JP2018191005A - Apparatus and method for bonding substrates - Google Patents

Abstract

An apparatus and corresponding method for forming a conductive direct bond between a bonding surface of a first substrate and a bonding surface of a second substrate. A component of plasma, especially ions, is introduced into an oxide layer on at least one of bonding surfaces of a first substrate and a second substrate set in a sample chamber, thereby forming an oxide layer. The bonding surface of the first substrate 1 and the bonding surface of the second substrate 14 are bonded by varying the stoichiometric ratio of the layer 2 . [Selection drawing] Fig. 5

Description

  The present invention provides an apparatus for forming a direct conductive bond between a bonding surface of a first substrate and a bonding surface of a second substrate according to claim 1, and a corresponding method according to claim 7. About.

  In particular, when bonding a plurality of substrates made of metal or metallized, a plurality of substrates having a metallized surface, a plurality of semiconductor substrates or a plurality of compound semiconductor substrates, oxidation of the bonding surface of the substrate to be bonded Plays an important role. This is because oxidation makes the bonding process difficult. The oxide prevents or reduces the formation of mechanical and / or electrical high quality contact connections. Accompanying this is that the throughput is especially worse due to prolonged high temperature heating and cooling times, and as the temperature during bonding has increased or has to be increased, The expansion due to the temperature difference has a great influence on the mutual orientation or position adjustment accuracy of the plurality of substrates. Furthermore, for example in certain MEMS and / or semiconductor devices, high process temperatures cannot be used, for example in microchips or memory chips.

  In the prior art, a wet etching process is used in particular to remove oxides that are formed on the substrates and thus prevent or at least make it difficult to optimally bond the substrates by the bonding process. Yes. In this wet etching process, hydrofluoric acid or a mixture containing hydrofluoric acid is mainly used. After the oxide is reduced, a surface terminated with hydrogen atoms is generated. This hydrophobic surface is suitable for forming a so-called pre-bond. However, if it is desired to permanently bond two wafers together, the hydrogen generated by the reduction process and terminating the substrate surface is removed from the bonding interface, and the permanent bond between the two substrate surfaces, eg, silicon surfaces, is removed. In order to obtain the above, it is necessary to heat-treat the wafer laminate at an elevated temperature. The substrate laminate is heat-treated after the surfaces are contact-connected. The silicon wafer is heat treated at a temperature of, for example, about 700 ° C. to ensure such a permanent bond. This type of method is used in particular for making multilayer metal, semiconductor, glass or ceramic joints. A particularly important field of application is the production of photovoltaic multilayer cells and photonic crystals, in particular silicon photonic crystals.

One of the major constraints in the fabrication of multi-layer cells is that the size and shape of the lattice structures of the individual semiconductor materials are not compatible. This leads to defects in the resulting semiconductor layer when producing individual layers by directly growing a plurality of layers up and down. These defects impair the quality of the layers formed, especially the achievable efficiency for converting light into electrical energy. This efficiency, also referred to as quantum efficiency, defines the ratio of charge carriers that can be used by a photoprocess to the number of absorbed photons for a given wavelength for a solar cell. From here, the following parameters are practically restricted. That is,
a) The number of active layers realizable in the structure. This is today limited to two to a maximum of three layers due to the problems described above.
b) Optimization of the individual layers for the optimal wavelength range. What is not practically possible today is to optimize the individual layers completely freely with respect to the wavelength range and the conversion characteristics for converting the light associated therewith into electrical energy. This is because the compatibility of lattice structures must always be compromised.
c) Use of more convenient materials. For example, it may be desirable for a given wavelength to use silicon or germanium. This is because these materials allow an ideal compromise between efficiency and cost. However, these materials are often not usable. This is because the lattice structure is not fully compatible with other structures used in the cell.

  Oxide treatment prior to subsequent bonding processes, particularly oxide removal, is often performed with hydrofluoric acid. After oxide removal, surface contamination and in particular oxide regeneration may occur.

  Another problem associated with this is also that the process results of the bonded substrate stack will be different if the waiting time between oxide removal and subsequent processing of the substrate is different.

  Another disadvantage of the conventional method is that the etching process must be matched to the oxide to be etched. Thus, in some cases, different etch chemistries are required for different semiconductor materials.

  Furthermore, depending on the material, the process requirements for the type of waiting time until subsequent processing and the type of process ambient conditions (for example, an inert atmosphere with no O2 and possibly no water) may also vary. For these reasons, a bonding apparatus for bonding a plurality of different substrates made of different materials may become extremely complicated. In addition, the introduction of new materials for manufacturing due to different requirements due to different materials can also result in significant process development costs.

  Another possibility for oxide removal is a physical process in addition to the chemical processes already mentioned above. One of the most important physical processes for oxide removal is sputtering. Sputtering is the removal of atoms on the surface of the substrate by an ionized sputtering gas ion collision process accelerated by an electric and / or magnetic field.

  However, when sputtering, there is a disadvantage that particles are inherently formed by this process. This is because it is the nature of this process to remove material from the surface by a physical process. This material is deposited at various locations in the process chamber and sublimed from this location, either deposited on the substrate to be bonded or directly sublimated again on the substrate. These particles hinder optimal, i.e. void-free, bonding results. Furthermore, for the sputtering process, very high ion energy is required to be able to remove material from the surface of the substrate. This causes some of the ions to be implanted into the substrate, thereby damaging the layer near the surface. This damaged layer can generally be several nm thick, typically 5 to 10 nm thick. However, since these damages can negatively affect the bonding connection with respect to the characteristics of the electrical and optical parameters, these damages are undesirable and are problematic in practice.

