JP4383999B2 - Method for measuring cleanliness of semiconductor wafer storage member - Google Patents

Description

  The present invention relates to a method for measuring the cleanliness of a semiconductor wafer storage member used for storage or transportation of semiconductor wafers, and in particular, quantitatively detects foreign particles adhering to the wafer storage member or generated from the wafer storage member itself. It relates to a cleanliness measuring method to be evaluated.

  FIG. 5 shows an example of a wafer case that is a wafer storage member for storing or transporting a semiconductor wafer made of silicon, a III-V group compound, a II-VI group compound, or the like. The wafer case 1 includes a wafer basket 4 for storing wafers W in parallel, a wafer case main body 2 for storing the baskets, an upper lid 3 for the wafer case main body 2, and a wafer for holding and holding the wafers W in the wafer basket 4. Including presser 6 and packing 5.

  In order to minimize particles adhering to the wafer when the wafer W is stored or transported, it is required that the wafer case always be kept clean. Particles adhering to the wafer surface need to be controlled to a size of 0.06 μm in recent years. Of course, particles adhering to the inside of the wafer case or generated from the wafer case itself are also measured to a size of 0.06 μm and cleaned. It is important to evaluate the degree.

  As a method for evaluating the cleanliness of such a wafer case, pure water is injected into the wafer case, then a vibration is applied for a certain period of time with a shaker, and particles in pure water before and after vibration are counted with a liquid particle counter. Thus, a method for evaluating the cleanliness of the wafer case based on the increased amount is provided (see, for example, Patent Document 1).

  As another method, there has been proposed a method in which deaerated water is injected into a measurement tank, an object to be measured is immersed in the deaerated water, and the number of particles in the deaerated water is measured with a submerged particle counter ( For example, see Patent Document 2). In this method, bubbles are generated depending on the gas dissolved in pure water by using degassed water, and particles are quantified.

  However, in the above measurement method, the influence of bubbles in pure water taken in by vibration, immersion, etc. cannot be excluded, and it is doubtful whether only foreign substances can be accurately measured as particles, and the actual number of particles Had the problem of being unknown.

  In addition, since these methods use an in-liquid particle counter, particles that can be detected are at most 0.1 μm in size, and particles smaller than this cannot be evaluated. However, there is a problem that it cannot be applied to the current situation where detection of finer particles is required with the miniaturization.

Japanese Patent No. 3003550 JP 2001-276760 A

  The present invention has been made in view of such a problem, and particles adhering to the semiconductor wafer storage member or generated from the semiconductor wafer storage member itself are not affected by bubbles present in pure water. An object of the present invention is to provide a method for measuring the cleanliness of a wafer storage member that is detected with high accuracy.

The present invention has been made in order to solve the above-mentioned problems, and is a method for measuring the cleanliness of a semiconductor wafer storage member, which is for inspection in which the number of particles is counted in advance after contacting the wafer storage member with pure water. After extracting pure water brought into contact with the housing member onto the wafer surface, dropping and drying, the number of particles on the wafer surface for inspection is counted, and the number of particles increased before and after dropping of pure water is obtained. the increase in the number that provides cleanliness measurement method of a semiconductor wafer accommodation member, characterized in that to evaluate the cleanliness of the wafer housing member.

  As described above, after the wafer storage member is brought into contact with pure water, the pure water brought into contact with the storage member is extracted on the surface of the wafer for inspection in which the number of particles has been counted in advance, and is dropped and dried. By counting the number of particles on the wafer surface and calculating the increase in the number of particles before and after the addition of pure water, the effect of bubbles in pure water is completely eliminated, and the number of particles is measured accurately and reliably, and stored in the wafer. The quality of the member can be determined.

Further, the state in which the wafer housing member is brought into contact with pure water, it is not preferable to extract the pure water the wafer housing member after a predetermined time vibration.

  As described above, the pure water is extracted after the wafer storage member is vibrated for a predetermined time in a state where the pure water is brought into contact with the wafer storage member, so that the wafer storage member is attached to the wafer storage member. Particles generated from itself can be measured with higher accuracy. Although a large amount of bubbles are generated in the pure water due to vibration, the influence of the bubbles can be eliminated in the present invention, so that the number of particles can be accurately measured.

