JP5850075B2 - Manufacturing method of surface emitting laser element - Google Patents

Description

  The present invention relates to a method for manufacturing a surface emitting laser element, and more particularly to a method for manufacturing a surface emitting laser element that emits laser light in a direction perpendicular to a substrate.

  A vertical cavity surface emitting laser element (Vertical Cavity Surface Emitting Laser) emits light in a direction perpendicular to a substrate, and is an edge emitting semiconductor laser element that emits light in a direction parallel to the substrate. In recent years, it has been attracting attention because of its low price, low power consumption, small size, suitable for two-dimensional devices, and high performance.

The surface emitting laser element has a constricted structure in order to increase current inflow efficiency. As this constriction structure, a constriction structure obtained by selective oxidation of an Al (aluminum) As (arsenic) layer (hereinafter, also referred to as “oxidized constriction structure” for convenience. For example, see Patent Document 1) is often used. . In this oxidized constriction structure, after a mesa having a predetermined size with a selective oxidation layer made of p-AlAs exposed on the side surface is formed, the mesa is selectively placed from the side surface of the mesa by placing it in a high-temperature steam atmosphere. In this case, an unoxidized region in the selective oxidation layer remains in the vicinity of the center of the mesa. This non-oxidized region becomes a driving current passing region (current passing region) of the surface emitting laser element. Thus, current constriction can be easily achieved. The refractive index of a layer oxidized with Al (Al _x O _y ) (hereinafter abbreviated as “oxidized layer”) in the oxidized constriction structure is about 1.6, which is lower than that of the semiconductor layer. Thereby, a refractive index difference in the lateral direction is generated in the resonator structure, and light is confined in the center of the mesa, so that the light emission efficiency can be improved. As a result, excellent characteristics such as low threshold current and high efficiency can be realized.

  As an application field of the surface emitting laser element, an optical writing light source (oscillation wavelength: 780 nm band) in a printer, a writing light source (oscillation wavelength: 780 nm band, 850 nm band) in an optical disk apparatus, and a LAN (Local Area) using an optical fiber are used. And a light source (oscillation wavelength: 1.3 μm band, 1.5 μm band) of an optical transmission system such as Network). Furthermore, it is also expected as a light source for light transmission between boards, within a board, between chips of an integrated circuit (LSI: Large Scale Integrated circuit), and within a chip of an integrated circuit.

  In these application fields, the light emitted from the surface emitting laser element (hereinafter also referred to as “emitted light”) is often required to have a circular cross-sectional shape. In order to make the cross-sectional shape of the emitted light circular, it is necessary to suppress oscillation of higher-order transverse modes.

  For example, Patent Document 2 discloses a method of controlling an oscillation lateral mode by forming an optically transparent film on the emission surface and providing a difference in reflectance between the central portion and the peripheral portion of the light emitting region. .

  By the way, as shown in FIG. 23 (A) and FIG. 23 (B) as an example, the inventors have an optically transparent film (hereinafter also referred to as “optical filter” for convenience). ), And a detailed study, a new finding was obtained that the relative positional relationship between the current passing region and the optical filter affects the light emission angle. Here, in the XYZ three-dimensional orthogonal coordinate system, the direction perpendicular to the substrate surface is the Z-axis direction. And an optical filter is two rectangular optical filters which make the Y-axis direction a longitudinal direction and are opposed in the X-axis direction.

  The “light exit angle” means an inclination angle in a direction in which the intensity of radiated light is maximum with respect to a direction perpendicular to the substrate surface (here, the Z-axis direction), and is clockwise with respect to the direction perpendicular to the substrate surface. The direction inclined to + is defined as +, and the direction inclined counterclockwise is defined as −.

  Then, when viewed from the direction perpendicular to the substrate surface, the relationship between the light emission angle and the positional deviation amount (hereinafter abbreviated as “deviation amount”) of the center of gravity of the two optical filters with respect to the center of the current passage region, and 24 and 25.

  FIG. 24 shows the experimental results when the centroids of the two optical filters are shifted along the Y-axis direction with respect to the center of the current passing region. When the shift direction is + Y direction, it is + and −Y direction. -. According to this, the light emission angle in the X-axis direction is substantially constant even when the shift amount is changed, and the value is also substantially 0 deg. On the other hand, the light emission angle in the Y-axis direction tended to increase in magnitude (absolute value) as the amount of deviation (absolute value) increased.

  FIG. 25 shows the experimental results when the centroids of the two optical filters are shifted along the X-axis direction with respect to the center of the current passage region. When the shift direction is + X direction, it is + and −X direction. -. According to this, the light emission angle in the Y-axis direction is substantially constant even when the shift amount is changed, and the value thereof is also substantially 0 deg. On the other hand, the light emission angle in the X-axis direction tended to increase in magnitude (absolute value) as the amount of deviation (absolute value) increased.

  In order to obtain a high-definition image in the image forming apparatus, it is important to form a circular and minute light spot at a desired position on the surface to be scanned. Then, in order to form a circular and minute light spot at a desired position on the surface to be scanned, the magnitude (absolute value) of the light emission angle of the surface emitting laser element is determined by all experiments and theoretical calculations. The direction needs to be 0.2 deg or less.

  Therefore, referring to FIG. 24, FIG. 25, and the like, it is necessary to suppress the magnitude (absolute value) of the deviation amount in the surface emitting laser element to 0.1 μm or less.

  However, with the technique disclosed in Patent Document 2, it is difficult to stably mass-produce surface emitting laser elements having a deviation amount (absolute value) of 0.1 μm or less.

  The present invention has been made on the basis of the novel findings obtained by the inventors described above, and has the following configuration.

The present invention is a method for manufacturing a surface-emitting laser element having a relatively high reflectivity portion and a low portion are formed on the emission region due to differences in the presence or absence and thickness of the dielectrics layer, the lower the substrate Forming a mesa structure in which at least the selective oxidation layer is exposed on a side surface in a laminate in which a reflector, a resonator structure including an active layer, and an upper reflection mirror including a selective oxidation layer are laminated; Prior to the step of oxidizing the selectively oxidized layer of the mesa structure to form a constricted structure in which the oxide surrounds a current passing region, and the step of forming the mesa structure. to, look including a second pattern defining the outer shape of the first pattern and the mesa structure that defines the boundaries of the relatively high reflectivity portion and a lower portion, said first and second patterns to form a first resist pattern having openings between A step, a method for manufacturing a surface-emitting laser element including a.