  Another fundamental problem in manufacturing multilayer cells is the general heat treatment for many processes. This heat treatment is performed at a temperature between 100 ° C and 700 ° C. At such high temperatures, the raw materials used are mechanically loaded. This mechanical load is particularly characterized by multiple thermal stresses when the temperature difference is large. These thermal stresses depend on the thermal expansion coefficient and temperature difference. Since multiple raw materials are welded together along the bonding interface, if these raw materials cannot expand freely from each other, the difference in thermal expansion coefficient will cause a correspondingly large thermal stress if there is a temperature difference. become. Since the selection of raw materials is very often done by different ambient conditions, thermal stress can only be avoided by making the temperature difference as small as possible within the process step.

  It should be further noted here that the material combination that is trying to provide the greatest benefit by the bonding process is just the right way to try to integrate multiple materials with different lattice parameters and / or different coefficients of thermal expansion. It is the least compatible with the heat treatment process. This is because the largest difference in thermal expansion usually occurs at this time.

  Accordingly, an object of the present invention is to provide an apparatus and method for bonding that can perform the bonding process more efficiently and with high quality.

  This problem is solved by the characterizing features of claims 1 and 7. Advantageous embodiments of the invention are described in the dependent claims. The present invention also includes all combinations of combinations of at least two of the plurality of characteristic configurations shown in the specification, claims, and / or drawings. Within the range of values shown here, values within the listed boundaries are also disclosed as boundary values and can be claimed in any combination.

  The present invention describes an apparatus and method for plasma treating an oxide layer of a substrate. This plasma treatment is either a complete removal, a partial removal and / or a change in the stoichiometry of the oxide layer and / or an amorphization of the whole layer or at least the surface layer in the present invention. Can be tied.

  In particular, the invention allows in-situ processing of the oxide layer in the plasma chamber, which plasma consists of at least one reducing gas, in particular hydrogen.

  By means of the device according to the invention and the method according to the invention, the oxide treatment and the subsequent bonding process can be carried out in a working chamber completely sealed to the atmosphere or in a module connected to the working chamber. As a result, after the oxide is treated, the surface is prevented from being newly oxidized.

In the present invention,
(1) Using a reducing gas in a plasma chamber, a plurality of substrates having oxide layers changed as desired are manufactured,
(2) Transport these substrates to the bonding module in a vacuum environment, particularly in a high vacuum environment,
(3) An apparatus and method are described that allow these substrates to be bonded together in a bonding module.

In the present invention, the change is
Changing the stoichiometric ratio of the oxide during and / or after depositing, and / or
Removing a predetermined amount of the existing oxide layer to the desired new oxide layer thickness, or
It is understood that the oxide layer is completely removed and / or that the oxide layer is made amorphous.

This is realized by an apparatus capable of exposing the substrate to a plasma containing a reducing gas. Here in particular H ₂ is used in a mixture with at least one second, in particular inert gas. An advantageous variant has been found to be the use of a H ₂ / Ar mixture.

The gas mixture H ₂ / Ar is optimal due to the mass ratio between argon and oxygen. Argon atoms, which are slightly heavier than oxygen, are ionized by the plasma and accelerated towards the oxide to be reduced, which is broken down physically, in particular mechanically, by the kinetic energy. The oxygen freed by this is then trapped accordingly by hydrogen molecules, hydrogen ions or hydrogen radicals. The thermodynamically stable water formed thereby is then removed from the surface in order to prevent reverse reaction to the metal oxide. Helium is unsuitable due to its small mass. Neon atoms have a larger mass than oxygen atoms, with only a slight difference. Krypton and another noble gas are too costly and too rare to be economically suitable for oxide crushing.

Another reducing gas according to the invention is, for example,
Nitrogen oxides and / or
Carbon monoxide and / or
Methane and / or
Hydrogen and / or
Acetic acid vapor and / or
・ Citric acid vapor.

As an inert gas, for example,
Xenon and / or
Argon and / or
Helium and / or
Nitrogen and / or
・ Carbon dioxide is used.

  The substrate is exposed to the plasma in a process chamber, for example in a vacuum. This causes a change in the oxide layer. This change can be due to either a change in the stoichiometry of the oxide and / or removal of the oxide layer thickness to the desired and desired value, or complete removal of the oxide, or amorphization. Caused by

  The ion energy of the plasma is less than 1000 eV, preferably less than 500 eV, more preferably less than 250 eV, even more preferably less than 150 eV, and most preferably between 30 and 150 eV.

  Subsequently, the plurality of substrates are aligned with each other and in contact with each other, either in the same bonding module, or advantageously in a proprietary bonding module that is specially configured. Here, these substrates are bonded. This bonding is further facilitated by the optional application of force, which ensures that these substrates are securely contacted over the entire surface. Here, the transfer between the plasma module and the bonding module is performed in a high vacuum environment by a moving device. These substrates are preferably transported by a robot.

  In the present invention, it is possible to either treat only the surface of one substrate or treat the surface of two substrates before the bonding process of the two substrates.

Advantages of the invention
Can be used universally for many different substrate materials and oxide types,
・ Process results are reproducible.
・ By performing the process in a high vacuum that prevents surface contamination, the product quality is high,
・ Environmental impact is small,
・ Cost-effective,
There are no waste products to be disposed of,
• The substrate surface ideally does not damage at all, or only slightly, or at least accurately positionable damage occurs due to implantation.

  The idea of the present invention is to treat the oxide at least in the region near the surface, for example by reducing the stoichiometric ratio of the oxide by means of a reducing gas and / or gas mixture in the plasma apparatus. And / or making the oxide amorphous. Therefore, in the present invention, atomic gas and / or molecular gas is used.

  The present invention is basically based on processing a substrate in a reducing atmosphere of plasma. For this purpose, basically all atmospheres of at least one gas suitable for causing oxide reduction of the oxide present on the bonding surface are conceivable.

