JP5467923B2 - Manufacturing method of silicon wafer for metal contamination evaluation - Google Patents

Description

  The present invention relates to a silicon wafer for metal contamination evaluation used for evaluating and monitoring metal contamination during handling of a silicon wafer and a method for manufacturing the same.

Various devices are manufactured using a silicon wafer. When contamination by unintended impurities occurs in a device manufacturing process, the electrical characteristics of the device often deteriorate. For this reason, manufacturing of material substrates and devices is performed in various forms while checking for contamination.
Of these, contamination with metal elements adversely affects the electrical characteristics of the device even with extremely small amounts of contamination, and therefore, in general, extremely high-purity materials and advanced cleaning are performed in the semiconductor manufacturing process.

Nevertheless, in the actual semiconductor device manufacturing process, deterioration of electrical characteristics and reduction of yield may occur due to metal contamination.
For this reason, it is common to manufacture devices while confirming that no metal contamination has occurred.

There are various methods for evaluating wafer metal contamination with high sensitivity, but methods that measure the lifetime and diffusion length of wafers are widely used as methods with short measurement time and excellent sensitivity. .
This method of measuring the lifetime and diffusion length is to monitor the contamination level by electrically measuring the decay rate and diffusion length of excess minority carriers due to the deep level created by the contaminating metal, which is a problem with contamination. It is known as an effective method because it is directly related to the leakage current of the PN junction, which is an electrical characteristic that tends to occur.

However, direct measurement of the lifetime and diffusion length of an actual product wafer is difficult because it is difficult to measure because of various factors.
Also, metal contamination often occurs in the heat treatment process. Therefore, contamination management is performed by confirming that there is no contamination from the apparatus.
Specifically, it is often the case that a monitor wafer is put into the apparatus to perform heat treatment, and the lifetime or diffusion length of the wafer is measured to confirm that the apparatus is kept clean.

  When metal contamination is managed in this way, it is necessary for operation to set predetermined management standards and management values. Therefore, silicon wafers used for this contamination management are managed as such. It has been used.

This monitor wafer for lifetime measurement must be a wafer that is essentially free from metal contamination.
However, since wafers that monitor particle contamination can be used even if they are contaminated, recycling processing is widely performed, but lifetime monitoring wafers are basically not subjected to recycling processing.

Furthermore, since it is necessary to induce excess minority carriers to change the electrical resistance, it is necessary to use a wafer having a relatively high resistance. In addition, a substrate on which a gettering process (for example, formation of a polysilicon film) having a surface level that promotes recombination of minority carriers on the front and back surfaces of the wafer cannot be used.
Also, in the heat treatment process where heat treatment is performed at a relatively high temperature for a long time, oxygen dissolved in the crystals becomes precipitates, reducing the lifetime (shortening the lifetime), and sensitivity for metal contamination evaluation. Therefore, a wafer having a relatively low oxygen concentration is often used as the monitor wafer.

Recently, it has been required to manage the amount of iron (Fe) atoms dissolved in silicon at a level of 1 × 10 ¹⁰ atoms / cm ³ or less, and various improvements in the performance of measuring instruments have been required. It is proceeding in various ways.
In particular, SPD (surface photovoltage) measurement without heat treatment and PCD (photoconductivity decay) by chemical passivation are widely used from the conventional surface passivation by thermal oxide film formation. Thus, high sensitivity measurement is possible.

F, Burkeen et. al. “Visualizing the Wafer's Edge” Spring 2007, Yield Management Solutions p18, KLA Tencor Milind S Kulkarni, et. al. “The aggregation dynamics of self-interstitials in growing Czochralski silicon crystals” Journal of Crystal Growth 284 (2005) 353-368.

As described above, the measurement sensitivity of the PCD method and the SPV method for evaluating metal contamination of silicon wafers has increased. As a result, contamination that is thought to be caused by heat treatment is observed on the outer periphery of the evaluation target wafer. Is increasing.
However, on the other hand, there are many cases where the pollution source cannot be clearly understood.

  By the way, the yield of devices is generally poor at the periphery (see Non-Patent Document 1).

  As described above, since the outer peripheral portion of the silicon wafer is a portion where particles are frequently generated from the portion in contact with the boat or the handling jig, countermeasures for contamination as a countermeasure against the yield of the outer peripheral portion are not always actively promoted. There is a side that did not exist.

Moreover, the reliability of evaluation may be low as a background to the progress of metal contamination countermeasures at the outer periphery.
One of the reasons for reducing the reliability of the outer peripheral contamination evaluation is that the passivation for removing the effect of surface recombination in the PCD measurement has been performed by oxidation treatment. This is probably because it was often determined that the thermal oxidation occurred.

  Here, in the contamination evaluation, an evaluation method that does not perform heat treatment such as PCV by SPV or chemical passivation has recently been widely used, but the reliability of the contamination evaluation of the outer peripheral portion has been improved. That's not true.

As described above, even if the contamination is confirmed on the monitor wafer in the device process, the contamination is often taken for granted even though the contamination at the measurement stage does not occur.
However, in order to improve the yield of device manufacturing, it can be said that improving the reliability of the contamination evaluation on the outer periphery of the wafer is an essential issue.

  The present invention has been made in view of the above problems, and realizes an improvement in the reliability of the measurement result on the outer periphery of the monitor wafer in the evaluation of metal impurity contamination by PCD, SPV, etc. for contamination control during semiconductor processes. An object of the present invention is to provide a silicon wafer for evaluating metal contamination and a method for manufacturing the same.