  According to this, it is possible to stably mass-produce surface emitting laser elements having a deviation amount (absolute value) of 0.1 μm or less while controlling the oscillation transverse mode.

It is a figure for demonstrating schematic structure of the laser printer which concerns on one Embodiment of this invention. It is the schematic which shows the optical scanning device in FIG. It is a figure for demonstrating the surface emitting laser element contained in the light source in FIG. 4A and 4B are diagrams for explaining the substrate of the surface emitting laser element. It is the figure which expanded the active layer vicinity. FIGS. 6A to 6C are views (No. 1) for describing a method of manufacturing a surface emitting laser element, respectively. It is a figure for demonstrating the resist pattern 120a and the resist pattern 120b. FIGS. 8A and 8B are views (No. 2) for describing the method for manufacturing the surface emitting laser element, respectively. It is a figure for demonstrating a 2nd resist pattern. It is AA sectional drawing of FIG. FIGS. 11A to 11C are views (No. 3) for describing the method for manufacturing the surface emitting laser element, respectively. FIGS. 12A to 12D are views (No. 4) for describing the method for manufacturing the surface emitting laser element, respectively. It is the figure (the 1) which took out and expanded the mesa upper surface in Drawing 12 (D). FIG. 13 is an enlarged view (No. 2) of the mesa upper surface in FIG. It is a figure for demonstrating the modification of the manufacturing method of a surface emitting laser element. It is a longitudinal cross-sectional view of the surface emitting laser element corresponding to FIG. FIG. 17A to FIG. 17G are views (No. 1) for describing modifications of the high reflectance portion 122 and the low reflectance portion 121, respectively. FIGS. 18A to 18C are diagrams (No. 2) for describing a modified example of the high reflectance portion 122 and the low reflectance portion 121, respectively. It is a figure for demonstrating the deformation | transformation of the cross-sectional shape by baking of the resist pattern 120a. It is a figure for demonstrating a surface emitting laser array. It is AA sectional drawing of FIG. It is a figure for demonstrating schematic structure of a color printer. FIG. 23A and FIG. 23B are diagrams for explaining the optical filter and the light emission angle, respectively. It is a figure for demonstrating the relationship between the deviation | shift amount of the optical filter regarding a Y-axis direction, and a light-projection angle. It is a figure for demonstrating the relationship between the deviation | shift amount of an optical filter regarding a X-axis direction, and a light-projection angle.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows a schematic configuration of a laser printer 1000 as an image forming apparatus according to an embodiment.

  The laser printer 1000 includes an optical scanning device 1010, a photosensitive drum 1030, a charging charger 1031, a developing roller 1032, a transfer charger 1033, a charge eliminating unit 1034, a cleaning unit 1035, a toner cartridge 1036, a paper feeding roller 1037, a paper feeding tray 1038, A registration roller pair 1039, a fixing roller 1041, a paper discharge roller 1042, a paper discharge tray 1043, a communication control device 1050, a printer control device 1060 that comprehensively controls the above-described units, and the like are provided. These are housed in predetermined positions in the printer housing 1044.

  The communication control device 1050 controls bidirectional communication with a host device (for example, a personal computer) via a network or the like.

  The photosensitive drum 1030 is a cylindrical member, and a photosensitive layer is formed on the surface thereof. That is, the surface of the photoconductor drum 1030 is a scanned surface. The photosensitive drum 1030 rotates in the direction of the arrow in FIG.

  The charging charger 1031, the developing roller 1032, the transfer charger 1033, the charge removal unit 1034, and the cleaning unit 1035 are each disposed in the vicinity of the surface of the photosensitive drum 1030. Then, along the rotation direction of the photosensitive drum 1030, the charging charger 1031 → the developing roller 1032 → the transfer charger 1033 → the discharging unit 1034 → the cleaning unit 1035 are arranged in this order.

  The charging charger 1031 uniformly charges the surface of the photosensitive drum 1030.

  The optical scanning device 1010 scans the surface of the photosensitive drum 1030 charged by the charging charger 1031 with a light beam modulated based on image information from the host device, and corresponds to the image information on the surface of the photosensitive drum 1030. A latent image is formed. The latent image formed here moves in the direction of the developing roller 1032 as the photosensitive drum 1030 rotates. The configuration of the optical scanning device 1010 will be described later.

  The toner cartridge 1036 stores toner, and the toner is supplied to the developing roller 1032.

  The developing roller 1032 causes the toner supplied from the toner cartridge 1036 to adhere to the latent image formed on the surface of the photosensitive drum 1030 to visualize the image information. Here, the latent image to which the toner is attached (hereinafter also referred to as “toner image” for the sake of convenience) moves in the direction of the transfer charger 1033 as the photosensitive drum 1030 rotates.

  Recording paper 1040 is stored in the paper feed tray 1038. A paper feed roller 1037 is disposed in the vicinity of the paper feed tray 1038, and the paper feed roller 1037 takes out the recording paper 1040 one by one from the paper feed tray 1038 and conveys it to the registration roller pair 1039. The registration roller pair 1039 temporarily holds the recording paper 1040 taken out by the paper supply roller 1037, and in the gap between the photosensitive drum 1030 and the transfer charger 1033 according to the rotation of the photosensitive drum 1030. Send it out.

  A voltage having a polarity opposite to that of the toner is applied to the transfer charger 1033 in order to electrically attract the toner on the surface of the photosensitive drum 1030 to the recording paper 1040. With this voltage, the toner image on the surface of the photosensitive drum 1030 is transferred to the recording paper 1040. The recording sheet 1040 transferred here is sent to the fixing roller 1041.

  In the fixing roller 1041, heat and pressure are applied to the recording paper 1040, whereby the toner is fixed on the recording paper 1040. The recording paper 1040 fixed here is sent to the paper discharge tray 1043 via the paper discharge roller 1042 and is sequentially stacked on the paper discharge tray 1043.

