ELECTROSTATIC CHUCK HEATER AND FILM DEPOSITION APPARATUS

There is provided an electrostatic chuck heater including: a ceramic plate having a first surface for bearing a wafer on which a film is to be deposited, and a second surface opposite the first surface, and including ESC electrodes and a heater electrode which are built therein; a ceramic shaft which is attached to the second surface of the ceramic plate and which comprises an internal space for accommodating an ESC rod connected to the ESC electrodes and a heater rod connected to the heater electrode; a plurality of lift pin holes penetrating the ceramic plate from the first surface to the second surface; and a plurality of protrusions arranged on the first surface of the ceramic plate with equal spacing from each other and with rotational symmetry about a central axis of each of the lift pin holes.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electrostatic chuck heater and a film deposition apparatus.

2. Description of the Related Art

In a film deposition apparatus for semiconductor manufacturing processes, a ceramic heater is used as a support stage for uniformly controlling the wafer temperature. A ceramic heater comprising an electrostatic chuck to enable stable wafer chucking is also known.

Patent Literature 1 (JP6948458B) discloses an electrostatic chuck heater of the Johnsen-Rahbek type, which is used to form a conducting film on a wafer. This electrostatic chuck heater comprises: a disc-shaped ceramic base having electrostatic electrodes and resistive heating elements; and a hollow shaft attached to the ceramic base. The surface of the ceramic substrate is embossed with a plurality of protrusions and raised portions that can contact the wafer in predetermined areas, and these protrusions and raised portions (hereinafter collectively referred to as protrusions) are said to enable stable chucking of the wafer.

Various other susceptors having a surface embossed with a plurality of protrusions are known (see Patent Literature 2 (JP6792455B, in particular,FIG.3A), Patent Literature 3 (JP2020-191450A, in particular,FIG.3), and Patent Literature 4 (JP6818351B, in particular,FIG.7), for example). As disclosed in these documents, the plurality of protrusions embossed on the surface of a conventional susceptor are generally arranged with equal spacing and with symmetry about the central axis of the wafer to be placed on the susceptor.

CITATION LIST

Patent Literature

SUMMARY OF THE INVENTION

As described above, by arranging a plurality of embossed protrusions with equal spacing on the surface of the susceptor, stable wafer chucking in each area is possible, which contributes to the deposition of a film of uniform thickness on the wafer. Moreover, the contact area between the susceptor surface and the wafer can be reduced by the interposition of the protrusions, and as a result, contamination caused by contact with the susceptor can be reduced, and the adsorption force attracting the wafer to the susceptor can be optimized to facilitate removal of the wafer.

However, as disclosed in Patent Literatures 2 to 4, the plate portion of the susceptor on which the wafer will be placed may have lift pin holes in addition to embossed protrusions. Lift pin holes are holes used to insert lift pins for lifting the wafer from below after deposition or other processing, and multiple (for example, three or four) lift pin holes are located at a distance from each other. In this case, as illustrated inFIGS.5and6, in a conventional layout in which protrusions118on the surface of a plate112are arranged with equal spacing and with symmetry about the central axis CPof the plate112, the plurality of protrusions118surrounding a lift pin hole116cannot be arranged with rotational symmetry about the central axis CHof the lift pin hole116. Moreover, the protrusions118cannot be provided at locations that overlap the lift pin hole116, and as a result, the protrusions118must be omitted at such locations. For example, in the portion A enclosed by the chain line inFIG.5, the protrusion118that should have been provided according to the regular arrangement overlaps with the lift pin hole116, and therefore is omitted. The result is that, as illustrated inFIGS.5and6, the plurality of protrusions118around the lift pin hole116are arranged asymmetrically or non-uniformly with respect to the lift pin hole116, leading to unstable electrostatic adsorption and increased warpage of the wafer W, which is strongly electrostatically adsorbed to the plate112but supported only by the protrusions118. In this case, since the wafer W does not warp concentrically with respect to the lift pin hole116, the warpage is non-uniform. Non-uniform warpage of the wafer W may result in the deposition of a film of non-uniform thickness on the wafer W.

The inventors have currently found that by arranging the plurality of protrusions on the ceramic plate with equal spacing from each other and with rotational symmetry about the central axis of each of the lift pin holes, it is possible to provide an electrostatic chuck heater that can equalize the warpage of the wafer around the lift pin holes.

