Patent Application
20090304975
The present application claims priority under 35 U.S.C. §119 of Japanese Application No. 2008-148566 filed on Jun. 5, 2008, the disclosure of which is expressly incorporated by reference herein in its entirety.
1. Field of the Invention
The present invention relates to an epitaxial silicon wafer having an epitaxial film only on the front side (one side) and a method for producing the epitaxial silicon wafer.
2. Description of the Related Art
Silicon wafers are produced in various steps at which first a single crystal ingot (silicon single crystal) is pulled up by the CZ (Czochralski) method and the ingot is subjected to slicing, beveling, lapping, etching, mirror polishing and washing, for example. However, it is anticipated that as wafers become progressively larger in size, in association with production of the single crystal ingot and silicon wafers, there may be a greater difficulty in producing a defect-free crystal (COP-free crystal) due to technical problems of pulling up the ingot, yields and others.
Therefore, in order to make the front side of a wafer on which a device is formed defect-free, hereinafter, such a method will become predominant that the vapor phase epitaxial method disclosed in Japanese Unexamined Patent Publication No. H06-112120, for example, is used to grow an epitaxial film on the front side (mirror surface) of a large-sized wafer which is, for example, 450 mm or more in diameter.
However, where a bulk wafer (silicon wafer) is different in material from an epitaxial film or where a dopant contained in the bulk wafer is different in concentration from that contained in the epitaxial film, an epitaxial silicon wafer will have the following problems. More specifically, since atoms forming the bulk wafer are different in lattice constant from atoms forming the epitaxial film, it is more likely that the silicon wafer and also the epitaxial silicon wafer will warp. These wafers, examples of which are described in Japanese Unexamined Patent Publication No. H06-112120, will warp more greatly as they are increased in size.
Therefore, there is presented an idea that, as a silicon wafer adopted is, for example, a wafer obtained from a highly resistant boron-doped single crystal ingot (0.1 Ω·cm or more in specific resistance) in which the boron concentration is less than 2.7×1017 atoms/cm3. Thereby, stress resulting from a difference in atomic radius between a bulk wafer and an epitaxial film is decreased, and when the epitaxial film is grown on the front side of the wafer, it is less likely that the wafer warps greatly. Further, since the epitaxial film is grown on a wafer lower in boron concentration, a dopant is dispersed outwardly from the back side of the wafer, thus suppressing the occurrence of auto-doping phenomena where the dopant penetrates the epitaxial film on a device forming face. Still further, it is known that boron inside the wafer becomes a seed growth of intrinsic gettering (IG). However, as compared with a wafer higher in boron concentration, a wafer lower in boron concentration is low in intrinsic gettering performance.
Thus, as a result of intensive research, the inventor has found that in production of an epitaxial silicon wafer, some intrinsic gettering functions may be imparted to a silicon wafer which is 450 mm or more in diameter and 0.1 Ω·cm or more (high resistance) in specific resistance. The inventor has also found that even a wafer, the one side of which is epitaxially grown, is less likely to warp greatly and provided with a high intrinsic gettering performance and has thus accomplished the present invention.
A non-limiting feature of the present invention is to provide an epitaxial silicon wafer in which on growing an epitaxial film only on the front side of a large-sized wafer which is 450 mm or more in diameter, the wafer can be decreased in warpage to obtain a high intrinsic gettering performance and a method for producing the epitaxial silicon wafer.
A first non-limiting aspect of the invention provides an epitaxial silicon wafer in which an epitaxial film is grown only on the front side of a silicon wafer obtained by processing a silicon single crystal pulled up by the CZ method which is 450 mm or more in diameter and 0.1 Ω·cm or more in specific resistance, and the epitaxial silicon wafer has intrinsic gettering functions.
According to this aspect of the invention, intrinsic gettering functions are imparted to a silicon wafer at a high resistance of 0.1 Ω·cm or more in specific resistance and 450 mm or more in diameter, thereby even a large-sized wafer which is 450 mm or more in diameter is less likely to warp greatly after the growth of an epitaxial film and is able to obtain a high intrinsic gettering performance.
The silicon wafer may be available in any size, as long as the diameter is 450 mm or more. Single crystal silicon which is the same as the wafer may be adopted as a material of the epitaxial film. Also, acceptable is a material different from the wafer, for example, gallium or arsenic. The thickness of the epitaxial film is, for example, from several μm to 150 μm for high polar devices or power devices and 10 μm or less for MOS devices.