In order to solve the above problems, the present invention provides a metal contamination evaluation silicon wafer for evaluating metal contamination, wherein the silicon contamination evaluation silicon wafer has an oxygen concentration of 0.7 × 10 ¹⁸ atoms / cm ^3. The following is a CZ silicon wafer having a resistivity of 1 Ωcm or more, and the CZ silicon wafer is obtained by reducing the diameter relative to the diameter of the growth ingot and removing the outer peripheral portion. Provide silicon wafers for use.

A CZ silicon wafer having an oxygen concentration of 0.7 × 10 ¹⁸ atoms / cm ³ or less and a resistivity of 1 Ωcm or more has a low oxygen concentration. For example, even if heat treatment is performed at 1100 ° C. for about 1 hour, Precipitation does not affect the lifetime and diffusion length, and the resistivity is 1 Ωcm or more, so that the lifetime and diffusion length can be evaluated by highly sensitive PCD, SPV and the like. .
Since the outer peripheral portion is removed by reducing the diameter relative to the diameter of the growth ingot, it contains a large amount of impurities from the external atmosphere during the growth of the crystal ingot, and the lifetime and diffusion length are significantly reduced. The CZ silicon wafer from which the region outside the OSF ring to be removed is removed, and in particular, the accuracy of evaluation of metal impurity contamination at the outer periphery of the wafer can be greatly improved as compared with the conventional case. Therefore, a monitor wafer capable of evaluating metal impurity contamination with higher reliability than conventional ones, which eliminates the decrease in lifetime and the decrease in diffusion length due to oxygen precipitation at the wafer outer periphery, which is easily promoted by heat treatment. It is a silicon wafer for metal contamination evaluation suitable for the above.

When the oxygen concentration is higher than 0.7 × 10 ¹⁸ atoms / cm ³ , oxygen precipitation is increased, which greatly affects the measurement of lifetime and diffusion length.
If the resistivity is lower than 1 Ωcm, it is difficult to accurately measure lifetime and diffusion length.
Therefore, the CZ silicon wafer of the present invention is made of a wafer having an oxygen concentration of 0.7 × 10 ¹⁸ atoms / cm ³ or less and a resistivity of 1 Ωcm or more.

The present invention also provides a method for producing a silicon wafer for metal contamination evaluation for evaluating metal contamination, wherein at least the oxygen concentration is 0.7 × 10 ¹⁸ atoms / cm ³ or less and the resistivity is determined by CZ method. A single crystal ingot is grown so as to be 1 Ωcm or more, the outer peripheral portion of the grown single crystal ingot is removed and the diameter is reduced, and then a silicon wafer is cut out from the ingot after the diameter reduction for evaluating the metal contamination Provided is a method for producing a silicon wafer for metal contamination evaluation, characterized by producing a silicon wafer.

Thus, by removing the outer diameter of the single crystal ingot grown so that the oxygen concentration is 0.7 × 10 ¹⁸ atoms / cm ³ or less and the resistivity is 1 Ωcm or more by the CZ method, the cost is reduced. Although it rises and is not so suitable for regular pollution control monitors, the electrical characteristics and yield of products can be reduced to the usual 300 mm by flowing the silicon wafer for metal contamination evaluation manufactured in this way into the actual device process. Compared to the case of manufacturing using a wafer, it is easy and reliable to confirm whether the cause of the decrease in the yield at the outer periphery is due to the nature of the crystal or the process conditions. Become.
In other words, it can be used as a monitor wafer for directly evaluating whether the cause of the decrease in the yield at the outer peripheral portion is metal contamination or the crystal characteristics of the wafer. A silicon wafer for metal contamination evaluation that can be greatly improved can be efficiently manufactured.

  Here, the diameter of the growing single crystal ingot is set to 320 mm or more, the removal amount of the outer peripheral portion of the single crystal ingot is set to at least 10 mm or more from the outer peripheral portion, and the silicon wafer for metal contamination evaluation having a diameter of 300 mm is manufactured. The diameter of the growing single crystal ingot is set to 220 mm or more, the removal amount of the outer periphery of the single crystal ingot is set to at least 10 mm from the outer periphery, and the silicon wafer for metal contamination evaluation having a diameter of 200 mm is provided. Can be produced.

A silicon wafer for metal contamination evaluation for a monitor with a diameter of 300 mm can also be produced by excluding the outer periphery using a 450 mm wafer, but a single crystal ingot to be grown has a large diameter (diameter of 320 mm or more from 300 mm). ) And removing the outer peripheral portion at least 10 mm or more in width to manufacture a 300 mm wafer, it is possible to more easily manufacture a contamination evaluation wafer from which a portion where oxygen precipitation is likely to occur is removed from the outer peripheral portion of the wafer. .
Also, a silicon wafer for metal contamination evaluation having a diameter of 200 mm can be produced by removing the outer peripheral portion of a single crystal ingot having a diameter of 220 mm or more at least 10 mm in width in the same manner as the silicon wafer for metal contamination evaluation having a diameter of 300 mm. In addition, a highly reliable silicon wafer for evaluating metal contamination having a desired diameter can be manufactured.

Furthermore, in the present invention, a method for manufacturing a metal contamination evaluation silicon wafer for evaluating metal contamination, wherein the oxygen concentration is 0.7 × 10 ¹⁸ atoms / cm ³ or less and the resistivity is at least by CZ method. A silicon wafer for metal contamination evaluation, characterized in that a single crystal ingot is grown so as to be 1 Ωcm or more, a CZ silicon substrate is cut out from the grown single crystal ingot, and then the outer peripheral portion of the CZ silicon substrate is removed. A manufacturing method is provided.

