WO2010044279A1 - ゲッタリングシンクを有する固体撮像素子用エピタキシャル基板、半導体デバイス、裏面照射型固体撮像素子およびそれらの製造方法 - Google Patents
ゲッタリングシンクを有する固体撮像素子用エピタキシャル基板、半導体デバイス、裏面照射型固体撮像素子およびそれらの製造方法 Download PDFInfo
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- WO2010044279A1 WO2010044279A1 PCT/JP2009/005428 JP2009005428W WO2010044279A1 WO 2010044279 A1 WO2010044279 A1 WO 2010044279A1 JP 2009005428 W JP2009005428 W JP 2009005428W WO 2010044279 A1 WO2010044279 A1 WO 2010044279A1
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- laser beam
- gettering sink
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- epitaxial
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Classifications
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
- H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
- H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic Table or AIIIBV compounds with or without impurities, e.g. doping materials
- H01L21/26—Bombardment with radiation
- H01L21/263—Bombardment with radiation with high-energy radiation
- H01L21/268—Bombardment with radiation with high-energy radiation using electromagnetic radiation, e.g. laser radiation
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
- H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
- H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic Table or AIIIBV compounds with or without impurities, e.g. doping materials
- H01L21/30—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26
- H01L21/322—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26 to modify their internal properties, e.g. to produce internal imperfections
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L27/00—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
- H01L27/14—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation
- H01L27/144—Devices controlled by radiation
- H01L27/146—Imager structures
- H01L27/14601—Structural or functional details thereof
- H01L27/14603—Special geometry or disposition of pixel-elements, address-lines or gate-electrodes
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L27/00—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
- H01L27/14—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation
- H01L27/144—Devices controlled by radiation
- H01L27/146—Imager structures
- H01L27/14683—Processes or apparatus peculiar to the manufacture or treatment of these devices or parts thereof
- H01L27/14698—Post-treatment for the devices, e.g. annealing, impurity-gettering, shor-circuit elimination, recrystallisation
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- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10S117/00—Single-crystal, oriented-crystal, and epitaxy growth processes; non-coating apparatus therefor
- Y10S117/903—Dendrite or web or cage technique
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Definitions
- the present invention relates to an epitaxial substrate for a solid-state imaging device, a semiconductor device, a back-illuminated solid-state imaging device, and a method for manufacturing the same, and relates to a technique capable of easily forming a gettering sink in a short time.
- This application is filed in Japan on October 16, 2008, Japanese Patent Application Nos. 2008-267341, 2008-267342, and 2008-267343, and was filed in Japan on March 23, 2009. Claim priority based on each of Japanese Patent Application No. 2009-069601, the contents of which are incorporated herein.
- a solid-state imaging device is manufactured, for example, by using an epitaxial substrate obtained by growing an epitaxial layer on one surface of a semiconductor substrate and forming a circuit made of a photodiode or the like on the epitaxial layer.
- the dark leakage current of the photodiode is a problem.
- the cause of dark leakage current is considered to be heavy metal contamination of the substrate (wafer) in the manufacturing process.
- a heavy metal gettering sink is formed inside or on the back surface of the semiconductor wafer, and the heavy metal is collected in the gettering sink, thereby reducing the heavy metal concentration in the photodiode formation portion. Things have been done.
- a semiconductor memory is manufactured by forming a device on one surface of a silicon substrate (silicon wafer) made of, for example, a silicon single crystal.
- a silicon substrate silicon wafer
- the back surface side of the silicon substrate is shaved to reduce the thickness to about 50 ⁇ m, for example.
- a gettering method is generally known as a method for removing heavy metals from a silicon substrate.
- a heavy metal capture region called a gettering site is formed on a silicon substrate, and the heavy metal is collected at the gettering site by annealing or the like, thereby reducing the heavy metal in the element formation region.
- an IG (intrinsic gettering) method for forming an oxygen precipitate on the silicon substrate for example, Patent Document 1
- Patent Document 2 An EG (exotic tricktering) method (for example, Patent Document 2) that forms a gettering site is known.
- Non-Patent Document 1 A method is also known in which a heat treatment is performed on a semiconductor substrate to form an oxygen precipitation portion inside the substrate, and the oxygen precipitation portion serves as a gettering sink (for example, Non-Patent Document 1). M. Sano, S. Sumita, T. Shigematsu and N. Fujino, Semiconductor Silicon 1994.eds. HRHuff et al. (Electrochem. Soc., Pennington 1994)
- the IG method is used in a pre-process for forming a device on a silicon substrate, and requires a heat treatment temperature of 600 ° C. or higher in order to remove heavy metals diffused in the silicon substrate.
- the heat treatment temperature performed after the device is formed on the silicon substrate is almost 400 ° C. or less, and there is a problem that the heavy metal mixed in the thinning process after the device formation cannot be sufficiently captured.
- the thickness of semiconductor devices is required to be 50 to 40 ⁇ m or less, and further about 30 ⁇ m. At such a level of thickness, most of the gettering sink formed on the silicon substrate is scraped off in the thinning process, so that sufficient gettering capability cannot be obtained.
- a large-diameter substrate such as a 300 mm wafer, which is becoming the mainstream in recent years, is polished on both sides. It is difficult to form itself.
- An epitaxial substrate for a solid-state imaging device in which a gettering sink can be easily formed in a short time and there is no fear of heavy metal contamination when the gettering sink is formed.
- a manufacturing method is provided.
- one embodiment of the present invention provides an epitaxial substrate for a solid-state imaging device that can be manufactured at low cost with little heavy metal contamination.
- one embodiment of the present invention provides a method for manufacturing a semiconductor device that can easily and reliably remove a contaminated heavy metal from a device formation region after the formation of the semiconductor device.
- one embodiment of the present invention provides a semiconductor device in which there is no fear of characteristic deterioration due to heavy metal even when the thickness is reduced.
- a method of manufacturing an epitaxial substrate for a solid-state imaging device a step of growing an epitaxial layer on one surface of a semiconductor substrate to form an epitaxial substrate, and a laser through a condensing unit toward the epitaxial substrate.
- a gettering sink in which a multiphoton absorption process is generated in the minute region by changing the crystal structure of the minute region by injecting a beam and condensing the laser beam on an arbitrary minute region of the semiconductor substrate.
- a step of annealing the epitaxial substrate at a predetermined temperature to capture the heavy metal in the gettering sink a predetermined temperature to capture the heavy metal in the gettering sink.
- the laser beam has a wavelength range that can be transmitted through the epitaxial substrate, and the condensing unit condenses the laser beam at an arbitrary position in the thickness direction of the semiconductor substrate.
- the laser beam is preferably an ultrashort pulse laser beam having a pulse width of 1.0 ⁇ 10 ⁇ 15 to 1.0 ⁇ 10 ⁇ 8 seconds and a wavelength of 300 to 1200 nm.
- the semiconductor substrate is made of single crystal silicon
- the gettering sink includes amorphous silicon. It is preferable that the gettering sink is formed at a position overlapping the formation area of the solid-state imaging device.
- the epitaxial substrate for a solid-state imaging device is an epitaxial substrate for a solid-state imaging device manufactured by the method for manufacturing an epitaxial substrate for a solid-state imaging device, and the gettering sink is an embedded type that forms at least the solid-state imaging device. In a region overlapping with the photodiode formation position, it is provided with a size in the range of 50 to 150 ⁇ m in diameter and 10 to 150 ⁇ m in thickness.
- the gettering sink is preferably formed in a density range of 1.0 ⁇ 10 5 to 1.0 ⁇ 10 7 pieces / cm 2 .
- a laser beam is incident on the epitaxial substrate through a condensing unit, and the laser beam is condensed on an arbitrary minute region inside the semiconductor substrate.
- a multiphoton absorption process is generated in a minute region inside the semiconductor substrate, and a gettering sink in which only the crystal structure of the minute region is changed can be formed easily and in a short time.
- an epitaxial substrate for a solid-state imaging device of the present invention capable of realizing a solid-state imaging device having excellent imaging characteristics with excellent heavy metal gettering capability and low leakage current during darkness. Can provide.
- the method of manufacturing a semiconductor device includes a step of forming an insulating film on one surface of a semiconductor substrate, and a laser beam incident from the other surface of the semiconductor substrate via a light collecting unit, so that an arbitrary minute region of the semiconductor substrate is formed. Condensing the laser beam to form a multi-photon absorption process in the minute region and forming a gettering sink in which the crystal structure of the minute region is changed, and the semiconductor substrate at a predetermined temperature. Annealing and capturing the heavy metal in the gettering sink.
- the laser beam has a wavelength range that can be transmitted through the semiconductor substrate, and the condensing unit condenses the laser beam at an arbitrary position in the thickness direction of the semiconductor substrate.
- the laser beam is preferably an ultrashort pulse laser beam having a pulse width of 1.0 ⁇ 10 ⁇ 15 to 1.0 ⁇ 10 ⁇ 8 seconds and a wavelength of 300 to 1200 nm.
- the semiconductor substrate is made of single crystal silicon
- the gettering sink includes at least part of amorphous silicon.
- the gettering sink is preferably formed at least in a position overlapping with a device formation region.
- the semiconductor device of the present invention is manufactured by the method for manufacturing a semiconductor device.
- the gettering sink is preferably formed in a density range of 1.0 ⁇ 10 5 to 1.0 ⁇ 10 6 pieces / cm 2 .
- a laser beam is incident on a semiconductor substrate through a condensing unit, and the laser beam is focused on an arbitrary minute region inside the semiconductor substrate, thereby providing a semiconductor substrate. It is possible to easily and quickly form a gettering sink in which a multiphoton absorption process is generated in a minute region inside the substrate and only the crystal structure of the minute region is changed.
- the semiconductor device of the present invention it is possible to provide a semiconductor device that has excellent characteristics of gettering heavy metals and has little leakage current even if the thickness is reduced.
- the method for manufacturing a backside illumination type solid-state imaging device includes a step of growing an epitaxial layer on one surface of a semiconductor substrate to form an epitaxial substrate, and a laser beam incident on the epitaxial substrate via a condensing means.
- the laser beam has a wavelength range that can be transmitted through the epitaxial substrate, and the condensing unit condenses the laser beam at an arbitrary position in the thickness direction of the semiconductor substrate.
- the laser beam is preferably an ultrashort pulse laser beam having a pulse width of 1.0 ⁇ 10 ⁇ 15 to 1.0 ⁇ 10 ⁇ 8 seconds and a wavelength of 300 to 1200 nm.
- the semiconductor substrate is preferably made of single crystal silicon, and the gettering sink preferably contains amorphous silicon.
- the gettering sink is preferably formed at least in a position overlapping with a formation region of the photodiode. It is preferable that a buried oxide film having an SOI structure is further formed between the gettering sink and the epitaxial layer.
- An epitaxial substrate for a solid-state imaging device includes a semiconductor substrate, an epitaxial layer formed on one surface of the semiconductor substrate, and a laser beam incident on the semiconductor substrate via a focusing unit.
- a laser beam incident on the semiconductor substrate via a focusing unit.
