JP2009249234A - Method for judging metal contamination in low-resistance silicon single crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for judging whether metal contamination has occurred or not in a low-resistance silicon single crystal that is as in a grown state to be delivered as a product and is difficult to measure the life time. <P>SOLUTION: When a silicon single crystal is pulled up by CZ (Czochralski) method, a single crystal having a high resistance is pulled up in a top side to grow a high resistance portion Lb, then a dopant is supplied to a melt (the dopant is supplied at a time when the crystal is pulled up to a portion indicated by a white arrow in the figure) and a single crystal having a low resistance is pulled up. Whether metal contamination has occurred or not in the low-resistance single crystal is judged by measuring a life time of the high resistance part in the obtained silicon single crystal. The yield of a low-resistance silicon single crystal as a product is effectively improved by employing an embodiment of reducing a diameter of the high-resistance single crystal than a diameter of the low-resistance single crystal or an embodiment including a step of gradually increasing the diameter and a step of gradually decreasing the diameter. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for determining the presence or absence of metal contamination in a low-resistance silicon single crystal whose lifetime is difficult to measure.

  A silicon wafer used as a semiconductor substrate is a process in which a grown silicon single crystal ingot is cut into blocks and sliced (wafer cutting), followed by mechanical polishing (lapping), gettering treatment, heat treatment, washing, and many other processes. In addition, after inspection, the wafer is shipped as a wafer that satisfies the required quality.

  In this silicon wafer, contamination with metals such as iron, copper and nickel becomes a problem. This is because metal impurities in the silicon single crystal, particularly the heavy metal, deteriorate the performance of the semiconductor device, for example, causing deterioration of the oxide film breakdown voltage and increase of leakage current.

  One method of determining metal contamination is to measure the recombination lifetime (hereinafter simply referred to as the lifetime) of the silicon wafer carrier. Therefore, non-destructive and quick measurement is possible. The (rate) attenuation method (microwave PCD method) is widely used. However, in the determination of metal contamination using the microwave PCD method, the resistivity of a silicon wafer having a specific resistance (resistivity) of 3 Ωcm or less is very low because of the measurement principle, and the microwave reflectance is extremely high. Become. Therefore, since the output of the μ-PCD detector is saturated or microwave noise is superimposed, it is difficult to detect a change in reflectance due to excess carrier injection, and it is difficult to measure lifetime. .

  Therefore, when determining the presence or absence of metal contamination on a low-resistance silicon wafer, atomic absorption spectrometry or secondary ion mass spectrometry (SIMS method) must be used, which is expensive and takes a lot of time for evaluation. Will be required.

  By the way, in recent years, there are increasing cases in which silicon single crystals are shipped as products in an as-grown state without being sliced. In that case, the resistivity and the like must be inspected while maintaining the as-grown shape. Regarding metal contamination, it is necessary to ensure that there is no contamination in the state of as-grown silicon single crystal.

  As for the resistivity of an as-grown silicon single crystal, Patent Document 1 discloses a method for obtaining the resistivity without cutting a semiconductor single crystal such as silicon shipped as a product. This method is a single crystal pulling method in which a semiconductor single crystal is grown while pulling up a semiconductor single crystal from a semiconductor melt, and a first step of pulling up a sample single crystal for resistivity measurement, and a single product that becomes a product continuously with the sample single crystal. A pulling method including a second step of pulling up the crystal. Since the product single crystal is formed continuously with the sample single crystal, if the resistivity of the sample single crystal is measured, the product single crystal is not cut. The resistivity can be obtained.

On the other hand, Patent Document 2 proposes a single crystal pulling method capable of continuously pulling a plurality of types of single crystals having different resistivity by one pulling. This single crystal pulling method is a method of changing the resistivity of a single crystal that is supplied at any time during pulling and then pulling up, and is known per se. In order to solve the problem that the single crystal growth becomes unstable and the single crystal undergoes transition or polycrystallization, a cylindrical partition is provided in the crucible containing the raw material melt, and a dopant is added to the outer region. It is a supply method.
JP 2005-324970 A JP-A-4-21585

  As described above, the carrier lifetime measurement is used for evaluating the metal contamination of the silicon single crystal, and the microwave PCD method is frequently used. However, a low-resistance silicon wafer having a resistivity of 3 Ωcm or less has a problem in that it is difficult to measure lifetime and metal contamination cannot be evaluated. Furthermore, when shipping a product with the silicon single crystal grown, it is necessary to ensure that there is no metal contamination without cutting the single crystal. However, a method for solving these problems has not yet been established.

  The present invention has been made in view of such circumstances, and provides a method for determining the presence or absence of metal contamination in a low resistance silicon single crystal that is shipped in a grown state and is difficult to measure lifetime. The purpose is to do.

