A method for manufacturing polycrystalline silicon chunks for recharge.

Abstract

To provide such a polycrystalline silicon mass for recharging that it is difficult for a foreign matter adhering or adsorbing to the surface of the polycrystalline silicon mass upon recharging to mix into melt.SOLUTION: There is provided such a polycrystalline silicon mass for recharging that a foreign matter adhering or adsorbing to the surface of the acid-cleaned polycrystalline silicon mass is removed by irradiation of a laser beam having a wavelength of 1,060 nm-1,080 nm. Preferably, the foreign matter is a compound containing at least one kind of element selected from B (boron), C (carbon) and P (phosphorous).SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a polycrystalline silicon block for recharge, which is used to add and charge a polycrystalline raw material (hereinafter referred to as "recharge") when pulling and manufacturing a silicon single crystal for producing a silicon single crystal wafer used as a semiconductor integrated circuit substrate by the Czochralski (CZ) method. Manufacturing method Regarding. [Background technology]

[0002] In recent years, in order to reduce the manufacturing cost of silicon single crystals, a method called multi-pulling using the CZ method has become widespread (see, for example, Patent Document 1 (claim 7, page 4, lines 14-18)). In this multi-pulling method, the grown single crystal is removed from a single crystal manufacturing apparatus, a recharge tube holding solid raw materials is introduced into the single crystal manufacturing apparatus, the entire surface of the remaining melt in the crucible is solidified by lowering the heating power of the heater, and then the solid raw materials in the recharge tube are filled onto the solidified surface while increasing the heating power of the heater, the recharge tube is removed from the single crystal manufacturing apparatus, and then all the solid raw materials in the crucible are melted, and single crystal growth is performed again to grow multiple single crystals.

[0003] According to this method, raw materials can be easily loaded and removed from the single crystal manufacturing equipment without the need to install a conventional raw material supply device, and solid raw materials can be directly added to the solidified molten surface in the crucible.Moreover, a supply speed suitable for recharging is achieved, and recharging can be performed smoothly and efficiently in a short time, which is said to improve single crystal productivity.

[0004] As polycrystalline silicon chunks, which are solid raw materials used in such multi-pulling methods, normal pulling methods, or float zone (FZ) methods using zone melting, polycrystalline silicon chunks having a surface boron concentration of 1 to 50 ppta and a phosphorus concentration of 1 to 50 ppta (see Patent Document 2 (Claim 1, paragraphs

[0038] , and paragraphs

[0050] to

[0099] )) and chunk polycrystalline silicon having a surface carbon concentration of 0.5 to 35 ppbw (see Patent Document 3 (Claim 1, paragraphs

[0040] to

[0103] )) are disclosed.

[0005] The polycrystalline silicon chunks shown in Patent Document 2 are obtained through the steps of a) depositing polycrystalline silicon in a Siemens reactor, b) crushing the polycrystalline silicon, c) cleaning the polycrystalline silicon fragments, and d) packaging the polycrystalline silicon fragments. In particular, in c) cleaning the polycrystalline silicon fragments, the polycrystalline silicon fragments are washed with an oxidizing cleaning solution in the preliminary purification, washed with a cleaning solution containing nitric acid and hydrofluoric acid in the main purification, and further washed with an oxidizing cleaning solution in the hydrophilization. In the invention disclosed in Patent Document 2, dopants (B, P, As, Al) are analyzed for FZ single crystals produced from polycrystalline materials (SEMI MF 1723) by photoluminescence analysis according to SEMI MF 1398.