Consequently, an objective of the present invention is to provide an electrostatic chuck heater capable of equalizing the warpage of the wafer around the lift pin holes.

The present invention provides the following aspects:

An electrostatic chuck heater to be used in a film deposition apparatus, the electrostatic chuck heater comprising:a ceramic plate having a first surface for bearing a wafer on which a film is to be deposited, and a second surface opposite the first surface, and comprising ESC electrodes and a heater electrode which are built therein;a ceramic shaft which is attached to the second surface of the ceramic plate and which comprises an internal space for accommodating an ESC rod connected to the ESC electrodes and a heater rod connected to the heater electrode;a plurality of lift pin holes penetrating the ceramic plate from the first surface to the second surface; anda plurality of protrusions arranged on the first surface of the ceramic plate with equal spacing from each other and with rotational symmetry about a central axis of each of the lift pin holes.

The electrostatic chuck heater according to Aspect 1, wherein the plurality of protrusions are arranged asymmetrically about a central axis of the ceramic plate.

The electrostatic chuck heater according to Aspect 1 or 2, wherein the plurality of protrusions are arranged according to a regular pattern with one selected from the group consisting of a circle, a square, an equilateral triangle, and a regular hexagon as a constituent unit.

The electrostatic chuck heater according to Aspect 3, wherein a circumscribed circle of the constituent unit of the regular pattern has a diameter of 4 mm to 30 mm.

The electrostatic chuck heater according to Aspect 3 or 4, wherein the constituent unit of the regular pattern is an equilateral triangle.

The electrostatic chuck heater according to Aspect 5, wherein one side of the equilateral triangle is 4 mm to 30 mm.

The electrostatic chuck heater according to Aspect 5 or 6, wherein the plurality of protrusions are arranged to have 3-fold rotational symmetry or 6-fold rotational symmetry about the central axis of each of the lift pin holes.

The electrostatic chuck heater according to any one of Aspects 1 to 7, wherein the distance between central axes of adjacent protrusions is 4 mm to 30 mm.

The electrostatic chuck heater according to any one of Aspects 1 to 8, wherein the protrusions have a height of 0.001 mm to 0.1 mm.

The electrostatic chuck heater according to any one of Aspects 1 to 9, wherein the lift pin holes have a circular shape in a plan view.

The electrostatic chuck heater according to any one of Aspects 1 to 10, wherein the lift pin holes are three or four in number.

The electrostatic chuck heater according to any one of Aspects 1 to 11, wherein the lift pin holes have a diameter of 1 mm to 5 mm.

The electrostatic chuck heater according to any one of Aspects 1 to 12, further comprising the ESC rod and the heater rod in the inner space of the ceramic shaft.

A film deposition apparatus comprising a deposition chamber and the electrostatic chuck heater according to any one of Aspects 1 to 13 located inside the deposition chamber.

DETAILED DESCRIPTION OF THE INVENTION

An electrostatic chuck heater according to the present invention is used in a film deposition apparatus, particularly a film deposition apparatus for semiconductor manufacturing processes. The electrostatic chuck heater functions as a susceptor in the film deposition apparatus, whereby a wafer on which a film is to be deposited is chucked by electrostatic adsorption while being heated. Typical examples of film deposition apparatuses to which the electrostatic chuck heater can be applied include a chemical vapor deposition (CVD) apparatus (for example, thermal CVD apparatus, plasma CVD apparatus, optical CVD apparatus, and MOCVD apparatus) and a physical vapor deposition (PVD) apparatus.

FIGS.1and2illustrate an example of an electrostatic chuck heater. The electrostatic chuck heater10illustrated inFIGS.1and2comprises a ceramic plate12, a ceramic shaft14, a plurality of lift pin holes16, and a plurality of protrusions18. ESC electrodes20and a heater electrode22are built in the ceramic plate12. The ceramic plate12has a first surface12afor bearing a wafer W on which a film is to be deposited and a second surface12bopposite the first surface12a, the ceramic shaft14being attached to the second surface12b. The ceramic shaft14comprises an internal space for accommodating an ESC rod24connected to the ESC electrodes20and heater rods26connected to the heater electrode22. The lift pin holes16are provided so as to penetrate the ceramic plate12from the first surface12ato the second surface12b. The protrusions18are arranged on the first surface12aof the ceramic plate12with equal spacing from each other and with rotational symmetry about the central axis CHof each of the lift pin holes16. In this way, by arranging the plurality of protrusions18on the ceramic plate12with equal spacing from each other and with rotational symmetry about the central axis CHof each of the lift pin holes16, the warpage of the wafer W around the lift pin holes16can be equalized.

