Abstract:
In order to prevent a sample from thermally expanding and contracting when the sample is placed on a sample stage inside a vacuum chamber, the related art has proposed a coping method of awaiting observation by setting a standby time from when the wafer is conveyed into the vacuum chamber until the wafer and the sample table are brought into thermal equilibrium. In addition, the coping method is configured so as to await the observation until the wafer is cooled down to room temperature when the wafer is heated in the previous step. Consequently, throughput of an apparatus decreases. A temperature control mechanism which can control temperature of the sample is installed inside a mini-environment device. The sample temperature control mechanism controls the temperature of the sample inside the mini-environment device so as to become a setting temperature which is set in view of a lowered temperature of the sample inside a load lock chamber.

Description:
TECHNICAL FIELD 
     The present invention relates to an apparatus for processing a sample, and for example, the present invention is applicable to an apparatus and a charged particle radiation apparatus which have a sample temperature control mechanism. 
     BACKGROUND ART 
     As semiconductor devices have recently been miniaturized, not only manufacturing apparatuses but also inspection or evaluation apparatuses need to be more precise corresponding to the miniaturization. A measurement apparatus for evaluating whether or not shapes and dimensions of a pattern formed on a semiconductor wafer are correct includes a scanning electron microscope provided with a length measurement function (hereinafter, referred to as a critical dimension-scanning electron microscope (CD-SEM) or a length measurement scanning electron microscope (SEM) in some cases). 
     As disclosed in PTL 1, the length measurement SEM is an apparatus which radiates an electron beam onto a wafer, performs image processing on a secondary electron signal obtained therefrom, and determines an edge of a pattern from a change in light density therein so as to derive dimensions. 
     In order to correspond to the miniaturization of the semiconductor devices, it is important to obtain a secondary electron image having much less noise by employing high observation magnification. Therefore, it is necessary to improve contrast by superimposing many secondary electron images on one another. A precise sub-nanometer order is required for a relative position change between an electron beam radiation position and a measurement target pattern on the wafer when an SEM image is acquired. 
     Here, if there is a temperature difference between the wafer serving as an observation target and a sample table of a sample stage on which the wafer is mounted in a vacuum chamber, the wafer is subjected to thermal expansion and contraction until the wafer is brought into a thermal equilibrium state. This thermal expansion and contraction causes the above-described relative position change, thereby degrading the SEM image. 
     In order to convey the wafer present in the atmospheric environment into the vacuum chamber, it is necessary to use a load lock chamber or the like. That is, after the wafer is conveyed to the load lock chamber at the atmospheric pressure, the inside of the load lock chamber is subjected to vacuum evacuation, and the wafer is conveyed onto the sample table inside the vacuum chamber. The vacuum evacuation of the load lock chamber is rapidly carried out. Accordingly, air temperature inside the load lock chamber is lowered due to adiabatic expansion. As a result, the wafer is cooled. If the wafer is conveyed to the sample table in this state, a temperature difference occurs between the wafer and the sample table. 
     In addition, even in a case where the wafer is observed immediately after the wafer is heated through a baking process in the previous step (wafer processing step), the temperature difference is likely to similarly occur between the wafer and the sample table. 
     In order to solve these problems, the related art has proposed a coping method of awaiting observation by setting a standby time from when the wafer is conveyed into the vacuum chamber until the wafer and the sample table are brought into thermal equilibrium. In addition, the coping method is configured so as to await the observation until the wafer is cooled down to room temperature when the wafer is heated in the previous step. 
     In addition, PTL 2 discloses a technique of providing a temperature control mechanism inside the load lock chamber. 
     CITATION LIST 
     Patent Literature 
     PTL 1: JP-A-9-166428 
     PTL 2: JP-A-10-303092 
     SUMMARY OF INVENTION 
     Technical Problem 
     The coping method of setting a standby time before observation as described above decreases the throughput of an apparatus. In addition, according to the technique of controlling the temperature inside the load lock chamber as disclosed in PTL 2, heat transfer performance is poor. Consequently, a long time is required until the temperature of a sample (wafer) becomes a desired temperature, thereby decreasing the throughput of the apparatus. 
