Polysilicon rod and polysilicon rod manufacturing method

Abstract

To provide a polysilicon rod or the like improved in single crystallization failure of an FZ method by specifying the size of a grain boundary face and the corresponding grain boundary ratio, which are features of a grain boundary, the interface between particles.SOLUTION: In a polysilicon rod, an average of grain boundary features in an area of 2 / 3 from a cross-sectional center of the polysilicon rod, the area excluding a core, has the following characteristics: a corresponding grain boundary ratio exceeds 20%, a grain boundary length exceeds 550 mm / mm2, and a random grain boundary length does not exceed 800 mm / mm2.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a raw material polysilicon for improving the defect rate in single crystal production, and a method for producing the same. [Background technology]

[0002] In the manufacturing of semiconductor devices, the manufacturing process of single crystal silicon must maintain productivity by controlling impurities and lattice defects. Currently, the mainstream single crystal manufacturing methods include the FZ (Floating Zone) method and the CZ (Czochralski) method. Of these, the FZ method is a polycrystalline silicon method. This method involves directly heating a reconnecting rod with high-frequency heating to obtain a single crystal, and has advantageous features for impurity control compared to the CZ method, which uses a quartz crucible.

[0003] In the FZ method, defects occur when single crystal growth is hindered, causing dislocations and resulting in crystal defects in the single crystal rod. One of the causes of single crystal growth inhibition is the phenomenon of polysilicon remaining unmelted, causing defects.

[0004] In this FZ method, the crystal characteristics of the raw material polysilicon rod used are closely related to the defects in the FZ that occur during single crystal production.

[0005] In the single crystal growth process of the FZ method, the occurrence of FZ defects is a major issue because it significantly reduces productivity.

[0006] The production of polysilicon rods as raw materials for the FZ method is mainly carried out using the Siemens method, which is a CVD method in which the raw material silane gas is deposited in air on a heated silicon rod. do.

[0007] Patent documents 1 to 4 disclose polysilicon rods characterized by the area ratio of needle-like crystals and coarse grains and the size of crystal grains. Patent documents 5 to 7 disclose polysilicon rods characterized by the Miller indices obtained by X-ray diffraction. <111> or <220> In Patent Document 8, a method of selecting a single crystal raw material based on the peak intensity or number of peaks is disclosed. <222> A polysilicon rod characterized by a diffraction intensity of [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2008-285403 A [Patent Document 2] JP 2013-193902 A [Patent Document 3] JP 2014-28747 A [Patent Document 4] JP 2017-197431 A [Patent Document 5] JP 2013-217653 A [Patent Document 6] JP 2015-3844 A [Patent Document 7] JP 2016-150885 A [Patent Document 8] JP 2019-19010 A DISCLOSURE OF THEINVENTION [Problem to be solved by the invention]

[0009] (1) None of the methods in Patent Documents 1 to 8 provide high quantitativeness and reproducibility. This is because the cause of poor single crystallization in the FZ method is the large particles of polysilicon (whose size, distribution, and crystal orientation are not consistent). This is because the focus has been on the following factors:

[0010] The present invention provides a polysilicon rod etc. in which the single crystallization failure caused by the FZ method is improved by the grain boundary width and the ratio of coincident grain boundaries, which are characteristics of the grain boundaries corresponding to the boundaries between particles.

[0011] For example, the silicon rod with the largest crystal grain is a single crystal silicon rod. When considering a model of crystallizing this single crystal by the FZ method, the defect rate due to the raw material can be said to be zero. When this single crystal is divided, grain boundaries appear. The corresponding grain boundary closest to the single crystal bond is Σ3, and the corresponding lattice point A grain boundary that has no or no regularity is a random grain boundary, and a grain boundary that contains a lot of Σ3, which is the bonding surface closest to a single crystal, can be said to be close to a single crystal.