  The neutralization unit 1034 neutralizes the surface of the photosensitive drum 1030.

  The cleaning unit 1035 removes the toner remaining on the surface of the photosensitive drum 1030 (residual toner). The surface of the photosensitive drum 1030 from which the residual toner has been removed returns to the position facing the charging charger 1031 again.

  Next, the configuration of the optical scanning device 1010 will be described.

  As shown in FIG. 2 as an example, the optical scanning device 1010 includes a deflector-side scanning lens 11a, an image plane-side scanning lens 11b, a polygon mirror 13, a light source 14, a coupling lens 15, an aperture plate 16, and a cylindrical lens 17. , A reflection mirror 18, a scanning control device (not shown), and the like. These are assembled at predetermined positions in the housing 30.

  In the following, for convenience, the direction corresponding to the main scanning direction is abbreviated as “main scanning corresponding direction”, and the direction corresponding to the sub scanning direction is abbreviated as “sub scanning corresponding direction”.

  The coupling lens 15 converts the light beam output from the light source 14 into substantially parallel light.

  The aperture plate 16 has an aperture and defines the beam diameter of the light beam through the coupling lens 15.

  The cylindrical lens 17 forms an image of the light flux that has passed through the opening of the aperture plate 16 in the vicinity of the deflection reflection surface of the polygon mirror 13 via the reflection mirror 18 in the sub-scanning corresponding direction.

  The optical system arranged on the optical path between the light source 14 and the polygon mirror 13 is also called a pre-deflector optical system. In the present embodiment, the pre-deflector optical system includes a coupling lens 15, an aperture plate 16, a cylindrical lens 17, and a reflection mirror 18.

  As an example, the polygon mirror 13 has a hexahedral mirror having an inscribed circle radius of 18 mm, and each mirror serves as a deflecting reflection surface. The polygon mirror 13 deflects the light flux from the reflection mirror 18 while rotating at a constant speed around an axis parallel to the sub-scanning corresponding direction.

  The deflector-side scanning lens 11 a is disposed on the optical path of the light beam deflected by the polygon mirror 13.

  The image plane side scanning lens 11b is disposed on the optical path of the light beam via the deflector side scanning lens 11a. Then, the light beam that has passed through the image plane side scanning lens 11b is irradiated onto the surface of the photosensitive drum 1030, and a light spot is formed. This light spot moves in the longitudinal direction of the photosensitive drum 1030 as the polygon mirror 13 rotates. That is, the photoconductor drum 1030 is scanned. The moving direction of the light spot at this time is the “main scanning direction”. The rotation direction of the photosensitive drum 1030 is the “sub-scanning direction”.

  The optical system arranged on the optical path between the polygon mirror 13 and the photosensitive drum 1030 is also called a scanning optical system. In the present embodiment, the scanning optical system includes a deflector side scanning lens 11a and an image plane side scanning lens 11b. Note that at least one folding mirror is disposed on at least one of the optical path between the deflector side scanning lens 11a and the image plane side scanning lens 11b and the optical path between the image plane side scanning lens 11b and the photosensitive drum 1030. May be.

  The light source 14 includes a surface emitting laser element 100 as shown in FIG. 3 as an example. In this specification, the laser oscillation direction is defined as the Z-axis direction, and two directions perpendicular to each other in a plane perpendicular to the Z-axis direction are described as the X-axis direction and the Y-axis direction. FIG. 3 is a view showing a cut surface when the surface emitting laser element 100 is cut in parallel to the XZ plane.

  The surface emitting laser element 100 is a surface emitting laser element having an oscillation wavelength of 780 nm, and includes a substrate 101, a lower semiconductor DBR 103, a lower spacer layer 104, an active layer 105, an upper spacer layer 106, an upper semiconductor DBR 107, and the like. Yes.

  The surface of the substrate 101 is a mirror-polished surface, and as shown in FIG. 4A, the normal direction of the mirror-polished surface (main surface) is crystal orientation with respect to the crystal orientation [1 0 0] direction. [1 1 1] An n-GaAs single crystal substrate inclined 15 degrees (θ = 15 degrees) in the A direction. That is, the substrate 101 is a so-called inclined substrate. Here, as shown in FIG. 4B, the crystal orientation [0 −1 1] direction is arranged in the + X direction, and the crystal orientation [0 1 −1] direction is arranged in the −X direction.

Returning to FIG. 3, the lower semiconductor DBR 103 is laminated on the surface of the substrate 101 on the + Z side via a buffer layer (not shown), and includes a low refractive index layer made of n-Al _0.9 Ga _0.1 As, 37.5 pairs of high refractive index layers made of n-Al _0.3 Ga _0.7 As are provided. Between each refractive index layer, in order to reduce an electrical resistance, a composition gradient layer having a thickness of 20 nm in which the composition is gradually changed from one composition to the other composition is provided. Each refractive index layer includes 1/2 of the adjacent composition gradient layer, and is set to have an optical thickness of λ / 4 when the oscillation wavelength is λ. When the optical thickness is λ / 4, the actual thickness D of the layer is D = λ / 4n (where n is the refractive index of the medium of the layer).

The lower spacer layer 104 is laminated on the + Z side of the lower semiconductor DBR 103 and is a layer made of non-doped Al _0.6 Ga _0.4 As.

The active layer 105 is stacked on the + Z side of the lower spacer layer 104. As shown in FIG. 5 as an example, the active layer 105 has a triple quantum well structure having three quantum well layers 105a and four barrier layers 105b. Is a layer. Each quantum well layer 105a is made of Al _0.12 Ga _0.88 As, and each barrier layer 105b is made of Al _0.3 Ga _0.7 As.

The upper spacer layer 106 is laminated on the + Z side of the active layer 105 and is a layer made of non-doped Al _0.6 Ga _0.4 As.

  The portion composed of the lower spacer layer 104, the active layer 105, and the upper spacer layer 106 is also referred to as a resonator structure, and includes a half of the adjacent composition gradient layer, and has an optical thickness of one wavelength. It is set so as to be an appropriate thickness. The active layer 105 is provided at the center of the resonator structure at a position corresponding to the antinode in the standing wave distribution of the electric field so that a high stimulated emission probability can be obtained.