Any epitaxial method may be adopted, for example, a vapor phase epitaxial method, a liquid phase epitaxial method or a solid phase epitaxial method. Of these methods, the vapor phase epitaxial method includes, for example, a normal-pressure vapor phase epitaxial method, a reduced-pressure vapor phase epitaxial method and an organic-metal vapor phase epitaxial method. In the vapor phase epitaxial method, for example, an epitaxial silicon wafer is kept horizontal (with the front side and the back side kept parallel to each other) and accommodated at a wafer accommodating part. Used is a susceptor which is circular in a planar view and able to place one sheet of the wafer. The vapor phase epitaxial method may include homoepitaxy in which the same material as a silicon wafer is epitaxially grown and heteroepitaxy in which a material different from the wafer such as (GaAs) is epitaxially grown.
A vapor phase epitaxial growth apparatus may be structured in any way as long as it is a one-side vapor phase epitaxial growth apparatus in which an epitaxial film can be grown only on one side of a silicon wafer. The vapor phase epitaxial growth apparatus may include a sheet type, or a pancake type, a barrel type, a hot-wall type and a cluster type capable of processing a plurality of silicon wafers at the same time.
A method for imparting intrinsic gettering functions to a silicon wafer includes, for example, doping of a nitrogen element in a range of 1×1013 to 1×1015 atoms/cm3 to a melt (silicon) and doping of a carbon element in a range of 1×1015 to 1×1017 atoms/cm3 to a melt.
The invention described in accordance with a second non-limiting aspect further provides an epitaxial silicon wafer in which the silicon wafer contains at least one of a nitrogen element in a range of 1×1013 to 1×1015 atoms/cm3 and a carbon element in a range of 1×1015 to 1×1017 atoms/cm3.
According to this second aspect of the invention, a silicon wafer contains any one of a nitrogen element in a range of 1×1013 to 1×1015 atoms/cm3, a carbon element in a range of 1×1015 to 1×1017 atoms/cm3 and both the nitrogen element and the carbon element. Thereby, the wafer is less likely to warp greatly after the growth of an epitaxial film. As a result, it is possible to decrease the warpage of the wafer and also obtain a high intrinsic gettering performance.
The invention described in accordance with a third non-limiting aspect provides a method for producing an epitaxial silicon wafer in which an epitaxial film is grown only on the front side of a silicon wafer obtained from a silicon single crystal pulled up from a melt inside a crucible by the CZ method which is 0.1 Ω·cm or more in specific resistance and 450 mm or more in diameter, and the method for producing the epitaxial silicon wafer in which intrinsic gettering functions are imparted to the silicon wafer by doping at least one of (1) a nitrogen element in a range of 1×1013 to 1×1015 atoms/cm3 to the melt and (2) a carbon element in a range of 1×1015 to 1×1017 atoms/cm3 to the melt.
According to the invention described in accordance with this third aspect, intrinsic gettering functions are imparted to a high resistance large-sized silicon wafer which is 450 mm or more in diameter and 0.1 Ω·cm or more in specific resistance. More specifically, performed is at least one of doping of a nitrogen element in a range of 1×1013 to 1×1015 atoms/cm3 to a silicon melt, doping of a carbon element in a range of 1×1015 to 1×1017 atoms/cm3 to the melt and doping of both the nitrogen element and the carbon element. Thereby, the wafer is less likely to warp greatly after the growth of the epitaxial film. As a result, it is possible to decrease the warpage of the wafer and obtain a high intrinsic gettering performance.
As a method for increasing the specific resistance of a silicon wafer, adopted is a method for adding a dopant such as boron or phosphorus to a silicon melt in a crucible when an ingot is pulled up. Other dopants such as arsenic and antimony may be added.
When the nitrogen element is doped to the melt at less than 1×1013 atoms/cm3, there is caused a drawback that the gettering performance is insufficient due to insufficient internal precipitation. Further, when in excess of 1×1015 atoms/cm3, there a drawback in that an epitaxial film is broken through due to excessive internal precipitation.
When the carbon element is doped to the melt at less than 1×1015 atoms/cm3, there is found a drawback that the gettering performance is insufficient. Further, when in excess of 1×1017 atoms/cm3, there a drawback in that the quality of the epitaxial film is deteriorated.