If it is a method for removing the outer peripheral portion of a large-diameter CZ silicon substrate, its production quantity is limited, but since there is no problem with cost by using a non-standard product, it can be handled sufficiently easily in practice. It is possible.
Thus, by removing the outer peripheral portion of the large-diameter CZ silicon substrate, there is little waste, the oxygen concentration is sufficiently low as 0.7 × 10 ¹⁸ atoms / cm ³ or less, and the resistivity is sufficiently ^high as 1 Ωcm or more. In addition, it is possible to easily and inexpensively manufacture a silicon wafer for metal contamination evaluation that can improve the evaluation accuracy as compared with the prior art.

  Here, the diameter of the CZ silicon substrate is 300 mm, the removal amount of the outer peripheral portion of the CZ silicon substrate is at least 20 mm or more from the outer peripheral portion, and the silicon wafer for metal contamination evaluation having a diameter of 200 mm can be produced. Further, the metal contamination evaluation silicon wafer having a diameter of 150 mm can be manufactured by setting the diameter of the CZ silicon substrate to 200 mm and the removal amount of the outer peripheral portion of the CZ silicon substrate to at least 15 mm or more from the outer peripheral portion.

Thus, regarding the silicon wafer for metal contamination evaluation for contamination evaluation for a diameter of 200 mm, an oxygen concentration of 300 mm in diameter is 0.7 × 10 ¹⁸ atoms / cm ³ or less and the resistivity is 1 Ωcm or more. For example, it can be manufactured by removing the outer peripheral portion of a non-standard product, and by leaving such a central portion of the CZ silicon substrate, only the outer peripheral portion where the oxygen precipitation of the 300 mm diameter CZ silicon substrate easily occurs is excluded. The manufacturing itself is easy.
Similarly, with respect to a silicon wafer for metal contamination evaluation for a diameter of 150 mm, an oxygen concentration of 200 mm in diameter is 0.7 × 10 ¹⁸ atoms / cm ³ or less, and a resistivity of 1 Ωcm or more is, for example, a nonstandard product. It is possible to manufacture by removing the outer periphery.

  Further, the removal of the outer peripheral portion of the CZ silicon substrate is preferably performed by reducing the diameter by decentering the CZ silicon substrate by 5 mm or more in a predetermined direction with respect to the orientation flat or notch of the CZ silicon substrate.

Actually, when the presence or absence of metal contamination is evaluated by a silicon wafer for metal contamination evaluation, if the lifetime decreases in the periphery of the wafer, it is difficult to determine whether it is due to metal contamination or crystal.
On the other hand, by decentering a certain distance in a predetermined direction and removing the outer peripheral portion to fabricate a silicon wafer for metal contamination evaluation, the lifetime is reduced due to oxygen precipitation. In this case, the lifetime distribution is shifted from the wafer center in a predetermined direction, so that the cause of contamination can be clearly determined by separating from the contamination pattern by heat treatment. Therefore, it becomes possible to manufacture a silicon wafer for metal contamination evaluation for monitoring, which can evaluate the presence or absence of metal impurity contamination with higher reliability.

  Then, after cutting out the CZ silicon substrate from the single crystal ingot, at least one CZ silicon substrate is extracted, a passivation film is formed on the surface of the extracted CZ silicon substrate by chemical passivation, and a wafer life is formed by a PCD method. After measuring the time and confirming that the wafer lifetime is 600 μsec or more including the outer peripheral portion of the extracted CZ silicon substrate, the outer peripheral portion of the CZ silicon substrate is preferably removed.

It is desirable that the silicon wafer for metal contamination evaluation has a sufficiently long lifetime at the end of the wafer process, including contamination of the outer peripheral portion during crystal growth. Therefore, by confirming that the wafer lifetime is 600 μsec or more, that is, the Fe concentration is 1 × 10 ¹⁰ atoms / cm ³ or less, it is possible to evaluate the presence or absence of metal contamination with higher reliability. A wafer is obtained.

As described above, there is an increase in device sophistication or the production of image sensors that are sensitive to metal contamination in the process. Under such circumstances, the increase in sensitivity of contamination monitors in semiconductor processes is increasing. It is becoming important.
In the road map of public organizations related to semiconductors, metal contamination is set to be greatly reduced as devices become finer.
However, since the periphery of the wafer has many opportunities to come into contact with the robot arm or the like during transportation, and the yield is likely to decrease due to dust generation or contamination, it is important to improve the reliability of the contamination assessment at that location. .

  And according to this invention, the reliability of the contamination evaluation of a wafer outer peripheral part can be improved significantly compared with the past, and the contamination countermeasure can be taken appropriately. In addition, since silicon contamination can be evaluated more accurately and appropriate measures can be taken, a silicon wafer for metal contamination evaluation that can improve the characteristics and yield of semiconductor devices and a method for manufacturing the same are provided. become.

It is the figure which showed an example of lifetime distribution of the silicon wafer which performed the heat processing for a long time. It is the figure which showed an example of the lifetime distribution of the silicon wafer where the fall of the lifetime resulting from oxygen precipitation and the fall of the lifetime resulting from metal contamination appeared simultaneously. It is the figure which showed the relationship between the iron concentration of a silicon wafer, a minority carrier lifetime (lifetime), and diffusion length. It is the figure which showed the evaluation result of the lifetime distribution of the silicon wafer of Example 1 and Comparative Example 1. (A) is Comparative Example 1, and (B) is Example 1. It is the figure which showed the evaluation result of the lifetime distribution of the silicon wafer of Example 2 and Comparative Example 2. (A) is Comparative Example 2, and (B) is Example 2.

  Hereinafter, the silicon wafer for metal contamination evaluation according to the present invention, its manufacturing method, and the effects thereof will be specifically described.

