JP2010283083A - Surface emitting semiconductor laser, method for manufacturing surface emitting semiconductor laser, surface emitting laser array element, optical scanning device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reliable surface emitting semiconductor laser having a high yield. <P>SOLUTION: The surface emitting semiconductor laser includes, on a surface of a semiconductor substrate, a lower reflector, an active layer composed of a semiconductor material, a selective oxidation layer having a current narrowing structure by oxidizing a partial area of the semiconductor material and an upper reflector, and emits a laser beam vertically to the semiconductor substrate surface by connecting a lower electrode and an upper electrode to the semiconductor substrate and the upper reflector, respectively, and carrying a current between the upper electrode and the lower electrode. A mesa structure region and an electrode pad region are formed by etching the upper reflector, the selective oxidation layer and the active layer. A first dielectric layer and a second dielectric layer are formed in the mesa structure region and the electrode pad region, and the area of the second dielectric layer formed in the electrode pad region is smaller than that of the first dielectric layer. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a surface emitting semiconductor laser, a method for manufacturing a surface emitting semiconductor laser, a surface emitting laser array element, an optical scanning device, and an image forming apparatus.

  A VCSEL (Vertical Cavity Surface Emitting Laser) is a semiconductor laser that emits light in a direction perpendicular to a substrate to be formed, and is lower in cost and higher performance than an edge emitting semiconductor laser. Therefore, it is used for applications such as a light source for optical communication such as optical interconnection, a light source for optical pickup, and a light source for image forming apparatuses such as laser printers.

  As the characteristics of the surface emitting semiconductor laser used for such applications, there is a demand for an active layer having a large gain, a low threshold and a high output, excellent reliability, and a controlled polarization direction.

  Usually, a surface emitting semiconductor laser is formed by laminating a semiconductor film on an n-type GaAs substrate. Specifically, a lower reflective mirror (DBR) made of a semiconductor multilayer film formed by alternately laminating films made of AlGaAs and AlAs on an n-type GaAs substrate, and a lower clad made of AlGaAs. Layers, multiple quantum well active layers made of GaAs, upper cladding layers made of AlGaAs, selective oxidation layers made of AlGaAs or AlAs that become part of the current constriction layer, and films made of AlGaAs and AlAs are alternately stacked. The upper reflective mirror (DBR) composed of the semiconductor multilayer film formed in this manner is sequentially laminated, the mesa structure is formed by etching the laminated semiconductor layer, and the side wall and the periphery of the formed mesa structure are insulated. An electrode coated with a body material and provided on the top surface of the mesa structure; The laser light is emitted from the light emitting surface opened in the upper surface of the mesa structure by passing a current between the electrodes provided on the n-type GaAs substrate.

  Such a surface emitting semiconductor laser arrayed two-dimensionally is called a surface emitting laser array element (surface emitting laser array). In such a surface emitting semiconductor laser having a mesa structure, an oxidation region is formed in a selective oxidation layer formed between the upper cladding layer and the upper reflecting mirror, thereby narrowing the opening region. A structure with higher performance is called a selective oxidation type VCSEL. In this selective oxidation type VCSEL, when the above semiconductor layers are stacked, an AlAs film or an AlGaAs film having a high Al composition is grown as a part of the distributed Bragg reflector DBR, and the current is generated by selectively oxidizing the AlAs layer. A constriction structure is provided inside the VCSEL.

  In such a surface emitting semiconductor laser, controlling the oscillation transverse mode of laser light oscillated from the surface emitting semiconductor laser element and controlling the polarization of the laser light are important issues, and various attempts are made. Has been made.

  In Patent Document 1, in addition to the current confinement structure, an optically transparent film is formed on the surface serving as the emission surface of the surface-emitting type semiconductor laser, and the difference in reflectance between the central portion and the peripheral portion in the light emitting region is obtained. A surface-emitting semiconductor laser element having a structure in which the transverse mode is controlled by providing is disclosed. In this surface emitting semiconductor laser element, the reflectance of the higher-order transverse mode can be reduced by the film provided on the periphery of the light emitting region on the emission surface, and even when the width of the current path region is widened, It enables single basic transverse mode oscillation and realizes mode control and reduction of operating voltage.

  By the way, the surface emitting semiconductor laser described in the cited document 1 is a current that flows in an optically transparent film (optical film) formed on the surface of the light emitting surface of the surface emitting semiconductor laser and a selective oxidation layer. The relative alignment with the constriction region is determined by the alignment accuracy in the photolithography process when forming the optical film. The alignment accuracy depends on the apparatus or the person, and is about 0.5 to 1 μm. If this alignment accuracy shift causes a positional shift in the light output direction between the optical film and the current confinement region, the light output angle Will tilt.

  The present invention has been made in view of the above contents, and has a high yield and high reliability, a surface emitting semiconductor laser, a method of manufacturing a surface emitting semiconductor laser, a surface emitting laser array element, an optical scanning device, and an image. A forming apparatus is provided.