The invention described in accordance with a fourth non-limiting aspect further provides a method for producing the epitaxial silicon wafer in which after growth of the epitaxial film, the front side of the epitaxial film and the back side of the silicon wafer are polished at the same time.
According to the invention described in the fourth aspect, after growth of the epitaxial film, the front side of the epitaxial film and the back side of the silicon wafer are polished at the same time (i.e., they are polished generally simultaneously), by which both sides of the epitaxial silicon wafer can be increased in planarization. It is also possible to reduce the time necessary in the step of polishing the epitaxial film on both sides of the wafer and to increase productivity.
As a method for polishing both the front side and the back side of an epitaxial silicon wafer, provided is a sheet-type double side polishing method in which an epitaxial silicon wafer is polished on the front side and the back side at the same time between a lower surface plate having a polishing cloth stretched out on the upper face and an upper surface plate having a polishing cloth stretched out on the lower face. Further, there may be provided a double side polishing method in which no sun gear is used and a carrier plate having an epitaxial silicon wafer accommodated at a wafer retaining hole is allowed to perform circular movements not in conjunction with rotation on its own axis between a polishing cloth-equipped lower surface plate and a polishing cloth-equipped upper surface plate.
According to the inventions described in accordance with the first and third non-limiting aspects, intrinsic gettering functions are imparted to a large-sized and high-resistant silicon wafer which is 450 mm or more in diameter and 0.1 Ω·cm or more in specific resistance, thereby the wafer is less likely to warp greatly after the growth of an epitaxial film. As a result, it is possible to decrease the warpage of the epitaxial silicon wafer and also obtain a high intrinsic gettering performance.
In particular, according to the invention described in accordance with the fourth non-limiting aspect, after the growth of the epitaxial film, the front side of the epitaxial film and the back side of the silicon wafer are polished at the same time. Thereby, the epitaxial silicon wafer can be increased in planarization on both sides, and also the time necessary in the step of polishing the epitaxial film on both sides of the wafer can be reduced to increase the productivity.
The present invention is further described in the detailed description which follows, in reference to the noted plurality of drawings by way of non-limiting examples of exemplary embodiments of the present invention, in which like reference numerals represent similar parts throughout the several views of the drawings, and wherein:
The particulars shown herein are by way of example and for purposes of illustrative discussion of the embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the present invention. In this regard, no attempt is made to show structural details of the present invention in more detail than is necessary for the fundamental understanding of the present invention, the description is taken with the drawings making apparent to those skilled in the art how the forms of the present invention may be embodied in practice. Hereinafter, a description will be given specifically for the example of the present invention.
Referring now to the drawings wherein like characters represent like elements, in
Hereinafter, a description will be given for a method for producing the epitaxial silicon wafer of the example 1 in the present invention by referring to the flow chart of
As illustrated in the flow chart of
Next, the epitaxial film 12 is grown on the front side of the silicon wafer 11 by a vapor phase epitaxial method (S106). Thereafter, the front side of the epitaxial film 12 and the back side of the silicon wafer 11 are polished at the same time (S107). Thereby, produced is the epitaxial silicon wafer 10 (S108).
A description will be given specifically for individual steps.
In the step of pulling up the ingot (S100), a crystal growth apparatus shown in
In
A thermal resistance type heater 51 is arranged outside the crucible 44 so as to be concentric with respect to the wall of the crucible 44. A cylindrical thermal insulation tube 52 is arranged outside the heater 51 along the inner face of the circumferential wall of the main chamber 42. A circular thermal insulation plate 53 is arranged on the bottom face of the main chamber 42.
A pulling-up shaft 55 capable of rotating and moving up and down on the same shaft with respect to the supporting shaft 45 (a wire will do) is hung through the pull chamber 43 on the center line of the crucible 44. A seed crystal C is loaded at the lower end of the pulling-up shaft 55.
Next, a description will be given specifically for a method for growing a silicon single crystal by using the crystal growth apparatus 40.
A silicon raw material for crystallization and boron for an impurity are fed into the crucible 44 so as to give 1.0 Ω·cm in specific resistance of the silicon single crystal S. Pressure inside the chamber 41 is reduced to 25 Torr, and argon gas which contains nitrogen gas in 100 L/min is introduced thereinto. Next, a resultant inside the crucible 44 is dissolved by the heater 51 to form a melt 56 inside the crucible 44.
