WO2020208146A1

WO2020208146A1 - Wafer boat and treatment device for wafers

Info

Publication number: WO2020208146A1
Application number: PCT/EP2020/060170
Authority: WO
Inventors: Michael Klick; Lutz Eichhorn; Dirk SUCHLAND
Original assignee: Plasmetrex Gmbh
Priority date: 2019-04-10
Filing date: 2020-04-09
Publication date: 2020-10-15
Also published as: DE102019002647A1

Abstract

The invention relates to a wafer boat for the plasma treatment of disk-shaped wafers, in particular semiconductor wafers, to a plasma treatment device for receiving a wafer boat of this type, and to a method for the plasma treatment of wafers in a wafer boat of this type. The wafer boat has a plurality of plates made of an electrically conductive material which are arranged in parallel with one another and each have at least one receptacle for a wafer on the sides of the plates that face one another. The plates are connected to one another in such a way that a first number of the plates forms a first group of electrically interconnected plates and a second number of the plates forms a second group of electrically interconnected plates, the plates of the first group and of the second group being provided in alternation and at least one plate not electrically connected to the plates of the first or second group being provided between plates of the first and second groups in each case. In the method, a plurality of wafers are held in the receptacles of the wafer boat and a high-frequency alternating voltage is applied between the plates of the first and second groups of plates in order to produce, during a process phase, a series of at least two plasmas between plates of the first and second groups of plates in each case, said at least two plasmas being separated by the at least one plate not electrically connected to the plates of the first or second group.

Description

Wafer boat and treatment device for wafers

The present invention relates to a wafer boat and a treatment device for wafers which are suitable for generating a plasma between wafers accommodated therein.

In semiconductor and solar cell technology, it is known to subject disk-shaped substrates made of different materials, which are hereinafter referred to as wafers regardless of their geometric shape and material, to different processes.

In this case, the wafers are often both individual treatment processes and batch processes, i.e. Processes in which several wafers are treated at the same time. For both individual and batch processes, the wafers have to be brought into the desired treatment position. In batch processes, this is usually done by inserting the wafers into so-called boats, which have receptacles for a large number of wafers. In the boats, the wafers are usually arranged parallel to one another. Such boats can be passive, so that they have no other function besides a holding function during the processing of the wafers.

But there are also wafer boats that are used, for example, for plasma processing of wafers in semiconductor or solar cell technology, which in addition to the holding function also have an electrode function. Here, the wafer boat is formed, for example, by a large number of electrically conductive plates, which usually consist of graphite. The plates are arranged essentially parallel to one another, and receiving slots for receiving wafers are formed between adjacent plates. The sides of the plates facing one another each have corresponding receiving elements for wafers, so that wafers can be received on each of these sides. As receiving elements there are usually pins on each side of the plate facing another plate provided, which accommodate the wafer. In each receiving slot, at least two wafers can thus be completely received between the plates in such a way that they are opposite one another. Adjacent plates of the wafer boat are usually electrically insulated from one another and an alternating voltage, usually in the kHz range or also in the MHz range, is applied between directly adjacent plates during the process. As a result, a plasma is intended to be formed between the plates and in particular between the wafers held on the respective plates in order to provide a plasma treatment such as, for example, plasma deposition or plasma nitridation of layers.

For the arrangement of the plates to one another, spacer elements are used, each of which has a predetermined length for setting predetermined distances between the plates. Furthermore, electrically conductive elements are used at the contact ends of the plates in order to connect every second plate in an electrically conductive manner in order to be able to apply the same potential to it. These conductive elements have as low a resistance as possible in order to allow uniform loading of the plates and to limit losses in the elements.

Plasma deposition processes (PECVD) in wafer boats can advantageously be used at higher frequencies, e.g. 13.56 MHz. From a certain number of wafers for simultaneous processing in a boat, for example with more than 300 wafers, a high current of over 50A for example (typically 100A for approx. 400 wafers) is required. This high current leads to high power losses on contact and connection elements due to ohmic losses, high voltages and thus parasitic plasmas due to lead inductances.