  The present invention provides a lower reflector formed by alternately laminating semiconductor films having different refractive indexes on a surface of a semiconductor substrate, an active layer made of a semiconductor material on the lower reflector, Formed by alternately laminating a selective oxidation layer in which a current confinement structure is formed by oxidizing a partial region of a semiconductor material on the active layer and a semiconductor film having a different refractive index on the selective oxidation layer. A lower electrode is connected to the semiconductor substrate, and an upper electrode is connected to the upper reflector, and a current is passed between the upper electrode and the lower electrode, whereby the semiconductor In a surface emitting semiconductor laser that emits a laser beam perpendicular to a substrate surface, a mesa structure region and an electrode pad are formed by etching the upper reflecting mirror, the selective oxidation layer, and the active layer. A first dielectric layer and a second dielectric layer are formed in the mesa structure region and the electrode pad region, and the second dielectric layer formed in the electrode pad region is formed. The body layer is formed in a region narrower than the first dielectric layer.

  Further, according to the present invention, in the portion where the laser light is emitted in the mesa structure region, the first region including only the first dielectric layer or the second dielectric layer, and the first dielectric layer, A second region in which the second dielectric layer is laminated, and one of the first region and the second region is a film that intensifies light having a wavelength of the laser light; The other is a film thickness that weakens the light of the wavelength of the laser beam.

  Further, according to the present invention, the first dielectric layer and the second dielectric layer have a wavelength emitted by the surface emitting semiconductor laser as λ, and the refraction of the material constituting the first dielectric layer When the refractive index is n1 and the refractive index of the material constituting the second dielectric layer is n2, the film thickness of the first dielectric layer is λ / 4 × n1, and the second dielectric The film thickness of the layer is λ / 2 × n2, or the film thickness of the first dielectric layer is λ / 2 × n1, and the film thickness of the second dielectric layer is λ / 4 × It is n2.

  Further, the present invention is characterized in that the first dielectric layer formed in the electrode pad region is divided into a plurality of regions.

  The present invention also provides a lower reflecting mirror, an active layer, a selective oxidation layer in which a current confinement structure is formed by oxidizing a part of a semiconductor material, and an upper reflecting mirror on a surface of a semiconductor substrate. Forming a first dielectric layer on the upper reflector, and forming the first dielectric layer, and then forming the active layer, the selective oxidation layer, and the upper reflector. A step of forming a mesa structure region and an electrode pad region, a step of forming the second dielectric layer in the mesa structure region and the electrode pad region, and an upper portion of the mesa structure region. Forming an upper electrode, and forming a lower electrode on the back surface of the semiconductor substrate, wherein the first dielectric layer formed in the electrode pad region is the formation of the second dielectric layer. Be narrower than the area And butterflies.

  Further, the present invention provides the step of forming the first dielectric layer, wherein the first dielectric layer formed in the electrode pad region forms the first dielectric layer, and then The first dielectric layer is formed by dividing the first dielectric layer into a plurality of regions by etching the first dielectric layer.

  Further, the present invention is characterized in that a plurality of the surface emitting semiconductor lasers described above are arranged on the same semiconductor substrate.

  The present invention also provides an optical scanning device that scans a surface to be scanned with a light beam, the light source unit having the surface-emitting laser array element described above, and a deflecting unit that deflects the light beam from the light source unit; And a scanning optical system for condensing the light beam deflected by the polarizing means on the surface to be scanned.

  In addition, the present invention includes at least one image carrier and at least one optical scanning device according to claim 8 that scans a light beam including image information with respect to the at least one image carrier. It is characterized by that.

  According to the present invention, the image is a color image.

  According to the present invention, it is possible to provide a surface emitting semiconductor laser, a surface emitting semiconductor laser manufacturing method, a surface emitting laser array element, an optical scanning device, and an image forming apparatus with high yield and high reliability.

Configuration of conventional surface emitting semiconductor laser Correlation diagram between displacement in V direction and emission angle Correlation diagram between positional deviation in H direction and emission angle Configuration of a surface emitting semiconductor laser that eliminates misalignment Configuration of surface-emitting type semiconductor laser in the first embodiment Configuration diagram of another surface emitting semiconductor laser according to the first embodiment Top view of first dielectric layer of surface-emitting type semiconductor laser according to the first embodiment (1) Top view of the first dielectric layer of the surface emitting semiconductor laser according to the first embodiment (2) Top view of the first dielectric layer of the surface emitting semiconductor laser according to the first embodiment (3) Top view of the first dielectric layer of the surface emitting semiconductor laser according to the first embodiment (4) Top view of first dielectric layer of surface-emitting type semiconductor laser according to the first embodiment (5) Top view of the first dielectric layer of the surface emitting semiconductor laser according to the first embodiment (6) Process drawing (1) of the manufacturing method of the surface emitting semiconductor laser in 1st Embodiment Process drawing (2) of the manufacturing method of the surface emitting semiconductor laser in 1st Embodiment 14 is a top view in the process of FIG. Process drawing (3) of the manufacturing method of the surface emitting semiconductor laser in 1st Embodiment 16 is a top view and an enlarged view in the process of FIG. Process drawing (4) of the manufacturing method of the surface emitting semiconductor laser in 1st Embodiment Process drawing of the manufacturing method of the surface emitting semiconductor laser in 1st Embodiment (5) Process drawing of the manufacturing method of the surface emitting semiconductor laser in 1st Embodiment (6) Process drawing of the manufacturing method of the surface emitting semiconductor laser in 1st Embodiment (7) Configuration of an image forming apparatus according to a second embodiment Schematic diagram of an optical scanning device according to the second embodiment Schematic diagram of surface-emitting laser array element in the second embodiment Configuration of an image forming apparatus capable of color printing according to the second embodiment

  Next, the form for implementing this invention is demonstrated below.