[0006] The chunk polycrystalline silicon shown in Patent Document 3 is obtained through the steps of a) deposition of polycrystalline silicon in a Siemens reactor, b) pulverization of polycrystalline silicon, c) cleaning of polycrystalline silicon by heat treatment, and d) wet chemical cleaning of polycrystalline silicon, and e) packaging of polycrystalline silicon. In particular, in c) cleaning of polycrystalline silicon by heat treatment, polycrystalline silicon having carbon contamination on the surface is heat treated under an inert gas atmosphere in a reactor at a temperature of 350 to 600°C to clean it. The polycrystalline silicon after the heat treatment has a surface carbon concentration of 0.5 to 35 ppbw. In d) wet chemical cleaning of polycrystalline silicon, the polysilicon chunks are washed with an oxidizing cleaning solution in the pre-purification operation, washed with a cleaning solution containing nitric acid and hydrofluoric acid in the main purification operation, and further washed with an oxidizing cleaning solution in the hydrophilization. The quantitative determination of the surface carbon content of polycrystalline silicon shown in US Pat. No. 5,399,633 is carried out with a modified RC612 carbon analyzer from Leco Corporation, USA, by complete oxidation of all surface carbon contamination with oxygen to carbon dioxide. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] International Publication No. 2002 / 068732 [Patent Document 2] JP 2013-151413 A [Patent Document 3] JP 2013-170122 A [Non-patent literature]

[0008] [Non-Patent Document 1] Carl L. Yaws et al., “Process Feasibility Study in Support of Silicon Material Task I” DOE / JPL / 954343 (1981) [Non-Patent Document 2] Hiroo Miyabe, "Self-modulation of laser light at short wavelengths absorbed by silicon", Ryukoku Journal of Science and Technology No. 76, vol. 31-1 Supplement (2018) Summary of the Invention [Problem to be solved by the invention]

[0009] As shown in Patent Document 1, when a polycrystalline silicon lump, which is a solid raw material, is recharged in a crucible and melted, the volatilization or evaporation time of the components adsorbed on the surface of the polycrystalline silicon lump is shorter than when the polycrystalline silicon lump is filled in the crucible from the beginning and melted, and the adsorbed components are more likely to be incorporated into the melt. Conventionally, even in standards such as SEMI, elements such as B (boron), C (carbon), and P (phosphorus) present on the surface of polycrystalline silicon are not defined, and it is considered that contamination by elements that vaporize during heating in the conventional method of initially filling and then heating has become a problem in the recharge method. For this reason, it has been required that the polycrystalline silicon lump for recharge contains fewer components that are easily volatilized during melting, such as B (boron), C (carbon), P (phosphorus), and As (arsenic).

[0010] The invention shown in Patent Document 2 provides polycrystalline silicon with little surface contamination, and is said to have little volatile components, but the numerical ranges of surface B and P concentrations defined in this invention have technical problems, and the analytical values ​​of highly volatile components are questionable. For the general surface metal concentration of polysilicon, SEMI MF 1724 specifies a method of dissolving with acid and analyzing it. However, B and P cannot be measured by this method. Therefore, in the invention shown in Patent Document 2, the surface concentration is calculated by comparing the photoluminescence analysis values ​​(SEMI MF1389) of a sample with equivalent bulk B and P concentrations and a sample obtained by single crystallizing the sample to be analyzed by the FZ method.

[0011] However, in the invention shown in Patent Document 2, the surface contamination of the "brother rod" to be compared is not evaluated and is considered to be zero. In addition, since heating and melting are required when single crystallizing by the FZ method and some of the surface adsorbed B and P scatters, it is thought that the relative concentration difference between single crystal silicon produced by the FZ method under the same conditions is qualitatively reflected. Therefore, although the evaluation method shown in Patent Document 2 may be reproducible, the obtained numerical value includes the fluctuation of the conditions in the FZ method, so it cannot be said to universally indicate the surface contamination level of the sample, and it is questionable whether the contamination level according to the analysis value can be guaranteed when the polycrystalline silicon lump shown in Patent Document 2 is used for recharging.

[0012] The invention shown in Patent Document 3 claims that the surface carbon concentration can be reduced to 0.5 to 35 ppbw by performing heat treatment in an inert gas atmosphere at a temperature of 350 to 600° C. However, this method may cause contamination other than carbon during heating and cooling, and requires cleaning with an oxidizing cleaning solution after the heat treatment.

