Abstract:
A charged particle beam apparatus includes: a charged particle beam generator which generates a charged particle beam; a projection optical system which generates a lens field to focus the charged particle beam on an external substrate; and deflectors arranged so as to surround an optical axis of the charged particle beam; the deflectors generating a deflection field which is superposed on the lens field to deflect the charged particle beam and to control a position to irradiate the substrate, and being configured so that intensity of the deflection field in a direction of the optical axis is changed in accordance with an angle with which the charged particle beam should fall onto the substrate.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims benefit of priority under 35USC §119 to Japanese Patent Application No. 2004-013392, filed on Jan. 21, 2004, the contents of which are incorporated by reference herein. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a charged particle beam apparatus, a charged particle beam control method, a substrate inspection method and a method of manufacturing a semiconductor device. 
     2. Related Background Art 
     Heretofore, for a deflector used in a charged particle beam apparatus, for example, an electrostatic deflector, a quadruple or octal deflector has been generally used which comprises four or eight electrodes arranged to surround an optical axis, and positive and negative voltages are applied to the electrodes facing across the optical axis to produce an electrostatic field which controls a charged particle beam. This will be specifically described with reference to the drawings. 
       FIGS. 9A to 9D  are sectional views showing an electrostatic deflector described in T. H. P. Chang et al, Multiple electron-beam lithography, Microelectron. Eng. 57-58 (2001) 117-135.  FIG. 9A  is a sectional view of a quadruple deflector  820  comprising four fan-shaped flat electrodes EL 820   a  to EL 820   d , which is cut along a plane perpendicular to an optical axis Ax, and  FIG. 9B  is a sectional view of the deflector  820  along an X axis of  FIG. 9A . Further,  FIG. 9C  is a sectional view of an octal deflector  822  comprising eight fan-shaped electrodes EL 822   a  to EL 822   h , which is cut along a plane perpendicular to an optical axis Ax, and  FIG. 9D  is a sectional view of the deflector  822  along an X axis of  FIG. 9C . 
     Describing, for example, the octal deflector  822  shown in  FIG. 9C , for deflection in a forward direction (arrow direction) on the X axis, a voltage of (√2−1) V is applied to the electrode EL 822   a , V to the electrode EL 822   b , V to the electrode EL 822   c , (√2−1) V to the electrode EL 822   d , −(√2−1) V to the electrode EL 822   e , −V to the electrode EL 822   f , −V to the electrode EL 822   g , and −(√2−1) V to the electrode EL 822   h , so that a tertiary term of the electrostatic deflection field disappears to allow for a wider uniform electric field area. This enables beam deflection with significantly reduced deflection aberration. 
     Also, a proposal has been made to improve optical performance in an electron beam lithography apparatus using the deflectors shown in  FIGS. 9A to 9D .  FIG. 10  is a partial configuration diagram showing an electron beam lithography apparatus described in Japanese laid open (kokai) No. 2001-283760. In an electron beam irradiation device  900  shown in  FIG. 10 , an electrostatic main deflector  952  is disposed in a magnetic field of a magnetic objective lens  954 , and a pre-deflector  950  is disposed on an object surface side of the objective lens  954  while a post-deflector  953  is disposed on an image surface side of the objective lens  954 . The electron beam irradiation device  900  shown in  FIG. 10  is used in the electron beam lithography apparatus, and widely deflects an electron beam EB on a wafer W which is a sample, in order for a faster lithography process. Therefore, a deflection system is optimized in such a manner that deflecting voltages are lowered by maintaining high deflection sensitivity and that coma aberration and an incidence angle of the electron beam EB on the wafer W will be 0. The optimization of the deflection system in the device of  FIG. 10  is implemented in accordance with locations of a plurality of deflectors on the optical axis, a voltage ratio among the deflectors, and phase setting. 