  First, a surface emitting semiconductor laser including the background to the present invention will be described. FIG. 1 shows a configuration of a surface emitting semiconductor laser having a simplified configuration. FIG. 1A is a top view of a surface-emitting type semiconductor laser, and FIG. 1B is a cross-sectional view taken along an alternate long and short dash line 1A-1B. This figure schematically shows a main part of a surface emitting semiconductor laser, and shows a state in which an upper reflecting mirror 12 is formed on a selective oxidation layer 11 and an optical film 13 is further formed thereon. Is. The optical film 13 is formed in two strips at positions on both sides of the current confinement region 11b. The selective oxidation layer 11 is oxidized at its periphery, and an oxidized region 11a that is oxidized and a current confinement region 11b that is not oxidized are formed.

  In such a configuration, FIG. 2 shows the results of experiments on the relationship between the amount of deviation and the light emission angle when the optical film 13 is displaced from the predetermined position in the V direction shown in FIG. As shown in FIG. 2, when the position of the optical film 13 is shifted in the V direction, the light emission angle does not vary in the H direction, but the emission angle is inclined in the V direction depending on the amount of deviation. . Specifically, when the position of the 0.5 μm optical film is shifted, the emission angle in the V direction is inclined by about 0.18 °.

  FIG. 3 shows the result of an experiment on the relationship between the amount of deviation and the light emission angle when the optical film 13 is displaced from the predetermined position in the H direction shown in FIG. As shown in FIG. 3, when the position of the optical film 13 is shifted in the H direction, the light emission angle does not vary in the V direction, but the emission angle is inclined in the H direction depending on the amount of deviation. . Specifically, when the position of the 0.5 μm optical film is shifted, the emission angle in the V direction is inclined by about 0.65 °.

  Furthermore, by adding both the deviation in the V direction and the deviation in the H direction, the emission angle is more greatly inclined in the V direction and the H direction. As described above, when the emission angle is greatly inclined, a high-definition image cannot be obtained in the optical scanning device and the image forming apparatus. For this reason, in order to obtain a high-definition image, it is necessary to suppress the emission angle within a range of ± 0.2 °, and the alignment accuracy at this time requires an accuracy of ± 0.1 μm or less. The

  Therefore, as shown in FIG. 4, an optical film 35 is formed on the upper surface of the mesa region 28 in the surface emitting semiconductor laser. The optical film 35 is formed of a film having an optical film thickness of 3λ / 4 and a film having an optical film thickness of λ / 2. Specifically, in the surface emitting semiconductor laser, a lower reflecting mirror 22, a lower spacer layer 23, a multiple quantum well active layer 24, an upper spacer layer 25, and a part of the periphery are oxidized on an n-type GaAs substrate 21. The selective oxide layer 26, the upper reflecting mirror 27, and the first dielectric layer 31 to be the current confinement layer are laminated and etched to form the mesa region 28 and the electrode pad region 29, and then the second dielectric layer. The body layer 32 and the upper electrode 33 are formed, and the lower electrode 34 is formed on the back surface of the n-type GaAs substrate 21. The opening in the mesa region 28 is a region formed by a laminated film of the first dielectric layer 31 and the second dielectric layer 32 in the central portion and the peripheral portion in the region composed of the second dielectric layer 32. Is formed. The optical film 30 is formed by the second dielectric layer 32 so that the optical film thickness is λ / 2 at the central portion, and the first dielectric layer 31 is further optically connected at the peripheral portion. By forming the target film thickness to be λ / 4, the optical film thickness in the peripheral portion can be set to 3 × λ / 4 by the first dielectric layer 31 and the second dielectric layer 32. it can. By adopting such a configuration, the emission angle can be suppressed within a range of ± 0.2 °. The optical film thickness is λ / 4, where D = λ / 4 × N, where the actual film thickness is D and the refractive index is N, and the optical film thickness is λ / 2. When the actual film thickness is D and the refractive index is N, D = λ / 2 × N. Specifically, when the oscillation wavelength λ of the surface-emitting type semiconductor laser in the present embodiment is 780 nm, the film thickness of the first dielectric layer 31 is the same as that of the material constituting the first dielectric layer 31. When the refractive index N is 1.89, the optical film thickness is 103 nm, which is λ / 4, and the film thickness of the second dielectric layer 32 is the refractive index N of the material constituting the second dielectric layer 32. Is 1.89, the optical film thickness is 206 nm, which is λ / 2.

  At this time, in the electrode pad region 29, the first dielectric layer 31 is formed, and then etching for forming a mesa structure is performed to form the second dielectric layer 32. Then, the second dielectric film 32 is likely to be peeled off from the edge portion of the first dielectric layer 31. It is considered that stress is generated by laminating the second dielectric layer 32 at the end where the first dielectric layer 31 is etched, and film peeling is likely to occur due to this stress. .