[0013] In addition, polycrystalline silicon is crushed and processed to an appropriate size for easy use, but since silicon is a brittle material and polycrystalline, its surface is easily uneven, and sharp blade marks are easily formed. For this reason, when members, jigs, etc. come into contact with the polycrystalline silicon surface during the processing process, wear powder from the members, jigs, etc. is likely to adhere as foreign matter. In addition, when silicon is crushed, fine cracks may be formed on the surface, and if foreign matter adheres to such cracks, it is difficult to remove the foreign matter. For this reason, in the above-mentioned processing with the oxidizing cleaning solution, the need to increase the amount of silicon dissolved by etching the silicon surface and the processing time also increase. As a result, the cost increases and productivity decreases due to the increase in the amount of oxidizing cleaning solution used. In addition, this also leads to an increase in silicon loss due to etching, which leads to a decrease in the yield of polycrystalline silicon and an increase in processing costs. In addition, even in the method using heat treatment, if the amount of adhesion is large or the adhesion is strong, it takes time to heat and evaporate, and as a result, the processing time is likely to be long.

[0014] The object of the present invention is to provide a polycrystalline silicon block for recharging in which foreign matter adhering to or adsorbed on the surface of the polycrystalline silicon block during recharging is unlikely to be mixed into the melt. Manufacturing method The purpose of this invention is to provide In this case, the foreign matter attached to or adsorbed on the surface is assumed to be so-called outgassing contamination arising from substances surrounding the polycrystalline silicon chunk. This refers to substances that are solid at room temperature but volatilize by reacting with molecular substances that have a slight vapor pressure or slight acidity contained in the air, and which are attached to or adsorbed on the polycrystalline silicon surface after acid cleaning. [Means for solving the problem]

[0015] A first aspect of the present invention is a polycrystalline silicon chunk for recharge, obtained by removing foreign matter adhering to or adsorbed on the surface of an acid-washed polycrystalline silicon chunk by irradiation with laser light having a wavelength of 1060 nm to 1080 nm.

[0016] A second aspect of the present invention is an invention based on the first aspect, which is a polycrystalline silicon block for recharging, in which a foreign matter attached or adsorbed to the surface of the polycrystalline silicon block is a compound containing at least one element selected from B (boron), C (carbon) and P (phosphorus). Effect of the Invention

[0017] The polycrystalline silicon block for recharging according to the first aspect of the present invention has been acid washed and any foreign matter adhering to or adsorbed on its surface has been removed by irradiation with laser light having a wavelength of 1060 nm to 1080 nm, thereby having the advantage that the foreign matter is less likely to be mixed into the molten liquid during recharging.

[0018] The polycrystalline silicon block for recharging according to the second aspect of the present invention has a feature in that the foreign matter adhering to or adsorbed on its surface is a compound containing at least one element selected from B (boron), C (carbon) and P (phosphorus), and is removed by laser light, so that the foreign matter is less likely to be mixed into the molten liquid during recharging. [Brief description of the drawings]

[0019] [Figure 1] 1 is a perspective view showing a state in which a plurality of polycrystalline silicon chunks placed in a container according to a first embodiment of the present invention are being cleaned by a laser cleaning device. [Diagram 2] 1 is an enlarged cross-sectional view showing a state in which a polycrystalline silicon chunk placed in a container according to a first embodiment of the present invention is being laser cleaned. FIG. [Diagram 3] FIG. 2 is a plan view showing a state in which a laser beam of the laser cleaning device according to the first embodiment of the present invention is moved in a direction perpendicular to a straight scanning line. [Figure 4] FIG. 2 is a plan view showing a state in which a laser beam of the laser cleaning device according to the first embodiment of the present invention is moved in a direction oblique to a straight scanning line. [Diagram 5] 13 is a diagram showing a state in which a polycrystalline silicon chunk placed in a container in which a liquid moves is irradiated with laser light in a second embodiment of the present invention. FIG. [Figure 6] FIG. 2 is a GC chart in Example 1 measured by a thermal desorption gas chromatograph mass spectrometer. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Next, an embodiment of the present invention will be described with reference to the drawings. The number of polycrystalline silicon chunks shown in the following Figs. 1 to 5 is an example, and is not limited to this number, and can be increased as necessary.