Due to availability and attractive cost, it is preferred to use H _{2 in the} present invention. It is known in the literature that multiple oxides can be reduced by H ₂ on a semiconductor substrate. However, this generally requires very high temperatures (> 600 ° C.). This is unacceptable for many substrates, especially complex compound semiconductor substrates. This is because, in the worst case, material decomposition occurs (for example, GaAs decomposes at 400 ° C.), or at least the layer structure changes due to the diffusion process. Thus, an important uniform phase of the present invention is that the oxide reduction is carried out at low temperatures, best below 200 ° C., preferably below 150 ° C., more preferably below 100 ° C., most preferably at room temperature. It is to configure the process so that it can be broken.

  To make this possible, the plasma is ignited from a selected atmosphere. Due to the ion energy of the ions formed in the plasma and impinging on the substrate, sufficient energy is supplied or available so that the above reaction occurs at a very low temperature, preferably at room temperature. And / or the oxide is made amorphous. As a result, the material can be processed with a great deal of heat load.

  By setting parameters, many different substrates can be processed with the same basic idea, without changing the underlying chemistry. Advantageously, using a gas mixing system that is part of a gas supply system for the process chamber, a gas mixture of two or more gases can be adjusted depending on the equation and adapted to different substrates. Can do.

  Basically, any type of plasma chamber is conceivable for performing the above process. This includes CCP chambers (“capacitively coupled plasma”), ICP chambers (“inductively coupled plasma”) and remote plasma chambers.

  However, in the present invention, the CCP chamber is advantageous due to its simple structure and high productivity. The spacing between the electrodes is greater than 2 mm, advantageously greater than 6 mm, more preferably greater than 9 mm, even more preferably greater than 12 mm and most preferably greater than 16 mm. In the present invention, in particular, the lower electrode is configured as a substrate holder at the same time. This substrate holder can be configured as a vacuum sample holder as an alternative and more advantageously as an electrostatic sample holder. It is also conceivable to incorporate heating and / or cooling elements that allow a (slow) temperature change of the substrate.

  The frequency of the alternating voltage applied to the upper electrode is preferably higher than the frequency of the alternating voltage applied to the lower electrode. There is preferably a difference of at least 10 times, more preferably at least 100 times, even more preferably at least 250 times between these frequencies. Thereby, the mutual influence of these frequencies can be reduced. The higher frequency can take a value of, for example, 13.56 MHz or 27 MHz, whereas the frequency that can be supplied to the lower electrode can take, for example, 40 kHz, 100 kHz or 400 kHz. In this apparatus, the higher frequency is exclusively associated with ionization of the atmosphere, while the lower frequency is associated with ion acceleration to the substrate surface. Thereby, the density of plasma and the ion energy with which an ion collides with a board | substrate can be set separately. This is advantageous because this process can be better controlled. This is because in the present invention, the ion density and the ion energy can be adjusted separately and independently of each other.

In an advantageous embodiment for reducing the oxide of the Si wafer, the frequency of the alternating voltage of the upper electrode is 13.56 MHz and the frequency of the alternating voltage of the lower electrode is 80 kHz to 120 kHz. The electric power for the upper electrode and the lower electrode is, for example, 50 W to 500 W. The gas mixture is preferably a mixture of H ₂ / Ar, the concentration value of which is between 100% H ₂ /0% Ar and 0% H ₂ /100% Ar, in particular 1%. It has no other trivial ingredients. The above concentrations are advantageously lower than the 80% H _2, more advantageously lower than the 60% H _2, further below the 40% H ₂ in more advantageously, most preferably less than 20% H _2.

In order to ensure a uniform process result, the gas supply is distributed uniformly over the periphery of the plasma chamber. Similarly, the absorption of gas from the plasma chamber takes place in uniform form, in particular through outlets distributed around it. During the plasma treatment process, a gas mixture is continuously passed through the chamber, whereby reaction products generated during the reduction, particularly H ₂ O, are carried out of the chamber. This is important. This is because, in order to achieve better oxide reduction, in particular, more reduction reactions will be carried out than new oxidation of Si with H ₂ O. In order to ensure uniformity of this reaction across the wafer, in particular, the gas should flow uniformly in the chamber during the process, resulting in a uniform concentration of process gas.

  The ion energy with which the particles collide with the substrate surface is mainly controlled by the lower electrode. This energy is chosen to be small so that on the one hand the oxide processing on the substrate surface is successful, and on the other hand only a minimal implantation is performed which minimizes the substrate surface and the accompanying damage.

  On the other hand, however, it may be desirable to form an adjustable and controlled damage to the substrate surface in order to form a relatively weak layer of mechanical robustness. In this way, preferably, after a plurality of substrates are contact-connected, the nano gap between the surfaces can be closed by compression based on a high pressing force. The pressure applied to the surface is 0.01 MPa to 10 MPa, preferably 0.1 MPa to 8 Ma, more preferably 1 MPa to 5 MPa, and most preferably 1.5 MPa to 3 MPa. These values roughly correspond to the application of a force of 1 kN to 320 kN on a circulating 200 mm substrate. This controlled damage advantageously results in the present invention to amorphize the oxide or at least the oxide region near the surface. The surface amorphization is preferably effected by adjusting the ion energy. This amorphous region can surround the entire oxide layer, but is advantageously limited to a region near the surface. The thickness of this amorphous layer is in particular less than 10 nm, preferably less than 5 nm, more preferably less than 1 nm and most preferably less than 0.1 nm.

  Preferably, during the course of the process, the process is first started with a gas mixture that is optimal for oxide reduction, and after successful oxide reduction, the gas mixture is changed to damage the surface as desired. It is conceivable to replace it with an optimal mixture. This can be done dynamically during the above process, and in particular by a control device assisted by software.