Further, a count of the number of particles, Ru can be performed by laser scattering method which counts the number of scatterers generated on the surface of the object to be measured by irradiating a laser. In this case, the laser scattering method, it is not preferable can detect the scattering of the following sizes 0.1 [mu] m.

  As described above, by using the laser scattering method, it is possible to detect a scatterer having a size of 0.1 μm or less, and detect the level of particles that could not be detected by the conventional liquid particle counter, thereby cleaning the wafer storage member. Can be evaluated.

Furthermore, as a test wafer for the use, size is not preferable be used as more than the number of particles 0.04μm is 16 / cm ² or less on its surface.

As described above, the inspection wafer to be used has a surface with a number of particles having a size of 0.04 μm or more and 16 particles / cm ² or less, thereby reducing noise during measurement and performing more accurate measurement. Can do.

In this case, as a test wafer for the use, it is not preferable to use a material obtained by forming an oxide film on the surface thereof.

  In this way, by using an inspection wafer having an oxide film formed on the surface, the surface of the inspection wafer becomes hydrophilic, dripped pure water soaks into the oxide film, and foreign substances present in the pure water are oxidized. Since it remains on the film surface, the number of particles adhering to the wafer storage member can be measured more accurately and reliably and the quality of the wafer storage member can be judged.

In this case, as a test wafer for the use, Ru can be used a semiconductor silicon single crystal wafer.

  Thus, by using a semiconductor silicon single crystal wafer as the inspection wafer, a wafer having a clean mirror surface necessary for measurement can be easily obtained. Cleanliness is required, and storage and transportation are necessary for storing and transporting large quantities. Therefore, use the wafers that are to be stored in the wafer storage member as inspection wafers, and perform measurements according to the actual situation. be able to.

  As described above, according to the present invention, after bringing the wafer storage member into contact with the pure water, the pure water brought into contact with the storage member is extracted and dropped onto the surface of the inspection wafer on which the number of particles has been counted in advance. -After drying, count the number of particles on the surface of the wafer for inspection, and calculate the number of particles without being affected by bubbles in pure water by obtaining the number of particles increased before and after dropping pure water, The cleanliness of the wafer storage member can be evaluated.

  Conventionally, the cleanliness of a semiconductor wafer storage member has been measured by injecting pure water into the wafer storage member and measuring the number of particles in the pure water with an in-liquid particle counter. However, there is a problem that it is unclear whether only foreign matters can be accurately measured as particles by eliminating the influence of bubbles in pure water. Therefore, the present inventors conducted the following investigation on the measurement using the liquid particle counter.

  Prepare a beaker made of Teflon (registered trademark) with an internal volume of 1 L (liter), wash it with alcohol, then wash it with a pure water shower for 1 hour, and then wash it with pure water for 5 hours. I did it.

0.7 L of deaerated pure water was gently poured into the beaker, and immediately after that, 10 mL of pure water in the beaker was sampled, and particles of pure water were measured with a submerged particle counter. Thereafter, the beaker was lightly swung and then left, and the relationship between the standing time and the measured value of the liquid particle counter was investigated. The results are shown in Table 1.

  Although the number of particles immediately after the injection of pure water, that is, before the oscillation is four at 0.1 μm or more, the number of particles at 0.1 μm or more is greatly increased to 38438 due to slight oscillation. After leaving for 40 minutes, it decreases to 31829. After 5520 minutes, the number decreased to 17794, but the number increased significantly compared to 4 before swinging.

  Considering that the beaker is sufficiently cleaned, it is unlikely that such a large number of particles are attached to the wall surface of the beaker. In addition, the number of particles decreases with the standing time after swinging, but if the particles are actually present in pure water, the number of particles should remain unchanged regardless of the standing time. Such a phenomenon is considered to be that bubbles are generated in pure water due to rocking and disappear with time, and it is reasonable to think that the liquid particle counter counts the generated bubbles. is there.