     However, if an attempt is made to further increase the resolution of the electron beam irradiation device  900  shown in  FIG. 10  or to increase the amount of deflection of the electron beam EB, more deflectors are arranged inside, in front of and in the rear of the objective lens  954 , thus increasing the number of components and wires on the periphery of a pole piece of the objective lens  954 . This increases the burden on mechanical assembly, and makes it difficult to produce a higher vacuum on the periphery of the pole piece due to an increase of exhaust resistance. Another problem is an increase in the number of power sources due to the increase in the number of deflectors. On the other hand, there is a limit to the actual number of deflectors and to arrangement space, which does not allow for optimal locations on a physical design, thus making it difficult to further improve performance. 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the invention, there is provided a charged particle beam apparatus comprising: 
     a charged particle beam generator which generates a charged particle beam; 
     a projection optical system which generates a lens field to focus the charged particle beam on an external substrate; and 
     deflectors arranged so as to surround an optical axis of the charged particle beam; the deflectors generating a deflection field which is superposed on the lens field to deflect the charged particle beam and to control a position to irradiate the substrate, and being configured so that an intensity of the deflection field is changed in a direction of the optical axis in accordance with an angle with which the charged particle beam should fall onto the substrate. 
     According to a second aspect of the invention, there is provided a charged particle beam apparatus comprising: 
     a charged particle beam generator which generates a charged particle beam; 
     a projection optical system which generates a lens field to focus the charged particle beam on an external substrate; and 
     deflectors comprising electrodes or magnetic cores arranged to surround an optical axis of the charged particle beam; the deflectors generating a deflection field which is superposed on the lens field and deflecting the charged particle beam by the deflection field to control a position to irradiate the substrate, wherein space between surfaces of the electrodes or magnetic cores across the optical axis changes stepwise in a direction of the optical axis. 
     According to a third aspect of the invention, there is provided a charged particle beam apparatus comprising: 
     a charged particle beam generator which generates a charged particle beam; 
     a projection optical system which generates a lens field to focus the charged particle beam on an external substrate; and 
     deflectors comprising electrodes or magnetic cores arranged to surround an optical axis of the charged particle beam; the deflectors generating a deflection field which is superposed on the lens field and deflecting the charged particle beam by the deflection field to control a position to irradiate the substrate, the deflectors being formed so that surfaces across the optical axis of the electrodes or magnetic cores have an angle of inclination to a direction of the optical axis and the angle of inclination changes in the optical axis direction. 
     According to a fourth aspect of the invention, there is provided a method of controlling a charged particle beam which is generated and applied to a substrate, the method comprising: 
     generating a lens field to focus the charged particle beam on the substrate; and 
     generating a deflection field which is superposed on the lens field control a position to irradiate the substrate by deflecting the charged particle beam, the deflection field being configured so that intensity thereof in a direction of the optical axis is changed in accordance with an angle with which the charged particle beam should fall onto the substrate. 
     According to a fifth aspect of the invention, there is provided a substrate inspection method comprising: 
     generating a charged particle beam to irradiate a substrate; 
     generating a lens field to focus the charged particle beam on the substrate; 
     generating a deflection field which is superposed on the lens field to control a position to irradiate the substrate by deflecting the charged particle beam, the deflection field being configured so that intensity thereof in a direction of the optical axis is changed in accordance with an angle with which the charged particle beam should fall onto the substrate; and 
     detecting at least one of secondary charged particles, reflected charged particles and back scattering charged particles produced from the wafer by the irradiation of the charged particle beam, in order to create a two-dimensional image representing a state in a surface of the substrate. 
