JP2012204505A - Semiconductor ultraviolet light receiving element and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor ultraviolet light receiving element having a novel structure, which suppresses separation of a metal electrode for wiring-bonding from an organic electrode.SOLUTION: A semiconductor ultraviolet light receiving element comprises a semiconductor layer formed of a II group oxide semiconductor or a group III nitride semiconductor and above a part of an insulating foundation; an ultraviolet-transmitting organic electrode covering an upper and a side surface of the semiconductor layer and having an edge reaching above the insulating foundation; and a metal electrode for wire-bonding extending from the organic electrode to the insulating foundation and ensuring a bonding region above the insulating foundation.

Description

  The present invention relates to a semiconductor ultraviolet light receiving element and a method for manufacturing the same.

  There has been proposed a photovoltaic type ultraviolet sensor in which a metal such as Pt having a film thickness exhibiting ultraviolet transparency is formed on a ZnO substrate using a Schottky electrode (see Patent Document 1).

    By using an organic conductive material such as PEDOT: PSS as a Schottky electrode formed on a ZnO-based semiconductor, the dark current at a reverse bias voltage is very small compared to a general metal electrode such as Pt. It has been shown that the characteristics of these are improved (see Patent Document 2).

  A pedestal portion made of an insulating film is formed on a part of the ZnO-based semiconductor, an organic electrode is formed on the ZnO-based semiconductor so as to cover the pedestal portion, and an electrode for wire bonding is formed on the organic electrode above the pedestal portion. The technique which prevents peeling of the electrode for wire bonding at the time of wire bonding is proposed by the element structure (refer patent document 3).

  An ultraviolet sensor in which an organic electrode is formed on a GaN-based semiconductor has also been proposed (see Patent Document 4).

  The organic electrode has weak adhesion to the metal electrode for wire bonding, and the wire bonding electrode is easily peeled off during wire bonding.

  A technique for controlling the polarity of a ZnO-based semiconductor layer grown on a nonpolar single crystal substrate has been proposed (see Patent Document 5).

  A technique for producing a high resistivity and high purity zinc oxide single crystal has been proposed (Patent Document 6).

JP 2007-201393 A JP 2008-211203 A JP 2010-205891 A JP 2010-56504 A Japanese Patent Laid-Open No. 2005-197410 JP 2010-70424 A

  An object of the present invention is to provide a semiconductor ultraviolet light receiving element having a novel structure in which peeling of a metal electrode for wire bonding from an organic electrode is suppressed, and a method for manufacturing the same.

  According to one aspect of the present invention, a semiconductor layer formed of a group II oxide semiconductor or a group III nitride semiconductor, a top surface and a side surface of the semiconductor layer are covered above a part of an insulating base, and an end portion is An ultraviolet transparent organic electrode formed so as to reach the insulating base, and wire bonding that extends from the organic electrode onto the insulating base and secures a bonding region above the insulating base. A semiconductor ultraviolet light receiving element having a metal electrode is provided.

  Since the metal electrode for wire bonding is formed so as to straddle the organic electrode and the insulating base, peeling of the metal electrode for wire bonding is suppressed.

1A to 1C are schematic cross-sectional views illustrating main manufacturing steps of a light receiving element according to a first embodiment of the present invention. 1D and 1E are schematic cross-sectional views showing main manufacturing steps of the light receiving element according to the first embodiment of the present invention. FIG. 2 is a schematic sectional view showing the overall structure of the light receiving device of the first embodiment. FIG. 3A is a graph showing the IV characteristics of the light receiving element of the first embodiment, FIG. 3B is a schematic circuit diagram of a light response characteristic measuring circuit, and FIG. 3C is a light receiving characteristic of the first embodiment. It is a graph which shows the optical response characteristic of an element. FIG. 4 is a schematic cross-sectional view showing a light receiving element according to a modification of the first embodiment. FIG. 5 is a schematic cross-sectional view showing the light receiving element of the second embodiment. 6A to 6E are schematic plan views illustrating examples of arrangement of the organic electrode, the metal electrode for wire bonding, and the exposed region of the insulating base. FIG. 7 is a schematic cross-sectional view showing the light receiving element of the third embodiment. 8A to 8C are schematic cross-sectional views showing main manufacturing steps of the light receiving element of the fourth embodiment. 8D and 8E are schematic cross-sectional views showing main manufacturing steps of the light receiving element of the fourth embodiment. FIG. 9 is a schematic cross-sectional view showing a light receiving element according to a modification of the fourth embodiment. 10A and 10B are schematic cross-sectional views of a light receiving element according to a comparative example. FIG. 11 is a graph showing the relationship between the energy gap of Mg _x Zn _1-x O and the Mg composition x.

  First, a semiconductor ultraviolet light receiving element according to a comparative example will be described.

  FIG. 10A is a schematic cross-sectional view of a light receiving element according to a comparative example. In the light receiving element of the comparative example, molecular beam epitaxy (MBE) is used as a method for growing the semiconductor layer.

On the c-plane sapphire substrate 101, an Mg beam and an O radical beam are simultaneously irradiated to grow the MgO layer 102 to a thickness of about 10 nm. The growth conditions of the MgO layer 102 are, for example, a growth temperature of 650 ° C., an Mg flux of 0.05 nm / s, an O ₂ flow rate of O source gun of ₂ sccm / RF power of 300 W.

  The MgO layer 102 serves as a polarity control layer for growing a ZnO-based semiconductor layer grown thereon on a Zn polarity plane (+ c plane). Regarding the technology for controlling the polarity of the ZnO-based semiconductor layer grown above the nonpolar single crystal substrate via the MgO layer, refer to “Best Mode for Carrying Out the Invention” in Japanese Patent Laid-Open No. 2005-197410. Is explained in the column.

On the MgO layer 102, a Zn beam and an O radical beam are simultaneously irradiated to grow the ZnO buffer layer 103 to a thickness of about 30 nm. The growth conditions of the ZnO buffer layer 103 are, for example, a growth temperature of 300 ° C., a Zn flux of 0.1 nm / s, an O ₂ flow rate of O source gun of ₂ sccm / RF power of 300 W. After the growth of the ZnO buffer layer 103, annealing is performed at 900 ° C. for 30 minutes in order to improve crystallinity and surface flatness.