The present invention is therefore based on the object of providing a wafer boat and a method for plasma treatment of wafers, which enable improved processing of the wafers. According to the invention, this object is achieved by a wafer boat according to claim 1, a plasma treatment device according to claim 11 and a method according to claim 16. Further refinements of the invention emerge from the respective subclaims.

In particular, a wafer boat is provided for the plasma treatment of disc-shaped wafers, in particular semiconductor wafers, which has the following: a plurality of plates made of an electrically conductive material, arranged parallel to one another, each having at least one receptacle for a wafer on their mutually facing sides, which have a receiving area of the plates, the plates being interconnected in such a way that a first number of the plates forms a first group of electrically conductively interconnected plates, a second number of the plates forms a second group of electrically conductively interconnected plates, the plates of the first and second group are provided alternately and between plates of the first and second groups at least one plate is provided, which is not electrically connected to the plates of the first or second group.

This structure of the wafer boat allows at least two plasmas to be connected in series during operation. The high-frequency current thus not only flows through a plasma but, for example, two plasmas which are each separated by the at least one plate that is not electrically connected to the plates of the first or second group. Since, for example, every second plate - the plate lying between the plates of the first and second group of plates - is not in contact in a boat, the voltage of the non-contacted plates is set automatically via an essentially capacitive voltage division. There is thus a series connection of plasmas between the plates of the first and second group of plates. In one embodiment of the invention, every fourth of the plates is electrically conductively connected to the others within the first and second groups. This enables two plasmas to be connected in series between the plates of the first and second groups, which are separated by the at least one plate that is not electrically connected to the plates of the first or second group.

In a further embodiment, two plates, which are not electrically connected to the plates of the first or second group, are provided between plates of the first and second group. This enables a series connection of three plasmas between the plates of the first and second group. In order to produce a plasma, however, a correspondingly higher voltage is required between the plates of the first and second group of plates in comparison to the previous embodiment in order to achieve a corresponding plasma ignition. In this embodiment, for example, within the first and second group, every sixth of the plates is electrically conductively connected to the others.

Preferably, the plates are each held at a distance from one another via spacer elements, the spacer elements each being insulating or having a resistance of at least 20 kΩ, preferably in the range of 40 kΩ. In the case of the spacer elements with a resistance of at least 20kΩ, it is possible to cause a current to flow through the spacer elements by applying a direct voltage or a low-frequency alternating voltage between the plates of the first and second group of plates, thereby creating a resistance heating effect. In the case of a high-frequency alternating voltage, however, the spacer elements have an insulating effect. The spacer elements can for example consist of polysilicon.

In one embodiment, the plates of at least the first and second group each have contact lugs at their longitudinal ends, which are electrically conductively connected via contact elements to contact lugs of other plates of the same group, the contact lugs of the plates first group are in a different plane than the contact tabs of the plates of the second group. Compared to the wafer boat described in the introduction, in which every second plate is connected in an electrically conductive manner, the number of contact elements for connecting the plates is reduced, whereby the thermal capacity of the boat can be reduced. In this way, for example, a heating phase can be shortened and the temperature distribution over the boat can be more even.

The combined thermal mass of the sum of the contact elements and the sum of the contact lugs is preferably smaller than the thermal mass of the rest of the wafer boat, in particular less than 1/10 of the thermal mass of the rest of the wafer boat. Furthermore, the impedance of the sum of the contact blocks and the sum of the contact lugs is preferably smaller than the impedance of the rest of the wafer boat.

In another embodiment, the plates of at least the first and second groups are each electrically conductively connected via at least one contact element extending below the plates, the contact elements for the plates of the first and second group being spaced from one another in the longitudinal direction of the plates. This structure makes it possible in a particularly advantageous manner that an electrical contact with a feed line contact with low inductance on the bottom of the boat can be established by lowering the boat. Thus the weight of the boat can be used for a high pressure force in the contact. This ensures a high level of reliability and a uniform current density distribution.