     According to a sixth aspect of the invention, there is provided a method of manufacturing a semiconductor device comprising a substrate inspection method, the substrate inspection method including: 
     generating a charged particle beam to irradiate a substrate; 
     generating a lens field to focus the charged particle beam on the substrate; 
     generating a deflection field which is superposed on the lens field to deflect the charged particle beam and control a position to irradiate the substrate, the deflection field being configured so that intensity thereof in a direction of the optical axis is changed in accordance with an angle with which the charged particle beam should fall onto the substrate; and detecting at least one of secondary charged particles, reflected charged particles and back scattering charged particles produced from the wafer by the irradiation of the charged particle beam, in order to create a two-dimensional image representing a state in a surface of the substrate. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings: 
         FIG. 1  is a block diagram showing a schematic configuration in one embodiment of a charged particle beam apparatus according to the present invention; 
         FIG. 2A  is a sectional view showing one example of a deflector according to prior art; 
         FIGS. 2B and 2C  are sectional views showing specific examples of main deflectors formed in such a manner that electrode surfaces on an optical axis side have three steps along an optical axis; 
         FIGS. 3A to 3C  are sectional views showing specific examples of the main deflectors in which the electrode surfaces on the optical axis side are inclined; 
         FIGS. 4A and 4B  are sectional views showing specific examples of the main deflectors divided in an optical axis direction to configure a three-stage deflector; 
         FIGS. 5A and 5B  are diagrams showing distribution diagrams of a magnetic field of an objective lens and electrostatic fields of the main deflectors; 
         FIG. 6  is a diagram explaining the relationship between changes in the distribution of the electrostatic fields of the main deflectors and an electron beam trajectory; 
         FIGS. 7A and 7B  are sectional views showing specific examples of the main deflectors which generate electrostatic fields Ed and Ee shown in  FIG. 5B ; 
         FIGS. 8A to 8C  are diagrams showing specific examples of a deflector having movable mechanisms coupled to electrodes; 
         FIGS. 9A to 9D  are sectional views showing one example of deflectors according to prior art; and 
         FIG. 10  is a partial configuration diagram showing one example of an electron beam lithography apparatus according to prior art. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Several embodiments of the present invention will hereinafter be described in reference to the drawings. In the following embodiments, an electron beam lithography apparatus will be described which uses an electron beam as a charged particle beam to draw patterns on a wafer. 
       FIG. 1  is a block diagram showing a schematic configuration of one embodiment of a charged particle beam apparatus according to the present invention. An electron beam lithography apparatus  1  shown in  FIG. 1  comprises an electron beam column  10 , power sources PS 1  to PS 8 , an electron beam detector  56 , an electron detector controller  58 , and a control computer  60  to control the entire apparatus. 
     The electron beam column  10  includes an electron gun  12 , an aperture  14 , an illumination lens  16 , a forming aperture  18 , a reduction lens  22 , a pre-main deflector  24 , a sub deflector  26 , a main deflector  28  characterizing the present embodiment, and a post-main deflector  52 . The electron gun  12  generates and accelerates an electron beam EB to irradiate a wafer W which is a sample. The aperture  14  has a rectangular or round opening, which defines a sectional shape of the electron beam EB. The forming aperture  18  has an opening with a shape corresponding to a desired pattern. The illumination lens  16  adjusts magnification so that the electron beam EB has a desired beam diameter. The reduction lens  22  reduces the beam diameter of the electron beam EB. An objective lens  54  has its focal distance adjusted so that the electron beam EB is imaged on an upper surface of the wafer W. The pre-main deflector  24 , the main deflector  28 , the post-main deflector  52  and the sub deflector  26  control the irradiation position of the electron beam EB on the wafer W. In the present embodiment, the objective lens  54  comprises a magnetic lens, the reduction lens  22  comprises an electrostatic lens, and the pre-main deflector  24 , the main deflector  28 , the post-main deflector  52  and the sub deflector  26  are all electrostatic deflectors. The pre-main deflector  24 , the main deflector  28  and the post-main deflector  52  are controlled so that a drawing area (main deflection area) is scanned with the electron beam EB referring to a position of an XY stage with regard to the wafer W mounted on the unshown XY stage, and the sub deflector  26  controls the irradiation position of the electron beam EB so that drawing is performed in sub deflection areas subdivided from the main deflection area. 
     Operations of elements in the electron beam column  10  are as follows. 
     The electron beam EB generated and accelerated by the electron gun  12  irradiates the aperture  14 . The electron beam EB which has passed through the aperture  14  moves toward the forming aperture  18 . The electron beam EB has its magnification adjusted by the illumination lens  16  to have a beam diameter which is sufficiently large and is as large as required for the opening of the forming aperture  18 . The electron beam EB starts as a pattern beam originating from the forming aperture  18 , and is reduced at the reduction lens  22 , and then passes through the electrostatic pre-main deflector  24 , the sub deflector  26 , the main deflector  28  and the post-main deflector  52  so that its irradiation position is adjusted, whereby the electron beam EB is projected on the upper surface of the wafer W just in focus by the magnetic objective lens  54 . 