[0012] (2) Bell jar type reactors are generally used for CVD reactions using the Siemens process. The inner wall of the reactor receives radiation from the heated rod, and if the inner wall is mirror-like, it has a high reflectivity and returns the radiant energy from the rod to the rod. However, if the inner wall becomes cloudy, the reflectivity decreases, and the energy absorbed by the wall increases, and it is not returned to the rod. The cause of the cloudiness is that the raw material chlorosilanes undergoes hydrolysis with moisture in the air when the reactor is opened between batches, and the reflectivity tends to decrease with each batch. This makes it difficult to always produce polysilicon rods under the same conditions, and by feeding back the grain boundary characteristics of the previous batch to the reaction conditions of the next batch, it is possible to produce polysilicon with the desired grain boundaries. [Means for solving the problem]

[0013] The inhibiting factor for single crystallization by the FZ method is the characteristics of the grain boundaries. By measuring and analyzing these and feeding them back to the manufacturing conditions, it becomes possible to manufacture polysilicon rods suitable for single crystallization by the FZ method.

[0014] Looking at the single crystallization process using the FZ method, the area near the center of the polysilicon rod reaches the single crystal growth surface immediately after melting, and is therefore susceptible to the effects of grain boundaries, whereas the area near the periphery of the polysilicon rod passes through a heating zone created by induced current, and is therefore less affected than the area near the center.

[0015] Specifically, the central area during single crystallization by the FZ method should preferably have a short random grain boundary length and a long grain boundary length, and as it moves away from the center, a shorter grain boundary length is acceptable.

[0016] Therefore, in the region excluding the seed core among the 2 / 3 region from the center of the cross section of the polysilicon rod, The average of the coincidence grain boundary ratio exceeds 20% and the grain boundary length is 550 mm / mm 2 of which the random grain boundary length is over 800 mm / mm 2 It is advantageous to have a rod containing no more than 100% polysilicon. The ratio exceeds 25% and the grain boundary length is 650 mm / mm 2 of which the random grain boundary length is greater than 700 mm / mm 2 Polysilicon rods not exceeding 1000 μm are preferred.

[0017] When applied to the entire polysilicon rod, the average of the entire polysilicon rod excluding the seed core has a corresponding grain boundary ratio of more than 20% and a grain boundary length of 550 mm / mm 2 of which the random grain boundary length is over 800 mm / mm 2 It is advantageous to have a rod containing no more than 100% polysilicon. The ratio exceeds 25% and the grain boundary length is 650 mm / mm 2 of which the random grain boundary length is greater than 700 mm / mm 2 Polysilicon rods not exceeding 1000 μm are preferred.

[0018] The closer the coincidence grain boundary ratio is to 100%, the better, but this manufacturing condition is close to epitaxial growth, and the cost merit is poor with current technology. Also, when trying to make the grain boundary length longer, the random grain boundary length is set to 700 mm / mm 2 To keep it below this level, the proportion of corresponding grain boundaries must also be large. Length 3000mm / mm 2 The following is realistic.

[0019] As mentioned above, in the Siemens method of manufacturing polysilicon rods, the environment inside the reactor gradually changes, so polysilicon is analyzed at regular intervals and the results are used to determine the CVD conditions. It is possible to feed back the results to the manufacturing conditions. The coincident grain boundary ratio, which is a characteristic of the grain boundary, the grain boundary length, which is an index of the grain boundary width, and the random grain boundary length obtained from these are quantitative values, and are characterized by being able to be correlated with the manufacturing conditions. In addition, in product design, it becomes possible to control the grain boundary characteristics from the inner circumference to the outer circumference of the polysilicon rod, making it possible to provide polysilicon rods that meet the customer's requirements. Effect of the Invention

[0020] According to one aspect of the present invention, 1. The FZ method makes it possible to reduce the rate of single crystallization defects, improve yields, and increase productivity. 2. Feedback from grain boundary characteristics to manufacturing conditions makes it possible to stably produce polysilicon rods. [Brief description of the drawings]