[0021] <First embodiment> The polycrystalline silicon block for recharging in this embodiment is acid-washed with a chemical solution such as fluoronitric acid and dried, and then foreign matter attached or adsorbed to the surface is removed by a laser cleaning device described below. As shown in Fig. 1, this laser cleaning device 10 includes a processing head 11 and a main body control unit 12. The main body control unit 12 includes a laser oscillator 13 and a control unit 14 that controls the processing head 11 and the laser oscillator 13. The processing head 11 includes a built-in galvano scanner (not shown) that rotates and controls an axis to which a reflecting mirror that reflects pulsed laser light from the laser oscillator 13 is attached.

[0022] A container 1 with an open top is placed below the laser cleaning device 10, and multiple polycrystalline silicon chunks 2 (seven in FIG. 1) are placed in the container 1 without overlapping as objects to be cleaned. Foreign matter 4 is attached to the surfaces of these polycrystalline silicon chunks 2 as shown in FIG. 2. Examples of foreign matter include impurities that are invisible to the naked eye, such as organic matter. In FIG. 2, the same elements as in FIG. 1 are given the same reference numerals. Note that instead of the container 1 on which the polycrystalline silicon chunks are placed, a table 5 with a flat surface may be used as shown in FIGS. 3 and 4. The material of the container 1 or table 5 may be resin, paper, or the like, in addition to quartz or silicon.

[0023] The processing laser light source of the laser cleaning device 10 must have a wavelength that is absorbed by silicon, and a narrow pulse width laser light source is suitable from the viewpoint of foreign matter removal efficiency because it can heat only the surface area. From this viewpoint, pulse lasers such as Nd:YAG (1064 nm) and Yb:fiber (1060 nm to 1080 nm), which are widely used in industry, can be cited as practically usable laser light sources. The wavelengths of the Nd:YAG and Yb:fiber lasers mentioned above have energies close to the band gap of silicon, so they penetrate slightly into the silicon block and are absorbed in the surface layer of the silicon block, heating the silicon block. As a result, impurities adsorbed on the surface of the silicon block can be volatilized and removed.

[0024] The intensity of the laser light from the laser cleaning device 10 is 500 kJ / m 2 The following is preferable, but cannot be determined in general terms for reasons described later. It is believed that the impurities are volatilized by the surface temperature of the silicon block rising instantaneously to 300°C to 600°C due to the irradiation of the laser light, and if a laser light with a short pulse width is used, the heated area is limited, so the intensity of this laser light is 1 kJ / m 2 Even if the amount is only a small amount, it is possible to expect the effect of removing impurities. The silicon chunks are irregularly shaped fragments, and it is practically difficult to irradiate the entire surface of the silicon chunks with laser light uniformly and completely. In order to remove impurities on the surface of the silicon chunks, the area of ​​the silicon chunks to be irradiated with the laser light is preferably at least 80% of the surface area of ​​the silicon chunks. It is more preferable that it is 95% or more. The reason for specifying 80% or more of the surface area is that the silicon chunks are irregularly shaped fragments, and it is practically difficult to irradiate the surface uniformly and completely, and 80% or more is the preferred area as the limit at which the effect can be obtained. To achieve this, for example, a method can be used in which the silicon chunks are arranged without overlapping on a table that transmits laser light, such as quartz glass, and the laser light is irradiated from both the top and bottom.