     The power sources PS 1  to PS 8  are connected to the control computer  60 , and also connected to the electron gun  12 , the illumination lens  16 , the reduction lens  22 , the objective lens  54 , the pre-main deflector  24 , the sub deflector  26 , the main deflector  28  and the post-main deflector  52 , respectively, and the power sources PS 1  to PS 8  apply, to the elements connected to, voltages whose values are controlled in accordance with command signals supplied from the control computer  60 . 
     The electron beam detector  56  is disposed between the post-main deflector  52  and the wafer W, and detects at least one of a secondary electron, a reflected electron and a back scattering electron produced on the wafer W by the irradiation of the electron beam EB and supplies a detection signal to the electron detector controller  58 . The electron detector controller  58  processes the detection signal from the electron beam detector  56  to supply the control computer  60  with an image signal which is to be a two-dimensional electron image (SEM image) representing the state in the surface of the wafer W. On the basis of this image signal the control computer  60  makes adjustments such as focusing of the electron beam EB. 
     The electron beam EB is, in the objective lens  54 , subjected to lens force (Lorentz force) from a magnetic field excited by the objective lens  54 , and thus changes its trajectory. If the electrostatic deflector is disposed in the magnetic field of the objective lens  54  to produce an electrostatic field, the trajectory of the electron beam EB is further changed under the lens force by the magnetic field and deflecting force by the electrostatic field at the same time. This trajectory form greatly affects deflection aberration on the wafer W and the irradiation angle of the electron beam EB to the wafer W. By producing an electrostatic deflection field in accordance with magnetic field distribution of the objective lens  54 , deflection sensitivity can be further increased and the deflection aberration can be further reduced. Moreover, the incidence angle to the wafer W can be controlled such that the electron beam EB falls on the wafer W substantially perpendicularly thereto, and it is thus possible to minimize displacement of a drawing position and/or a change in a pattern shape each of which is caused by a slight change in distance between the wafer W and the objective lens  54 . 
     The main deflector  28  disposed in the magnetic field of the objective lens  54  in  FIG. 1  is configured so as to be able to form desired electrostatic deflection field distribution in an optical axis direction. Thus, intensity of a deflection field superposed on a lens field of the objective lens  54  changes in the direction of its optical axis Ax so that the electron beam EB falls on the wafer W at a desired incidence angle while the deflection aberration is reduced. 
     Some of the specific configurations of the main deflector  28  will be described referring to  FIGS. 2A to 5B .  FIGS. 2B to 4B  respectively show sectional views of main deflectors  282 ,  284 ,  290 ,  292 ,  294 ,  302 ,  304  along the optical axis direction of the electron beam EB, in a similar manner to  FIGS. 9B and 9D . Sections perpendicular to the optical axis directions of the main deflectors  282  to  306  respectively shown in  FIGS. 2B to 4B  and  8 A are the same as those of deflectors  820 ,  822  shown in  FIGS. 9A ,  9 C and  FIGS. 9B and 9D . 
     The main deflectors  282 ,  284  shown in  FIGS. 2B and 2C  are formed in such a manner that electrode surfaces on the side of the optical axis Ax have three steps along the optical axis. In the main deflector  282  of  FIG. 2B , electrodes EL 282   b , EL 282   d  facing each other across the optical axis Ax comprise three steps having lengths L 1  , L 2 , L 3  when viewed from an object surface side in the direction of the optical axis Ax, and are formed so that a distance Φ 1 , Φ 2 , Φ 3  between the electrodes is greater in the step closer to the wafer W (image surface side). Further, in the main deflector  284  of  FIG. 2C , electrodes EL 284   b , EL 284   d  facing each other across the optical axis Ax comprise three steps having lengths L 11 , L 12 , L 13 in the direction of the optical axis Ax when viewed from an object surface side, and are formed so that an interelectrode distance Φ 11  in the step on the object surface side is larger than an interelectrode distance Φ 12  in the middle step and so that an interelectrode distance Φ 13  in the step on the image surface side is the largest. For easier comparison with a conventional deflector, the deflector  820  shown in  FIG. 9A  is again shown in  FIG. 2A . 
