Float-zone device with adjustable capacitor

Abstract

The invention relates to a float-zone device which is designed to produce, during a float-zone process, a monocrystalline rod from a polycrystalline rod by successively melting the polycrystalline rod in zones along the vertical direction thereof using an inductive heating process carried out by continuously introducing thermal power via a coil unit (5) of the float-zone device, said coil unit moving along the vertical direction of the polycrystalline rod and surrounding the polycrystalline rod in spaced relation thereto, wherein during the float-zone process, the current thermal power originates from the current active power of a transmission unit (4), which comprises a capacitor (1), of the float-zone device, said transmission unit electrically interacting with the coil unit (5). The capacitor (3) can be adjusted and is designed to keep the frequency of the transmission unit (4) set to a specifiable and substantially constant value during the float-zone process.

Description

[0001] Float zone device with adjustable capacitor

[0002] Technical area

[0003] The invention relates to a float zone device and a method for producing a single crystal rod, in particular made of silicon, from a polycrystal rod, in particular made of silicon, by means of a float zone process on the float zone device.

[0004] State of the art and technical task

[0005] The float zone process for producing a single-crystal silicon rod shows that the frequency of the transmitter unit varies greatly depending on the load.

[0006] In typical float-zone processes, the load during drop formation is comparatively low, resulting in a significantly lower frequency in the transmitter unit than, for example, towards the end of the single-crystal rod being produced at maximum load. This frequency response between the initial phase (drop formation up to the cone) and the phase of the finished single-crystal rod is typically approximately 150 to 200 kHz.

[0007] In this context, it has also been shown that, due to the interaction of coils and capacitors for frequency generation, a so-called "power gap" can occur in transmitter units. Such a power gap has the negative effect that the power loss always generated by the transmitter unit is extremely pronounced in this frequency range. For example, with a specified configuration of a transmitter unit for a float-zone device, a power gap can occur in a frequency range of 2800 to 3000 kHz.

[0008] The problem with single-crystal rod production using the float-zone process is that, during the float-zone process, far too little effective power reaches the single-crystal rod as thermal power in this power gap, which can lead to unforeseeable effects on the single-crystal rod (e.g., freezing, dripping, dislocations, etc.). The present invention is therefore based on the objective, technical problem of simply providing a float-zone device and a method for producing a single-crystal rod using the float-zone process, which do not have the aforementioned disadvantages or at least have them to a lesser extent, and which, in particular, avoid a load-related frequency response, which can be in the range of 150 to 200 kHz, for example, during the float-zone process.

[0009] The object is achieved by a float zone device according to claim 1, as well as by a method for producing a single crystal rod by means of a float zone process according to the features of claim 7.

[0010] Description of the invention

[0011] The invention has recognized that, given the known requirement that, when producing a float-zone single-crystal rod, the aim is to achieve the most predictable and reproducible effective power input into the crystal rod from the start of the float-zone process with heating of the crystal rod to the end of the production of the single-crystal rod, the power provided by the transmitter unit in this frequency range must also behave accordingly.

[0012] The invention is based on the technical teaching that a substantially constant active power can be easily introduced into the polycrystal rod via the transmitter unit in the form of thermal power zone by zone via the coil unit (to produce a single-crystal rod with substantially uniform material properties) if the float-zone device or the float-zone process is designed such that the frequency of the transmitter unit is kept at a predeterminable and substantially constant value throughout the entire float-zone process (by continuously adjusting it via the float-zone process). This fixed frequency setting is achieved by the transmitter unit comprising an adjustable capacitor.By adjusting the frequency with a capacitor during the float-zone process, the disadvantages described above, known from the prior art, can be completely overcome; in particular, the disadvantageous load-related frequency response, which can be in the range of 150 to 200 kHz, for example, and its negative effects on the process can be avoided.

[0013] According to a first aspect, the invention therefore relates to a float zone device which is designed to produce the single crystal rod from a polycrystal rod, in particular made of silicon, during a float zone process by successive, zone-by-zone melting along the height direction of the polycrystal rod by inductive heating by means of the continuous introduction of thermal power via a coil unit of the float zone device which moves along the height direction of the polycrystal rod and surrounds the polycrystal rod at a distance from it.

[0014] A current thermal power during the float zone process originates from a current active power of a transmitter unit, comprising a capacitor, of the float zone device, wherein the transmitter unit electrically interacts with the coil unit, in particular via a power generator unit.

[0015] The capacitor is adjustable and is designed to keep the frequency of the transmitter unit set to a predeterminable and essentially constant value during the float zone process.