A Zn beam, O radical beam, and Ga beam are simultaneously irradiated on the ZnO buffer layer 103 to grow a Ga-doped n-type ZnO layer 104 with a thickness of about 2 μm. The growth conditions of the n-type ZnO layer 104 are, for example, a growth temperature of 900 ° C., a Zn flux of 0.3 nm / s, an O source flow rate of ₂ sccm / RF power of 300 W, and a Ga cell temperature of 380 ° C.

On the n-type ZnO layer 104, a Zn beam and an O radical beam are simultaneously irradiated to grow an undoped ZnO layer 105 to a thickness of about 1.5 μm. The growth conditions of the undoped ZnO layer 105 are, for example, a growth temperature of 900 ° C., a Zn flux of 0.05 nm / s, an O ₂ flow rate of O source gun of ₂ sccm / RF power of 300 W.

  A resist resist pattern for etching the undoped ZnO layer 105 is formed on the undoped ZnO layer 105. Using this resist pattern as a mask, the undoped ZnO layer 105 is etched with an acid to expose the n-type ZnO layer 104. The resist pattern is removed and cleaning is performed.

  Next, an organic electrode 106 made of a conductive polymer is formed on the undoped ZnO layer 105. Specifically, for example, PEDOT: PSS can be used as the material of the organic electrode 106. PEDOT: PSS is a polythiophene derivative poly3,4-ethylenedioxythiophene (PEDOT) containing polystyrene sulfonic acid (PSS) as a carrier dopant and water dispersant. For example, dimethyl sulfoxide (DMSO) is added to PEDOT: PSS as a conductivity increasing agent. In addition, the organic electrode forming material of the below-mentioned Example is the same as that of the comparative example.

  First, a lift-off pattern for forming the organic electrode 106 is formed on the undoped ZnO layer 105 with a resist. Thereafter, ultraviolet (UV) ozone cleaning is performed. Then, PEDOT: PSS to which a conductivity increasing agent is added is applied by spin coating (thickness after the heat treatment), for example, 30 nm in thickness, and the organic electrode 106 is formed by lift-off. After lift-off, for example, heat treatment is performed at 200 ° C. for 20 minutes using a hot plate.

  The undoped ZnO layer 105 has higher resistance than the Ga-doped n-type ZnO layer 104 doped with n-type impurities, but exhibits n-type conductivity. The organic electrode 106 forms a Schottky electrode with respect to the undoped ZnO layer 105 and is ultraviolet transmissive. Photovoltaics are generated by the ultraviolet rays that have passed through the organic electrode 106 and entered the undoped ZnO layer 105. In such a semiconductor ultraviolet light receiving element, by using a Schottky electrode, it is not necessary to form a p-type semiconductor that is difficult to form as compared with an n-type semiconductor layer.

  A metal mask 107 is formed on the organic electrode 106 by depositing an Au layer having a thickness of 100 nm by electron beam (EB) evaporation using a metal mask. On the n-type ZnO layer 104 exposed by etching the undoped ZnO layer 105, a Ti layer 108a having a thickness of 10 nm is formed, and an Au layer 108b having a thickness of 500 nm is stacked on the Ti layer 108a to form an ohmic electrode 108. To do. In this manner, the light receiving element of the comparative example is manufactured.

  Thereafter, the light receiving element of the comparative example is bonded onto the stem by die bonding and wire bonding, and the light receiving device of the comparative example is manufactured.

  FIG. 10B is a schematic cross-sectional view showing a light receiving element of a comparative example at the time of wire bonding. An Au wire 112 is bonded to a wire bonding metal electrode 107 formed on the organic electrode 106 via an Au ball 111.

  However, the light receiving element of the comparative example has poor adhesion between the wire bonding metal electrode 107 and the organic electrode 106, and the wire bonding metal electrode 107 easily peels from the organic electrode 106.

  The inventors of the present application propose a semiconductor ultraviolet light receiving element in which peeling of the metal electrode for wire bonding from the organic electrode is suppressed as described below.

  Next, the semiconductor ultraviolet light receiving element according to the first embodiment will be described. Also in the first embodiment, MBE is used as a method for growing a semiconductor layer, as in the comparative example. 1A to 1E are schematic cross-sectional views showing main manufacturing steps of the light receiving element of the first embodiment.

  Reference is made to FIG. 1A. For example, an MgO layer 2 is grown on the c-plane sapphire substrate 1 under the same conditions as in the comparative example, a ZnO buffer layer 3 is grown on the MgO layer 2 and annealed, and an n-type ZnO layer is formed on the ZnO buffer layer 3. 4 is grown, and an undoped ZnO layer 5 is grown on the n-type ZnO layer 4. The ZnO-based semiconductor layer above the MgO layer 2 grows on the Zn plane.

The carrier concentrations of the (Ga-doped) n-type ZnO epi layer 4 and the undoped ZnO epi layer 5 are, for example, 8.0 × 10 ¹⁷ cm ⁻³ and 7.6 × 10 ¹⁵ cm ⁻³ , respectively.

In order to satisfactorily form a Schottky junction suitable as a light receiving element, the carrier concentration of the semiconductor layer in contact with the organic electrode is preferably as low as 1 × 10 ¹⁶ cm ⁻³ or less, for example. By growing the ZnO-based semiconductor layer on the Zn surface, it is easy to stably form a semiconductor layer having a low carrier concentration.

On the undoped ZnO layer 5, a resist pattern RP1 is formed. The resist pattern RP1 has an opening that exposes a region where the ohmic electrode 70 is disposed in a later step. Using the resist pattern RP1 as a mask, the undoped ZnO layer 5 is etched by wet etching using an acidic solution to expose the n-type ZnO layer 4. As the acidic solution, HCl, HNO ₃ , HF, aqua regia, EDTA solution, buffered HF, or the like can be used. Further, dry etching may be used. Thereafter, the resist pattern RP1 is removed and cleaning is performed.