     The main deflectors  290 ,  292 ,  294  shown in  FIGS. 3A to 3C  have inclined electrode surfaces on the side of the optical axis Ax. In the main deflector  290  shown in  FIG. 3A , electrodes EL 290   b , EL 29   d  are arranged so as to have an interelectrode distance Φa 0  at the upper surfaces, and are formed so that the electrode surface on the optical axis side is inclined at an angle θa 0  to the optical axis direction. In the main deflector  292  of  FIG. 3B , electrodes EL 292   b , EL 292   d  are arranged so as to have an interelectrode distance Φa 1  at the upper surfaces, and are formed so that the electrode surface on the optical axis side is variably angled at θa 1 , θa 2 , θa 3  to the optical axis Ax along with lengths La 1 , La 2 , La 3  in the optical axis direction when viewed from the object surface side. Moreover, in the main deflector  294  shown in  FIG. 3C , electrodes EL 294   b , EL 294   d  are arranged to have an interelectrode distance Φa 2  at the upper surfaces, and have inclined surfaces angled at θa 11  to the optical axis Ax up to a portion having a length La 11  from the object surface side, but the remainder on the image surface side (portion beyond the length La 11  from the object surface side in the optical axis direction) are formed to be parallel with the optical axis. 
     The main deflector  302  shown in  FIG. 4A  is configured in such a form that the main deflector  282  shown in  FIG. 2B  is divided along planes each intersecting the boundaries of three steps, wherein electrodes EL 302   b   1 , EL 302   d   1  at the upper step (object surface side) have a length Lb 1  in the direction of the optical axis Ax and are arranged so that the electrode surfaces on the optical axis side are separate from each other at a distance Φb 1  and wherein electrodes EL 302   b   2 , EL 302   d   2  at the middle step have a length Lb 2  in the direction of the optical axis Ax and are arranged so that the electrode surfaces on the optical axis side are separate from each other at a distance Φb 2  and wherein electrodes EL 302   b   3 , EL 302   d   3  at the lower step (image surface side) have a length Lb 3  in the direction of the optical axis Ax and are arranged so that the electrode surfaces on the optical axis side are separate from each other at a distance Φb 3 . 
     The main deflector  304  shown in  FIG. 4B  is configured in such a form that the main deflector  292  shown in  FIG. 3B  is divided along planes each intersecting boundaries of the three-stepped portions with different angles of inclination, wherein electrodes EL 304   b   1 , EL 304   d   1  at the upper step (object surface side) have a length Lb 11  in the direction of the optical axis Ax and electrodes EL 304   b   2 , EL 304   d   2  at the middle step have a length Lb 12  in the direction of the optical axis Ax and electrodes EL 304   b   3 , EL 304   d   3  at the lower step (image surface side) have a length Lb 13  in the direction of the optical axis Ax. The electrodes EL 304   b   1 , EL 304   d   1  at the upper step are arranged so that the upper surfaces thereof are separate from each other at a distance Φb 11 . Further, the electrode surfaces on the optical axis side of the electrodes EL 304   b   1 , EL 304   d   1  at the upper step are inclined at an angle θb 1  to the direction of the optical axis Ax, and the electrode surfaces on the optical axis side of the electrodes EL 304   b   2 , EL 304   d   2  at the middle step are inclined at an angle θb 2  to the direction of the optical axis Ax, and the electrode surfaces on the optical axis side of the electrodes EL 304   b   3 , EL 304   d   3  at the lower step are inclined at an angle θb 3  to the direction of the optical axis Ax. 
     In the various main deflectors described above, the distribution shape of the deflection electric field can be changed by adjusting the length in the optical axis direction, the distance between the electrode surfaces on the optical axis side, or the angle to the optical axis direction in the electrode surface on the optical axis side, and as a result, the incidence angle of the electron beam EB to the wafer W can be controlled for an arbitrary angle. This will be specifically described using distribution diagrams of a magnetic field and electric fields in  FIGS. 5A and 5B  and an electron beam trajectory diagram of  FIG. 6 . Describing the main deflector  282  shown in  FIG. 2B  as an example, by adjusting the distances Φ 1 , Φ 2 , Φ 3  between the electrodes facing each other across the optical axis Ax and the lengths L 1 , L 2 , L 3  of the respective steps in the optical axis direction, the distribution shape of the electrostatic deflection field can be changed into Ea to Ee as shown in  FIG. 5B , with respect to an objective lens magnetic field B in the direction along the optical axis Ax as shown in  FIG. 5A . The distribution of the electrostatic deflection field superposed on the lens field of the objective lens is changed as in Ea to Ee shown in  FIG. 5B , such that the trajectory of the electron beam EB is changed as shown by signs TJa to Tje of  FIG. 6 , respectively. 
