Abstract:
Disclosed herein is a plasma processing apparatus and a plasma processing method capable of performing plasma processing by performing temperature control of a sample table in accordance with a process step to be performed on a sample. The plasma processing apparatus performs plasma processing on a sample in accordance with a process recipe with the sample being placed on a sample table in which each of a plurality of areas is temperature-controlled by a temperature control means, wherein the process recipe includes a plurality of temperature setting parameters for the sample table, and the plasma processing is performed on the sample in accordance with the process recipe which is prepared for each of a plurality of process steps.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to a plasma processing apparatus and, more particularly, to a plasma processing apparatus capable of performing temperature control of a sample table for placing thereon a sample such as a semiconductor wafer for plasma processing.  
           [0002]    For example, Japanese Patent Laid-open No. 2002-76103 discloses that, for the purpose of improving an accuracy in etching a semiconductor wafer, an interior of a sample table for placing thereon a sample is divided into two parts of an inner part and an outer part, and coolants having different temperatures are supplied separately to the inner part and the outer part to perform the etching with a temperature gradient being applied to the sample table, thereby processing a surface of the semiconductor wafer uniformly.  
           [0003]    An example of process recipes which have heretofore been used in the plasma processing apparatus is shown in FIG. 7. As is apparent from FIG. 7, temperatures set by a temperature control unit are irrespective of the etching recipe, and the set temperature of the inner part of the table is always 20° C. and the set temperature of the outer part of the table is always 0° C. It is possible to achieve a uniformity in final etching amounts of the semiconductor wafer surface by positively applying the temperature gradient to the sample table as mentioned above, not by setting the whole sample table to a uniform temperature.  
           [0004]    A comparison between final etching amounts of (a) a case of setting the whole sample table to 20° C. and (b) final etching amounts of a case of setting the inner part to 20° C. and the outer part to 0° C. is shown in FIG. 8. A final etching distribution in the case of (a) is in the shape of an inversed U (a curve), while that in the case of (b) is uniform. This is because, when a plurality of temperature settings for the sample table are varied from one another, considerable changes are expected to occur in a reaction on and adsorption to sidefaces of an etching pattern although only minor changes occur in compositions of injected radicals and ions, influence of a density distribution of plasma, and intensity of the injections. That is to say, a reaction rate is increased with the temperature rise of the sample table and an adhesion coefficient of reaction products to the sidefaces is decreased. As a result, the sidefaces become thinner by the temperature rise to thereby enable a reduction in the etching amount. On the other hand, on a periphery of the etching pattern, the final etching amount is increased because re-adhesion of the reaction products is likely to occur due to the temperature decrease of the semiconductor wafer.  
           [0005]    In order to achieve high-performance and low power consumption of semiconductor devices, a gate length of the semiconductor devices is being made shorter every year. Since the gate length is an important dimension which determines a device characteristic, it is called a CD (critical dimension) value or an etching amount. An allowable deviation of the gate length in a gate etching process is on the order of a several nanometers, and a slightest deviation in the manufacture process can cause defects in the products. Further, since a diameter of the sample is being made larger and larger, a difference between an etching result of a central part of the sample and an etching result of a peripheral part of the sample is likely to occur. Therefore, there is a demand for elaborate temperature control which is suitable for the process.  
         SUMMARY OF THE INVENTION  
         [0006]    The present invention has been made in view of the above problems, and an object of the invention is to provide a plasma processing apparatus capable of performing temperature control of a sample table depending on a process performed on a sample for plasma processing.  
           [0007]    The present invention employs the following means in order to solve the above problems.  
           [0008]    The object of the present invention is achieved by a plasma processing apparatus for performing plasma processing on a sample in accordance with a process recipe with the sample being placed on a sample table in which each of a plurality of areas is temperature-controlled by a temperature control means, wherein the process recipe includes a plurality of temperature setting parameters for the sample table, and the plasma processing is performed on the sample in accordance with the process recipe which is prepared for each of a plurality of process steps.  
           [0009]    Further, the above object is achieved by a plasma processing apparatus for performing plasma processing on a sample in accordance with a process recipe with the sample being placed on a sample table in which each of a plurality of areas is temperature-controlled by a temperature control unit, wherein the process recipe includes a plurality of temperature setting parameters for the sample table, and the plasma processing is performed on the sample in accordance with the process recipe in which at least one of set temperatures of the temperature setting parameters is altered in response to a processing result of a preceding process performed on the sample, the processing result being obtained prior to the plasma processing.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    Other objects and advantages of the invention will become apparent from the following description of embodiments with reference to the accompanying drawings in which:  
         [0011]    [0011]FIG. 1 is a diagram showing an example of an etching apparatus to which the present invention is applied;  
         [0012]    [0012]FIG. 2 is a diagram showing an example of process recipes according to the present invention;  
         [0013]    [0013]FIG. 3 is a diagram showing an example of an etching system using the etching apparatus to which the present invention is applied;  
         [0014]    [0014]FIG. 4 is a flowchart from a step of photolithography to a step of altering a set temperature of a temperature control unit;  
         [0015]    [0015]FIG. 5 is a flowchart from a step of inputting measured mask dimensions to a step of calculating a temperature correction value;  
         [0016]    [0016]FIG. 6 is a diagram showing an example of an etching apparatus, to which the present invention is applied, including a wafer temperature sensor;  
         [0017]    [0017]FIG. 7 is a diagram showing an example of conventional process recipes; and  
         [0018]    [0018]FIG. 8 is a diagram showing a comparison between final etching amounts of a case of controlling the whole sample table to have a uniform temperature and final etching amounts of a case of applying a temperature gradient to the sample table. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0019]    A first embodiment of the present invention will hereinafter be described with reference to accompanying drawings.  
