Patent Publication Number: US-2010110605-A1

Title: Electrostatic chuck assembly for plasma reactor

Description:
CROSS REFERENCE 
     This application claims foreign priority under Paris Convention and 35 U.S.C. §119 to each of Korean Patent Application No. 10-2008-0109242, filed 5 Nov. 2008 with the Korean Intellectual Property Office. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a plasma reactor used in a semiconductor manufacturing process. More particularly, the present invention relates to an electrostatic chuck assembly of the plasma reactor. 
     2. Description of the Related Art 
     In general, an electrostatic chuck is positioned on a cathode assembly installed within a reaction chamber of a plasma reactor. Within the reaction chamber, the electrostatic chuck is used to fix a target object (e.g., a wafer or glass substrate) to be etched or deposited with etching material, to a cathode assembly. The target object is fixed to an upper part of the electrostatic chuck by an electrostatic attractive force that is generated when a Direct Current (DC) power source is supplied to the electrostatic chuck. In order to smoothly etch the target object within the reaction chamber, the target object has to be fixed to the upper part of the electrostatic chuck firmly, e.g., enough to endure a pressure of Helium (He) gas of 30 Torr or more applied to a rear surface side of the target object. 
     In designing and manufacturing an electrostatic chuck assembly, the most important item is to protect the electrostatic chuck from plasma ions. A design for protecting the electrostatic chuck is most important to lengthen the lifetime of a process kit around the electrostatic chuck and decrease an economical loss. In general, the lifetime of the electrostatic chuck should be kept until the plasma reactor performs a wafer treatment process of at least one hundred thousand cycles. The lifetime of the electrostatic chuck and the process kit around the electrostatic chuck can be lengthened or shortened depending on a structure of the electrostatic chuck assembly. Also, operation performance (particularly, etching performance) of the plasma reactor can vary depending on the structure of the electrostatic chuck assembly. 
     Compared to a chemical etching process, an oxide film etching process using physical impact for applying physical energy to plasma ions and etching a surface of a wafer is much affected by a change of the structure of the electrostatic chuck assembly. That is, the oxide film etching process can be improved or deteriorated in quality depending on the structure of the electrostatic chuck assembly or the etching performance of the plasma reactor. Accordingly, the structure of the electrostatic chuck assembly should be optimized to lengthen the lifetime of the electrostatic chuck and improve the etching performance of the plasma reactor. 
       FIG. 1  is a schematic diagram illustrating a conventional electrostatic chuck assembly. For simplification of the drawings, illustration of a cathode assembly is omitted in  FIG. 1 . The electrostatic chuck assembly  10  includes an electrostatic chuck  20 , a Radio Frequency (RF) couple ring  30 , an electrostatic chuck cover ring  40 , and a cathode assembly cover ring  50 . The RF couple ring  30  and the electrostatic chuck cover ring  40  surround an outer circumference of an upper part of the electrostatic chuck  20 . The electrostatic chuck cover ring  40  is positioned on an upper part of the RF couple ring  30 . Because the RF couple ring  30  and the electrostatic chuck cover ring  40  are fitted to the outer circumference of the upper part of the electrostatic chuck  20 , the upper part of the electrostatic chuck  20  should be designed to have a protruded length (D) of at least 10 mm or more. 
     The RF couple ring  30  can be of metal material such as aluminum, etc. The cathode assembly cover ring  50  surrounds outer circumferences of the RF couple ring  30  and the electrostatic chuck cover ring  40  and an outer circumference of a lower part of the electrostatic chuck  20 . A wafer  80  is safely mounted on a surface of a top of the electrostatic chuck  20 . When a DC power source is supplied to the electrostatic chuck  20 , static electricity is generated in the electrostatic chuck  20  and as a result, the wafer  80  is fixed to the surface of the top of the electrostatic chuck  20 . A power supply unit  60  supplies the DC power source to the electrostatic chuck  20  through a RF noise filter  70 . 