- the gettering sink is preferably provided at least in a region overlapping with the formation position of the photodiode and having a diameter of 50 to 150 ⁇ m and a thickness of 10 to 150 ⁇ m.
- the gettering sink is preferably formed in a density range of 1.0 ⁇ 10 5 to 1.0 ⁇ 10 7 pieces / cm 2 .
- the laser beam is incident on the epitaxial substrate via the condensing means, and the laser beam is condensed on an arbitrary minute region inside the semiconductor substrate.
- a multiphoton absorption process is generated in a minute region inside the semiconductor substrate, and a gettering sink in which only the crystal structure of the minute region is changed can be formed easily and in a short time.
- the heavy metal contained in the epitaxial layer is surely captured by the gettering sink, so that it is possible to suppress the dark leakage current of the photodiode, which is a factor that deteriorates the imaging characteristics of the back-illuminated solid-state imaging device. Therefore, it is possible to realize a back-illuminated solid-state imaging device having excellent imaging characteristics.
- solid-state imaging capable of realizing a back-illuminated solid-state imaging device having excellent imaging characteristics with excellent heavy metal gettering capability, low dark leakage current, and excellent imaging characteristics.
- An epitaxial substrate for an element can be provided.
- a method for manufacturing a silicon wafer according to an aspect of the present invention includes a slicing step of slicing a silicon single crystal ingot to obtain a silicon wafer, a laser beam incident on the silicon wafer via a condensing unit, A multi-photon absorption step for forming a gettering sink in which a multi-photon absorption process is caused in the micro area by changing the crystal structure of the micro area by condensing the laser beam in the micro area; and the multi-photon And a polishing step of mirror polishing the silicon wafer that has undergone the absorption step.
- a lapping step for polishing the silicon wafer may be further provided between the slicing step and the multiphoton absorption step.
- An etching step for etching the silicon wafer may be further provided between the slicing step and the multiphoton absorption step.
- the laser beam has a wavelength range that allows transmission through the epitaxial wafer, and the condensing unit condenses the laser beam at an arbitrary position in the thickness direction of the silicon wafer.
- the laser beam is preferably an ultrashort pulse laser beam having a pulse width of 1.0 ⁇ 10 ⁇ 15 to 1.0 ⁇ 10 ⁇ 8 seconds and a wavelength of 300 to 1200 nm.
- the gettering sink preferably includes silicon having an amorphous structure.
- the method for producing an epitaxial wafer according to the present invention includes at least an epitaxial step of growing an epitaxial layer of a silicon single crystal on one surface of the silicon wafer obtained by the method for producing a silicon wafer.
- the method for manufacturing a solid-state imaging device of the present invention includes at least an element forming step for forming an embedded photodiode on one surface of the epitaxial wafer obtained by the method for manufacturing an epitaxial wafer.
- the gettering sink may be formed with a size in the range of 50 to 150 ⁇ m in diameter and 10 to 150 ⁇ m in thickness at least in a region overlapping with the formation position of the embedded photodiode.
- the gettering sink may be formed so as to have a density in the range of 1.0 ⁇ 10 5 to 1.0 ⁇ 10 7 pieces / cm 2 .
- the silicon wafer is mirror-polished (polishing process), thereby irradiating with laser light. Fine scratches (ablation) on the surface of the generated silicon wafer can be completely removed. Thereby, there can be obtained a silicon wafer which has no fine scratches on the surface due to laser irradiation and which has a gettering sink formed inside by a multiphoton absorption process.
- an epitaxial wafer excellent in heavy metal gettering ability can be obtained.
- a solid-state imaging device of the present invention it is possible to realize a solid-state imaging device that has excellent imaging characteristics with excellent heavy metal gettering capability and little dark leakage current.
- FIG. 1 is an enlarged cross-sectional view showing an epitaxial substrate for a solid-state imaging device according to an embodiment of the present invention.
- the epitaxial substrate (epitaxial substrate for solid-state imaging device) 11 includes a semiconductor substrate 12 and an epitaxial layer 13 formed on one surface 12 a of the semiconductor substrate 12. In the vicinity of one surface 12a of the semiconductor substrate 12, gettering sinks 14, 14,... For capturing heavy metals of the epitaxial substrate 11 are formed.
- Such an epitaxial substrate 11 can be suitably used as a substrate for a solid-state imaging device.
- the semiconductor substrate 12 may be a silicon single crystal wafer, for example.
- the epitaxial layer 13 may be a silicon epitaxial growth film grown from one surface 12 a of the semiconductor substrate 12.
- the gettering sink 14 may have a structure in which a part of a silicon single crystal is made amorphous (amorphous like).
- the gettering sink 14 has an ability to capture heavy metals only by a slight strain in its crystal structure, and can serve as a gettering sink by only making a part of it amorphous.
- the gettering sink 14 is formed by modifying the crystal structure by causing a multiphoton absorption process in a part of the semiconductor substrate 12 by condensing the laser beam. A method for forming such a gettering sink 14 will be described later in detail in a method for manufacturing an epitaxial substrate for a solid-state imaging device.
- the gettering sink 14 only needs to be formed at a position that overlaps at least the formation region S1 of each solid-state image sensor when the solid-state image sensor is formed using the epitaxial substrate 11.
- one gettering sink 14 may be formed in a disk shape having a diameter R1 of 50 to 150 ⁇ m, more preferably 75 to 125 ⁇ m, and a thickness T1 of 10 to 150 ⁇ m, more preferably 10 to 100 ⁇ m.
- the formation depth D1 of the gettering sink 14 is preferably about 0.5 to 2 ⁇ m from the one surface 12a of the semiconductor substrate 12. D1 is more preferably 0.8 to 1.5 ⁇ m.
- FIG. 2 is a cross-sectional view showing an example of a solid-state imaging device created using the epitaxial substrate for a solid-state imaging device of the present invention.
- the solid-state imaging device 160 uses an epitaxial substrate 11 in which a p-type epitaxial layer 13 is formed on a p + -type semiconductor substrate (silicon substrate) 12 and a gettering sink 14 is further formed on the semiconductor substrate 12.
- a first n-type well region 161 is formed at a predetermined position of the epitaxial layer 12. Inside the first n-type well region 161, a p-type transfer channel region 163, an n-type channel stop region 164, and a second n-type well region 165 constituting a vertical transfer register are formed.
- a transfer electrode 166 is formed at a predetermined position of the gate insulating film 162. Between the p-type transfer channel region 163 and the second n-type well region 165, a photodiode 169 in which an n-type positive charge storage region 167 and a p-type impurity diffusion region 168 are stacked is formed. An interlayer insulating film 171 that covers them and a light shielding film 172 that covers the surface excluding the portion directly above the photodiode 169 are provided.
- the heavy metal contained in the epitaxial substrate 11 is reliably captured by the gettering sink 14 formed on the semiconductor substrate 12, so that the imaging characteristics of the solid-state imaging device 160 are deteriorated.
- the dark leakage current of the photodiode 169 as a factor can be suppressed. Therefore, by forming the solid-state imaging device 160 using the epitaxial substrate 11 of the present invention, the solid-state imaging device 160 having excellent imaging characteristics with little dark leakage current can be realized.
- FIG. 3 is a cross-sectional view showing an outline of a method for manufacturing an epitaxial substrate for a solid-state imaging device.
- a semiconductor wafer 12 is prepared (see FIG. 3A).
- the semiconductor wafer 12 may be, for example, a silicon single crystal wafer manufactured by slicing a silicon single crystal ingot.
- an epitaxial layer 13 is formed on one surface 12a of the semiconductor wafer 12 (see FIG. 3B).
- an epitaxial growth apparatus may be used to introduce the source gas while heating the semiconductor wafer 12 to a predetermined temperature, and to grow the epitaxial layer 13 made of a silicon single crystal on the one surface 12a.
- the semiconductor wafer 12 on which the epitaxial layer 13 is formed is set on the laser irradiation device 120, and the laser beam is irradiated from the epitaxial layer 13 side while the semiconductor wafer 12 is moved (see FIG. 3C).
- the laser beam emitted from the laser generator 115 is focused by the condensing lens (condensing means) 111 so that the condensing point (focal point) is deeper than the one surface 12 a of the semiconductor wafer 12 by about several tens of ⁇ m. It is focused on.
- the crystal structure of the semiconductor wafer 12 is modified in this depth region, and the gettering sink 14 is formed. Between the gettering sink 14 and the epitaxial layer 13, an unmodified layer remains with a substantially constant thickness over the entire surface. The process of forming the gettering sink 14 will be described in detail later.
- the semiconductor wafer 12 on which the epitaxial layer 13 and the gettering sink 14 are formed is further heated to a predetermined temperature by the annealing device 180 (see FIG. 3D).
- the annealing device 180 see FIG. 3D.
- FIG. 4 is a schematic diagram showing an example of a laser irradiation apparatus for forming a gettering sink on a semiconductor wafer.
- the laser irradiation device 120 includes a laser generator 115 that oscillates the laser beam Q11, a pulse control circuit (Q switch) 116 that controls the pulse of the laser beam Q11, and the laser beam Q11 to reflect the traveling direction of the laser beam Q11.
- a beam splitter (half mirror) 117a that converts 90 ° toward the semiconductor wafer 12 and a condensing lens (condensing means) 111 that condenses the laser beam Q11 reflected by the beam splitter 117a are provided.
- This apparatus includes a stage 140 on which the semiconductor wafer 12 on which the epitaxial layer 13 is formed is placed.
- the stage 140 is controlled by the stage control circuit 145 so as to be movable in the vertical direction Y and the horizontal direction X in order to focus the focused laser beam Q21 at an arbitrary position on the semiconductor wafer 12. .
- the laser generator 115 and the pulse control circuit 116 are not particularly limited as long as they can irradiate a laser beam capable of forming a gettering sink by modifying a crystal structure at an arbitrary position inside the semiconductor wafer.
- a titanium sapphire laser that can oscillate in a wavelength range that allows transmission through a semiconductor wafer and in a short pulse period is suitable.
- Table 1 shows specific examples of suitable laser irradiation conditions for each of a general semiconductor wafer and a silicon wafer.
- the optical path width of the laser beam Q11 generated by the laser generator 115 is converged by the condensing lens 111, and the converged laser beam Q21 forms a focal point at an arbitrary depth position G1 of the semiconductor wafer 12 (collection).
- the stage 140 is controlled in the vertical direction Y.
- the condensing lens 111 has a magnification of, for example, 10 to 300 times, N.P. It is preferable that A is 0.3 to 0.9 and the transmittance with respect to the wavelength of the laser beam is 30 to 60%.
- the laser irradiation device 120 further includes a visible light laser generator 119, a beam splitter (half mirror) 117b, a CCD camera 130, a CCD camera control circuit 135, an imaging lens 112, a central control circuit 150, and a display means 151. ing.
- the visible light laser beam Q31 generated by the visible light laser generator 119 is reflected by the beam splitter (half mirror) 117b, changes its direction by 90 °, and reaches the epitaxial layer 13 of the semiconductor wafer 12.
- the light is reflected by the surface of the epitaxial layer 13, passes through the condensing lens 111 and the beam splitters 117 a and 117 b, and reaches the imaging lens 112.