         [0020]    [0020]FIG. 1 is diagram showing an example of an etching apparatus to which the present invention is applied.  
         [0021]    A sample to be etched such as a wafer  2  is placed on a sample table  10  in an etching reactor  1 . Various etching gases are supplied to the etching reactor  1  from cylinders  3  via valves  4 . The etching reactor  1  has an air-tight structure so as to create a vacuum atmosphere by evacuating the reactor  1  using a vacuum pump (not shown) via an exhaust port  5  extending to a peripheral bottom of the etching reactor  1 . A plasma generation source  6  is used for generating plasma  7  in the etching reactor  1 . A high frequency power source  9  for applying injection energy to ions in the plasma  7  and a direct current power source  11  used for electrostatically attracting the wafer  2  on an electrode are connected with an electrode support shaft  8  for supporting the electrode. Coolant circulation paths  12  and  13  used for controlling a temperature of the sample table  10  are provided at an outer peripheral part of the sample table  10 , and coolant circulation paths  14  and  15  for controlling a temperature of the sample table  10  are provided at an inner peripheral part of the sample table  10 . One end of each of the coolant circulation paths  12  and  13  is connected to a temperature control unit  16 , and one end of each of the coolant circulation paths  14  and  15  is connected to a temperature control unit  17 .  
         [0022]    Although two temperature control units are used for controlling the temperatures in the present embodiment, a plurality of coolants may be prepared by using one temperature control unit and a temperature converter which is provided at a position midway of a circulation path.  
         [0023]    [0023]FIG. 2 is a diagram showing an example of process recipes in the first embodiment of the present invention.  
         [0024]    In a typical plasma processing apparatus, a controller microcomputer for a plasma processing apparatus controls devices and components required for the process in accordance with a process recipe in which many processing parameters such as processing time, a pressure in the vacuum reactor, power to be supplied to the plasma generation unit, process gas flow rates, and high frequency power to be applied to the sample table are preset.  
         [0025]    Also, in the case where the plasma processing for one substrate is performed through a plurality of divided process steps in such a manner that processing on a resist layer is performed in STEP 1, processing on a SiN layer is performed in STEP 2, and processing on a polysilicon layer is performed in STEP 3, the devices and components are controlled for processing in accordance with parameter settings of a process recipe for the next process step every time the process steps are switched from one to another.  
         [0026]    The present invention enables an optimum temperature control of the sample table for each of the process steps in view of the process steps and types of layers by allowing a plurality of temperature setting parameters for the sample table to be included in each of the process recipes for the process steps and by associating the sample table with the process recipes. Thus, it is possible to control the final etching amount of the wafer surface.  
         [0027]    In addition, it is unnecessary to stop the temperature control of the sample table during a halt of the processing on the sample, and it is possible to perform the temperature control continuously on the set temperatures which have been employed in the preceding process step. Also, it is possible to perform the temperature control in advance of processing on a next sample by setting the temperatures to the set temperatures which will be employed in a first process step of the processing on the next sample.  
         [0028]    A second embodiment of the present invention will hereinafter be described with reference to the accompanying drawings.  
         [0029]    In general, it is usual to use the same recipe in the bulk production which is operated with the same process. This is because satisfactory reproducibility is achieved if plasma characteristic and so forth are kept at a constant level. Further, an alteration in a recipe (hereinafter referred to as “plasma recipe”) which influences on the plasma characteristic can be a waste of data which have been accumulated by now. To find out a new optimum process recipe we must have trial and error for which a considerable time and cost will be spent. However, even if the etching process is performed by using the same plasma recipe, it is difficult to attain a constant etching result in some cases due to various disturbances such as changes with time and variation in production caused in the subsequent process step. Therefore, the following configuration is employed in the present embodiment in view of the above problems.  
         [0030]    [0030]FIG. 3 is a diagram showing an example of an etching system using an etching apparatus to which the present invention is applied.  
         [0031]    An inspection device  31  is a CD-SEM (also called “length measuring SEM”) for measuring an etching amount of a sample of a preceding process step or a film thickness measurement instrument for measuring a layer thickness, the CD-SEM and the instrument being used prior to performing an etching process. An inspection device  32  serves to measure a final etching amount (etching amount after the etching process). In the present embodiment, both of the inspection devices  31  and  32  are CD-SEMs.  
