JP4571843B2 - Method for evaluating semiconductor wafer storage case - Google Patents

Description

  The present invention relates to a method for evaluating a housing case for a semiconductor silicon wafer such as a silicon wafer.

  In order to store and transport a semiconductor wafer such as a silicon wafer, a dedicated storage case (semiconductor wafer storage case) is used. This semiconductor wafer storage case is formed by injection molding or the like using synthetic resin typified by polypropylene (PP), polycarbonate (PC), polybutylene terephthalate (PBT), and other various elastomers. Also, as an example of such a semiconductor wafer storage case, FOSB (abbreviation of Front Open Shipping Box) and the like are widely known.

  This storage case stores a semiconductor wafer in a wafer storage section called a cassette, and covers the opening of the case main body that stores the cassette with a cover (cover) to block outside air. It was intended to prevent contamination by contaminants such as particles, organic matter, and metal components and maintain the cleanliness of the semiconductor wafer in a high state (for example, Patent Document 1 and Patent Document 2).

  In addition, when the semiconductor wafer is stored in the case main body, the storage case is hermetically sealed so as to block the semiconductor wafer as a stored item from the outside air. As this sealing means, for example, a tape may be wound around the outer periphery of the fitting portion between the case body and the lid, but there is a sealing method in which the lid is fitted to the case body via a gasket made of an endless elastic body. It is used.

  By the way, in such a storage case, since the inside of the semiconductor wafer is sealed when the semiconductor wafer is stored, organic components that ooze or volatilize over time from the synthetic resin constituting the storage case adhere to the semiconductor wafer. As a result, the semiconductor wafer may be contaminated. Such contamination in the storage case is caused by the active state of the surface of the semiconductor wafer that has been subjected to final cleaning (the cleaning process immediately before storage when the semiconductor wafer is stored in the semiconductor wafer storage case, the same applies hereinafter). Because of its high reactivity, ionic impurities are easily adsorbed, but the inside of the sealed storage case has a high organic gas partial pressure, making it susceptible to disturbance of organic contamination. Is considered to be the cause.

  Therefore, it is necessary for the manufacturer of the storage case to confirm the presence or absence of organic matter in the storage case when the semiconductor wafer is stored for a long period of time. On the other hand, various evaluation techniques have been implemented for this purpose, but the storage case is evaluated by confirming the change over time of the surface of the semiconductor wafer by storing the silicon wafer in the storage case for a predetermined period. Is often performed.

As shown in the flowchart of FIG. 6, the conventional storage case evaluation method first measures LPD (abbreviation of Light Point Defects, hereinafter the same), which is a surface impurity, on the finally cleaned semiconductor wafer (step ( In the figure, abbreviated as S. The same shall apply hereinafter) 1, 2), stored in a storage case (step 3), and packed in a polyethylene (PE) bag or the like as necessary to seal the storage case (step 4). .
Next, after putting the sealed storage case into a clean room and storing it for a predetermined period (step 5), the stored semiconductor wafer is taken out and the LPD on the surface of the semiconductor wafer is measured again (step 6). The increase / decrease in the LPD before and after the storage process was confirmed, the change over time in the contamination level on the surface of each semiconductor wafer was confirmed (step 7), and the storage case was evaluated.

Thus, in the conventional evaluation method, in order to observe the change over time of the storage case, it was considered that storage in a clean room was essential. In addition, the storage period in the clean room is an empirical value, and about 3 to 6 months is generally taken into consideration in consideration of the period from storage to use of the semiconductor wafer.

JP-A-8-186162 JP-A-10-154750

  However, in the conventional evaluation method, since the storage time in the clean room was as long as about 3 to 6 months, it was not possible to cope with the case where the evaluation result was urgently required. In addition, in the process of storing for a long time using a clean room, the work becomes complicated and the cost is high. Therefore, there is a need for an evaluation technique that can confirm whether there is a change over time in a short period of time by a simple means. It was.