  The above exchange of the gas mixture can also involve adaptation of the frequency generation settings for the lower and / or upper electrodes. This preferably allows the power of the lower and / or upper frequency generators to be adapted, the voltage and current boundary values for these generators to be changed and the frequency to be changed. Again, this can be done dynamically by the control device described above. These parameters can be used to set the thickness of the layer to be damaged, the density of the damage, and the species or metering of ions that are optionally implanted.

  Therefore, in many cases, the above damage is accompanied by amorphization of the region near the surface.

  When the oxide is removed from the semiconductor substrate, the above reduction generally exposes the underlying single crystal or at least crystalline semiconductor wafers (defects by MOCVD, eg, fewer growth defects). .

  Thus, the general process flow is to set the substrate in the plasma chamber for at least one of the plurality of bonding layers, for example, oxide reduction, the oxide reduction process, and the top of the substrate. And an optional process to change / damage the layers as desired.

  The plurality of substrates are further transported to a bonding chamber in a high vacuum environment working space where they are mechanically and / or optically aligned and contacted with each other. Optionally, a (large) force is applied to them and they are compressed together. These substrates can subsequently be removed. In the present invention, the bonding chamber can be the same as the above-described plasma chamber, that is, it can be a bonding plasma chamber.

In the present invention, the above high vacuum environment is in particular 1 × 10 ⁻⁵ mbar, more preferably 5 × 10 ⁻⁶ mbar, even more preferably 1 × 10 ⁻⁶ mbar, most preferably 5 × 10 ^−7. mbar, most preferably having a pressure of less than 9 × 10 ⁻⁸ mbar.

In another embodiment, the reduction process according to the present invention is not used for complete removal of the oxide, but is used to adjust the correct stoichiometry of the oxide. In particular, this makes it possible to form a layer having an excess of one or more elements that bind to oxygen. For example, silicon oxide is not a stoichiometrically correct form of SiO ₂ and is a non-stoichiometric SiO _{2 -x} . Therefore, in general, for example, a non-stoichiometric composition SiO _{2 -x} occurs, where x is 0-2. Similar considerations apply to other oxides. This non-stoichiometry can be understood in terms of crystal physics as the absence of an oxygen atom at that position in the crystal lattice. The absence of oxygen atoms increases the atomic vacancy density. The vacancies themselves have important implications for all types of transport processes.

  In another embodiment, rather than using the reduction process according to the present invention to completely remove the oxide, it is used to make an oxide layer of a given layer thickness. Here, the already existing oxide layer is removed to the desired layer thickness by the reduction process according to the invention. The layers thus formed are then, for example, International Publication No. 2012/100786 (PCT / EP2011 / 0002299), International Publication No. 2012/136267 (PCT / EP2011 / 055470), International Publication No. 2012/136266 ( PCT / EP2011 / 055469), International Publication No. 2012/136268 (PCT / EP2011 / 055471). In the present invention, the oxide is greater than 1 nm, preferably greater than 100 nm, more preferably greater than 10 μm, even more preferably greater than 100 μm, most preferably greater than 1000 μm prior to the removal process. large. After the removal process, the oxide is preferably less than 100 μm, more preferably less than 10 μm, even more preferably less than 100 nm, very preferably less than 10 nm, most preferably Smaller than 1 nm.

  The desired change in the oxide layer is also used in particular to make a more optimal hybrid bond. Hybrid bonding is again a bond between two surfaces consisting of a conductive region and a non-conductive region. The conductive region is a region mainly made of metal, particularly a region made of copper, while the non-conductive region is a region mainly made of a dielectric such as silicon oxide. Since the dielectric region and the electrical region are polished to the same level in particular, the plurality of electrical regions are completely surrounded by one dielectric and thus isolated from the surroundings. Such two hybrid surface orientations, contact connections and bonding form a hybrid bond and thus advantageously form a connection between two substrates where the conductive and non-conductive regions are bonded together.

  The substrate of the present invention is particularly a Si substrate having Cu—Cu bonding on the bonding surface, and a plurality of such Si substrates are bonded in a further step of the process. In the present invention, alternatively, for example, another metal layer made of Au, W, Ni, Pd, Pt, Sn, or the like, or a combination made of a plurality of metals can be used. Examples of this are Si-coated wafers with Al, Cu- and Sn-coated Si wafers, Si-coated Si wafers, or Cu, which is common in the industry, under Cu and for example A Si substrate coated with a barrier layer known to those skilled in the art comprising Ti, Ta, W, TiN, TaN, TiW, etc. is used, where the barrier layer will prevent Cu diffusion into the Si. It is what. Such diffusion barriers are known to those skilled in the art.

  According to this, what is important in the present invention is a working space which can be closed from the surroundings, ie from an oxidizing atmosphere, in particular sealed and advantageously hermetically closed, and correspondingly a plurality of modules connected thereto. In these modules, it is possible to perform both the reduction of the oxide layer optionally present on the bonding surface, preferably on the entire substrate, as well as the bonding. Thereby, in this invention, it can prevent that the new oxidation of a bonding surface is performed between reduction | restoration and a bonding process. Depending on the nature of the substrate, in particular the nature of the metal coating present on the substrate, different components of the atmosphere can act oxidatively. In many cases, however, oxygen and oxygen-containing compounds can have an oxidizing action. Thus, particularly in the workspace, in addition to using a reducing medium composition, the oxygen and water / water vapor concentrations are greatly reduced or approximately zero. Since a plurality of modules are connected in the work space, the substrate can be transported between the plurality of modules of the module group without exposing the substrate to the atmosphere again. Although only one module is connected to the work space, embodiments are also conceivable in which this module can perform all necessary work according to the present invention. In this case, this workspace is used only for loading and unloading operations.