Furthermore, a plasma treatment device for wafers is provided, which has a process space for receiving a wafer boat of the type described above. The plasma treatment device also has means for controlling or regulating a process gas atmosphere in the process space and at least one voltage source which can be connected in a suitable manner to the plates of the first and second group of plates, in order to apply sufficient electrical voltage between the plates of the first and second group of plates to generate between the plates of the first and second group of plates a series of at least two plasmas which are separated by the at least one plate which are not electrically connected the plates of the first or second group is connected. Such a plasma treatment device enables an improved plasma treatment of wafers.

The at least one voltage source is preferably suitable for applying at least one high-frequency alternating voltage and optionally a direct voltage or a low-frequency alternating voltage. While the high-frequency alternating voltage is suitable for plasma generation, the optional direct voltage or low-frequency alternating voltage can be used in combination with certain spacer elements for resistance heating.

In one embodiment, the plasma treatment device has at least one additional heating unit for heating the process space and the wafers received therein.

In the method, a large number of wafers are accommodated in wafer boats of the type described above, which are located in a process chamber. To treat the wafer, a high-frequency alternating voltage is applied between the plates of the first and second group of plates in such a way that, during a process phase, a row of at least two plasmas is generated between the plates of the first and second group of plates, which are generated by the at least one plate which is not electrically connected to the plates of the first or second group are separated. This allows the advantages already mentioned above to be achieved.

The temperature and / or the gas atmosphere in the process chamber is preferably controlled or regulated before and / or during the plasma generation. In one embodiment of the method, before the high-frequency alternating voltage is applied between the plates of the first and second group of plates, a direct voltage or a low-frequency alternating voltage is applied in order to cause a current to flow in spacer elements between the plates and thereby a resistance heating effect.

The invention is explained in more detail below with reference to the drawings; in the drawings shows:

1 shows a schematic side view of a wafer boat;

FIG. 2 shows a schematic plan view of the wafer boat according to FIG. 1;

3 shows a schematic front view of the wafer boat according to FIG. 1;

4 shows a schematic view of a plasma treatment device with a wafer boat accommodated therein according to FIG. 1;

5 shows a schematic plan view of an alternative wafer boat for use in a plasma treatment device; and

6 shows a schematic front view of the wafer boat according to FIG. 1.

Terms used in the description such as above, below, left and right relate to the representation in the drawings and should not be viewed as restrictive. But you can describe preferred versions. The wording essentially related to parallel, perpendicular or angle specifications should include deviations of ± 3 °, deviations preferably being less than ± 1 °.

In the following, the basic structure of a wafer boat 1 for use in a plasma treatment device is explained in more detail with reference to FIGS. 1 to 3, FIG. 1 showing a schematic side view of a wafer boat 1 and FIGS. 2 and 3 showing a top view and a front view. The same reference symbols are used in the figures, provided that the same or similar elements are described. The wafer boat 1 is formed by a multiplicity of plates 6, contacting units 7 and clamping units 8. The illustrated wafer boat 1 is especially suitable for a layer deposition from a plasma, for example of Si3N4, SiNx, a-Si, etc., and in particular a plasma nitriding of wafers.

The plates 6 each consist of an electrically conductive material and are designed in particular as graphite plates, it being possible for the plate base material to be coated or surface treated depending on the process. The plates 6 each have six cutouts 10 which are covered by the wafers during the process, as will be explained in more detail below. Although six recesses are provided per plate 6 in the form shown, it should be noted that a larger or smaller number can also be provided.

In the embodiment shown, a total of twenty-three plates 6 are provided, which are arranged essentially parallel to one another via the corresponding contacting units 7 and clamping units 8, in order to form receiving slots 11 between them. With twenty-three plates 6, twenty-two of the receiving slots 11 are thus formed. However, the invention is not limited to a specific number of plates.

