Patent Publication Number: US-2009223450-A1

Title: Member of substrate processing apparatus and substrate processing apparatus

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a member of a substrate processing apparatus and a substrate processing apparatus, and in particular relates to a member of a substrate processing apparatus having an yttria coating. 
     2. Description of the Related Art 
     A substrate processing apparatus has a processing container in which a wafer for a semiconductor device (hereinafter referred to merely as a “wafer”) as a substrate is accommodated, and the wafer is subjected to plasma processing in the processing container. When the wafer is subjected to plasma processing in the processing container, a member in the processing container is sputtered by ions of the plasma. When the member is sputtered by the ions, the member becomes damaged, and a part of the damaged member may fall off to produce particles, and the particles may become attached to the wafer. When the particles become attached to the wafer, a short circuiting occurs in a semiconductor device manufactured from the wafer, resulting in the yield of semiconductor devices decreasing. 
     Accordingly, to prevent particles from being produced, a member coated with an yttria (Y 2 O 3 ) coating having high resistance to plasma has been disclosed as a member in the processing container (see, for example, Japanese Laid-open Patent Publication (Kokai) No. 2003-321760). 
     On the other hand, to prevent particles from being attached to the wafer, detection of particles in the processing container using an ISPM (In Situ Particle Monitor) has been carried out. Specifically, if the ISPM detects particles in the processing container while plasma processing is being carried out on wafers one by one, an action such as stopping the plasma processing is taken. This action can prevent the particles from becoming attached to a wafer planned to be processed next, and thus a decrease in the yield of semiconductor devices can be prevented. It should be noted that in general, the lower limit of the size of a particle that can be detected by the ISPM is 150 nm. 
     However, even in the case of a member having an yttria coating with high resistance to plasma as described above, if a wafer is repeatedly subjected to various kinds of plasma processing, the member is heavily sputtered by various plasmas, and hence the yttria coating on the surface of the member becomes damaged, and a surface layer of the yttria coating may fall off to produce particles. 
     On the other hand, the lower limit of the size of a particle that can be detected by the ISPM is about 150 nm as described above, but in general, an yttria coating has a tight structure, and hence a particle produced from the yttria coating is minute and 100 nm in size or smaller. For this reason, the ISPM cannot detect minute particles produced from the yttria coating. 
     Therefore, even in the case the ISPM is used, it is impossible to detect minute particles produced from a member having an yttria coating and prevent the minute particles from becoming attached to a wafer. 
     SUMMARY OF THE INVENTION 
     The present invention provides a member of substrate processing apparatus and a substrate processing apparatus, which can prevent minute particles from becoming attached to a wafer. 
     Accordingly, in a first aspect of the present invention, there is provided a member of a substrate processing apparatus that has a processing container in which a substrate is accommodated, and in which the substrate is subjected to plasma processing in the processing container, the member being disposed in the processing container and comprising a base material and an yttria coating that coats the base material, wherein the yttria coating comprises a first yttria layer coated on the base material, and a second yttria layer laminated on at least a part of the first yttria layer, and a structure of the second yttria layer is looser than a structure of the first yttria layer. 
     According to the first aspect of the present invention, because the yttria coating that coats the base material is comprised of the first yttria layer laminated on the base material, and the second yttria layer laminated on at least a part of the first yttria layer, a surface layer of the first yttria layer on which the second yttria layer is not laminated and a surface layer of the second yttria layer are exposed to plasma. Because the structure of the second yttria layer is looser than the structure of the first yttria layer, the second yttria layer falls off before the first yttria layer, and relatively large particles are produced from the second yttria layer when the first and second yttria layer are exposed to plasma. The relatively large particles can be detected by the conventional ISPM as well, and hence the falling-off of the first yttria layer can be detected using the conventional ISPM in advance, and for example, by stopping the subsequent plasma processing, minute particles can be prevented from being produced from the first yttria layer. As a result, minute particles can be prevented from becoming attached to the substrate. 
     The first aspect of the present invention can provide a member of a substrate processing apparatus, wherein particles constituting the second yttria layer have a size of not less than 250 nm. 
     According to the first aspect of the present invention, because particles constituting the second yttria layer have a size of not less than 250 nm, particles produced from the second yttria layer have a size of not less than 250 nm. On the other hand, the lower limit of the size of a particle that can be detected by the conventional ISPM is 150 nm. Thus, particles produced from the second yttria layer can be reliably detected using the conventional ISPM. 
     The first aspect of the present invention can provide a member of a substrate processing apparatus, wherein particles constituting the first yttria layer have a size of less than 100 nm. 
