JP2010028023A - Environment monitoring method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To easily and speedily grasp change in manufacture environment of a semiconductor device. <P>SOLUTION: A silicon wafer is left in a monitor environment, for example, in a manufacturing device, a clean room, etc., as it is for a certain time and the film thickness of an oxide film formed on a silicon wafer surface meanwhile is found (steps S1 to S4). Then an increment in the film thickness in the leaving time is compared with a threshold of an increment in film thickness allowed in a normal monitoring environment; when the threshold is exceeded, it is determined that the monitoring environment is abnormal, and qualitative analysis and quantitative analysis of the silicon wafer are made to examine the cause of the abnormality (steps S5, S6). Change of the monitoring environment can easily and speedily be grasped by using the increment in film thickness of the oxide film formed on the silicon wafer. Further, only when the abnormality is found, detailed analysis is made to lower the analytic cost. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an environment monitoring method, and more particularly to an environment monitoring method for monitoring a manufacturing environment of a semiconductor device.

In semiconductor device manufacturing, it is important to keep the environment inside the manufacturing apparatus and the clean room, which can greatly affect the product yield, within a certain standard.
Conventionally, in the field of manufacturing semiconductor devices, several methods for monitoring the manufacturing environment have been proposed. For example, regarding the analysis of contaminants contained in a liquid such as a cleaning solution, a silicon wafer that has been treated with hydrofluoric acid or the like is immersed in the liquid to be analyzed, and the surface of the silicon wafer that has been pulled up is analyzed by analyzing the adhered substances. A method for analyzing the pollutants is proposed (see Patent Document 1). In addition, a silicon wafer is immersed in an anion solution to introduce an anionic group on the surface, and it is placed in a monitor environment. By analyzing the metal contaminants attached by electrostatic attraction, the contamination level of the monitor environment is improved. A method for evaluation has also been proposed (see Patent Document 2). In addition, attempts have been made to increase the sensitivity and shorten the analysis time by forcibly sending clean room air to the silicon wafer surface and attaching a large amount of contaminants contained in the clean room air to the surface in a short time. (See Patent Document 3).

As a method for analyzing the adhered substance on the silicon wafer surface, for example, when the adhered substance is a metal, it is known to use a plasma emission mass spectrometry (ICP-MS) method. In addition, a total reflection tendency X-ray analysis (TXRF) method suitable for elements other than aluminum, a microwave photoconductive decay (μ-PCD) method and surface light performed after diffusing contaminants attached to a silicon wafer by heat treatment A voltage (SPV) method and the like are also known. When the adhering substance is an organic substance, the analysis method includes a thermal desorption gas chromatograph mass spectrometry (TD-GC-MS) method, a wafer thermal desorption gas chromatograph mass spectrometry (WTD-GC-MS) method, and the like. Are known.
Japanese Patent Laid-Open No. 11-248893 Japanese Patent Laid-Open No. 10-31009 JP 2000-28596 A

  However, in order to monitor the environment such as liquids and spaces used in semiconductor device manufacturing, if a contaminant is attached to the surface of the silicon wafer and analyzed, the analysis takes a long time. A lot of man-hours are required. In addition, the analysis can be expensive.

  In order to manufacture semiconductor devices stably, it is necessary to monitor the environment inside the manufacturing equipment and clean room regularly. However, analysis is frequently performed in terms of time, man-hours, cost, etc. required for analysis. May be difficult. In addition, if the analysis time and process are long or the frequency of analysis is low, feedback of analysis results to the production line is delayed, and it is difficult to quickly grasp changes in the environment inside the manufacturing apparatus and clean room.

  In view of these points, an object of the present invention is to provide an environment monitoring method capable of easily and quickly grasping a change in the manufacturing environment of a semiconductor device.

  In order to solve the above problems, the following environmental monitoring method is provided. This environmental monitoring method includes a step of leaving a wafer in a monitoring environment for a certain period of time and a step of obtaining the thickness of an oxide film formed on the wafer surface by leaving it to stand.

  In this environmental monitoring method, a wafer is left in a monitoring environment for a certain period of time, and the film thickness of an oxide film formed on the wafer surface is determined by being left as it is.

  According to the disclosed environment monitoring method, it is possible to easily and quickly grasp changes in the monitoring environment.

Hereinafter, it will be described in detail with reference to the drawings.
FIG. 1 is a diagram illustrating an example of a flow of an environment monitoring method.
Here, a silicon wafer is used for environmental monitoring in a semiconductor manufacturing apparatus, a clean room, or the like. In performing environmental monitoring, first, the film thickness of the oxide film is measured for the silicon wafer for environmental monitoring (step S1). For this film thickness measurement, for example, an ellipsometer that optically measures the film thickness is used.

  Then, after measuring the thickness of the oxide film in step S1, the silicon wafer is left for a certain period of time in a monitoring environment such as a semiconductor manufacturing apparatus or a clean room (step S2). On the left silicon wafer, an oxide film (including an oxide film containing or adhering an organic substance) is formed with a film thickness corresponding to the leaving time due to the atmosphere of the monitoring environment. The details of the formation behavior of the oxide film will be described later.

  After the silicon wafer is left in the monitor environment for a certain period of time, the film thickness of the oxide film is measured using the ellipsometer in the same manner as described above for the silicon wafer after being left (step S3).

  After the film thickness measurement of the oxide film in step S3, the difference between the film thickness measurement result and the film thickness measurement result in step S1, that is, formed on the silicon wafer surface during standing in the monitor environment. The thickness of the oxide film (thickness increase amount) is obtained (step S4).

  Next, it is determined whether or not the monitor environment is in a normal state by using the film thickness increase amount during the standing determined in step S4 (step S5). The determination of whether or not the monitor environment is normal is performed by comparing the film thickness increase amount while the monitor environment is left with a preset threshold value of the film thickness increase amount allowed in the monitor environment.