  When an attempt is made to evaluate contamination of an actual product wafer using PCD or SPV, a wafer having low resistivity or a wafer in which a dopant is diffused causes noise to increase because the PCD signal and SPV signal decrease. In addition, in silicon wafers that have undergone a heat treatment process to some extent, oxygen precipitation is affected, making it impossible to directly evaluate the contamination of product wafers.

For this reason, it is common to flow a monitor wafer that has not been heat-treated to a specific heat treatment step and evaluate the level of contamination in that step.
In addition, since most metal contamination occurs during the heat treatment process, the monitor wafer is put into the process to be evaluated and subjected to heat treatment that is almost equivalent to the product, and the presence or absence of metal contamination is measured by measuring SPV and lifetime. Is evaluated.

However, when contamination evaluation is performed in a heat treatment process for a long time at a relatively high temperature, a decrease in lifetime and diffusion length due to oxygen precipitation may occur in a swirl shape.
When the lifetime or SPV is affected by oxygen precipitation, it often becomes prominent at the outer peripheral portion, but on the other hand, sometimes the lifetime of the outer peripheral portion is increased.

For example, FIG. 1 shows an example of lifetime characteristics of a silicon wafer that has been heat-treated for a long time. As shown in FIG. 1, the region 4 with a long lifetime corresponds to the OSF ring of the crystal, and the outside thereof. Then, there are a region 2 having a slightly short lifetime and a region 1 having a short lifetime, and the lifetime is reduced. In addition, the lifetime is lower than the OSF ring region where oxygen precipitation is difficult to occur because there is some oxygen precipitation in the center, and there is a region 3 having a slightly longer lifetime.
This significant decrease in lifetime outside the OSF ring is attributed to oxygen precipitation, and this region has been found to correspond well with oxygen precipitation observed inside the crystal by defect etching or the like. That is, it can be said that the lifetime distribution as shown in FIG. 1 reflects not the metal contamination but the crystal characteristics.

In addition, FIG. 2 shows that a decrease in lifetime due to oxygen precipitation and a decrease in lifetime due to metal contamination, which the present invention intends to solve, were observed at the same time. It is the figure which showed an example of lifetime distribution of the silicon wafer when it becomes difficult to judge.
As shown in FIG. 2, a lifetime decrease (region 1 with a short lifetime) is observed only on the outer peripheral portion of the wafer.
If this lifetime reduction is contamination from the furnace body of the heat treatment furnace, the lifetime reduction at the orientation flat portion should be along the orientation flat. However, in this case, the region where the lifetime is reduced has a ring shape and should be determined to be due to the crystal.

Although silicon wafers having the same specifications are arranged before and after this silicon wafer, they are charged into the heat treatment furnace, but the orientation flats are not completely aligned. Naturally, it is confirmed by the inspection at the stage of crystal growth completion that the outer periphery of the ingot is not contaminated during the ingot growth.
For this reason, it can be understood from this data alone that it is not possible to judge whether there is metal contamination from the heat treatment furnace or due to the characteristics of the monitor wafer.

  Therefore, in order to improve the reliability of the contamination evaluation on the outer periphery of the wafer, it is important to evaluate the metal contamination due to PCD and SPV in the heat treatment process using a monitor wafer that suppresses oxygen precipitation of the wafer as much as possible.

Here, in order to realize a wafer that directly suppresses the influence of oxygen precipitation and has uniform oxygen precipitation characteristics up to the outer periphery of the wafer, that is, a wafer that does not have a region where oxygen precipitation is likely to occur on the outer periphery. This is a countermeasure that is easy to realize by using a low crystal.
However, monitor wafers have not been strictly controlled because of the desire to use as cheap a wafer as possible from the viewpoint of cost reduction. In order to fulfill the original purpose, it can be said that the use of a low oxygen concentration substrate is particularly necessary for evaluating the contamination of the outer periphery. However, in order to reliably suppress oxygen precipitation at the outer peripheral portion, it is necessary to manufacture a crystal having an extremely low oxygen concentration (for example, <0.45 × 10 ¹⁸ atoms / cm ³ ).

  Also, if we try to eliminate the influence of oxygen precipitation at the outer periphery, the variation in precipitation characteristics will be large, so the oxygen concentration will have to be extremely low, but there will be very restrictions on technology and cost in crystal production. As it becomes larger, many problems remain for application to monitor wafers.

With the recent development of simulation technology, the growth rate of silicon crystal, the vacancies in the crystal, their aggregates (voids), and the phenomenon such as the promotion of oxygen precipitation by vacancies have been analyzed semi-quantitatively.
However, the discussion about the crystal growth direction is exclusively, and it cannot be said that sufficient discussion and control methods have been established for the characteristics of the outer periphery of the ingot (see Non-Patent Document 2).

In addition, a silicon wafer for monitoring metal contamination during heat treatment is required to have uniform lifetime characteristics before and after heat treatment if there is no contamination.
However, it has become apparent that the properties of crystals are changed by the heat treatment, and the lifetime characteristics are also changed along with the improvement of the sensitivity of the lifetime measurement.

In order to eliminate such cases, the present inventors have conducted intensive studies. As a result, in order to suppress oxygen precipitation on the monitor wafer, the oxygen concentration in the crystal should be low. Considering low temperature, if the oxygen precipitation does not affect the lifetime by heat treatment at 1100 ° C. for about 1 hour, there is no problem with respect to the wafer center as long as it is 0.7 × 10 ¹⁸ atoms / cm ³ or less. However, in view of the tendency for oxygen precipitation on the outer periphery of the wafer to be very likely to occur, the heat treatment conditions are becoming easier to occur. The idea was to cut the crystal ingot after growing the caliber crystal.