The plates 6 each have, at least on their side facing an adjacent plate 6, groups of three receiving elements 12 each, which are arranged such that they can receive a wafer in between. The groups of the receiving elements 12 are each arranged around each recess 10, as is indicated schematically in FIG. 1. The wafers can be received in such a way that the receiving elements each contact different side edges of the wafer. A total of six groups of receiving elements for receiving a semiconductor wafer are provided in the longitudinal direction of the plate elements (corresponding to the recesses 10). At their ends, some of the plates 6 have contact lugs 13 projecting in the longitudinal direction, which are used for electrical contacting of the plates 6, as will be explained in more detail below. Three embodiments of plates 6 are provided, which differ with regard to the contact tabs 13. In one embodiment, the contact lugs 13 are each carried out directly adjacent to the lower edge (type 1), while in another embodiment they are spaced from the lower edge (type 2), the distance to the lower edge being greater than the height of the contact lugs 13 of the Panels of the other embodiment. There is also an embodiment which has no contact lugs (type 3). The embodiments of plates 6 are arranged in the wafer boat 1 in such a way that plates of type 1 and type 2 alternate and in each case a plate of type 3 is arranged between them. As can best be seen in the view according to FIG. 2, the contact lugs 13 of plates 6 of type 1 and of type 2 lie on different levels in the arrangement of the wafer boat 1. In every fourth plate 6, however, the contact lugs 13 lie in the same plane. In this way, two spaced-apart contact planes are formed by the contact lugs 13.

The contact lugs 13 lying in a respective contact plane are electrically connected via contact elements, which are also referred to as contact blocks 15, made of a material with good electrical conductivity, in particular graphite, and are arranged at a predetermined distance from one another. In the area of the contact lugs 13 and in each of the contact blocks 15, at least one through opening is provided. In the mutually aligned state, these allow a clamping element 16 to be passed through, which has a shaft part (not visible) and a head part, such as a screw, for example. The plates 6 can then be fixed to one another via a counter-element acting on the free end of the shaft part, such as a nut 17, for example. Here, the plates are fixed to one another in two different groups in such a way that the plates of type 1 and type 2 alternate and one in between Type 3 disk is included. The tensioning element 16 can consist of electrically conductive material, but this is not necessary. The contact blocks 15 each preferably have the same length (in the direction that defines the distance between contact lugs 13 of the plates 6), namely corresponding to the width of four receiving slots 11 plus the width of three plates 6. The contact blocks 15 are preferably designed so that they have a low thermal mass and in particular the sum of the contact blocks should have a lower thermal mass than the sum of the plates 6. Preferably, the combined thermal mass of the sum of the contact blocks and the sum of the contact lugs 13 of the plates should be less than the thermal mass the sum of the plates 6 minus the thermal mass of the respective contact lugs 13.

Furthermore, further through openings are provided in the plates adjacent to the upper edge and the lower edge, each of which allows a clamping element 19, which has a shaft part (not visible) and a head part, such as a screw of the clamping unit 8, to pass through. These can in turn interact with corresponding counter-elements 20, such as nuts. In the embodiment shown, seven through-openings are provided adjacent to the upper edge and seven through-openings are provided adjacent to the lower edge. In this case, four through openings are arranged around each recess 10, approximately symmetrically to it. As a further part of the tensioning unit, a large number of spacer elements 22 are provided, which are designed, for example, as spacer sleeves with essentially the same length. The spacer elements 22 are each arranged in the area of the respective through openings between directly adjacent plates 6.

The shaft parts of the tensioning element 19 are each dimensioned such that they can extend through corresponding openings in all plates 6 as well as respective spacer elements 22 located between them. All the plates 6 can then be fixed essentially parallel to one another via the at least one counter element 20. However, there are here too other clamping units with spacer elements 22 are conceivable, which arrange the plates 6 with spacer elements 22 in between them essentially parallel and clamp them. In the embodiment shown, 308 spacer elements are provided for 22 receiving slots and a total of 14 spacer elements 22 per slot (seven adjacent to the upper edge and seven adjacent to the lower edge).