     The first aspect of the present invention can provide a member of a substrate processing apparatus, wherein the substrate processing apparatus comprises a mounting stage that is disposed in the processing container and has a mounting surface on which the substrate is mounted, and an exhausting unit that is connected to the processing container and exhausts gas out of the processing container, and the second yttria layer is disposed between the mounting surface and the exhausting unit. 
     According to the first aspect of the present invention, the second yttria layer is disposed between the mounting surface on which the substrate is mounted and the exhausting unit that exhausts gas out of the processing container. Particles produced from the second yttria layer are caught up in gas exhausted by the exhausting unit and exhausted out of the processing container, and hence do not bend round to the mounting surface. Thus, particles produced from the second yttria layer can be prevented from becoming attached to the substrate. 
     The first aspect of the present invention can provide a member of a substrate processing apparatus, which is an inner wall of the processing container. 
     According to the first aspect of the present invention, because the member is the inner wall of the processing container, the degree to which the inner wall of the processing container wears can be detected by detecting particles produced from the inner wall of the processing container using the conventional ISPM. 
     The first aspect of the present invention can provide a member of a substrate processing apparatus, which is a test piece disposed in the processing container. 
     According to the first aspect of the present invention, because the member is the test piece disposed in the processing container, the degree to which the processing container wears can be indirectly detected by detecting particles produced from the test piece using the conventional ISPM. 
     The first aspect of the present invention can provide a member of a substrate processing apparatus, wherein the processing container comprises a sub processing container into which plasma enters, and the test piece is disposed in the sub processing container. 
     According to the first aspect of the present invention, the processing container has the sub processing container into which plasma enters, and the member is the test piece disposed in the sub processing container. Thus, particles produced from the second yttria layer can be detected using the conventional ISPM while preventing the test piece from obstructing the flow of gas in the processing container. 
     Accordingly, in a second aspect of the present invention, there is provided a substrate processing apparatus that has a processing container in which a substrate is accommodated, and in which the substrate is subjected to plasma processing in the processing container, comprising a member that is disposed in the processing container and comprises a base material and an yttria coating that coats the base material, wherein the yttria coating comprises a first yttria layer coated on the base material, and a second yttria layer laminated on at least a part of the first yttria layer, and a structure of the second yttria layer is looser than a structure of the first yttria layer. 
     The features and advantages of the invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view schematically showing the construction of a substrate processing apparatus to which a member of the substrate processing apparatus according to an embodiment of the present invention is applied; 
         FIG. 2  is an enlarged view of an area A in  FIG. 1 ; 
         FIGS. 3A ,  3 B, and  3 C are views useful in explaining how particles are produced from an yttria base layer and an yttria upper layer of an yttria coating in  FIG. 2 ; 
         FIG. 4  is a cross-sectional view schematically showing the construction of a first variation of the substrate processing apparatus in  FIG. 1 ; 
         FIG. 5  is an enlarged view of an area B in  FIG. 4 ; and 
         FIG. 6  is a cross-sectional view schematically showing the construction of a second variation of the substrate processing apparatus in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The present invention will now be described in detail with reference to the drawings showing a preferred embodiment thereof. 
     First, a description will be given of a member of a substrate processing apparatus according to an embodiment of the present invention. 
       FIG. 1  is a cross-sectional view schematically showing the construction of the substrate processing apparatus to which the member of the substrate processing apparatus according to the present embodiment is applied. The substrate processing apparatus is constructed such as to carry out plasma etching on a wafer as a substrate. 
     Referring to  FIG. 1 , the substrate processing apparatus  10  has a chamber  11  (processing container) in which a wafer W having a diameter of, for example, 300 mm is accommodated. A cylindrical susceptor  12  (mounting stage) on which the wafer W is mounted is disposed in the chamber  11 . In the substrate processing apparatus  10 , a side exhaust path  13  that acts as a flow path through which gas above the susceptor  12  is exhausted out of the chamber  11  is formed between an inner side wall of the chamber  11  and the side face of the susceptor  12 . An exhaust plate  14  is disposed part way along the side exhaust path  13 . 
     The exhaust plate  14  is a plate-shaped member having a large number of holes therein and acts as a partition plate that partitions the chamber  11  into an upper portion and a lower portion. In the upper portion (hereinafter referred to as the “reaction chamber”)  15  of the chamber  11  partitioned by the exhaust plate  14 , plasma is produced, but the exhaust plate  14  captures or reflects plasma produced in the reaction chamber  15  to prevent leakage of the plasma into the lower portion (hereinafter referred to as the “exhaust chamber”)  16  of the chamber  11 . 