  Actually, there is a limit to the accuracy of diameter control, so when a single crystal ingot is grown, cutting of several millimeters is performed, but grinding more than that increases loss and cost, It was considered unrealistic to carry out the production of monitor wafers used in large quantities.

However, considering that the technology for completely controlling the oxygen precipitation of the CZ wafer has not been established, the oxygen concentration in the crystal is reduced to such an extent that the crystal growth process is not affected (the oxygen concentration is 0.7 × 10 ^18). atoms / cm ³ or less), and having a resistivity of 1 Ωcm or more and further reducing the diameter of the growth ingot to remove the outer peripheral portion, the influence of the outer peripheral portion of the wafer can be minimized. Compared to the above, the inventors have thought that the reliability of metal contamination evaluation can be greatly improved, and completed the present invention.

Hereinafter, the present invention will be described in detail, but the present invention is not limited thereto.
The silicon wafer for metal contamination evaluation for evaluating metal contamination of the present invention is smaller than the diameter of the growth ingot having an oxygen concentration of 0.7 × 10 ¹⁸ atoms / cm ³ or less and a resistivity of 1 Ωcm or more. It is made of a CZ silicon wafer having a diameter removed from the outer periphery.

Thus, the silicon wafer for metal contamination evaluation of the present invention is composed of a CZ silicon wafer having an oxygen concentration of 0.7 × 10 ¹⁸ atoms / cm ³ or less and a resistivity of 1 Ωcm or more. Since the concentration is low, for example, even if heat treatment is performed at about 1100 ° C. for about 1 hour, there is an advantage that oxygen precipitation does not affect the lifetime and diffusion length. Further, since the resistivity is 1 Ωcm or more, the lifetime and diffusion length can be evaluated by highly sensitive PCD, SPV and the like.

  The CZ silicon wafer is reduced in diameter relative to the diameter of the growth ingot and the outer peripheral portion is removed. The CZ silicon wafer contains a large amount of impurities from the external atmosphere during the growth of the crystal ingot, and the lifetime and diffusion length are significantly reduced. The area outside the visible OSF ring has been removed. For this reason, there is no decrease in the lifetime and diffusion length due to crystals at the outer periphery of the wafer, and the monitor is made of a silicon wafer whose outer periphery is not removed without reducing the diameter of the growth ingot as in the past. Compared with a silicon wafer for metal contamination evaluation, the presence or absence of metal contamination can be evaluated with high accuracy over the entire wafer.

  That is, a monitor wafer capable of evaluating the presence or absence of contamination by metal impurities in a semiconductor process such as heat treatment with higher accuracy than before, and evaluating the presence or absence of metal contamination using such a silicon wafer for metal contamination evaluation of the present invention. As a result, the reliability of the evaluation of metal contamination in the semiconductor process can be greatly improved, and a silicon wafer with less metal contamination can be manufactured at a high yield.

In addition, in a CZ silicon wafer having an oxygen concentration higher than 0.7 × 10 ¹⁸ atoms / cm ^3, even when the outer peripheral portion is removed and the diameter is reduced, oxygen precipitation is large, and it is useful for measuring lifetime and diffusion length. It has a big impact. If the resistivity is lower than 1 Ωcm, it is difficult to accurately measure the lifetime and the diffusion length.
Therefore, the silicon wafer for metal contamination evaluation of the present invention is made of a CZ silicon wafer having an oxygen concentration of 0.7 × 10 ¹⁸ atoms / cm ³ or less and a resistivity of 1 Ωcm or more.

  The silicon wafer for metal contamination evaluation of the present invention as described above can be manufactured by the method for manufacturing a silicon wafer for metal contamination evaluation of the present invention as shown below, and an example thereof is shown below. Is not limited to these.

First, a single crystal ingot is grown by the CZ method so that the oxygen concentration is 0.7 × 10 ¹⁸ atoms / cm ³ or less and the resistivity is 1 Ωcm or more.
The single crystal ingot grown here is not particularly limited except for the oxygen concentration of 0.7 × 10 ¹⁸ atoms / cm ³ or less and the resistivity of 1 Ωcm or more. What is necessary is just to make it a condition.

Then, the outer periphery of the previously grown single crystal ingot is removed to reduce the diameter.
As a method for reducing the diameter of the growth ingot by removing the outer peripheral portion, the same method as the cylindrical grinding step for making a common diameter can be used, and the method is not particularly limited.
Here, the removal amount of the outer peripheral portion of the single crystal ingot is desirably 8 mm or more, which is larger than the removal amount in a general cylindrical grinding process.

Then, a silicon wafer for metal contamination evaluation having a diameter of 300 mm can be manufactured by setting the diameter of the growing single crystal ingot to 320 mm or more and the removal amount of the outer periphery of the single crystal ingot to at least 10 mm from the outer periphery.
A silicon wafer for metal contamination evaluation for a monitor having a diameter of 300 mm can be produced by excluding the outer periphery of a silicon wafer having a diameter of 300 mm or more, for example, 450 mm, but as described above, a single crystal ingot to be grown is used. Can be made by making the diameter 320 mm or more and removing at least 10 mm or more of the outer periphery.
As a result, a silicon wafer for evaluating metal contamination for a diameter of 300 mm, which can accurately evaluate the presence or absence of metal contamination, in which the outer periphery of the wafer that causes a decrease in lifetime and diffusion length is reliably removed, can be more easily evaluated. And it becomes possible to manufacture reliably.

