Float zone apparatus with adjustable capacitor, and methods for producing single-crystal ingot and wafer

Abstract

The present invention relates to a floating zone apparatus configured to produce a single crystal ingot from a polycrystalline rod during a floating zone process by induction heating through which thermal power is continuously introduced via a coil unit (5) of the floating zone apparatus, thereby melting a continuous region along the vertical direction of the polycrystalline rod. The coil unit moves along the vertical direction of the polycrystalline rod and surrounds the polycrystalline rod at a distance. The current thermal power during the floating zone process is derived from the current effective power of an emitter unit (4), which includes a capacitor (1) that interacts electrically with the coil unit (5). The capacitor (3) is adjustable and configured to maintain the frequency of the emitter unit (4) modulated at a specifyable and substantially constant value during the floating zone process.

Description

Technical Field

[0001] The present invention relates to a float zone apparatus and a method for producing a single crystal ingot (more particularly a single crystal ingot of silicon) from a polycrystalline rod (more particularly a polycrystalline rod of silicon) by a float zone process on the float zone apparatus. Prior Art

[0002] In the float zone process for producing single crystal ingots of silicon, it can be seen that the frequency variation of the transmitter unit is highly dependent on the load.

[0003] In a typical float zone process, it can be seen that during droplet making, the load is relatively low and, for example, at maximum load, the frequency established in the transmitter unit is significantly lower than the frequency established later towards the end of the production of the single crystal ingot. This frequency response between the start (droplet making to cone) and the finished single crystal ingot phase typically reaches about 150 to 200 kHz.

[0004] In the transmitter unit, it also becomes apparent in this context that so-called "power holes" can be created due to the interaction of the coil unit and the capacitors used to generate the frequency. This type of overall power has the undesirable consequence that the dissipation power always generated by the transmitter unit is extremely significant in this frequency range. For example, for a given number of transmitter units of a floating zone device, a power hole can occur in the frequency range of 2800 kHz to 3000 kHz.

[0005] Therefore, a problematic situation in producing single crystal ingots by a floating zone process is that during the floating zone process, too little effective power arrives in the power void as thermal power for the single crystal ingot, and thus there may be unpredictable effects on the single crystal ingot (e.g., freezing-in, dripping, dislocation, etc.).

[0006] The invention is therefore based on the objective technical problem of providing in a simple manner a float zone device and a method for producing a single crystal ingot by means of a float zone process, in which the above-mentioned disadvantages are not present or at least exist to a lower extent and in particular a load-induced frequency response is avoided during the float zone process, which frequency response can be, for example, in the range of 150 kHz to 200 kHz.

[0007] The object is achieved by a floating zone device having the following characteristics, and is also achieved by a method for producing single crystal ingots by a floating zone process having the following characteristics.

[0008] A floating zone device is configured to produce a single crystal ingot from a polycrystalline rod by successive zonal melting along the vertical direction of the polycrystalline rod during a floating zone process by induction heating with continuous introduction of thermal power through a coil unit (5) of the floating zone device, the coil unit moving along the vertical direction of the polycrystalline rod and surrounding the polycrystalline rod at a certain distance, wherein the current thermal power during the floating zone process is derived from the current effective power of a transmitter unit (4) of the floating zone device, the transmitter unit comprising a capacitor (1), the transmitter unit (4) electrically interacting with the coil unit (5) in particular via a power generator unit, in The capacitor (1) is adjustable and is configured to keep the modulated frequency of the transmitter unit (4) at a prescribable and substantially constant value during the floating zone process, in particular independently of the load.