Returning to FIG. 3, the upper semiconductor DBR 107 is stacked on the + Z side of the upper spacer layer 106, and includes a low refractive index layer made of p-Al _0.9 Ga _0.1 As and p-Al _0.3 Ga _0.7 As. 24 pairs of high refractive index layers made of

  Between the refractive index layers in the upper semiconductor DBR 107, a composition gradient layer is provided in which the composition is gradually changed from one composition to the other composition in order to reduce electrical resistance. Each refractive index layer is set to have an optical thickness of λ / 4 including 1/2 of the adjacent composition gradient layer.

  A selective oxidation layer 108 made of p-AlAs is provided at a position optically separated from the resonator structure in the upper semiconductor DBR 107 by λ / 4. In FIG. 3, for convenience, the selective oxide layer 108 is illustrated between the upper semiconductor DBR 107 and the resonator structure.

  A contact layer (not shown) made of p-GaAs is provided on the + Z side of the upper semiconductor DBR 107.

  Note that a structure in which a plurality of semiconductor layers are stacked on the substrate 101 is also referred to as a “stacked body” for convenience in the following.

  Next, a method for manufacturing the surface emitting laser element 100 will be described.

(1) The above laminate is formed by crystal growth by metal organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE) (see FIG. 6A).

Here, trimethylaluminum (TMA), trimethylgallium (TMG), and trimethylindium (TMI) are used as Group III materials, and phosphine (PH ₃ ) and arsine (AsH ₃ ) are used as Group V materials. ing. Further, carbon tetrabromide (CBr ₄ ) and dimethyl zinc (DMZn) are used as the raw material for the p-type dopant, and hydrogen selenide (H ₂ Se) is used as the raw material for the n-type dopant.

(2) Using the P-CVD method (plasma CVD method), an optically transparent dielectric layer 111a made of P-SiN (SiN _x ) is formed (see FIG. 6B). Here, the optical thickness of the dielectric layer 111a is set to λ / 4. Specifically, since the refractive index n of SiN is 1.89 and the oscillation wavelength λ is 780 nm, the actual film thickness (= λ / 4n) is set to 103 nm.

(3) A first resist is applied to the surface of the dielectric layer 111a, and a resist pattern 120a for defining the outer shape of the mesa structure and a region corresponding to a portion having a low reflectance in the emission region are masked A resist pattern 120b and a resist pattern 120c for masking a region where the electrode pad is formed are formed (see FIG. 6C).

  Here, since the resist pattern 120a and the resist pattern 120b are formed at the same time, there is no deviation in the positional relationship between the resist pattern 120a and the resist pattern 120b.

  As shown in FIG. 7, the resist pattern 120 a is a square pattern whose outer shape is a square shape with a side length L <b> 4 and a width L <b> 5. As shown in FIG. 7, the resist patterns 120b are two rectangular patterns having a length L2 in the X-axis direction and a length L3 in the Y-axis direction, and are arranged so as to have an interval L1 in the X-axis direction. ing. Here, as an example, L1 = 5 μm, L2 = 2 μm, L3 = 8 μm, L4 = 20 μm, and L5 = 2 μm.

  Further, the centers of gravity of the two resist patterns 120b are shifted by L10 to the + Y side from the center of the resist pattern 120a. In this embodiment, since the substrate 101 is an inclined substrate (see FIGS. 4A and 4B), the crystal orientations perpendicular to the four side walls of the mesa structure are different (see FIG. 7). If the crystal orientation is different, a difference in oxidation rate is likely to occur during oxidation. As a result, the center of the constricted structure in which the oxide surrounds the current passing region is shifted from the center of the mesa structure.

  The oxidation rate in the present embodiment is a direction inclined by 15 degrees from the [0 1 1] direction to the [1 1 1] A direction> [0 1 -1] direction = [0 -1 1] direction> [0 -1 -1] direction and a direction inclined by 15 degrees in the [1 1 1] A direction.

  Therefore, the center of the constriction structure is shifted by about 0.6 μm from the [0 −1 −1] direction to the [1 1 1] A direction by 15 degrees with respect to the center of the mesa structure.

  Accordingly, the centers of the constricted structures and the centers of gravity of the two resist patterns 120b are relatively substantially matched by shifting the centers of gravity of the two resist patterns 120b in advance by L10 (here, 0.6 μm).

  In addition, since the dependence of the oxidation rate on the plane orientation depends on the oxidation conditions, the shift amount and shift direction shown here are merely examples, and the present invention is not limited to this.

  Hereinafter, the resist patterns formed here are also collectively referred to as “first resist patterns”.

  By the way, the first resist is a general positive resist, and here, OFPR800-64cp manufactured by Tokyo Ohka Co., Ltd. is used. For the application of the first resist, a spin coater whose rotational speed is adjusted so as to have a film thickness of about 1.6 μm is used. Then, a first resist pattern is formed through exposure, development, and post-baking (for example, heating at 120 ° C. for 2 minutes).

(4) The laminated body on which the first resist pattern is formed is placed on a hot plate set at 150 ° C. and heated for 5 minutes. Thereby, the first resist pattern is cured. Hereinafter, this process is also referred to as “curing process”.

(5) The dielectric layer 111a is etched by ECR etching using Cl ₂ gas. As a result, the portion of the dielectric layer 111a that is not masked by the first resist pattern is removed (see FIG. 8A).

(6) A second resist is applied to form a second resist pattern 123 that covers a region surrounded by the resist pattern 120a (see FIG. 8B). As shown in FIG. 9, the second resist pattern 123 is a square pattern having a side length L6. Here, as an example, L6 = 18 μm. L7 = 1 μm.

  The second resist is the same type of resist as the first resist, and can be formed under the same conditions.

  By the way, since the first resist pattern is cured before the second resist is applied, the first resist pattern is not dissolved by the solvent of the second resist when the second resist is applied. In addition, a two-layer resist structure can be formed. The heating temperature in the first resist pattern curing process is preferably 150 ° C. or higher. According to experiments, when the heating temperature was 140 ° C., the first resist was melted just by applying the second resist, and the shape of the first resist pattern collapsed.