     A dry etching process of a plasma reactor is briefly described below. A target object such as the wafer  80 , etc. is conveyed to the top of the electrostatic chuck  20  within a reaction chamber. If so, a reaction gas is injected into the reaction chamber, and a vacuum system is activated to maintain the internal of the reaction chamber at a constant vacuum degree. Then, if the internal of the reaction chamber reaches a vacuum degree suitable to an etching process, an RF power is applied to an inductive coil of the plasma reactor, a bias RF power is supplied to a lower electrode (i.e., a cathode), and a DC power source is supplied to the electrostatic chuck  20 . As a result, as illustrated in  FIG. 1 , plasma ions  91  and  92  apply physical impacts to a surface of the wafer  80  and at the same time, a chemical reaction between the plasma ions  91  and  92  and the wafer  80  occurs. At this time, the RF power is supplied even to the RF couple ring  30  and resultantly, the plasma ions  92  are incident on a surface of the electrostatic chuck cover ring  40  in an almost perpendicular direction. 
     If the RF power is not or insufficiently supplied to the RF couple ring  30 , as indicated by a dotted line arrow, the plasma ions  92  are incident on an edge of the wafer  80  and the electrostatic chuck cover ring  40  in a slant direction having a constant angle (θ) on the basis of a direction (i.e., a solid line arrow) perpendicular to the surface of the electrostatic chuck cover ring  40 . The reason is that a bias power (i.e., energy of the plasma ions  91  and  92 ) on a top surface of the electrostatic chuck  20  (i.e., on a surface of the electrostatic chuck  20  contacting with the wafer  80 ) is greater than a bias power on a surface of the electrostatic chuck  20  contacting with a bottom surface of the RF couple ring  30 . Accordingly, the plasma ions  92  incident on the edge of the electrostatic chuck  20  are incident toward the top surface of the electrostatic chuck  20 . 
     Because the angle (θ) can vary depending on a degree of an attractive force by which the RF couple ring  30  attracts the plasma ions  92 , for the sake of improving a process quality at the edge of the wafer  80  and lengthening the lifetime of the electrostatic chuck cover ring  40 , it is important that the RF couple ring  30  is installed on the surface of the electrostatic chuck  20  such that the RF couple ring  30  attracts the plasma ions  92  by a suitable attractive force. 
     However, the RF couple ring  30  is not fully adhered between a surface of the electrostatic chuck  20  and the electrostatic chuck cover ring  40  but is simply fitted, i.e., floated between the electrostatic chuck  20  and the electrostatic chuck cover ring  40 . Thus, although the RF couple ring  30  is enabled, it is almost impossible that the plasma ions  92  are perpendicularly incident on the surface of the electrostatic chuck cover ring  40 . 
     Also, the RF couple ring  30  is not fully adhered between the surface of the electrostatic chuck  20  and the electrostatic chuck cover ring  40 . Thus, there are secondary problems such as shortening the lifetime of the electrostatic chuck cover ring  40  resulting from the slant incidence of the plasma ions, increasing an arcing phenomenon of the electrostatic chuck, increasing the number of particles, shortening a cleaning period of the reaction chamber, etc. 
     The plasma ions  92  are incident on the edge of the wafer  80  in the slant direction having the constant angle (θ), thus deteriorating a process quality at the edge of the wafer  80 .  FIG. 2  illustrates the wafer  80  dry-etched within the reaction chamber with an RF power not supplied to the RF couple ring  30 . After the wafer  80  is cut along a cutting line C-C′, when viewing its cut surface, a profile of contact holes (H 1  to H 3 ) formed in the wafer  80  is illustrated in a lower part of  FIG. 2 . It can be appreciated from  FIG. 2  that the contact hole (H 2 ) formed in a center of the wafer  80  has a normal profile perpendicular to a bottom surface of the wafer  80  but, as the plasma ions  92  are incident on the slant, the contact holes (H 1  and H 3 ) formed in the edge of the wafer  80  are inclined and thus have an abnormal profile. 