That is, as described above, in a conventional susceptor, the protrusions118on the surface of the plate112are generally arranged with equal spacing and with symmetry about the central axis CPof the plate112, as illustrated inFIGS.5and6. In this case, the plurality of protrusions118around the lift pin hole116are arranged asymmetrically or non-uniformly with respect to the lift pin hole116, leading to unstable electrostatic adsorption and increased warpage of the wafer W, which is strongly electrostatically adsorbed to the plate112but supported only by the protrusions118. In particular, since the wafer W does not warp concentrically about the central axis CHof the lift pin hole116, the warpage is non-uniform and may result in the deposition of a film of non-uniform thickness on the wafer W. According to the electrostatic chuck heater10of the present invention, this problem is resolved or lessened. This is because by arranging the plurality of protrusions18with equal spacing from each other and with rotational symmetry about the central axis CHof each of the lift pin holes16as illustrated inFIGS.2and3, the warpage of the wafer W around the lift pin holes16is equalized. That is, the central axis CHof each lift pin hole16is configured to be located at the center of a polygon (an equilateral triangle inFIG.2) connecting the plurality of protrusions18closest to the lift pin hole16, and therefore the warpage of the wafer W is distributed concentrically from the central axis CHof the lift pin hole16, resulting in uniform warpage in the circumferential direction of a concentric circle. Furthermore, since warpage of the wafer W affects the film thickness when depositing a film on the wafer W, by making the warpage of the wafer W around the lift pin holes16uniform, a uniform film thickness can be achieved. That is, by using the electrostatic chuck heater10according to the present invention in a film deposition apparatus, uniformity of thickness can be improved for a film deposited on the wafer W.

The following are considered to be reasons why uniform film thickness can be achieved by making the warpage of the wafer W around the lift pin holes16uniform. First, the lift pin holes16are presupposed to be areas free of the heater electrode22. Consequently, the wafer temperature over the lift pin holes16is lower than the wafer temperature in other areas, and as a result, singularities easily occur in the film thickness during deposition in the areas where the wafer temperature is lower (that is, the film thickness around the lift pin holes16tends to vary specifically in contrast with the stable film thickness in areas distant from the lift pin holes16). Also, it is assumed that the shorter the distance between the wafer W and the ceramic plate12, the greater the heat conduction from ceramic plate12and the higher the temperature of the wafer W. In this regard, if the protrusions18are arranged with rotational asymmetry about the lift pin holes16around the lift pin holes16where singularities easily occur as described above, the distance between the wafer W and the ceramic plate12is not rotationally symmetrical due to warpage and the wafer temperature becomes more uneven, thereby broadening the area of the singularities, resulting in further lowering of the uniformity of the film thickness. If chips are mounted onto the wafer W in which the uniformity of film thickness is lowered in this way, yield may be lowered. In this respect, it is thought that the lift pin holes16and surrounding areas, which have poor film thickness distribution to begin with, are further aggravated by the unequal arrangement of the protrusions18, leading to lower yield. According to the present invention, such defects are eliminated or reduced as described above.

Other than the arrangement of the protrusions18on the first surface12a, the ceramic plate12is not particularly limited and may have a configuration similar to a ceramic plate adopted in a known electrostatic chuck heater. The major portion (namely, the ceramic base) of the ceramic plate12other than the ESC electrodes20and the heater electrode22preferably is composed of aluminum nitride from the standpoint of, among other things, excellent thermal conductivity, high electrical insulation, and thermal expansion characteristics similar to silicon. A preferable shape of the ceramic plate12is a disc shape. However, the plan view shape of the disc-shaped ceramic plate12does not have to be completely circular, and may also be an incomplete circle with a portion missing, like with orientation flat (OF), for example. The size of the ceramic plate12is not particularly limited and may simply be determined appropriately according to the diameter of the wafer W that is expected to be used, but in the case of a circular shape, the diameter is typically 150 mm to 450 mm, such as approximately 300 mm, for example.