  Particularly conceivable in the present invention is to connect additional modules to the work space in order to further optimize the process, which is especially before and / or after the substrate to be bonded in the work space. This is done to measure processing and / or physical and / or chemical properties. The important steps can be heating, reduction, orientation (alignment), cooling, layer thickness measurement, bonding strength measurement, and the like.

  It is particularly advantageous to carry out the above according to the invention when a plurality of other modules according to the invention are arranged around the working space, in particular including mobile devices, in particular reduction modules and bonding modules. And these modules can be docked specifically in the work space. This mobile device is preferably a commercially available industrial robot with a corresponding end effector. Here, these modules can in particular be arranged or arranged in a star or cluster around the central module.

  In the most ideal case, a reduction module and a bonding module are configured to maximize the overall equipment throughput for the above process steps.

  In a particularly advantageous embodiment, at least two modules are arranged before the bonding module. At least one of these is a reduction module and the second module is a kind of storage module. The bonding chuck is loaded on the reduction module together with the mounted wafer and processed. Thereafter, the bonding chuck is temporarily stored in the storage module and is ready to be used for bonding at any time. In a special embodiment, the storage module can be configured as a reduction module. The reduction module is advantageously configured to accommodate a plurality of bonding chucks and / or a plurality of substrates simultaneously.

  A particularly unique aspect of the present invention lies in how these layers can be deposited in a conductive and optically transmissive form while at the same time being cost-effective. Further, the preparation of the substrate necessary for this will be described.

  The method described here is preferably suitable for stacking multilayer solar cells. As an alternative, however, this method can be applied to any (especially optical) material, in particular any other structure that requires a plurality of optically transmissive and conductive connections between semiconductor material, glass and ceramic. And can be used to form components. In these sectors, more and more applications are increasing due to the increasing importance of solid state light sources such as LEDs and lasers in many application fields such as lighting, communications and material processing. doing. In the display manufacturing sector, new and innovative manufacturing technologies are gaining importance. This is because it is desirable to incorporate an additional function of touch detection (such as feedback in the area of the touch screen) into the display.

The advantages of the present invention are in particular
Conductive, optically transmissive bonding interface or connection layer,
An extremely thin, robust and long-lasting bonding interface or layer (s),
Temperature-resistant bonding interface or layer (s),
・ High efficiency (manufacturing is fast and cost advantageous)
It is.

  A central and particularly unique aspect of the present invention is the use of transparent and conductive oxides to create a conductive and optically transmissive connection layer between substrates. The connection is made in particular by wafer bonding, preferably by direct bonding, and more preferably by direct bonding with plasma activity.

As a transparent oxide conductor (also called "Transparent Conductive Oxid" or "TCO" for short) in English, especially indium oxide (also called "Indium-tin-oxid" or "ITO" for short) Tin is used. Hereafter, the abbreviation ITO is used instead of indium tin oxide. ITO is widely used in the manufacture of LCD displays where optically transparent conductors are used. Alternatively, the following materials are used. That is,
• Doped zinc oxide, especially aluminum doped zinc oxide ("Aluminium doped Zinc Oxide", abbreviated "AZO"), gallium doped zinc oxide (English: "Gallium doped Zinc Oxide", abbreviated) "GZO"),
-Zinc oxide doped with fluorine (English: "Fluorine Tin Oxide", "FTO" for short), and
• Antimony tin oxide (English: “Antimony Tin Oxide”, “ATO” for short) is used. In principle, any material with a corresponding doping that is oxidizable and that has particularly desired properties, in particular electrical conductivity and optical transparency, can be used.

  According to the invention, in this connection, the material is greater than 10e1 S / cm, preferably greater than 10e2 S / cm, more preferably greater than 10e3 S / cm (common in semiconductor technology for temperatures of 300 K). It has electrical conductivity when it has electrical conductivity (measured by a 4-probe method). The optical transmission (transmission), defined as the percentage of light in a given wavelength region that passes through a layer in general use, is at least greater than 80% through a thin film of commonly used thickness. Preferably greater than 87%, more preferably greater than 93% and even more preferably greater than 96%.

  In the present invention, a wavelength region ranging from 300 nm to 1800 nm is advantageously used for photovoltaic applications. In other words, the related wavelength range is wider than the wavelength range visible to the human eye. This is to ensure that the UV component of light and the IR component of light can also be converted into electrical energy. In multi-layer solar cells, the uppermost layer already processes a portion of this spectrum and thus converts it into electrical energy, so that the bonding connection described above can be used even when the wavelength range where transmission is possible is somewhat narrow. Can accept. Thus, in particular, the above transmission values apply at least to wavelengths longer than 600 nm, preferably longer than 500 nm, more preferably longer than 400 nm, most preferably longer than 350 nm. Furthermore, these transmission values are in particular in the entire wavelength region starting from the minimum wavelength up to 1300 nm, preferably up to 1500 nm, more preferably up to 1700 nm, most preferably up to 1800 nm. Make sure that is true.

In the present invention, the above oxide is deposited on the substrate to be connected using the following method. That is,
・ MO CVD, metalorganic molecular beam deposit,
It is deposited using spray pyrolysis, pulsed laser deposition (PLD) or sputtering.

  In order to ensure the desired properties of the layer, it is critical in the present invention to ensure the correct mixing ratio. In particular, the oxygen percentage can improve the optical transmission in some of the above oxides, and this must be ensured that the oxygen percentage is not too high. is there. This is because otherwise, the conductivity is lowered.