The tensioning elements 19 are preferably made of an electrically insulating material, while the spacer elements 22 can be made of an electrically insulating or a conductive material. If the spacer elements 22 consist of an electrically conductive material, in particular, the material has such a high resistance that the spacer elements serve as a resistance element when a direct or low frequency voltage with sufficient amplitude is applied, but none when a high frequency voltage is applied (to generate a plasma between the plates) Provide substantial damping of wave propagation. For the low-frequency voltage, in particular, a frequency range from 1 to 10 KHz and for the high-frequency voltage a range above 40 KHz - especially frequencies in the MHz range - are taken into account. In the illustrated embodiment with the selected distribution, each spacer element should, for example, have a resistance of greater than 3kΩ, in particular greater than 20kΩ or even greater than 40kΩ. For example, the spacer elements can consist of doped silicon, polysilicon or another suitable material that on the one hand is not impaired by the process and on the other hand does not impair the process, in particular does not introduce any impurities into the process. While the plates 6 of a group (upper contact nose 13 / lower contact nose 13) are electrically connected and fixed to one another via the contact elements 15, all of the plates are connected and fixed to one another via the spacer elements 22.

The following is the basic structure of a plasma treatment device 30, in which a wafer boat 1 of the above type (but also a conventional wafer boat) can be used, explained in more detail with reference to FIG. 4, FIG. 4 showing a schematic side view of the treatment device 30.

The treatment device 30 consists of a process chamber part 32 and a control part 34. The process chamber part 32 consists of a tube element 36 which is closed on one side and which forms a process chamber 38 inside. The open end of the tubular element 36 is used to load the process chamber 38 and it can be closed and hermetically sealed via a closing mechanism (not shown), as is known in the art. The pipe element consists of a suitable material that does not introduce any impurities into the process, is electrically insulated and can withstand the process conditions in terms of temperature and pressure (vacuum), such as quartz. At its closed end, the tubular element 36 has gas-tight feedthroughs for the supply and discharge of gases and electricity, which can be designed in a known manner. Corresponding supply and discharge lines could, however, also be provided at the other end or also laterally at a suitable location between the ends.

The tubular element 36 is surrounded by a casing 40 which thermally insulates the tubular element 38 from the environment. Between the casing 40 and the tubular element 36, a heating device, not shown in detail, is provided, such as a resistance heater, which is suitable for heating the tubular element 36. Such a sausage device can, for example, also be provided in the interior of the tubular element 36, or the pipe element itself could be designed as a sausage device. At the moment, however, preference is given to an external curing device, and in particular one that has different, individually controllable meat circles.

In the interior of the tubular element 36, receiving elements, not shown in detail, are provided which have a receiving plane for receiving a wafer boat 1 (which is only partially shown in Fig. 4), which can for example be of the above type. However, the wafer boat can also be inserted into the tubular element 36 in such a way that it rests on the wall of the tubular element 36. The wafer boat is held essentially above the receiving plane and is arranged approximately in the middle of the tubular element. By means of appropriate receiving elements and / or a direct placement on the tubular element, a receiving space is thus defined in combination with the dimensions of the wafer boat, in which a properly inserted wafer boat is located. The wafer boat can be handled as a whole in the loaded state into and out of the process chamber 38 via a suitable handling mechanism (not shown). In this case, when the wafer boat is loaded, electrical contact is automatically established with at least one contact block 15 of each of the groups of plates 6 having a contact block, as will be explained in more detail below.

In the interior of the tubular element 36, a lower gas guide tube 44 and an upper gas guide tube 46 are also provided, which consist of a suitable material such as quartz and allow process gas to be fed in or discharged.

The control part 34 of the treatment device 30 will now be explained in more detail below. The control part 34 has a gas control unit 60, vacuum control unit 62, an electrical control unit 64 and a temperature control unit (not shown), all of which can be controlled jointly via a higher-level controller, such as a processor. The temperature control unit is connected to the heating unit (not shown) in order to primarily control or regulate the temperature of the tubular element 36 or the process chamber 38.