  Accordingly, an object of the present invention is to evaluate a storage case for storing a semiconductor wafer, and a semiconductor wafer storage case evaluation method capable of confirming a change with time of generation of impurities in the storage case in a short period of time. Is to provide.

According to the method for evaluating a semiconductor wafer storage case of claim 1 of the present invention, in evaluating the change over time of the semiconductor wafer due to contaminant exudation from the semiconductor wafer storage case made of synthetic resin, After measuring the impurities and storing the semiconductor wafer on which the impurities on the surface are measured in a semiconductor wafer storage case to be in a sealed state, the semiconductor wafer storage case is stored in a clean room for 30 days or more . Applying moisture absorption / release treatment that adds or removes moisture to the semiconductor wafer storage case, and after the moisture absorption / release treatment, measure the impurities on the semiconductor wafer surface again and compare with the measurement results before sealing. Features.

The method for evaluating a semiconductor wafer storage case according to claim 2 of the present invention is the semiconductor wafer storage case evaluation method according to claim 1 , wherein the moisture absorption / release treatment is performed by the following (a) and (b):
(A) a wetting step in which the temperature is 30 to 50 ° C. and the humidity is 60% RH or more;
(B) a cooling step with a temperature of 0 ° C. or lower;
This cycle is characterized by repeating the cycle once or several times.

According to the semiconductor wafer storage case evaluation method of the first aspect of the present invention, in evaluating the change over time of the semiconductor wafer due to contaminant leaching in the semiconductor wafer storage case made of synthetic resin, In place of long-term storage in a clean room in the case evaluation method, a semiconductor wafer storage case is stored in a clean room for 30 days or more , and moisture is absorbed or released by the semiconductor wafer storage case after storage. Since the change over time of the generation of impurities in the storage case can be evaluated in a relatively short period of time, the test time is greatly shortened and the evaluation results are required early Even so, it can respond quickly.
In addition, since the test is easily performed, the workability is good and the cost efficiency is excellent because the test is performed at a low cost.

According to the semiconductor wafer storage case evaluation method of the first aspect of the present invention, in the evaluation method described in the first aspect, the moisture absorption and desorption treatment includes the following (a) and (b):
(A) a wetting step in which the temperature is 30 to 50 ° C. and the humidity is 60% RH or more;
(B) a cooling step with a temperature of 0 ° C. or lower;
This cycle is repeated once or several times, so that moisture is efficiently applied to or removed from the semiconductor wafer storage case in the moisture absorption / release treatment, and the reliability of the evaluation is further improved. Can do.

The method for evaluating a semiconductor wafer storage case according to the present invention is a method for evaluating the time-dependent change of wafer contaminant exudation in a semiconductor wafer storage case made of a synthetic resin. After storing the measured semiconductor wafer and sealing it, the semiconductor wafer storage case is stored in a predetermined standard environment, and moisture is applied to or removed from the stored semiconductor wafer storage case. Wet treatment,
After the moisture absorption / release treatment, the impurities on the surface of the semiconductor wafer are measured again and compared with the measurement results before sealing.

  Here, FIG. 1 shows an example of a semiconductor wafer storage case to be evaluated. The semiconductor wafer storage case 1 shown in FIG. 1 (hereinafter sometimes simply referred to as “storage case 1”) is a cassette provided with an alignment slot 3 for storing a plurality of semiconductor wafers (not shown) aligned in parallel. 2, a case main body 4 that accommodates the cassette 2, a lid body 5 that covers the upper opening 4 a of the case main body 4 via a gasket 6, and a wafer holder that holds and cushions the semiconductor wafer in the cassette 2. It consists of part 7.

This storage case 1 is made of a polyolefin resin such as polyethylene (PE) and polypropylene (PP), polycarbonate (PC), polybutylene terephthalate (PBT) and other synthetic resins represented by various elastomers. It can obtain by carrying out injection molding to the desired shape of the member.
Further, as the gasket 6 that is interposed between the case main body 4 and the lid and keeps both in a sealed state, a thermoplastic resin elastomer such as a polyester elastomer or a polyolefin elastomer can be preferably used.