  In order to achieve the above object, the present inventor, when pulling up the silicon single crystal, pulls up the high resistance single crystal at the top, and when the pulling length becomes about 50 to 100 mm, Determine the presence or absence of metal contamination in the low-resistance silicon single crystal by growing the low-resistance single crystal by additional doping in the solution and measuring the lifetime of the high-resistance portion on the top side of the obtained single crystal. Was invented.

  In the above-mentioned Patent Document 2, it is described that a plurality of types of single crystals having different resistivities are pulled up by supplying a dopant in the middle of pulling, but the method invented by the present inventor is supplying a dopant in the middle of pulling. Is measured at the above timing and the lifetime of the top-side high resistance portion before the additional doping is measured is shipped as a product as it is grown, and it is difficult to measure the lifetime. This is a method for determining metal contamination in a silicon single crystal.

  Furthermore, with regard to this metal contamination determination method, the effect was confirmed by actually pulling and growing a low-resistance silicon single crystal.

The gist of the present invention resides in the following metal contamination determination method for a low resistance silicon single crystal.
That is, when the crucible is filled with a silicon raw material and melted and grown while pulling up the silicon single crystal from the melt, the high resistance portion is pulled on the top side to grow the high resistance portion, To determine the metal contamination of the low resistance single crystal by supplying the dopant to the melt and pulling up the low resistance single crystal and measuring the lifetime of the high resistance portion of the resulting silicon single crystal. This is a method for determining metal contamination.

  The term “low resistance single crystal” used herein refers to a silicon single crystal having a resistivity of 0.001 to 3 Ωcm. The lower limit of the resistivity is set to 0.001 Ωcm because the lower limit of the specific resistance of the single crystal shipped as a product is this value. Further, the “high resistance single crystal” is a silicon single crystal capable of performing lifetime measurement, that is, having a resistivity exceeding 3 Ωcm. Those having a resistivity of about 10 Ωcm or more are desirable.

  In the method for determining metal contamination of a low resistance silicon single crystal according to the present invention, if the diameter of the high resistance single crystal is made smaller than the diameter of the low resistance single crystal, Yield can be improved.

  Moreover, in the metal contamination determination method for a low resistance silicon single crystal according to the present invention, the step of pulling up the high resistance single crystal includes a step of gradually increasing the diameter of the single crystal and a step of gradually decreasing the single crystal. Embodiments can be taken.

  According to the method for determining metal contamination of a low-resistance silicon single crystal of the present invention, the presence or absence of metal contamination in a silicon single crystal shipped as a product, especially a low-resistance silicon single crystal whose lifetime is difficult to measure. Can be determined.

  The metal contamination determination method of the low resistance silicon single crystal according to the present invention is a method of filling a crucible with a silicon raw material and melting it, and then growing the silicon single crystal from the melt while growing the single crystal with a high resistance on the top side. After raising the high resistance portion by pulling up, by supplying a dopant to the melt to pull up the low resistance single crystal, by measuring the lifetime of the high resistance portion of the obtained silicon single crystal, It is a method characterized by determining metal contamination of a low-resistance single crystal.

  There are various methods for producing a silicon single crystal used for a semiconductor substrate. Among them, the Czochralski method (CZ method) is widely adopted. In the CZ method, a high-purity silicon raw material is charged into a quartz crucible, and the raw material is melted with a heater disposed around the crucible in an inert gas atmosphere. Then, a seed crystal is immersed in the surface of the melt, This is a method of growing the single crystal on the lower end face of the seed crystal by pulling it upward while rotating it.

  When pulling, adjust the speed, reduce the seed crystal diameter and go through the necking process (step) to form the neck, then lower the pulling speed to gradually increase the crystal diameter and form the shoulder Then, the process moves to pulling up the constant diameter part. After the constant-diameter portion reaches a predetermined length, the crystal diameter is gradually decreased, and the pulling-up is completed by separating the foremost portion from the melt, whereby a silicon single crystal having a predetermined shape is obtained. The necking (seed squeezing) is an essential process performed to remove high-density dislocations introduced into the seed crystal by heat shock when the seed crystal is brought into contact with the silicon melt.

  Also in the metal contamination determination method of the present invention, it is assumed that the silicon single crystal is pulled and grown by the CZ method. The metal contamination determination method of the present invention will be described below with reference to the drawings.

  FIG. 1 is a diagram schematically illustrating an entire silicon single crystal obtained by applying the metal contamination determination method of the present invention. As shown in the figure, below the neck portion 2 formed on the lower end surface of the seed crystal 1, a shoulder portion 3 and a constant-diameter portion 4 having a predetermined length and the same diameter are formed.