     A lower radio frequency power source  17  is connected to the susceptor  12  in the chamber  11  via a lower matcher  18 , and supplies predetermined radio frequency electrical power to the susceptor  12 . The susceptor  12  thus acts as a lower electrode. The lower matcher  18  reduces reflection of the radio frequency electrical power from the susceptor  12  so as to maximize the efficiency of the supply of the radio frequency electrical power into the susceptor  12 . 
     An electrostatic chuck  20  having an electrostatic electrode plate  19  therein is provided in an upper portion of the susceptor  12 . The electrostatic chuck  20  is formed by placing an upper disk-shaped member, which has a smaller diameter than a lower disk-shaped member having a certain diameter, over the lower disk-shaped member. It should be noted that the electrostatic chuck  20  is made of a ceramic. When a wafer W is mounted on the susceptor  12 , the wafer W is disposed on the upper disk-shaped member of the electrostatic chuck  20 . 
     A DC power source  21  is electrically connected to the electrostatic electrode  19  of the electrostatic chuck  20 . Upon a positive DC high voltage being applied to the electrostatic electrode plate  19 , a negative potential is produced on a surface of the wafer W which faces the electrostatic chuck  20  (hereinafter referred to as “the rear surface of the wafer W”). A potential difference thus arises between the electrostatic electrode plate  19  and the rear surface of the wafer W, and hence the wafer W is attracted to and held on the upper disk-shaped member of the electrostatic chuck  20  through a Coulomb force or a Johnsen-Rahbek force due to the potential difference. 
     Moreover, an annular focus ring  22  is mounted on the electrostatic chuck  20  such as to surround the attracted and held wafer W. The focus ring  22  is made of a conductive member such as silicon, and focuses plasma in the reaction chamber  15  toward a front surface of the wafer W, thus improving the efficiency of the plasma etching. 
     An annular coolant chamber  23  that extends, for example, in a circumferential direction of the susceptor  12  is provided inside the susceptor  12 . A coolant, for example, cooling water or a Galden (registered trademark) fluid, at a low temperature is circulated through the coolant chamber  23  via a coolant piping  24  from a chiller unit (not shown). The susceptor  12  cooled by the low-temperature coolant cools the wafer W and the focus ring  22  via the electrostatic chuck  20 . 
     A plurality of heat transfer gas supply holes  25  are opened to a portion of the upper surface of the upper disk-shaped member of the electrostatic chuck  20  on which the wafer W is attracted and held (hereinafter referred to as the “attracting surface”). The heat transfer gas supply holes  25  are connected to a heat-transmitting gas supply unit (not shown) via a heat-transmitting gas supply line  26 , and the heat-transmitting gas supply unit supplies helium (He) gas as a heat transfer gas into a gap between the attracting surface and the rear surface of the wafer W via the heat transfer gas supply holes  25 . The helium gas supplied into the gap between the attracting surface and the rear surface of the wafer W effectively transfers heat from the wafer W to the electrostatic chuck  20 . 
     A showerhead  27  is disposed in a ceiling portion of the chamber  11  such as to face the susceptor  12 . An upper radio frequency power source  29  is connected to the showerhead  27  via an upper matcher  28 , and the upper radio frequency power source  29  supplies predetermined radio frequency electrical power to the showerhead  27 . The showerhead  27  thus acts as an upper electrode. It should be noted that the upper matcher  28  has a similar function to the lower matcher  18  described above. 
     The showerhead  27  has a ceiling electrode plate  31  having a number of gas holes  30  therein, a cooling plate  32  that detachably suspends the ceiling electrode plate  31 , and a lid member  33  that covers the cooling plate  32 . Moreover, a buffer chamber  34  is provided inside the cooling plate  32 , and a process gas introducing pipe  35  is connected to the buffer chamber  34 . The showerhead  27  supplies gas supplied to the buffer chamber  34  through the process gas introducing pipe  35  into the reaction chamber  15  via the gas holes  30 . In the substrate processing apparatus  10 , radio frequency electrical power is supplied to the susceptor  12  and the showerhead  27  to supply radio frequency electrical power into the reaction chamber  15 , whereby the process gas supplied from the showerhead  27  is turned into high-density plasma in the reaction chamber  15 . The wafer W is subjected to the plasma etching by the plasma. 