  Further, when the second resist is exposed, the first resist pattern protruding from the second resist pattern 123 is also exposed. However, since the first resist pattern is cured, it is not developed in the subsequent development process, and no dimensional change occurs in the first resist pattern.

  As an example, the second resist pattern 123 is for protecting the contact area and the emission area on the mesa surface as shown in FIG. Here, L6 is 18 μm, which is 2 μm smaller than the outer shape of the resist pattern 120a. This difference of 2 μm becomes a margin for misalignment.

(7) A mesa structure in which the stacked body is etched by the ECR etching method using Cl ₂ gas using the first resist pattern and the second resist pattern 123 as an etching mask, and at least the selectively oxidized layer 108 is exposed on the side surface. Form a body (hereinafter abbreviated as “mesa”). Here, the bottom surface of the etching is positioned on the upper surface of the lower spacer layer 104 (see FIG. 11A).

  Since the outer shape of the resist pattern 120a determines the outer shape of the mesa, there is no deviation in the positional relationship between the outer shape of the mesa and the region corresponding to the portion having a low reflectance in the emission region.

(8) Immerse in an acetone solution and remove the etching mask by ultrasonic cleaning (see FIG. 11B).

(9) The laminated body is heat-treated in water vapor. As a result, Al (aluminum) in the selectively oxidized layer 108 is selectively oxidized from the outer peripheral portion of the mesa, and an unoxidized region 108b surrounded by the Al oxide 108a remains in the central portion of the mesa. (See FIG. 11C). In other words, a so-called oxidized constriction structure is formed that restricts the drive current path of the light emitting part only to the central part of the mesa. The non-oxidized region 108b is a current passage region (current injection region). In this way, for example, a square current passing region having a width of 4.5 μm is formed.

(10) An optically transparent dielectric layer 111b made of P-SiN (SiN _x ) is formed using a P-CVD method (see FIG. 12A). Here, the optical thickness of the dielectric layer 111b is set to 2λ / 4. Specifically, since the refractive index n of SiN is 1.89 and the oscillation wavelength λ is 780 nm, the actual film thickness (= 2λ / 4n) is set to 206 nm.

(11) An etching mask for opening a window in the contact region is formed on the upper surface of the mesa.

(12) The dielectric layer 111b is etched with BHF to open a window in the contact region.

(13) Immerse in an acetone solution and remove the etching mask by ultrasonic cleaning (see FIG. 12B).

(14) A square resist pattern having a side of 10 μm is formed in a region to be a light emitting portion on the upper part of the mesa, and a p-side electrode material is deposited. As the electrode material on the p side, a multilayer film made of Cr / AuZn / Au or a multilayer film made of Ti / Pt / Au is used.

(15) Lift off the electrode material deposited in the region to be the light emitting portion above the mesa to form the p-side electrode 113 (see FIG. 12C). A region surrounded by the p-side electrode 113 is an emission region.

(16) After polishing the back side of the substrate 101 to a predetermined thickness (for example, about 100 μm), an n-side electrode 114 is formed (see FIG. 12D). As the n-side electrode material, a multilayer film made of AuGe / Ni / Au or a multilayer film made of Ti / Pt / Au is used.

(17) Ohmic conduction is established between the p-side electrode 113 and the n-side electrode 114 by annealing. Thereby, the mesa becomes a light emitting part.

(18) Cut for each chip.

  Incidentally, FIGS. 13 and 14 show enlarged views of only the mesa portion in FIG. 12D. The shape of the emission region 125 is a square having a side length of 10 μm. In the present embodiment, the emission region 125 is covered with a transparent dielectric film made of P-SiN. This dielectric film has a high reflectivity portion 122 with an optical thickness of 2λ / 4 and a relatively high reflectivity, and two low reflectivity with an optical thickness of 3λ / 4 and a relatively low reflectivity. It consists of a reflectance portion 121.

  The two low-reflectance portions 121 are respectively located at the end portions of the emission region 125 with respect to the X-axis direction. When viewed from the Z-axis direction, the center of the two low-reflectance portions 121 and the center of the current passing region 108b The deviation amount was 0.1 μm or less.

  When the light emission angles were measured for the plurality of surface-emitting laser elements 100 manufactured in this way, the light emission angles with respect to the X-axis direction and the light emission angles with respect to the Y-axis direction were all within ± 0.2 deg. .

  As apparent from the above description, in the method for manufacturing the surface emitting laser element 100, the method for manufacturing the surface emitting laser element of the present invention is used.

  As described above, according to the surface emitting laser element 100 according to the present embodiment, the lower semiconductor DBR 103, the resonator structure including the active layer 105, the upper semiconductor DBR 107 including the selective oxidation layer 108, and the like are provided on the substrate 101. Are stacked.

  The emission region 125 is entirely covered with an optically transparent dielectric made of P-SiN, and has a high reflectance portion 122 having a relatively high reflectance and two low reflectances having a relatively low reflectance. Part 121.

  Since the resist pattern 120a and the resist pattern 120b are formed at the same time when the surface emitting laser element 100 is manufactured, the positional relationship between the outer shape of the mesa and the two low-reflectance portions 121 can be stably stabilized with high accuracy. A desired positional relationship can be obtained. Therefore, even if the surface emitting laser element 100 is mass-produced, the amount of deviation (absolute value) between the center of gravity of the two low-reflectance portions 121 and the center of the current passage region 108b is stable when viewed from the Z-axis direction. Therefore, the size (absolute value) of the light emission angle can be stably set to 0.2 deg or less in all directions.

  In this case, in the surface emitting laser element 100, when the p-side electrode 113 is removed and viewed from the direction perpendicular to the substrate surface, the edge portion on the upper surface of the mesa is an optically transparent dielectric made of P-SiN. The thickness of the coated dielectric is the same as that of the portion where the dielectric is composed of two layers (low reflectance portion 121).

  Further, in the emission region, since the reflectance at the peripheral portion is relatively lower than the reflectance at the central portion, it is possible to suppress higher-order transverse mode oscillation without reducing the light output of the fundamental transverse mode. . That is, the oscillation transverse mode can be controlled.