Further, the seed crystal C loaded at the lower end of the pulling-up shaft 55 is submerged into the melt 56, and the pulling-up shaft 55 is pulled up axially while the crucible 44 and the pulling-up shaft 55 are allowed to rotate in the reverse direction with respect to one another, thus growing the silicon single crystal S below the seed crystal C. Thereby, obtained is a silicon single crystal (ingot) S which is 1×1014 atoms/cm3 in nitrogen element and 1.0 Ω·cm in specific resistance by boron dope.
In the slicing step (S101), a wire saw in which a wire is wound around three group rollers arranged in a triangular shape when viewed from the side is used. The wire saw slices many silicon wafers 11 from the silicon single crystal S.
In the subsequent beveling step (S102), a beveling grind stone in rotation is pressed against an outer circumference of the silicon wafer 11 to effect beveling.
In the lapping step (S103), a double side lapping machine is used to lap both sides of the silicon wafer 11 at the same time. More specifically, both sides of the silicon wafer 11 are lapped between the upper and the lower surface plates rotating at a predetermined speed.
In the etching step (S104), the silicon wafer 11 after lapping is submerged into an acid etching solution pooled in an etching tank to effect etching, thereby removing damage resulting from the beveling and the lapping.
In the double side polishing step (S105), a double side polishing machine free of a sun gear is used to mirror-polish the both sides of the silicon wafer 11 at the same time.
Hereinafter, a description will be given specifically for a structure of the double side polishing machine structured so as to be free of a sun gear by referring to
As shown in
The carrier circular movement mechanism 19 is provided with an annular carrier holder 20 for holding the carrier plate 110 from outside. The carrier circular movement mechanism 19 is connected to the carrier holder 20 via a connecting structure.
Four bearing units 20b projected outward at every 90 degrees are placed on an outer circumference of the carrier holder 20. An eccentric shaft 24a installed in a projecting manner at an eccentric position of the upper face of an eccentric arm 24 formed in a small-sized circular disk shape is inserted into each of the bearing units 20b. Further, a rotating shaft 24b is installed vertically at the center of the lower face of each of these four eccentric arms 24. These rotating shafts 24b are inserted into four bearing units 25a which are placed at every 90 degrees on an annular base 25, with the respective leading ends projected downward. Sprockets 26 are firmly fixed to the respective leading ends of the rotating shafts 24b projected below. A timing chain 27 is hung over on each of the sprockets 26 continuously in a horizontal state. These four sprockets 26 and the timing chain 27 cause the four rotating shafts 24b to rotate at the same time so that the four eccentric arms 24 move circularly in synchronization.
Of these four rotating shafts 24b, one of them is formed in a longer shape, and the leading end thereof projects further below than the sprocket 26, at which a gear 28 for power transmission is firmly fixed. The gear 28 is meshed with a large-sized driving gear 30 firmly fixed on an output shaft of a circular movement motor 29 extending upward.
Therefore, on actuation of the circular movement motor 29, the rotating force thereof will be transmitted to the timing chain 27 via the gears 30, 28 and the sprocket 26 firmly fixed to the longer rotating shaft 24b. The timing chain 27 rotates circumferentially, by which the four eccentric arms 24 rotate at the center of the rotating shaft 24b within a horizontal plane in synchronization via the other three sprockets 26. Thereby, the carrier holder 20 connected together with each of the eccentric shafts 24a and a carrier plate 110 held by the holder 20 perform circular movements without rotation on its own axis within a horizontal plane parallel with the plate 110. More specifically, the carrier plate 110 rotates, with such a state kept that it is eccentric only by a distance L from an axis line e between the upper surface plate 120 and the lower surface plate 130. The polishing cloth 15 is stretched out on each face opposing the surface plates 120, 130. The distance L is equal to a distance between the eccentric shaft 24a and the rotating shaft 24b. The circular movements without rotation on its own axis allow all points on the carrier plate 110 to exhibit a small-circular locus equal in dimension. Thereby, the silicon wafer 11 accommodated at a wafer accommodating portion 11a formed on the carrier plate 110 is polished on the both sides.
Next, a description will be given specifically for the epitaxial growth step (S106) by using a sheet-type vapor phase epitaxial growth apparatus by referring to
As shown in
A recessed counterbore (wafer accommodating portion) 62 which accommodates the silicon wafer 11 in a horizontally kept state (a state in which the front side and the back side are in a horizontal position) is formed at an inner circumference on the upper face of the susceptor 61. The counterbore 62 is made up of a circumferential wall 62a, a 6 mm-wide step 62b which is annular in a planar view and a bottom plate (bottom wall face of the counterbore) 62c.