Refer to FIG. 1B. A resist pattern RP2 is formed. The resist pattern RP2 has an opening exposing a region where wire bonding is performed on the wire bonding metal electrode 7W formed in a later step. Using the resist pattern RP2 as a mask, the undoped ZnO layer 5, the n-type ZnO layer 4, the ZnO buffer layer 3, and the MgO layer 2 are etched with an acidic solution to expose the sapphire substrate 1. As the acidic solution, HCl, HNO ₃ , HF, aqua regia, EDTA solution, buffered HF, or the like can be used. Further, dry etching may be used. Thereafter, the resist pattern RP2 is removed and cleaning is performed.

  Reference is made to FIG. 1C. A resist pattern RP3 is formed. The resist pattern RP3 has an opening that exposes a region where the organic electrode 6 is formed. After performing UV ozone cleaning, PEDOT: PSS to which a conductivity increasing agent is added is applied by spin coating (thickness after heat treatment), for example, with a thickness of 30 nm. The organic electrode 6 is formed by lift-off that removes unnecessary portions of PEDOT: PSS together with the resist pattern RP3. After lift-off, for example, heat treatment is performed at 200 ° C. for 20 minutes using a hot plate.

  The organic electrode 6 covers the upper surface of the undoped ZnO layer 5 and the laminated side surface of the undoped ZnO layer 5, the n-type ZnO layer 4, the ZnO buffer layer 3, and the MgO layer 2, and the end of the portion covering the laminated side surface is It reaches on the sapphire substrate 1 exposed in the etching process of FIG. 1B.

  Reference is made to FIG. 1D. An ohmic electrode 70 and a wire bonding metal electrode 7W are formed. The ohmic electrode 70 is also wire-bonded in a later step, but the wire-bonding metal electrode 7W is simply referred to as a wire-bonding metal electrode 7W.

  Using a metal mask having openings in the formation region of the ohmic electrode 70 and the formation region of the wire bonding metal electrode 7W, a Ti layer 7a having a thickness of 10 nm, for example, is formed by EB vapor deposition. A 500 nm Au layer 7b is laminated to form an ohmic electrode 70 and a wire bonding metal electrode 7W simultaneously.

  The ohmic electrode 70 is formed on the n-type ZnO layer 4 exposed in the etching process of FIG. 1A. The metal electrode for wire bonding 7 </ b> W is an organic material on the side surface of the organic electrode 6 on the upper surface of the undoped ZnO layer 5 and the side surface of the undoped ZnO layer 5, n-type ZnO layer 4, ZnO buffer layer 3, and MgO layer 2. The sapphire substrate 1 is formed so as to cover the electrode 6 and exposed in the etching process of FIG. 1B.

  The wire bonding metal electrode 7W is disposed so as to extend from the organic electrode 6 to the sapphire substrate 1 which is an insulating base, and covers a part of the organic electrode 6 to secure a translucent region. A wide area to be a wire bonding region is secured in the upper part of the substrate 1. The Ti layer 7a functions as an adhesion layer with the sapphire substrate 1 which is an insulating base.

  Since the organic electrode 6 covers the upper surface of the undoped ZnO layer 5 and the laminated side surfaces of the undoped ZnO layer 5, n-type ZnO layer 4, ZnO buffer layer 3, and MgO layer 2, the wire bonding metal electrode 7W The short circuit which contacts the electroconductive ZnO layers 3-5 is prevented.

  In this way, the light receiving element of the first embodiment is manufactured. Thereafter, the light receiving element of the first embodiment is bonded onto the stem by die bonding and wire bonding, and the light receiving device of the first embodiment is manufactured.

  FIG. 1E is a schematic cross-sectional view showing the light receiving element of the first embodiment during wire bonding.

  FIG. 2 is a schematic sectional view showing the overall structure of the light receiving device of the first embodiment. The sapphire substrate 1 of the light receiving element is die-bonded on one electrode 21 a of the stem 21 via an adhesive 22. The ohmic electrode 7O (the upper Au layer 7b) of the light receiving element and the electrode 21a are wire-bonded with Au wires 12 through Au balls 11 and 13, respectively.

  The wire bonding metal electrode 7 </ b> W (the upper Au layer 7 b) of the light receiving element and the other electrode 21 b of the stem 21 are wire-bonded with Au wires 15 via Au balls 14 and 16. Au balls 14 are arranged in the upper region of the sapphire substrate 1 of the wire bonding metal electrode 7W. The upper side of the light receiving element is covered with a container 23 in which an ultraviolet transmission window 24 is formed.

  In the light receiving element of the first embodiment, the wire bonding metal electrode 7W is formed over the organic electrode 6 and the insulating substrate 1, so that the wire bonding metal electrode from the organic electrode 6 during wire bonding is formed. 7W peeling is suppressed.

  The electrical characteristics of the light receiving element of the first embodiment will be described. A positive voltage is applied to the anode side with the semiconductor layer 4 side (ohmic electrode 7O side) as the cathode (cathode) and the organic electrode 6 side (wire bonding metal electrode 7W side) as the Schottky electrode as the anode (anode). The case is a forward bias, and the case where a negative voltage is applied is a reverse bias. A light receiving element is used as a reverse bias or an applied voltage of 0V.

  FIG. 3A is a graph showing current-voltage characteristics (IV characteristics) of the light receiving element of the first embodiment. The horizontal axis represents the applied voltage, and the vertical axis represents the absolute value of the current and is log-displayed. The dark current is indicated by a broken line and the photocurrent is indicated by a solid line. An LED (0.035 μW) having a wavelength of 365 nm was used as a light source during photocurrent measurement.

  Looking at the characteristics at the reverse bias used as the light receiving element, the dark current in the dark state where no light is irradiated is 1 nA or less when the voltage is applied to -4V. The photocurrent at the time of light irradiation is several tens of nA when a voltage up to -4V is applied.

  The response characteristics of the light receiving element of the first embodiment at the time of light incidence (on time) and light shielding (off time) will be described.

  FIG. 3B is a circuit diagram schematically showing an optical response characteristic measurement circuit. The light receiving element is represented by a diode, and a resistor R (91 kΩ) is connected between the terminal on the organic electrode side and the ground potential. A DC voltage source Vias (−1 V) is connected between the terminal on the semiconductor layer side of the light receiving element and the ground potential. Light hν is incident on the light receiving element.