     Other aspects and novel features will become apparent from the following description and the accompanying drawings. 
     Solution to Problem 
     As means for achieving aspects disclosed in the present application, a schematic configuration of representative means will be briefly described as follows. 
     That is, an apparatus for processing a sample includes a temperature control mechanism installed therein which can control the temperature of a sample inside a mini-environment device. 
     Advantageous Effects of Invention 
     According to the above-described apparatus for processing a sample, throughput of an apparatus can be considerably improved. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is an overall configuration diagram of a length measurement SEM according to an embodiment. 
         FIG. 2  is an overall configuration diagram of a length measurement SEM according to Modification Example 1. 
         FIG. 3  is an overall configuration diagram of a length measurement SEM according to Modification Example 2. 
         FIG. 4  is an overall configuration diagram of a length measurement SEM according to Modification Example 3. 
         FIG. 5  is a configuration diagram of an apparatus according to the embodiment. 
         FIG. 6  is a flowchart illustrating an operation method of the length measurement SEM according to the embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, an apparatus according to an embodiment will be described in detail with reference to the drawings. 
       FIG. 5  is a configuration diagram of the apparatus according to the embodiment. An apparatus  10  has a vacuum chamber  9 , a load lock chamber  12 , and a mini-environment device  13 . The apparatus  10  processes a sample on a sample table  6  inside the vacuum chamber  9 . The load lock chamber  12  conveys the sample into the vacuum chamber  9  from the atmospheric environment. The mini-environment device  13  forms a small clean environment inside a clean room, and conveys the sample into the load lock chamber  12  from a conveyance-purpose sealed container. In addition, the mini-environment device  13  has a temperature control mechanism TCS for the sample inside the mini-environment device  13 . In this manner, before the sample is observed, the sample is quickly controlled so as to have a desired temperature in the atmospheric environment which shows good heat transfer performance. Accordingly, throughput of the apparatus can be considerably improved by omitting a standby time inside the vacuum chamber  9 . 
     Preferably, a first temperature sensor  8  for measuring the temperature of the sample table  6  is accommodated in the vacuum chamber  9 . A second temperature sensor  7  for measuring the temperature of the sample inside the mini-environment device  13  is preferably accommodated in the mini-environment device  13 . In addition, it is preferable to cause the sample temperature control mechanism TCS to measure the temperature of the sample table  6  so as to control the temperature of the sample inside the mini-environment device  13  to become a setting temperature which is set in view of a lowered temperature of the sample inside the load lock chamber  12 . In this manner, prior to observation, various samples having different temperature are quickly controlled so as to have a desired temperature in the atmospheric environment which shows good heat transfer performance. Accordingly, throughput of the apparatus can be considerably improved by omitting a standby time inside the vacuum chamber  9 . 
     EMBODIMENT 
     Hereinafter, according to an embodiment, a length measurement SEM which is a charged particle radiation apparatus will be described as an example. However, without being limited thereto, the embodiment is also applicable to electron microscopes, ion microscopes, defect inspection apparatuses, or the like. In addition, the apparatus according to the embodiment is also applicable to not only the charged particle radiation apparatuses but also manufacturing apparatuses, inspection apparatuses, and evaluation apparatuses for processing a sample in vacuum. Additionally, in addition to a wafer, the sample includes those which have a pattern formed on a substrate, such as photomasks, reticles, liquid crystal display devices, and the like. 
       FIG. 1  is an overall configuration diagram of the length measurement SEM according to the embodiment. A length measurement SEM  100  has a column  104 , a vacuum chamber  109 , a load lock chamber  112 , and a mini-environment device  113 . The vacuum chamber  109  accommodates a sample stage  106  for mounting a wafer (sample)  105  thereon. The load lock chamber  112  is configured to convey the wafer  105  into the vacuum chamber from the atmospheric environment. The mini-environment device  113  is configured to form a small clean environment inside a clean room. 