[0021] [Figure 1] FIG. 1 is a diagram showing the relationship between grain boundary length and coincident grain boundary ratio. [Diagram 2] A graph showing the relationship between grain boundary length and the Σ3 coincidence grain boundary ratio. [Diagram 3] A figure showing images of a Σ3 coincidence grain boundary, a Σ9 coincidence grain boundary, a random grain boundary, and a Σ3-49 coincidence grain boundary. [Figure 4] FIG. 1 is a schematic diagram for explaining an overview of a measurement method 1 in an embodiment of the present invention. [Diagram 5] FIG. 2 is a schematic diagram for explaining an overview of a measurement method 2 in an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] A horizontal plane perpendicular to the growth direction of the polysilicon rod is cut out, and the crystal orientation of all the crystal grains exposed on the measurement surface is measured using EBSD (electron backscatter diffraction) at 1μm intervals. The state of the grain boundary is calculated from the difference in the orientation and angle of adjacent crystals in the obtained data matrix. A Σ3 correspondence grain boundary is a grain boundary where one correspondence lattice point appears for every three atoms. The grain boundary has many corresponding lattice points, which means that the thermal and physical properties of the grain boundary are similar to those of a single crystal.

[0023] Corresponding grain boundary ratio Σ3 detected using EBSD analysis software (TSL Solutions, Inc.) The corresponding grain boundaries are Σ3 to Σ49. Σ3 and Σ9 account for about 80% of all the corresponding grain boundaries Σ3 to Σ49, and Σ3 is slightly more abundant than Σ9. As the Σ value increases, the interval between the corresponding lattice points increases and the boundary becomes closer to a random grain boundary. Therefore, in this embodiment, the corresponding grain boundary ratio is calculated using the sum of the corresponding grain boundaries Σ3 to Σ9, and is used as an index. Note that Σ1 is a single crystal.

[0024] Since grain boundaries are the boundaries between grains, when the surface is observed, they are obtained as a surface and the grain boundaries are shown as an area, but the information obtained by measuring with actual equipment is a line (from the time of surface observation, it becomes the length of the boundary line). Therefore, in this embodiment, the coincidence grain boundary ratio is Coincident grain boundary ratio = Observed coincident grain boundary boundary / Observed grain boundary boundary (%) (See Figure 3.)

[0025] There are boundaries that exceed Σ49 in the boundary line. The "boundaries of the observed grain boundaries" in the above formula are all grain boundaries observed by the above EBSD analysis software. In this embodiment, as described above, "Σ3~49" are called coincidence grain boundaries. The boundaries in the coincidence grain boundaries are "boundaries of the observed grain boundaries". It is roughly 50-60% of the "borderline."

[0026] In the EBSD analysis software, for example, in the case of x150, the crystal orientation (angle) of the observation surface is measured at 1 μm intervals. is measured. If the change in the continuous data obtained is greater than a certain angle, it is considered to be a grain boundary. The corresponding grain boundary "Σ3~49" can be obtained from the orientation and direction of the crystals that sandwich this grain boundary. do.

[0027] Observed grain boundary boundary > "Σ3~49 corresponding grain boundary" boundary > "Σ3~Σ9 corresponding grain boundary" boundary The boundaries of the grain boundaries observed include coincident grain boundaries and grain boundaries that are not coincident grain boundaries. Therefore, the coincident grain boundary ratio is calculated by dividing the sum of the boundaries of the "Σ3 to Σ9 coincident grain boundaries" by the "Σ3 This is calculated by dividing the boundary line of "~49 grain boundary" by the sum of the boundary lines exceeding Σ49.

[0028] Grain boundaries with a low density of coincidence lattice points (grain boundaries close to random grain boundaries) have high energy and are unstable. Therefore, if there are many grain boundaries with a low density of coincidence lattice points, this can trigger the falling off of unmelted particles on the FZ melting surface, causing FZ defects. On the other hand, by using a polysilicon rod with physical properties close to those of a single crystal as a raw material in the FZ method, stable melting can be obtained.

[0029] Grain boundary length The grain size of single crystals in polysilicon is currently not distinguishable from grain boundaries in images such as SEM. Therefore, it is difficult to measure accurately. By measuring the crystal orientation on a grain-by-grain basis using the above-mentioned EBSD or the like, the grain boundary length on the measurement surface can be obtained, and the average grain size can be indirectly expressed. By dividing the grain boundary length on the measurement surface by the measurement area, the grain boundary length per unit area can be obtained. In this embodiment, this is taken as the grain boundary length (unit: length / area), which is an index of the width of the grain boundary surface. do.