[0025] In the laser cleaning device 10 configured as described above, it is preferable to rotate and control the axis in the galvano scanner to scan the laser light 3 reflected by the galvano scanner in the processing head 11 in the Y-axis direction in FIG. 1 to form a scanning line 6. In the cleaning method of the present embodiment, the laser light 3 is irradiated so that the scanning line 6 covers the entire Y-axis direction of a plurality of polycrystalline silicon chunks 2 (two or three in FIG. 1) as shown in FIG. 1. While forming the scanning line 6, the processing head 11 is moved in the X-axis direction in FIG. 1 perpendicular to the scanning line 6, to laser clean the surfaces of all of the polycrystalline silicon chunks 2 (seven in FIG. 1). The processing head 11 may be moved back and forth in the X-axis direction, or the polycrystalline silicon chunks 2 in the container may be turned over, and irradiation with the scanning line 6 of the laser light 3 may be repeated.

[0026] As the scanning line 6 of the laser light 3 moves in the X-axis direction, as shown in Figure 2, foreign matter 4 attached or adsorbed to the surface of the polycrystalline silicon block 2 absorbs the laser light 3 and evaporates, or is subjected to the impact pressure of the plasma 7 and is removed from the surface of the polycrystalline silicon block 2.

[0027] The machining head 11 may be moved not only in a direction perpendicular to the scanning line 6 of the laser light 3 as shown in Fig. 3, but also in a direction oblique to the scanning line 6 as shown in Fig. 4 in accordance with the position where the polycrystalline silicon block 2 is placed. In Figs. 3 and 4, the same elements as in Fig. 1 are given the same reference numerals. Although not shown, instead of moving the machining head 11, the machining head 11 may be fixed and the stage 5 may be moved.

[0028] <Second embodiment> As shown in FIG. 5, multiple acid-cleaned polycrystalline silicon chunks 2 (six in FIG. 5) are arranged in a container 8 so as not to overlap. In a second embodiment, the polycrystalline silicon chunks before laser cleaning may be acid-cleaned and then dried without being subjected to the same steps. In FIG. 5, the same elements as in FIG. 1 are given the same symbols. A liquid 9 such as pure water, ultrapure water, ion-exchanged water, etc. is stored in the container 8. A supply pipe 8a for the liquid 9 is connected to the lower right side of the container 8, and a discharge pipe 8b for the liquid 9 is connected to the upper left side of the container 8. The height of the discharge pipe 8b is set so that the liquid level in the container 8 is higher than the top ends of the multiple polycrystalline silicon chunks 2 arranged in the container, so that the polycrystalline silicon chunks 2 in the container are always in the liquid. A processing head (not shown in Figure 5) of the laser cleaning device is provided above this container 8, and the laser light 3 reflected by the processing head is configured to move in the direction indicated by the arrow in Figure 5 while forming a straight scanning line.

[0029] In a laser cleaning device configured as described above, first, liquid 9 is supplied to container 8 through supply pipe 8a and discharged through discharge pipe 8b, so that liquid 9 moves within container 8. Next, laser light 3 is irradiated from the processing head onto the surfaces of multiple polycrystalline silicon chunks 2 arranged in container 8. The laser light 3 spreads over the upper surfaces of all polycrystalline silicon chunks 2 in container 8 as the processing head moves, forming a straight scanning line. This removes foreign matter from the upper surfaces of all polycrystalline silicon chunks 2. The removed foreign matter floats in the liquid, but is transported by the moving liquid and discharged from discharge pipe 8b. This prevents the foreign matter from re-adhering to the surfaces of polycrystalline silicon chunks 2.

[0030] In the above-mentioned container 8, the discharge pipe 8b is provided at the top of the container, but as an example, the discharge pipe 8c may also be provided at the bottom end of the container, as shown by the dashed line in Fig. 5. By using this discharge pipe 8c, foreign matter that does not float in the liquid can be transported from the bottom side of the container to the outside of the container 8 by the moving liquid.