     Configuration examples of the deflector to form Ed and Ee among the five distributions of the electric fields shown in  FIG. 5B  are shown in  FIGS. 7A and 7B . Each of deflectors  392  and  394  shown in these drawings is formed with one electrode in which the electrode surface of the optical axis side is formed in a stepped shape. 
     Furthermore, in the case of the main deflector  292  having the inclined electrode surface shown in  FIG. 3B , the distribution of the deflection field can be changed similarly to the case of the main deflector  282  described above, by adjusting the distance Φa 1  between the electrodes of the main deflector, the inclination angles θa 1 , θa 2 , θa 3  to the optical axis Ax and the lengths La 1 , La 2 , La 3  in the optical axis direction. Moreover, even when the main deflectors  302 ,  304  of  FIGS. 4A and 4B  with the divided electrode are used, the three-stepped electrodes (EL 302   b   1 , EL 302   b   2 , EL 302   b   3  if the main deflector  302  is taken as an example) divided in the direction of the optical axis Ax can be controlled with the same power source, if adjustments are made for the distance between the deflection electrodes (Φb 1 , Φb 2 , Φb 3 ), the lengths between the electrodes (Lb 1 , Lb 2 , Lb 3 , Lb 11 , Lb 12 , Lb 13 ) and the inclination angles of the electrode surface (θb 1 , θb 2 , θb 3 ). 
     Furthermore, as shown in  FIG. 8A , the (multistep) main deflector  306  multi-divided in the direction of the optical axis Ax is used and movable mechanisms EL 402   a   1  to EL 402   h   1 , EL 402   a   2  to EL 402   h   2  respectively connected to electrodes (EL 306   a   1  to EL 306   h   1 , EL 306   a   2  to EL 306   h   2 ) are provided, such that, for example, an inside diameter (distance between optical axis side surfaces of the opposite electrodes) of the main deflector can be adjusted from Φc 2  (see  FIG. 8B ) to Φc 12  (see  FIG. 8C ) to create a desired distribution of deflection electric field in the optical axis direction. 
     The incidence angle of the electron beam EB to the wafer W is preferably perpendicular in exposure devices, but a greater incidence angle to the optical axis may be preferable in other fields such as electron microscopes, in which case the angle can naturally be controlled by the shape of the deflector. 
     Particularly, because the irradiation angle of the electron beam to a sample can be freely changed using the main deflector shown in  FIG. 8A , it is possible to acquire, with high resolution, both an SEM image (top-down image) from above the wafer W which can be obtained by perpendicular incidence of the electron beam EB onto the wafer W, and an SEM image (inclined image) obliquely from above the wafer W which can be obtained by oblique incidence of the electron beam EB onto the wafer W. Further, it is also possible to obtain three-dimensional shape using right and left inclined images. 
     In this way, according to the present embodiment, intensity distribution of the deflection field superposed on the lens field of the objective lens can be arbitrarily changed. Further, even when mechanical locations of the deflectors in the direction along the optical axis can not be moved due to lack or absence of space resulting from mechanical arrangement, a deflection point can be moved by changing the electrode shape, thereby making it possible to optimize a deflection system. 
     Furthermore, by using the above-described electron beam apparatus in manufacturing processes of semiconductor devices, patterns can be drawn or inspected with high resolution while the deflection aberration on the wafer W is reduced, thus enabling the manufacture of semiconductor devices with a higher yield ratio. 
     While the embodiments of the present invention have been described above, the present invention is not at all limited to the above embodiments, and various modifications can naturally be made within the scope thereof. 
     For example, the electrostatic deflector has been used as the deflector for a charged particle beam in the embodiments described above, but the present invention is limited thereto, and a magnetic deflector may be used. When the magnetic deflector is used, ferrite may be used as magnetic cores instead of, for example, the electrodes described in  FIGS. 2B to 4B . 
     Furthermore, while the exposure apparatus using the electron beam as the charged particle beam has been described, the present invention can naturally be applied to all the charged particle beam apparatuses as long as they use the deflectors.