  The present embodiment has been made in view of the above points, and is a surface emitting semiconductor laser in which optical films 35 having different film thicknesses are formed on the exit surface in order to suppress the exit angle within a predetermined range. In this case, by forming a predetermined pattern made of the first dielectric layer 31 in the electrode pad region 29 or by not forming the first dielectric layer 31 in the electrode pad region 29, the dielectric film is peeled off. , Improve yield and improve reliability.

[First Embodiment]
A first embodiment according to the present invention will be described. The present embodiment is a surface emitting semiconductor laser (VCSEL). Based on FIG. 5, the surface emitting semiconductor laser in the present embodiment will be described. FIG. 5A is a cross-sectional view of a surface emitting semiconductor laser, and FIG. 5B is an enlarged view of a mesa structure region.

  The surface-emitting type semiconductor laser according to the present embodiment has a lower reflection formed by alternately stacking a high refractive index semiconductor film and a low refractive index semiconductor film on a semiconductor substrate 41 made of n-GaAs. A mirror 42 is formed, a lower spacer layer 43 is formed thereon, a multiple quantum well layer 44 is formed thereon, an upper spacer layer 45 is formed thereon, and a selective oxide layer 46 is formed thereon. Furthermore, an upper reflecting mirror 47 configured by alternately laminating a high refractive index semiconductor film and a low refractive index semiconductor film is formed.

The lower reflecting mirror 42 is laminated on the surface of the semiconductor substrate 41 through a buffer layer (not shown), and a layer made of n-type Al _0.9 Ga _0.1 As as a low refractive index layer and n as a high refractive index layer. It is formed by alternately stacking 37.5 pairs of type Al _0.3 Ga _0.7 As. At this time, when the oscillation wavelength of the surface emitting semiconductor laser to be formed is λ, the optical thicknesses of the high refractive index layer and the low refractive index layer are set to be λ / 4. In addition, the interface between the high refractive index layer and the low refractive index layer gradually decreases in composition from the high refractive index layer to the low refractive index layer or from the low refractive index layer to the high refractive index layer in order to reduce electrical resistance. A changing 20 nm composition gradient layer is provided. When determining the optical thickness described above, the optical thicknesses in the high refractive index layer and the low refractive index layer each include a thickness that is ½ of the thickness of the composition gradient layer. An optical thickness of λ / 4 is D = λ / 4N where D is the actual film thickness and N is the refractive index.

The lower spacer layer 43 is laminated on the lower reflecting mirror 42, and is formed of non-doped Al _0.6 Ga _0.4 As.

The multiple quantum well layer 44 is stacked on the lower spacer layer 43, and is configured by alternately stacking three quantum well layers and four barrier layers. Each quantum well layer is made of Al _0.12 Ga _0.88 As, and each barrier layer is made of Al _0.3 Ga _0.7 As.

The upper spacer layer 45 is stacked on the multiple quantum well layer 44 and is formed of non-doped Al _0.6 Ga _0.4 As.

  The portion composed of the lower spacer layer 43, the multiple quantum well layer 44, and the upper spacer layer 45 is also called a resonator structure, and the entire optical thickness is the oscillation of the surface emitting semiconductor laser to be formed. It is comprised so that it may become substantially the same as a wavelength. Further, the multiple quantum well layer 44 is provided at the center of the resonator structure, which is a position corresponding to the antinode in the standing wave distribution of the electric field, so as to obtain a high stimulated emission probability.

The upper reflecting mirror 47 is laminated on the upper spacer layer 45, and is composed of a p-type Al _0.9 Ga _0.1 As layer which is a low refractive index layer and a p-type Al _0.3 layer which is a high refractive index layer. It is formed by alternately stacking 24 pairs of layers made of Ga _0.7 As. The low refractive index layer and the high refractive index layer are formed so that each optical thickness is λ / 4. Similarly to the case of the lower reflecting mirror 22, the low refractive index layer and the high refractive index layer are provided. A composition gradient layer is provided at the interface to reduce electrical resistance.

  The selective oxidation layer 46 is provided in the upper reflecting mirror 47 at a position optically separated from the resonator structure by λ / 4, and is made of p-type AlAs. For the sake of convenience, the selective oxidation layer 46 is shown as being formed between the upper spacer layer 45 and the upper reflecting mirror 47. After selectively forming a mesa structure, the selective oxidation layer 46 is partially oxidized by oxidation with water vapor or the like to form an oxidized region (oxidized region) 46a and a non-oxidized region (current confinement region) 46b.

  After the semiconductor layers are stacked in this way, the mesa structure region 48 and the electrode pad region 49 are formed by etching, and the first dielectric layer 51 and the second dielectric material are formed on the light emission surface in the mesa structure region 48. An optical film 55 composed of the layer 52 is formed. At this time, in the electrode pad region 49, the first dielectric layer 51 is formed in a predetermined pattern, and the second dielectric layer 52 is formed so as to cover the upper part thereof. The first dielectric layer 51 formed on the electrode pad region 49 has an end portion different from the end portion of the semiconductor layer generated by etching, and relieves stress generated by the second dielectric layer 52. be able to. An upper electrode 53 is formed on the mesa structure region 48, and a lower electrode 54 is formed on the back surface of the semiconductor substrate 41.