  Examples of the semiconductor wafer stored in the storage case 1 include a silicon wafer and a gallium / arsenic wafer. In general, the size of these semiconductor wafers is about 4 to 12 inches, and a predetermined number of wafers are aligned and loaded in the center of the cassette 2 constituting the storage case 1.

The method for evaluating a semiconductor wafer storage case according to the present invention uses the semiconductor wafer storage case 1 for the semiconductor wafer storage case in evaluating the time-dependent change of wafer contaminant exudation in the semiconductor wafer storage case made of the synthetic resin having the above-described structure. The storage case 1 that contains the wafer and is sealed is stored under a predetermined standard environment, and the semiconductor wafer storage case after storage is subjected to moisture absorption / release treatment for applying or removing moisture. After the moisture release treatment, the presence of impurities in the semiconductor wafer is confirmed. For example, the procedure is preferably as follows.
Here, examples of the wafer contaminant that oozes out from the storage case 1 include organic substances and various ion components.

First, the finally cleaned semiconductor wafer is stored in the semiconductor wafer storage case 1 to be evaluated. In addition, the semiconductor wafer to be stored is measured for surface impurities before being stored in the storage case 1, and when measuring impurities on the surface of the semiconductor wafer, the number of LPDs existing on the surface of the semiconductor wafer is counted. do it. Since these are typical impurities existing on the surface of the semiconductor wafer, it is possible to easily confirm the temporal change in the generation of impurities in the housing case 1.
The “final cleaning” in the present invention corresponds to a cleaning process immediately before storage when the semiconductor wafer is stored in the semiconductor wafer storage case 1.
The LPD is a generic term for deposits or defects (scratches, etc.) on the wafer surface that are detected as scatterers when a laser is irradiated on the wafer surface.

  When the measurement of impurities on the surface of the semiconductor wafer is completed, the wafer is mounted in parallel in the alignment slot 3 constituting the storage case 1 and the cassette 2 is stored in the semiconductor wafer storage case 1.

  When the semiconductor wafer is stored in the storage case 1 in this way, the case main body 4 and the lid 5 of the storage case 1 are sealed through the gasket 6. In the evaluation method of the present invention, after the container is sealed in this way, the storage case 1 may be packaged with a packaging bag made of polyethylene (PE), polypropylene, or the like. Can be held in.

In the evaluation method of the present invention, instead of storing the storage case 1 in which the semiconductor wafer is stored and sealed in a clean room for a predetermined period (for example, June), first, the storage case 1 is placed in a predetermined standard environment. And save.
Here, the storage in the standard environment refers to storing the storage case 1 in a constant and stable environment. For example, the storage case 1 is stored in a clean room with a constant condition, or a constant temperature and humidity chamber (for example, a constant condition). And storage under a temperature condition of 23 ° C. and a humidity condition of 45% RH). In particular, by adopting a clean room, the conditions under the standard environment can be standardized and stabilized, and the reliability of evaluation can be further increased.
In addition, in the case of adopting clean room storage as standard environment storage, for example, it may be in an environment of about class 100, temperature of about 23 ° C., and humidity of about 45% RH.

Storage period under standard environment typified by a clean room or the like, it is good preferable to 3 0 days or more. If the storage period is shorter than 30 days, the effect may not be sufficiently exhibited. The storage period may be approximately 60 days as the upper limit.

  Next, a moisture absorption / release treatment for applying or removing moisture is performed on the semiconductor wafer storage case 1 after being stored in a standard environment. This moisture absorption / release treatment is performed for the purpose of simulating a temporal change in the inside of the storage case 1 in a conventional clean room. Water is added to the storage case 1 or the supplied water is removed. The treatment conditions are not particularly limited as long as the treatment to be removed is repeatedly performed, but for example, the treatment conforming to the standard such as JIS C60068-2-38 or the constant temperature and humidity chamber The cycle including the following (a) wetting step and (b) cooling step may be performed as one cycle, and this cycle may be repeated once or several times.