[0009] A method for producing a single crystal ingot (more particularly a single crystal ingot of silicon) from a polycrystalline rod (more particularly a polycrystalline rod of silicon) by a floating zone process on a floating zone apparatus as described above, in During the float zone process, the single crystal ingot is produced from the polycrystalline rod by continuous zone melting along the vertical direction of the polycrystalline rod by induction heating with continuous introduction of thermal power via a coil unit (5) of the float zone device, the coil unit moving along the vertical direction of the polycrystalline rod and surrounding the polycrystalline rod at a certain distance, wherein the current thermal power during the float zone process is derived from the current effective power of a transmitter unit (4) of the float zone device, the transmitter unit (4) comprising a capacitor (1), the transmitter unit (4) interacting electrically with the coil unit (5) in particular via a power generator unit, wherein During the floating zone process, the capacitor (1) implemented in an adjustable manner keeps the frequency of the transmitter unit (4) at a predeterminable and substantially constant value in a modulatable manner during the floating zone process. Summary of the invention

[0010] The present invention has recognized that with respect to known requirements, namely, that in the production of floating zone single crystal ingots the aim is to maximize the predictability and reproducibility of the effective power input into the crystal rod from the beginning of the floating zone process accompanied by heating of the crystal rod to the end of the single crystal ingot production, the power provided by the transmitter unit in this frequency range must also behave accordingly.

[0011] In this respect, the invention is based on the following technical teaching: if a float zone device or a float zone process is configured such that the frequency of the transmitter unit modulated at a predeterminable and substantially constant value is maintained throughout the float zone process (by regulatory tracking via continuous modulation during the float zone process), then a substantially constant effective power can be introduced regionally in a simple manner into the polycrystalline rod via the transmitter unit in the form of thermal power via the coil unit (for the production of a single-crystal ingot with substantially uniform physical properties). This fixed modulation of the frequency is achieved by the transmitter unit comprising an adjustable capacitor.

[0012] The described adaptation of the frequency by means of a capacitor during the floating zone process makes it possible to completely overcome the above-mentioned disadvantages known from the prior art; in particular, as a result, an unfavorable, load-induced frequency response (which may, for example, be in the range of 150 to 200 kHz) and its negative consequences for the process can be avoided.

[0013] Therefore, in a first aspect, the present invention relates to a float zone apparatus, which is configured to produce a single crystal ingot from a polycrystalline rod (more particularly a polycrystalline rod of silicon) through continuous zone melting along the vertical direction of the polycrystalline rod by induction heating by continuously introducing thermal power through a coil unit of the float zone equipment during the float zone process, the coil unit moving along the vertical direction of the polycrystalline rod and surrounding the polycrystalline rod at a certain distance.

[0014] Here, the current thermal power during the float zone process originates from the current effective power of the transmitter unit, which comprises the capacitor of the float zone device and which interacts electrically with the coil unit, in particular via a power generator unit.

[0015] The capacitor is configured in an adjustable manner and is here configured to keep the frequency of the transmitter unit modulated at a predeterminable and substantially constant value during the float zone process.

[0016] As a result, in particular the problematic situations known from the prior art of fluctuations in active power or effective power can be avoided.

[0017] By using an adjustable capacitor, load-dependent frequency shift can be avoided.

[0018] In a preferred variation, the adjustable capacitor may be configured as an adjustable variable capacitor.

[0019] In a preferred variant, the adjustable capacitor can be operated by an actuating drive via a control circuit, the setting of the capacitor possibly being triggered via a motor unit. Triggered by the setting of the capacitor, the motor unit modulates the frequency to a predeterminable value continuously, preferably independently of the load, during the floating zone process.

[0020] In a further preferred variant, the adjustable capacitor may be configured to maintain the modulatable frequency substantially at a constant value during the floating zone pulling process, which constant value may be in the range of 2600 kHz to 3100 kHz, preferably in the range of 2850 kHz to 3000 kHz, and more preferably substantially corresponds to 2970 kHz. However, the floating zone device according to the invention is not limited to these frequency values and may also be implemented for frequencies above or below these value ranges.

[0021] In a further preferred embodiment, the single crystal ingot may include a starting cone, a substantially shaped cylindrical ingot portion and a tail cone, and the floating zone device may be configured to modulate the frequencies of the starting cone, the cylindrical ingot portion and the tail cone to specified values independently of each other via triggering of an adjustable capacitor.

[0022] In a further preferred variant, the adjustable capacitor can be configured to avoid a load-induced frequency response, in particular in the range of 150 to 200 kHz, during a float zone process for producing a single crystal ingot from a multicrystalline rod.