  Also, a silicon wafer for metal contamination evaluation with a diameter of 200 mm is prepared by removing at least 10 mm or more of the outer periphery of a single crystal ingot with a diameter of 220 mm or more in the same manner as the silicon wafer for metal contamination evaluation with a diameter of 300 mm. It is possible to manufacture a highly reliable silicon wafer for metal contamination evaluation having a desired diameter.

Thereafter, the silicon wafer is cut out from the ingot after the diameter reduction to produce a silicon wafer for metal contamination evaluation.
Here, for example, a wafer-like silicon wafer is cut out (slicing process) from an ingot whose diameter has been reduced and the outer peripheral part has been removed, and chamfering (beveling process) is performed in order to drop the corners of the peripheral part of the cut silicon wafer. it can. Furthermore, lapping can be applied to eliminate unevenness on the surface of the silicon wafer, increase flatness, and minimize processing distortion during slicing. Thereafter, the processing strain layer formed on the surface layer of the semiconductor wafer during lapping can be removed by mixed acid etching (etching).

As described above, when the outer peripheral portion of the single crystal ingot grown so as to have an oxygen concentration of 0.7 × 10 ¹⁸ atoms / cm ³ or less and a resistivity of 1 Ωcm or more is removed by the CZ method, the diameter of the single crystal is reduced. Wafer manufacturing costs increase because the outer periphery of the ingot is removed, making it less suitable for regular contamination control monitors from a cost standpoint.
However, even if such disadvantages are subtracted, there are significant advantages as shown below.
For example, by flowing a silicon wafer for metal contamination evaluation manufactured by such a method to an actual device process, compared with the case where the electrical characteristics and yield of a product are evaluated using a normal 300 mm wafer, It is possible to easily and surely grasp whether the cause of the decrease in yield is due to the nature of the crystal or the process condition, and it is possible to confirm with high reliability whether the silicon wafer is low in metal contamination. it can.
Therefore, it is possible to obtain a monitor wafer that can directly and reliably evaluate whether the cause of the decrease in the yield of the outer peripheral portion is due to metal contamination or the crystal characteristics of the wafer. Therefore, it can certainly contribute to the improvement of the process and the improvement of the device manufacturing yield.

  In addition, the metal contamination evaluation silicon wafer of the present invention can be manufactured by the following method for manufacturing a metal contamination evaluation silicon wafer, but the present invention is not limited thereto.

First, a single crystal ingot is grown by the CZ method so that the oxygen concentration is 0.7 × 10 ¹⁸ atoms / cm ³ or less and the resistivity is 1 Ωcm or more.
The single crystal ingot grown here is not particularly limited except for the oxygen concentration of 0.7 × 10 ¹⁸ atoms / cm ³ or less and the resistivity of 1 Ωcm or more. What is necessary is just to make it a condition.

Then, the CZ silicon substrate is cut out from the previously grown single crystal ingot.
This cutting can also be performed under general conditions. For example, the cutting can be performed by a cutting device such as an inner peripheral slicer or a wire saw. Thereafter, at least one of lapping, etching, and polishing can be performed.

Thereafter, a predetermined amount of the outer peripheral portion of the CZ silicon substrate cut out earlier is removed to obtain a metal contamination evaluation silicon wafer having a desired diameter.
Here, the removal amount of the outer peripheral portion of the CZ silicon substrate is desirably 8 mm or more as described above.

  The diameter reduction at the wafer stage can be applied instead of the diameter reduction by cylindrical grinding of the ingot. For example, a 300 mm wafer having a thickness of 775 μm is cut and processed into a 200 mm mirror wafer, thereby obtaining a wafer excluding the outer periphery of the ingot.

In such a case, a silicon wafer for metal contamination evaluation having a diameter of 200 mm can be manufactured by setting the diameter of the CZ silicon substrate to 300 mm and the removal amount of the outer periphery of the CZ silicon substrate to at least 20 mm or more from the outer periphery.
Thus, for a silicon wafer for metal contamination evaluation for contamination evaluation for a diameter of 200 mm, for example, a CZ silicon substrate having an oxygen concentration of 300 mm in diameter of 0.7 × 10 ¹⁸ atoms / cm ³ or less and a resistivity of 1 Ωcm or more. Among them, it is possible to manufacture by selecting an amount not to be used for a device manufacturing process such as a non-standard product and removing the outer peripheral portion of the selected CZ silicon substrate.
With this method, it is possible to manufacture a highly reliable silicon wafer for metal contamination evaluation by simply excluding the outer peripheral portion where the impurity concentration is high or oxygen precipitation is likely to occur among the 300 mm diameter CZ silicon substrate. It is very easy.

Further, a silicon wafer for metal contamination evaluation with a diameter of 150 mm can be manufactured by setting the diameter of the CZ silicon substrate to 200 mm and the removal amount of the outer periphery of the CZ silicon substrate to at least 15 mm from the outer periphery.
Similarly, a silicon wafer for metal contamination evaluation for a diameter of 150 mm is a non-standard product among CZ silicon substrates having an oxygen concentration of 200 mm in diameter of 0.7 × 10 ¹⁸ atoms / cm ³ or less and a resistivity of 1 Ωcm or more. It is possible to manufacture by selecting an amount not to be used in the device manufacturing process and removing the outer peripheral portion of the selected CZ silicon substrate.

  Further, the removal of the outer peripheral portion of the CZ silicon substrate can be reduced in diameter by decentering 5 mm or more from the center of the CZ silicon substrate in a predetermined direction with respect to the orientation flat or notch of the CZ silicon substrate.