[0031] As a result of carrying out and analyzing various experiments in addition to the examples described below, the theoretical basis of the present invention is considered to be as follows. First, the reduction in contamination does not necessarily depend on the intensity of the laser light (W / m 2 ) is not proportional to the concentration of contamination in the polycrystalline silicon block that is cleaned by laser cleaning. This is because the degree of contamination that is removed depends on the form in which the foreign matter is attached, and because the heat of the irradiated laser light escapes into the silicon block, resulting in a loss of energy from the laser light.

[0032] For example, there is a possibility that a small amount of phosphorus may remain in the oxide film even after acid cleaning, and since this is tightly bound, it is thought that it cannot be removed by laser irradiation. On the other hand, the phosphorus that was intentionally attached to the surface of the silicon block by leaving it in the clean room was attached from the gas phase and is thought to be attached in the form of molecules with a relatively high vapor pressure, and is thought to be easily removed by irradiation with laser light. In addition, as for boron, which was also contaminated in the clean room, it is thought that the removal effect may be low because it is a compound with a lower vapor pressure than phosphorus.

[0033] The boiling points of the organic molecules detected in outgassing contamination vary widely, from the 100°C range to over 600°C, but it is believed that the removal effect will be achieved if the surface temperature of the silicon block reaches 300°C to 600°C.

[0034] The pulse width of the laser used in the embodiment is estimated to be slightly more than 100 ns. The average diffusion length of heat in silicon can be calculated from this pulse width as follows: Using the thermal diffusivity a=λ / ρCp equation from the physical properties of silicon (25°C) listed below in Non-Patent Document 1, the thermal diffusivity a is 0.89 [cm 2 / s]. Thermal conductivity λ=0.353 [cal / sec cm °C] Density ρ=2.329 [g / cm 3 ] Specific heat Cp=4.78 [cal / gr-mol°C] The average heat diffusion distance x is generally x = (2ατ) 1 / 2(α: thermal transfer rate, τ: heating time ≒ laser beam passing time). By substituting the value of the thermal diffusivity a for α in this formula, the average diffusion distance of heat in silicon is calculated to be about 4 μm with a pulse width of 100 ns. The light transmittance cannot be accurately estimated because reliable data is not available on the part that strongly depends on the wavelength, but the penetration depth is estimated to be 100 μm to several hundred μm. At this time, the energy of the laser light is considered to be absorbed to a depth of 100 μm to several hundred μm from the surface of the silicon lump, although some of it is lost through reflection. However, there are also reports that this transmittance varies greatly depending on the temperature and the intensity of the laser light (see Non-Patent Document 2), and from this report, it is considered that the light may penetrate to a depth of 1 mm or more in some cases. On the other hand, it is considered possible to concentrate it to 10 μm or less. Therefore, if it is possible to absorb it to a depth of 1 μm from the surface of the silicon lump, the intensity of the laser light is 1 kJ / m 2 Even if the laser is turned on, the temperature rise is calculated to be about 600K. By optimizing the wavelength, pulse width, temperature, etc., the laser light intensity can be increased to 1 to several kJ / m 2 Even if the amount is only a small amount, it is expected to be effective in removing contamination from silicon chunks.

[0035] In the results of the examples described below, the laser light was not optimized, and it is believed that the effect of reducing contamination on the surface of the silicon block was somewhat incomplete, with the surface temperature only being heated to below 300° C. However, conversely, when used as a recharge raw material, it is believed that a volatile surface contamination removal effect equivalent to that of the initially charged raw material is obtained, which led to the present invention. Based on this idea, it is sufficient for the intensity of the irradiated laser light to obtain the effect shown in the examples, and it is preferable to irradiate it at an intensity as low as possible. In order to obtain the effect of laser cleaning, it is preferable that the pulse width is narrow so that the absorption rate near the surface is high, and although it is difficult to quantitatively express the wavelength and intensity with high absorption efficiency because it is possible that the absorption efficiency changes due to two-photon absorption and self-heating, it is preferable that the laser light has a wavelength and intensity with high absorption efficiency.