A gas supply port which allows a predetermined carrier gas (H2 gas) and predetermined source gas (SiHCl3 gas) to flow parallel with the front side of the wafer at an upper space hollow of the chamber is placed at one side portion of the chamber. Further, a gas discharge port is formed on the other side portion of the chamber.
On epitaxial growth, the silicon wafer 11 is laid laterally on the counterbore 62, with the front side and the back side of a wafer kept horizontal. Next, an epitaxial film 12 is grown on the front side of the silicon wafer 11. More specifically, the carrier gas and the source gas are introduced into a reaction chamber through corresponding gas supply ports. The pressure inside the chamber is kept at 100±20 KPa and silicon formed by thermal decomposition or reduction of the source gas is deposited at the reaction speed of 3.5 to 4.5 μM/minute on the silicon wafer 11 heated at high temperatures of 1000° C. to 1150° C. Thereby, the epitaxial film 12 which is approximately 10 μm in thickness of the silicon single crystal is formed on the front side of the silicon wafer 11. Thus, produced is the epitaxial silicon wafer 10.
In the subsequent simultaneous polishing step of the epitaxial silicon wafer 10 (S107), a double side polishing machine structured so as to be free of a sun gear which is used in the double side polishing sep (S105) is used to mirror-polish the front side of the epitaxial film 12 and the back side of the silicon wafer 11 at the same time. Thus, produced is the epitaxial silicon wafer 10 (S108).
As described so far, intrinsic gettering functions are imparted to the silicon wafer 11 which is 0.1 Ω·cm in specific resistance and 450 mm in diameter. Therefore, even a large-sized silicon wafer 11 which is 450 mm in diameter is decreased in stress due to a difference in atomic radius between the bulk wafer 11 and the epitaxial film 12 on growth of the epitaxial film 12. Thereby, even when the epitaxial film 12 is grown only on the front side of the wafer on which a device is formed, it is less likely that the silicon wafer 11 and also the epitaxial silicon wafer 10 will warp greatly. Thus, it is possible to decrease the warpage of the epitaxial silicon wafer 10. Further, since the epitaxial film 12 is grown on the silicon wafer 11 lower in boron concentration, a dopant is dispersed outwardly from the back side of the wafer, thus suppressing the occurrence of auto-doping phenomena where the dopant penetrates the epitaxial film 12 on which a device is formed.
A nitrogen element at 1×1014 atoms/cm3 has been doped to the silicon wafer 11. As a result, although the silicon wafer 11 is a high resistant wafer lower in boron concentration, it is provided with a high intrinsic gettering performance.
Further, after the epitaxial growth step, a double side polishing machine structured so as to be free of a sun gear is used to polish the front side of the epitaxial film 12 and the back side of the silicon wafer 11 at the same time. Thereby, the epitaxial silicon wafer 10 can be increased in planarization. Further, the time necessary for the polishing can be reduced to increase productivity.
It is noted that the front side of the epitaxial film 12 and the back side of the silicon wafer 11 are not polished at the same time but may be polished by one side separately.
In the example 1, as a method for imparting intrinsic gettering functions to the silicon wafer 11, there is adopted a method in which the nitrogen element at 1×1014 atoms/cm3 is doped to the melt 56. However, in place of this method, there may be adopted a method in which carbon powder may be added so as to give 1×1017 atoms/cm3 to the melt 56. Further, both the nitrogen dope and the carbon dope may be performed.
It is noted that the foregoing examples have been provided merely for the purpose of explanation and are in no way to be construed as limiting of the present invention. While the present invention has been described with reference to exemplary embodiments, it is understood that the words which have been used herein are words of description and illustration, rather than words of limitation. Changes may be made, within the purview of the appended claims, as presently stated and as amended, without departing from the scope and spirit of the present invention in its aspects. Although the present invention has been described herein with reference to particular structures, materials and embodiments, the present invention is not intended to be limited to the particulars disclosed herein; rather, the present invention extends to all functionally equivalent structures, methods and uses, such as are within the scope of the appended claims.
The present invention is not limited to the above described embodiments, and various variations and modifications may be possible without departing from the scope of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2008-148566 | Jun 2008 | JP | national |