The ESC electrodes20and heater electrode22are built into or embedded in the ceramic plate12. The ESC electrodes20are an abbreviation of electrostatic chuck (ESC) electrodes, and are also referred to as electrostatic electrodes. The ESC electrodes20are preferably circular thin-layer electrodes with a slightly smaller diameter than the ceramic plate12, and may be mesh electrodes made of fine metal wires woven into a mesh-like sheet, for example. The ESC electrodes20may also be used as plasma electrodes. That is, by applying high frequencies to the ESC electrodes20, the ESC electrodes20can also be used as plasma electrodes and films can be deposited by the plasma CVD process. The ESC rod24for supplying electric power is connected to the ESC electrodes20, and the ESC rod24is connected to an external power source (not illustrated) through the internal space of the ceramic shaft14. When a voltage is applied by the external power source, the ESC electrodes20chuck the wafer W placed on the first surface12a. The chucking force at this time is the Johnsen-Rahbek force because the aluminum nitride forming the major portion of the ceramic plate12has a volume resistivity from 1×108Ωcm to 1×1013Ωcm. The heater electrode22is not particularly limited and may be, for example, a conductive coil obtained by winding a single wire throughout the entire surface of the ceramic plate12. The heater rods26for supplying electric power are connected to both ends of the heater electrode22, and the heater rods26are connected to a heater power source (not illustrated) through the internal space of the ceramic shaft14. When electric power is supplied from the heater power source, the heater electrode22heats up and heats the wafer W placed on the first surface12a. The heater electrode22is not limited to a coil and may also be ribbons (long thin sheets) or a mesh, for example.

The lift pin holes16are provided penetrating the ceramic plate12from the first surface12ato the second surface12b. As described above, the lift pin holes16are holes used to insert lift pins (not illustrated) for lifting the wafer W from below after deposition. That is, after deposition, the lift pins are passed through the lift pin holes16to stick out from the first surface12aof the ceramic plate12and lift up the wafer W, thereby allowing for easy removal of the wafer W from the electrostatic chuck heater10.

The plan view shape of the lift pin holes16may be any shape, such as circular or polygonal, but preferably circular. The lift pin holes16provided in the ceramic plate12are preferably three or four in number, more preferably three. By having a small number of holes in this way, it is possible to secure a large effective area on the ceramic plate12while also ensuring enough fulcrums for lifting the wafer W with the lift pins (not illustrated). The diameter of the lift pin holes16is not particularly limited, but is preferably 1 mm to 5 mm, more preferably 2 mm to 4 mm, even more preferably 2 mm to 3 mm.

The protrusions18are for contacting the bottom surface of the wafer W and supporting the wafer W, and are arranged on the first surface12aof the ceramic plate12with equal spacing from each other and with rotational symmetry about the central axis CHof each of the lift pin holes16. Therefore, unlike the layout typically adopted in the technology of the related art (seeFIG.5, for example), the protrusions18may be arranged asymmetrically about the central axis CPof the ceramic plate12. The shape of the individual protrusions18is not particularly limited, but is preferably cylindrical. The diameter of the individual protrusions18is not particularly limited, but is preferably 0.1 mm to 8 mm, more preferably 0.5 mm to 5 mm, even more preferably 0.5 mm to 4 mm, especially preferably 0.70 mm to 2.54 mm. The protrusions18preferably are formed as one with the ceramic plate12by an embossing or other process. Consequently, the protrusions18also are preferably composed of aluminum nitride, similarly to the ceramic plate12. The height of the protrusions18is not particularly limited, but is preferably 0.001 mm to 0.1 mm, more preferably 0.005 mm to 0.08 mm, even more preferably 0.01 mm to 0.05 mm, especially preferably 0.01 mm to 0.03 mm. The distance between the central axes of adjacent protrusions18is preferably 4 mm to 30 mm, more preferably 5 mm to 26 mm, even more preferably 7 mm to 26 mm, especially preferably 7 mm to 15 mm.