[0016] This makes it possible to avoid, in particular, the problem known from the state of the art, namely fluctuations in the effective power or active power.

[0017] The adjustable capacitor can prevent load-dependent frequency shifts.

[0018] In preferred variants, the adjustable capacitor can be designed as an adjustable variable capacitor. In preferred variants, the adjustable capacitor can be operated by means of an actuator via a control loop, whereby the control of the capacitor position can be carried out via a motor unit. Preferably, the motor unit continuously adjusts the preset frequency value, independent of the load, via the float zone process by controlling the capacitor position.

[0019] In further preferred variants, the adjustable capacitor can be configured to maintain the adjustable frequency during the float-zone pulling process substantially at a constant value, which may be in the range of 2600 kHz to 3100 kHz, preferably in the range of 2850 kHz to 3000 kHz, more preferably substantially corresponding to 2970 kHz. However, the float-zone device according to the invention is not limited to these frequency values ​​and can also be implemented at a frequency below or above these value ranges.

[0020] In further preferred variants, the single-crystal rod can comprise an initial cone, a substantially shaped cylindrical rod section and an end cone, wherein the float zone device can be designed to set the predeterminable value of the frequency for the initial cone, the cylindrical rod section and the end cone independently of one another via the control of the adjustable capacitor.

[0021] In further preferred variants, the adjustable capacitor can be designed to avoid a load-related frequency response, in particular in a range of 150 to 200 kHz, during the float zone process for producing a single crystal rod from a polycrystal rod.

[0022] In particular, the coil unit is designed as a high-performance induction coil.

[0023] As far as the basic melting process of the polycrystal rod is concerned, this occurs in the device according to the invention and in the method according to the invention in a known manner, so that this aspect will not be discussed in detail here. By providing the adjustable capacitor according to the invention (or in combination with one or more of its preferred variants) on the float zone device and for the method according to the invention (or in combination with one or more of its preferred variants), which uses the adjustable capacitor, the following advantages arise, among others, for the single crystal rod to be produced: Possibility of operating the process again in the optimal frequency range for melting the polycrystal rod and producing a single crystal rod of approximately 3000 kHz. Avoiding passing through the power hole and thus process stability during the float zone process. This, among other things,The installation of the float-zone device components, especially the high-frequency induction coil, is significantly facilitated. The ability to set optimal frequency settings in various process phases during the float-zone process results in increased yield. Influencing melt movement and thus reducing dislocations within the single-crystal rod being produced; furthermore, preferably, optimization of the radial resistance (described as the radial resistance variation RRV) during the float-zone process due to continuous changes or adjustments to the frequency setting in the rod phase.

[0024] According to a second aspect, the invention therefore relates to a method for producing a single-crystal rod, in particular made of silicon, from a polycrystal rod, in particular made of silicon, by means of a float-zone process on the float-zone device according to the invention or (in combination with one of its preferred variants as described above), wherein • during the float-zone process, the single-crystal rod is produced from the polycrystal rod by successive, zone-by-zone melting along the height direction of the polycrystal rod by inductive heating by means of the continuous introduction of thermal power via a coil unit of the float-zone device moving along the height direction of the polycrystal rod and surrounding the polycrystal rod at a distance, wherein a current thermal power during the float-zone process originates from a current active power of a transmitter unit, comprising a capacitor, of the float-zone device,which interacts electrically with the coil unit, in particular via a power generator unit, and wherein,

[0025] • during the float zone process, the capacitor, which is designed to be adjustable, keeps the frequency of the transmitter unit at a predeterminable and essentially constant value adjustable via the float zone process.

[0026] In preferred variants, the adjustable capacitor can be operated by means of an actuator via a control loop, whereby the position of the capacitor can be controlled via a motor unit.

[0027] In preferred variants, the adjustable capacitor can be designed as an adjustable variable capacitor.

[0028] In further preferred variants, the motor unit can continuously adjust the preset value of the frequency, independent of the load, via the float zone process by controlling the position of the capacitor.

[0029] In further preferred variants, the single-crystal rod can comprise an initial cone, a substantially shaped cylindrical rod section, and an end cone, wherein the predeterminable frequency value can be set independently of one another via the control of the adjustable capacitor for the initial cone, the cylindrical rod section, and the end cone. In further preferred variants, the predeterminable frequency value can be in the range from 2600 kHz to 3100 kHz, preferably in the range from 2850 kHz to 3000 kHz, more preferably substantially 2970 kHz. However, the method according to the invention is not limited to these frequency values ​​and can also be implemented at a frequency below or above the value ranges.