  In addition, the region having a relatively high reflectivity at the center of the emission region is shaped to have anisotropy in two directions orthogonal to each other, and the anisotropy is intentionally generated in the lateral confinement action with respect to the laser beam. Therefore, the stability of the polarization direction can be improved.

  Further, it is possible to suppress higher-order transverse modes and stabilize the polarization direction without reducing the area of the current passing region 108b. As a result, the electrical resistance of the surface emitting laser element does not increase, and the current density in the current confinement region does not increase, so that the element life is not reduced.

  In addition, since the entire emission region is covered with the dielectric, oxidation and contamination of the emission region can be suppressed.

  In addition, since the side surface of the mesa is covered with the dielectric layer 111b, destruction of elements caused by moisture absorption is suppressed, and long-term reliability can be improved.

  In addition, since the first resist and the second resist are the same type of resist, a large process change is not necessary for the conventional manufacturing method.

  According to the optical scanning device 1010 according to the present embodiment, the light source 14 includes the surface emitting laser elements 100 and 100 ′. In this case, since a single fundamental transverse mode laser beam can be obtained when the size of the emission angle (absolute value) is 0.2 deg or less, a circular and small light spot is formed at a desired position on the surface of the photosensitive drum 1030. It can be formed easily. In addition, since the polarization direction is stable, it is not easily affected by distortion of the light spot or fluctuation in light quantity. Accordingly, it is possible to form an image of a minute light spot having a circular shape and high light density at a desired position on the photosensitive drum 1030 with a simple optical system. Therefore, it is possible to perform optical scanning with high accuracy.

  Since the laser printer 1000 according to the present embodiment includes the optical scanning device 1010, it is possible to form a high-quality image.

In the above embodiment, in the step (3), instead of the resist pattern 120b, as shown in FIG. 15 as an example, a region corresponding to a portion having a high reflectance at the central portion of the emission region is masked. A resist pattern 120d may be formed. In this case, in the step (10), the dielectric layer 111b is formed to have an optical thickness of λ / 4 or (λ / 4) + (an even multiple of λ / 4). FIG. 16 shows an example of a vertical cross-sectional view of the surface-emitting laser element manufactured as described above (referred to as “surface-emitting laser element 100 ′” for convenience). In FIG. 16, SiO ₂ is used for the dielectric layer 111a, and SiN is used for the dielectric layer 111b. Here, the film thickness of the dielectric at the center of the emission region is 2λ / 4, and the film thickness of the surrounding dielectric is λ / 4. The central portion of the emission region becomes the high reflectance portion 122 and the periphery thereof becomes the low reflectance portion 121. In this surface emitting laser element 100 ′, the difference in reflectance between the high reflectance portion and the low reflectance portion becomes larger than that in the surface emitting laser element 100, so that the fundamental transverse mode output can be further increased.

In the above-described embodiment, the case where the dielectric layer is P-SiN has been described. However, the present invention is not limited to this. For example, any of SiO _x , TiO _x, and SiON may be used. The same effect can be obtained by designing the film thickness according to the refractive index of each material.

  Moreover, although the said embodiment demonstrated the case where the shape of each low-reflectance part 121 was a rectangle, it is not limited to this. For example, as shown in FIGS. 17A to 17C, the shape of each low reflectance portion 121 may be a curved shape.

  Moreover, although the said embodiment demonstrated the case where the low-reflectivity part was isolate | separated into two, it is not limited to this, For example, it shows to FIG.17 (D)-FIG.17 (G). As such, the low reflectance portion may be in a shape that is not separated.

  Further, as shown in FIGS. 18A to 18C, the high-order mode is selectively operated by lowering the reflectance at the center of the emission region and increasing the reflectance at the periphery. May be.

  Moreover, although the said embodiment demonstrated the case where both the 1st resist and the 2nd resist were positive resists, it is not limited to this. For example, the first resist may be a negative resist (for example, OMR85-45cp manufactured by Tokyo Ohka Kogyo Co., Ltd.) and the second resist may be a positive resist (for example, OFPR800-64cp manufactured by Tokyo Ohka Kagaku Co., Ltd.). Even in this case, when the surface emitting laser element 100 is manufactured, the positional relationship between the outer shape of the mesa and the two low reflectance portions 121 can be stably set to a desired positional relationship with high accuracy.

  In this case, since the solvent of each resist is different, the first resist pattern is not dissolved even if the second resist is applied thereon after the first resist pattern is formed. Therefore, the first resist pattern need not be cured.

  In this case, even if the portion of the first resist pattern that protrudes from the second resist pattern is exposed, the composition of the first resist changes so that the portion exposed to light is cured, so the first resist pattern changes. There is no dimensional change in the resist pattern. Of course, since the developing solutions themselves are different, the first resist pattern is not developed when the second resist pattern is developed, so that the dimension of the first resist pattern does not change.

  Further, in this case, even if the second resist pattern needs to be reworked due to misalignment or error, the type of resist is different, so that no dimensional change occurs in the first resist pattern. For example, when reworking the second resist pattern, even if the second resist is removed by exposing the entire surface to expose the second resist and developing it with a developer for the second resist, This resist pattern is resistant to the developer of the second resist and therefore does not cause dimensional change.

  By the way, when the hardening process of the 1st resist pattern is performed, the cross-sectional shape of a 1st resist pattern may deform | transform into a convex lens shape circularly (refer FIG. 19). In dry etching, the etched sidewall angle is determined by the etching selectivity between the resist and the material to be etched. This is because the resist pattern recedes by etching not only the material to be etched but also the resist itself, and the side wall of the material to be etched is inclined by the amount of the receding. This inclination reflects the cross-sectional shape of the resist pattern, and when the cross-sectional shape is rounded, the side wall angle of the material to be etched varies, and there is a concern that the electrode wiring breaks over this step.

  In this case, prior to the curing process of the first resist pattern, the first resist pattern may be irradiated with UV light (ultraviolet light) while heating the stacked body. Thereby, the surface of the first resist pattern is cured, and the cross-sectional shape can be prevented from being deformed into a convex lens shape by the curing process.