The gas control unit 60 is in communication with a multiplicity of different gas sources 66, 67, 68, such as for example gas cylinders, which contain different gases. In the form shown are three gas sources shown, although any other number can of course also be provided. For example, the gas sources can provide di-chlorosilane, tri-chlorosilane, SihU, phosphine, borane, di-borane, German, Ar, h, TMA Nhh, N2 and various other gases at corresponding inputs of the gas control unit 60. The gas control unit 60 has two outlets, one of which is connected to the lower gas guide tube 44 and the other to a pump 70 of the negative pressure control unit 62. The gas control unit 60 can connect the gas sources to the outlets in a suitable manner and regulate the flow of gas as is known in the art. The gas control unit 60 can thus introduce different gases into the process chamber, in particular via the lower gas guide tube 44.

The vacuum control unit 62 essentially consists of the pump 70 and a pressure regulating valve 72. The pump 70 is connected to the upper gas guide tube 46 via the pressure regulating valve 72 and can pump the process chamber to a predetermined pressure via this. The connection from the gas control unit 60 to the pump is used to dilute process gas pumped out of the process chamber with N2, if necessary.

The electrical control unit 64 has at least one voltage source which is suitable to provide at least one of the following at an output thereof, a direct voltage, a low-frequency voltage and a high-frequency voltage. The output of the electrical control unit 64 is connected via a line to a contacting unit for the wafer boat in the process chamber. The line is introduced through the jacket 40 and into the tubular element 36 via a corresponding duct suitable for vacuum and temperature. The line is constructed in particular in such a way that it is designed as a coaxial line 74 with an inner conductor and an outer conductor. The coaxial line 74 leads essentially to the contact areas of the wafer boat 1. The inner and outer conductors are connected to different groups (type 1 or type 2) of the plates 6 in a suitable manner. FIGS. 5 and 6 show an alternative wafer boat 1 that can be used in a plasma treatment device 30 of the above type. In this embodiment, the same reference symbols are used insofar as the same or similar elements are described.

The wafer boat 1 is again formed by a multiplicity of plates 6, contacting units 7 and clamping units 8. In contrast to the panels 6 of the first embodiment, the panels 6 of this embodiment are all of type 3, i. they have no contact lugs at their longitudinal ends. Otherwise the plates can be constructed in the same way as before. As before, the plates 6 are arranged and fixed essentially parallel to one another by means of clamping units 8 with clamping elements 19, counter elements 20 and spacer elements 22.

An essential difference to the wafer boat of the first embodiment lies in the contacting units 7, which are formed here by two contact elements 80, 82. The contact elements 80, 82 extend essentially perpendicular to and below the plates 6. The contact elements 80, 82 are spaced apart from one another in the longitudinal direction of the plates 6 and are preferably arranged symmetrically with respect to a center plane of the plates 6.

The contact elements 80, 82 each have a main body 84 and 84 'and contact projections 86 and 86'. The contact projections 86 and 86 'are each constructed in such a way that they receive a lower edge of a plate 6 and can make electrical contact. The contact projections 86 and 86 ′ are spaced apart in the longitudinal direction of the contact elements 80, 82 such that in each case every fourth plate 6 of the wafer boat is electrically contacted by a respective contact element 80, 82. This again results in electrical contacting in which a non-electrically contacted plate 6 is arranged between plates 6 with different electrical contacts. Instead of the contact projections 86 and 86 'on the contact elements 80, 82, it would also be possible downward on plates 6 to be electrically contacted to provide protruding contact lugs which can be electrically connected by receptacles in contact elements 80, 82 or also separate contact elements (similar to contact elements 15). If the plates 6 have contact lugs projecting downwards, only two different types of plates would be necessary for the construction of the wafer boat, a type without lugs and a type with a contact lug projecting downwards which is offset with respect to a longitudinal center plane. This can then be connected to one or the other contact element 80, 82 by corresponding rotation of the plates.

This arrangement of the contact-making units 7 enables, in particular, contact-making by placing it on a supply line contact (within a process chamber). Thus, electrical contact with a feed line contact with low inductance on the bottom of the boat can be established by lowering the boat. The weight of the boat can be used for a high pressure force in the contact, which ensures high reliability and an even current density distribution.