     If the plasma ions  92  are incident on the electrostatic chuck cover ring  40  in the slant direction having the constant angle (θ), the electrostatic chuck cover ring  40  is abnormally etched and thus, the lifetime of the electrostatic chuck cover ring  40  can be suddenly shortened. Referring to  FIG. 1 , as the plasma reactor performs wafer treatment processes repeatedly, a new or non-etched electrostatic chuck cover ring  40  (an ‘A’ portion) is gradually etched. At this time, if an etching process is performed with the RF power not supplied to the RF couple ring  30 , the electrostatic chuck cover ring  40 ′ can be abnormally etched as illustrated in an ‘A′’ portion of  FIG. 1 . In order to prevent abnormal etching of the electrostatic chuck cover ring  40 ′ and improve a quality of an etching process at the edge of the wafer  80 , the electrostatic chuck assembly  10  has to inevitably include the RF couple ring  30 . Thus, because including the RF couple ring  30 , the conventional electrostatic chuck assembly  10  has a problem that its structure is complex and also its manufacturing cost increases. Also, although the electrostatic chuck assembly  10  includes the RF couple ring  30 , it is very difficult to completely operate the RF couple ring  30 , i.e., to perform an operation of making the plasma ions  92  be perpendicularly incident on the surface of the electrostatic chuck cover ring  40 . Thus, the electrostatic chuck assembly  10  still has an incomplete coupling problem of the RF couple ring  30 . 
     SUMMARY OF THE INVENTION 
     An aspect of exemplary embodiments of the present invention is to address at least the problems and/or disadvantages and to provide at least the advantages described below. Accordingly, an aspect of exemplary embodiments of the present invention is to provide an electrostatic chuck assembly for overcoming an incomplete coupling problem of a Radio Frequency (RF) couple ring and at the same time, by minimizing an incidence angle (θ) of plasma ions and optimizing a structure of the electrostatic chuck assembly such that the plasma ions are perpendicularly incident on a surface of an electrostatic chuck cover ring at an edge of an electrostatic chuck, making the RF couple ring unnecessary, lengthening the lifetime of the electrostatic chuck cover ring, and improving etching performance of a plasma reactor. 
     To achieve these and other advantages in accordance with the purpose of the present invention, there is provided an electrostatic chuck assembly for a plasma reactor. The electrostatic chuck assembly includes an electrostatic chuck, an electrostatic chuck cover ring, and a cathode assembly cover ring. The electrostatic chuck includes a body part and a protrusion part. The body part has a disk shape of a first diameter. The protrusion part is formed integrally with the body part and protrudes from the body part, and has a disk shape of a second diameter less than the first diameter. The electrostatic chuck cover ring is disposed to surround an outer circumference of the protrusion part, and protects the body part of the electrostatic chuck from plasma ions generated as the plasma reactor operates. The cathode assembly cover ring is disposed at an upper part of the cathode assembly to surround an outer circumference of the electrostatic chuck cover ring and an outer circumference of the body part. In order to allow the electrostatic chuck cover ring to have a cut surface of an ‘L’ shape after the electrostatic chuck cover ring is etched by the plasma ions, a length (G) of the protrusion part protruding from the body part is set to be in the range of 1.0 mm≦G≦7.0 mm irrespective of a diameter of a target object safely mounted on an upper surface of the protrusion part. 
     As described above, the electrostatic chuck assembly according to the present invention optimizes its structure, particularly, a structure of the electrostatic chuck, thereby being able to overcome an incomplete coupling problem of an RF couple ring and at the same time, by minimizing an incidence angle (θ) of plasma ions at an edge of the electrostatic chuck and making the plasma ions be perpendicularly incident on a surface of the electrostatic chuck cover ring at the edge of the electrostatic chuck, make installation of the RF couple ring unnecessary, lengthen the lifetime of the electrostatic chuck cover ring, and improve etching performance of a plasma reactor. 
     Also, by optimizing a length (G) of a protrusion part of the electrostatic chuck and a diameter (R 1 ) of the protrusion part, there is no need to specifically design a shape of a focus ring outside the electrostatic chuck cover ring or add a complex additional element such as the RF couple ring to a lower part of the electrostatic chuck cover ring, thus being able to decrease an equipment manufacturing cost of a plasma reactor. On the other hand, by optimizing the length (G) of the protrusion part of the electrostatic chuck and the diameter (R 1 ) of the protrusion part, protection of the electrostatic chuck and a process quality of an edge of a target object (i.e., a wafer) can be guaranteed. 