  The ultraviolet laser beam was turned on and off with a chopper, and the output voltage V of the resistor R at an applied voltage of −1 V to the light receiving element was measured as an optical response voltage with an oscilloscope. As the ultraviolet laser, a He—Cd laser (1 μW) having a wavelength of 325 nm was used.

  FIG. 3C is a graph showing optical response characteristics of the light receiving element of the first embodiment. The magnitude of the output voltage is indicated by an arrow. An output voltage of 12 mV was obtained. When converted into light receiving sensitivity, about 130 mA / W was obtained.

  From the above measurement results, it was confirmed that the ZnO-based semiconductor element of the first example functions as an ultraviolet light receiving element.

  FIG. 4 is a schematic cross-sectional view of a light receiving element according to a modification of the first embodiment. The light receiving element of this modification has a structure in which the MgO layer 2 that is a polarity control layer is left by etching in the process of FIG. 1B.

  The organic electrode 6 is formed in the same manner as described with reference to FIG. 1C, and includes an upper surface of the undoped ZnO layer 5 and a stacked side surface of the undoped ZnO layer 5, the n-type ZnO layer 4, and the ZnO buffer layer 3. The end of the portion covering and covering the laminated side surface reaches the exposed upper surface of the MgO layer 2.

  The wire bonding metal electrode 7 </ b> W is formed in the same manner as described with reference to FIG. 1D, the edge of the organic electrode 6 on the upper surface of the undoped ZnO layer 5, the undoped ZnO layer 5, and the n-type ZnO layer 4. And the organic electrode 6 on the stacked side surface of the ZnO buffer layer 3 and the exposed upper surface of the MgO layer 2.

  Since the organic electrode 6 covers the laminated side surfaces of the undoped ZnO layer 5, the n-type ZnO layer 4, and the ZnO buffer layer 3, a short circuit where the wire bonding metal electrode 7W contacts the ZnO layers 3 to 5 is prevented. Yes. Similarly to the sapphire substrate 1 of the first embodiment, the MgO layer 2 also becomes an insulating base, so that even if the wire bonding metal electrode 7W is formed on the upper surface of the MgO layer 2, no short circuit occurs.

  The wire bonding metal electrode 7W is formed on the upper surface of the MgO layer 2, so that the wire bonding metal electrode 7W is formed as compared with the electrode structure of the first embodiment in which the wire bonding metal electrode 7W is formed on the upper surface of the sapphire substrate 1. An improvement in the adhesion of the electrode 7W can be expected.

Next, a semiconductor ultraviolet light receiving element according to the second embodiment will be described. In the second embodiment, a high resistance ZnO substrate is used instead of the sapphire substrate of the first embodiment. Japanese Patent Application Laid-Open No. 2010-70424 discloses a method for producing a zinc oxide single crystal having high resistivity and high purity. According to this method, a high-resistance ZnO substrate having a Li concentration of 1.0 × 10 ¹⁶ atoms / cm ³ or less and a resistivity of 1 × 10 ¹⁰ Ω · cm or more can be obtained. In this embodiment, it is preferable to use a high-resistance ZnO substrate having a resistivity of 10 ⁶ Ω · cm or more. A high-resistance substrate having a resistivity of 10 ⁶ Ω · cm or more can be substantially treated as an insulating substrate. MBE is used as a method for growing the semiconductor layer.

FIG. 5 is a schematic cross-sectional view of the light receiving element of the second embodiment. A ZnO buffer layer 32 is grown to a thickness of 30 nm by simultaneously irradiating a Zn beam and an O radical beam on the high-resistance Zn surface ZnO (0001) substrate 31. The growth conditions of the ZnO buffer layer 32 are, for example, a growth temperature of 300 ° C., a Zn flux of 0.1 nm / s, an O ₂ flow rate of O source gun of ₂ sccm / RF power of 300 W. After the growth of the ZnO buffer layer 32, annealing is performed at 900 ° C. to improve crystallinity and surface flatness.

A Zn beam, O radical beam, and Ga beam are simultaneously irradiated on the ZnO buffer layer 32 to grow a Ga-doped n-type ZnO layer 33 with a thickness of about 2 μm. The growth conditions of the n-type ZnO layer 33 are, for example, a growth temperature of 900 ° C., a Zn flux of 0.3 nm / s, an O source flow rate of ₂ sccm / RF power of 300 W, and a Ga cell temperature of 380 ° C.

On the n-type ZnO layer 33, a Zn beam and an O radical beam are simultaneously irradiated to grow an undoped ZnO layer 34 to a thickness of about 1.5 μm. The growth conditions of the undoped ZnO layer 34 are, for example, a growth temperature of 900 ° C., a Zn flux of 0.15 nm / s, an O ₂ flow rate of O source gun of ₂ sccm / RF power of 300 W.

  After the formation of the undoped ZnO layer 34, the undoped ZnO layer 34 is etched to expose the n-type ZnO layer 33 in the arrangement region of the ohmic electrode 36O in the same manner as described in the first embodiment with reference to FIG. 1A. Let

  Next, the undoped ZnO layer 34, the n-type ZnO layer 33, and the ZnO buffer layer 32 are etched in the same manner as described with reference to FIG. 1B in the first embodiment to form the wire bonding metal electrode 36W. The high resistance ZnO substrate 31 is exposed in the region.

  Next, the organic electrode 35 is formed in the same manner as described in the first embodiment with reference to FIG. 1C. The organic electrode 35 covers the upper surface of the undoped ZnO layer 34 and the laminated side surface of the undoped ZnO layer 34, the n-type ZnO layer 33, and the ZnO buffer layer 32, and the end of the portion covering the laminated side surface is exposed to a high resistance. It reaches on the ZnO substrate 31.

  Next, similarly to the process described with reference to FIG. 1D in the first embodiment, the Ti layer 36a and the Au layer 36b are laminated using a metal mask, and the ohmic electrode 36O and the wire bonding metal electrode 36W are formed. Form simultaneously. The ohmic electrode 36O is formed on the n-type ZnO layer 33. The wire bonding metal electrode 36 </ b> W covers the edge of the organic electrode 35 on the upper surface of the undoped ZnO layer 34, and the organic electrode 35 on the stacked side surface of the undoped ZnO layer 34, n-type ZnO layer 33, and ZnO buffer layer 32. Further, it is formed so as to cover the high resistance ZnO substrate 31.