  FIG. 6 shows another configuration of the surface emitting semiconductor laser according to the present embodiment. This surface emitting semiconductor laser forms a lower reflecting mirror 62 constituted by alternately laminating a high refractive index semiconductor film and a low refractive index semiconductor film on a semiconductor substrate 61 made of n-GaAs. Then, a lower spacer layer 63 is formed thereon, a multiple quantum well layer 64 is formed thereon, an upper spacer layer 65 is formed thereon, a selective oxide layer 66 is formed thereon, An upper reflecting mirror 67 configured by alternately stacking a refractive index semiconductor film and a low refractive index semiconductor film is formed. A mesa structure region 68 and an electrode pad region 69 are formed by etching, and an optical film 75 composed of a first dielectric layer 71 and a second dielectric layer 72 is formed at the light emitting portion of the mesa structure region 68. In the electrode pad region 69, the first dielectric layer 71 is not formed, and the second dielectric layer 72 is continuously formed from the mesa structure region 68. An upper electrode 73 is formed on the mesa structure region 68, and a lower electrode 74 is formed on the back surface of the semiconductor substrate 61.

  FIG. 7 is a top view showing a region where the first dielectric layer 71 is formed in the surface emitting semiconductor laser shown in FIG. The first dielectric layer 71 is formed only in a part of the mesa region 68 and is not formed in the electrode pad region 69. As described above, since the first dielectric layer 71 is not formed in the electrode pad region 69, film peeling of the second dielectric layer 72 due to the first dielectric layer 71 does not occur.

  8 to 12 are top views showing various patterns in the region where the first dielectric layer 71 is formed in the surface emitting semiconductor laser shown in FIG.

  As shown in FIG. 8, the first dielectric layer 51 is formed in a part of the mesa region 48, and in the electrode pad region 49, the outer peripheral corners are formed to be rounded. Yes.

  As shown in FIG. 9, the first dielectric layer 51 is formed in a part of the mesa region 48, and the electrode pad region 49 is formed in a plurality of rectangular shapes.

  As shown in FIG. 10, the first dielectric layer 51 is formed in a part of the mesa region 48, and the electrode pad region 49 is formed in a fine checkered pattern.

  As shown in FIG. 11, the first dielectric layer 51 is formed in a part of the mesa region 48, and a plurality of fine rectangular patterns are formed in the electrode pad region 49. .

  As shown in FIG. 12, the first dielectric layer 51 is formed in the mesa region 48. In the electrode pad region 49, a plurality of patterns with rounded rectangular corners shown in FIG. Is formed.

  As described above, in the electrode pad region 49, the first dielectric layer 51 has a rounded corner shape, or the first dielectric layer 51 is divided into a plurality of fine patterns to form the second The stress in the dielectric layer 52 can be relaxed and the occurrence of film peeling can be suppressed.

(Manufacturing method of surface emitting semiconductor laser)
Next, a method for manufacturing the surface emitting semiconductor laser in the present embodiment will be described.

  First, as shown in FIG. 13, on a semiconductor substrate 41 made of n-GaAs, a lower reflecting mirror 42, a partial spacer layer 43, a multiple quantum well layer 44, an upper spacer layer 45, a selective oxidation layer 46, an upper reflecting mirror. 47 is stacked, and a first dielectric layer 51 is formed on the upper reflecting mirror 47.

The lower reflector 42, the partial spacer layer 43, the multiple quantum well layer 44, the upper spacer layer 45, the selective oxide layer 46, and the upper reflector 47 are formed by using trimethylaluminum (TMA) as a group III material. Trimethylgallium (TMG) and trimethylindium (TMI) are used, and phosphine (PH ₃ ) and arsine (AsH ₃ ) are used as Group V materials. 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.

  The first dielectric layer 51 is formed by forming a film on the upper reflecting mirror 47 by a plasma CVD (Chemical Vapor Deposition) method. Specifically, a silicon nitride (SiN) film is formed to 103 nm. Note that the first dielectric layer 51 to be formed may have an optical film thickness that is an odd multiple of λ / 4.

  Next, as shown in FIG. 14, a first resist pattern 81 is formed by a first photolithography process, and then the first dielectric layer 51 is etched by an etching process. Specifically, a photoresist is applied to the surface of the first dielectric layer 51, and a first resist pattern 81 is formed by performing exposure, development, and post-baking with an exposure apparatus. Thereafter, the first resist pattern 81 is formed. The first dielectric layer 51 where the resist pattern 81 is not formed is removed by dry etching or the like. Thereby, in the mesa region 48, the optical film part 51a made of the first dielectric layer 51 and the mesa pattern peripheral part 51b are formed. Thus, by forming, relative positional deviation between the position of the optical film part 51a and the mesa structure does not occur. At this time, also in the electrode pad region 49, the dielectric pattern portion 51c can be formed simultaneously. At this time, the shape of the dielectric pattern portion 51 c formed of the first dielectric film 51 is, for example, a pattern having the shape shown in FIGS. 8 to 12.

  The photoresist was formed by applying OFPR800-64cp (manufactured by Tokyo Ohka Kogyo Co., Ltd.) with a spin coater and adjusting the number of rotations so that the film thickness was about 1.6 μm. Further, after development, baking is performed on a hot plate at 150 ° C. for 5 minutes. As a result, the first resist pattern 81 does not melt even when it is subsequently immersed in the developer.