[0036] When compared with conventional methods of heating and removing the polycrystalline silicon, the laser cleaning of the present invention is superior in that the temperature rise of the polycrystalline silicon chunk itself is small, thereby effectively avoiding contamination from contact parts, etc., and the polycrystalline silicon chunk obtained by this laser cleaning has the advantage that foreign matter adhering to or adsorbed on the surface of the polycrystalline silicon chunk is less likely to mix with the molten liquid during recharge. EXAMPLES

[0037] Next, examples of the present invention will be described in detail together with comparative examples. First, we will explain Example 1 in which a polycrystalline silicon lump sample that had been acid-washed and dried was irradiated with laser light, and Comparative Example 1 in which laser light was not irradiated. Next, we will explain Example 2 in which a polycrystalline silicon lump sample that had been acid-washed and dried was left in a clean room to be forcibly contaminated, and then irradiated with laser light, and Comparative Example 2 in which laser light was not irradiated.

[0038] <Example 1> Thirty-two samples of polycrystalline silicon chunks with long side lengths of 10 mm to 40 mm were etched and cleaned with fluoronitric acid, rinsed with pure water, and then dried. As in FIG. 1 showing seven silicon chunk samples, although not shown, 32 dried polycrystalline silicon chunk samples were arranged on a silicon table. In this state, cleaning was performed using a laser cleaning device (product name: Eraser, manufactured by Tosei Electrobeam Co., Ltd.). As a result, 32 samples of Example 1 were obtained. Since volatile gases were generated during cleaning, a suction hood was brought close so that the generated gases could be sucked in.

[0039] As shown in Figure 1, during cleaning, the surface of the polycrystalline silicon block was irradiated with a pulsed laser beam (wavelength 1060nm to 1080nm, pulse frequency 55kHz) with an average output of 63W while scanning linearly at a speed of 3900mm / s, and the container was moved back and forth twice at a speed of 165mm / min in a direction perpendicular to the scanning line of the laser beam. Here, the pulse width was not specified because the device was commercially available, but it was evaluated to be about 100ns. The amplitude of the laser beam was set to 50mm. After two round trips were completed, the polycrystalline silicon block was turned over and irradiated with the laser beam in the same manner.

[0040] <Comparative Example 1> As in Example 1, 32 samples of polycrystalline silicon chunks with long side lengths of 10 mm to 40 mm sampled from the same production lot as the 32 samples of Example 1 were etched and cleaned with fluoronitric acid, rinsed with pure water, and then dried. The 32 dried polycrystalline silicon chunk samples were not laser cleaned. As a result, 32 samples of Comparative Example 1 were obtained.

[0041] <Comparative test 1 and evaluation> Of the 32 samples obtained in each of Example 1 and Comparative Example 1, the surface carbon concentration of four samples from each was measured using a thermal desorption gas chromatograph / mass spectrometer (TD-GC / MS), and the average value was calculated. The number of measurements, N, was 3. Of the 32 samples, 10 samples were taken from each sample in the number required for measuring the surface boron concentration and phosphorus concentration, and then they were eluted with 2 wt% HF and the surface boron concentration and surface phosphorus concentration were measured by ICP-MS (Inductively Coupled Plasma Mass Spectrometry) to calculate the average value. The number of measurements, N, was 2. The concentrations of carbon, boron, and phosphorus on the sample surface under each condition are shown in Table 1 below.

[0042] [Table 1]

[0043] As is clear from Table 1, the carbon concentration of the measured sample surface was 0.57 ppmw in Comparative Example 1, whereas it was low at 0.20 ppmw in Example 1. On the other hand, the boron concentration of the sample surface was 0.002 ppbw in both Example 1 and Comparative Example 1, and the phosphorus concentration of the sample surface was less than 0.010 ppbw in both Example 1 and Comparative Example 1, with no difference being observed. This suggests that the boron concentration and phosphorus concentration were both contaminated at levels close to the analytical limit of the ICP-MS even before laser cleaning.