     Also, by optimizing the length (G) of the protrusion part of the electrostatic chuck and the diameter (R 1 ) of the protrusion part, an etching profile of the electrostatic chuck cover ring has an ‘L’ shape (indicated by a B′ portion of  FIG. 3 ) and thus, is able to obtain an effect of an equipment maintenance side such as lengthening the lifetime of the electrostatic chuck cover ring, decreasing an arcing phenomenon of the electrostatic chuck, decreasing the number of particles, lengthening a cleaning period of the reaction chamber, etc. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a schematic diagram illustrating a conventional electrostatic chuck assembly; 
         FIG. 2  is a diagram illustrating a wafer etched by a plasma reactor including the electrostatic chuck assembly of  FIG. 1 ; 
         FIG. 3  is a schematic diagram illustrating an electrostatic chuck assembly according to an exemplary embodiment of the present invention; 
         FIG. 4  is a side diagram of an electrostatic chuck illustrated in  FIG. 3 ; 
         FIG. 5  is a plan diagram of an electrostatic chuck illustrated in  FIG. 3 ; 
         FIG. 6  is a diagram illustrating an example of a plasma reactor including the electrostatic chuck assembly of  FIG. 3 ; 
         FIG. 7  is a diagram illustrating a wafer etched by the plasma reactor of  FIG. 6 ; and 
         FIG. 8  is a diagram illustrating an etching rate by each region of a wafer etched by the plasma reactor of  FIG. 6 . 
     
    
    
     Throughout the drawings, the same drawing reference numerals will be understood to refer to the same elements, features and structures. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Exemplary embodiments of the present invention will now be described in detail with reference to the annexed drawings. In the following description, a detailed description of known functions and configurations incorporated herein has been omitted for conciseness. 
       FIG. 3  is a schematic diagram illustrating an electrostatic chuck assembly according to an exemplary embodiment of the present invention. The electrostatic chuck assembly  100  includes an electrostatic chuck  110 , an electrostatic chuck cover ring  120 , and a cathode assembly cover ring  130 . The electrostatic chuck  110  includes a body part  111  and a protrusion part  112 . The body part  111  and the protrusion part  112  are each formed in a disk shape ( FIG. 5 ). The protrusion part  112  is formed integrally with the body part  111  and protruded from the body part  111 . A diameter (R 1 ) of the protrusion part  112  is less than a diameter (R 2  in  FIG. 4 ) of the body part  111 . 
     The electrostatic chuck cover ring  120  is disposed to surround an outer circumference of the protrusion part  112 . As a plasma reactor  200  (illustrated in  FIG. 6 ) including the electrostatic chuck assembly  100  operates, plasma ions  182  are generated. After the electrostatic chuck cover ring  120  is etched by the plasma ions  182 , the electrostatic chuck cover ring  120  has a cut surface of an ‘L’ shape (indicated by a ‘B′’ portion of  FIG. 3 ). For the sake of this, a length (G) of the protrusion part  112  protruded from the body part  111  is set to be in a range of 1.0 mm≦G≦7.0 mm irrespective of a diameter of a target object  170  (e.g., a wafer) safely mounted on an upper surface of the protrusion part  112 . The outer circumference of the protrusion part  112  is surrounded only by the electrostatic chuck cover ring  120 . 
     Referring to  FIG. 3 , as the plasma reactor  200  performs wafer treatment processes repeatedly, a new or non-etched electrostatic chuck cover ring  120  (indicated by the ‘B’ portion) is gradually etched. As a result, as indicated in the ‘B″’ portion of  FIG. 3 , the electrostatic chuck cover ring  120  is etched to have the cut surface of the ‘L’ shape. The reason why the electrostatic chuck cover ring  120  is etched to have the cut surface of the ‘L’ shape is that, when the target object  170  is etched by the plasma reactor  200 , by setting the length (G) of the protrusion part  112  protruded from the body part  111  to the range of 1.0 mm≦G≦7.0 mm, the plasma ions  182  are perpendicularly incident on a surface of the electrostatic chuck cover ring  120 . In contrast to this, if the length (G) of the protrusion part  112  protruded from the body part  111  is set to, for example, 10 mm or more, when the target object  170  is etched by the plasma reactor  200 , the plasma ions  182  are incident on the surface of the electrostatic chuck cover ring  120  in a slant direction. 