- the visible light laser Q31 that has reached the imaging lens 112 is picked up by the CCD camera 130 as a surface image of the semiconductor wafer 12, and the picked-up data is input to the CCD camera control circuit 135. Based on the input imaging data, the stage control circuit 145 controls the amount of movement of the stage 140 in the horizontal direction X.
- FIG. 5 is a schematic diagram showing how a gettering sink is formed on a semiconductor wafer by a laser beam.
- the laser beam Q11 emitted from the laser generator 115 is converged by a condensing lens (condensing means) 111. Since the converged laser beam Q21 has a wavelength range that can be transmitted with respect to silicon, the laser beam Q21 reaches the surface of the epitaxial layer 13 and then enters as it is without being reflected.
- the semiconductor wafer 12 on which the epitaxial layer 13 is formed is positioned so that the condensing point (focal point) of the laser beam Q21 is a predetermined depth D1 from the one surface 12a of the semiconductor wafer 12. Thereby, the multi-photon absorption process occurs in the semiconductor wafer 12 only at the condensing point (focal point) of the laser beam Q21.
- the multiphoton absorption process irradiates a specific part (irradiation region) with a large amount of photons in a very short time, so that a large amount of energy is selectively absorbed only in the irradiation region. It causes a reaction such as a change in the crystal bond in the region.
- a laser beam is focused on an arbitrary area inside the semiconductor wafer 12 to modify the semiconductor wafer having a single crystal structure at the focal point (focal point), and a partially amorphous-like crystal. Give rise to structure.
- the crystal structure may be modified to such an extent that a capturing action of heavy metals occurs, that is, a slight strain is generated in the crystal structure.
- the semiconductor structure is modified by modifying the crystal structure of the minute region.
- a gettering sink 14 can be formed in an arbitrary minute region of the wafer 12.
- the laser beam for forming the gettering sink 14 is a laser beam without modifying the crystal structure of the epitaxial layer 13 or the semiconductor wafer 12 in the optical path before the laser beam reaches the focal point (focal point). It is important to ensure that the beam can be transmitted reliably.
- the laser beam irradiation conditions are determined by a forbidden band (energy band gap) which is a basic physical property value of a semiconductor material. For example, since the forbidden band of a silicon semiconductor is 1.1 eV, the transmittance becomes remarkable when the incident wavelength is 1000 nm or more. In this way, the wavelength of the laser beam can be determined in consideration of the forbidden band of the semiconductor material.
- a low-power laser As a laser beam generation device, it is preferable to use a low-power laser because a high-power laser such as a YAG laser may transfer thermal energy not only to a predetermined depth position but also to the surrounding area.
- a high-power laser such as a YAG laser may transfer thermal energy not only to a predetermined depth position but also to the surrounding area.
- the low-power laser for example, an ultrashort pulse laser such as a femtosecond laser is suitable.
- the ultrashort pulse laser can set the wavelength of the laser beam in an arbitrary range by exciting a titanium sapphire crystal (solid laser crystal) using a semiconductor laser or the like.
- the ultrashort pulse laser can reduce the pulse width of the excitation laser beam to 1.0 ⁇ 10 ⁇ 15 femtoseconds or less, so that the diffusion of thermal energy generated by excitation can be suppressed compared to other lasers, and the laser beam is focused. Light energy can be concentrated only at a point (focal point).
- the gettering sink 14 formed by modifying the crystal structure by the multiphoton absorption process probably has an amorphous-like crystal structure.
- the ultrashort pulse laser having the characteristics shown in Table 1 is a laser having a small amount of energy.
- the semiconductor substrate 120 is rapidly heated locally. Enough energy.
- the temperature of the condensing point (focal point) G of the laser beam reaches a high temperature of 9900 to 10000K. Because the light is collected, the heat input range is very narrow.
- the focal point is moved by moving the stage on which the semiconductor wafer 12 is placed or scanning the laser beam, the focal point (focal point) before the movement is moved.
- the amount of heat input at has decreased rapidly and a rapid cooling effect is obtained.
- the number of irradiation pulses per irradiation point is preferably 10 to 10,000 pulses, and more preferably 10 to 100 pulses.
- the wavelength of the laser beam exceeds 1200 nm, the photon energy (laser beam energy) decreases because of the long wavelength region. For this reason, there is a possibility that sufficient photon energy for modifying the inside of the semiconductor substrate cannot be obtained even if the laser beam is condensed, and the wavelength of the laser beam is preferably 1200 nm or less.
- the position of the condensing point (focal point) G1 of the laser beam that is, the position where the gettering sink 14 is formed on the semiconductor substrate 12 can be controlled by moving the stage up and down. Besides moving the stage up and down, the position of the condensing point (focus) G1 of the laser beam can also be controlled by controlling the position of the condensing means (condensing lens).
- the gettering sink 14 when the gettering sink 14 is formed by modifying the position 2 ⁇ m deep from the surface 12a of the semiconductor substrate 12, the wavelength of the laser beam is set to 1080 nm and the transmittance is 60%.
- a modified portion (gettering sink) can be formed by imaging (condensing) a laser beam at a position of 2 ⁇ m from the surface using a lens (magnification 50 ⁇ ) and generating a multiphoton absorption process.
- the gettering sink 14 obtained by modifying the crystal structure of the minute region of the semiconductor substrate 12 is formed in a disk shape having a diameter R1 of 50 to 150 ⁇ m and a thickness T1 of 10 to 150 ⁇ m, for example. Just do it.
- the formation depth D1 of the gettering sink 14 is preferably about 0.5 to 2 ⁇ m from the one surface 12a of the semiconductor substrate 12.
- Each gettering sink 14 may be formed at least on the epitaxial substrate 11 at a position overlapping with the solid-state imaging element formation region S1.
- the gettering sinks 14 may be formed with a formation pitch P1 of 0.1 to 10 ⁇ m.
- the gettering sink 14 may be uniformly formed on the entire semiconductor substrate at a predetermined depth with respect to the semiconductor substrate, for example.
- FIG. 6 is a schematic view showing a state of forming a gettering sink in the epitaxial substrate.
- the gettering sinks 14 may be formed below the solid-state imaging element formation region S1 on the epitaxial substrate 11, respectively.
- the epitaxial substrate 11 is scanned along the X direction while being shifted in the Y direction at the periphery so that the laser beam Q1 is scanned over the entire area of the epitaxial substrate 11, and the laser beam Q1 is irradiated under a predetermined condition. If so, the gettering sinks 14, 14... Can be formed on the entire epitaxial substrate 11.
- the formation density of the gettering sink 14 in the entire epitaxial substrate 11 can be set by the scanning pitch B1 of the laser beam Q1.
- the formation density of the gettering sink 4 is preferably in the range of 1.0 ⁇ 10 5 to 1.0 ⁇ 10 7 pieces / cm 2 , for example.
- the formation density of the gettering sink 14 can be verified by the number of oxygen precipitates obtained by observation with a cross-sectional TEM (transmission electron microscope).
- a laser beam is incident on the epitaxial substrate via the light condensing means, and the laser beam is incident on an arbitrary minute region inside the semiconductor substrate.
- a multiphoton absorption process occurs in a minute region inside the semiconductor substrate, and a gettering sink in which only the crystal structure of the minute region is changed can be formed easily and in a short time. become.
- FIG. 7 is an enlarged sectional view showing a NAND flash memory which is an example of the semiconductor device of the present invention.
- the NAND flash memory (semiconductor device) 21 includes a p + type semiconductor substrate 22 and a first insulating film 23 formed on one surface 22 a of the semiconductor substrate 22. On the one surface 23a of the first insulating film 23, a floating gate 25, a second insulating film 26, and a control gate 27 are sequentially stacked.
- n + -type source region 28 and a drain region 29 are formed around the formation region of the floating gate 25 on the one surface 22 a side of the semiconductor substrate 2. Gettering for capturing heavy metal of the semiconductor substrate 22 at a position overlapping the device formation region S2 in the semiconductor substrate 22, for example, at a position overlapping the region where the floating gate 25, the second insulating film 26, the control gate 27, etc. are stacked. A sink 24 is formed.
- the semiconductor substrate 22 may be a silicon single crystal wafer, for example.
- the first insulating film 23 may be an SiO 2 film obtained by oxidizing the surface of a silicon single crystal wafer.
- the second insulating film 26 may be a silicon nitride (SiN) film, for example.
- the gettering sink 24 may have a structure in which a part of a silicon single crystal is made amorphous (amorphous like).
- the gettering sink 24 has the ability to capture heavy metals only by a slight strain in its crystal structure, and can serve as a gettering sink by making only a small part amorphous.
- the gettering sink 24 is formed by modifying the crystal structure by causing a multiphoton absorption process in a part of the semiconductor substrate 22 by condensing the laser beam. A method of forming such a gettering sink 24 will be described later in detail in a semiconductor device manufacturing method.
- the gettering sink 24 should just be formed in the position which overlaps with the formation area S2 of each device at least.
- one gettering sink 24 may be formed in a disk shape having a diameter R2 of 50 to 150 ⁇ m, more preferably 75 to 125 ⁇ m, and a thickness T2 of 10 to 150 ⁇ m, more preferably 10 to 100 ⁇ m.
- the formation depth D2 of the gettering sink 24 is preferably about 0.5 to 2 ⁇ m from the one surface 2a of the semiconductor substrate 2. D2 is more preferably 0.8 to 1.5 ⁇ m.
- the NAND flash memory 21 configured as described above, when a control voltage is applied to the control gate 27, electrons are tunneled from the p + type semiconductor substrate 22 through the first insulating film 23 toward the floating gate 25. Is injected. As a result, a data write state is established. Since the floating gate 25 is surrounded by an insulator such as the first insulating film 23 and the second insulating film 26, the memory state is maintained even when the power is turned off.
- the semiconductor device of the present invention is not limited to the NAND flash memory as described above, but also applies to various semiconductor devices typified by a flash memory such as a NOR flash memory or a semiconductor memory such as a DRAM. Applicable to.
- FIG. 8 is a sectional view showing an outline of a semiconductor device manufacturing method step by step.
- a semiconductor substrate 22 is prepared (see FIG. 8A).
- the semiconductor substrate 22 may be, for example, a silicon single crystal wafer manufactured by slicing a silicon single crystal ingot.
- a first insulating film 23 is formed on one surface 22a of the semiconductor substrate 22 (see FIG. 8B).
- the first insulating film 23 may be a silicon oxide film (SiO 2 ) obtained by oxidizing one surface of a silicon single crystal wafer.
- the surface of the semiconductor substrate 22 may be oxidized by heating the semiconductor substrate 22 to a predetermined temperature using an annealing apparatus.
- a device including a floating gate 25, a second insulating film 26, a control gate 27, a source region 28, a drain region 29, and the like is formed on one surface 22a of the semiconductor substrate 22 by, for example, photolithography. It forms (refer FIG.8 (c)).
- FIG. 9 is a schematic diagram showing an example of a laser irradiation apparatus 120 for forming a gettering sink on a semiconductor substrate.
- the laser irradiation device 120 may be the same as that used in the above-described embodiment. Suitable laser irradiation conditions may be the same as in Table 1 described above.