  For example, in a normal monitoring environment, the relationship between the silicon wafer leaving time and the increase in film thickness during that time is acquired in advance. And, when the film thickness increase amount in the constant standing time actually obtained in the processing of steps S1 to S4 is the same as or less than the film thickness increase amount in the same leaving time in the relationship acquired in advance, It is determined that the monitor environment is in a normal state. If it exceeds, it is determined that the monitor environment is in an abnormal state.

  If it is determined that the monitor environment is in a normal state based on the comparison between the actually measured value and the threshold value, the environment monitor process is terminated. Thereafter, the same or different silicon wafers are used, and the processing after step S1 may be continuously performed for the monitor environment.

  In addition, if it is determined that the monitoring environment is in an abnormal state by comparing the measured value with the threshold value, qualitative analysis and quantitative analysis of the substance attached to the silicon wafer used for the actual measurement is performed. Then, the cause of the abnormality is investigated (step S6).

The above processing can be performed for each monitoring environment to be monitored.
Next, a silicon wafer used in the above environment monitoring method will be described.

  As an environmental monitoring silicon wafer, an oxide film (including an oxide film intentionally formed in addition to a natural oxide film) is formed on the surface of the silicon wafer, or all oxide films existing on the surface of the silicon wafer. Alternatively, a part of which is removed can be used. Regardless of the type of silicon wafer used for environmental monitoring, environmental monitoring can be carried out according to the flow of steps S1 to S6.

  When a silicon wafer from which the oxide film is removed is used for environmental monitoring, the film thickness measurement of the oxide film in step S1 is not necessarily performed. When the oxide film thickness measurement in step S1 is not performed as described above, the result obtained by the oxide film thickness measurement in step S4 is formed on the surface of the silicon wafer while being left in the monitor environment. It can be regarded as the thickness of the oxide film (amount of increase in film thickness).

  The removal of the oxide film from the silicon wafer can be performed, for example, by a heat treatment in a hydrogen atmosphere. By performing the heat treatment in such a hydrogen atmosphere, the oxide film on the silicon wafer surface is reduced and removed, and the silicon crystal on the silicon wafer surface is terminated by hydrogen atoms (hydrogen termination). The heat treatment can be performed, for example, under conditions of hydrogen 20 Torr (1 Torr = 133.322 Pa), 1000 ° C., and 10 seconds. The heat treatment conditions are appropriately adjusted according to the thickness (initial film thickness) of the oxide film existing on the surface of the silicon wafer before the heat treatment.

  In a silicon wafer that has been heat-treated in a hydrogen atmosphere, when the thickness of the oxide film is measured with an ellipsometer, a value of approximately less than 0.05 nm is obtained as the thickness value. In the silicon wafer subjected to the heat treatment in the hydrogen atmosphere, the minimum film thickness value is stably shown, and the variation in the film thickness value obtained between different silicon wafers is small. It is also possible not to perform film thickness measurement.

Here, the result of examining the presence or absence of heat treatment in a hydrogen atmosphere and the difference in the subsequent oxide film formation behavior on the silicon wafer surface will be described.
First, four types of samples a, b, c and d having different oxide film thicknesses on the silicon wafer surface were prepared.

  Sample a is a silicon wafer in which an oxide film is reduced and removed by performing a heat treatment at 1000 ° C. for 10 seconds in an atmosphere containing 20 Torr of hydrogen (the rest is an inert gas). In addition, the initial film thickness of the oxide film of the sample a measured with the ellipsometer after this heat processing was 0.01 nm.

  Sample b was heat-treated in an atmosphere containing 5 Torr of oxygen (the rest being an inert gas) at 900 ° C. for 50 seconds, and an oxide film (thermal oxidation) having an initial film thickness of 1.0 nm (measured with an ellipsometer) on the surface. This is a silicon wafer on which a film is formed.

  Sample c is a silicon wafer having an oxide film with an initial film thickness of 1.7 nm (measured with an ellipsometer) formed on the surface by heat treatment in an oxygen atmosphere of 760 Torr at 900 ° C. for 8 seconds.

  Sample d is heat-treated at 850 ° C. for 30 seconds in a mixed atmosphere containing oxygen and hydrogen at 8 Torr (the rest is an inert gas), and an oxide film with an initial film thickness of 3.2 nm (measured with an ellipsometer) is formed on the surface. It is the formed silicon wafer.

In addition, the thickness measurement of the oxide film by the ellipsometer of samples a, b, c, and d was performed using a helium-neon laser having a wavelength of 633 nm, and the refractive index of the oxide film was fixed at 1.462.
Such samples a, b, c, and d were left for a certain period of time in three different monitor environments x, y, and z as follows.

  The monitor environment x is in a FOUP (Front Opening Universal Pod) excellent in airtightness, which is a container for transporting silicon wafers compliant with SEMI (Semiconductor Equipment and Materials Institute) standards. The silicon wafers of samples a, b, c, and d were each left for a certain time in a sealed FOUP.

  The monitor environment y is near the entrance of a clean room where semiconductor devices are manufactured. The silicon wafers of samples a, b, c, and d were each placed in an open FOUP and left for a certain period of time near the clean room entrance.

  The monitor environment z is near the center of a clean room where semiconductor devices are manufactured. The silicon wafers of samples a, b, c, and d were each placed in an open FOUP and left in the vicinity of the center of the clean room for a certain period of time.

  When the samples a, b, c, and d were averaged over a period of time, no significant difference was observed in the monitor environments y and z with respect to humidity. Regarding the temperature, the monitor environment y was higher by about 0.3 ° C. than the monitor environment z.

The following FIGS. 2 to 5 show the relationship between the standing time and the amount of increase in the thickness of the oxide film when the samples a, b, c, and d are left in such monitor environments x, y, and z, respectively.
FIG. 2 is a diagram showing the relationship between the standing time when the sample a is left in the monitor environment x, y, z and the film thickness increase amount of the oxide film. FIG. 3 is a diagram showing the relationship between the standing time when the sample b is left in the monitor environment x, y, z and the amount of increase in the thickness of the oxide film. FIG. 4 is a diagram showing the relationship between the standing time when the sample c is left in the monitor environment x, y, z and the amount of increase in the thickness of the oxide film. FIG. 5 is a diagram showing the relationship between the standing time when the sample d is left in the monitor environment x, y, z and the amount of increase in the thickness of the oxide film.