Specifically, irradiation with UV light can be performed using a UV dry cleaner (UV-1) manufactured by Samco. This apparatus is an apparatus for removing organic substances on the substrate surface by UV light and ozone. However, by introducing nitrogen instead of oxygen, an effect of only UV light can be obtained. The wavelengths of the UV light are 253.7 nm and 184.9 nm, and the power is 110 W (the lamp is 0.35 W / cm ² because φ200 mm). The laminate was heated to 130 ° C. and irradiated with UV light for 5 minutes, so that it could withstand the subsequent curing treatment (heating at 150 ° C. for 5 minutes).

  In the above embodiment, the case where the optical thickness of the dielectric layer 111a is λ / 4 has been described. However, the present invention is not limited to this. In short, the optical thickness may be an odd multiple of λ / 4.

  In the above embodiment, the case where the optical thickness of the dielectric layer 111b is 2λ / 4 has been described. However, the present invention is not limited to this. In short, the optical thickness may be an even multiple of λ / 4.

  In the above embodiment, the light source 14 may include the surface emitting laser array 200 shown in FIG. 20 as an example instead of the surface emitting laser element 100.

  In the surface emitting laser array 200, a plurality (21 in this case) of light emitting portions arranged in a two-dimensional manner are formed on the same substrate. Here, the X-axis direction in FIG. 20 is a main-scanning corresponding direction, and the Y-axis direction is a sub-scanning corresponding direction. The plurality of light emitting units are arranged such that the intervals between the light emitting units are equal to d2 when all the light emitting units are orthogonally projected onto a virtual line extending in the Y-axis direction. In the present specification, the interval between the light emitting units means the distance between the centers of the two light emitting units. Further, the number of light emitting units is not limited to 21.

  Each light emitting portion has the same structure as the surface emitting laser element 100 described above, as shown in FIG. The surface emitting laser array 200 can be manufactured by the same method as the surface emitting laser element 100 described above. Therefore, in each light emitting unit, when viewed from the Z-axis direction, the magnitude (absolute value) of the deviation amount between the center of gravity of the two low reflectance portions 121 and the center of the current passing region 108b is 0.1 μm or less. The light emission angle can be 0.2 deg or less in all directions. Further, it is possible to obtain a plurality of laser beams in a single fundamental transverse mode having a uniform polarization direction between the light emitting units. Accordingly, it is possible to form 21 minute light spots having a circular shape and high light density at desired positions on the photosensitive drum 1030 at the same time.

  Further, in the surface-emitting laser array 200, the intervals between the light emitting portions when the respective light emitting portions are orthogonally projected onto the virtual line extending in the sub-scanning corresponding direction are equal intervals d2, and therefore the photosensitive drum 1030 is adjusted by adjusting the lighting timing. In the above, it can be considered that the configuration is the same as the case where the light emitting units are arranged at equal intervals in the sub-scanning direction.

  For example, if the distance d2 is 2.65 μm and the magnification of the optical system of the optical scanning device 1010 is doubled, high-density writing of 4800 dpi (dots / inch) can be performed. Of course, higher density can be achieved by increasing the number of light emitting sections in the main scanning corresponding direction, or by arranging the array in which the pitch d1 in the sub scanning corresponding direction is narrowed to further reduce the interval d2, or by reducing the magnification of the optical system. And higher quality printing becomes possible. Note that the writing interval in the main scanning direction can be easily controlled by the lighting timing of the light emitting unit.

  In this case, the laser printer 1000 can perform printing without decreasing the printing speed even if the writing dot density increases. Further, when the writing dot density is the same, the printing speed can be further increased.

  By the way, it is preferable that the groove | channel between two light emission parts shall be 5 micrometers or more for the electrical and spatial separation of each light emission part. This is because if it is too narrow, it becomes difficult to control etching during production. Further, the mesa size (length of one side) is preferably 10 μm or more. This is because if it is too small, heat will be accumulated during operation and the characteristics may be deteriorated.

  Further, in the above embodiment, instead of the surface emitting laser element 100, a surface emitting laser array manufactured in the same manner as the surface emitting laser element 100 and in which the light emitting portions similar to the surface emitting laser element 100 are arranged one-dimensionally is used. It may be used.

  In the above embodiment, the case where the normal direction of the main surface of the substrate is inclined 15 degrees toward the crystal orientation [1 1 1] A direction with respect to the crystal orientation [1 0 0] direction is described. However, the present invention is not limited to this. When an inclined substrate is used as the substrate, the normal direction of the main surface of the substrate is inclined toward one direction of crystal orientation <1 1 1> with respect to one direction of crystal orientation <1 0 0>. Just do it.

  Moreover, although the said embodiment demonstrated the case where a board | substrate was an inclination board | substrate, it is not limited to this.

  Moreover, although the said embodiment demonstrated the case where the oscillation wavelength of a light emission part was a 780 nm band, it is not limited to this. The oscillation wavelength of the light emitting unit may be changed according to the characteristics of the photoreceptor.

  The surface-emitting laser element 100 and the surface-emitting laser array 200 can be used for applications other than the image forming apparatus. In that case, the oscillation wavelength may be a wavelength band such as a 650 nm band, an 850 nm band, a 980 nm band, a 1.3 μm band, and a 1.5 μm band depending on the application. In this case, a mixed crystal semiconductor material corresponding to the oscillation wavelength can be used as the semiconductor material constituting the active layer. For example, an AlGaInP mixed crystal semiconductor material can be used in the 650 nm band, an InGaAs mixed crystal semiconductor material can be used in the 980 nm band, and a GaInNAs (Sb) mixed crystal semiconductor material can be used in the 1.3 μm band and the 1.5 μm band.

  Further, by selecting the material and configuration of each reflecting mirror according to the oscillation wavelength, a light emitting unit corresponding to an arbitrary oscillation wavelength can be formed. For example, other than AlGaAs mixed crystal such as AlGaInP mixed crystal can be used. The low refractive index layer and the high refractive index layer are preferably a combination that is transparent with respect to the oscillation wavelength and can take a difference in refractive index as much as possible.

  In the above embodiment, the laser printer 1000 is described as the image forming apparatus. However, the present invention is not limited to this.

  For example, an image forming apparatus that directly irradiates laser light onto a medium (for example, paper) that develops color with laser light may be used.