(A) Wetting step:
In the wetting step, it is preferable that the temperature is 30 to 50 ° C. and the humidity is 60% RH or more. Moreover, what is necessary is just to perform this wetting process for about 3 to 5 hours, for example. This wetting process takes into account the high temperature and high humidity state during transportation of the housing case 1 housing the semiconductor wafer.

(B) Cooling step:
In the cooling step, the storage case 1 is cooled at a temperature of 0 ° C. or lower. For example, the temperature is set to −20 to 0 ° C. and may be performed for about 2 to 4 hours. In addition, this cooling process may be performed by dividing the process into a plurality of processes.
In the cooling step, the humidity condition is arbitrary, and may be appropriately determined according to the type of storage case 1, temperature conditions, and the like.

  Here, the number of cycles may be about 3 to 6 times. By setting the number of cycles to such a number, the correlation between the storage process in the conventional clean room and the promotion process is improved.

  In addition, you may make it perform the following (c) standard process between (a) wetting process and (b) cooling process. If it does in this way, the case 1 for storage can be sent to the following process in the state accustomed to the standard atmosphere.

(C) Standard process:
In the standard process, the temperature is preferably about 10 to 30 ° C. and the humidity is about 40 to 60% RH, and the time may be about 3 to 5 hours.

  In the evaluation method of the present invention, after the moisture absorption / release treatment, impurities on the surface of the semiconductor wafer are measured again. Such measurement may be performed in accordance with the above-described measurement of impurities on the surface before storage in the storage case 1. That is, the number of LPDs present on the surface of the semiconductor wafer is measured, and the obtained result may be compared with the result obtained by measuring before storing in the storage case.

  In order to evaluate the change of the storage case 1 over time, the increase / decrease in the impurities of the LPD may be confirmed. For example, the increase / decrease amount of LPD per predetermined number of semiconductor wafers stored in the storage case 1 It is good also as a parameter | index by calculating | requiring the average value. Further, with respect to a predetermined number of semiconductor wafers stored in the storage case 1, the degree of increase / decrease in LPD per semiconductor wafer is divided into a specific range, and the number of semiconductor wafers corresponding to the specific range The relationship may be confirmed by representing the relationship in a histogram.

Next, an example of the evaluation method of the present invention will be described with reference to the flowchart of FIG.
First, after the semiconductor wafer stored in the storage case 1 to be evaluated is finally cleaned (step 1), impurities on the surface of the semiconductor wafer are measured with an LPD measuring device or the like (step 2). The semiconductor wafer whose impurities on the surface are measured is mounted in the alignment slot 3 of the cassette 2 constituting the storage case 1, and the semiconductor wafer is stored in the storage case 1 (step 3), and the storage case is sealed. After making it into a state, it is packed with double polyethylene (PE bag) (step 4).

The storage case 1 was stored for a predetermined time (for example, 30 days or more) in a standard environment such as a clean room (step 5-1). The storage case 1 was placed in a thermo-hygrostat and described above. (A) Wetting process and (b) Cooling process are defined as one cycle, and a moisture absorption / release treatment is performed by repeating this cycle several times (step 5-2).

When such moisture absorption and desorption treatment is completed, the housing case 1 is taken out from the constant temperature and humidity chamber, the sealed state is opened, the semiconductor wafer is taken out, and impurities on the surface of the semiconductor wafer are measured (step 6).
Then, this result is compared with the result obtained in step 2 described above, and the change in the generation of impurities in the storage case 1 over time is evaluated by confirming the change in impurities on the surface of the semiconductor wafer. (Step 7).

  According to the semiconductor wafer storage case evaluation method of the present invention, in evaluating the time-dependent change of the wafer contaminant exudation in the semiconductor wafer storage case made of synthetic resin, the conventional semiconductor wafer storage case evaluation method Instead of long-term storage in a clean room, the semiconductor wafer storage case 1 is stored under a predetermined standard environment, and the semiconductor wafer storage case 1 after storage is subjected to moisture absorption and desorption processing for applying or removing moisture. As a result, the temporal change in the generation of impurities in the storage case 1 can be evaluated in a relatively short period of time, so that the test time can be shortened. For example, the evaluation result can be obtained early. Even if it is a case, it can respond quickly.