Next, the relationship between the measured value by the liquid particle counter and dissolved oxygen was investigated. As in the experiment of Table 1, the used beaker was washed with a 1 L Teflon (registered trademark) beaker with alcohol, then washed with a pure water shower for 1 hour, and further washed with pure water for 5 hours. It was a pouring. Deaerated 0.7 L of pure water was injected into the beaker, 10 mL of pure water immediately after injection was sampled, and particles were measured with an in-liquid particle counter. Further, pure water was sampled to measure dissolved oxygen. Then, after gently shaking by hand several times, 10 mL of pure water was sampled and the particles in the liquid and dissolved oxygen were measured in the same manner. Further, after gently shaking again several times by hand, 10 mL of pure water was sampled and the particles in the liquid and dissolved oxygen were measured in the same manner. The results are shown in Table 2. FIG. 6 is a graph of Table 2.

  From Table 2, it can be seen that the number of particles in the liquid increases rapidly each time rocking is performed, and dissolved oxygen also increases in proportion to this. In other words, it is considered that oxygen in the air was taken into the pure water by rocking and bubbles were formed.

  From the above experiment, the present inventors have determined that it is practically impossible to accurately measure particles in the liquid because bubbles are generated by slight fluctuation even in deaerated water. It was.

  Therefore, as a result of repeated studies, the present inventors have extracted the pure water that has been brought into contact with the storage member onto the surface of the wafer for inspection in which the number of particles has been counted in advance after contacting the semiconductor wafer storage member with pure water. After dropping and drying, count the number of particles on the surface of the wafer for inspection and calculate the number of particles before and after dropping pure water, and count the number of particles without being affected by bubbles in pure water. The present inventors have found that the cleanliness of the wafer storage member can be evaluated and completed the present invention.

Hereinafter, although this invention is demonstrated in detail, this invention is not limited to these.
An example of the method for measuring the cleanliness of the semiconductor wafer storage member of the present invention will be described with reference to the flowchart shown in FIG.
First, an inspection wafer is prepared (Step 1). The wafer used as the inspection wafer is not particularly limited. For example, when a semiconductor silicon single crystal wafer is used, the wafer to be stored in the wafer storage member is used as the inspection wafer, and the cleanliness measurement according to the actual situation is performed. It can be performed. Of course, a glass substrate, a metal plate or the like whose surface has been polished may be used as an inspection wafer.

As this inspection wafer, it is desirable to use a wafer having an oxide film formed on the surface thereof. The thickness of the oxide film is not particularly limited, but is more preferably 1 nm or more. When this oxide film is formed, the surface of the wafer for inspection becomes hydrophilic, and the dropped pure water soaks into the oxide film without forming a watermark, and foreign matter present in the pure water remains on the oxide film surface. To do. It is preferable that the watermark does not exist because it can cause noise during particle measurement. Therefore, if an inspection wafer on which an oxide film is formed is used, particles can be measured more accurately and reliably and the quality of the wafer storage member can be judged. In order to form an oxide film on the wafer surface, it is easy to clean with an NH ₄ OH / H ₂ O ₂ (so-called SC1) solution often used for cleaning silicon wafers. Alternatively, the oxide film can be similarly formed by immersing the wafer in pure water in which O ₃ is dissolved.
The upper limit of the thickness of the oxide film need not be particularly limited, but 1000 nm is sufficient.

Further, it is desirable to use an inspection wafer that has a small number of particles measured on the surface thereof. This is because when the number of particles is small, noise in measurement is reduced, and measurement with higher accuracy is possible. Specifically, the number of particles having a size of 0.04 μm or more on the surface of the inspection wafer is preferably 16 particles / cm ² or less.

Furthermore, when the number of particles in Step 2 or Step 6 is measured by a laser scattering method that counts the number of bright spots, that is, the number of laser light scatterers, caused by foreign matter or crystal defects on the wafer surface by laser irradiation. The point defects present on the inspection wafer are measured as scatterers and become noise. Therefore, measurement with higher accuracy is possible with fewer point defects. It is preferable to use a wafer having few point defects and satisfying that the number of particles having a size of 0.04 μm or more is 16 particles / cm ² or less on the surface of the inspection wafer.