[0044] GC charts measured by a thermal desorption gas chromatograph mass spectrometer used in the comparative test in Example 1 and Comparative Example 1 are shown in FIG. 6. From these GC charts, it was found that highly volatile impurities that can be removed by irradiation with laser light include caprolactam, TXIB (2,2,4-trimethyl-1,3-pentanediol diisobutyrate), C 19 H 40 The boiling points of these components were 267°C, 280°C, and 330°C, respectively, and it can be determined from the GC positions of the peaks of other unidentified components that compounds with boiling points of 400°C or less were also removed.

[0045] The current quality level for carbon (C) as a surface impurity is about 0.01 ppmw, whereas phosphorus (P) and boron (B) require a quality level of 0.001 ppba. In the analysis of Example 1, compounds of P and B were not detected, but organic compounds containing C were detected, so it was presumed that boron compounds and phosphorus compounds, which have similar vapor pressures, were also removed.

[0046] <Example 2> Forty samples of polycrystalline silicon chunks with long side lengths of 10 mm to 40 mm sampled from the same production lot as the 32 samples of Example 1 were etched and cleaned with fluoronitric acid, rinsed with pure water, and dried in the same manner as in Example 1. Then, the samples were left in a clean room for 24 hours. Twenty of the polycrystalline silicon chunks left in the clean room were laser cleaned in the same manner as in Example 1 to obtain samples of Example 2.

[0047] <Comparative Example 2> As samples of Comparative Example 2, 20 polycrystalline silicon chunks similar to those in Example 2 were prepared, except that laser cleaning was not performed.

[0048] <Comparative test 2 and evaluation> The boron and phosphorus concentrations on the sample surfaces were measured and average values ​​were calculated for 10 samples of Example 2 and 10 samples of Comparative Example 2 using the same method as in Example 1 and Comparative Example 1. The number of measurements, N, was 2. The results are shown in Table 2 below.

[0049] [Table 2]

[0050] As is clear from Table 2, the boron concentration on the sample surface in the measured sample was "0.010 ppbw" in Example 2, which was slightly lower than "0.011 ppbw" in Comparative Example 2. Also, the phosphorus concentration on the sample surface was "0.012 ppbw" in Example 2, which was significantly lower than "0.041 ppbw" in Comparative Example 2. From these findings, it was confirmed that laser cleaning was effective in removing forcibly contaminated boron and phosphorus.

[0051] From the comparative test of Example 2 and Comparative Example 2, it was inferred that the boron concentration and phosphorus concentration on the sample surface were low even in Example 1, where the effect of laser cleaning could not be confirmed due to the level of contamination near the analytical limit of the ICP-MS. [Industrial Applicability]

[0052] The polycrystalline silicon chunks of the present invention can be utilized for recharging. [Explanation of symbols]

[0053] 1,8 container 2. Polycrystalline silicon block 3. Laser light 4 Foreign object 5 units 6 Scanning Line 7. Plasma 9 liquid 10 Laser cleaning device 11 Processing head 12 Main unit control section 13 Laser Oscillator 14 Control section

Claims

1. removing foreign matter adhering to or adsorbed on the surface of the acid-washed polycrystalline silicon block by irradiating the surface with a laser beam having a wavelength of 1060 nm to 1080 nm; A method for producing polycrystalline silicon chunks for recharge, characterized in that the C (carbon) content is 0.20 ppmw or less, the B (boron) content is 0.010 ppbw or less, and the P (phosphorus) content is 0.012 ppbw or less.

2. A method for producing polycrystalline silicon chunks for recharging as described in claim 1, wherein the foreign matter attached or adsorbed to the surface of the polycrystalline silicon chunks is a compound containing at least one element selected from B (boron), C (carbon) and P (phosphorus).

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