  First, as shown in FIGS. 3 to 5, the samples b, c, and d each having an oxide film having an initial film thickness of 1.0 nm, 1.7 nm, and 3.2 nm are compared with the monitor environments x and z. Thus, the amount of increase in the film thickness in the monitor environment y that is easily affected by the inflow and outflow of outside air increases. There is no significant difference in film thickness increase between the monitor environment x in the FOUP and the monitor environment z near the center of the clean room.

  In these samples b, c, and d, in any of the monitor environments x, y, and z, the thickness of the oxide film is rapidly increased in the region where the leaving time is short. Thereafter, the rate of increase in the thickness of the oxide film decreases and tends to be saturated from about 24 hours.

  In samples b, c, and d in which an oxide film is formed in advance, as shown in FIGS. 3 to 5, the oxide film thickness increases as the standing time elapses regardless of the initial film thickness of the oxide film. There is a trend. However, as in the monitor environments x and z, there may be a case where a significant difference cannot be found in the film thickness increase behavior of the oxide film between different monitor environments.

  On the other hand, as shown in FIG. 2, in the case of the sample a that has been previously heat-treated in a hydrogen atmosphere, the oxide film changes with the passage of the standing time in any of the monitor environments x, y, and z. There is a tendency for the film thickness increase to increase linearly. Thus, the tendency of the oxide film thickness increase in sample a is clearly different from the tendency of the oxide film thickness increase in samples b, c, and d shown in FIGS. In sample a, the oxide film is reduced and removed from the surface of the silicon wafer by heat treatment in a hydrogen atmosphere. Further, since the surface is hydrogen-terminated, it takes time to replace hydrogen at the silicon crystal end with oxygen in the atmosphere. In short, it is considered that rapid oxidation when left untreated is suppressed.

  Further, in sample a, the amount of increase in the thickness of the oxide film with respect to the standing time becomes the largest in the monitor environment y near the clean room entrance and exit which is easily affected by the outside air flow, and then increases in the monitor environment z near the center of the clean room. The monitor environment x in the FOUP is the smallest. As described above, when the sample a is used, the amount of increase in the thickness of the oxide film in different monitor environments x, y, and z can be distinguished as a significant difference. In the sample a, the difference in the increase in the thickness of the oxide film due to the monitor environments x, y, and z clearly appears, and the monitor environments x, z that were unknown in the samples b, c, and d in which the oxide films are formed in advance. The difference in the amount of increase in film thickness clearly appears.

  When monitoring the environment, by using a sample a of a silicon wafer that has been heat-treated in a hydrogen atmosphere, an appropriate relationship between the standing time and the increase in the thickness of the oxide film is obtained for each of the different monitoring environments x, y, and z. can do. Therefore, for each monitor environment x, y, z, it is possible to more appropriately evaluate the change in each state from the thickness (thickness increase amount) of the oxide film formed as a result of leaving for a certain period of time. .

Even if the samples b, c, and d are used for the environment monitor, it is possible to evaluate the change in the state of a certain monitor environment.
Next, the results of XPS (X-ray Photoelectron Spectroscopy) measurement on samples a, b, c, and d will be described.

FIG. 6 is a diagram showing the results of XPS measurement.
In XPS measurement, constituent elements and their electronic states of samples a, b, c, and d are analyzed by detecting photoelectrons generated by irradiating the surfaces of samples a, b, c, and d with X-rays having a predetermined energy. . Photoelectrons (low bond energy side (Si-Si bond) peak) generated from silicon 2p orbit of silicon wafer and photoelectrons (high bond energy side (Si-O bond) generated from silicon 2p orbit of oxide film) The film thickness of the oxide film can be estimated from the intensity ratio with respect to the peak.

  FIG. 7 is a diagram showing a comparison between the thickness of the oxide film obtained from the XPS measurement result of sample b and the thickness of the oxide film measured by an ellipsometer. FIG. 8 is a diagram showing a comparison between the thickness of the oxide film obtained from the XPS measurement result of sample c and the thickness of the oxide film measured by an ellipsometer.

  Note that the XPS measurement and the film thickness measurement using an ellipsometer are performed on a plurality of samples b and c that are left in each monitor environment x, y, and z for a certain period of time. 7 and 8, the average values (Ave (ellipsometer), Ave (XPS)), maximum values (Max (ellipsometer), Max (XPS)), and minimum values (Max) obtained as a result of each measurement are shown. Min (ellipsometer), Min (XPS)).

  In samples b and c, according to the result of measuring the thickness of the oxide film by the ellipsometer shown in FIGS. 3 and 4, the oxide film thickness is the most in the monitor environment y among the monitor environments x, y, and z. There was a tendency to become thicker. However, from the measurement results shown in FIG. 7 and FIG. 8, regarding the thickness measurement of the oxide film, it is clear between the thickness of the oxide film obtained by ellipsometer measurement and the thickness of the oxide film obtained from the XPS measurement result. There is no correlation.

  Generally, when an ultrathin film on the surface of a silicon wafer is exposed to the atmosphere and the oxide film is measured with an ellipsometer, an increase in film thickness is observed at a rate of about 0.005 nm / h. This increase depends on the initial film thickness as well as the environment in which the silicon wafer is left. Factors that affect the neglected environment include temperature, humidity, and inorganic and organic pollutants. Most of this increase is lost when heat of about 100 ° C. is applied or laser irradiation is performed, and it is recognized that the influence of organic matter is great. In the XPS measurement described above, since the thickness of the oxide film is estimated from the intensity ratio of the Si—Si bond peak and the Si—O bond peak, the presence of such organic substances is not taken into account for the film thickness value. On the other hand, the measurement of the thickness of the oxide film using an ellipsometer is a technique for optically measuring the thickness of the oxide film, and therefore the thickness value of the oxide film can be obtained in consideration of the presence of such organic substances. Such a point is considered to be one of the reasons why the film thickness obtained by XPS measurement and ellipsometer measurement do not match.