  Since the upper surface of the undoped ZnO layer 34 and the side surfaces of the undoped ZnO layer 34, the n-type ZnO layer 33, and the ZnO buffer layer 32 are covered with the organic electrode 35, the undoped ZnO layer 34, the n-type ZnO layer 33, and A short circuit between the ZnO buffer layer 32 and the wire bonding metal electrode 36W is prevented.

  Further, since the wire bonding metal electrode 36 </ b> W is formed across the organic electrode 35 and the high-resistance substrate 31, peeling of the wire bonding metal electrode 36 </ b> W from the organic electrode 35 is suppressed.

  In this way, the light receiving element of the second embodiment is manufactured. Thereafter, the light receiving element of the second embodiment is bonded onto the stem by die bonding and wire bonding, and the light receiving device of the second embodiment is manufactured.

  6A to 6E are schematic plan views showing various arrangement examples of the organic electrode OE, the wire bonding metal electrode WE, and the exposed region IS of the insulating base on the light receiving element. In addition, the vicinity of the metal electrode WE for wire bonding is illustrated, and the ohmic electrode formation region is omitted.

  In FIG. 6A, a square insulating base exposed region IS is arranged at the corner of the light receiving element, and the other part is covered with the organic electrode OE, and a circular wire arranged on the insulating base exposed region IS. The bonding metal electrode WE protrudes from the insulating base exposed region IS onto the organic electrode OE and overlaps.

  In FIG. 6B, a square-shaped insulating base exposed region IS is disposed inside the light receiving element, and the periphery thereof is covered with an organic electrode OE, for circular wire bonding disposed on the insulating base exposed region IS. The metal electrode WE protrudes from the insulating base exposed region IS onto the organic electrode OE and overlaps.

  In FIG. 6C, a circular insulating base exposed region IS is disposed inside the light receiving element, and the organic electrode OE is covered around the circular insulating base exposed region IS. The insulating base exposed region IS has a radius larger than that of the insulating base exposed region IS. A large circular metal electrode WE for wire bonding is arranged.

  In FIG. 6D, a square insulating base exposed region IS is arranged at the corner of the light receiving element, and the other part is covered with the organic electrode OE, and the wire bonding metal electrode WE is within the insulating base exposed region IS. And a rod-shaped portion extending from the circular portion in the vertical direction and the horizontal direction and extending on the organic electrode OE.

  In FIG. 6E, a square-shaped insulating base exposed region IS is disposed inside the light receiving element, and the periphery thereof is covered with the organic electrode OE, and the wire bonding metal electrode WE fits in the insulating base exposed region IS. It has a circular portion and a rod-shaped portion extending from the circular portion in the vertical direction and the horizontal direction and extending on the organic electrode OE.

In the first and second embodiments, ZnO is used as the light receiving semiconductor layer, but MgZnO can also be used as the light receiving semiconductor layer. Mg _x Zn _1-x O in which the Mg composition x is specified has a wurtzite structure when 0 ≦ x <0.6, and a rock salt structure when 0.6 ≦ x ≦ 1. Incidentally, _Mg x _{Zn 1-x} O of Mg composition x 0 represents the ZnO.

FIG. 11 is a graph showing the relationship between the energy gap of Mg _x Zn _1-x O (wurtzite structure) and the Mg composition x. In Mg _x Zn _1-x O having a wurtzite structure, when the Mg composition x is increased from 0 to 0.6, the energy gap increases from 3.3 eV (wavelength 376 nm) to 4.4 eV (wavelength 282 nm). Further, in Mg _x Zn _1-x O having a rock salt structure, when the Mg composition x is increased from 0.6 to 1.0, the energy gap increases from 5.4 eV (wavelength 230 nm) to 7.8 eV (wavelength 159 nm). . As the energy gap increases, the light receiving sensitivity wavelength shifts to the short wavelength side. By using this, the wavelength can be selected.

  The ultraviolet rays of sunlight are classified into UV-A (320 to 400 nm), UV-B (280 to 320 nm), and UV-C (280 nm or less), but UV-C is absorbed by the ozone layer and reaches the ground surface. Since it does not reach, normal ultraviolet rays are substantially UV-A and UV-B. For example, UV-C is included only in a flame or the like.

By using Mg _x Zn _1-x O having a rock salt structure with a large energy gap, it becomes possible to detect only UV-C (280 nm or less) having a short wavelength. Therefore, for example, it can be used as a flame sensor for detecting a flame containing UV-C.

In the case of growing the _{Mg x Zn 1-x} O rock salt structure, as a growth substrate, it is preferable to use MgO substrate having the same rock salt structure.

In the above embodiment, a sapphire substrate (Al ₂ O ₃ ) is used as the insulating substrate, but AlN, MgO, or the like can also be used as the insulating substrate.

  In the above embodiment, a Ga-doped n-type ZnO layer is used as the n-type ZnO-based semiconductor layer on which the ohmic electrode is formed. However, undoped ZnO having an increased n-type carrier concentration without adding an n-type impurity. It is also possible to use a system semiconductor layer.

The ZnO buffer layer, for example, the growth temperature of 300 ° C., Zn flux 0.11 nm / s, _{O 2} flow rate of O source gun 1 sccm / RF power 250 W, with Mg flux 0nm / s~0.03nm / s, undoped Mg _x A Zn _1-x O layer (0 ≦ x ≦ 0.3) is grown to a thickness of 50 nm to 300 nm. Thereafter, the substrate temperature is increased to 950 ° C., and annealing is performed for 5 to 30 minutes to improve crystallinity and surface flatness and increase n-type carrier concentration. This is repeated several times and laminated to a thickness of about 2 μm.

  Next, a semiconductor ultraviolet light receiving element according to a third embodiment will be described. In the first and second embodiments, a ZnO-based semiconductor ultraviolet light receiving element using a group II oxide semiconductor as the light receiving semiconductor layer was produced. In the third embodiment, a GaN-based semiconductor ultraviolet light receiving element using a group III nitride semiconductor as a light receiving semiconductor layer is manufactured.