- the optical path width of the laser beam Q11 generated by the laser generator 115 is converged by the condensing lens 111, and the converged laser beam Q21 forms a focal point at an arbitrary depth position G2 of the semiconductor substrate 22 (
- the stage 140 is controlled in the vertical direction Y so that the light is condensed.
- the condensing lens 111 has a magnification of, for example, 10 to 300 times, N.P. It is preferable that A is 0.3 to 0.9 and the transmittance with respect to the wavelength of the laser beam is 30 to 60%.
- the visible light laser beam Q31 generated by the visible light laser generator 119 is reflected by the beam splitter (half mirror) 117b, changes its direction by 90 °, and reaches the semiconductor substrate 22.
- the visible light laser beam Q31 is reflected by the surface of the semiconductor substrate 22 (on the other surface 22b side), passes through the condensing lens 111 and the beam splitters 117a and 117b, and reaches the imaging lens 112.
- the visible light laser Q 31 that has reached the imaging lens 112 is picked up by the CCD camera 130 as a surface image of the semiconductor substrate 22, and the picked-up data is input to the CCD camera control circuit 135. Based on the input imaging data, the stage control circuit 145 controls the amount of movement of the stage 140 in the horizontal direction X.
- the semiconductor substrate 22 is placed so that the other surface 22 b side is an upper surface (laser incident surface) with respect to the stage 140.
- the laser beam Q11 emitted from the laser generator 115 is converged by a condensing lens (condensing means) 111. Since the converged laser beam Q21 has a wavelength region that can be transmitted through silicon, the laser beam Q21 reaches the other surface 22b of the semiconductor substrate 22 and then enters as it is without being reflected.
- the semiconductor substrate 22 is positioned so that the condensing point (focal point) of the laser beam Q21 is a predetermined depth D2 from the one surface 22a of the semiconductor substrate 22. As a result, the semiconductor substrate 22 undergoes a multiphoton absorption process only at the condensing point (focal point) of the laser beam Q21.
- a semiconductor beam having a single crystal structure is modified at a condensing point (focal point) by condensing a laser beam on an arbitrary region inside the semiconductor substrate 22, and a partially amorphous-like crystal.
- the crystal structure may be modified to such an extent that a capturing action of heavy metals occurs, that is, a slight strain is generated in the crystal structure.
- the condensing point (focal point) of the laser beam Q21 obtained by converging the laser beam Q11 in an arbitrary minute region inside the semiconductor substrate 22 is set, and the semiconductor structure is modified by modifying the crystal structure of the minute region.
- a gettering sink 24 can be formed in an arbitrary minute region of the substrate 22.
- the laser beam for forming the gettering sink 24 does not have energy for modifying the crystal structure of the semiconductor substrate 22 in the optical path before the laser beam reaches the focal point (focal point), and the laser beam It is important to ensure that the beam can be transmitted reliably.
- the laser beam irradiation conditions are determined by a forbidden band (energy band gap) which is a basic physical property value of a semiconductor material. For example, since the forbidden band of a silicon semiconductor is 1.1 eV, the transmittance becomes remarkable when the incident wavelength is 1000 nm or more. In this way, the wavelength of the laser beam can be determined in consideration of the forbidden band of the semiconductor material.
- a low-power laser As a laser beam generation device, it is preferable to use a low-power laser because a high-power laser such as a YAG laser may transfer thermal energy not only to a predetermined depth position but also to the surrounding area.
- a high-power laser such as a YAG laser may transfer thermal energy not only to a predetermined depth position but also to the surrounding area.
- the low-power laser for example, an ultrashort pulse laser such as a femtosecond laser is suitable.
- the ultrashort pulse laser can set the wavelength of the laser beam in an arbitrary range by exciting a titanium sapphire crystal (solid laser crystal) using a semiconductor laser or the like.
- the ultrashort pulse laser can reduce the pulse width of the excitation laser beam to 1.0 ⁇ 10 ⁇ 15 femtoseconds or less, so that the diffusion of thermal energy generated by excitation can be suppressed compared to other lasers, and the laser beam is focused. Light energy can be concentrated only at a point (focal point).
- the gettering sink 24 formed by modifying the crystal structure by the multiphoton absorption process probably has an amorphous-like crystal structure.
- the ultrashort pulse laser having the characteristics shown in Table 1 is a laser having a small amount of energy.
- the semiconductor substrate 22 is rapidly heated locally. Enough energy.
- the temperature of the condensing point (focus) G2 of the laser beam reaches a high temperature of 9900 to 10000K.
- the heat input range is very narrow, and when the condensing point (focal point) is moved by the movement of the stage on which the semiconductor substrate 22 is placed or the scanning of the laser beam, the condensing point (focal point) before the movement.
- the amount of heat input at has decreased rapidly and a rapid cooling effect is obtained.
- the wavelength of the laser beam exceeds 1200 nm, the photon energy (laser beam energy) decreases because of the long wavelength region. For this reason, there is a possibility that sufficient photon energy for modifying the inside of the semiconductor substrate cannot be obtained even if the laser beam is condensed, and the wavelength of the laser beam is preferably 1200 nm or less.
- the position of the condensing point (focal point) G2 of the laser beam that is, the position where the gettering sink 24 is formed on the semiconductor substrate 22 can be controlled by moving the stage up and down. Besides moving the stage up and down, the position of the condensing point (focal point) G2 of the laser beam can be controlled by controlling the position of the condensing means (condensing lens).
- the gettering sink 24 when the gettering sink 24 is formed by modifying the position of 2 ⁇ m from the surface of the semiconductor substrate, the wavelength of the laser beam is set to 1080 nm and the condensing lens with a transmittance of 60% (magnification 50)
- the modified portion (gettering sink) can be formed by forming (condensing) a laser beam at a position of 2 ⁇ m from the surface by using (multiple) and generating a multiphoton absorption process.
- the gettering sink 24 obtained by modifying the crystal structure of a minute region of the semiconductor substrate 22 may be formed in a disk shape having a diameter R2 of 50 to 150 ⁇ m and a thickness T2 of 10 to 150 ⁇ m, for example.
- the formation depth D2 of the gettering sink 24 is preferably about 0.5 to 2 ⁇ m from the one surface 22a of the semiconductor substrate 22.
- Each gettering sink 24 should just be formed in the position which overlaps with element formation region S2 of the semiconductor substrate 22.
- the gettering sinks 24 may be formed at intervals of 0.1 to 10 ⁇ m between adjacent gettering sinks 24.
- the gettering sink 4 is preferably formed uniformly over the entire semiconductor substrate at a predetermined depth, for example.
- the gettering sink 14 (24) may be formed below the element formation region in the semiconductor substrate.
- the laser beam Q1 is scanned along the X direction while being shifted in the Y direction at the periphery so that the laser beam Q1 is scanned over the entire other surface (back surface) of the semiconductor substrate 11 (22) on which the device is formed. If the beam Q1 is irradiated under a predetermined condition, gettering sinks 24, 24,... Can be formed on the entire semiconductor substrate 22.
- the formation density of the gettering sink 24 can be set by the scanning pitch B1 of the laser beam Q1.
- the formation density of the gettering sink 24 is preferably in the range of 1.0 ⁇ 10 5 to 1.0 ⁇ 10 6 pieces / cm 2 , for example.
- the formation density of the gettering sink 24 can be verified by the number of oxygen precipitates obtained by observation with a cross-sectional TEM (transmission electron microscope).
- the semiconductor substrate 22 on which the gettering sink 24 is formed as described above is further heated to a predetermined temperature by the annealing device 280 (see FIG. 8E).
- the annealing device 280 see FIG. 8E.
- the heavy metal diffused in the semiconductor substrate 22 is collected in the gettering sink 24, and a NAND flash memory (semiconductor device) with very little heavy metal in the element formation portion can be obtained.
- the laser beam is incident on the semiconductor substrate via the condensing means, and the laser beam is condensed on an arbitrary minute region inside the semiconductor substrate.
- FIG. 10 is an enlarged cross-sectional view showing an epitaxial substrate for a solid-state imaging device according to another aspect of the present invention.
- the epitaxial substrate (epitaxial substrate for solid-state imaging device) 31 is a substrate (wafer) suitable for manufacturing a back-illuminated solid-state imaging device, and has an SOI structure formed near the semiconductor substrate 32 and the one surface 32a of the semiconductor substrate 32.
- a buried oxide film 35 and an epitaxial layer 33 formed on one surface 32 a of the semiconductor substrate 32 are provided. Below the buried oxide film 35, gettering sinks 34, 34,... For capturing heavy metals of the epitaxial substrate 31 are formed.
- Such an epitaxial substrate 31 can be suitably used as a substrate for a back-illuminated solid-state imaging device.
- the semiconductor substrate 32 may be, for example, a silicon single crystal wafer.
- the epitaxial layer 33 may be any silicon epitaxial growth film grown from the one surface 32 a of the semiconductor substrate 32.
- the buried oxide film 35 is formed inside the semiconductor substrate by, for example, a method of bonding the substrate on which the oxide film is formed and the semiconductor substrate, or by implanting oxygen from one surface of the semiconductor substrate by ion implantation and oxidizing it by heating. A method of forming the buried oxide film (BOX layer) 35 may be used.
- the gettering sink 34 may have a structure in which a part of a silicon single crystal is made amorphous (amorphous like).
- the gettering sink 34 has the ability to capture heavy metals only by the presence of a slight strain in its crystal structure.
- the gettering sink 34 can play a role as a gettering sink by making only a small part amorphous.
- the gettering sink 34 is formed by modifying the crystal structure by causing a multiphoton absorption process in a part of the semiconductor substrate 32 by condensing the laser beam. A method for forming such a gettering sink 34 will be described later in detail in a method for manufacturing a back-illuminated solid-state imaging device.
- the gettering sink 34 only needs to be formed at a position that overlaps at least the formation region S ⁇ b> 3 of each back-illuminated solid-state image sensor when the back-illuminated solid-state image sensor is formed using the epitaxial substrate 31.
- one gettering sink 34 may be formed in a disk shape having a diameter R3 of 50 to 150 ⁇ m, more preferably 75 to 125 ⁇ m, and a thickness T3 of 10 to 150 ⁇ m, more preferably 10 to 100 ⁇ m.
- the formation depth D3 of the gettering sink 34 is preferably about 0.5 to 2 ⁇ m from the one surface 2a of the semiconductor substrate 2.
- the depth D3 is more preferably 0.8 to 1.5 ⁇ m.
- FIG. 11 is a cross-sectional view showing an example of a back-illuminated solid-state image sensor created using the epitaxial substrate for a solid-state image sensor of the present invention.
- the back-illuminated solid-state imaging device 360 includes a photodiode 361 formed on the epitaxial layer 33, an insulating layer 362 formed on one surface (front surface) 33 a side of the epitaxial layer 33, and wiring formed inside the insulating layer 362. 363.
- the back-illuminated solid-state imaging device 360 is thinned by removing the semiconductor substrate by grinding at the time of formation.
- Incident light F ⁇ b> 3 enters from the other surface (back surface) 33 b side of the epitaxial layer 33 and is detected by the photodiode 361.