[0030] Random grain boundary length There are various coincidence boundaries among grain boundaries other than the Σ3 to Σ9 coincidence boundaries, but as the Σ value increases, the interval between the coincidence lattice points becomes longer and the characteristics of grain boundaries with low Σ values ​​(low grain boundary energy and stability) are lost. For this reason, for convenience, the sum of Σ larger than Σ9 is defined as a random grain boundary, and the unit area The random grain boundary length is calculated from the hit grain boundary length.

[0031] In order to reduce crystal defects and increase yields in the FZ method, it is better to use raw materials with as long a grain boundary length as possible, a low Σ value, a large coincidence grain boundary ratio, and a short random grain boundary length. However, the coincidence grain boundary ratio and the grain boundary length are in a contradictory relationship in most cases. For example, polysilicon manufactured under conditions that increase the coincidence grain boundary ratio will have a short grain boundary length. For this reason, it is important to find the best point for both grain boundary characteristics.

[0032] The reason why crystal grains fall off and the growth of single crystals is hindered is because the bonds at the grain boundaries are weak and unstable. The more random grain boundaries with fewer bonds between corresponding lattice points, the more likely they are to peel off from the molten surface. If the Σ value of the grain boundary properties is low and the ratio of corresponding grain boundaries is high, the bonds at the grain boundaries are strong and stable, and crystal grains are less likely to fall off. In addition, the falling off of crystal grains due to random grain boundaries occurs at a temperature lower than the melting temperature of the single crystal because the energy of the grain boundaries is high. Therefore, the fallen single crystal particles are not sufficiently heated and melted, and the unmelted and semi-melted matter reaches the single crystal growth surface in the form of clusters, causing crystal defects. The unmelted and semi-melted matter depends on the size of the fallen crystal grains, and the larger they are, the longer they remain, making them more likely to reach the single crystal growth surface.

[0033] The manufacturing conditions required to obtain the desired grain boundary characteristics include the temperature of the rod surface, the reaction pressure, and the concentration of the raw material silane. A regression analysis of these factors yields the coefficient of determination, R 2 A correlation of 0.8 or higher is obtained. The same is true when more parameters are added and machine learning is used. The obtained correlation can be used as feedback to the device to track changes in the state inside the reactor and set optimal reaction conditions.

[0034] While the FZ method is moving toward larger diameter equipment, the traditional small diameter equipment is still widely used. Different equipment requires different grain boundary characteristics. Even equipment of the same type has its own quirks, and by performing this analysis, it is possible to manufacture polysilicon rods that meet the needs of the user.

[0035] As a measurement method, for example, the embodiment shown in FIG. 4 (hereinafter also referred to as "measurement method 1") may be used. The prepared silicon rod is cut and sliced ​​at any desired locations (three locations in the embodiment shown in FIG. 4) to cut out samples. The samples thus obtained are measured. Since the characteristics are basically the same on both sides of the leg of the U-rod, it is also possible to measure only one side of the leg.

[0036] The measurement results showed that in all the cut samples, the average grain boundary characteristics in the region excluding the seed core among the two-thirds region from the center of the cross section of the polysilicon rod had a coincidence grain boundary ratio of more than 20% and a grain boundary length of 550 mm / mm 2 The random grain boundary length exceeds 800 mm / mm 2 or the average grain boundary characteristics of the entire polysilicon excluding the seed core are such that the corresponding grain boundary ratio exceeds 20%. , and the grain boundary length is 550 mm / mm 2 The random grain boundary length exceeds 800 mm / mm 2 If it does not exceed this value, it indicates that the FZ yield is good under the conditions.

[0037] Therefore, it is expected that the subsequent batches of polysilicon rods manufactured under the same conditions will also give favorable results. Note that with each batch, the reactor wall loses its luster and the efficiency of radiant heat changes, so the environment inside the reactor gradually changes even under the same conditions, but this change is not dramatic. Therefore, for a certain period of time (for example, about one month), it is expected that the subsequent batches of polysilicon rods manufactured under the same conditions will also give favorable results.