FIG. 7 is a schematic cross-sectional view of the light receiving element of the third embodiment. On the c-plane sapphire substrate 41, a GaN buffer layer 42, an n-type GaN layer 43 (for example, 3 μm in thickness), and an undoped GaN layer 44 (for example, 2 μm in thickness) are grown by MOCVD. The carrier concentration of the undoped GaN layer 44 is, for example, 1.2 × 10 ¹⁶ cm ⁻³ .

  On the undoped GaN layer 44, a resist pattern having an opening exposing a region where the ohmic electrode 46 is disposed in a later step is formed, and using this resist pattern as a mask, the undoped GaN layer 44 is formed by reactive ion etching (RIE). Is etched to expose the n-type GaN layer 43. Thereafter, the resist pattern is removed and cleaning is performed.

  Next, a resist pattern having an opening exposing a region where the wire bonding metal electrode 47 is disposed in a later step is formed, and using this resist pattern as a mask, the undoped GaN layer 44, the n-type GaN layer 43, Then, the GaN buffer layer 42 is etched to expose the sapphire substrate 41. Thereafter, the resist pattern is removed and cleaning is performed.

  Next, a resist pattern having an opening exposing the formation region of the organic electrode 45 is formed, and PEDOT: PSS to which a conductivity increasing agent is added is applied by spin coating (with a thickness after the heat treatment), for example, 30 nm in thickness. Then, the organic electrode 45 is formed by lift-off to remove unnecessary portions of PEDOT: PSS. After lift-off, for example, heat treatment is performed at 200 ° C. for 20 minutes using a hot plate.

  The organic electrode 45 covers the upper surface of the undoped GaN layer 44 and the laminated side surface of the undoped GaN layer 44, the n-type GaN layer 43, and the GaN buffer layer 42, and the end of the portion covering the laminated side surface is an exposed sapphire substrate. 41 is reached.

  Next, a 50 nm thick Ti layer 46a, for example, is formed on the exposed n-type GaN layer 43 by EB vapor deposition using a metal mask, and a 100 nm thick Pt layer 46b, for example, is stacked on the Ti layer 46a. The ohmic electrode 46 is formed by stacking, for example, an Au layer 46c having a thickness of 500 nm on the Pt layer 46b.

  Next, a 50 nm thick Ti layer 47 a is formed by EB vapor deposition using a metal mask, and a 500 nm thick Au layer 47 b is stacked on the Ti layer 47 a to form a wire bonding metal electrode 47. To do.

  The metal electrode 47 for wire bonding covers the edge of the organic electrode 45 on the upper surface of the undoped GaN layer 44 and the organic electrode 45 on the stacked side surface of the undoped GaN layer 44, the n-type GaN layer 43, and the GaN buffer layer 42. Further, it is formed so as to cover the exposed sapphire substrate 41.

  In this way, the light receiving element of the third embodiment is manufactured. Thereafter, the light receiving element of the third embodiment is bonded onto the stem by die bonding and wire bonding, and the light receiving device of the third embodiment is manufactured.

In the third embodiment, GaN is used as the light receiving semiconductor layer, but Al _z Ga _1-z N (0 ≦ z ≦ 1) can also be used as the light receiving semiconductor layer. Increasing the Al composition z increases the energy gap and shifts the light receiving sensitivity wavelength to the short wavelength side. By using this, the wavelength can be selected.

  Next, a semiconductor ultraviolet light receiving element according to a fourth embodiment will be described. The light receiving element of the fourth embodiment has two light receiving semiconductor layers having different light receiving sensitivity wavelength bands. For example, a ZnO-based semiconductor having a wurtzite structure is used as the light receiving semiconductor layer, and MBE is used as a method for growing the semiconductor layer. 8A to 8E are schematic cross-sectional views showing main manufacturing steps of the light receiving element of the fourth embodiment.

  Refer to FIG. 8A. For example, under the same conditions as in the first embodiment, an MgO layer 52 is grown on the c-plane sapphire substrate 51, a ZnO buffer layer 53 is grown on the MgO layer 52 and annealed, and an n-type ZnO layer is formed on the ZnO buffer layer 53. A layer 54 is grown, and an undoped ZnO layer 55 is grown on the n-type ZnO layer 54. The energy gap of the undoped ZnO layer 55 is 3.3 eV (the wavelength is 376 nm).

On the undoped ZnO layer 55, a Zn beam, Mg beam, and O radical beam are simultaneously irradiated to grow a MgZnO layer 56 having a wurtzite structure to a thickness of about 1.5 μm, for example. The growth conditions of the MgZnO layer 56 are, for example, a growth temperature of 900 ° C., a Zn flux of 0.2 nm / s, an Mg flux of 0.04 nm / s, an O ₂ flow rate of O source gun of ₂ sccm / RF power of 300 W. In this example, the Mg composition of the undoped MgZnO layer 56 is 0.35, and at this time, the energy gap is 3.95 eV (the wavelength is 314 nm).

  On the undoped MgZnO layer 56, a resist pattern RP51 is formed. The resist pattern RP51 covers a region where the undoped MgZnO layer 56 is left as a light receiving semiconductor layer and exposes other regions.

  Using the resist pattern RP51 as a mask, the undoped MgZnO layer 56 is etched by wet etching or dry etching to expose the undoped ZnO layer 55. Thereafter, the resist pattern RP51 is removed.

  Refer to FIG. 8B. A resist pattern RP52 is formed. The resist pattern RP52 covers a region where the undoped MgZnO layer 56 is left as a light receiving semiconductor layer and a region where the undoped ZnO layer 55 is left as a light receiving semiconductor layer, and the other regions are exposed.

  Using the resist pattern RP52 as a mask, the undoped ZnO layer 55 is etched by wet etching or dry etching to expose the n-type ZnO layer 54. Thereafter, the resist pattern RP52 is removed.

  Reference is made to FIG. 8C. A resist pattern RP53 is formed. The resist pattern RP53 has an opening that exposes the sapphire substrate 51 in the region where the wire bonding metal electrodes 58WA and 58WB to be formed later are disposed.