The operation of the plasma treatment device 30 will now be explained in more detail with reference to the drawings, wherein a plasma-assisted silicon nitride or aluminum oxide deposition in a plasma excited by 13.56 MHz is described as an example. The treatment device 30 can, however, also be used for other deposition processes supported by plasma, with the plasma also being able to be excited by other frequencies, for example in the range of 40 kHz. The coaxial line 74 is, however, provided and optimized especially for frequencies in the MHz range.

First of all, it is assumed that a loaded wafer boat 1 of the type described above (according to FIG. 1) is loaded into the process chamber 38 and that the latter is closed by the closing mechanism (not shown). The wafer boat 1 is loaded in such a way that in each of the receiving slots 1 1 a total of 12 wafers, in the present example in particular Si wafers, are received, namely six on each of the plates 6. The wafers are received in such a way that they lie opposite one another in pairs, as is known in the art.

In this state, the interior is at ambient pressure and can be flushed or flooded with N2, for example, via the gas control unit 60 (in combination with the negative pressure control unit 62).

The tubular element 36 and thus the process chamber 38 are heated by the heating device (not shown) in order to put the wafer boat 1 and the wafers accommodated therein on a

If a wafer boat 1 of the type with high-resistance spacer elements is provided, a DC or low-frequency AC voltage can be applied to the wafer boat 1 via the electrical control unit 64 in order to support the heating. In this case, the voltage is sufficiently high so that current is conducted via the high-resistance spacer elements 22 and these act as resistance heating elements. As a result, heating power is specifically introduced into the receiving slots 11, so that the predetermined temperature can be reached much more quickly than when it is heated from the outside. Depending on the resistance of the spacer elements, voltages in the range from at least 200 V to approximately 1 kV are taken into account in order to achieve a sufficient current flow and sufficient heating of the spacer elements 22.

When the predetermined temperature of the wafer boat 1 and thus the entire unit (wafer boat 1, wafer and tubular element 36) is reached, the electrical control unit 64 can first be deactivated and the process chamber is pumped down to a predetermined negative pressure via the negative pressure control unit 62. When the predetermined negative pressure is reached, a desired process gas such as, for example, S1H4 / N H3 for silicon nitride deposition is supplied via the gas control unit 60 in a defined mixing ratio depending on the required Layer properties introduced, while the negative pressure continues to be maintained via the negative pressure control unit 62 by sucking off the introduced process gas.

An HF voltage with a frequency of 13.56 MFIz is now applied to the wafer boat 1 via the electrical control unit 64, an electrically non-contacted plate being arranged between the plates 6 to which the voltage is applied. As a result, two plasmas are ignited in series between the plates 6 to which the voltage is applied. The high-frequency current not only flows through a plasma, but also through two plasmas, each of which is separated by the plate that is not electrically contacted. The voltage of the non-contacted plate is set automatically via an essentially capacitive voltage division, so that a corresponding plasma ignition is made possible. There is thus a series connection of plasmas between the plates of the first and second group of plates. A sufficiently high voltage must be applied between the plates 6 to which the voltage is applied.

Plasmas are generated between the plates 6 and in particular between the wafers accommodated in the wafer boat 1, and silicon nitride is deposited on the wafers with the aid of plasma. The gas flow is maintained during the deposition process in order to avoid local depletion of the process gas with regard to the active components. After a sufficient deposition time for the desired layer thickness, the electrical control unit 64 is deactivated again and the gas supply is stopped or switched to N2 in order to flush the process chamber 38 and, if necessary, ventilate it at the same time (adjustment to atmospheric pressure). The process chamber 38 can then be brought back to ambient pressure.

As can be seen from the above description, the wafer boat 1 of the above type - independently of other components of the treatment device - offers the advantage that several plasmas in series can be switched, whereby the required current and the associated problems for operating the plasmas can be reduced.

The wafer boat 1 was explained in more detail on the basis of specific embodiments of the invention with reference to the drawing, without being limited to the specifically illustrated embodiments. In particular, two or more electrically non-contacted plates could also be provided between electrically contacted plates 6, for example. The plates 6 of the wafer boat 1 can also have different dimensions and, in particular, be dimensioned to accommodate a different number of wafers.