     Moreover, an exhaust system  36  (exhausting unit) exhausting gas inside the chamber  11  is connected to the exhaust chamber  16 . The exhaust system  36  has a roughing line  37  and a main exhausting line  38 . The roughing line  37  has a dry pump (DP) (not shown) connected thereto, and roughs the interior of the chamber  11 . The main exhausting line  38  has a turbo-molecular pump (TMP)  39 , which reduces the pressure in the chamber  11  down to a high vacuum state. Specifically, the DP reduces the pressure in the chamber  11  from atmospheric pressure down to an intermediate vacuum state (e.g. a pressure of not more than 1.3×10 Pa (0.1 Torr)), and the TMP is operated in collaboration with the DP to reduce the pressure in the chamber  11  down to a high vacuum state (e.g. a pressure of not more than 1.3×10 −3  Pa (1.0×10 −5  Torr)), which is at a lower pressure than the intermediate vacuum state. The main exhausting line  38  also has a branch line  40  connected to the roughing line  37 , and in the roughing line  37  and the branch line  40 , there are disposed valves V 1  and V 2  that can interrupt the roughing line  37  and the branch line  40 , respectively. It should be noted that an APC valve (not shown) controls the pressure in the chamber  11 . 
     Further, an ISPM  41  is disposed part way along the roughing line  37 . The ISPM  41  has a laser light oscillator (not shown) that irradiates laser light toward a central axis of the roughing line  37 , and a photomultiplier (not shown) that has a focus at an intersection of the central axis of the roughing line  37  and the laser light. In the roughing line  37 , the photomultiplier receives scattered light produced when particles pass the irradiated laser light, and laser light attenuated by particles. The received scattered light and attenuated light are converted into electric signals and transmitted to a PC (not shown). The PC detects the number and size of particles flowing in the roughing line  37  based on the transmitted electric signals. The exhaust system  36  exhausts gas including particles inside the chamber  11 , and thus the ISPM  41  can detect particles produced in the chamber  11 . Alternatively, the ISPM  41  may be provided part way along the main exhausting line  38 . 
     Here, there is a limit to the resolution of the photomultiplier, and the lower limit of the size of a particle that can be detected by the ISPM  41  is 150 nm. The present inventors carried out various experiments so as to evaluate the detecting efficiency of the ISPM  41 , and ascertained that the detecting efficiency of the ISPM  41  is about 80% when the size of a particle is 300 nm, the detecting efficiency of the ISPM  41  is about 50% when the size of a particle is 250 nm, and the detecting efficiency of the ISPM  41  is about 1% when the size of a particle is 200 nm. 
     Moreover, in the substrate processing apparatus  10 , an inner wall (base material) of the chamber  11  is coated with an yttria coating  50  ( FIG. 2 ). The yttria coating  50  is comprised of an yttria base layer  51  (first yttria layer) coated on the entire surface of the inner wall of the chamber  11 , and an yttria upper layer  52  (second yttria layer) laminated on a part of the yttria base layer  51 . The yttria base layer  51  is a normal yttria layer, and has a so-called “tight” structure in which there are minute pores (not shown). On the other hand, the yttria upper layer  52  has a so-called “loose” structure in which there are larger pores as compared with the yttria base layer  51  as shown in  FIG. 2 . Specifically, the sizes of particles constituting the yttria base layer  51  are less than 100 nm, and the sizes of particles constituting the yttria base layer  51  are not less than 250 nm. 
     In the yttria coating  50 , the yttria upper layer  52  is disposed such as to face the side exhaust path  13 . Specifically, the yttria upper layer  52  is disposed between the mounting surface of the susceptor  12  and the exhaust plate  14  as viewed in the vertical direction in  FIG. 1 . 
     In the substrate processing apparatus  10 , when radio frequency electrical power is supplied to the susceptor  12  and the showerhead  27 , plasma is produced in the chamber  11  (reaction chamber  15 ) as described above. The produced plasma collide with the inner wall of the chamber  11  and so on as indicated by outline arrows in the figure by bias voltage applied to the surface of the wafer W and the inner wall of the chamber  11 , and the yttria coating  50  is physically sputtered by ions of the plasma ( FIG. 3A ). 
     Because the yttria upper layer  52  has the “loose” structure, it has lower resistance to physical shocks than the yttria base layer  51  having the “tight” structure, and hence a part of the yttria upper layer  52  falls off to produce particles due to the sputtering by the plasma before the yttria base layer  51  (see  FIG. 3B ). Moreover, because the yttria upper layer  52  falls off relatively widely due to its structure, and relatively large particles e.g. particles with a size of not less than 250 nm are produced from the yttria upper layer  52 . 