  Using the resist pattern RP53 as a mask, the n-type ZnO layer 54, the ZnO buffer layer 53, and the MgO layer 52 are etched by wet etching or dry etching to form a concave portion TR in which the sapphire substrate 51 is exposed at the bottom. Thereafter, the resist pattern RP53 is removed.

  In this embodiment, the light receiving element portion LSA that uses the undoped ZnO layer 55 as the light receiving semiconductor layer and the light receiving element portion LSB that uses the undoped MgZnO layer 56 as the light receiving semiconductor layer are separated by the recess TR, and are common to the bottom of the recess TR. In addition, wire bonding metal electrodes 58WA and 58WB are disposed.

  Reference is made to FIG. 8D. A resist pattern RP54 is formed. The resist pattern RP54 has an opening exposing a formation region of the organic electrode 57A connected to the undoped ZnO layer 55 and a formation region of the organic electrode 57B connected to the undoped MgZnO layer 56.

  After performing UV ozone cleaning, PEDOT: PSS to which a conductivity increasing agent is added is applied by spin coating (thickness after heat treatment), for example, with a thickness of 30 nm. Organic electrodes 57A and 57B are formed by lift-off to remove unnecessary portions of PEDOT: PSS together with resist pattern RP54. After lift-off, for example, heat treatment is performed at 200 ° C. for 20 minutes using a hot plate.

  The organic electrode 57A covers the upper surface of the undoped ZnO layer 55 and the stacked side surface of the undoped ZnO layer 55, the n-type ZnO layer 54, the ZnO buffer layer 53, and the MgO layer 52, and the end of the portion covering the stacked side surface is It reaches on the exposed sapphire substrate 51.

  The organic electrode 57B covers the upper surface of the undoped MgZnO layer 56 and the stacked side surfaces of the undoped MgZnO layer 56, the undoped ZnO layer 55, the n-type ZnO layer 54, the ZnO buffer layer 53, and the MgO layer 52, and covers the stacked side surfaces. The end of the part reaches the exposed sapphire substrate 51.

  Reference is made to FIG. 8E. The wire bonding metal electrode 58WA and ohmic electrode 58OA of the light receiving element portion LSA and the wire bonding metal electrode 58WB and ohmic electrode 58OA of the light receiving element portion LSB are formed.

  Using a metal mask having an opening in the formation region of these electrodes, a Ti layer 58a having a thickness of, for example, 50 nm is formed by EB vapor deposition, and an Au layer 58b having a thickness of, for example, 500 nm is stacked on the Ti layer 58a to receive light. The wire bonding metal electrode 58WA and ohmic electrode 58OA of the element portion LSA and the wire bonding metal electrode 58WB and ohmic electrode 58OB of the light receiving element portion LSB are formed simultaneously.

  The metal electrode 58WA for wire bonding is an organic material on the side of the laminated layer of the organic electrode 57A on the upper surface of the undoped ZnO layer 55 and the undoped ZnO layer 55, n-type ZnO layer 54, ZnO buffer layer 53, and MgO layer 52. It is formed so as to cover the electrode 57A and further cover the sapphire substrate 51.

  The metal electrode 58WB for wire bonding includes the edge of the organic electrode 57B on the upper surface of the undoped MgZnO layer 56, the undoped MgZnO layer 56, the undoped ZnO layer 55, the n-type ZnO layer 54, the ZnO buffer layer 53, and the MgO layer 52. It is formed so as to cover the organic electrode 57 </ b> B on the stacked side surface and further cover the sapphire substrate 51.

  The ohmic electrode 58OA is formed on the n-type ZnO layer 54 on the light receiving element portion LSA side, and the ohmic electrode 58OB is formed on the n-type ZnO layer 54 on the light receiving element portion LSB side.

  For each of the light receiving element portions LSA and LSB, the upper and side surfaces of the conductive ZnO-based semiconductor layer laminated portion are covered with organic electrodes 57A and 57B, wire bonding metal electrodes 58WA and 58WB, and a conductive ZnO-based semiconductor layer. Is prevented from short circuiting.

  In addition, for each of the light receiving element portions LSA and LSB, wire bonding metal electrodes 58WA and 58WB are formed across the organic electrodes 57A and 57B and the insulating substrate 51, so that the organic electrodes 57A and 57B Peeling of the wire bonding metal electrodes 58WA and 58WB is suppressed.

  In this way, the light receiving element of the fifth embodiment is manufactured. Thereafter, the light receiving element of the fifth embodiment is bonded onto the stem by die bonding and wire bonding, and the light receiving device of the fifth embodiment is manufactured.

  The light receiving element of the fourth embodiment can be used, for example, in a measuring instrument that measures ultraviolet rays of sunlight for sunburn countermeasures. As described above, the ultraviolet rays of sunlight are substantially UV-A (320 to 400 nm) and UV-B (280 to 320 nm).

  The light receiving element portion LSA having the ZnO layer 55 as the light receiving semiconductor layer is suitable for measurement of UV-A (320 to 400 nm) and UV-B (280 to 320 nm) because it has light receiving sensitivity to ultraviolet rays having a wavelength of 376 nm or less.

  On the other hand, the light receiving element portion LSB having the light receiving semiconductor layer as the MgZnO layer 56 is suitable for the measurement of UV-B (280 to 320 nm) because it has a light receiving sensitivity to ultraviolet rays having a Mg composition of 0.35 and a wavelength of 314 nm or less. The intensity of UV-A can also be estimated by subtracting the photocurrent measured at the light receiving element portion LSB from the photocurrent measured at the light receiving element portion LSA.

  In the fourth embodiment, the MgZnO layer is formed on the upper side of the ZnO layer. However, the ZnO layer may be formed on the upper side of the MgZnO layer.

  As described above, by epitaxially growing another light receiving semiconductor layer having the same crystal structure as that of the light receiving semiconductor layer and having a different energy gap on a part of the light receiving semiconductor layer, a plurality of light receiving sensitivity wavelength bands different from each other on the same substrate. The light receiving element portion can be made.

  As a first modification of the fourth embodiment, the wire bonding metal electrodes 58WA and 58WB may be formed on the MgO layer 52 while leaving the MgO layer 52, as in the modification of the first embodiment. it can.