  Here, the Si wafer is dominated by vacancy-type point defects depending on the manufacturing method of the ingot, the region where the agglomerates exist (hereinafter referred to as V-Rich region) and the interstitial silicon point defects are dominant. It is divided into a region where aggregates are present (hereinafter referred to as I-Rich regions), a defect-free region (hereinafter referred to as N region) where there are no agglomerates of vacancy type point defects and agglomerates of interstitial silicon point defects. Regarding the control of these regions, Voronkov discloses a technique for controlling the ingot pulling speed (V) and the temperature gradient (G) at the ingot / melting surface interface in the pulling method in the Si ingot manufacturing stage (Journal of Crystal Growth, Vol 59, 1982, pp 625-643).

Since the Si wafer cut out from V-Rich or I-rich has agglomerates of point defects, these are measured as scatterers by the laser light scattering method, and thus become measurement noise. On the other hand, since there are no point defect aggregates in the wafer in the N region, the number of scatterers having a size of 0.04 μm or more is less than 5000 (that is, 16 / cm ² or less) in a wafer having a diameter of 200 mm by the laser light scattering method. It can be a certain wafer.
As a method for manufacturing such a wafer, for example, there is a Si wafer composed of an N region as disclosed in JP-A 1-1393. As another example, for example, Japanese Patent Laid-Open No. 2000-5349 proposes a method of manufacturing while controlling so as to be an N region in a crystal doped with N ₂ in a pulling method. In addition to this, even when a wafer or an epitaxial wafer in which point defect aggregates are eliminated by annealing is used, it is possible to achieve 16 / cm ² or less of scatterers having a size of 0.04 μm or more detected by the laser scattering method.

  When the inspection wafer is prepared, the number of particles on the surface of the inspection wafer is measured (Step 2). The number of particles obtained by this measurement is taken as 1 for measurement. The method for measuring the particles is not particularly limited, and existing equipment can be used, but it is preferable to perform the laser scattering method. As a particle counter using such a laser scattering method, a device capable of detecting up to about 0.04 μm is commercially available recently, and the detection limit of the liquid particle counter used in the conventional method is 0.1 μm. Compared to this, there is a merit that even smaller particles can be evaluated. Thus, by using a laser scattering type particle counter (for example, Surfscan SP-1 manufactured by KLA-Tencor) capable of detecting a scatterer having a size of 0.1 μm or less, it cannot be evaluated with a conventional liquid particle counter. It becomes possible to evaluate the cleanliness of the wafer storage member to a certain level.

  Subsequently, pure water is brought into contact with the wafer housing member (Step 3). The method of bringing pure water into contact with the wafer housing member is not particularly limited. For example, pure water is injected into the wafer case main body 2 shown in FIG. 5 by about 80% of its internal volume, and the upper lid 3 is closed. It is done. At this time, by setting the wafer presser 6, the wafer basket 4, and the packing 5, the cleanliness of these storage members can be evaluated together. On the other hand, when it is desired to measure only the wafer basket 4, packing 5, wafer presser 6, etc., they are brought into contact by being immersed in pure water. That is, the method of contacting each member with water may be selected as appropriate depending on the shape.

  Next, it is preferable to vibrate the wafer storage member in contact with the pure water for a certain time (Step 4). Thus, if the pure water is extracted after vibrating the wafer storage member for a certain time in a state where pure water is in contact with the wafer storage member, the wafer storage member adheres to the wafer storage member or from the wafer storage member itself. This is because the generated particles are surely transferred in pure water, and the cleanliness of the wafer storage member can be measured more accurately. In this case, if vibration is applied, an enormous amount of bubbles are generated in the pure water. However, in the present invention, there is no problem because the influence of the bubbles generated in the pure water can be eliminated in a subsequent process. The conditions for vibration are not particularly limited, and for example, the vibration may be performed in the X-axis and Y-axis directions at a frequency of 50 to 2000 Hz and an acceleration of 2G to 50G for 0.5 to 30 minutes, respectively. However, this vibration step may be omitted depending on the purpose.

  Next, the pure water brought into contact with the wafer housing member is extracted, and the number of particles is dropped onto the surface of the inspection wafer that has been measured in Step 2 and dried (Step 5). The amount of pure water extracted is not particularly limited, but it can be measured more accurately if it is 0.01 mL or more. The drying method may be natural drying or the like.