[0038] If the measurement results satisfy the above conditions and are favorable, a good yield can be produced by performing FZ using the leg that has not been cut out by slicing in Figure 4. In Figure 4, the part that was sliced ​​to create the sample can also be a CZ chunk.

[0039] For example, the following steps can be taken:

[0040] Measure using method 1, and connect the opposite leg to the leg that met the above conditions. (If the manufacturing equipment is the same, one will be used as the representative.)

[0041] At this time, For all silicon rods grown on silicon core wires in the same chamber, measurement method 1 If the above conditions are met and the leg passes, a single crystal may be grown in the FZ using the leg opposite to the leg that passed. Perform measurement method 1 on the representative of the inside and outside of the chamber, and if the above conditions are met and passed, you can grow single crystals on the remaining part in the FZ, One of the representative samples is measured using measurement method 1, and if it satisfies the above conditions and passes, the remaining samples may be grown as single crystals by FZ.

[0042] Furthermore, from the viewpoint of quality, the areas near the electrodes and the bridges are cut and the central portion without cracks becomes the ingot for FZ. Therefore, as another measurement method, for example, the embodiment shown in FIG. 5 may be used.

[0043] As shown in FIG. 5, in the embodiment where only the upper part near the bridge and the lower part near the electrode are cut out to prepare a sample (hereinafter also referred to as "measurement method 2"), the FZ rod can also be obtained from the leg on which the sample was prepared. Samples are taken from the parts of the ingot outside the effective length, mainly near the electrodes, and analysis is performed on resistance values, metal components, etc.

[0044] In Measuring Method 2, for example, the following procedure can be adopted.

[0045] Measure using Measuring Method 2, and if both feet on the side opposite to the foot that has been measured and meets the above conditions and passes the inspection, perform single crystal growth by FZ using both feet (if the manufacturing apparatuses are of the same type, one can be representative).

[0046] At this time, It is also possible to perform 100% inspection using Measuring Method 2 and perform single crystal growth by FZ on those that meet the above conditions and pass the inspection. Perform Measuring Method 2 on the representative on the outside in the same way as the representative on the inside of the chamber. If it meets the above conditions and passes the inspection, it is also possible to perform single crystal growth by FZ on all of them. Perform measurement using Measuring Method 2 on one of the representatives. If it meets the above conditions and passes the inspection, it is also possible to perform single crystal growth by FZ on all of them.

[0047] If the inspection results are different even when the manufacturing apparatuses are of the same type, or if the same silicon rod cannot be manufactured even under the same manufacturing conditions, it is also possible to perform either Measuring Method 1 or 2 on each apparatus.

[0048] If it is the case where the lots are different in the same apparatus and the characteristics gradually disappear, it is considered that deposits have accumulated inside the bell jar, resulting in a decrease in radiant heat.

[0049] Even in this case, it is possible to continue to review the manufacturing conditions, or perform internal cleaning of the bell jar to return it to the initial state. However, when performing electrolytic polishing for internal cleaning of the bell jar, since it is costly, continuing to review the manufacturing conditions is a realistic option.

Example

[0050] <Relationship between FZ Results and Grain Boundary Characteristics> Creation of Polysilicon Rod Crystal samples were prepared using the Siemens method with trichlorosilane and hydrogen as the raw materials, and the grain boundary characteristics were measured using EBSD. The results of an actual pulling experiment using the FZ method are shown below. If dislocations were found in the crystal as a result of the single crystallization experiment using the FZ method, it was judged as × (failed). The measurement results are also shown in Figure 1. [Table 1]

[0051] Sampling for grain boundary characterization Since it is not practical to measure the grain boundary characteristics of the entire rod, the average grain boundary characteristics were obtained by sampling. 1) The effective length (electrode side and bridge side) of a U-rod taken out of a Siemens CVD device was Wafers with a thickness of 10 mm were cut out from both ends of the substrate (removed) (see FIG. 5). 2) At the angle formed by the intersection of the lines connecting the longest and closest parts of the wafer's outer periphery to the seed core, a line segment a was drawn to the outer periphery, bisecting the angle on the acute angle side. 3) Cut out samples at 20 mm intervals from the core wire along line segment a, and measure within a range of 0.5 mm x 0.5 mm or more. The grain boundary characteristics were measured using a TIM EBSD instrument (Step 1.0 microns) to obtain the average grain boundary characteristics. The calculation took into account that cylindrical grinding was performed in the process. 4) In the radial direction of growth, the reaction conditions (rod temperature, reaction pressure, raw material concentration, raw material supply rate, CVD equipment, radiant heat received by the rod from the outside, and other factors that affect the grain boundaries) are the same throughout the reaction batch. The entire section was determined by measuring representative points.