     After that, if the sputtering by the ions is continued, particles are produced not only from the yttria upper layer  52  but also from the yttria base layer  51 . Because the yttria base layer  51  has the “tight” structure, minute particles e.g. particles with a size of 100 nm or less are produced from the yttria base layer  51  (see  FIG. 3C ). 
     Here, because the lower limit of the size of a particle that can be detected by the ISPM  41  is 150 nm, particles with a size of 100 nm or less cannot be detected by the ISPM  41 . On the other hand, particles with a size of not less than 250 nm can be detected by the ISPM  41  with a high detecting efficiency of about 50%. 
     Because particles are produced from the yttria upper layer  52  before the yttria base layer  51  as described above, the state in which particles produced from the yttria upper layer  52  have been detected can be considered to be the state in which the possibility that particles are produced from the yttria base layer  51  has increased. Thus, in the substrate processing apparatus  10 , if particles produced from the yttria upper layer  52  are detected by the ISPM  41 , production of particles from the yttria base layer  51  can be detected in advance. 
     Moreover, if the yttria upper layer  52  continues to produce particles, the yttria upper layer  52  wears. Because the yttria upper layer  52  is a structural element of the inner wall of the chamber  11 , the degree to which the inner wall of the chamber wears can be detected by detecting particles produced from the yttria upper layer  52 . 
     For the reasons stated above, if the plasma etching is stopped when particles produced from the yttria upper layer  52  are detected, minute particles can be prevented from being produced from the yttria base layer  51 . As a result, minute particles can be prevented from becoming attached to the wafer W. 
     Moreover, in the substrate processing apparatus  10 , because the yttria upper layer  52  is disposed such as to face the side exhaust path  13 , relatively large particles produced from the yttria upper layer  52  are caught up in gas exhausted via the exhaust line  37  and exhausted out of the chamber  11 . Here, because the yttria upper layer  52  is disposed between the mounting surface of the susceptor  12  and the exhaust plate  14  in the side exhaust path  13 , relatively large particles produced from the yttria upper layer  52  do not go above the mounting surface, that is, above the wafer W, and hence relatively large particles produced from the yttria upper layer  52  can be prevented from becoming attached to the wafer W. It should be noted that the location at which the yttria upper layer  52  is disposed is not limited to the location facing the side exhaust path  13 , but has to be a location that is exposed to plasma in the chamber  11  and below the mounting surface. 
     Although in the above described present embodiment, the inner wall of the chamber  11  has the yttria upper layer  52 , a test piece  60  (see  FIG. 5 ) formed by coating a base material  61  with the yttria coating  50  as shown in  FIG. 4  may be disposed in the chamber  11 , for example, in the side exhaust path  13  instead of disposing the yttria upper layer  52  on the inner wall of the chamber  11 . By disposing the test piece  60  in the chamber  11 , the degree to which a structural member of the chamber  11  wears can be indirectly detected. In this case, the yttria upper layer  52  may be provided on any surface of the test piece  60  which is exposed to the chamber  11 , but particularly, as shown in  FIG. 5 , if the yttria upper layer  52  is provided on a surface  64  facing a space above the wafer W where the density of plasma is high, the yttria upper layer  52  can be reliably sputtered, whereby the degree to which a structural member of the chamber  11  wears can be accurately detected. 
     Moreover, the test piece  60  should not necessarily be provided in the chamber  11 . For example, as shown in  FIG. 6 , a sub chamber  70  (sub processing container) of which interior communicates with the side exhaust path  13  may be provided on a side of the chamber  11 , and the test piece  60  may be disposed in the sub chamber  70 . Because the sub chamber  70  does not lie on an exhaust path for gas in the chamber  11 , the flow of gas in the chamber  11  is not obstructed by the test piece  60 . Further, because the interior of the sub chamber  70  communicates with the side exhaust path  13 , plasma enters into the sub chamber  70 . Thus, particles are also produced from the yttria upper layer  52  of the test piece  60  in the sub chamber  70 , and hence by disposing the test piece  60  in the sub chamber  70 , the degree to which a structural member of the chamber  11  wears can be accurately detected. It should be noted that the yttria upper layer  52  may be provided on an inner wall of the sub chamber  70 . 
     Further, although in the present embodiment described above, the yttria coating  50  is applied to the substrate processing apparatus  10  that carries out the plasma etching on the wafer W, the yttria coating  50  may be applied to the substrate processing apparatus that carries out other processing using plasma such as CVD processing on the wafer W.