  In general, bonding connections (also referred to as connection layers, bonding interfaces) are created, where this is done by depositing a precursor layer structure on the substrate to be bonded. Subsequently, particularly at room temperature, the layers are joined by plasma activation, which results in prebonding (temporary bonding). During the subsequent heat treatment process (annealing), the precursor layer structure is converted into a layer made of a transparent oxide conductor, and at the same time the bonding connection is strengthened. Particularly advantageously, the amorphous layer present at least in the surface region can affect the bonding process. By applying a corresponding force, a region near the surface can be shaped, which ensures an optimal closure of the micro and / or nanopores.

  In particular when using forming gas, the oxide layer can be changed according to the invention and in particular completely removed by one process based on sputtering and oxide reduction.

  As an alternative or in addition to this measure, it is advantageous in the present invention to minimize the time between the change of the oxide layer and the contact connection, in particular less than 2 hours. Is less than 30 minutes, more preferably less than 15 minutes, ideally less than 5 minutes. This can minimize undesired and variable oxide growth that occurs after the oxide layer is adjusted as desired.

  By setting a predetermined pressure in the vacuum chamber, the mean free path length for plasma ions can be changed or adjusted according to the present invention.

  In the case of capacitive coupling, it is advantageous to place two electrodes in the plasma chamber.

  Here, the optimality of the two contact surfaces is set by setting the parameters of the (different) frequency, amplitude, one of the two electrodes, particularly preferably the bias voltage applied to the second electrode, and the chamber pressure parameters of the two electrodes. Clash occurs.

  By configuring the plasma activation device as a capacitively coupled dual frequency plasma facility, the ion density and the acceleration of ions toward the wafer surface can be set separately. This allows the achievable process results to be set and optimally adapted to the application requirements within one wide window.

  The bias voltage in particular is in the form of a second, especially lower electrode base voltage, and affects the impact (velocity) of the electrode on the contact connection surface of the substrate accommodated on the second electrode. Used especially for damping or accelerating.

  With the above parameters, the quality of the amorphous layer in particular can be adjusted, and in the following, a particularly advantageous embodiment will be described.

  In an inductively coupled plasma source, corresponding similar considerations for capacitively coupled alternating voltages can be incorporated into the multiple alternating currents utilized to form the magnetic field. In the present invention, it is also conceivable that the plasma of the inductively coupled plasma source is operated by alternating currents or alternating magnetic fields of different intensity and / or frequency so that the plasma has the corresponding inventive characteristics.

  In remote plasma, the plasma that is actually used is formed in an external plasma source and introduced into the sample chamber. In particular, the plasma components, in particular ions, are transported to the sample chamber. The plasma transfer from the plasma source to the substrate chamber can be ensured by different components such as sluice gates, accelerators, magnetic and / or electron lenses, diaphragms and the like. All considerations that apply to capacitive and / or inductively coupled plasmas regarding the frequency and / or strength of electric and / or magnetic fields apply to all components that ensure formation and / or plasma transfer from the plasma source to the substrate chamber. It should be true for this. For example, it is conceivable that plasma is formed in the plasma source chamber by capacitive or inductive coupling according to the parameters of the present invention, and then enters the substrate chamber via the members shown above.

  In another advantageous embodiment of the invention, it is most preferred at a temperature generally below 300 ° C, preferably below 200 ° C, more preferably below 150 ° C, more preferably below 100 ° C. Irreversible bond formation at room temperature, especially for a maximum of 12 days, more preferably for a maximum of 1 day, even more preferably for a maximum of 1 hour, most preferably for a maximum of 15 minutes . Another advantageous heat treatment method is dielectric heating by microwaves.

Here Of particular advantage, the irreversible bonding is greater than 1.5 J / m ^2, especially greater than 2J / m ^2, preferably greater than 2.5 J / m ² bond strength This is the case.

  The use of solar energy using photovoltaic facilities is becoming increasingly important. This is because fossil energy carriers are barely sufficient in the medium term and are becoming a major environmental problem in production and use, especially due to the impact on the greenhouse effect. What is needed to increase the competitiveness of photovoltaics from a purely economic point of view is to improve light conversion efficiency at the same cost, or at most moderate cost increases. However, there is a limit to the achievable efficiency. These limitations are mainly due to the limitation that only light in a limited wavelength region can be processed by individual semiconductor materials and cannot be converted into electrical energy.

  It is particularly advantageous to use the present invention to produce multilayer solar cells or “multi-junction solar cells” which are widely known in the single-layer or English language.

  Here, the individual layers are stacked vertically in the solar cell. Incident light first strikes the top layer optimized to convert light in a predetermined first wavelength region into electrical energy. Light in a wavelength region that cannot be adequately processed by this layer passes through the first layer, is below it and is optimized to process the second wavelength region to form electrical energy. Hit two layers. Optionally, in this multi-layer solar cell, light in a wavelength region that cannot be sufficiently processed by this second layer can strike the third layer below, where the third layer is It is optimized to process three wavelengths of light and convert it to electrical energy. From a purely theoretical perspective, one can imagine that many such layers are possible. In practice, such cells are configured such that the top layer into which incident light enters first handles the wavelength region with the shortest wavelength. The second layer then processes a short wavelength region, and so on. In the present invention, not only a two-layer structure is conceivable, but three or more layers can be implemented. In this case, the plurality of layers are electrically conductive in the vertical direction, that is, have the lowest possible resistance and are optically transmissively connected to each other. The deposition of these layers is carried out in particular by the so-called “Metalorganic Chemical Vapor Deposition”, abbreviated “MO CVD” process, and the deposition of the two active layers of the multicell is carried out in particular “in-situ”. That is, these substrates are deposited without being exposed to the normal ambient atmosphere between the multiple deposition processes. Preferably, a barrier layer (second or fourth oxide layer) and / or a buffer layer (second or fourth oxide layer) are placed between the plurality of active layers, resulting in these layers. Improve cell quality.