[0052] <Examples of reaction condition analysis and feedback> As an example, we will take the reaction in which a polysilicon manufacturing device using the Siemens method passes an electric current through a silicon seed core connected to electrodes, generating heat and maintaining a constant temperature. The gas phase is made up of hydrogen and chlorosilane, and a deposited layer of polysilicon is formed on the surface of the heated silicon seed core, resulting in a polysilicon rod.

[0053] The reaction conditions were the chlorosilane concentration and the surface temperature of the polysilicon rod during the CVD reaction. and analyzed its relationship with the grain boundary characteristics. The results are shown in a diagram in Figure 2. Assuming that point A is the current condition, if only the chlorosilane concentration is changed to a higher concentration from point A, the grain boundary characteristics will change toward point B, and if only the rod temperature is lowered from point A, the grain boundary characteristics will change toward point C. Furthermore, if the chlorosilane concentration is changed to point B and the rod temperature to point C, polysilicon with the grain boundary characteristics of point D will be obtained.

[0054] By applying actual measurement results to Figure 2 and keeping it up to date, it is possible to constantly adjust the optimal reaction conditions to obtain polysilicon rods with the desired grain boundary characteristics.

[0055] Feedback to manufacturing conditions method 1: As a method of designing the grain boundary characteristics from the center to the outer periphery of the polysilicon rod, when the diameter is small, the rod surface temperature is relatively increased to increase the area with a high corresponding grain boundary ratio, and as the diameter increases, the surface temperature of the silicon rod is lowered and the chlorosilane concentration is increased (to prevent the heat inside the silicon rod from increasing), thereby increasing the grain boundary length and manufacturing a polysilicon rod with an "optimum area."

[0056] Feedback to manufacturing conditions method 2: As the diameter becomes larger, high frequency waves are applied, the surface temperature is raised (the surface temperature can be raised by preventing the heat inside the silicon rod from rising), and the chlorosilane concentration in the chamber is increased to produce a polysilicon rod with an "appropriate region."

Claims

1. A polysilicon rod in which the average grain boundary characteristics of the area excluding the seed core within the two-thirds area from the center of the cross section of the polysilicon rod have the following characteristics: The coincidence grain boundary ratio exceeds 20% and the grain boundary length is 550 mm / mm 2 The random grain boundary length exceeds 800 mm / mm 2 Polysilicon rod not exceeding.

2. The polysilicon rod according to claim 1, wherein the coincident grain boundary ratio exceeds 25%, the grain boundary length exceeds 650 mm / mm 2 , and the random grain boundary length does not exceed 700 mm / mm 2 .

3. A polysilicon rod according to claim 1 or 2, wherein the corresponding grain boundary ratio does not exceed 90% and the grain boundary length, which is an index of the width of the grain boundary, does not exceed 3000 mm / mm 2 .

4. A polysilicon rod having the following average grain boundary characteristics throughout the polysilicon, excluding the seed core: A polysilicon rod having a coincident grain boundary ratio of more than 20%, a grain boundary length of more than 550 mm / mm 2 , and a random grain boundary length of not more than 800 mm / mm 2 .

5. The polysilicon rod according to claim 4, wherein the coincident grain boundary ratio exceeds 25%, the grain boundary length exceeds 650 mm / mm 2 , and the random grain boundary length does not exceed 700 mm / mm 2 .

6. A polysilicon rod according to claim 4 or 5, wherein the coincident grain boundary ratio does not exceed 90% and the grain boundary length, which is an index of the width of the grain boundary, does not exceed 3000 mm / mm 2 .

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