  Subsequently, the number of particles on the surface of the inspection wafer dried in Step 5 is measured (Step 6). The number of particles obtained by this measurement is taken as the measurement number 2. For the measurement of the number of particles, the same method as used in Step 2 is used.

  Next, the number of particles measured in Step 2 (measurement number 1) is subtracted from the number of particles measured in Step 6 (measurement number 2) to obtain the number of particles in pure water extracted in Step 5, and based on the result. The cleanliness of the wafer storage member is evaluated and the quality is judged (Step 7).

  If the method for measuring the cleanliness of the semiconductor wafer storage member as described above, unlike the conventional measurement method using a particle counter in liquid, the number of particles is counted without being affected by bubbles in pure water, The quality of the wafer storage member can be determined. In addition, if a particle counter that can detect scatterers with a size of 0.1 μm or less by the laser scattering method is used, particles smaller than the measurement method using the conventional liquid particle counter (detection lower limit 0.1 μm) are also detected. Thus, the cleanliness of the wafer storage member can be evaluated.

Examples of the present invention will be described below, but the present invention is not limited thereto.
(Examples and comparative examples)
Cleanliness is measured using a wafer case for housing 25 8 "φ silicon wafers as a semiconductor wafer storage member (evaluation before manual cleaning), and then the wafer case is manually cleaned and cleaned again. The measurement was performed (evaluation after manual cleaning), and a flow chart showing the outline is shown in FIG.

  First, an inspection wafer was prepared (Step 1). As an inspection wafer, an 8 ".phi. Silicon wafer having an orientation <100>, p-type, and prepared by controlling the pulling conditions so that the entire surface of the wafer is in the N region was prepared. The wafer was SC1 cleaned in the process, and an oxide film was formed on the surface about 5 nm.When this wafer was used as it was (hereinafter referred to as an oxide film wafer), a wafer from which the surface oxide film was removed by HF cleaning was used. Comparison was made in each case (hereinafter referred to as bare Si wafer), and three oxide film wafers and three bare Si wafers were prepared.

  Next, on the surface of the wafer for inspection, a scatterer having a size of 0.065 μm or more was measured using a laser scattering type Surfscan SP1 manufactured by Kla-Tencor, and the measurement value was set to 1 (Step 2). ).

  Subsequently, for the wafer case 1 shown in FIG. 5, the wafer holder 6, the wafer basket 4, and the packing 5 are set in the wafer case body 2, 3 L of pure water is injected, and the upper lid 3 is closed (Step 3). .

  Next, the wafer case 1 was loaded on a shaker, and was vibrated for 1 minute in the X-axis and Y-axis directions at a frequency of 400 Hz and an acceleration of 10 G (Step 4).

  Next, the upper lid 3 was opened, 0.1 mL of pure water in the wafer case 1 was extracted, dropped onto a wafer for inspection that had been measured by the laser scattering method at Step 2, and naturally dried (Step 5).

  Subsequently, the number of particles on the surface of the inspection wafer dried in Step 5 was measured by Surfscan SP1 manufactured by Kla-Tencor, as in Step 2, and this measurement value was set to 2 (Step 6).

  The measurement number 1 was subtracted from the measurement number 2 to evaluate the cleanliness of the wafer case (Step 7).

  As a comparative example, after the wafer case 1 was left for 20 minutes after Step 4, 10 mL of pure water in the wafer case 1 was extracted in the same manner as before, and particles in the pure water were measured with a liquid particle counter.

  Next, the wafer case 1 after Step 7 was manually cleaned. The wafer case 1 was washed with alcohol, then poured in a pure water shower for 1 hour, and then poured in pure water for 5 hours.

Further, for the wafer case 1 after the manual cleaning, the cleanliness measurement in Step 1 to Step 7 and the particle counter measurement in liquid after being left for 20 minutes were performed again.
The results are shown in Table 3. 3 and 4 are graphs showing the results of Table 3.

  As shown in Table 3 and FIG. 3, in the cleanliness measurement method using a conventional submerged particle counter (comparative example), the particles in the wafer case after manual cleaning have a size of 0.1 μm or more and 0.15 μm or more. The number of particles is decreasing, but the number of particles of 0.2 μm or larger is increasing, and the number of particles converted to 0.1 μm increases despite sufficient manual cleaning. As a result.