Considering the presence of organic substances on the surface of the silicon wafer after being left as such, the carbon abundance ratios of samples a, b, c and d were similarly determined by XPS measurement.
FIG. 9 is a diagram showing an example of the XPS measurement result. Moreover, FIG. 10 is a figure which shows the carbon abundance ratio of sample a, b, c, d.

  As shown in FIG. 9, the intensity of photoelectrons generated from the 1s orbit of carbon when a predetermined sample is irradiated with X-rays varies depending on the abundance of carbon in the sample (1.6 atom%, 4.5 atom%). To do.

  From the knowledge shown in FIG. 9, according to the XPS measurement, the carbon abundance ratio of the samples a, b, c, and d can be obtained based on the intensity of photoelectrons generated from the carbon 1s orbital. FIG. 10 shows the carbon abundance ratios of the obtained samples a, b, c, and d. The carbon abundance ratio is obtained on the assumption that the constituent elements of the samples a, b, c, and d are three kinds of silicon, oxygen, and carbon.

  As shown in FIG. 10, the contained carbon can be detected by XPS measurement for samples a, b, c, and d after standing. From FIG. 10, it was recognized that the carbon abundance ratios of the samples a, b, c, and d tend to be the lowest in the monitor environment x, and then the highest in the monitor environment z and the monitor environment y. In particular, the tendency is prominent in sample a. In sample a, the carbon abundance ratio is clearly high in the monitor environment y where the amount of increase in film thickness due to standing is the largest, and the increase in film thickness is affected by the adhesion of organic substances in addition to oxidation. Can do.

  Since the carbon abundance ratio shown in FIG. 10 is not an absolute amount, when the thickness of the oxide film is increased, even if the same amount of carbon as the thinner oxide film is included, the abundance ratio of the carbon is Lower. In this regard, it should be noted that the samples b, c, and d in which an oxide film is formed in advance may overlook the presence of carbon adhering to the samples. Since sample a is heat-treated in a hydrogen atmosphere to reduce and remove the oxide film, it can be said that it is easy to detect the presence of carbon adhering to the sample a by XPS measurement.

  As described above, the XPS measurement cannot identify the deposit, but can evaluate the possibility of the presence of the organic substance. However, depending on the thickness of the oxide film, it is difficult to accurately evaluate. In addition, it is difficult to obtain the thickness of the oxide film, and further the amount of increase in film thickness due to leaving it in consideration of the presence of organic matter.

  On the other hand, in the optical film thickness measurement of an oxide film using an ellipsometer, the amount of increase in film thickness can be easily determined including the film thickness of the oxide film and the presence of attached organic matter. The film thickness measurement by an ellipsometer is suitable as a technique used when trying to grasp the change in the monitor environment that may contain organic substances by the increase in the thickness of the oxide film caused by leaving the silicon wafer in the monitor environment.

  As explained above, by determining the increase in the thickness of the oxide film formed on the surface of the silicon wafer left in the monitor environment by optical film thickness measurement, it is possible to easily and appropriately change the monitor environment state. I can grasp it. As a silicon wafer for environmental monitoring, a silicon wafer that has been heat-treated in a hydrogen atmosphere is suitable regardless of the monitoring environment, but even with a silicon wafer on which an oxide film has been formed in advance, It is possible to grasp the change of the state.

  By performing simple environmental monitoring using a silicon wafer in this way, it is possible to quickly grasp the presence or absence of abnormality in the monitoring environment and take countermeasures. When an abnormality in the monitor environment is found, analysis costs can be reduced by performing more detailed analysis such as qualitative analysis and quantitative analysis.

  In addition to the XPS measurement as described above, various methods can be used for the analysis. For example, as an analysis method for specifying a metal element, an ICP-MS method, a TXRF method, a μ-PCD method, an SPV method, and the like can be given. Examples of the analysis method for specifying the organic substance include a TD-GC-MS method and a WTD-GC-MS method.

Next, an application example of the environment monitoring method as described above will be described.
FIG. 11 is a schematic configuration diagram of an example of a semiconductor manufacturing apparatus.
A semiconductor manufacturing apparatus 10 shown in FIG. 11 is installed in a clean room. The semiconductor manufacturing apparatus 10 includes a wafer standby / transfer unit 11, a filter installation unit 12, a processing chamber 13, and a FOUP installation unit 14.

  The wafer standby / transfer unit 11 includes shutters 11 a and 11 b in the vicinity of the FOUP installation unit 14 and between the processing chamber 13. The wafer standby / transfer unit 11 can be connected to the shutter 11a of the FOUP 20 in which the wafer W is stored. The wafer standby / transfer unit 11 is connected to the FOUP 20, and a robot arm (not shown) is connected to the FOUP 20 when the shutter 20a of the FOUP 20 and the shutter 11a of the wafer standby / transfer unit 11 are opened. Thus, the wafer W is taken in and out.

  The wafer standby / transfer section 11 is at atmospheric pressure, and clean room air flows in a down flow through a filter installation section 12 having a particle removal filter (not shown).

  When the shutter 11b of the wafer standby / transfer unit 11 is opened, the processing chamber 13 is configured so that the wafer W can be taken in and out with the wafer standby / transfer unit 11 by a robot arm.

  When processing the wafer W by the semiconductor manufacturing apparatus 10 having such a configuration, first, the FOUP 20 installed in the FOUP installation unit 14 is connected to the wafer standby / transfer unit 11 and the shutters 11a and 20a are opened. . Then, the wafer W in a predetermined slot is transferred from the FOUP 20 to the wafer standby / transfer unit 11 by the robot arm. Thereafter, the shutter 11b is opened, and the wafer W is further transferred to the processing chamber 13 by the robot arm. After the shutter 11b is closed, processing is performed there. The processed wafer W is returned to the original slot of the FOUP 20 by the robot arm after the shutter 11b is opened. In this way, the wafers W in the FOUP 20 are processed one after another. After the processing of all the wafers W in the FOUP 20, the shutters 11a and 20a are closed, and the FOUP 20 is transferred to the next process with the shutter 20a closed.