The plurality of protrusions18preferably are arranged according to a regular pattern (or so as to form such a regular pattern) with one selected from the group consisting of a circle, a square, an equilateral triangle, and a regular hexagon as a constituent unit. That is, the plurality of protrusions18preferably are arranged so that the centers are located on virtual lines (for example, at the vertices in the case of a polygonal shape) that form a regular pattern comprising a repeating plurality of the above constituent unit. In other words, a virtual figure drawn by connecting the centers of adjacent protrusions18preferably forms a regular pattern in which one selected from the group consisting of a circle, a square, an equilateral triangle, and a regular hexagon serves as the constituent unit. For example, in the electrostatic chuck heater10illustrated inFIG.2, the virtual figure drawn by connecting the centers of adjacent protrusions18is an equilateral triangle. In the electrostatic chuck heater10′ illustrated inFIG.4, the virtual figure drawn by connecting the centers of adjacent protrusions18is a regular hexagon. In particular, in terms of the ease of arranging the protrusions18with equal spacing from each other across the entire first surface12a, the constituent unit of the regular pattern is more preferably a square, an equilateral triangle, or a regular hexagon, even more preferably an equilateral triangle or a regular hexagon, especially preferably an equilateral triangle. In this sense, it can be said that the protrusions18preferably are arranged to have 3-fold rotational symmetry as illustrated inFIG.2, or 6-fold rotational symmetry as in the electrostatic chuck heater10′ illustrated inFIG.4, about the central axis CHof each of the lift pin holes16. The size of the constituent unit of the regular pattern is not particularly limited, but the circumscribed circle of the constituent unit has a diameter that is preferably 4 mm to 30 mm, more preferably 5 mm to 26 mm, even more preferably 7 mm to 26 mm, especially preferably 7 mm to 15 mm. In the case in which the constituent unit of the regular pattern is an equilateral triangle, one side of the equilateral triangle is preferably 4 mm to 30 mm, more preferably 5 mm to 26 mm, even more preferably 7 mm to 26 mm, especially preferably 7 mm to 15 mm.

The ceramic shaft14is a hollow shaft attached to the second surface12bof the ceramic plate12, and may have a configuration similar to a ceramic shaft adopted in a known electrostatic chuck heater or ceramic heater. The ceramic shaft14includes an internal space for accommodating the ESC rod24and the heater rods26. The ceramic shaft14preferably is composed of a ceramic material similar to the ceramic plate12. Consequently, the ceramic shaft14preferably is composed of aluminum nitride. The upper edge of the ceramic shaft14preferably is bonded to the second surface12bof the ceramic plate12by solid-state bonding or diffusion bonding. The outer diameter of the ceramic shaft14is not particularly limited, but is approximately 40 mm, for example. The inner diameter of the ceramic shaft14(the diameter of the inner space) is not particularly limited, but is approximately 36 mm, for example.

The electrostatic chuck heater10may further comprise the ESC rod24and the heater rods26in the inner space of the ceramic shaft14. One end of the ESC rod24is connected to the ESC electrodes20, and the other end is connected to the external power source (not illustrated). Similarly, one end of the heater rods26is connected to the heater electrode22, and the other end is connected to the heater power source (not illustrated). With this configuration, electric power supply paths to the ESC electrodes20and the heater electrode22are secured.

As described above, the electrostatic chuck heater according to the present invention is used in a film deposition apparatus, particularly a film deposition apparatus for semiconductor manufacturing processes. Therefore, according to another aspect of the present invention, there is provided a film deposition apparatus comprising a deposition chamber (not illustrated) and the electrostatic chuck heater10set up inside the deposition chamber. As described above, examples of such a film deposition apparatus include a chemical vapor deposition (CVD) apparatus (for example, thermal CVD apparatus, plasma CVD apparatus, optical CVD apparatus, and MOCVD apparatus) and a physical vapor deposition (PVD) apparatus.

A method of using the electrostatic chuck heater10in the film deposition apparatus is as follows. The electrostatic chuck heater10is disposed inside the chamber of the film deposition apparatus, and the wafer W is placed on the protrusions18of the ceramic plate12. Thereafter, a voltage is applied to the ESC electrodes20, thereby chucking the wafer W with the Johnsen-Rahbek force. Additionally, the temperature of the ceramic plate12is calculated on the basis of a detection signal from a thermocouple (not illustrated), and the voltage and current applied to the heater electrode22are controlled so that the temperature is a target temperature. In such a state, a film may simply be deposited on the upper surface of the wafer W by CVD or the like. After deposition, the lift pins (not illustrated) are passed through the lift pin holes16to stick out from the first surface12aof the ceramic plate12and lift up the wafer W, thereby assisting with the removal of the wafer W from the electrostatic chuck heater10.