- the back-illuminated solid-state imaging device 360 having such a configuration reliably captures heavy metals contained in the epitaxial layer 33 by the gettering sink 34 formed on the semiconductor substrate 32 of the epitaxial substrate 31 (see FIG. 10) used for manufacturing. Therefore, the dark leakage current of the photodiode 361, which is a factor that deteriorates the imaging characteristics of the backside illumination type solid-state imaging device 360, can be suppressed. Therefore, the backside illumination type solid-state imaging device 360 having excellent imaging characteristics can be realized.
- 12 to 14 are cross-sectional views showing an outline of a method for manufacturing a back-illuminated solid-state imaging device.
- the semiconductor substrate 32 is prepared (see FIG. 12A).
- the semiconductor substrate 32 may be, for example, a silicon single crystal wafer manufactured by slicing a silicon single crystal ingot.
- an epitaxial layer 33 is formed on one surface 32a of the semiconductor substrate 32 (see FIG. 12B).
- an epitaxial growth apparatus may be used to introduce the source gas while heating the semiconductor substrate 32 to a predetermined temperature, and to grow the epitaxial layer 33 made of silicon single crystal on the one surface 32a.
- a buried oxide film (BOX layer) 35 is preferably formed inside the semiconductor substrate 32.
- the semiconductor substrate 32 on which the epitaxial layer 33 is formed is set on the laser irradiation apparatus 120, and the laser beam is irradiated while moving the semiconductor substrate 32 (see FIG. 12C).
- the laser beam emitted from the laser generator 115 is focused by the condensing lens (condensing means) 111 so that the condensing point (focal point) is deeper than the one surface 32 a of the semiconductor substrate 32 by several tens of ⁇ m. Focused. Thereby, the crystal structure of the semiconductor substrate 32 is modified, and the gettering sink 34 is formed.
- FIG. 15 is a schematic view showing an example of a laser irradiation apparatus used in a process of forming a gettering sink on a semiconductor substrate. Since the laser irradiation apparatus 120 may be the same as that used in the above-described embodiment, the description thereof is omitted. Suitable laser irradiation conditions may be the same as in Table 1 described above.
- the optical path width of the laser beam Q11 generated by the laser generator 115 is converged by the condensing lens 111, and the converged laser beam Q21 forms a focal point at an arbitrary depth position G3 of the semiconductor substrate 32 (collection).
- the stage 140 is controlled in the vertical direction Y.
- the condensing lens 111 has a magnification of, for example, 10 to 300 times, N.P. It is preferable that A is 0.3 to 0.9 and the transmittance with respect to the wavelength of the laser beam is 30 to 60%.
- the visible light laser beam Q31 generated by the visible light laser generator 119 is reflected by the beam splitter (half mirror) 117b, changes its direction by 90 °, and reaches the epitaxial layer 33 of the semiconductor substrate 32.
- the light is reflected by the surface of the epitaxial layer 33, passes through the condensing lens 111 and the beam splitters 117 a and 117 b, and reaches the imaging lens 112.
- the visible light laser Q31 that has reached the imaging lens 112 is picked up by the CCD camera 130 as a surface image of the semiconductor substrate 2, and the picked-up data is input to the CCD camera control circuit 135. Based on the input imaging data, the stage control circuit 145 controls the amount of movement of the stage 140 in the horizontal direction X.
- FIG. 16 is a schematic diagram showing how a gettering sink is formed on a semiconductor substrate by a laser beam.
- the laser beam Q11 emitted from the laser generator 115 is converged by a condensing lens (condensing means) 111. Since the converged laser beam Q21 has a wavelength range that can be transmitted through silicon, the laser beam Q21 reaches the back surface of the semiconductor substrate 32 and then enters as it is without being reflected.
- the semiconductor substrate 32 on which the epitaxial layer 33 is formed is positioned so that the condensing point (focal point) of the laser beam Q21 is a predetermined depth D3 from the one surface 32a of the semiconductor substrate 32.
- the semiconductor substrate 32 undergoes a multiphoton absorption process only at the condensing point (focal point) of the laser beam Q21.
- a laser beam is focused on an arbitrary region inside the semiconductor substrate 32 to modify the semiconductor substrate having a single crystal structure at the focusing point (focal point), and a partially amorphous-like crystal.
- the crystal structure may be modified to such an extent that a capturing action of heavy metals occurs, that is, a slight strain is generated in the crystal structure.
- the condensing point (focal point) of the laser beam Q21 obtained by converging the laser beam Q11 in an arbitrary minute region inside the semiconductor substrate 32 is set, and the crystal structure of the minute region is modified, thereby modifying the semiconductor.
- a gettering sink 34 can be formed in an arbitrary minute region of the substrate 32.
- the laser beam for forming the gettering sink 34 is a laser beam without modifying the crystal structure of the epitaxial layer 33 or the semiconductor substrate 32 in the optical path before the laser beam reaches the focal point (focal point). It is important to ensure that the beam can be transmitted reliably.
- the laser beam irradiation conditions are determined by a forbidden band (energy band gap) which is a basic physical property value of a semiconductor material. For example, since the forbidden band of a silicon semiconductor is 1.1 eV, the transmittance becomes remarkable when the incident wavelength is 1000 nm or more. In this way, the wavelength of the laser beam can be determined in consideration of the forbidden band of the semiconductor material.
- a low-power laser As a laser beam generation device, it is preferable to use a low-power laser because a high-power laser such as a YAG laser may transfer thermal energy not only to a predetermined depth position but also to the surrounding area.
- a high-power laser such as a YAG laser may transfer thermal energy not only to a predetermined depth position but also to the surrounding area.
- the low-power laser for example, an ultrashort pulse laser such as a femtosecond laser is suitable.
- the ultrashort pulse laser can set the wavelength of the laser beam in an arbitrary range by exciting a titanium sapphire crystal (solid laser crystal) using a semiconductor laser or the like.
- the ultrashort pulse laser can reduce the pulse width of the excitation laser beam to 1.0 ⁇ 10 ⁇ 15 femtoseconds or less, so that the diffusion of thermal energy generated by excitation can be suppressed compared to other lasers, and the laser beam is focused. Light energy can be concentrated only at a point (focal point).
- the gettering sink 34 formed by modifying the crystal structure by the multiphoton absorption process probably has an amorphous-like crystal structure.
- the ultrashort pulse laser having the characteristics as shown in Table 1 is a laser having a small energy amount.
- the semiconductor substrate 32 is rapidly heated locally. Enough energy.
- the temperature of the condensing point (focal point) G of the laser beam reaches a high temperature of 9900 to 10000K.
- the heat input range is very narrow, and when the condensing point (focal point) is moved by moving the stage on which the semiconductor substrate 32 is placed or scanning with a laser beam, the condensing point (focal point) before the movement is reached.
- the amount of heat input at has decreased rapidly and a rapid cooling effect is obtained.
- the wavelength of the laser beam exceeds 1200 nm, the photon energy (laser beam energy) decreases because of the long wavelength region. For this reason, there is a possibility that sufficient photon energy for modifying the inside of the semiconductor substrate cannot be obtained even if the laser beam is condensed, and the wavelength of the laser beam is preferably 1200 nm or less.
- the position of the condensing point (focus) G3 of the laser beam that is, the position where the gettering sink 34 is formed on the semiconductor substrate 32 can be controlled by moving the stage up and down. Besides moving the stage up and down, the position of the condensing point (focal point) G3 of the laser beam can also be controlled by controlling the position of the condensing means (condensing lens).
- the gettering sink 34 when the gettering sink 34 is formed by modifying the position of 2 ⁇ m from the surface of the semiconductor substrate, the wavelength of the laser beam is set to 1080 nm, and a condensing lens with a transmittance of 60% (magnification 50)
- the modified portion (gettering sink) can be formed by forming (condensing) a laser beam at a position of 2 ⁇ m from the surface by using (multiple) and generating a multiphoton absorption process.
- the gettering sink 34 obtained by modifying the crystal structure of the minute region of the semiconductor substrate 32 is formed in a disk shape having a diameter R3 of 50 to 150 ⁇ m and a thickness T3 of 10 to 150 ⁇ m, for example. Just do it.
- the formation depth D3 of the gettering sink 34 is preferably about 0.5 to 2 ⁇ m from the one surface 32a of the semiconductor substrate 32.
- Each gettering sink 34 only needs to be formed at least in a position overlapping the formation region S3 of the back-illuminated solid-state imaging device on the epitaxial substrate 360.
- the gettering sinks 34 may be formed at intervals of a formation pitch P of 0.1 to 10 ⁇ m.
- the gettering sink 34 may be uniformly formed on the entire semiconductor substrate at a predetermined depth with respect to the semiconductor substrate, for example.
- the state of formation of the gettering sink in the epitaxial substrate is the same as that of FIG. 6 described above.
- the gettering sink 34 (14 in FIG. 6) may be formed below the formation region of the back-illuminated solid-state imaging device in the epitaxial substrate 31 (11 in FIG. 6). For example, the epitaxial substrate 31 is scanned along the X direction while being shifted in the Y direction at the periphery so that the laser beam Q1 is scanned over the entire area of the epitaxial substrate 31, and the laser beam Q1 is irradiated under a predetermined condition. If so, gettering sinks 34, 34... Can be formed on the entire epitaxial substrate 31.
- the formation density of the gettering sink 34 in the entire epitaxial substrate 31 can be set by the scanning pitch B1 of the laser beam Q1.
- the formation density of the gettering sink 34 is preferably in the range of 1.0 ⁇ 10 5 to 1.0 ⁇ 10 7 pieces / cm 2 , for example.
- the formation density of the gettering sink 34 can be verified by the number of oxygen precipitates obtained by observation with a cross-sectional TEM (transmission electron microscope).
- the gettering sink 34 is formed on the epitaxial substrate 31 by the process described in detail (see FIG. 12D).
- a large number of photodiodes 361 are formed in the epitaxial layer 33 using the epitaxial substrate 31 on which the gettering sink 34 is formed.
- An insulating layer 362 and a wiring 363 are formed on the one surface 33a side of the epitaxial layer 33 (see FIG. 13A). The surface of the insulating layer 362 is planarized.
- the epitaxial substrate 31 on which the photodiode 361 and the wiring 363 are formed is heated to a predetermined temperature by the annealing device 380 (see FIG. 13B).
- the heavy metal diffused in the semiconductor substrate 32 is collected in the gettering sink 34, and the heavy metal concentration in the element formation portion, that is, the region where the photodiode 361 is formed can be made extremely low.
- a support substrate 390 is attached to the one surface 362a side of the insulating layer 362 (see FIG. 13C).
- the attachment of the support substrate 390 is to prevent the epitaxial substrate 31 from being damaged in the subsequent thinning process.
- a silicon wafer may be used as the support substrate 390.
- the epitaxial substrate 131 to which the support substrate 390 is attached is ground from the other surface (back surface) 32a side of the semiconductor substrate 32 using a grinding device or the like.
- a grinding device or the like For example, all of the semiconductor substrate 32 and a part of the epitaxial layer 33 may be removed by grinding to reduce the thickness (see FIG. 14A).
- the back-illuminated solid-state imaging device 360 is completed through the steps described above (see FIG. 14B).