In such a semiconductor manufacturing apparatus 10, first, the effect of providing a chemical filter together with a particle removal filter in the filter installation unit 12 was investigated.
Here, a silicon wafer having an oxide film with a thickness of 1.24 nm is used, and this silicon wafer is respectively used for the wafer standby / transfer section 11 when the chemical filter is not provided in the filter installation section 12 and when the chemical filter is provided. Left for a certain time. After standing for a certain period of time, the film thickness of the oxide film was measured at nine different locations on the left silicon wafer surface. The results are shown in FIG.

FIG. 12 is a diagram showing the change over time of the thickness of the oxide film. FIG. 12 shows the average value (Ave), maximum value (Max), and minimum value (Min) of the measured film thickness.
In the case where no chemical filter was provided in the filter installation unit 12, an increase in the thickness of the oxide film of 0.12 nm was observed when the wafer W was left in the wafer standby / transfer unit 11 for 120 minutes. On the other hand, when a chemical filter is provided in the filter installation unit 12, the increase in the thickness of the oxide film is about 0.02 nm even if the wafer W is left in the wafer standby / transfer unit 11 for 120 minutes. The amount was reduced to about 1/6.

Thus, it can be said that the chemical filter is effective in suppressing oxidation of the wafer W.
However, such a chemical filter depends on its installation environment, but its filter performance gradually deteriorates after installation. In order to ensure a certain level of filter performance, its lifetime is generally 2 years. It is said to be about. In the semiconductor manufacturing apparatus 10, when the installed chemical filter deteriorates, the wafer W in the wafer standby / transfer unit 11 and the wafer W in the FOUP 20 communicating with the wafer standby / transfer unit 11 are oxidized and processed. It is possible that a desired process cannot be performed in the chamber 13. In addition, the wafer W after processing in the processing chamber 13 may be oxidized after being returned to the FOUP 20.

Therefore, the influence of such deterioration of the chemical filter on the environment in the wafer standby / transfer unit 11 was examined.
First, using the semiconductor manufacturing apparatus 10, 25 silicon wafers are provided for each of the case where a chemical filter that has been installed for two years is provided in the filter installation unit 12 and the case where a chemical filter that is less than half a year has been provided. Heat treatment in a hydrogen atmosphere was continuously performed.

  That is, first, the FOUP 20 containing 25 silicon wafers is connected to the wafer standby / transfer unit 11 and the shutters 11a and 20a are opened. From the FOUP 20, a silicon wafer in a predetermined slot is sequentially transferred to the wafer standby / transfer unit 11 and the processing chamber 13, where heat treatment is performed in a hydrogen atmosphere. Then, the heat-treated silicon wafer is transferred from the processing chamber 13 to the original slot of the FOUP 20. Next, the silicon wafer in another slot in the FOUP 20 is similarly heat-treated in a hydrogen atmosphere, and after the heat treatment, the silicon wafer is returned to the original slot. In this way, the silicon wafers in the FOUP 20 are successively heat-treated in a hydrogen atmosphere, and after all the silicon wafers are heat-treated, the shutters 11a and 20a are closed.

  During this heat treatment, the air in the clean room flows into the wafer standby / transfer unit 11 via the filter installation unit 12. When heat treatment is performed according to the procedure described above, the silicon wafers with earlier heat treatment order are left longer in the FOUP 20 in communication with the wafer standby / transfer unit 11 into which the clean room air flows. Will be.

  The heat treatment of the 25 silicon wafers as described above took about 103 minutes. And after heat-processing 25 silicon wafers, the film thickness measurement of the oxide film of the silicon wafer was implemented immediately. Film thickness measurement was performed on silicon wafers in which the order of heat treatment was 1 to 5, 10, 15, 20, 22 to 25th. Moreover, about each silicon wafer, the film thickness measurement of nine different places in the surface was implemented. The results are shown in FIG.

  FIG. 13 is a diagram showing the results of film thickness measurement. FIG. 13 shows the average values (Ave (less than half a year), Ave (two years) of the film thickness measured after each heat treatment when the chemical filter of the semiconductor manufacturing apparatus 10 is less than half a year and two years have passed since installation. Progress)), maximum values (Max (less than half a year), Max (elapsed two years)), and minimum values (Min (less than half a year), Min (elapsed two years)).

  From FIG. 13, when the semiconductor manufacturing apparatus 10 provided with a chemical filter that has been installed for two years in the filter installation part 12 is used, the film thickness of the oxide film increases as the heat treatment order in the hydrogen atmosphere becomes earlier. A tendency to thicken is observed. This is because the filter performance of a chemical filter that has been installed for two years has deteriorated, and moreover, silicon wafers with earlier heat treatment orders as described above will be exposed to the clean room atmosphere longer. .

  On the other hand, as shown in FIG. 13, in the case where the semiconductor manufacturing apparatus 10 provided with a chemical filter of less than half a year from the installation in the filter installation unit 12, there is a certain tendency between the order of the heat treatment and the film thickness of the oxide film. It is not allowed. If the chemical filter maintains a certain level of filter performance, the formation of an oxide film can be suppressed even if a silicon wafer that has been subjected to the heat treatment in an early order is exposed to the clean room atmosphere that has passed through the chemical filter.

  Note that, as shown in FIG. 13, the film thickness of the oxide film of the silicon wafer that was delayed in the heat treatment sequence was the same regardless of which chemical filter was used. Can be said to be comparable.

  Thus, the deterioration of the chemical filter changes the environment in the wafer standby / transfer unit 11. In other words, it is possible to evaluate whether or not the chemical filter of the filter installation unit 12 has deteriorated by monitoring the environmental change in the wafer standby / transfer unit 11.