[0023] The coil unit is particularly configured as a high-performance induction coil.

[0024] With regard to the basic operation of melting the polycrystalline rod, this is carried out in a manner known for the device according to the invention and for the method according to the invention, so that this aspect will not be discussed further here.

[0025] Providing the adjustable capacitor of the present invention (or one or more combinations of its preferred variants) on the floating zone device, and the method of the present invention (or in combination with one or more preferred variants) using the adjustable capacitor, provides advantages for the single crystal ingot to be produced, including the following: Ø The process can again be operated in the optimum frequency range of about 3000 kHz to melt multicrystalline rods and produce single crystal ingots. Ø Avoiding power holes and thus achieving process stability during the float zone process. One of the results is that operation in the float zone device components (especially the high-frequency induction coil) becomes easier. Ø The optimum frequency modulation can be modulated at different process stages during the float zone process, thereby increasing the yield. Ø Influence on the melting movement and thereby reduction of dislocations within the produced single crystal ingot; in addition, preferably, due to the continuous change / adaptation of the frequency modulation in the ingot stage, the radial resistance during the floating zone process is optimized (described in the form of radial resistance variation (RRV)).

[0026] Thus, according to a second aspect, the present invention relates to a method for producing a single crystal ingot (more particularly a single crystal ingot of silicon) from a polycrystalline rod (more particularly a polycrystalline rod of silicon) by means of a float zone process on a float zone apparatus according to the present invention (or in combination with one of its preferred variants as described above), wherein · producing a single crystal ingot from a polycrystalline rod by continuous zone melting along the vertical direction of the polycrystalline rod during a float zone process by induction heating with continuous introduction of thermal power via a coil unit of the float zone device, the coil unit moving along the vertical direction of the polycrystalline rod and surrounding the polycrystalline rod at a certain distance, wherein the current thermal power during the float zone process is derived from the current effective power of a transmitter unit of the float zone device, the transmitter unit comprising a capacitor, the transmitter unit interacting electrically with the coil unit in particular via a power generator unit, and wherein During the float zone process, a capacitor implemented in an adjustable manner keeps the frequency of the transmitter unit at a predeterminable and substantially constant value in a modulable manner during the float zone process.

[0027] In a preferred variant, the adjustable capacitor can be operated by an actuation drive and via a control circuit, the setting of the capacitor possibly being triggered via a motor unit.

[0028] In a preferred variation, the adjustable capacitor may be configured as an adjustable variable capacitor.

[0029] In a further preferred variant, the motor unit can continuously modulate the frequency to a predeterminable value during the float zone process independently of the load and via a set triggering of the capacitor.

[0030] In a further preferred variant, the single crystal ingot may comprise a start cone, a substantially shaped cylindrical ingot portion and an end cone, for which independently of one another a prescribable value of the frequency may be modulated via triggering of an adjustable capacitor.

[0031] In a further preferred variant, the prescribable value of the frequency can be in the range of 2600 kHz to 3100 kHz, preferably in the range of 2850 kHz to 3000 kHz, and even more preferably corresponds substantially to 2970 kHz. However, the method according to the invention is not limited to these frequency values and can also be implemented for frequencies above or below these value ranges.

[0032] The capacitor is preferably arranged in the primary circuit of the transformer of the transmitter unit. In an alternative variant, the capacitor can also be arranged in the secondary circuit of the transformer of the transmitter unit.

[0033] The invention further relates to a method for producing wafers of semiconductor material from a single-crystal ingot, more particularly a single-crystal ingot of silicon, which has been produced by means of a method according to the invention for producing a single-crystal ingot, more particularly a single-crystal ingot of silicon, by means of a float zone process, or in combination with one or more of its preferred variants, on a 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 ingot, at least the following steps are performed: Slice a single crystal ingot into thin wafers, · subjecting at least one of the thin wafers of semiconductor material to a chemical and / or mechanical further treatment, the further treatment comprising at least one further treatment step from the following: edge rounding, lapping, cleaning, polishing, deposition of an oxide layer, epitaxial growth of a single crystal layer (more particularly epitaxial growth of a silicon layer or epitaxial growth of a SiGe layer or a GaN layer). Simple diagram description

[0034] 1 shows a schematic diagram of details of a float zone apparatus, including a transmitter unit 4 having an adjustable capacitor 1 of the present invention, a coil unit 5, and an ingot (shown within the coil unit 5 and extending a distance relative thereto) during a float zone process.