  On the other hand, in the cleanliness measuring method according to the present invention, as shown in FIG. 4, in both the bare Si wafer and the oxide film wafer, the cleanliness is better in the wafer case after cleaning than in the wafer case before cleaning. Therefore, the measurement results reflected the decrease in the number of particles due to manual cleaning.

However, the measurement result using the bare Si wafer shown in FIG. The number of particles before cleaning increased by 3 but when viewed under a condenser lamp, white haze was generated at the pure water / Si wafer interface where the pure water dropped on the Si wafer spread. The watermark was generated. This is considered to be caused by measuring haze as a scatterer.
On the other hand, in the case of a wafer with an oxide film, such a phenomenon was not recognized, and more accurate measurement was possible.

  As described above, if the method for measuring the cleanliness of a semiconductor wafer storage member according to the present invention is used, particles adhering to the semiconductor wafer storage member or generated from the semiconductor wafer storage member itself are affected by bubbles present in pure water. It can be seen that the detection can be performed with high accuracy without receiving the signal. Furthermore, if a particle counter capable of detecting a scatterer having a size of 0.1 μm or less by a laser scattering method is used, even a small particle that cannot be detected by a conventional liquid particle counter (detection lower limit 0.1 μm) can be detected. The cleanliness of the wafer storage member can be evaluated at a high level.

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

For example, a semiconductor wafer storage member to which the present invention can be applied is not limited to a silicon wafer storage member, and may be a wafer storage member that requires high cleanliness such as a compound semiconductor.
Further, in the evaluation of the present invention, the cleanliness of the space or room in which the evaluation is performed is preferably good, and is preferably set to class 100 or less.

It is a flowchart which illustrates roughly an example of the cleanliness measuring method of the semiconductor wafer storage member of this invention. It is a flowchart which illustrates an Example and a comparative example roughly. It is the graph which measured the cleanliness of the wafer case before and after manual cleaning using the conventional cleanliness measuring method (comparative example). It is the graph which measured the cleanliness of the wafer case before and behind manual cleaning using the wafer for an inspection by the cleanliness measuring method according to the present invention (example). (A) Bare Si wafer, (b) Wafer with oxide film. It is a perspective view showing an example of a wafer case used for storage or transportation of a semiconductor wafer. It is the graph which investigated the relationship between the measured value by the particle counter in liquid, and dissolved oxygen.

Explanation of symbols

1 ... wafer case, 2 ... wafer case body, 3 ... top cover,
4 ... Wafer basket, 5 ... Packing, 6 ... Wafer holder, W ... Wafer.

Claims (6)

A method for measuring the cleanliness of a semiconductor wafer storage member, wherein the wafer storage member is brought into contact with pure water, and then contacted with the storage member on the surface on which the oxide film of the inspection wafer is previously counted. The extracted pure water was extracted, dropped and dried, and the number of particles on the surface of the inspection wafer on which the oxide film was formed was counted to obtain the number of particles increased before and after the addition of pure water. A method for measuring the cleanliness of the semiconductor wafer storage member, wherein the cleanliness of the wafer storage member is evaluated by:   2. The cleanliness measurement of a semiconductor wafer storage member according to claim 1, wherein the pure water is extracted after the wafer storage member is vibrated for a predetermined time in a state where pure water is in contact with the wafer storage member. Method.   3. The semiconductor wafer storage according to claim 1, wherein the counting of the number of particles is performed by a laser scattering method that counts the number of scatterers generated on the surface of the object to be measured by irradiating a laser. A method for measuring the cleanliness of a member.   4. The method for measuring the cleanliness of a semiconductor wafer storage member according to claim 3, wherein the laser scattering method can detect a scatterer having a size of 0.1 [mu] m or less. 5. The inspection wafer to be used according to claim 1, wherein the number of particles having a size of 0.04 μm or more and 16 particles / cm ² or less is used on the surface thereof. A method for measuring the cleanliness of a semiconductor wafer storage member. As test wafers using the cleanliness measurement method of a semiconductor wafer accommodation member according to any one of claims 1 to 5, characterized by using a semiconductor silicon single crystal wafer.

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