         [0032]    A database  33  accumulates relational expressions in which a set temperature of the sample table to be altered is calculated if an inspection result obtained by the aforementioned inspection and a target etching amount which is an initial design value are given. Also, every time the etching process is performed, the database  33  accumulates data other than those described above, such as an etching amount of each of the layers in a preceding process (before the etching process), a final etching amount, a final shape (shape after the etching process), plasma emission during the process, and an etching rate.  
         [0033]    A flowchart from a step of photolithography to a step of changing the set temperature by the use of the temperature control unit is shown in FIG. 4.  
         [0034]    A sample which has been subjected to a photolithography process (Step  41 ) undergoes the processing on a plurality of zones of ZONE  1  and ZONE  2  branched for pre-measurement (hereinafter referred to as “CD pre-measurement”) of mask dimensions using the CD-SEM  31  (Steps  42  and  43 ). Temperature correction value of the respective zones to be altered are calculated from the CD pre-measurement results and the data stored in the database  33  including the target etching amounts, the types of the layers to be processed, etc. (Steps  45  and  46 ). The set temperatures are altered after comparing the calculated temperature correction values with the set temperatures defined in the plasma recipe (Step  47 ).  
         [0035]    Although the sample table temperature is divided into the inner part temperature and the outer part temperature in the present embodiment, the present invention is not limited thereto, and it is possible to perform the temperature control by dividing the sample table into a larger number of areas.  
         [0036]    A flowchart from a step of inputting measured mask dimensions to a step of calculating temperature correction values is shown in FIG. 5.  
         [0037]    First of all, the target final etching amounts are inputted into the database  33  (Step  52 ). The mask dimensions of the respective zones are measured to be inputted into the database  33  (Step  51 ). Then, the measured mask dimensions of the respective zones are compared with the target final etching amounts. A rate correction value of each of the zones can be calculated by, for example, dividing each of differences obtained by the comparison by the etching time of STEP 1 (Steps  53  and  54 ). As is apparent from FIG. 5, since the mask dimension measurement value (a) is larger than the target final etching amount (b), the etching process must be performed to be larger than the normal etching amount. Then, temperature correction values of the respective zones are calculated from the calculated rate correction values and the relational expressions of the types of the layers to be processed and the temperatures of the sample table stored in the database  33  (Step  55 ).  
         [0038]    An alteration unit (not shown) or the like for altering the set temperatures based on the database  33  and the temperature correction values may be provided either in the etching apparatus or in the inspection device. Alternatively, the alteration unit may be connected with a host computer or the like which is linked to a network of a semiconductor manufacture line.  
         [0039]    In the present invention, even if a deviation from a target etching amount occurs on a product during a process preceding to the etching process, such as a photolithography process, it is possible to perform etching including corrections for achieving initial design values in the etching process owing to the above-described configuration. Further, if the result of the etching is inspected, the inspection result is compared with the target final etching amount to thereby judge whether or not the current set temperatures of the sample table are proper, and then the temperatures are properly altered until the desired etching amount is achieved, it is also possible to assimilate machine differences among etching apparatuses.  
         [0040]    Further, since the variations in semiconductor surfaces, such as U-shape distribution and inversed U-shape distribution, are suppressed in the present embodiment by properly altering the temperatures of the sample table without altering the plasma recipe which influences on the plasma characteristic, the present embodiment is free from serious side effects.  
         [0041]    In addition, although the case where the plasma recipe is not altered is described in the present embodiment, it is apparent that the present invention is applicable to apparatuses in which the plasma recipe is altered during the processing.  
         [0042]    A third embodiment of the present invention will hereinafter be described with reference to the accompanying drawings.  
         [0043]    [0043]FIG. 5 is a diagram showing an example of an etching apparatus, to which the present invention is applied, including a wafer temperature sensor  62 .  
         [0044]    Conventional temperature control units for the sample table perform a temperature control with respect to set temperatures by monitoring coolants or the like by using a temperature sensor which is provided in the temperature control units. However, the temperatures of the coolants monitored by the temperature control unit can sometimes differ from actual temperatures of a backface of a wafer. Also, for a comparison between a first wafer and a twenty-fifth wafer after the start of processing, for example, the twenty-fifth wafer tends to be high in temperature due to radiation heat from the etching reactor. Furthermore, since heat input is greater on an outer peripheral part of the wafer, the temperature of the outer peripheral part tends to be higher than that of a central part of the wafer. Therefore, in the present embodiment, the temperatures of the backface of the wafer are directly measured by the use of the wafer temperature sensor  62  or an electrode temperature sensor (not shown) to provide the measurement results as monitor values of the temperature control unit, thereby improving an effect of controlling an etching amount of the wafer surface in each of processes, each of process steps, and each of layers.  
         [0045]    While the invention has been described in its preferred embodiments, it is to be understood that the words which have been used are words of description rather than limitation and that changes within the purview of the appended claims may be made without departing from the true scope and spirit of the invention in its broader aspects.