In addition, since the test is easily performed, the workability is good, and the cost efficiency is excellent because the test is performed at a low cost.
According to the semiconductor wafer storage case evaluation method of this aspect, it is possible to evaluate the change with time in the generation of impurities in the storage case 1 with higher reliability.

It should be noted that the present invention is not limited to the above-described embodiments, and modifications and improvements as long as the object of the present invention can be achieved are included in the present invention.
For example, the shape of the semiconductor wafer storage case 1 to be measured is specifically shown in FIG. 1, but if the storage case 1 is made of synthetic resin, the shape can be changed as appropriate.

Further, as an example of an evaluation index of the storage case 1, the increase or decrease of impurities such as LPD and heavy metal fine particles on the surface of the semiconductor wafer to be stored can be confirmed, or a predetermined number of semiconductor wafers stored in the storage case 1 can be checked. It was shown that the increase / decrease degree of impurities per semiconductor wafer is divided into a specific range, the number of semiconductor wafers corresponding to the specific range is displayed in a histogram, and the distribution is confirmed. Not.
In addition, specific means or the like for carrying out the present invention may have other structures or the like within a range in which the object of the present invention can be achieved.

  EXAMPLES Hereinafter, although an Example etc. are given and this invention is demonstrated more concretely, this invention is not limited to the content of an Example etc. at all.

[Test Example 1]
The evaluation method of the present invention was applied to the semiconductor wafer storage case having the configuration shown in FIG. 1 and compared with the conventional method.
That is, the conventional evaluation method shown in the flowchart of FIG. 6 (storage period in a clean room: 6 months) and the evaluation method of the present invention shown in the flowchart of FIG. The presence or absence of the correlation of the conventional evaluation method was confirmed.

[Reference Example 1]
The conventional evaluation method was implemented according to the flowchart shown in FIG. That is, 25 silicon wafers having a size of 8 inches were finally cleaned (Step 1), and LPD was measured for all 25 silicon wafers using a commercially available LPD measuring apparatus (Step 2).

  After the measurement, it is stored in the alignment slot of the cassette carrier constituting the storage case (step 3), and the case body and the lid are fitted to each other through a gasket to form a sealed state. The storage case was wrapped in a polyethylene (PE) bag (double) (step 4).

  After storing the packaging case for 6 months in a clean room with a clean degree of class 100 (Step 5), open the packaging case, take out the stored silicon wafer, and measure the LPD again. (Step 6), the number of increases in LPD was confirmed for each silicon wafer, and the number of silicon wafers with respect to the degree of increase / decrease in LPD was confirmed (Step 7). The result of carrying out this operation twice is shown in FIG.

[Example 1]
The evaluation method of the present invention was implemented according to the flowchart shown in FIG. That is, as in Reference Example 1 described above, after 25 silicon wafers having a size of 8 inches were finally cleaned (Step 1), the LPD was performed on all 25 silicon wafers using the LPD measuring apparatus shown in Reference Example 1 described above. Was measured (step 2).

  After the measurement, it is stored in the alignment slot of the cassette carrier constituting the storage case shown in FIG. 1 (step 3), and the case body and the lid are fitted with each other through a gasket to be in a sealed state. The sealed storage case was wrapped in a polyethylene (PE) bag (double) (step 4).

  The storage case after packaging was stored for 30 days or more in a clean room (23 ° C., 40% RH) with a clean degree of about 100 as a storage in a standard environment (step 5-1). After storage, constant temperature and humidity It put into the tank, the temperature-humidity cycle shown below was made into 1 cycle in order of (a) and (b), and 3-6 cycles were implemented continuously, and the moisture absorption / release process was performed (step 5-2).