  For example, when the semiconductor manufacturing apparatus 10 performs a predetermined process such as a film forming process on the wafer W, a heat treatment is performed in a hydrogen atmosphere at an appropriate place in the wafer standby / transfer unit 11 which is a monitor environment. The performed silicon wafer is placed for environmental monitoring. For example, it is arranged horizontally, that is, at a position where the clean room air from the filter installation unit 12 collides with the silicon wafer surface from the normal direction. Then, after a predetermined time, such as a predetermined number of days, months, years, or a predetermined number of treatments, the film thickness of the oxide film of the silicon wafer is measured, and the amount of increase in film thickness over the predetermined time And the degree of deterioration of the chemical filter is evaluated based on the amount of increase in the film thickness.

  In the evaluation, for example, the data shown in FIG. 13 or the relationship between the standing time and the film thickness increase amount as shown in FIG. 2 is used, and the chemical filter maintains a certain level of filter performance for a certain time. The value (threshold value) of the amount of increase in the thickness of the oxide film that is allowed by leaving is set in advance. Then, the amount of increase in the thickness of the oxide film measured in the silicon wafer after the elapse of a predetermined time after being installed in the wafer standby / transfer unit 11 is compared with a preset threshold for the amount of increase in thickness. When the measured value of the increase in film thickness exceeds the threshold value, it can be determined that the inside of the wafer standby / transfer unit 11 that is the monitor environment is not in a normal state, that is, the chemical filter has deteriorated.

When deterioration of the chemical filter is recognized, measures such as replacing the chemical filter of the semiconductor manufacturing apparatus 10 may be taken.
As the silicon wafer for environmental monitoring, it is possible to use a silicon wafer that has been heat-treated in the exemplified hydrogen atmosphere, and that in which an oxide film having a predetermined film thickness has been formed in advance. It is possible to evaluate the degree.

  In addition, the silicon wafer for environmental monitoring may be placed in the wafer standby / transfer section 11 in a vertical orientation in addition to a horizontal orientation. In that case, when setting the threshold value, for silicon wafers placed under the same conditions as the silicon wafer for environmental monitoring, the relationship between the standing time when the monitoring environment is normal and the increase in film thickness of the oxide film should be obtained. Good.

  In addition, when measuring the film thickness of an oxide film on a silicon wafer, if an in-plane distribution of the thickness of the oxide film is obtained by measuring the film thickness at multiple locations within the plane, the in-plane distribution Therefore, it is possible to estimate the flow of air, the flow of impurities, and the like.

  Here, a case where a silicon wafer for environmental monitoring is installed in the wafer standby / transfer unit 11 is illustrated, but such a silicon wafer for environmental monitoring supplies air to the FOUP 20 or a clean room. It can also be installed on the part. Regardless of where the silicon wafer for environmental monitoring is installed, information on the tendency to increase the thickness of the oxide film when it is left in the normal location is acquired in advance, and a threshold is set based on that information. deep. Then, the measured value of the increase in film thickness due to the silicon wafer being left for a certain period of time may be compared with a set threshold value to determine whether or not the installation environment of the silicon wafer is in a normal state.

Then, the specific example of the manufacturing method of the semiconductor device using the semiconductor manufacturing apparatus 10 provided with the above chemical filters is demonstrated.
FIG. 14 is a schematic cross-sectional view of the main part of the element isolation insulating film forming process, FIG. 15 is a schematic cross-sectional view of the main part of the first silicon oxide film forming process, and FIG. 16 is a schematic cross-sectional view of the main part of the second silicon oxide film forming process. 17 is a schematic cross-sectional view of a main part of a nitriding process, FIG. 18 is a schematic cross-sectional view of a main part of a gate processing process, and FIG. 19 is a schematic cross-sectional view of a main part of an impurity diffusion region and sidewall insulating film forming process.

  First, as shown in FIG. 14, an element isolation insulating film 31 that defines first and second element regions 40 and 50 is formed on a silicon wafer (silicon substrate) 30 after wet cleaning using an STI (Shallow Trench Isolation) method. Form.

  Next, pyrogenic oxidation at a temperature of 800 ° C. is performed to form a first silicon oxide film 41 on the first element region 40 of the silicon substrate 30 as shown in FIG. Further, thermal oxidation is performed at a temperature of 900 ° C., and as shown in FIG. 16, a second silicon oxide film 51 is formed on the second element region 50 of the silicon substrate 30 with a film thickness of 1 nm, for example. When the second silicon oxide film 51 is formed, the previously formed first silicon oxide film 41 is also oxidized and thickened. The film thickness of the first silicon oxide film 41 after the formation of the second silicon oxide film 51 is, for example, 7 nm.

  For the formation of the first and second silicon oxide films 41 and 51, a thin film forming apparatus having a configuration like the semiconductor manufacturing apparatus 10 described above can be used. That is, according to the above example, the silicon substrate 30 is transferred from the FOUP to the wafer standby / transfer section and the processing chamber in order, and the first silicon oxide film 41 or the second silicon oxide film 51 is formed there. Then, after the formation of the first silicon oxide film 41 or the formation of the second silicon oxide film 51, the silicon substrate 30 is returned to the original FOUP.

  In the formation of the thin first and second silicon oxide films 41 and 51 using such a thin film forming apparatus, even if the silicon substrate 30 is slightly oxidized outside the processing chamber or attached with organic substances, the first and second silicon oxide films are formed. The formation of the films 41 and 51, or subsequent processes and device performance may be affected. Therefore, clean room air is allowed to flow into the wafer standby / transfer section through the chemical filter, and a silicon wafer that has been previously heat-treated in a hydrogen atmosphere as described above is used for environmental monitoring in the wafer standby / transfer section. Keep it in place. And the film thickness measurement of an oxide film is implemented about the silicon wafer after a fixed time, and the degree of deterioration of the chemical filter of a filter installation part is evaluated by comparing the measurement result with a predetermined threshold value.