  FIG. 15 is a top view of the mesa region 48 formed as described above. In the mesa region 48, the first resist pattern 81 is formed on the two optical film portions 51a with a distance L1 being 5 μm apart, and the first resist pattern 81 on the optical film portion 51a has a length of one side. The length L2 is 2 μm, and the length L3 of the other side is 8 μm. The first resist pattern 81 on the two optical film portions 51a is formed in the substantially central portion of the first resist pattern 81 on the mesa pattern peripheral portion 51b, and the first resist pattern on the mesa pattern peripheral portion 51b. Reference numeral 81 denotes a square shape whose outer side has a side length L4 of 20 μm and a width L5 of 2 μm.

  Next, as shown in FIG. 16, a second resist pattern 82 is formed by a second photolithography process. The photoresist used as the second resist pattern 82 is the same material as the photoresist used as the first resist pattern 81. A second resist pattern 82 is formed by applying this photoresist on the surface on which the first resist pattern 81 is formed, and performing exposure and development with an exposure apparatus. After the development, post-baking is performed. The post-baking condition is baking at 120 ° C. for 2 minutes.

  FIG. 17A is a top view of the mesa region 48 formed as described above, and FIG. 17B is a cross-sectional view taken along the alternate long and short dash line 17A-17B. As shown in the drawing, the second resist pattern 82 is formed on the inner side of the first resist pattern 81 on the mesa pattern peripheral portion 51b. That is, the second resist pattern 82 is formed in a square shape having a side length L6 of 18 μm, and a width L7 is formed on the inner side of the outer shape of the first resist pattern 81 by 1 μm. However, as described above, since the first resist pattern 81 is baked by hot plate at 150 ° C. for 5 minutes, it is not removed even when the second resist pattern 82 is developed. By providing this length L7, the mesa structure can be formed at an appropriate position, which provides a margin for misalignment.

Next, as shown in FIG. 18, etching is performed by the ECR etching method using chlorine (Cl ₂ ) gas using the first resist pattern 81 and the second resist pattern 82 as a mask. Thereby, the groove part 83 is formed, and a mesa structure is formed. Since the outer shape of the mesa structure is determined by the first resist pattern 81, there is no positional deviation between the position of the mesa structure and the relative position of the optical film. Etching for forming the groove 83 is performed until the surface of the lower spacer layer 43 is exposed. Further, after the etching, the first resist pattern 81 and the second resist pattern 82 are removed by ultrasonic cleaning using an organic solvent.

  Next, as shown in FIG. 19, the selective oxidation layer 46 is oxidized from the surroundings by thermal oxidation in water vapor. As a result, an oxidized region 46a is formed, and a region that is not oxidized becomes a current confinement region 46b. The current confinement region 46b is a square having a side length of 4.5 μm, so that the distribution of higher-order transverse modes is 3 × in the optical film 55 due to the mutual relationship with the optical film 55 described later. Since it overlaps with the region of λ / 4, oscillation of higher-order transverse modes is suppressed. In the surface emitting semiconductor laser according to the present embodiment, this makes it possible to eliminate the inclination of the light emission angle.

  Next, as shown in FIG. 20, a second dielectric layer 52 is formed by a CVD method. The second dielectric layer 52 formed at this time is made of SiN, and is formed to have an optical thickness of λ / 2, that is, a thickness of 206 nm. Thereafter, by performing a photolithography process and an etching process, the contact portion 84 is formed by etching the second dielectric layer 52 in a region where the resist pattern is not formed. Thereby, optical films 55 having different film thicknesses are formed.

  Next, as shown in FIG. 21, the upper electrode 53 is formed so as to contact the contact portion 84, and the lower electrode 54 is formed on the back surface of the semiconductor substrate 41. The upper electrode 53 forms a square opening 85 having a side length of 10 μm in a region where the optical film 55 is formed as a light emission region. Specifically, a resist pattern is formed in a region to be the opening 85 to be formed, and then a laminated film made of Cr / AuZn / Au constituting the upper electrode 53 is formed, and then lift-off is performed with an organic solvent. To form. The laminated film constituting the upper electrode 53 may be a laminated film made of Ti / Pt / Au.

  Thereafter, the back surface of the semiconductor substrate 41 is polished to about 100 to 300 μm, and then the lower electrode 54 is formed. The lower electrode 54 is formed of a multilayer film made of AuGe / Ni / Au or a multilayer film made of Ti / Pt / Au. Thereafter, annealing is performed to form ohmic contact with the semiconductor layer in each of the upper electrode 53 and the lower electrode 54.

  Through the above steps, the surface-emitting type semiconductor laser in this embodiment can be manufactured.

[Second Embodiment]
Next, a second embodiment will be described. The present embodiment is an image forming apparatus using the surface emitting laser array element according to the present invention as a light source. This embodiment will be described with reference to FIG.

  A laser printer as an image forming apparatus according to the present embodiment includes an optical scanning device 100, a photosensitive drum 101, a charging charger 102, a developing roller 103, a toner cartridge 104, a cleaning blade 105, a paper feed tray 106, and a paper feed roller 107. , A registration roller pair 108, a fixing roller 109, a paper discharge tray 110, a transfer charger 111, a paper discharge roller 112, a charge removal unit 114, and the like.