Claims

1. Wafer boat for the plasma treatment of disc-shaped wafers, in particular semiconductor wafers, which has the following:

a plurality of plates made of an electrically conductive material, arranged parallel to one another, each having at least one receptacle for a wafer on their mutually facing sides, which define a receiving region of the plates;

characterized in that the plates are connected to one another in such a way that a first number of the plates forms a first group of electrically conductively connected plates, a second number of the plates forms a second group of electrically conductively connected plates, the plates of the first and second group are provided alternately and between plates of the first and second group at least one plate is provided, which is not electrically connected to the plates of the first or second group.

2. Wafer boat according to claim 1, wherein within the first and second groups every fourth of the plates is electrically conductively connected to the others.

3. Wafer boat according to claim 1, wherein between plates of the first and

second group two plates are provided, which is not electrically connected to the plates of the first or second group.

4. Wafer boat according to claim 1, wherein within the first and second group every sixth of the plates is electrically conductively connected to the others.

5. Wafer boat according to one of the preceding claims, wherein the plates are each held at a distance from one another via spacer elements, wherein the spacer elements are each insulating or one Have a resistance of at least 20kΩ, preferably in the range of 40kΩ.

6. Wafer boat according to one of the preceding claims, wherein the

Spacers consist of polysilicon.

7. Wafer boat according to one of the preceding claims, wherein the plates of at least the first and second groups each have contact lugs at their longitudinal ends which are electrically conductively connected via contact blocks to contact lugs of other plates of the same group, the contact lugs of the plates of the first group in a different one Levels lie like the contact tabs of the plates of the second group.

8. Wafer boat according to claim 6, wherein the combined thermal mass of the sum of the contact blocks and the sum of the contact lugs is smaller than the thermal mass of other wafer boats, in particular less than 1/10 of the thermal mass of the other wafer boat.

9. Wafer boat according to one of claims 7 or 8, wherein the impedance of the sum of the contact blocks and the sum of the contact lugs is smaller than the impedance of the other wafer boat.

10. Wafer boat according to one of the preceding claims, wherein the plates of at least the first and second groups are each electrically conductively connected via at least one contact element extending below the plates, the contact elements for the plates of the first and second group being spaced apart from one another in the longitudinal direction of the plates are.

1 1. Plasma treatment device for wafers, in particular

Semiconductor wafer, which has the following:

a process room for receiving a wafer boat according to one of the preceding claims;

Means for controlling or regulating a process gas atmosphere in the process space; and

at least one voltage source which can be connected to the plates of the first and second group of plates in a suitable manner in order to apply a sufficient electrical voltage between the plates of the first and second group of plates to produce a voltage between the plates of the first and second group of plates To generate series of at least two plasmas which are separated by the at least one plate which is not electrically connected to the plates of the first or second group.

12. Plasma treatment device according to claim 1 1, wherein the

at least one voltage source is at least one suitable

To apply high-frequency alternating voltage and optionally a direct voltage or a low-frequency alternating voltage.

13. Plasma treatment device according to claim 1 1 or 12, wherein the device has at least one additional heating unit for heating the process space and the wafer received therein.

14. A method for plasma treatment of wafers, in which a plurality of substrates, in particular semiconductor wafers, are accommodated in a wafer boat according to one of claims 1 to 10 in a process space of a plasma treatment device, the method having the following steps:

Applying a high frequency alternating voltage between the plates of the first and second group of plates in order to during a

Process phase between plates of the first and second group of plates to generate a row of at least two plasmas, which are separated by the at least one plate that is not electrically connected to the plates of the first or second group.

15. The method of claim 14, wherein the temperature and / or the

Gas atmosphere in the process chamber can be controlled or regulated.

16. The method of claim 14 or 15, wherein before the application of the

High-frequency alternating voltage between the plates of the first and second group of plates, a direct voltage or a low-frequency alternating voltage is applied in order to cause a current flow in spacer elements between plates and a resistance heating effect.