     The diameter (R 1 ) of the protrusion part  112  represents a diameter of an upper surface of the protrusion part  112  on which the target object  170  is safely mounted. Desirably, the diameter (R 1 ) of the protrusion part  112  is set less by 2.5 mm to 3.5 mm than a diameter of the target object  170 . For example, if the target object  170  is equal to a 300 mm wafer, it is ideal that even the diameter (R 1 ) of the protrusion part  112  is equal to about 300 mm but, because there is a handling error of a wafer conveying system, the diameter (R 1 ) of the protrusion part  112  should be always less than a diameter of the wafer. Thus, if the target object  170  is the 300 mm wafer, it is desirable that the diameter (R 1 ) of the protrusion part  112  is set to be in a range of 296.5 mm≦R 1 ≦297.5 mm. 
     The electrostatic chuck cover ring  120  is disposed to surround the outer circumference of the protrusion part  112  of the electrostatic chuck  110 . The electrostatic chuck cover ring  120  protects the body part  111  of the electrostatic chuck  110  from the plasma ions  182  that are generated as the plasma reactor  200  operates. The cathode assembly cover ring  130  is disposed to surround an outer circumference of the electrostatic chuck cover ring  120  and an outer circumference of the body part  111  of the electrostatic chuck  110 . 
     A power supply unit  140  supplies a Direct Current (DC) power source to the electrostatic chuck  110  through an RF noise filter  150 . A switch  160  can connect between the power supply unit  140  and the RF noise filter  150 . When the power supply unit  140  supplies the DC power source to the electrostatic chuck  110 , an attractive force by static electricity is generated in the electrostatic chuck  110  and thus, the target object  170  is fixed to an upper surface of the protrusion part  112 . 
       FIG. 6  is a diagram illustrating an example of a plasma reactor including the electrostatic chuck assembly of  FIG. 3 . Within a reaction chamber  201  of the plasma reactor  200 , a cathode assembly  202  is installed, and the electrostatic chuck assembly  100  is installed on an upper part of the cathode assembly  202 . A construction of the electrostatic chuck assembly  100  is identical with a construction described with reference to  FIG. 3 . 
     Gas injectors  203  and  204  are installed in a plurality of points of a side surface and top of the reaction chamber  201 . By the gas injectors  203  and  204 , a reaction gas is injected into the reaction chamber  201 . The top of the reaction chamber  201  is comprised of a dielectric window  205 . An inductive coil  206  (i.e., a plasma source for generating plasma within the reaction chamber  201 ) is installed around the dielectric window  205 . An RF power supply unit  208  applies an RF power source to the inductive coil  206  through an RF matching network  207 . By doing so, a magnetic field is formed in the inductive coil  206 . As the magnetic field is formed in the inductive coil  206 , plasma ions are generated within the reaction chamber  201 . 
     A switch  211  is connected between the power supply unit  209  and the RF noise filter  210 , and the RF noise filter  210  is connected to the electrostatic chuck  110 . When the switch  211  turns on, the power supply unit  209  supplies a DC power source to the electrostatic chuck  110  through the RF noise filter  210 . Bias impedance matching networks  212  and  213  are connected to a lower electrode (i.e., the cathode assembly  202 ). A low-frequency RF power supply unit  214  supplies a low-frequency bias RF power to a lower electrode through the bias impedance matching network  212 . A high-frequency RF power supply unit  215  supplies a high-frequency bias RF power to the lower electrode through the bias impedance matching network  213 . As a result, the low-frequency bias RF power and the high-frequency bias RF power are mixed and applied to the lower electrode (i.e., the cathode assembly  202 ). 