  FIG. 9 is a schematic sectional view showing a light receiving element of a second modification of the fourth embodiment. In this modification, the n-type ZnO layer 54 is not separated between the light receiving element portions LSA and LSB, and the ohmic electrode 58O connected to the n type ZnO layer 54 is shared by the light receiving element portions LSA and LSB. .

  In this modification, a recess TRA is formed outside the light receiving element portion LSA, and a recess TRB is formed outside the light receiving element portion LSB. On the sapphire substrate 51 exposed at the bottoms of the recesses TRA and TRB, a wire bonding metal electrode 58WA of the light receiving element portion LSA and a wire bonding metal electrode 58WB of the light receiving element portion LSB are arranged, respectively.

  In the examples described above, dimethyl sulfoxide (DMSO) was added and used as a conductivity increasing agent for the organic electrode (PEDOT: PSS). However, non-ethylene glycol, 1-methyl-2-pyrrolidone (NMP) and the like were used. Protic polar solvents may be used.

  Further, in the organic electrode formation, PEDOT: PSS was applied by spin coating, and the pattern was formed by lift-off. However, the pattern may be formed directly by screen printing using a conductive polymer for screen printing. Conductive polymers for screen printing are also formed from polythiophene derivatives.

  Although the present invention has been described with reference to the embodiments, the present invention is not limited thereto. It will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

1, 41, 51 Sapphire substrate 2, 52 MgO layer 3, 32, 53 ZnO buffer layer 4, 33, 54 n-type ZnO layer 5, 34, 55 Undoped ZnO layer 6, 35, 45, 57A, 57B Organic electrode 7W, 36W, 47, 58WA, 58WB Wire bonding metal electrodes 7O, 36O, 46, 58OA, 58OB Ohmic electrodes 11, 13, 14, 16 Au balls 12, 15 Au wire 21 Stem 22 Adhesive 23 Container 24 Ultraviolet transmitting window 31 High Resistive ZnO substrate 42 GaN buffer layer 43 n-type GaN layer 44 Undoped GaN layer 56 Undoped MgZnO layers RP1 to RP3, RP51 to RP54 Resist pattern LSA, LSB Light receiving element portion TR, TRA, TRB Recessed portion

Claims (10)

A first semiconductor layer formed of a group II oxide semiconductor or a group III nitride semiconductor over a part of the insulating base;
An ultraviolet transmissive first organic electrode formed so as to cover an upper surface and a side surface of the first semiconductor layer and have an end portion reaching the insulating base;
A semiconductor ultraviolet light receiving element, comprising: a first wire bonding metal electrode extending from the first organic electrode on the insulating base and securing a bonding region above the insulating base.   The semiconductor ultraviolet light receiving element according to claim 1, wherein the first organic electrode includes a polythiophene derivative including a carrier dopant. The semiconductor ultraviolet light receiving element according to claim 1, wherein the insulating base is formed of any one of Al ₂ O ₃ , AlN, MgO, and ZnO.   The semiconductor ultraviolet light receiving element according to claim 1, wherein the first wire bonding metal electrode is formed of a multilayer metal film including a Ti film and an Au film. The group II oxide semiconductor may be wurtzite Mg _x Zn _1-x O (0 ≦ x <0.6) or rock salt structure Mg _x Zn _1-x O (0.6 ≦ x ≦ It is 1) The semiconductor ultraviolet light receiving element of any one of Claims 1-4. The first semiconductor layer is formed of Mg _x Zn _1-x O (0 ≦ x <0.6) having a wurtzite structure,
The semiconductor ultraviolet light receiving element according to claim 1, wherein the insulating base is an MgO layer that controls a growth polarity of the first semiconductor layer. The group III nitride _{semiconductor, Al z Ga 1-z N} (0 ≦ z ≦ 1) semiconductor ultraviolet light-receiving element according to any one of claims 1 to 4,. Further, a second semiconductor layer formed of a group II oxide semiconductor or a group III nitride semiconductor on the other part of the insulating base and having a different energy gap from the first semiconductor layer;
An ultraviolet transmissive second organic electrode formed so as to cover an upper surface and a side surface of the second semiconductor layer and have an end portion reaching the insulating base;
The metal wire for second wire bonding according to any one of claims 1 to 7, further comprising: a second wire bonding metal electrode extending from the second organic electrode on the insulating base and securing a bonding region above the insulating base. The semiconductor ultraviolet light receiving element as described. Forming a first semiconductor layer with a group II oxide semiconductor or a group III nitride semiconductor above a part of the insulating base layer;
Forming an ultraviolet transmissive first organic electrode that covers an upper surface and a side surface of the first semiconductor layer, and an end portion of which reaches the insulating base;
Forming a first wire bonding metal electrode that extends from the first organic electrode onto the insulating base and secures a bonding region above the insulating base; . The step of forming the first semiconductor layer with a group II oxide semiconductor or a group III nitride semiconductor above a part of the insulating base layer,
The first semiconductor is formed on the insulating base layer, and a second semiconductor layer is formed on the first semiconductor layer by a group II oxide semiconductor or group III nitride semiconductor having an energy gap different from that of the first semiconductor layer. Forming a step;
Etching a partial region of the second semiconductor layer to expose the first semiconductor layer;
An edge of the first region where the upper surface of the first semiconductor layer is exposed is defined, a side surface of the first semiconductor layer is exposed on a side surface, a recess exposing the insulating base on a bottom surface, and an upper surface of the second semiconductor layer is exposed Forming an edge of the second region to be formed, exposing a side surface of the laminated layer of the second semiconductor layer and the first semiconductor layer on a side surface, and forming a recess exposing the insulating base on a bottom;
The step of forming the first organic electrode includes forming the first organic electrode that covers an upper surface and a side surface of the first semiconductor layer in the first region and whose end reaches the insulating base, and the second organic electrode. Forming an ultraviolet transmissive second organic electrode that covers the upper surface and side surfaces of the second semiconductor layer in the region, and whose end reaches the insulating base;
The step of forming the first wire bonding metal electrode includes forming the first wire bonding metal electrode, extending from the second organic electrode onto the insulating base, and above the insulating base. Forming a second wire bonding metal electrode that secures a bonding region on the semiconductor ultraviolet light receiving element according to claim 9.