Patent Publication Number: US-2009236316-A1

Title: Substrate processing method and substrate processing apparatus

Description:
The present invention is based on Japanese Patent Application No. 2008-075019. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a substrate processing method and a substrate processing apparatus. 
     As a method for processing a substrate with keeping high etching rate, a “boiling point control method” is known. Boiling point control is control performed for the cycle of starting supply of pure water when the temperature of an etchant reaches a pure water addition start temperature, which is the boiling point of the etchant and halting the pure water supply when the temperature of the etchant becomes a pure water addition halt temperature, which is a temperature several degree C. lower than the boiling point. Using this boiling point control, the concentration of an etchant around its boiling point is stabilized to perform product processing with keeping etching rate high. 
     Meanwhile, in order to provide substrates subjected to proper etching processing, Japanese Patent Laid-Open Nos. 2006-114590 and 2001-205158 made the proposals described below. 
     Japanese Patent Laid-Open No. 2006-114590 describes the etching method that the suitable etching time is calculated based on the difference between a predetermined temperature (base temperature) and the temperature of a process fluid after a certain period of time from semiconductor substrates loading into an etch tank. It also describes when the etching processing time becomes long and exceeding a predetermined threshold value, the process control unit determines that an abnormality has occurred and gives an alarm about filter clogging. 
     Also, Japanese Patent Laid-Open No. 2001-205158 describes an etching method using a wet processing apparatus adopting chemical treatment (etching) and wet cleaning in the same tank that the concentration of a chemical (etching) solution is calculated based on integrated flow rates of the concentrated chemical solution and added pure water, and the temperature of the chemical solution is measured, thereby processing time for substrates is determined. 
     However, the present inventors have noticed that there remain the following problems even if these techniques are used. 
       FIG. 4  is a graph indicating the relationship between the temperature of a chemical solution and etching time of silicon nitride film when performing boiling point control. The chemical solution in the etch tank is heated by, e.g., a heater. A boiling point control method is a method in which the boiling point is controlled by repeating the cycle of starting pure water supply when the temperature of the chemical solution is increased to a pure water addition start temperature (t 1 ) as a result of heating, and halting the pure water supply when the temperature is decreased to a pure water addition halt temperature (t 2 ). In this case, the pure water addition start temperature is set to the boiling point of the chemical solution, enabling the temperature of the chemical solution to be brought close to the boiling point while the concentration of the chemical solution being kept within a certain range. Consequently, the temperature of the chemical solution can be maintained at a temperature around the boiling point, enabling the high etching rate to be kept high. 
     However, deterioration of, e.g., the heater for heating the chemical solution causes difficulty in an increase in the temperature of the chemical solution, which may result in the temperature of the chemical solution being not maintained around the boiling point. In  FIG. 4 , the section of T 25  onwards indicates variations in the temperature of the chemical solution when the heater has deteriorated. As illustrated in  FIG. 4 , the time from T 23  to T 24  (when the heater has deteriorated) is longer compared to the time from T 21  to T 22  (normal condition). Consequently, a sufficient number of cycles cannot be provided for a certain period of time, the time of the state in which the etching rate of the chemical solution is high (normal condition) is reduced, which causes a problem in that etching process is finished without obtaining a sufficient etching amount. 
     It has been difficult to detect such decrease in etching amount. Also, controlling the etching rate of the chemical solution to be high (the temperature and concentration of the chemical solution) requires highly-accurate interlock control to he performed by monitoring fluctuations, such as the heat value (voltage and current) of the heater, and such control has been unable to be performed because of, e.g., individual difference among heaters. 
     Also, although the interlock control can be adopted for the lower temperature of the chemical solution outside a set range, monitoring cannot be performed for the chemical solution temperature within the set range. Consequently, it is highly likely that a process in which a sufficient etching amount cannot be set generates a residual nitride film. Furthermore, because of difficulty in mechanically detecting such problem, the substrate processing continues, which causes a problem in an increase in substrates with an insufficient etching amount. 
     SUMMARY 
     The present invention provides a substrate processing method for each lot comprising the steps of: 
     immersing a substrate in a chemical solution stored in an etch tank; 
     heating the chemical solution; 
     repeating a cycle of starting supply of pure water to the etch tank while the chemical solution being heated when a temperature of the chemical solution reaches a value t 1  and halting the supply of pure water when the temperature of the chemical solution is lowered to a value t 2  (t 1 &gt;t 2 ); and 
     counting the number of the cycles during a predetermined period of time; 
     wherein when the number of the cycles falls outside a preset range of cycle counts, a notice that the number of the cycles falling outside the preset range of the numbers is provided, and start of processing a substrate in a subsequent lot is halted. 