  Specifically, in the rotation direction of the photosensitive drum 101, the charging charger 102, the developing roller 103, the transfer charger 111, the static elimination unit 114, and the cleaning blade 105 are arranged in the vicinity of the photosensitive drum 101.

  A photosensitive layer is formed on the surface of the photosensitive drum 101. Here, the photosensitive drum 101 is configured to rotate clockwise as shown in the figure. The charging charger 102 has a function of uniformly charging the surface of the photosensitive drum 101.

  The optical scanning device 100 irradiates the surface of the photosensitive drum 101 charged by the charging charger 102 with light modulated based on image information from a host device such as a personal computer. By this light irradiation, a latent image corresponding to the image information is formed on the surface of the photosensitive drum 101. The area where the latent image is formed on the surface of the photosensitive drum 101 moves in the direction in which the developing roller 103 is provided as the photosensitive drum 101 rotates. Details of the optical scanning device 100 will be described later.

  The toner cartridge 104 stores toner, and this toner is supplied to the developing roller 103. The developing roller 103 causes the toner supplied from the toner cartridge 104 to adhere to the latent image formed on the surface of the photoconductive drum 101 to visualize the image information on the surface of the photoconductive drum 101. Thereafter, as the photosensitive drum 101 rotates, the area where the toner is attached to the latent image on the surface of the photosensitive drum 101 moves in the direction in which the transfer charger 111 is provided.

  Recording paper 113 is stored in the paper feed tray 106. A paper feed roller 107 is disposed in the vicinity of the paper feed tray 106, and the paper feed roller 107 takes out the recording paper 113 one by one from the paper feed tray 106 and conveys it to the registration roller pair 108. The registration roller pair 108 is disposed in the vicinity of the transfer charger 111, temporarily holds the recording sheet 113 taken out by the paper feeding roller 107, and exposes the recording sheet 113 in accordance with the rotation of the photosensitive drum 101. It is sent out toward the gap between the body drum 101 and the transfer charger 111.

  The transfer charger 111 is charged with a reverse polarity to the toner on the surface of the photoconductor 101 in order to electrically attract the toner on the surface of the photoconductor drum 101 to the recording paper 113. The toner on the surface of the photosensitive drum 101 is transferred to the recording paper 113 by this charge, that is, an image formed by the toner is transferred to the recording paper 113. Thereafter, the recording sheet 113 is sent to the fixing roller 109.

  In the fixing roller 109, heat and pressure are applied to the recording paper 113, whereby the toner is fixed on the recording paper 113. Here, the recording paper 113 on which the image is fixed is sent to the paper discharge tray 110 via the paper discharge roller 112, and is sequentially stacked on the paper discharge tray 110.

  The neutralization unit 114 neutralizes the surface of the photosensitive drum 101. The cleaning blade 105 removes toner remaining on the surface of the photosensitive drum 101 (residual toner). The removed residual toner is configured to be reusable. The surface of the photosensitive drum 101 from which the residual toner has been removed moves again in the direction in which the charging charger 102 is provided.

(Optical scanning device)
Next, the optical scanning device 100 will be described with reference to FIG.

  The optical scanning device 100 includes a light source unit 121, a coupling lens 122, an aperture plate (aperture) 123, an anamorphic lens 124, a polygon mirror 125, a deflector side scanning lens 126, an image plane side scanning lens 127, and a processing device 140. Etc.

  The light source unit 121 includes a surface emitting laser array in which a plurality of surface emitting semiconductor lasers according to the first embodiment are formed.

  The coupling lens 122 is for making the light beam emitted from the light source unit 121 substantially parallel light.

  The aperture plate 123 has an aperture and is for defining the beam diameter of the light beam from the coupling lens 122.

  The anamorphic lens 124 forms a light beam that condenses the light beam that has passed through the aperture plate 123 into parallel light in the main scanning direction, and is condensed near the surface of the polygon mirror 125 in the sub-scanning direction.

  The polygon mirror 125 is formed in a regular hexagonal column shape, and a mirror surface is formed so that the six side surfaces are reflective surfaces. The polygon mirror 125 is rotated at a constant speed in a direction indicated by an arrow by a motor (not shown), and with this rotation, the light beam is deflected at a constant angular speed in the main scanning direction.

  The light deflected by the polygon mirror 125 forms an image on the surface of the photosensitive drum 101 by the deflector side scanning lens 126 and the image plane side scanning lens 127.

  For example, the processing device 140 generates image data based on image information from a higher-level model such as a personal computer, and generates a surface emitting semiconductor laser drive signal in the light source unit 121 according to the generated image data. Output to.

  As shown in FIG. 24, the light source unit 121 includes a surface emitting laser array in which surface emitting laser elements (VCSEL) are two-dimensionally arranged in an array. The surface emitting lasers are arranged with a predetermined sufficient interval in the main scanning direction, and the arrangement of the surface emitting lasers in the main scanning direction is arranged while being shifted by a spot interval C in the sub scanning direction. In this manner, the arrays arranged in the main scanning direction while being shifted by the spot interval C in the sub scanning direction are formed at predetermined pitches P in the sub scanning direction. By arranging in this way, it is possible to make the interval between the perpendicular lines perpendicular to the sub-scanning direction from the center of each surface emitting laser equal (the spot interval C is equal). Thus, by controlling the lighting timing of each surface emitting laser, the same configuration as when light sources are arranged on the photosensitive drum 101 at narrow regular intervals in the sub-scanning direction can be obtained. .