  In the metal contamination determination method of the present invention, when pulling up a silicon single crystal by the CZ method, first, a high resistance single crystal is pulled on the top side to grow a high resistance portion. At this time, as shown in FIG. 1, seed necking is performed to form the neck portion 2, and then the crystal diameter is gradually increased to form the shoulder portion 3, and the constant diameter portion 4 is lifted. The range indicated by the symbol La in the figure is the high resistance portion. The crystal diameter of the high resistance portion La is not particularly limited. The silicon single crystal illustrated in FIG. 1 is a case where the crystal diameter of the high resistance portion La is the same as the diameter of the constant diameter portion 4, but as will be described later, is smaller than the crystal diameter of the low resistance portion which is a product. It is desirable to do.

  The high resistance portion La may be a single crystal having a resistivity exceeding 3 Ωcm so that the lifetime measurement can be performed. However, the higher the resistance, the higher the sensitivity of the lifetime measurement. It is desirable to use a silicon single crystal having a resistivity of about 10 Ωcm or a high resistance silicon single crystal to which no dopant is added.

  The pull-up length of the high resistance portion La is desirably about 50 to 100 mm. If the pull-up length is too long, the yield of the low-resistance silicon single crystal to be pulled after this will be lowered.

  Subsequently, the dopant is supplied to the melt to pull up the low-resistance single crystal. The white arrow in FIG. 1 indicates that the dopant was supplied when the single crystal was pulled up to the site indicated by the arrow. The reason why the dopant is supplied is to grow a low-resistance silicon single crystal shipped as a product from this portion downward. What is necessary is just to adjust the dopant concentration of a melt by adjusting the supply amount of a dopant according to the required resistivity.

  In the above-mentioned Patent Document 2, a method is proposed in which a cylindrical partition wall is provided in a crucible containing a raw material melt and a dopant is supplied to the outer region. Since the influence on the single crystal growth due to the undulation of the liquid surface is slight, the installation of the cylindrical partition is not necessarily required.

  In the case where the crystal diameter of the high resistance portion La is smaller than the crystal diameter of the constant diameter portion 4, when the dopant is supplied to pull up the low resistance single crystal, the crystal diameter is reduced to the crystal diameter of the product single crystal. Increase gradually.

  Finally, the metal contamination of the low resistance silicon single crystal is determined by measuring the lifetime of the high resistance portion La of the obtained silicon single crystal, that is, the silicon single crystal having the high resistance portion La on the top side.

  Since the low-resistance silicon single crystal is continuous with the high-resistance portion, if the low-resistance silicon single crystal has metal contamination derived from the silicon raw material, it is considered that the high-resistance portion is also contaminated in the same way. be able to. Therefore, by measuring the lifetime of the high resistance portion, it is possible to determine the presence or absence of metal contamination of the low resistance silicon single crystal that is the product.

  The method for measuring the lifetime is not particularly limited. For example, a microwave PCD method that is commercially available for non-destructive and quick measurement and is widely used for quality evaluation of wafers may be used.

  In the metal contamination determination method of the present invention, an embodiment in which the diameter of the high-resistance single crystal (high-resistance portion) is made smaller than the diameter of the low-resistance silicon single crystal (this is referred to as Embodiment 1). It is desirable to take.

  FIG. 2 is a diagram schematically illustrating the entire silicon single crystal obtained by applying the metal contamination determination method of the first embodiment.

  Since the high resistance portion only performs lifetime measurement and does not become a product, the diameter of the high resistance portion Lb is made smaller than the diameter of the low resistance silicon single crystal (constant diameter portion 4) as shown in FIG. If the ratio of the high resistance portion Lb to the whole single crystal pulled is decreased, the yield of the low resistance silicon single crystal as a product can be improved.

  In the metal contamination determination method of the present invention, the step of pulling up the high resistance single crystal (high resistance portion) includes a step of gradually increasing the diameter of the single crystal and a step of gradually decreasing the single crystal. It is desirable to adopt a form (this is referred to as a second embodiment).

  FIG. 3 is a diagram schematically illustrating the entire silicon single crystal obtained by applying the metal contamination determination method according to the second embodiment. The portion 5a in which the diameter of the high resistance portion Lc gradually increases and gradually decreases. It has the part 5b to do.

  The process of increasing and decreasing the diameter of the high resistance portion Lc is a process employed when pulling up a sample single crystal for resistivity measurement by the single crystal pulling method described in Patent Document 1 described above. In the metal contamination determination method of the present invention, if this step is applied to the single crystal pulling of the high resistance portion, the amount of pulling of the high resistance portion can be reduced by the amount that the diameter of the high resistance portion Lc is reduced. The yield of the low resistance silicon single crystal can be further improved. Further, gradually reducing the diameter of the high resistance portion, and further including the step of forming the neck portion 2a as shown in FIG. 3 is extremely effective in reliably achieving crystal dislocation elimination. It is.