     A throttling gate valve  216  and a turbo pump  217  are installed below the reaction chamber  201 . An exhaust valve  218  is installed at one side of the turbo pump  217 . 
       FIG. 7  is a diagram illustrating a wafer etched by the plasma reactor of  FIG. 6 . 
     After the wafer  170  is cut along a cutting line F-F′, when viewing its cut surface, a profile of contact holes (H 11  to H 13 ) formed in the wafer  170  is illustrated in a lower part of  FIG. 7 . It can be appreciated from  FIG. 7  that the contact holes (H 12 , and H 11  and H 13 ) formed in a center and edge of the wafer  170  have a normal profile perpendicular to a bottom surface (or a surface) of the wafer  170 . The reason why the contact holes (H 11  and H 13 ) are perpendicularly formed in the bottom surface (or a surface) of the wafer  170  as above is that the length (G) of the protrusion part  112  protruding from the body part  111  is set to be in the range of 1.0 mm≦G≦7.0 mm, and the diameter (R 1 ) of the protrusion part  112  is set less by 2.5 mm to 3.5 mm than the diameter of the target object  170 , thus optimizing a structure of the electrostatic chuck  110 . 
     If the diameter (R 1 ) of the protrusion part  112  is too small, at the time of an etching process of the plasma reactor  200 , a process quality of the edge of the wafer is deteriorated. To the contrary, if the diameter (R 1 ) of the protrusion part  112  is too large, there is an arcing problem of the electrostatic chuck  110 . Accordingly, the diameter (R 1 ) of the protrusion part  112  should be optimized through an experiment accompanying a high cost. 
     On the other hand, it is most ideal that the length (G) of the protrusion part  112  protruding from the body part  111  is equal to ‘0’. However, in this case, the electrostatic chuck cover ring  120  cannot be installed in the electrostatic chuck  110 . If the electrostatic chuck cover ring  120  is not installed in the electrostatic chuck  110 , an edge (i.e., an ‘E’ portion of  FIG. 5 ) of the body part  111  of the electrostatic chuck  110  is damaged due to impacts of plasma ions. Thus, the length (G) of the protrusion part  112  protruding from the body part  111  should be maintained as a specific value. 
     In optimizing the length (G) of the protrusion part  112  protruding from the body part  111 , data such as an etching rate of the electrostatic chuck cover ring  120 , an etching profile of the target object (i.e., the wafer)  170 , an etching rate and etching profile of an edge of the target object  170 , etc. should be experimentally obtained. According to the experimental data, when the electrostatic chuck cover ring  120  is of silicon, the etching rate of the electrostatic chuck cover ring  120  is equal to about 0.82 mm/200 Hrs. In conclusion, if securing a Mean Time Between Clean (MTBC) by 200 Hrs or more and simultaneously considering a process error, the length (G) of the protrusion part  112  protruding from the body part  111  should be equal to 1 mm or more. 
     Also, according to the experimental data, when the length (G) of the protrusion part  112  protruding from the body part  111  is equal to 7 mm or less, it is possible to secure a good etching profile of the electrostatic chuck cover ring  120  and a good etching rate (Table of  FIG. 8 ) and etching profile (illustrated in  FIG. 7 ) of the edge of the target object  170 . In Table of  FIG. 8 , an etching range corresponds to a difference between the maximum value and the minimum value of the etching rate, and uniformity can be expressed in Equation below. 
     
       
         
           
             
               Uniformity 
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     On the other hand, when the diameter (R 1 ) of the protrusion part  112  is set less by 20.5 mm to 3.5 mm than the diameter of the target object  170  in association with optimization of the length (G) of the protrusion part  112  protruding from the body part  111 , it is possible to secure a good etching profile of the electrostatic chuck cover ring  120  and a good etching rate (Table of  FIG. 8 ) and a good etching profile of the edge of the target object  170 . On the other hand, a design of the electrostatic chuck  110  and electrostatic chuck assembly  100  is optimized, thereby making it possible to simplify a process kit around the electrostatic chuck  110  and decrease a cost. 
     While the invention has been shown and described with reference to a certain preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.