- incident light F ⁇ b> 3 enters from the other surface (back surface) 33 b side of the epitaxial layer 33 and is detected by the photodiode 361.
- the laser beam is incident on the epitaxial substrate through the condensing means, and the laser beam is incident on an arbitrary minute region inside the semiconductor substrate.
- a multiphoton absorption process occurs in a minute region inside the semiconductor substrate, and a gettering sink in which only the crystal structure of the minute region is changed can be formed easily and in a short time. become.
- a gettering sink is formed as in the prior art, a long-time heat treatment is not necessary, and the manufacturing process of the back-illuminated solid-state imaging device can be simplified and the manufacturing cost can be reduced. Even with a double-side polished substrate typified by a 300 mm wafer, a gettering sink can be easily formed inside the semiconductor substrate.
- the photodiode of the back-illuminated solid-state imaging device is a factor that deteriorates the imaging characteristics. Dark leakage current can be suppressed. Therefore, a back-illuminated solid-state imaging device having excellent imaging characteristics can be realized.
- FIG. 17 is an enlarged cross-sectional view showing an epitaxial wafer suitable for manufacturing a solid-state imaging device, for example.
- the epitaxial wafer 41 includes a silicon wafer 42 and an epitaxial layer 43 formed on one surface 42 a of the silicon wafer 42. In the vicinity of one surface 42a of the silicon wafer 42, gettering sinks 44, 44,... For capturing heavy metals of the epitaxial wafer 41 are formed.
- the epitaxial wafer 41 can be suitably used as a substrate for a solid-state imaging device.
- the silicon wafer 42 may be, for example, a silicon single crystal substrate.
- the epitaxial layer 43 may be any silicon epitaxial growth film grown from the one surface 42 a of the silicon wafer 42.
- the gettering sink 44 may have a structure in which a part of a silicon single crystal is made amorphous (amorphous like).
- the gettering sink 44 has the ability to capture heavy metals only by the presence of a slight strain in the crystal structure, and can serve as a gettering sink by making only a small part amorphous.
- the gettering sink 44 is formed by modifying the crystal structure by causing a multiphoton absorption process in a part of the silicon wafer 42 by condensing the laser beam. A method for forming such a gettering sink 44 will be described later in detail in a method for manufacturing an epitaxial wafer.
- the gettering sink 44 only needs to be formed at a position overlapping at least the formation region S4 of each solid-state image sensor when the solid-state image sensor is formed using the epitaxial wafer 41, for example.
- one gettering sink 44 may be formed in a disk shape having a diameter R4 of 50 to 150 ⁇ m, more preferably 75 to 125 ⁇ m, and a thickness T4 of 10 to 150 ⁇ m, more preferably 10 to 100 ⁇ m.
- the formation depth D4 of the gettering sink 44 is preferably about 0.5 to 2 ⁇ m from the one surface 42a of the silicon wafer 42. A more preferable depth D4 is 0.8 to 1.5 ⁇ m.
- FIG. 18 is a cross-sectional view showing an example of a solid-state imaging device created using an epitaxial wafer obtained by the epitaxial wafer manufacturing method of the present invention.
- the solid-state imaging device 60 uses an epitaxial wafer 41 in which a p-type epitaxial layer 43 is formed on a p + -type silicon wafer (silicon substrate) 42 and a gettering sink 44 is formed on the silicon wafer 42.
- a first n-type well region 461 is formed at a predetermined position of the epitaxial layer 43.
- a p-type transfer channel region 463, an n-type channel stop region 464, and a second n-type well region 465 that constitute a vertical transfer register are formed.
- a transfer electrode 466 is formed at a predetermined position of the gate insulating film 462.
- a photodiode 469 in which an n-type positive charge accumulation region 467 and a p-type impurity diffusion region 468 are stacked is formed.
- An interlayer insulating film 471 that covers them and a light shielding film 472 that covers the surface except for the portion directly above the photodiode 469 are provided.
- the solid-state imaging device 460 having such a configuration deteriorates the imaging characteristics of the solid-state imaging device 460 because the heavy metal contained in the epitaxial wafer 41 is reliably captured by the gettering sink 44 formed on the silicon wafer 42.
- the leakage current in the dark of the photodiode 469 which is a factor, can be suppressed. Therefore, by forming the solid-state imaging device 460 using the epitaxial wafer 41 obtained by the manufacturing method of the present invention, a solid-state imaging device 460 having excellent imaging characteristics with little dark leakage current can be realized.
- 19 and 20 are cross-sectional views showing the silicon wafer manufacturing method and the epitaxial wafer manufacturing method step by step.
- a silicon wafer for example, a silicon single crystal ingot 8 grown by the Czochralski method (CZ method) is sliced (slicing step: see FIG. 19A), and the silicon wafer (sliced wafer) 2 (See FIG. 19B).
- CZ method Czochralski method
- the surface of the silicon wafer 42 is lapped using abrasive grains or the like (lapping step: see FIG. 19C).
- the lapped silicon wafer (lapping wafer) 2 is etched to remove crystal distortion of the silicon wafer caused by the slicing process or lapping process (etching process: see FIG. 19D).
- etching process for example, a mixed solution of hydrofluoric acid, nitric acid and acetic acid, or an alkaline solution such as sodium hydroxide may be used as the etching solution.
- the lapping process and the etching process may be performed as necessary, and are not necessarily essential processes.
- a grinding step of grinding the surface of the silicon wafer 42 by a grinder may be further provided.
- the silicon wafer 42 is set on the laser irradiation apparatus 20, and the laser beam is irradiated toward the one surface 42a while moving the silicon wafer 42 (multiphoton absorption process: see FIG. 20A).
- the laser beam emitted from the laser generator 115 is focused by a condensing lens (condensing means) 111 at a position where the condensing point (focal point) is several tens of ⁇ m deep from the one surface 42 a of the silicon wafer 42. It is condensed so that it becomes. Thereby, the crystal structure of the silicon wafer 42 is modified, and the gettering sink 44 is formed.
- FIG. 21 is a schematic diagram showing an example of a laser irradiation apparatus 120 for forming a gettering sink on a silicon wafer. This may be the same as that used in the previously described embodiment. Suitable laser irradiation conditions may be the same as in Table 1 described above.
- the optical path width of the laser beam Q11 generated by the laser generator 115 is converged by the condensing lens 111, and the focused laser beam Q21 forms a focal point at an arbitrary depth position G of the silicon wafer 42 (collection).
- the stage 40 is controlled in the vertical direction Y.
- the condensing lens 111 has a magnification of, for example, 10 to 300 times, N.P. It is preferable that A is 0.3 to 0.9 and the transmittance with respect to the wavelength of the laser beam is 30 to 60%.
- the visible light laser beam Q31 generated by the visible light laser generator 119 is reflected by the beam splitter (half mirror) 117b, changes its direction by 90 °, and reaches the epitaxial layer 43 of the silicon wafer.
- the light is reflected by the surface of the epitaxial layer 43, passes through the condensing lens 111 and the beam splitters 117a and 117b, and reaches the imaging lens 112.
- the visible light laser Q31 that has reached the imaging lens 112 is picked up by the CCD camera 130 as a surface image of the silicon wafer 42, and the picked-up data is input to the CCD camera control circuit 135. Based on the input imaging data, the stage control circuit 145 controls the amount of movement of the stage 140 in the horizontal direction X.
- FIG. 22 is a schematic diagram showing how a gettering sink is formed on a silicon wafer by a laser beam.
- the laser beam Q11 emitted from the laser generator 115 is converged by a condensing lens (condensing means) 111. Since the converged laser beam Q21 is in a wavelength range that can be transmitted through silicon, the laser beam Q21 reaches the surface of the epitaxial layer 43 and then enters as it is without being reflected.
- the silicon wafer 42 is positioned so that the condensing point (focal point) of the laser beam Q21 is a predetermined depth D4 from the one surface 42a of the silicon wafer 42.
- a multiphoton absorption process occurs in the silicon wafer 42 only at the condensing point (focal point) of the laser beam Q21.
- the silicon wafer having a single crystal structure is modified at a condensing point (focal point), and a partially amorphous-like crystal is obtained.
- the crystal structure may be modified to such an extent that a capturing action of heavy metals occurs, that is, a slight strain is generated in the crystal structure.
- the crystal structure of the minute region is modified, so that silicon A gettering sink 44 can be formed in an arbitrary minute region of the wafer 42.
- the laser beam for forming the gettering sink 44 can be reliably obtained without modifying the crystal structure of the silicon wafer 42 in the optical path before the laser beam reaches the focal point (focal point). It is important to make the conditions that allow transmission.
- the laser beam irradiation conditions are determined by a forbidden band (energy band gap) which is a basic physical property value of a semiconductor material. For example, since the forbidden band of a silicon semiconductor is 1.1 eV, the transmittance becomes remarkable when the incident wavelength is 1000 nm or more. In this way, the wavelength of the laser beam can be determined in consideration of the forbidden band of the semiconductor material.
- a low-power laser As a laser beam generation device, it is preferable to use a low-power laser because a high-power laser such as a YAG laser may transfer thermal energy not only to a predetermined depth position but also to the surrounding area.
- a high-power laser such as a YAG laser may transfer thermal energy not only to a predetermined depth position but also to the surrounding area.
- the low-power laser for example, an ultrashort pulse laser such as a femtosecond laser is suitable.
- the ultrashort pulse laser can set the wavelength of the laser beam in an arbitrary range by exciting a titanium sapphire crystal (solid laser crystal) using a semiconductor laser or the like.
- the ultrashort pulse laser can reduce the pulse width of the excitation laser beam to 1.0 ⁇ 10 ⁇ 15 femtoseconds or less, so that the diffusion of thermal energy generated by excitation can be suppressed compared to other lasers, and the laser beam is focused. Light energy can be concentrated only at a point (focal point).
- the gettering sink 44 formed by modifying the crystal structure by the multiphoton absorption process probably has an amorphous-like crystal structure.
- the laser beam it is necessary for the laser beam to rapidly heat and cool the condensing point (focal point) G locally.
- an ultrashort pulse laser having the characteristics shown in Table 2 to be described later is a laser having a small amount of energy, but the silicon wafer 420 is rapidly heated locally by focusing using the condensing lens 111. Enough energy to do.
- the temperature of the condensing point (focal point) G of the laser beam reaches a high temperature of 9900 to 10000K.
- the heat input range is very narrow, and if the focal point is moved by moving the stage on which the silicon wafer 42 is mounted or scanning the laser beam, the focal point (focal point) before moving is moved.
- the amount of heat input at has decreased rapidly and a rapid cooling effect is obtained.
- the wavelength of the laser beam exceeds 1200 nm, the photon energy (laser beam energy) decreases because of the long wavelength region. For this reason, there is a possibility that sufficient photon energy for modifying the silicon wafer cannot be obtained even if the laser beam is focused, and the wavelength of the laser beam is preferably 1200 nm or less.
- the position of the condensing point (focus) G4 of the laser beam that is, the position where the gettering sink 44 is formed on the silicon wafer 42 can be controlled by moving the stage up and down. Besides moving the stage up and down, the position of the condensing point (focal point) G4 of the laser beam can also be controlled by controlling the position of the condensing means (condensing lens).