     The present invention provides a substrate processing apparatus in which a substrate is processing by being immersed in a chemical solution for each lot, the apparatus comprising: 
     an etch tank that stores a chemical solution; 
     a heater that heats the chemical solution; 
     a temperature measuring unit that measures a temperature of the chemical solution in the etch tank; 
     a pure water supply unit that supplies pure water into the etch tank; 
     a controller that repeats a cycle of starting supply of pure water into the etch tank while the chemical solution being heated when the temperature measured by the temperature measuring unit reaches a value t 1  and halting the supply of pure water into the etch tank when the temperature is lowered to a value t 2  (t 1 &gt;t 2 ); 
     a counter that counts the number of the cycles during a predetermined period of time; 
     a notification unit that, when the number of the cycles counted by the counter falls outside a preset range of cycle counts, provides a notice that the number of the cycles falls outside of the preset range of the cycle counts; and 
     a halt unit that halts start of processing a substrate in a subsequent lot based on the notification of the notification unit. 
     This substrate processing is configured to count the number of repeated cycles of supplying pure water for maintaining an etching rate of a chemical solution to be high and halting the supply for a predetermined period of time, for each lot of substrates, and when the number of cycles falls outside a preset range of cycle counts, provide a notice to that effect. 
     According to the substrate processing method and substrate processing apparatus configured as described above, whether or not the etching amount in substrate processing is proper is detected based on the number of cycles during a predetermined period of time, and thus, a lot of substrates having defective etching can be found with good accuracy as well as defective etching being able to be prevented from occurring in subsequent lots. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, advantages and features of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a schematic cross-sectional view of a wafer processing apparatus according to the present invention; 
         FIG. 2  is a graph indicating a relationship between a temperature of a chemical solution and time in the present invention; 
         FIG. 3  is a flowchart for describing a wafer processing procedure according to the present invention; and 
         FIG. 4  is a graph indicating a relationship between a temperature of a chemical solution and time in related art. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The invention will be now described herein with reference to illustrative embodiments. Those skilled in the art will recognize that many alternative embodiments can be accomplished using the teachings of the present invention and that the invention is not limited to the embodiments illustrated for explanatory purposes. 
     Hereinafter, a preferred embodiment of a wafer processing method and a wafer processing apparatus according to the present invention will be described in details with reference to the drawings. For a description of the drawings, the same components are provided with the same reference numerals and the description thereof will not be repeated. 
     First Embodiment 
       FIG. 1  is a schematic cross-sectional view of a wafer processing apparatus according to the present invention. 
     As illustrated in  FIG. 1 , a wafer processing apparatus  100  includes: an etch tank  11  that stores phosphoric acid  10 ; a heater  13  (heating unit) that heats the phosphoric acid  10 ; a temperature sensor  15  (temperature measuring unit) that measures the temperature of the phosphoric acid  10  in the etch tank  11 ; a pure water supply valve  16  (pure water supply unit) that supplies pure water into the etch tank  11 ; a control unit  18 ; a counting unit  19 ; and a notification unit  20 . 
     The wafer processing apparatus  100  further includes a filter  12 , a pump  14  and a solenoid valve  17 . 
     The wafer processing apparatus  100  sequentially process wafers for each lot of wafers by immersing them in the phosphoric acid  10 . A nitride film formed on each wafer is etched by the phosphoric acid  10  (chemical solution). 
     The phosphoric acid  10  is stored in the etch tank  11 . 
     The pump  14  performs the operation of sucking the phosphoric acid  10  running over the etch tank  11 , sending it to the heater  13 , filtrating the phosphoric acid  10  heated by the heater  13  by means of the filter  12  and sending the phosphoric acid  10  back to the etch tank  11  (chemical solution circulation). 
     The heater  13  heats the phosphoric acid  10  circulated by the pump  14 . 
     The temperature sensor  15  measures the temperature of the phosphoric acid  10  in the etch tank  11 . 
     The control unit  18  controls the overall operation of the wafer processing apparatus  100 . The control unit  18  can send out signals based on, e.g., information from the respective components, and make determinations based on information. The control unit  18  can operate as described below, for example. 
     The control unit  18  performs control so that the cycle of the pure water supply valve  16  starting supply of pure water to the etch tank  11  when the temperature of the phosphoric acid  10  measured by the temperature sensor  15  reaches t 1  in the state in which the phosphoric acid  10  is heated, and halting supply of pure water to the etch tank  11  when the temperature is decreased to t 2  (t 1 &gt;t 2 ) is repeated a plurality of times. 