  When deterioration of the chemical filter is recognized from the film thickness measurement result of the silicon wafer after standing for a certain time, measures such as replacement of the chemical filter are taken to stabilize the first and second silicon oxide films 41 and 51 having a predetermined film thickness. To form.

  After the formation of the first and second silicon oxide films 41 and 51, plasma nitridation is performed to form the first and second silicon oxide films 41 and 51, respectively, as shown in FIG. The oxynitride films 41a and 51a are changed. The plasma nitriding process is performed, for example, by exciting nitrogen plasma with RF power of 500 W and introducing active nitrogen into the first and second silicon oxide films 41 and 51 under the conditions of room temperature and 20 mTorr.

  After the plasma nitriding process, a post-annealing process is performed. In the post-annealing process, for example, oxidation annealing (RTO) in a reduced pressure oxygen atmosphere at about 1000 ° C. and rapid temperature increase annealing (RTA) in a nitrogen atmosphere at about 1050 ° C. are continuously performed. Thereafter, the silicon substrate 30 is cooled.

  After the post-annealing process, polysilicon is deposited on the entire surface, and a predetermined gate process is performed by etching, so that a gate insulating film composed of the first and second silicon oxynitride films 41a and 51a, as shown in FIG. Then, first and second gate electrodes 42 and 52 made of polysilicon are formed.

  After the formation of the first and second gate electrodes 42 and 52, as shown in FIG. 19, the first and second low-concentration impurity diffusion regions (extension regions) 43 and 53, the sidewall insulating films 44 and 54, and the first First, second high-concentration impurity diffusion regions 45 and 55 are formed in this order.

  As a result, two types of MOS transistors are formed on the silicon substrate 30. After that, according to a conventional method, necessary interlayer insulating films, wirings, and the like are formed to complete the semiconductor device.

  Here, the case where the configuration like the semiconductor manufacturing apparatus 10 including the chemical filter is applied to a thin film forming apparatus for forming the first and second silicon oxide films 41 and 51 is illustrated. In addition, the configuration of the semiconductor manufacturing apparatus 10 described above can be similarly applied to apparatuses used in other processes, and environmental monitoring can be performed in the same manner.

  For example, for the post-annealing process in the manufacturing method, a heat treatment apparatus having a configuration like the semiconductor manufacturing apparatus 10 can be used. In that case, according to the above example, the silicon substrate 30 is sequentially transferred from the FOUP to the wafer standby / transfer section and the processing chamber, where post-annealing is performed, and after the processing, the silicon substrate 30 is returned to the original FOUP. A silicon wafer for environmental monitoring is installed in the wafer standby / transfer section, and the film thickness measurement result of the oxide film of the silicon wafer after a certain time is compared with a predetermined threshold value, so that the filter installation section Evaluate the degree of deterioration of the chemical filter.

  In addition, the configuration of the semiconductor manufacturing apparatus 10 described above can be similarly applied to a cleaning apparatus that performs wet cleaning, a film forming apparatus that forms polysilicon or an insulating film, an etching apparatus that performs gate processing, and the like. .

  In the above description, the thermal oxidation method is exemplified as the formation method when the oxide film is formed in advance on the silicon wafer for environmental monitoring. However, in addition to this, an oxide film having a predetermined thickness is formed by wet oxidation. May be. For the wet oxidation, for example, an aqueous solution (SC1) containing ammonia and hydrogen peroxide, an aqueous solution (SC2) containing hydrochloric acid and hydrogen peroxide, or the like can be used.

  In the above description, the method of removing the oxide film on the surface of the silicon wafer and terminating the hydrogen on the surface by heat treatment in a hydrogen atmosphere is exemplified. However, such oxide film removal by wet treatment using a hydrofluoric acid solution or the like is exemplified. Hydrogen termination may be performed.

  By the way, when a silicon wafer for environmental monitoring is left in a semiconductor manufacturing apparatus, a container having excellent hermeticity such as FOUP can be used for subsequent film thickness measurement without being exposed to an atmosphere different from the monitoring environment. It is preferable that it can be stored. In that case, the container may be transported to an apparatus for measuring the film thickness such as an ellipsometer, where the container is opened, the silicon wafer is taken out, and the film thickness is measured.

  When leaving a silicon wafer for environmental monitoring in place in a clean room, leave it in an open FOUP, and then measure the film thickness with the FOUP sealed in the subsequent film thickness measurement. The film thickness may be measured there.

  When placing a silicon wafer for environmental monitoring in a semiconductor manufacturing apparatus or in a container such as a FOUP, attention should be paid to the way in which the silicon wafer is placed. For example, the silicon wafer surface for environmental monitoring is arranged so as to be perpendicular or parallel to the air flow direction in the semiconductor manufacturing apparatus. In addition, when it is placed in a container such as FOUP, the flow of air in the container may change depending on the position in the container or the arrangement relationship (interval) with another silicon wafer stored in the container. Because of this, arrange them in consideration of them. Regardless of the arrangement, when setting the threshold, for silicon wafers arranged under the same conditions as the silicon wafer for environmental monitoring, the relationship between the standing time when the monitoring environment is normal and the amount of increase in the oxide film thickness Get it.

Regarding the embodiment described above, the following additional notes are further disclosed.
(Appendix 1) A process of leaving a wafer in a monitor environment for a certain period of time;
A step of determining the film thickness of the oxide film formed on the wafer surface by leaving;
An environmental monitoring method characterized by comprising:

(Supplementary note 2) The environmental monitoring method according to supplementary note 1, further comprising a step of reducing the surface of the wafer and terminating it with hydrogen before being left in the monitoring environment.
(Supplementary note 3) The environmental monitoring method according to supplementary note 2, wherein the wafer surface is reduced and hydrogen-terminated by heat-treating the wafer in a hydrogen atmosphere.