When the presence or absence of metal contamination is evaluated by a conventional silicon contamination evaluation silicon wafer, if the lifetime decreases in the periphery of the wafer, it is difficult to determine whether it is due to metal contamination or due to crystals.
On the other hand, as in the present invention, the diameter is reduced with respect to the diameter of the growth ingot, the outer peripheral portion is removed, and the diameter reduction method is performed in a predetermined direction with respect to the orientation flat or notch of the CZ silicon substrate. If the diameter is reduced by decentering 5 mm or more from the center of the substrate, even if the lifetime decreases due to oxygen precipitation, the method for removing the outer periphery is decentered. Therefore, the lifetime distribution is shifted in a predetermined direction from the wafer center. Therefore, it is possible to clearly grasp whether it is due to oxygen precipitation or due to contamination by heat treatment, and the cause of contamination can be easily determined.
Therefore, it is possible to obtain a silicon wafer for evaluation of metal contamination for monitoring which can evaluate the presence or absence of metal impurity contamination with higher reliability.

  After cutting the CZ silicon substrate from the single crystal ingot, at least one CZ silicon substrate is extracted, a passivation film is formed on the surface of the extracted CZ silicon substrate by chemical passivation, and the wafer lifetime is measured by the PCD method. After confirming that the wafer lifetime is 600 μsec or more including the outer peripheral portion of the extracted CZ silicon substrate, the outer peripheral portion of the CZ silicon substrate can be removed.

Regarding the silicon wafer for metal contamination evaluation, it is desirable to ensure that it has a sufficiently long lifetime at the end of the wafer process, including contamination of the outer periphery during crystal growth.
For example, the metal contamination amount of silicon wafers for highly integrated devices with a design rule of 0.1 μm is determined to be 1 × 10 ¹⁰ atoms / cm ³ or less in Fe concentration in the roadmap of related organizations. When the request is converted into a lifetime, it corresponds to approximately 600 μsec (see FIG. 3).
Therefore, in order to manage this level of metal contamination, the silicon wafer for metal contamination management needs to have a lifetime of at least 600 μsec at the wafer stage before heat treatment. Here, according to the method for producing a silicon wafer for metal contamination evaluation of the present invention that removes the outer peripheral portion of the CZ silicon substrate, the lifetime and diffusion length are not reduced due to the crystal even after the heat treatment. A monitor wafer capable of performing measurement with little variation in the plane is manufactured.
Therefore, at the end of the wafer processing step, the lifetime is inspected by the PCD method after chemical passivation without sampling and heat treatment, and by confirming that the lifetime is 600 μsec or more, the quality as a lifetime monitor is Can be clearly guaranteed on an ingot lot basis. Then, by removing the outer peripheral portion of the CZ silicon substrate obtained from this ingot, it becomes possible to efficiently manufacture a silicon wafer for metal contamination evaluation for monitoring that can perform highly sensitive metal impurity evaluation. .
FIG. 3 is a graph showing the relationship between the iron concentration of the silicon wafer, the minority carrier lifetime (lifetime), and the diffusion length.

  Thus, if it is a method of removing the outer peripheral portion of the large-diameter CZ silicon substrate, its production quantity is limited, but for example, a CZ silicon single crystal that has become a non-standard product can be used. The problem relating to the manufacturing cost of the monitor wafer can be reduced as compared with the case of reducing the diameter by removing the outer peripheral portion of the single crystal ingot. Therefore, the implementation is very easy and can be implemented sufficiently in terms of cost.

EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated more concretely, this invention is not limited to these.
(Example 1, Comparative Example 1)
Two types of silicon wafers for metal contamination evaluation for lifetime measurement having a diameter of 150 mm were prepared.
The first type is a commonly used crystal plane (100) crystal of P-type, boron-doped diameter 150 mm manufactured by CZ method, and the interstitial oxygen concentration is 13.0 ppma (0. 65 × 10 ¹⁸ atoms / cm ³ ) and the resistivity is about 8.0 Ωcm. The back surface of this silicon wafer is mirror-polished after etching, and no processing strain is formed (Comparative Example 1).
The second type has a diameter of 200 mm produced by the CZ method, a crystal plane (100), an interstitial oxygen concentration of 13.0 ppma (0.65 × 10 ¹⁸ atoms / cm ³ ), and a resistivity center of 7.5 Ωcm. The wafer was cut into a central portion of the CZ silicon substrate and processed to a diameter of 150 mm, and the thickness was processed to 625 μm, the same as the 150 mm wafer. In addition, the back surface of this silicon wafer is mirror-polished after etching, and no processing strain is formed (Example 1).

  After performing standard SC1 and SC2 cleaning on these two types of silicon wafers, they were put in an oxidation furnace at 700 ° C. in a nitrogen atmosphere and heat-treated at 1,050 ° C. for 120 minutes. The product was cooled to 700 ° C. and taken out from the oxidation furnace. Five dummy wafers were charged before and after these silicon wafers.

Next, the oxide film on the surface was removed with hydrofluoric acid, and the wafer lifetime was measured by chemical passivation (dip in iodine-ethanol solution).
The wafer lifetime was measured using a PCD wafer lifetime measuring instrument using near-infrared light excitation and 1 GHz microwave reflection. These results are shown in FIG.

Lifetime measurement for evaluating metal contamination in a heat treatment furnace using the silicon wafer of Comparative Example 1 in which the outer peripheral portion is not removed without being reduced in diameter with respect to the diameter of the growth ingot as used conventionally. As shown in FIG. 4A, the lifetime of the outer peripheral portion of the silicon wafer was lowered, and it seemed that there was contamination.
However, as shown in FIG. 4B, when the lifetime measurement is similarly performed using the silicon wafer of Example 1 whose diameter is reduced with respect to the diameter of the growth ingot, the decrease in the lifetime at the outer peripheral portion is as follows. , Staying in a slight range from the outer peripheral portion, the lifetime was reduced slightly in other parts.
That is, in the evaluation using the silicon wafer of Example 1, it was judged that there was almost no contamination during the heat treatment.