[0035] FIG. 2 shows a detail of the electrical equivalent circuit diagram of the transmitter unit 4 with the adjustable capacitor 1 in the transition region to the coil unit 5 (right side, open side in the equivalent circuit diagram). Implementation

[0036] The following describes a preferred exemplary embodiment of a floating zone apparatus of the present invention, which is configured to perform the method of the present invention for producing a single crystal ingot of silicon.

[0037] During the float zone process, a single crystal ingot (shown in FIG. 1 ) is produced from a polycrystalline rod on a float zone apparatus through continuous zone melting along the vertical direction of the polycrystalline rod by induction heating by continuously introducing thermal power through a coil unit 5 of the float zone apparatus, which moves along the vertical direction of the polycrystalline rod and surrounds the polycrystalline rod at a certain distance.

[0038] Here, the current thermal power during the float zone process originates from the current effective power of a transmitter unit 4 of the float zone device, which transmitter unit comprises a capacitor 1 and which interacts electrically with a coil unit 5 via a power generator unit 6 .

[0039] The capacitor 1 is adjustable and is configured to keep the frequency of the modulated transmitter unit 4 at a predeterminable and substantially constant value during the floating zone process, independently of the load.

[0040] The adjustable capacitor 1 is configured as an adjustable variable capacitor.

[0041] Here, the adjustable capacitor 1 can be operated by an actuating drive and via a control loop. The setting of the capacitor 1 is triggered via a motor unit 3, as shown quite schematically in FIG. 1 . Here, via the triggering of the setting of the capacitor 1, the motor unit 3 continuously modulates the frequency to a predeterminable value independently of the load during the floating zone process. The motor unit 3 is in turn triggered via a control unit 7, to which a frequency verification unit 2 is connected.

[0042] FIG. 2 shows a detail of the electrical equivalent circuit diagram of the transmitter unit 4 with the adjustable capacitor 1 of the invention in the transition region to the coil unit 5 (right, open side in the equivalent circuit diagram in FIG. 2 ), which is indicated in FIG. 2 . The transition from the primary circuit to the secondary circuit is indicated by a dashed line, representing a transformer. In this exemplary embodiment, the capacitor 1 is located in the primary circuit and has a modulatable, modifiable capacitance in the range of 100 to 1000 pF (picofarads) at a voltage of 20 kV (kilovolts). However, in different preferred variants of the invention, different modulations in different capacitance value ranges and different voltage ranges are also possible, and the invention is not limited to these values of the adjustable capacitor.

[0043] Here, the adjustable capacitor 1 is configured to maintain the modulatable frequency substantially at a constant value during the floating zone pulling process, which constant value substantially corresponds to 2970 kHz, and accordingly, compared to known embodiments of floating zone devices, is configured to avoid a load-induced frequency response during the floating zone process for producing a single crystal ingot from a multicrystalline rod, in particular in the range of 150 kHz to 200 kHz (in other words, in the case of embodiments of the present invention, the frequency response is theoretically close to 0, governed by the control characteristics, wherein fluctuations are typically about + / -2 kHz).

[0044] After producing a single crystal ingot of silicon, wafers of semiconductor material are produced from the single crystal ingot, and the following steps are performed: Slice a single crystal ingot into thin wafers, · subjecting at least one of the thin wafers of semiconductor material to a further chemical and mechanical treatment, the further treatment comprising the further processing steps of edge rounding, grinding, cleaning and polishing.