     Next, a conveyance route before the wafer  105  is observed will be described. The wafer  105  inside a front opening unified pod (FOUP)  118  is conveyed to a sample table  121  inside the load lock chamber  112  by an air conveyance robot  114  disposed inside the mini-environment device  113  after a gate valve  120  is opened. Thereafter, the gate valve  120  is closed so that the inside of the load lock chamber  112  is subjected to vacuum evacuation. Thereafter, a gate valve  110  installed between the vacuum chambers  109  is opened, and the wafer  105  is placed on the sample table  106  on a sample stage  107  by a vacuum conveyance robot  111 . 
     During observation, the sample stage  107  is driven so as to move the wafer  105  to any desired position. Two-dimensional scanning is performed on the wafer  105  by using an electron beam  102  radiated from an electron gun  101  disposed inside the column  104 . A signal (secondary electron signal, reflected electron signal, or the like) generated by the incident electron beam  102  is captured by a detector  103 . Although not illustrated, an observation image is displayed on an image display device, based on the detected signal. 
     According to the above-described embodiment, in the present embodiment, the temperature of the sample table  106  can always be measured by installing a temperature sensor A (first temperature sensor)  108  in the sample table  106 . In addition, the temperature of the wafer  105  which is an observation target can be measured by installing a temperature sensor B (second temperature sensor)  117  so as to come into contact with the wafer  105 , in a conveyance arm  116  of the air conveyance robot  114  present inside the mini-environment device  113 . Furthermore, a heat exchanger  119  is disposed in a fan filter unit (FFU)  115  installed so as to maintain a clean environment inside the mini-environment device  113 . Accordingly, wind which is set to have any desired temperature can be blown therefrom (this is also referred to as sample temperature control mechanism). 
       FIG. 6  is a flowchart illustrating an operation of the length measurement SEM according to the embodiment. A temperature control method in the conveyance route until the wafer (sample)  105  is observed will be described with reference to  FIG. 6 . When the wafer  105  inside the FOUP  118  is held by the conveyance arm  116 , a temperature (T 1 ) of the wafer  105  is measured (Step S 1 A). Concurrently with this process, a temperature (T 2 ) of the sample table  106  is also measured (Step S 1 B), and a temperature difference (T 1 -T 2 ) between the wafer  105  and the sample table  106  is acquired (Step S 2 ). A wind volume and a wind temperature of the FFU  115  are adjusted to control the temperature so that the temperature difference obtained here becomes a predetermined temperature difference (Step S 3 ). The wafer  105  is conveyed into the load lock chamber  112  (Step S 4 ). The subsequent processes until the observation are the same as those described above. That is, the load lock chamber  112  is subjected to the vacuum evacuation (Step S 5 ), and the wafer  105  is conveyed to the sample table  106  (Step S 6 ). 
     Although described above, the reason of controlling the temperature difference so as to become the predetermined temperature difference is that the wafer  105  is cooled due to adiabatic expansion when the inside of the load lock chamber  112  is subjected to the vacuum evacuation. For example, a method for obtaining the predetermined temperature difference includes the following three methods. 
     (1) Wafer Temperature Profile 
     The temperature of the wafer  105  to be cooled inside the load lock chamber  112  is measured in advance using a thermometer-incorporated wafer. The wafer has a function incorporated therein for storing the temperature in a time-series manner. The temperature can be measured by examining stored content after the wafer is unloaded from the apparatus. 
     (2) Sample Table Temperature Change 
     The wafer  105  whose temperature is controlled to several patterns by the FFU  115  is placed on the sample table  106 . Thereafter, the temperature sensor A 108  observes a temperature change in the respective patterns, and the predetermined temperature difference is obtained from the pattern whose temperature change is minimized. 
     (3) Relative Position Change 
     After the wafer  105  whose temperature is controlled to several patterns by the FFU  115  is placed on the sample table  106 , observation is performed by skipping the standby time until the wafer  105  and the sample table  106  are brought into thermal equilibrium so as to obtain a predetermined temperature difference from a pattern in which an amount of thermal expansion and contraction of the wafer  105  minimizes a relative position change. 
     According to any one of the above-described methods, an apparatus manufacturer can obtain a predetermined temperature difference, and then can register the predetermined temperature difference in an apparatus in advance before or when the apparatus is delivered to a user. 
     The above-described operation of the length measurement SEM according to the present embodiment is controlled by a control unit (not illustrated). 