     More specifically, when the value measured by the temperature sensor  15  reaches t 1 , the control unit  18  sends a signal to the solenoid valve  17  to supply air from the solenoid valve  17  to the pure water supply valve  16 , thereby operating the pure water supply valve  16  to supply pure water from the pure water supply valve  16  to the etch tank  11 . Also, when the value measured by the temperature sensor  15  reaches t 2 , the control unit  18  sends a signal to the solenoid valve  17  to halt supply of air from the solenoid valve  17  to the pure water supply valve  16 , thereby operating the pure water supply valve  16  to halt supply of pure water from the pure water supply valve  16  to the etch tank  11 . 
     Furthermore, the control unit  18  can control the temperature of the phosphoric acid  10  in the etch tank  11  based on measurement by the temperature sensor  15 , by heating the phosphoric acid  10  using the heater  13 . Also, it can make a halt unit  21  halt start of processing for subsequent lots of wafers, based on a notice from the notification unit  20 . Consequently, it is possible to prevent further occurrence of defective etching in subsequent lots of wafers. 
     The counting unit  19  counts the number of cycles during a predetermined period of time. The details will be described later. 
     The predetermined period of time refers to a period of time during which the counting unit  19  counts the number of cycles (monitoring time), and can be set in advance. Also, the point of time for starting monitoring time can be set according to conditions. 
     Where the number of cycles counted by the counting unit  19  falls outside a predetermined range, the notification unit  20  provides a notice that the number of cycles falls outside the predetermined range. Examples of the notice may include issuance of a warning sound and display of a warning. 
     Next, the operation of the wafer processing apparatus  100  illustrated in  FIG. 1  will be described using  FIGS. 2 and 3 . In the present embodiment, wafer processing is performed in the state in which the etching rate is high, and thus, a “boiling point control method” is employed. 
       FIG. 2  is a graph indicating the relationship between the temperature of the chemical solution and time in the present invention. In  FIG. 2 , t 0  denotes a temperature set for the phosphoric acid  10  in the etch tank  11 , t 1  denotes a pure water addition start temperature, and t 2  denotes a pure water addition halt temperature. The phosphoric acid  10  in the etch tank  11   1 s heated by the heater  13 . Pure water only needs to be one enabling provision of a fixed cycle in the present embodiment, and may contain impurities. 
     The boiling point control method is a method in which the boiling point is controlled by repeating the cycle of staring supply of pure water when the temperature of the phosphoric acid  10  is increased to t 1  by heating and halting supply of pure water when the temperature is decreased to t 2 . 
     In this case, t 1  is set to the boiling point of the phosphoric acid  10 , enabling the concentration of the phosphoric acid  10  to be kept within a certain range while the temperature of the phosphoric acid  10  being kept within the range of t 1  to t 2 . In other words, since the temperature of the phosphoric acid  10  is maintained around the boiling point while a preferable concentration being maintained, the etching rate can be kept high. 
     In such boiling point, the time from t 1  to t 2  (T 1 -T 2 ) is substantially fixed. Therefore, the number of cycles (number of cycles repeated) per unit time (cycles/hr) can be counted with the time from T 3  to T 4  set to one cycle. 
     The counting unit  19  counts opening and closing of the solenoid valve  17  that operates the pure water supply valve  16 , as one cycle, converts the count into the number of cycles per unit time (cycles/hr), and counts the number of cycles per unit time from the number of cycles (cycles/hr). In other words, the counting unit  19  can count the number of cycles for the monitoring time. Also, for the counting, a sequencer, a microcomputer, etc., can be used. 
     Meanwhile, “non-monitoring time” can be set relative to this monitoring time. The “non-monitoring time” is time during which the counting unit  19  does not operate. Hereafter, the “non-monitoring time” will be described. 
     As illustrated in  FIG. 2 , immediately after a lot of wafers being put in the etch tank  11 , the temperature of the phosphoric acid  10  sharply decreases and requires a certain period of time (T 5 -T 6 ) for the temperature to rise again to the set temperature (t 0 ). Thus, the counting unit  19  can be controlled so as not to start operation during the time from T 5  (putting-in of the lot) to T 6  as “non-monitoring time”. In other words, the time from the point of time when substrate processing is started and wafers are immersed in the phosphoric acid  10  to the point of time when the temperature of the phosphoric acid  10  rises to the set temperature (t 0 ) for the first time can be set as the “non-monitoring time”. 