  Further, an image forming apparatus using a silver salt film as the image carrier may be used. In this case, a latent image is formed on the silver salt film by optical scanning, and this latent image can be visualized by a process equivalent to a developing process in a normal silver salt photographic process. Then, it can be transferred to photographic paper by a process equivalent to a printing process in a normal silver salt photographic process. Such an image forming apparatus can be implemented as an optical plate making apparatus or an optical drawing apparatus that draws a CT scan image or the like.

  As an example, as shown in FIG. 22, a color printer 2000 including a plurality of photosensitive drums may be used.

  The color printer 2000 is a tandem multicolor printer that forms a full-color image by superimposing four colors (black, cyan, magenta, and yellow), and is a black station (photosensitive drum K1, charging device K2). , Developing device K4, cleaning unit K5, and transfer device K6), cyan station (photosensitive drum C1, charging device C2, developing device C4, cleaning unit C5, and transfer device C6), and magenta station ( The photosensitive drum M1, the charging device M2, the developing device M4, the cleaning unit M5, and the transfer device M6), and the yellow station (the photosensitive drum Y1, the charging device Y2, the developing device Y4, the cleaning unit Y5, and the transfer device Y6). ), Optical scanning device 2010, and transfer belt 2 80, and a fixing unit 2030.

  Each photoconductor drum rotates in the direction of the arrow in FIG. 22, and a charging device, a developing device, a transfer device, and a cleaning unit are arranged around each photoconductor drum along the rotation direction. Each charging device uniformly charges the surface of the corresponding photosensitive drum. The surface of each photoconductive drum charged by the charging device is irradiated with light by the optical scanning device 2010, and a latent image is formed on each photoconductive drum. Then, a toner image is formed on the surface of each photosensitive drum by a corresponding developing device. Further, the toner image of each color is transferred onto the recording paper on the transfer belt 2080 by the corresponding transfer device, and finally the image is fixed on the recording paper by the fixing unit 2030.

  The optical scanning device 2010 has a light source for each color including either a surface emitting laser element or a surface emitting laser array manufactured in the same manner as the surface emitting laser element 100. Therefore, the same effect as that of the optical scanning device 1010 can be obtained. In addition, since the color printer 2000 includes the optical scanning device 2010, the same effect as the laser printer 1000 can be obtained.

  By the way, in the color printer 2000, color misregistration may occur due to manufacturing error or position error of each component. Even in such a case, if each light source of the optical scanning device 2010 has a surface-emitting laser array similar to the surface-emitting laser array 200, color misregistration is reduced by selecting a light-emitting unit to be lit. can do.

  As described above, according to the method for manufacturing a surface emitting laser element of the present invention, a surface emitting laser element having a deviation amount (absolute value) of 0.1 μm or less can be stably controlled while controlling the oscillation transverse mode. Suitable for mass production.

  DESCRIPTION OF SYMBOLS 11a ... Deflector side scanning lens (a part of scanning optical system), 11b ... Image surface side scanning lens (a part of scanning optical system), 13 ... Polygon mirror (deflector), 14 ... Light source, 100 ... Surface emitting laser Elements 101, substrate, 103, lower semiconductor DBR (lower reflector), 104, lower spacer layer (part of the resonator structure), 105, active layer, 106, upper spacer layer (part of the resonator structure) , 107 ... Upper semiconductor DBR (upper reflector), 108 ... Selective oxidation layer, 108a ... Oxide, 108b ... Current passing region, 111a ... Dielectric layer, 111b ... Dielectric layer, 120a ... Resist pattern (first) 120b... Resist pattern (part of the first resist pattern), 120c... Resist pattern (part of the first resist pattern), 123. Stroke pattern, 125 ... Emission area, 200 ... Surface emitting laser array, 1000 ... Laser printer (image forming apparatus), 1010 ... Optical scanning apparatus, 1030 ... Photosensitive drum (image carrier), 2000 ... Color printer (image forming apparatus) ), 2010... Optical scanning device, K1, C1, M1, Y1... Photosensitive drum (image carrier).

US Pat. No. 5,493,577 Japanese Patent No. 3565902

Claims (8)

A method of manufacturing a surface emitting laser element in which a portion having a relatively high reflectance and a portion having a low reflectance are formed in an emission region due to the presence or absence of a dielectric layer and a thickness difference,
A mesa structure in which at least the selectively oxidized layer is exposed on a side surface of a laminate in which a lower reflector, a resonator structure including an active layer, and an upper reflector including a selectively oxidized layer are stacked on a substrate. Forming, and
Oxidizing the selectively oxidized layer of the mesa structure to form a constricted structure in which the oxide surrounds a current passing region;
Prior to the step of forming the mesa structure,
On the laminate, the first pattern, wherein relatively reflectance define the boundaries of the higher parts and the lower part, seen including a second pattern defining the outer shape of the mesa structure, said first And a step of forming a first resist pattern having an opening between the second patterns . The method of manufacturing a surface emitting laser element according to claim 1, wherein the second pattern is arranged around the first pattern. The method for manufacturing a surface emitting laser element according to claim 1, wherein the first and second patterns are separate bodies. It said first and second pattern, the surface emitting laser element according to any one of claims 1-3, characterized in that it is simultaneously formed by a single resist coated on the laminate Production method. The substrate is an inclined substrate;
In the step of forming the first resist pattern, the center of gravity of the first pattern and the second of the second pattern are suppressed so that the shift of the center of gravity of the center of the current passing region and the portion of the relatively low reflectance is suppressed. The method of manufacturing a surface emitting laser element according to claim 1, wherein the center of the pattern is shifted. 6. The method of manufacturing a surface emitting laser element according to claim 1, wherein the first and second patterns define a region in which an electrode surrounding the emission region is formed. . Covering the first pattern, and so as not to protrude from the second pattern, according to any one of claims 1-6, characterized by further comprising the step of forming a second resist pattern Manufacturing method of the surface emitting laser element. Prior to the step of forming the first resist pattern, a surface emitting laser according to any one of claims 1 to 7, characterized in that further comprising the step of forming a dielectric layer on the laminate Device manufacturing method.

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