- the gettering sink 44 when the gettering sink 44 is formed by modifying the position of 2 ⁇ m from the surface of the silicon wafer 42, the wavelength of the laser beam is set to 1080 nm and the condensing lens with a transmittance of 60% (magnification)
- the modified portion (gettering sink) can be formed by forming (condensing) a laser beam at a position 2 ⁇ m from the surface using a 50 ⁇ magnification and generating a multiphoton absorption process.
- the gettering sink 44 obtained by modifying the crystal structure of the micro region of the silicon wafer 42 is formed in a disk shape having a diameter R4 of 50 to 150 ⁇ m and a thickness T4 of 10 to 150 ⁇ m, for example. Just do it.
- the formation depth D4 of the gettering sink 44 is preferably about 0.5 to 2 ⁇ m from the one surface 42a of the silicon wafer 42.
- Each gettering sink 44 may be formed at least at a position overlapping with a semiconductor element formed in a later process, for example, a solid-state imaging element formation region S4.
- the gettering sinks 44 may be formed with a formation pitch P4 of 0.1 to 10 ⁇ m.
- the gettering sink 44 may be formed uniformly over the entire surface of the silicon wafer 42 at a predetermined depth with respect to the silicon wafer 42, for example. Good.
- the formation of the gettering sink in the silicon wafer is the same as that in FIG. 6 described above.
- the gettering sink 44 (14 in FIG. 6) may be formed below the formation area of the semiconductor element on the silicon wafer 42, for example, a solid-state imaging element.
- the laser beam Q1 is scanned along the X direction while being shifted in the Y direction at the periphery so that the laser beam Q1 is scanned over the entire area of the silicon wafer 42 (11 in FIG. 6). Can be formed on the entire silicon wafer 42.
- the formation density of the gettering sink 44 in the entire silicon wafer 42 can be set by the scanning pitch B1 of the laser beam Q1.
- the formation density of the gettering sinks 44 is preferably in the range of 1.0 ⁇ 10 5 to 1.0 ⁇ 10 7 pieces / cm 2 , for example.
- the formation density of the gettering sink 44 can be verified by the number of oxygen precipitates obtained by observation with a cross-sectional TEM (transmission electron microscope).
- the laser beam is irradiated onto the silicon wafer 42 by the multiphoton absorption process described in detail, a part of the silicon atoms on the surface layer of the one surface 42a of the silicon wafer 42 is evaporated by the laser beam, and fine scratches ( (Ablation) 42b occurs (see the right figure in FIG. 20A).
- the surface roughness of the one surface 42a of the silicon wafer 42 becomes, for example, 1.0 to 2.5 nm.
- the silicon wafer 42 is mirror-polished (polishing process: see FIG. 20B).
- the polishing process for example, using a polishing machine having a surface plate 476 with a polishing pad 475 attached, the surface of the silicon wafer 42 is mirror-polished in one process or a plurality of processes. In the polishing step, one side or both sides may be mirror-polished according to the specifications of the wafer.
- the silicon wafer 42 is mirror-polished (polishing process). By doing so, fine scratches (ablation) on the surface of the silicon wafer 42 caused by the irradiation of the laser beam can be completely removed. Thereby, there can be obtained a silicon wafer which has no fine scratches on the surface due to laser irradiation and which has a gettering sink formed inside by a multiphoton absorption process.
- the epitaxial layer 43 is formed on the one surface 42a of the silicon wafer 42 obtained through the above-described steps (see FIG. 20D).
- an epitaxial growth apparatus may be used to introduce the source gas while heating the silicon wafer 42 to a predetermined temperature, and to grow the epitaxial layer 43 made of silicon single crystal on the one surface 42a.
- the epitaxial wafer 41 on which the epitaxial layer 43 and the gettering sink 44 are formed may be heated to a predetermined temperature by an annealing device, for example (annealing step).
- an annealing device for example (annealing step).
- the heavy metal diffused in the silicon wafer 42 is collected in the gettering sink 44, and the epitaxial wafer 41 having very little heavy metal in the element forming portion is obtained.
- a semiconductor element for example, an embedded photodiode is formed using such an epitaxial wafer 41 (element forming step), a solid-state imaging element having excellent characteristics with suppressed dark leakage current can be obtained.
- a silicon wafer having a substrate diameter of 300 mm and a thickness of 0.725 mm is irradiated with a laser beam having the conditions shown in Table 2, and the density is set at a depth of 2 ⁇ m from the surface of the silicon wafer.
- a silicon wafer on which a modified portion (gettering sink) of 10 ⁇ 6 / cm 2 was formed was produced.
- a silicon wafer identical to the above-described embodiment was prepared as a conventional comparative example 1 except that no laser beam was irradiated.
- a wafer was prepared.
- Example 1 For each sample of Example 1, Comparative Example 1, and Comparative Example 2, the gettering effect was evaluated by the following method. First, each sample was washed with a mixed solution of ammonia water and hydrogen peroxide solution and a mixed solution of hydrochloric acid and hydrogen peroxide solution, and then by a spin coat contamination method, 1.0 ⁇ 10 12 atoms / The surface was contaminated by about cm 2 . Next, diffusion heat treatment was performed in a nitrogen atmosphere in a vertical heat treatment furnace at 1000 ° C. for 1 hour, and then Wright solution (48% HF: 30 ml, 69% HNO 3 : 30 ml, CrO 3 1 g + H 2 O 2 ml, acetic acid: 60 ml) was used to etch the surface of each sample. The number of etch pits (pits formed by etching nickel silicide) on the surface was observed with an optical microscope and the etch pit density (pieces / cm 2 ) was measured to evaluate the gettering ability of each sample.
- the measurement limit of the etch pit density in this method is 1.0 ⁇ 10 3 pieces / cm 2 . Evaluation of the gettering ability is good when the etch pit density is 1.0 ⁇ 10 3 pieces / cm 2 or less (below the measurement limit), exceeding 1.0 ⁇ 10 3 pieces / cm 2 and 1.0 ⁇ 10 5 pieces / cm 2. Less than cm 2 was allowed, and 1.0 ⁇ 10 5 pieces / cm 2 or more was made impossible.
- the time required for forming the oxygen precipitation portion serving as a gettering sink was evaluated as follows. Each sample was cleaved in the (110) direction, etched with the Wright solution, and then evaluated by observing the density (pieces / cm 2 ) of oxygen precipitates by observing the cleavage plane (sample cross section) with an optical microscope. Evaluation of the gettering ability was carried out by evaluating gettering ability by surface contamination with nickel element as in Example 1 described above.
- Comparative Example 1 As a result of verification, in Comparative Example 1, the etch pit density was 1.0 ⁇ 10 5 pieces / cm 2 , and no gettering effect was observed.