[0045] 1: Capacitor 2: Frequency verification unit 3: Motor unit 4: Transmitter unit 5: Coil unit 6: Power Generator Unit 7: Control unit

Claims

1. A float zone apparatus configured to: produce a single crystal ingot from a polycrystalline rod by induction heating through continuous successive zonal melting along the vertical direction of the polycrystalline rod by continuously introducing thermal power via a coil unit (5) of the float zone apparatus during a float zone process, the coil unit moving along the vertical direction of the polycrystalline rod and surrounding the polycrystalline rod at a certain distance, wherein the current thermal power during the float zone process is derived from the current effective power of a transmitter unit (4) of the float zone apparatus, the transmitter unit comprising a capacitor (1), the transmitter unit (4) being electrically interacting with the coil unit (5) specifically via a power generator unit, wherein the capacitor (1) is adjustable and configured to: maintain the frequency of the modulated transmitter unit (4) at a specified and substantially constant value, particularly independently of the load, during the float zone process. The capacitor (1) is configured to maintain the modulated frequency at a substantially constant value during the floating pull process, the constant value being in the range of 2600 kHz to 3100 kHz.

2. The floating area device as claimed in claim 1, wherein the capacitor (1) is operable by an actuating drive and via a control loop, and the setting of the capacitor (1) is triggered by a motor unit (3).

3. The floating zone device as claimed in claim 2, wherein the motor unit (3) is independent of the load during the floating zone process and continuously modulates the specified value of the frequency via the set trigger of the capacitor (1).

4. A floating zone device as described in any one of claims 1 to 3, wherein the single crystal ingot comprises a starting cone, a substantially shaped cylindrical ingot portion and a tail cone, the floating zone device being configured to independently modulate a specifiable value of the frequency of the starting cone, a specifiable value of the frequency of the cylindrical ingot portion and a specifiable value of the frequency of the tail cone via triggering of the capacitor (1).

5. The floating zone device as described in any one of claims 1 to 3, wherein the capacitor (1) is configured to avoid load-induced frequency response during the floating zone process for producing single crystal ingots from polycrystalline rods.

6. A method for producing a single crystal ingot from a polycrystalline rod by means of a floating zone process on a floating zone apparatus as claimed in any one of claims 1 to 5, wherein during the floating zone process, the single crystal ingot is produced from the polycrystalline rod by induction heating through continuous regional melting along the vertical direction of the polycrystalline rod by means of a coil unit (5) of the floating zone apparatus, the coil unit moving along the vertical direction of the polycrystalline rod and surrounding the polycrystalline rod at a certain distance, wherein the current heat power during the floating zone process is derived from the current effective power of an emitter unit (4) of the floating zone apparatus, the emitter unit (4) comprising a capacitor (1), the emitter unit (4) being electrically interacting with the coil unit (5) specifically via a power generator unit, wherein during the floating zone process, the capacitor (1), implemented in an adjustable manner, maintains the frequency of the emitter unit (4) in a modulated manner at a specifyable and substantially constant value, wherein the specifyable and substantially constant value of the frequency is within 2600. The range is from kHz to 3100 kHz.

7. The method as described in claim 6, wherein the capacitor (1) is operable by actuation and via a control loop, and the setting of the capacitor (1) is triggered by the motor unit (3).

8. The method as described in claim 7, wherein the motor unit (3) is independent of the load during the floating zone process and continuously modulates the specified value of the frequency via the set trigger of the capacitor (1).

9. The method as described in any one of claims 6 to 8, wherein the single crystal ingot comprises a starting cone, a substantially formed cylindrical ingot portion and a tail cone, wherein a specifiable value of frequency is modulated by triggering the capacitor (1) for each of the independent starting cone, cylindrical ingot portion and tail cone.

10. A method for producing wafers of semiconductor material from a single crystal ingot, the single crystal ingot being produced on a floating-area apparatus described in any one of claims 1 to 5 by a floating-area process as referred to in any one of claims 6 to 9, wherein, starting from the end of the method for producing the single crystal ingot, at least the following steps are performed: slicing the single crystal ingot into thin wafers; subjecting at least one of the thin wafers of semiconductor material to further chemical and / or mechanical processing, the further processing comprising at least one further processing step of: edge rounding, lapping, cleaning, polishing, deposition of an oxide layer, and epitaxial growth of a single crystal layer.

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