(Additional remark 4) It has the process of implementing the film thickness measurement of an oxide film with respect to the said wafer left to stand in the said monitor environment,
In the step of determining the film thickness of the oxide film formed on the wafer surface by leaving it to stand, the film thickness measurement of the oxide film is performed on the wafer after being left, and from the film thickness measurement result of the oxide film before and after being left to stand 4. The environmental monitoring method according to any one of appendices 1 to 3, wherein the film thickness of the oxide film formed on the wafer surface is obtained by being left standing.

  (Supplementary Note 5) In the step of obtaining the film thickness of the oxide film formed on the wafer surface by leaving it to stand, the film thickness of the oxide film is measured on the wafer after being left, and the film of the oxide film after being left to stand 4. The environmental monitoring method according to appendix 2 or 3, wherein the film thickness of the oxide film formed on the wafer surface is obtained by leaving it to stand based on the thickness measurement result.

(Additional remark 6) The environmental monitoring method of Additional remark 4 or 5 which implements the film thickness measurement of an oxide film with respect to the said wafer using an ellipsometer.
(Supplementary Note 7) Based on the relationship between the time for which the wafer is left in the monitor environment and the film thickness of the oxide film formed on the wafer surface by leaving the wafer, the film of the oxide film allowed in the monitor environment A step of presetting the thickness increase amount;
Comparing the film thickness of the oxide film formed on the wafer surface by leaving the film thickness with a preset film thickness increase amount, and determining whether the monitoring environment is normal;
The environmental monitoring method according to any one of appendices 1 to 6, characterized by comprising:

(Supplementary note 8) The environmental monitoring method according to supplementary note 7, wherein qualitative analysis or quantitative analysis is performed on the wafer when the environmental monitor is determined to be abnormal.
(Supplementary note 9) The environmental monitoring method according to any one of supplementary notes 1 to 8, wherein the monitor environment is a space in a clean room.

(Supplementary note 10) The environmental monitoring method according to any one of supplementary notes 1 to 8, wherein the monitoring environment is a space in a semiconductor manufacturing apparatus.
(Supplementary note 11) The environmental monitoring method according to any one of supplementary notes 1 to 10, wherein the wafer is a silicon wafer.

It is a figure which shows an example of the flow of an environment monitoring method. It is a figure which shows the relationship between the leaving time when the sample a is left in monitor environment x, y, z, and the film thickness increase amount of an oxide film. It is a figure which shows the relationship between the leaving time when the sample b is left in monitor environment x, y, z, and the film thickness increase amount of an oxide film. It is a figure which shows the relationship between the leaving time when the sample c is left in monitor environment x, y, z, and the film thickness increase amount of an oxide film. It is a figure which shows the relationship between the leaving time when the sample d is left in monitor environment x, y, z, and the film thickness increase amount of an oxide film. It is a figure which shows a XPS measurement result. It is a figure which shows the comparison with the film thickness of the oxide film obtained from the XPS measurement result of the sample b, and the film thickness of the oxide film measured with the ellipsometer. It is a figure which shows the comparison with the film thickness of the oxide film obtained from the XPS measurement result of the sample c, and the film thickness of the oxide film measured with the ellipsometer. It is a figure which shows an example of a XPS measurement result. It is a figure which shows the abundance ratio of the carbon of sample a, b, c, d. 1 is a schematic configuration diagram of an example of a semiconductor manufacturing apparatus. It is a figure which shows the time-dependent change of the film thickness of an oxide film. It is a figure which shows a film thickness measurement result. It is a principal part cross-sectional schematic diagram of an element isolation insulating film formation process. It is a principal part cross-sectional schematic diagram of a 1st silicon oxide film formation process. It is a principal part cross-sectional schematic diagram of a 2nd silicon oxide film formation process. It is a principal part cross-sectional schematic diagram of a nitriding process. It is a principal part cross-sectional schematic diagram of a gate processing process. It is a principal part cross-sectional schematic diagram of an impurity diffusion area | region and a side wall insulating film formation process.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Semiconductor manufacturing apparatus 11 Wafer stand-by / transfer part 11a, 11b, 20a Shutter 12 Filter installation part 13 Processing chamber 14 FOUP installation part 20 FOUP
30 Silicon substrate 31 Element isolation insulating film 40, 50 First and second element regions 41, 51 First and second silicon oxide films 41a and 51a First and second silicon oxynitride films 42 and 52 First and second gates Electrodes 43, 53 First and second low-concentration impurity diffusion regions 44, 54 Side wall insulating films 45, 55 First and second high-concentration impurity diffusion regions

Claims (5)

A process of leaving the wafer in a monitor environment for a certain period of time;
A step of determining the film thickness of the oxide film formed on the wafer surface by leaving;
An environmental monitoring method characterized by comprising:   2. The environmental monitoring method according to claim 1, further comprising a step of reducing the surface of the wafer and terminating the hydrogen before leaving the wafer in the monitoring environment. Having a step of measuring the thickness of the oxide film on the wafer to be left in the monitor environment;
In the step of determining the film thickness of the oxide film formed on the wafer surface by leaving it to stand, the film thickness measurement of the oxide film is performed on the wafer after being left, and from the film thickness measurement result of the oxide film before and after being left to stand 3. The environmental monitoring method according to claim 1, wherein the film thickness of the oxide film formed on the wafer surface is obtained by leaving it to stand.   In the step of determining the film thickness of the oxide film formed on the wafer surface by leaving it to stand, the film thickness of the oxide film is measured on the wafer after being left, and the film thickness measurement result of the oxide film after being left to stand is used. 3. The environmental monitoring method according to claim 2, wherein the film thickness of the oxide film formed on the wafer surface is obtained by leaving it to stand. Based on the relationship between the time for which the wafer is left in the monitoring environment and the thickness of the oxide film formed on the wafer surface by leaving the wafer, the amount of increase in the thickness of the oxide film allowed in the monitoring environment is determined. A step of presetting;
Comparing the film thickness of the oxide film formed on the wafer surface by leaving the film thickness with a preset film thickness increase amount, and determining whether the monitoring environment is normal;
The environment monitoring method according to claim 1, comprising:

Images