- Comparative Example 2 in the sample subjected to the heat treatment for 10 hours, the density of oxygen precipitates was 1.0 ⁇ 10 4 pieces / cm 2 and the etch pit density was 1.0 ⁇ 10 5 pieces / cm 2, which was almost getter. The ring effect was not recognized. Even in the sample subjected to the heat treatment for 20 hours, the density of oxygen precipitates is 1.0 ⁇ 10 5 pieces / cm 2 and the etch pit density is 1.0 ⁇ 10 4 pieces / cm 2 , and some gettering effect is recognized. Only stayed.
- gettering having an excellent gettering sink capability is achieved by modifying a crystal structure by irradiating a laser beam for a short time to generate a multiphoton absorption process only at a predetermined depth position of a semiconductor substrate.
- the sink can be easily formed at an arbitrary position.
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Abstract
Description
本願は、2008年10月16日に日本で出願された特願2008-267341号、特願2008-267342号、および特願2008-267343号、並びに2009年3月23日に日本で出願された特願2009-069601号のそれぞれに基づき優先権を主張し、その内容をここに援用する。
基板の重金属汚染を抑制するために、従来から、半導体ウェーハの内部あるいは裏面に重金属のゲッタリングシンクを形成し、ゲッタリングシンクに重金属を集める事によって、フォトダイオードの形成部分における重金属濃度を低減させることが行われてきた。
M.Sano, S.Sumita, T.Shigematsu and N. Fujino, SemiconductorSilicon 1994.eds. H.R.Huff et al.(Electrochem. Soc., Pennington 1994)
本発明の半導体デバイスの製造方法は、半導体基板の一面に絶縁膜を形成する工程と、前記半導体基板の他面から集光手段を介してレーザービームを入射させ、前記半導体基板の任意の微小領域に前記レーザービームを集光させることにより、前記微小領域に多光子吸収過程を生じさせ、前記微小領域の結晶構造を変化させたゲッタリングシンクを形成する工程と、前記半導体基板を所定の温度でアニールし、前記ゲッタリングシンクに重金属を捕獲させる工程とを少なくとも備えた。
本発明の裏面照射型固体撮像素子の製造方法は、半導体基板の一面にエピタキシャル層を成長させ、エピタキシャル基板を形成する工程と、前記エピタキシャル基板に向けて集光手段を介してレーザービームを入射し、前記半導体基板の任意の微小領域に前記レーザービームを集光させることにより、前記微小領域に多光子吸収過程を生じさせ、前記微小領域の結晶構造を変化させたゲッタリングシンクを形成する工程と、前記エピタキシャル基板に複数のフォトダイオードを形成する工程と、前記エピタキシャル基板を所定の温度でアニールし、前記ゲッタリングシンクに重金属を捕獲させる工程と、前記半導体基板の厚みを減じて、前記ゲッタリングシンクを含む領域を除去する工程とを少なくとも備えた。
本発明の一態様に係るシリコンウェーハの製造方法は、シリコン単結晶インゴットをスライスしてシリコンウェーハを得るスライス工程と、前記シリコンウェーハに向けて集光手段を介してレーザービームを入射し、任意の微小領域に前記レーザービームを集光させることにより、前記微小領域に多光子吸収過程を生じさせ、前記微小領域の結晶構造を変化させたゲッタリングシンクを形成する多光子吸収工程と、前記多光子吸収工程を経たシリコンウェーハを鏡面研磨するポリッシング工程とを少なくとも備えた。
図1は、本発明の一実施形態に係る固体撮像素子用エピタキシャル基板を示す拡大断面図である。エピタキシャル基板(固体撮像素子用エピタキシャル基板)11は、半導体基板12と、半導体基板12の一面12aに形成されたエピタキシャル層13とを備える。半導体基板12の一面12a近傍付近には、エピタキシャル基板11の重金属を捕捉するゲッタリングシンク14,14・・が形成されている。
次に、本発明に係る半導体デバイス、およびその製造方法の最良の実施形態について、半導体デバイスの一例としてNAND型フラッシュメモリを挙げ、図面に基づき説明する。
図10は、本発明の他の態様に係る固体撮像素子用エピタキシャル基板を示す拡大断面図である。エピタキシャル基板(固体撮像素子用エピタキシャル基板)31は、裏面照射型固体撮像素子の製造に好適な基板(ウェーハ)であり、半導体基板32と、半導体基板32の一面32a寄りに形成されたSOI構造の埋込酸化膜35と、半導体基板32の一面32aに重ねて形成されたエピタキシャル層33とを備える。埋込酸化膜35の下部には、エピタキシャル基板31の重金属を捕捉するゲッタリングシンク34,34・・が形成されている。
図17は、例えば固体撮像素子の製造に好適なエピタキシャルウェーハを示す拡大断面図である。エピタキシャルウェーハ41は、シリコンウェーハ42と、シリコンウェーハ42の一面42aに形成されたエピタキシャル層43とを備える。シリコンウェーハ42の一面42a近傍付近には、エピタキシャルウェーハ41の重金属を捕捉するゲッタリングシンク44,44・・が形成されている。
このため、レーザービームを集光させてもシリコンウェーハ内部の改質に十分な光子エネルギーを得ることができない虞があり、レーザービームの波長は1200nm以下とすることが好ましい。
長時間熱処理による酸素析出部を形成したシリコンウェーハのゲッタリング効果と比較するため、従来の比較例2として、10時間、および20時間の熱処理を施すこと以外は上述した比較例1と同一のシリコンウェーハを用意した。
まず、各サンプルを、アンモニア水と過酸化水素水の混合溶液および塩酸と過酸化水素水の混合溶液で洗浄した後、スピンコート汚染法により、重金属であるニッケルで1.0×1012atoms/cm2程度表面汚染させた。次に、縦型熱処理炉で1000℃、1時間、窒素雰囲気中で拡散熱処理を施し、その後、Wright液(48% HF:30ml、69% HNO3:30ml、CrO3 1g+H2O 2ml、酢酸:60ml)により各サンプルの表面をエッチングした。表面のエッチピット(ニッケルシリサイドがエッチングされて形成されるピット)の個数を光学顕微鏡により観察してエッチピット密度(個/cm2)を測定することにより、各サンプルのゲッタリング能力を評価した。
比較例2では、10時間の熱処理を施したサンプルでは、酸素析出物の密度が1.0×104個/cm2で、エッチピット密度も1.0×105個/cm2と殆どゲッタリング効果が認められなかった。20時間の熱処理を施したサンプルでも、酸素析出物の密度が1.0×105個/cm2で、エッチピット密度は1.0×104個/cm2となり多少のゲッタリング効果が認められるにとどまった。
Claims (33)
- 半導体基板の一面にエピタキシャル層を成長させ、エピタキシャル基板を形成する工程と、
前記エピタキシャル基板に向けて集光手段を介してレーザービームを入射し、前記半導体基板の任意の微小領域に前記レーザービームを集光させることにより、前記微小領域に多光子吸収過程を生じさせ、前記微小領域の結晶構造を変化させたゲッタリングシンクを形成する工程と、
前記エピタキシャル基板を所定の温度でアニールし、前記ゲッタリングシンクに重金属を捕獲させる工程と、
を備えた固体撮像素子用エピタキシャル基板の製造方法。 - 前記レーザービームは、前記エピタキシャル基板を透過可能な波長域であり、前記集光手段は、前記半導体基板の厚み方向における任意の位置に、前記レーザービームを集光させる請求項1記載の固体撮像素子用エピタキシャル基板の製造方法。
- 前記レーザービームは、パルス幅1.0×10-15~1.0×10-8秒、波長300~1200nmの範囲の超短パルスレーザービームである請求項1記載の固体撮像素子用エピタキシャル基板の製造方法。
- 前記半導体基板は単結晶シリコンからなり、前記ゲッタリングシンクはアモルファス構造のシリコンを含む請求項1記載の固体撮像素子用エピタキシャル基板の製造方法。
- 前記ゲッタリングシンクは、前記固体撮像素子の形成領域に重なる位置に形成される請求項1記載の固体撮像素子用エピタキシャル基板の製造方法。
- 請求項1記載の固体撮像素子用エピタキシャル基板の製造方法により製造された固体撮像素子用エピタキシャル基板であって、
前記ゲッタリングシンクは、少なくとも前記固体撮像素子を構成する埋込み型フォトダイオードの形成位置と重なる領域に、直径50~150μm、厚み10~150μmの範囲のサイズで設けられている固体撮像素子用エピタキシャル基板。 - 前記ゲッタリングシンクは、密度1.0×105~1.0×107個/cm2の範囲で形成されてなる請求項6記載の固体撮像素子用エピタキシャル基板。
- 半導体基板の一面に絶縁膜を形成する工程と、
前記半導体基板の他面から集光手段を介してレーザービームを入射させ、前記半導体基板の任意の微小領域に前記レーザービームを集光させることにより、前記微小領域に多光子吸収過程を生じさせ、前記微小領域の結晶構造を変化させたゲッタリングシンクを形成する工程と、
前記半導体基板を所定の温度でアニールし、前記ゲッタリングシンクに重金属を捕獲させる工程と、
を少なくとも備えた半導体デバイスの製造方法。 - 前記レーザービームは、前記半導体基板を透過可能な波長域であり、前記集光手段は、前記半導体基板の厚み方向における任意の位置に、前記レーザービームを集光させる請求項8記載の半導体デバイスの製造方法。
- 前記レーザービームは、パルス幅1.0×10-15~1.0×10-8秒、波長300~1200nmの範囲の超短パルスレーザービームである請求項8記載の半導体デバイスの製造方法。
- 前記半導体基板は単結晶シリコンからなり、前記ゲッタリングシンクは少なくともその一部にアモルファス構造のシリコンを含む請求項8記載の半導体デバイスの製造方法。
- 前記ゲッタリングシンクは、デバイスの形成領域と重なる位置に少なくとも形成されている請求項8記載の半導体デバイスの製造方法。
- 請求項8記載の半導体デバイスの製造方法により製造され、ゲッタリングシンクが密度1.0×105~1.0×106個/cm2の範囲で形成されてなる半導体デバイス。
- 半導体基板の一面にエピタキシャル層を成長させ、エピタキシャル基板を形成する工程と、
前記エピタキシャル基板に向けて集光手段を介してレーザービームを入射し、前記半導体基板の任意の微小領域に前記レーザービームを集光させることにより、前記微小領域に多光子吸収過程を生じさせ、前記微小領域の結晶構造を変化させたゲッタリングシンクを形成する工程と、
前記エピタキシャル基板に複数のフォトダイオードを形成する工程と、
前記エピタキシャル基板を所定の温度でアニールし、前記ゲッタリングシンクに重金属を捕獲させる工程と、
前記半導体基板の厚みを減じて、前記ゲッタリングシンクを含む領域を除去する工程と、
を少なくとも備えた裏面照射型固体撮像素子の製造方法。 - 前記レーザービームは、前記エピタキシャル基板を透過可能な波長域であり、前記集光手段は、前記半導体基板の厚み方向における任意の位置に、前記レーザービームを集光させる請求項14記載の裏面照射型固体撮像素子の製造方法。
- 前記レーザービームは、パルス幅1.0×10-15~1.0×10-8秒、波長300~1200nmの範囲の超短パルスレーザービームである請求項14記載の裏面照射型固体撮像素子の製造方法。
- 前記半導体基板は単結晶シリコンからなり、前記ゲッタリングシンクはアモルファス構造のシリコンを含む請求項14記載の裏面照射型固体撮像素子の製造方法。
- 前記ゲッタリングシンクは、前記フォトダイオードの形成領域と重なる位置に少なくとも形成される請求項14記載の裏面照射型固体撮像素子の製造方法。
- 前記ゲッタリングシンクと前記エピタキシャル層との間には、更にSOI構造の埋込酸化膜が形成される請求項14記載の裏面照射型固体撮像素子の製造方法。
- 半導体基板と、前記半導体基板の一面に形成されたエピタキシャル層と、前記半導体基板に向けて集光手段を介してレーザービームを入射し、前記半導体基板の任意の微小領域に前記レーザービームを集光させることにより、前記微小領域に多光子吸収過程を生じさせ、前記微小領域の結晶構造を変化させて形成したゲッタリングシンクと、前記ゲッタリングシンクと前記エピタキシャル層との間に形成されたSOI構造の埋込酸化膜と、を備えた固体撮像素子用エピタキシャル基板。
- 前記ゲッタリングシンクは、少なくとも前記フォトダイオードの形成位置と重なる領域に、直径50~150μm、厚み10~150μmの範囲のサイズで設けられている請求項20記載の固体撮像素子用エピタキシャル基板。
- 前記ゲッタリングシンクは、密度1.0×105~1.0×107個/cm2の範囲で形成されてなる請求項20記載の固体撮像素子用エピタキシャル基板。
- シリコン単結晶インゴットをスライスしてシリコンウェーハを得るスライス工程と、
前記シリコンウェーハに向けて集光手段を介してレーザービームを入射し、任意の微小領域に前記レーザービームを集光させることにより、前記微小領域に多光子吸収過程を生じさせ、前記微小領域の結晶構造を変化させたゲッタリングシンクを形成する多光子吸収工程と、
前記多光子吸収工程を経たシリコンウェーハを鏡面研磨するポリッシング工程と、
を少なくとも備えたシリコンウェーハの製造方法。 - 前記スライス工程と前記多光子吸収工程との間には、シリコンウェーハを研磨するラッピング工程を更に備えた請求項23記載のシリコンウェーハの製造方法。
- 前記スライス工程と前記多光子吸収工程との間には、シリコンウェーハをエッチングするエッチング工程を更に備えた請求項23記載のシリコンウェーハの製造方法。
- 前記レーザービームは、前記エピタキシャルウェーハを透過可能な波長域であり、前記集光手段は、前記シリコンウェーハの厚み方向における任意の位置に、前記レーザービームを集光させる請求項23記載のシリコンウェーハの製造方法。
- 前記レーザービームは、パルス幅1.0×10-15~1.0×10-8秒、波長300~1200nmの範囲の超短パルスレーザービームである請求項23記載のシリコンウェーハの製造方法。
- 前記ゲッタリングシンクはアモルファス構造のシリコンを含む請求項23記載のシリコンウェーハの製造方法。
- 請求項23記載のシリコンウェーハの製造方法によって得たシリコンウェーハの一面にシリコン単結晶のエピタキシャル層を成長させるエピタキシャル工程を少なくとも備えたエピタキシャルウェーハの製造方法。
- 請求項29記載のエピタキシャルウェーハの製造方法によって得たエピタキシャルウェーハの一面に埋込み型フォトダイオードを形成する素子形成工程を少なくとも備えた固体撮像素子の製造方法。
- 前記エピタキシャルウェーハを所定の温度でアニールし、前記ゲッタリングシンクに重金属を捕獲させるアニール工程を更に備えた請求項30記載の固体撮像素子の製造方法。
- 前記ゲッタリングシンクは、少なくとも前記埋込み型フォトダイオードの形成位置と重なる領域に、直径50~150μm、厚み10~150μmの範囲のサイズで形成する請求項30記載の固体撮像素子の製造方法。
- 前記ゲッタリングシンクは、密度が1.0×105~1.0×107個/cm2の範囲となるように形成する請求項30記載の固体撮像素子の製造方法。
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US20110248372A1 (en) | 2011-10-13 |
TWI419203B (zh) | 2013-12-11 |
US9281197B2 (en) | 2016-03-08 |
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