As described above, even in the metal contamination evaluation for the same heat treatment furnace, different results were obtained due to the difference in the properties of the monitor wafer.
Therefore, in the conventional method using the silicon wafer of Comparative Example 1, even if there is a decrease in the lifetime of the outer peripheral portion of the silicon wafer, which is a problem, it is often determined to be pending without determining that it is abnormal. From the result of using the silicon wafer of Example 1, it was clearly understood that the lifetime was not reduced due to metal contamination of the oxidation furnace.
Thus, by using a silicon wafer having a reduced diameter with respect to the growth ingot as in Example 1, it is possible to accurately evaluate whether the lifetime is caused by crystal or metal contamination. It was found that the presence or absence of metal contamination can be evaluated.

(Example 2, comparative example 2)
A center portion of a 300 mm diameter CZ silicon substrate produced by the CZ method having the same oxygen concentration and resistivity as in Example 1 was cut out to produce a silicon wafer having a diameter of 200 mm. In the cutting of the CZ silicon substrate, the center of the 200 mm wafer was cut from the center of the 300 mm diameter wafer by 40 mm in the notch direction with respect to the center of the 300 mm diameter CZ silicon substrate. Thereafter, the wafer was etched and polished so that the thickness of the wafer became 725 μm, thereby producing a monitor wafer having a diameter of 200 mm (Example 2).
Further, a normal monitor wafer having a diameter of 200 mm and an oxygen concentration / resistivity comparable to that of the above-mentioned 300 mm diameter wafer was prepared (Comparative Example 2).

  The above two types of silicon wafers were subjected to standard SC1 and SC2 cleaning, placed side by side in a boat, and heat-treated in a horizontal diffusion furnace. The atmosphere gas for the heat treatment was a nitrogen gas containing 3% oxygen, which was charged into a furnace at 800 ° C. and heated to 1150 ° C. for 120 minutes. Then, after cooling to 800 ° C. and taking out from the furnace, the oxide film was etched with hydrofluoric acid, then chemical passivation with iodine ethanol solution was performed, and the lifetime was measured by the PCD method. The results of lifetime measurement of these two types of silicon wafers are shown in FIG.

As shown in FIG. 5A, in the silicon wafer of Comparative Example 2, a region having a low lifetime was observed on the entire outer peripheral portion.
On the other hand, as shown in FIG. 5B, in the case where the silicon wafer of Example 2 that was eccentric and cut out from the 300 mm wafer was used, the lifetime was reduced only in a small portion of the outer periphery on the notch side. As can be seen, on the side opposite to the notch, the lifetime was reduced in a region corresponding to the outer peripheral portion of the 300 mm wafer.

As described above, in the silicon wafer of Comparative Example 2, a spot-like lifetime reduction portion that seems to be contaminated from particles in the wafer central portion and a region in which the lifetime was greatly reduced in the entire outer periphery of the wafer were seen. It was not observed in the silicon wafer of Example 2.
From these results, it was found that the decrease in the lifetime of the outer peripheral portion reflects the characteristics of the crystal and is not metal contamination from the furnace body. It was also found that if the direction of eccentricity and the size thereof are appropriately selected, the lifetime reduction due to the crystal characteristics can be distinguished from the lifetime reduction due to metal contamination.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has any configuration that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits the same effects. Are included in the technical scope.

1 ... A short lifetime area
2… A region with a slightly short lifetime,
3… A region with a slightly longer lifetime,
4 ... An area with a long lifetime.

Claims (5)

A method for producing a silicon wafer for evaluating metal contamination for evaluating metal contamination, comprising:
A single crystal ingot is grown by the CZ method so that the oxygen concentration is 0.7 × 10 ¹⁸ atoms / cm ³ or less and the resistivity is 1 Ωcm or more.
CZ silicon substrate is cut out from the grown single crystal ingot,
Thereafter, the CZ silicon substrate is cut out to remove the outer peripheral portion. The metal contamination evaluation silicon wafer having a diameter of 200 mm is manufactured by setting the diameter of the CZ silicon substrate to 300 mm and the removal amount of the outer periphery of the CZ silicon substrate to at least 20 mm or more from the outer periphery. 2. A method for producing a silicon wafer for metal contamination evaluation according to 1 . The metal contamination evaluation silicon wafer having a diameter of 150 mm is manufactured by setting the diameter of the CZ silicon substrate to 200 mm, and removing the outer peripheral portion of the CZ silicon substrate to at least 15 mm from the outer peripheral portion. 2. A method for producing a silicon wafer for metal contamination evaluation according to 1 . The removal of the outer peripheral portion of the CZ silicon substrate is performed by decentering the CZ silicon substrate by decentering it by 5 mm or more from the center of the CZ silicon substrate in a predetermined direction with respect to the orientation flat or notch of the CZ silicon substrate. The method for producing a silicon wafer for metal contamination evaluation according to any one of claims 1 to 3 . After the CZ silicon substrate is cut out from the single crystal ingot, at least one CZ silicon substrate is extracted, a passivation film is formed on the surface of the extracted CZ silicon substrate by chemical passivation, and a wafer lifetime is increased by a PCD method. measuring, after the wafer lifetime was sure that the 600μsec or more including the outer peripheral portion of the CZ silicon substrate was taken out the, claims and removing the outer peripheral portion of the CZ silicon substrate 1 A method for producing a silicon wafer for metal contamination evaluation according to any one of claims 1 to 4 .

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