  So far and / or in the following description of the drawings, a plurality of characteristic configurations of the apparatus have been disclosed, but these are also disclosed and applicable as method features and vice versa. It is.

  Further advantages, characterizing features and details of the invention result from the following description of several preferred embodiments and from the following exemplary embodiments.

It is sectional drawing of the board | substrate which has an oxide layer. FIG. 1b shows the substrate of FIG. 1a with an oxide layer altered by plasma according to a first embodiment of the present invention. FIG. 1b shows the substrate of FIG. 1a with an oxide layer reduced in thickness by plasma according to a second embodiment of the invention. FIG. 1b shows the substrate of FIG. 1a with an oxide layer completely removed by plasma according to a third embodiment of the present invention. 1 is a schematic view of a first embodiment of an apparatus according to the present invention, including a bonding chamber connected to a working chamber and a plasma chamber spatially separated therefrom; FIG. FIG. 3 is a schematic view of a second embodiment of the apparatus according to the invention comprising a bonding plasma chamber arranged in the working chamber. FIG. 4 is a schematic view of a third embodiment of an apparatus according to the present invention comprising a plurality of plasma chambers and a bonding chamber. 1 is a schematic view of a plasma chamber according to the present invention. 1 is a schematic view of a bonding chamber according to the present invention.

  In these figures, the advantages and characteristic features of the present invention are characterized by distinguishing reference signs, respectively, according to embodiments of the present invention. Components or features with the same function or the function of acting are characterized by the same reference numerals.

  In the first embodiment shown in FIG. 2, the plasma chamber 4 and the bonding chamber 5 are two independent modules of the module group 3, which are workable spaces 22 defined by the working chamber 7 that can be evacuated. Is particularly tightly connected. The working chamber 7 can be evacuated to a high vacuum, in particular controlled by a control device assisted by software. In the working chamber 7, a robot 6 provided especially for transporting transports the substrate 1 among the storage module 8, the plasma chamber 4, and the bonding chamber 5.

  In the second embodiment of the present invention, the plasma chamber 4 and the bonding chamber 5 are combined into a single module, that is, the bonding plasma chamber 20. The robot 6 transports the substrate 1 from the storage unit 8 to the bonding plasma chamber 20.

  In the third embodiment of the present invention, one or more plasma modules 4 or bonding modules 5 or bonding plasma modules 20 of the module group 3 are attached to the working chamber 7 and constitute the working chamber. In particular, the work space 22 is configured together. The robot 6 transports the substrate 1 from the storage unit 8 to the plasma module 4 and / or the bonding module 5 and / or the bonding plasma module 20, and in particular also transports the substrate 1 between them. Here, since a plurality of plasma modules 4 and / or a plurality of bonding modules 5 and / or a plurality of bonding plasma modules 20 are used according to the present invention, a relatively high throughput can be obtained. This process is controlled by the controller.

  In the first process of the present invention, the substrate 1 having the oxide layer 2 (FIG. 1 a) formed on the bonding surface 1 o is taken out from the storage unit 8 by the robot 6.

  The substrate 1 can be attached to a mobile sample holder and can thereby be transferred between the plasma module 4 and / or the bonding module 5 and / or the bonding plasma module 20. However, the substrate 1 can be transported without a movable sample holder. In this case, the substrate 1 is placed on a sample holder 15, which is already in the plasma module 4 and / or the bonding module 5 and / or the bonding plasma module 20, in particular fixedly incorporated therein.

  First, the robot 6 transports the substrate 1 to the plasma module 4. The plasma module 4 includes a gas supply unit 11 having a plurality of openings dispersed especially around the upper side, and an exhaust unit 12 having a plurality of openings dispersed especially around the lower side. The gas mixture of the present invention having a reducing gas is introduced into the plasma chamber 4 through the gas supply unit 11.

  Subsequently, ignition and / or maintenance of the plasma is performed between the lower electrode 9 and the upper electrode 10. The substrate 1 is preferably placed directly on the electrode. When the substrate 1 is placed on the sample holder 15, the sample holder 15 must be formed as the electrode 9 in the present invention.

  The reduction products are preferably removed from the plasma chamber 4, particularly continuously, via the exhaust part 12. Thereby, in the plasma module 4, one of the plurality of processes of the oxide layer 2 according to the present invention is performed.

  In the first variant of the invention, the oxide layer 2 is transformed into an oxide layer 2 ′ by the plasma 13, and this oxide layer 2 ′ has a stoichiometric ratio different from that of the oxide layer 2. (FIG. 1b). This different stoichiometric ratio can already be created by oxygen deficiency when depositing the oxide. Otherwise, by selecting the process parameters as desired, the stoichiometric ratio can be set by the plasma and / or at least varied.

  In the second variant, the oxide layer 2 having the starting state layer thickness d is thinned to the oxide layer 2 ″ having the final state layer thickness d ′ by the reducing gas in the plasma 13 (FIG. 1c). ).

  In the third variant, the oxide layer 2 is completely removed (FIG. 1d).

  Control of the state of the oxides 2, 2 ′, 2 ″ is preferably effected by a radiation source detector system comprising a radiation source 18 and a detector 19, by means of this radiation source detection system. The ', 2' 'surface 2o can be inspected preferably in-situ. The irradiation source 18 and / or the detector 19 can be provided inside and / or outside the plasma chamber 4. If they are provided externally, they are preferably connected in a vacuum-tight manner to the plasma chamber 4 via a flange 17. Any known physical measurement principle suitable for obtaining data about the state of the oxide layers 2, 2 ', 2' 'can be used as the source detector system. This belongs to thickness, porosity, and thus the density and reflectivity of the oxide layers 2, 2 ', 2' '.