     Consequently, processing in the state in which the etching rate is low can be monitored with high accuracy. 
     The number of cycles (cycles/hr) can be set in advance by setting the number of cycle “n” and an acceptable range “±α”. Where the number of cycles falls within the range of counts set in advance, substrate processing with a sufficient amount of etching is performed, enabling reduction of production of wafers with defective etching. Also, where the number of cycles falls under the lower limit of the preset range or higher, a more reliable etching amount can be ensured. A preferable predetermined range of cycle counts varies depending on whether or not a lot of wafers is contained in the etch tank  11 , and thus, data on the number of cycles “n” is collected for each of the state in which the lot of wafers is contained in the etch tank  11  and the state in which no lot of wafers is contained in the etch tank  11 , enabling calculation of a preferable predetermined range of cycle counts based on the average value and variations of the data. However, the number of cycles varies depending on, e.g., the output of the heating unit and the kind of the chemical solution, and thus, it is preferable that a preferable predetermined range of cycle counts is set from time to time by collecting data. 
     Next, the operation of the counting unit  19  and the control unit  18  will be described with reference to  FIG. 3 .  FIG. 3   1 s a flowchart for describing a wafer processing procedure according to the present invention. 
     The counting unit  19 , upon start operating (S 101 ), first detects whether or not a lot of wafers is contained in the etch tank  11  (S 102 ). If it detects a lot of wafers, it determines whether it is non-monitoring time or monitoring time (S 106 ), and if it determines that it is monitoring time, it counts the number of cycles (S 103 ) If it determines that it is non-monitoring time, the counting unit  19  does not count the number of cycles until it detects the next lot of wafers and determines that it is monitoring time. 
     Next, the control unit  18  determines whether or not the number of cycles during the monitoring time fall within a preset range of cycle counts (n±α cycles) (S 104 ) If it determines that the number of cycles falls within the preset range of cycle counts, it terminates wafer processing (S 105 ). Also, if it determines that the number of cycles falls outside the preset range of cycle counts, it make the notification unit  20  output an alarm to give a notice that the number of cycles falls outside the preset range of cycle counts (S 107 ). Furthermore, if the control unit  18  makes the notification unit  20  output an alarm, it determines the lot of wafers that is being processed, as a lot of wafers subjected to a warning, and holds the following waiting lot of wafers as it is and does not move it to the etch tank  11 , and halts wafer processing. Thus, when the number of cycles falls out side the predetermined range, interlocking is automatically performed. 
     Advantageous effects of the present embodiment will be described. 
     Wafer processing according to the present embodiment is configured so that: the cycle of supplying pure water and halting the supply for maintaining the etching rate of the phosphoric acid  10  to be high is repeated for each lot of wafers; and furthermore, the number of cycles is counted during monitoring time, and if the number of cycles counted falls outside a preset range of cycle counts, a notice to that effect is provided. The wafer processing apparatus  100  and wafer processing method configured as described above can detect whether or not the amount of etching in wafer processing is proper, based on the number of cycles during monitoring time, enabling finding a lot of wafers having defective etching with high accuracy as well as preventing defective etching from occurring in subsequent lots of wafers. 
     Furthermore, provision of non-monitoring time enables lots of wafers processed in a state in which the etching rate is low to be found with higher accuracy. 
     The technique described in Japanese Patent Laid-Open No. 2006-114590 relates to control of the temperature of a process fluid in relation to filter replacement. This technique uses the temperature at the time of use of a new filter as a reference to compensate the difference in temperature between the time of use of a new filter and the time of measurement, and does not perform the control of concentration. 
     Also, in the technique described in Japanese Patent Laid-Open No. 2001-205158, chemical solution processing time is calculated from variations of the concentration and the temperature. However, only the calculation of wafer processing time will result in continuance of an abnormal state. 
     In these references, since the etchant concentration is not stabilized around the boiling point by means of boiling point control, the situation in which a sufficient etching amount cannot be achieved cannot be known. According to the present invention, it is possible to know the situation in which the etching rate of the chemical solution for a certain period of time, which is to be kept high (normal state), is decreased and etching processing is performed with a sufficient amount of etching not provided. Accordingly, a substrate processing method and substrate processing apparatus arranged so that lots of wafers having defective etching can be found with good accuracy and defective etching is suppressed from occurring in subsequent lots of wafers can be provided. 
     The substrate processing apparatus and substrate processing method according to the present invention are not limited to the present embodiment, and various modifications can be made.