non-reactive, in particular noble gas, in particular helium.
15. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß das Wasserstoffplasma in Gegenwart anderer Gase mit den teilprozessierten Solarzellen in Kontakt gebracht wird.15. The method according to any one of the preceding claims, characterized in that the hydrogen plasma is brought into contact with the partially processed solar cells in the presence of other gases.
16. Verfahren nach dem vorhergehenden Anspruch, dadurch gekennzeichnet, daß als Gas wenigstens eines aus NH3,16. The method according to the preceding claim, characterized in that the gas is at least one of NH3,
S1H4, NO2 und/oder S1H2CI2 gewählt wird.S1H4, NO2 and/or S1H2CI2 is selected.
17. Verfahren nach einem der Ansprüche 15 oder 16, dadurch gekennzeichnet, daß die anderen Gase entfernt von den zu prozessierenden Halbleitern angeregt werden, insbesondere durch Mikrowellen, Laser- und/oder UV-Licht, vorzugsweise bis zur Plasmabildung .17. The method according to any one of claims 15 or 16, characterized in that the other gases are excited remotely from the semiconductors to be processed, in particular by microwaves, laser and / or UV light, preferably until plasma formation.
18. Verfahren nach einem der Ansprüche 15 bis 17, dadurch gekennzeichnet, daß der passivierende Wasserstoff des induzierten Wasserstoffplasmas durch Anregung mit Mikro- wellenenergie, Laserlicht uno/oder UV-Licht erzeugt wird.18. The method according to any one of claims 15 to 17, characterized in that the passivating hydrogen of the induced hydrogen plasma is generated by excitation with microwave energy, laser light and/or UV light.
19. Verfahren nach einem der vornergehenden Ansprüche, dadurch gekennzeichnet, daß das Gesamtvolumen des Halblei- ters, insbesondere der Solarzelle passiviert wird, insbesondere beid- bzw. allseitig.19. The method according to one of the preceding claims, characterized in that the total volume of the semiconductor ters, especially the solar cell, is passivated, especially on both or all sides.
20. Verfahren nach einem der vorhergehenden Ansprüche, da- durch gekennzeichnet, daß die Halbleiter, insbesondere20. Method according to one of the preceding claims, characterized in that the semiconductors, in particular
Solarzellen batchweise prozessiert werden.Solar cells are processed in batches.
21. Vorrichtung zur Herstellung von Halbleiterprodukten, insbesondere von Solarzellen aus einem multikristallmen Siliziumsubstrat , mit einem Reaktionsraum zur Prozessie- rung der Halbleiterprodukte, insbesondere Solarzellen, einer Quelle für passivierenden Wasserstoff, dadurch gekennzeichnet, daß die Quelle für passivierenden Wasserstoff einen Plasmagenerator, insbesondere einen Mikro- wellengenerator zur Mikrowelleninduktion von Plasma, umfaßt, der entfernt vom Reaktionsraum angeordnet ist, und der Reaktionsraum für die Ausfuhrung einer Niederdruck- CVD ausgelegt ist.21. Device for producing semiconductor products, in particular solar cells from a multicrystal silicon substrate, with a reaction space for processing the semiconductor products, in particular solar cells, a source for passivating hydrogen, characterized in that the source for passivating hydrogen is a plasma generator, in particular a micro - Wave generator for microwave induction of plasma, which is arranged remotely from the reaction space, and the reaction space is designed to carry out a low-pressure CVD.
22. Vorrichtung nach dem vorhergehenden Anspruch, dadurch gekennzeichnet, daß die Anlage zur gleichzeitigen Behandlung einer Vielzahl von Wafern langgestreckt ist und die WasserstoffInjektion quer zur Langsachse erfolgt.22. Device according to the preceding claim, characterized in that the system for the simultaneous treatment of a large number of wafers is elongated and the hydrogen injection takes place transversely to the longitudinal axis.
23. Vorrichtung nach dem vorhergehenden Anspruch, dadurch gekennzeichnet, daß quer zur Langsachse eine Mehrzahl von Wasserstoffplasma-I ektionsoffnungen vorgesehen ist, wobei vorzugsweise eine Mehrzahl von Wasserstoff- plasma-mduzierenden Mikrowellenanordnungen vorgesehen 23. Device according to the preceding claim, characterized in that a plurality of hydrogen plasma ection openings are provided transversely to the longitudinal axis, preferably a plurality of hydrogen plasma-inducing microwave arrangements being provided
24. Vorrichtung nach dem vorhergehenden Anspruch, gekennzeichnet durch eine Steuerung, die zur Ausfuhrung eines Verfahrens nach einem der vorhergehenden Verfahrens- Anspruche geeignet ist.24. Device according to the preceding claim, characterized by a control which is used to execute a Method according to one of the preceding method claims is suitable.
25. Vorrichtung nacn einem der vorhergehenden Vorrichtungs- anspruche, mit einem motorbetriebenen Beladesystem zur25. Device according to one of the preceding device claims, with a motor-operated loading system
Beschickung des Reaktπonsraumes mit teilprozessieren Halbleiterprodukten, insbesondere Wafern.Loading the reaction space with partially processed semiconductor products, especially wafers.
26. Vorrichtung nach einem der vorhergehenden Vorπchtungs- anspruche, worin der Reaktionsraum zumindest zwei Offnungen aufweist, über welche Halbleiterprodukte zu- und abgeführt werden können. 26. Device according to one of the preceding device claims, wherein the reaction space has at least two openings through which semiconductor products can be supplied and removed.
EP00965843A 1999-10-13 2000-09-12 Method and device for producing solar cells Ceased EP1228538A1 (en)

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DE19949279 1999-10-13
DE19949279 1999-10-13
DE19962896A DE19962896A1 (en) 1999-10-13 1999-12-23 Method and device for producing solar cells
DE19962896 1999-12-23
PCT/DE2000/003165 WO2001028005A1 (en) 1999-10-13 2000-09-12 Method and device for producing solar cells

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US6734037B1 (en) 2004-05-11

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