  An ellipsometer or diffractometer is preferably used, and in a special case a reflectometer is used.

  The first substrate 1 processed in this way is stored in a storage unit (not shown) disposed in the work space 22 in particular.

  In particular, the second substrate 14 of the present invention in which the bonding surface is similarly processed by the process of the present invention is transferred to the bonding chamber 5 together with or relative to the prepared first substrate 1. In the bonding chamber 5, a bonding process between the bonding surface of the first substrate 1 and the bonding surface of the second substrate 14 is executed. Bonders are known to those skilled in the art. How such a device is assembled, how the sample holder 15 and / or the pressure plate 16 are configured, how the two substrates are brought close to each other, It is known to those skilled in the art how to apply a force for bonding and how to evacuate the bonding chamber 5 via the exhaust part 21. The sample holder 15 can be configured as an electrostatic sample holder and / or a heated sample holder and / or a cooled sample holder. A sample holder 15 is preferably used for transport from the plasma chamber 4. The sample holder 15 is advantageously an electrostatic sample holder in order to ensure good thermal expansion of the substrate 1 in the sample holder 15. Mechanical clamping or vacuum clamping does not allow free thermal expansion of the substrate 1 to the same extent as the electrostatic sample holder 15. In a highly advantageous embodiment, the sample holder 15 is flushed with He from the front and / or back, in particular by a washing device incorporated in the sample holder 15, thereby ensuring or improving thermal coupling. The

  After the bonding process is successful, the robot 6 takes out the bonding laminate formed by bonding from the two substrates 1 and 14, and preferably stores it in the storage unit 8.

  1 substrate, 1o substrate surface, 2,2 ', 2' 'oxide layer, 2o oxide layer surface, 3 module group, 4 plasma chamber, 5 bonding chamber, 6 robot, 7 working chamber, 8 storage, 9 bottom Side electrode, 10 Upper electrode, 11 Gas supply unit, 12 Exhaust unit, 13 Plasma gas, 14 Second substrate, 15 Sample holder, 16 Pressure plate, 17 Flange, 18 Irradiation source, 19 Detector, 20 Bonding plasma chamber, 21 Discharge section, 22 working space, d, d 'thickness of oxide layer

Claims (12)

In an apparatus for forming a conductive direct bond between a bonding surface of a first substrate (1) and a bonding surface of a second substrate (14),
The device is
・ It has a work space (22) that can be airtightly closed and vacuumed.
・ In the work space (22),
a) at least one plasma chamber (4) for changing at least one of the plurality of bonding surfaces; and at least one bonding chamber (5) for bonding the plurality of bonding surfaces; and / or
b) At least one combination-type bonding plasma chamber (20) for changing at least one of the plurality of bonding surfaces and bonding the plurality of bonding surfaces.
It is included,
A device characterized by that. Module group from a substrate storage (8) for moving the first substrate and the second substrate in the work space (22), in particular connected in an airtight manner to the work space (22). (3) having a moving device (6) that moves to a plurality of modules;
The apparatus of claim 1. The plasma chamber (4) or the bonding plasma chamber (20) can be supplied with a reducing gas that changes the oxide layer (2) provided on at least one of the bonding surfaces.
The apparatus according to claim 1 or 2. The plasma chamber (4) or the bonding plasma chamber (20) has an upper electrode (10) capable of supplying an alternating voltage and a lower electrode (9) capable of supplying an alternating voltage,
Between the upper electrode (10) and the lower electrode (9) it is possible to apply ion energy of ions impinging on the substrate surface of less than 1000 eV, in particular less than 500 eV, preferably less than 250 eV,
The device according to claim 1. AC voltage having a frequency higher than the frequency of the AC voltage applied to the lower electrode (9) can be supplied to the upper electrode (10).
The apparatus according to claim 4. In particular, it has an irradiation source detection system that is docked in or arranged in the work space (22) and detects the state or state change of the bonding layer during the change,
Device according to any one of the preceding claims. Between the bonding surface of the first substrate (1) and the bonding surface of the second substrate (14) in a work space (22) that can be hermetically closed to the surroundings and can be evacuated. In a method of forming a conductive direct bond,
a) changing at least one of the plurality of bonding surfaces in the plasma chamber (4) and subsequently bonding to the bonding surface of the second substrate (14) in the bonding chamber (5), and / or ,
b) At least one of the plurality of bonding surfaces is changed in the bonding plasma chamber (20), and subsequently bonded to the bonding surface of the second substrate (14) in the bonding plasma chamber (20). ,
A method characterized by that. a) changing the oxide layer (2) on at least one of the plurality of bonding surfaces, and / or
b) by removing at least partly, in particular completely, a part of the oxide layer (2) of at least one of the bonding surfaces,
Make the change,
The method of claim 7. Due to the change, one or more of the following reducing gases are introduced into the plasma chamber (4):
Hydrogen,
Nitrogen oxides,
· Carbon monoxide,
・ Introduce methane,
The method according to claim 7 or 8. Mixing the reducing gas with one or more of the following inert gases:
Xenon,
Argon,
Helium,
· nitrogen,
・ Mix carbon dioxide,
The method of claim 9. Supplying the bonding layer with an ion energy of less than 1000 eV, in particular less than 500 eV, preferably less than 250 eV;
The ion energy is applied between the upper electrode (10) and the lower electrode (9) of the plasma chamber (4) and / or the bonding plasma chamber (20).
11. A method according to any one of claims 7 to 10. Supplying to the upper electrode (10) an AC voltage having a frequency higher than the frequency of the AC voltage applied to the lower electrode (9);
The method of claim 11.

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