     According to the above-described configurations and processes, prior to observation, various wafers  105  having different temperatures are quickly controlled so as to have desired temperatures in the atmospheric environment which shows good heat transfer performance. Accordingly, the throughput of the apparatus can be considerably improved by omitting the standby time inside the vacuum chamber  109 . In addition, since there is no temperature difference between the wafer and the sample table, the relative position change is not caused by thermal expansion and contraction. Accordingly, it is possible to very precisely measure and inspect the pattern. Furthermore, unlike PTL 2, the temperature of the load lock chamber is not changed. Therefore, there is no problem that the temperature of the adjacent vacuum chamber may also be unintentionally changed. 
     Modification Example 1 
       FIG. 2  is an overall configuration diagram of a length measurement SEM according to Modification Example 1. A configuration is adopted in which the temperature of the wafer  105  inside the mini-environment device  113  is predicted by causing a temperature sensor C (second temperature sensor)  201  to measure the temperature of the conveyance arm  116 . This configuration is advantageously adopted in terms of the contamination of the wafer  105 , since the temperature sensor C 201  does not come into contact with the wafer  105 . Other configurations, processes, and advantageous effects of a length measurement SEM  100 A are the same as those of the length measurement SEM  100  according to the embodiment in  FIG. 1 . 
     Modification Example 2 
       FIG. 3  is an overall configuration diagram of a length measurement SEM according to Modification Example 2. A configuration is adopted in which the temperature of the wafer  105  inside the mini-environment device  113  is measured by a temperature sensor D (third temperature sensor)  301  of a non-contact type. Other configurations, processes, and advantageous effects of a length measurement SEM  100 B are the same as those of the length measurement SEM  100  according to the embodiment in  FIG. 1 . 
     Modification Example 3 
       FIG. 4  is an overall configuration diagram of a length measurement SEM according to Modification Example 3. A configuration is adopted in which the temperature of the wafer  105  is controlled inside a separate temperature control chamber  401  which is installed inside the mini-environment device  113 . The heat exchanger  119  is not disposed inside the FFU  115 , and the heat exchanger  119  is disposed inside the temperature control chamber (sample temperature control mechanism)  401  which has an FFU function. According to this configuration, the temperature can be controlled in a chamber which is smaller than the mini-environment device  113 . Accordingly, the time required for controlling the wafer  105  so as to have a desired temperature is shortened. Other configurations, processes, and advantageous effects of a length measurement SEM  100 C are the same as those of the length measurement SEM  100  according to the embodiment in  FIG. 1 . In addition, although not illustrated, the same advantageous effect may also be obtained if the respective configurations described in Modification Example 1 in  FIG. 2  and Modification Example 2 in  FIG. 3  are applied to the configuration in  FIG. 4 . 
     Hitherto, the present invention has been described in detail with reference to the embodiment and the modification examples. However, without being limited to the above-described embodiment and modification examples, the present invention can be modified in various ways, as a matter of course. 
     REFERENCE SIGNS LIST 
     
         
         
           
               6 ,  106  SAMPLE TABLE 
               7  SECOND TEMPERATURE SENSOR 
               8  FIRST TEMPERATURE SENSOR 
               9 ,  109  VACUUM CHAMBER 
               10  APPARATUS 
               12 ,  112  LOAD LOCK CHAMBER 
               13 ,  113  MINI-ENVIRONMENT DEVICE 
               100 ,  100 A,  100 B,  100 C LENGTH MEASUREMENT SEM 
               101  ELECTRON GUN 
               102  ELECTRON BEAM 
               103  DETECTOR 
               104  COLUMN 
               105  WAFER (SAMPLE) 
               107  SAMPLE STAGE 
               108  TEMPERATURE SENSOR A 
               110  GATE VALVE 
               111  VACUUM CONVEYANCE ROBOT 
               114  AIR CONVEYANCE ROBOT 
               115  FFU 
               116  CONVEYANCE ARM 
               117  TEMPERATURE SENSOR B 
               118  FOUP 
               119  HEAT EXCHANGER 
               201  TEMPERATURE SENSOR C 
               301  TEMPERATURE SENSOR D 
               401  TEMPERATURE CONTROL CHAMBER