[0030] Preferably, the capacitor is arranged in the primary circuit of the transmitter unit's transformer. In alternative variants, it can also be arranged in the secondary circuit of the transmitter unit's transformer.

[0031] Furthermore, the invention relates to a method for producing a wafer of semiconductor material from a single-crystal rod, in particular from silicon, which was produced by the method according to the invention for producing a single-crystal rod, in particular from silicon, by means of a float zone process (or in combination with one or more of its preferred variants) on the float zone device according to the invention (or in combination with one or more of its advantageous variants), wherein starting from the end of the method for producing the single-crystal rod, at least the following steps follow:

[0032] • Sawing the single crystal rod into thin slices,

[0033] • Chemical and / or mechanical further treatment of at least one of the thin slices of semi-material, wherein the further treatment comprises at least one further treatment step of edge rounding, lapping, cleaning, polishing, depositing an oxide layer, epitaxial growth of a single-crystalline layer, in particular a silicon layer, or a SiGe layer or a GaN layer.

[0034] Short description of the figure

[0035] Figure 1 shows a schematic representation of a section of the

[0036] Float zone device comprising the transmitter unit 4 with the adjustable capacitor 1 according to the invention, the coil unit 5 and the crystal rod during the float zone process (indicated within the coil unit 5 and spaced therefrom).

[0037] Figure 2 shows a section of the electrical equivalent circuit diagram of the transmitter unit 4 in the transition area (right, open side in the equivalent circuit diagram) to the coil unit 5 with the adjustable capacitor 1 according to the invention.

[0038] Detailed description of a preferred embodiment

[0039] In the following, a preferred embodiment of the float zone device according to the invention is described, which is designed to carry out the method according to the invention for producing a single crystal rod made of silicon.

[0040] During a float zone process, a single crystal rod of silicon is produced at the float zone device from a polycrystal rod (indicated in Figure 1 ) by successive, zone-by-zone melting along the height direction of the polycrystal rod by inductive heating by means of the continuous introduction of thermal power via a coil unit 5 of the float zone device that moves along the height direction of the polycrystal rod and surrounds the polycrystal rod at a distance.

[0041] A current thermal power during the float zone process originates from a current active power of a transmitter unit 4 of the float zone device, comprising a capacitor 1, wherein the transmitter unit 4 electrically interacts with the coil unit 5 via a power generator unit 6.

[0042] The capacitor 1 is adjustable and designed to keep the frequency of the transmitter unit 5 set to a predeterminable and substantially constant value during the float zone process, independent of the load.

[0043] The adjustable capacitor 1 is designed as an adjustable variable capacitor.

[0044] The adjustable capacitor 1 is operated by means of an actuator via a control loop. The position of the capacitor 1 is controlled by a motor unit 3, as shown very schematically in Figure 1. The motor unit 3 continuously adjusts the preset frequency value, independent of the load, via the float zone process by controlling the position of the capacitor 1. The motor unit 3, in turn, is controlled by a control unit 7, with a frequency monitoring unit 2 interposed.

[0045] Figure 2 shows a section of the electrical equivalent circuit of the transmitter unit 4 in the transition area (right, open side in the equivalent circuit in Figure 2) to the coil unit 5 with the adjustable capacitor 1 according to the invention, marked in Figure 2. The transition from the primary circuit to the secondary circuit is indicated by the dashed line, which represents a transformer. In the present embodiment, the capacitor 1 is located within the primary circuit and has an adjustable, variable capacitance in the range from 100 to 1000 pF at a voltage of 20 kV. In other preferred variants of the invention, however, other settings in other capacitance value ranges and other voltage ranges are also possible, and the invention is not limited to these values ​​for the adjustable capacitor.

[0046] The adjustable capacitor 1 is designed to keep the adjustable frequency during the float zone pulling process essentially at a constant value, which essentially corresponds to 2970 kHz, and thus, in contrast to known designs of float zone devices, is designed to avoid a load-dependent frequency response, in particular in a range of 150 to 200 kHz, during the float zone process for producing a single crystal rod from a polycrystal rod (in other words, in the design according to the invention, the frequency response is theoretically close to 0, due to the control behavior with a fluctuation of usually approximately + / - 2 kHz).

[0047] After the single crystal rod is produced from silicon, discs of semiconductor material are produced from the single crystal rod, following the following steps:

[0048] • Sawing the single crystal rod into thin slices,

[0049] • Chemical and mechanical further treatment of the thin slices made of semi-material, whereby the further treatment includes the further treatment steps of edge rounding, lapping, cleaning and polishing.

