METHOD FOR PRODUCING POLYCRYSTALLINE SILICON

Abstract

A process for producing polycrystalline silicon and a gas phase deposition chamber for the same. The process includes introducing a reaction gas containing an amount of silane and/or an amount of at least one halosilane as well as an amount of hydrogen into a reaction space of a gas phase deposition reactor. The reaction space includes at least one heated support body upon which by deposition silicon is deposited to form the polycrystalline silicon. For the detection of dust depositions, at least one measuring apparatus is used to determine the amount of haze inside the reaction space during deposition.

Claims

1-15. (canceled)

16. A process for producing polycrystalline silicon, comprising: introducing a reaction gas comprising silane and/or at least one halosilane as well as hydrogen into a reaction space of a gas phase deposition reactor, wherein the reaction space comprises at least one heated support body upon which by deposition silicon is deposited to form the polycrystalline silicon, and wherein for detection of dust depositions at least one measuring apparatus is used to determine the haze inside the reaction space during the deposition.

17. The process of claim 16, wherein the measuring apparatus comprises a scattered radiation detector and/or extinction detector.

18. The process of claim 17, wherein the measuring apparatus further comprises an external source of electromagnetic radiation.

19. The process of claim 16, wherein the measuring apparatus comprises an optical camera; and wherein the haze is determined as a change in the quality of the images produced with the camera.

20. The process of claim 16, wherein the measuring apparatus comprises a temperature sensor; and wherein the haze is determined as a change in temperature.

21. The process of claim 20, wherein the temperature sensor is selected from the group comprising pyrometer, thermal imaging camera, thermocouple and combinations thereof.

22. The process of claim 16, wherein the measuring apparatus is a combination of an optical camera and a temperature sensor.

23. The process of claim 16, wherein the haze is determined at at least two different points of measurement.

24. The process of claim 16, wherein the haze is determined continuously during the entire deposition or discontinuously at various times during the deposition.

25. The process of claim 16, wherein the deposition is interrupted or terminated upon exceeding a threshold value of haze.

26. The process of claim 16, wherein upon exceeding or falling below a threshold value of haze at least one parameter selected from the group comprising reactor pressure, support body temperature, reaction gas composition and volume flow is varied.

27. The process of claim 16, wherein the deposition is controlled such that during deposition the haze is substantially constant.

28. The process of claim 16, wherein the gas phase deposition reactor is a Siemens reactor.

29. The process of claim 16, wherein the gas phase deposition reactor is a fluidized bed reactor.

30. A gas phase deposition reactor, comprising: a measuring apparatus for determining the haze inside the reaction space during deposition; and wherein the measuring apparatus comprises a scattered light detector and/or extinction detector having an external source of electromagnetic radiation.

Description

[0050] In respect of further embodiments of the reactor reference may be made to the above elucidations and the examples.

[0051] FIG. 1 shows the cross section of a gas phase deposition reactor for performing the process according to the invention.

[0052] FIG. 2 shows the cross section of a gas phase deposition reactor for performing the process according to the invention.

[0053] FIG. 3 shows the profile of temperature and exposure time in a dust deposition.

[0054] FIG. 1 shows the cross section of a gas phase deposition reactor 12 according to the invention in whose reaction space 13, which is delimited by a reactor wall 14, support bodies 16 are arranged. The support bodies 16 are silicon rods and for reasons of clarity only a portion of the rods is shown.

[0055] For haze measurement in the reaction space 13 the reactor 12 is provided with a measuring apparatus. This comprises a separate source of electromagnetic radiation arranged in front of a sightglass 21, presently a light source 10 (laser of 515 nm oder 488 nm). It further comprises an extinction detector 18 arranged opposite the light source 10 and likewise in front of a sightglass 21 (made of borosilicate or quartz glass). Furthermore, scattered light detectors 20, 22, 24 (appropriate CCD sensor arrays) are positioned at various angles to the radiation direction of the light source 10 in each case in front of a sightglass 21. The scattered light detectors 20, 22, 24 need not necessarily be at the same height as the source 10.

[0056] During dust deposition particles 17 begin to form in the reaction space 13. Through absorption these attenuate the light emitted by the source 10. This is registered by the extinction detector 18. Particles 17 further bring about increasing light scattering as may be captured by the scattered light detectors 20, 22, 24. The measured values are typically captured by a process control station and optionally also compared with the reference/normal values. Countermeasures may then be taken on the basis of these measured values. Since during dust deposition the particles 17 are normally uniformly distributed over the reaction space 13, the height at which the detectors 20, 22, 24 and the source 10 are mounted is in principle immaterial. It is preferable when they are mounted at the height of the middle third of the silicon rod height.

[0057] FIG. 2 shows a gas phase deposition reactor 12 in cross section, wherein in respect of the substantial elements reference may be made to FIG. 1. For the sake of clarity only one heated silicon rod is shown as a radiation-emitting support body 16. In this embodiment two detectors 26a, 26b (for example photodiodes and/or photomultipliers) are arranged in the reactor wall in each case in front of a sightglass 21. The arrows indicate both light scattered by the particles 7 formed by dust deposition and light attenuated by absorption. Schematically only light attenuated by absorption is incident on the detector 26a while both scattered light and light attenuated by absorption is incident on the detector 26b. Haze is thus determined as a change in the radiation incident on the sensor.

EXAMPLE

[0058] Plotted in FIG. 3 is a diagram of the profile of the measured support body temperature Om, its first derivative with respect to time t and the exposure time t.sub.B of a black-and-white camera arranged in front of the sightglass of a Siemens reactor against t (deposition time). The profile shown commences at a deposition time of 60 hours.

[0059] The Siemens reactor was equipped with 24 rod pairs and the type of the reactor is in principle immaterial to the performance of the invention. Determination of ϑ.sub.M was carried out on a polysilicon rod (at the height of the rod middle between the bridge and the electrode) with a pyrometer arranged in front of a sightglass. The data from the pyrometer were transferred to a process control station and plotted. The black-and-white camera was provided with a CMOS sensor and was likewise oriented into the reaction space approximately at the height of the rod middle. The camera continuously produced an image transferred to a processing software of the process control station. The software performed automatic adjustment of exposure time t.sub.B upon darkening or lightening.

[0060] After a deposition time of 60 hours ϑ.sub.M initially remained constant at about 1040° C. After about 5 minutes there was an (apparent) fall of ϑ.sub.M by about 12° C., wherein after about 4 minutes ϑ.sub.M returned to the previous value. That this irregularity was a short dust deposition was confirmed by the rise (from 360 to 450 μs) and fall of t.sub.B over the same time window (region inside the dashed line I) since a dust deposition results in a darkening of the image.

[0061] The profile of ϑ.sub.M in a dust deposition is in principle characterized in that the measured value changes more rapidly than would in fact be possible given the heat capacity of the silicon rods and the control path of the temperature control circuits. After a renewed phase of constancy (about 10 minutes) there was a significant fall in ϑ.sub.M in conjunction with a steep rise in t.sub.B. This abnormal curve profile was a complete dust deposition.

[0062] In a temporary dust deposition the process may recover when as a result of the gas flow more particles are discharged from the reactor via the exhaust gas than new particles are formed. However, when too many dust particles are formed in the reactor these can no longer be discharged from the reactor by the gas flow. When the reaction gas supply remains unchanged and heat input remains unchanged or is even increased, more dust particles are deposited than are blown out of the system and a permanent darkening of the reactor atmosphere results.

[0063] The irregularities in ϑ.sub.M and t.sub.B especially make it possible to determine a haze index according to which countermeasures are then taken (manually or automatically) to prevent the dust deposition.