(Temperature-humidity cycle)
(A) Wetting step 30-50 ° C., 60% RH or more, 3-5 hours (b) Cooling step −20-0 ° C., 2-4 hours

  Then, the storage case after the promotion processing is opened, the stored silicon wafer is taken out, and the LPD is measured again in the same manner as in Reference Example 1 (step 6). At the same time, the number of silicon wafers relative to the degree of increase / decrease in LPD was confirmed (step 7). The result of carrying out this operation twice is shown in FIG.

Comparing the results of FIG. 3 with the results of FIG. 4, in FIG. 3 and FIG. 4, there are wafers whose LPD is increased from the range of the normal distribution. From this result, the evaluation method of the present invention (Example 1) is the conventional one. It was confirmed that there was a correlation with the evaluation method (Reference Example 1).
Further, by using the evaluation method of Example 1, the test time can be shortened by about 5 months even when storage and moisture absorption / release treatment are performed in a standard environment.
From the measurement results, TDH (Time Dependent Haze) is likely to occur when organic substances, ionic components, and other contaminants originating from the storage case can be confirmed. Can be expected.

[Test Example 2]
Using the semiconductor wafer storage case having the configuration shown in FIG. 1, the rate of change over time with respect to the storage period in a clean room was measured.
That is, in Example 1, it was confirmed whether or not a change with time occurred on the surface of the semiconductor wafer when the storage period in the clean room was 0 days (same as Example 1), 20 days, 30 days, and 40 days.

  Here, as the change with time, the number of LPDs present on the surface of the semiconductor wafer is counted before the storage case is stored and after the acceleration process is performed and taken out from the storage case. It was determined that the change over time occurred. The number of generated wafers with respect to 50 semiconductor wafers was used as the generation rate (%). The results are shown in FIG.

From the results shown in FIG. 5, the rate of change with time is low until after 20 days, but the rate of occurrence increases rapidly as it approaches 30 days.
Therefore, in the evaluation of the storage case, in order to perform the evaluation with higher accuracy, it is effective to perform the promotion process after storing in the clean room for 30 days or more before performing the promotion process. To be judged.

  The method for evaluating a semiconductor wafer storage case according to the present invention can carry out confirmation of changes over time in the generation of impurities in a storage case for storing a semiconductor wafer such as a silicon wafer in a short period of time. It can be widely used as an accelerated test in the manufacturer of storage cases.

It is the schematic of the case for semiconductor wafer storage. It is the flowchart which showed the one aspect | mode of the evaluation method of this invention. In Example 1, it is the histogram which showed the relationship between the increase / decrease number of LPD, and the number of silicon wafers corresponding to it. In Reference Example 1, it is a histogram (retention period: 6 months) showing the relationship between the increase / decrease number of LPD and the number of silicon wafers corresponding thereto. It is a graph which shows the relationship between a preservation | save period and a time-dependent change incidence. It is the flowchart which showed the one aspect | mode of the conventional evaluation method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Semiconductor wafer storage case 2 ... Cassette 3 ... Alignment slot 4 ... Case main body 4a ... Upper opening part of a case main body 5 ... Cover body 6 ... Gasket 7 ... Wafer holding part

Claims (2)

In evaluating the time-dependent change of the semiconductor wafer due to contaminant leaching from the semiconductor wafer storage case made of synthetic resin,
Measure impurities on the final cleaned semiconductor wafer surface,
After storing the semiconductor wafer whose impurities on this surface were measured in a semiconductor wafer storage case and sealing it,
Store the semiconductor wafer storage case in a clean room for 30 days or more ,
Apply moisture absorption / release treatment to add or remove moisture from the semiconductor wafer storage case after storage,
After the moisture absorption / release treatment, the impurity on the surface of the semiconductor wafer is measured again and compared with the measurement result before sealing, the semiconductor wafer housing case evaluation method. In the evaluation method of the semiconductor wafer storage case according to claim 1 ,
The moisture absorption / release treatment is performed by the following (a) and (b)
(A) a wetting step in which the temperature is 30 to 50 ° C. and the humidity is 60% RH or more;
(B) a cooling step with a temperature of 0 ° C. or lower;
A method for evaluating a case for housing a semiconductor wafer, wherein one cycle is repeated once or several times.

Images