Claims

Claims 1. A float zone device which is designed to produce the single crystal rod from a polycrystal rod during a float zone process by successive, zone-by-zone melting along the height direction of the polycrystal rod by inductive heating by means of the continuous introduction of thermal power via a coil unit (5) of the float zone device which moves along the height direction of the polycrystal rod and surrounds the polycrystal rod at a distance from it, wherein a current thermal power during the float zone process originates from a current active power of a transmitter unit (4), comprising a capacitor (1), of the float zone device which electrically interacts with the coil unit (5), in particular via a power generator unit, characterized in that the capacitor (1) is adjustable and is designed toto keep the frequency of the transmitter unit (4) set to a predeterminable and essentially constant value during the float zone process, in particular independent of the load., 2. Float zone device according to claim 1, wherein the adjustable capacitor (1) is operable by means of an actuator via a control loop, the position of the capacitor (1) being controlled via a motor unit (3).

3. Float zone device according to claim 2, wherein the motor unit (3) continuously adjusts the predeterminable value of the frequency, independent of the load, via the float zone process by controlling the position of the capacitor.

4. Float zone device according to one of claims 1 to 3, wherein the single crystal rod has an initial cone, a substantially shaped Cylinder rod section and an end cone, wherein the float zone device is designed to set the predeterminable value of the frequency for the initial cone, the cylinder rod section and the end cone independently of one another via the control of the adjustable capacitor (1).

5. Float zone device according to one of claims 1 to 4, wherein the adjustable capacitor (1) is designed to keep the adjustable frequency during the float zone pulling process substantially at a constant value which is in the range of 2600 kHz to 3100 kHz, preferably in the range of 2850 kHz to 3000 kHz, preferably substantially equal to 2970 kHz.

6. Float zone device according to one of claims 1 to 5, wherein the adjustable capacitor (1) is designed to avoid a load-related frequency response, in particular in a range of 150 to 200 kHz, during the float zone process for producing a single crystal rod from a polycrystal rod.

7. A method for producing a single-crystal rod, in particular made of silicon, from a polycrystal rod, in particular made of silicon, by means of a float-zone process on a float-zone device according to one of claims 1 to 6, wherein • during the float zone process, the single crystal rod is produced from the polycrystal rod by successive, zone-by-zone melting along the height direction of the polycrystal rod by inductive heating by means of the continuous introduction of thermal power via a coil unit (5) of the float zone device moving along the height direction of the polycrystal rod and surrounding the polycrystal rod at a distance, wherein a current thermal power during the float zone process originates from a current active power of a transmitter unit (4), comprising a capacitor (1), of the float zone device, which is connected to the Coil unit (5), in particular via a power generator unit, electrically interacts, wherein • during the float zone process, the capacitor (1), which is adjustable, keeps the frequency of the transmitter unit (4) at a predeterminable and essentially constant value adjustable via the float zone process.

8. The method according to claim 7, wherein the adjustable capacitor (1) is operable by means of an actuator via a control loop, the position of the capacitor (1) being controlled via a motor unit (3).

9. The method according to claim 8, wherein the motor unit (3) continuously adjusts the predeterminable value of the frequency, independently of the load, via the float zone process by controlling the position of the capacitor (1).

10. The method according to any one of claims 7 to 9, wherein the single-crystal rod comprises an initial cone, a substantially shaped cylindrical rod section and an end cone, wherein the predeterminable value of the frequency is set independently of one another for the initial cone, the cylindrical rod section and the end cone via the control of the adjustable capacitor (1).

11. Method according to one of claims 7 to 10, wherein the predeterminable value of the frequency lies in the range from 2600 kHz to 3100 kHz, preferably in the range from 2850 kHz to 3000 kHz, preferably substantially corresponds to 2970 kHz.

12. A method for producing a wafer of semiconductor material from a single-crystal rod, in particular from silicon, which was produced by the method for producing a single-crystal rod, in particular from silicon, by means of a float-zone process according to one of claims 7 to 11 on a float-zone device according to one of claims 1 to 6, wherein, starting from the end of the process for producing the single crystal rod, at least the following steps follow: • Sawing the single crystal rod into thin slices, • Chemical and / or mechanical further treatment of at least one of the thin slices of semi-material, wherein the further treatment comprises at least one further treatment step of edge rounding, lapping, cleaning, polishing, depositing an oxide layer, epitaxial growth of a single-crystalline layer, in particular a silicon layer, or a SiGe layer or a GaN layer.

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