  As described above, according to the metal contamination determination method and the embodiment of the low resistance silicon single crystal of the present invention, it is determined whether or not there is metal contamination in the silicon single crystal that is shipped in a grown state. Can do. In particular, evaluation of metal contamination in a low-resistance silicon single crystal, whose lifetime is difficult to measure, is not easy even if the target is a wafer, and is expensive and time-consuming to perform atomic absorption spectrometry and secondary ion mass spectrometry. Although the method (SIMS method) must be used, the metal contamination can be easily determined by applying the determination method of the present invention.

  The method of the first embodiment was applied to grow a low resistance silicon single crystal having a high resistance portion on the top side, and the lifetime of the high resistance portion was measured by a microwave PCD method.

  A seed crystal is immersed in the surface of a silicon melt to which boron (B) is added as a dopant, and is rotated upward, and after a necking process, a silicon single crystal having a diameter of 4 inches (high height) is formed on the lower end surface of the seed crystal. Resistance part) was formed. The resistivity of this part was 10 Ωcm.

  When the pull-up length of the high resistance portion of the crystal reaches 4 mm with a diameter of 4 inches, B is additionally doped into the silicon melt, the pulling speed is decreased to gradually increase the crystal diameter, and the diameter of 6 inches, A low resistance silicon single crystal having a pulling length of 1300 mm was grown. The resistivity was 0.017 Ωcm.

  Similarly, a high resistance portion having a diameter of 4 inches and a pulling length of 50 mm is formed from the same B-added silicon melt, and a low resistance silicon single crystal having a diameter of 8 inches and a pulling length of 1700 mm is continuously grown. did. Further, from the same B-added silicon melt, a high resistance portion having a diameter of 4 inches was similarly formed, and a low resistance silicon single crystal having a diameter of 12 inches and a pulling length of 500 mm was continuously grown.

  When the lifetime of the high resistance portion of these three silicon single crystals (low resistance silicon single crystal having a high resistance portion at the top portion) was measured by the microwave PCD method, all could be measured without any problem. There was no difference in the measurement results. As a result, it was confirmed that the metal contamination determination method of the low resistance silicon single crystal according to the present invention can be applied to the evaluation of metal contamination in the low resistance silicon single crystal that is shipped as it is grown.

  The method of determining metal contamination of a low-resistance silicon single crystal according to the present invention, after growing a high-resistance portion on the top side by a CZ method, supplying a dopant to the melt and pulling up the low-resistance single-crystal silicon, This is a metal contamination determination method for measuring the lifetime of a high resistance portion. According to this method, it is possible to determine the presence or absence of metal contamination in a low-resistance silicon single crystal that is shipped in a grown state and is difficult to measure lifetime. By adopting an embodiment in which the diameter of the high resistance portion is made smaller than the diameter of the low resistance silicon single crystal, the yield of the low resistance silicon single crystal as a product can be improved, and the diameter of the high resistance portion is gradually increased. By adopting the embodiment including the step of causing and the step of gradually decreasing, in addition to the improvement of the yield, it is possible to reliably achieve dislocation-free crystal.

  Therefore, the metal contamination determination method of the present invention can be widely used in the field of manufacturing semiconductor substrate materials.

It is a figure which illustrates typically the whole silicon single crystal obtained by applying the metal contamination judging method of the present invention. It is a figure which illustrates typically the whole silicon single crystal obtained by applying the metal contamination judging method of Embodiment 1. It is a figure which illustrates typically the whole silicon single crystal obtained by applying the metal contamination judging method of Embodiment 2.

Explanation of symbols

1: Seed crystal 2, 2a: Neck part 3: Shoulder part 4: Constant diameter part 5a: Part where diameter gradually increases 5b: Part where diameter decreases gradually

Claims (3)

When the silicon raw material is filled in the crucible and melted and grown while pulling up the silicon single crystal from the melt,
After pulling up the high resistance single crystal on the top side and growing the high resistance part,
A dopant is supplied to the melt to pull up a low-resistance single crystal,
A metal contamination determination method for a low resistance silicon single crystal, wherein the metal contamination of a low resistance single crystal is determined by measuring a lifetime of a high resistance portion of the obtained silicon single crystal.   2. The method for determining metal contamination of a low resistance silicon single crystal according to claim 1, wherein the diameter of the high resistance single crystal is made smaller than the diameter of the low resistance single crystal.   3. The low-resistance silicon single crystal according to claim 1, wherein the step of pulling up the high-resistance single crystal includes a step of gradually increasing the diameter of the single crystal and a step of gradually decreasing the diameter. Metal contamination judgment method.

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