  For example, if the VCSEL has a diameter of 20 μm, a pitch P in the sub-scanning direction of 40 μm, and a spot interval C of 10 μm, the magnification in the optical system is about 1 ×, resulting in 2400 dpi (dots / inch). . Furthermore, by increasing the number of VCSELs arranged in the main scanning direction or by reducing the spot spacing C, it is possible to achieve higher density and to perform higher quality printing. Note that writing in the main scanning direction can be performed at high density by increasing the blinking timing of the VCSEL. In FIG. 24, the surface emitting laser array in the case where the number of VCSELs is 4 × 4 = 16 has been described. However, the number of VCSELs may be increased, and for example, even in the case of 4 × 10 = 40. Good.

  In this embodiment, since the light source is composed of a surface emitting semiconductor laser, it can be easily arranged in a two-dimensional manner, and a desired light source can be obtained at low cost. In this embodiment, an image forming apparatus such as a laser printer is described. However, the present invention is not limited to this, and can be applied to various image forming apparatuses having the above-described optical scanning device.

  For example, when the pitch P of each surface-emitting type semiconductor laser in the sub-scanning direction is 26.5 μm and 10 surface-emitting type semiconductor lasers are arranged in the main scanning direction, 10 The interval C is 2.65 μm. If the magnification in the optical system is set to double, writing dots can be formed on the photosensitive drum 101 at intervals of 5.3 μm. This corresponds to 4800 dpi (dots / inch), and high-density writing of 4800 dpi can be performed.

  Further, by increasing the number of surface emitting semiconductor lasers arranged in the main scanning direction, narrowing the pitch P, and further narrowing the spot interval C, it is possible to perform writing with higher density. Become. Note that the writing interval in the main scanning direction can be easily controlled by controlling the lighting timing of the surface emitting semiconductor laser as the light source.

  In the optical scanning device according to the present embodiment and the image forming apparatus using the same, the surface emitting semiconductor lasers according to the first to third embodiments that can be manufactured at low cost are used as the light source. Therefore, it is possible to obtain an optical scanning device and an image forming apparatus that are low in cost and high in quality at high speed.

(Image forming apparatus for forming a color image)
Next, an image forming apparatus for forming a color image will be described with reference to FIG.

  This image forming apparatus is a color laser printer, which is a dandem color machine including a plurality of photosensitive drums for color images.

  This color laser printer includes a black (K) photosensitive drum K1, a charging device K2, a developing device K4, a cleaning unit K5, a transfer charging unit K6, a cyan (C) photosensitive drum C1, and a charging unit. C2, developing unit C4, cleaning unit C5, transfer charging unit C6, magenta (M) photosensitive drum M1, charging unit M2, developing unit M4, cleaning unit M5, transfer charging unit M6, yellow (Y) photosensitive drum Y1, charger Y2, developing unit Y4, cleaning unit Y5, transfer charging unit Y6, optical scanning device 100, transfer belt 201, fixing unit 202, and the like.

  In this color laser printer, the optical scanning apparatus 100 includes a semiconductor laser for black, a semiconductor laser for cyan, a semiconductor laser for magenta, and a semiconductor laser for yellow. Each semiconductor laser is included in the present invention. It is comprised by the surface emitting semiconductor laser which concerns. The light beam from the black semiconductor laser is irradiated to the black photosensitive drum K1, the light beam from the cyan semiconductor laser is irradiated to the cyan photosensitive drum C1, and the light beam from the magenta semiconductor laser is magenta. The light beam from the yellow semiconductor laser is irradiated to the yellow photosensitive drum Y1, and the light beam from the yellow semiconductor laser is irradiated to the yellow photosensitive drum Y1.

  Each of the photosensitive drums K1, C1, M1, and Y1 rotates in the direction of the arrow, and in the order of the rotation direction, each of the chargers K2, C2, M2, and Y2, the developing devices K4, C4, M4, and Y4, for transfer. Charging means K6, C6, M6, Y6 and cleaning means K5, C5, M5, Y5 are arranged. Each of the chargers K2, C2, M2, and Y2 uniformly charges the surface of the corresponding photosensitive drum K1, C1, M1, and Y1. The charged surface of the photosensitive drums K1, C1, M1, and Y1 is irradiated with a light beam from the optical scanning device 100, and an electrostatic latent image is formed on the surface of the photosensitive drums K1, C1, M1, and Y1. It has become. Thereafter, toner images are formed on the surfaces of the photosensitive drums K1, C1, M1, and Y1 by the developing units K4, C4, M4, and Y4, and the transfer charging units K6, C6, M6, and Y6 corresponding to the toner images are formed. Thus, the toner images of the respective colors are transferred to the recording paper, and the image is fixed on the recording paper by the fixing unit 202. The cleaning means K5, C5, M5, and Y5 remove residual toner remaining on the surfaces of the corresponding photosensitive drums K1, C1, M1, and Y1.

  In this embodiment, the photosensitive drum is described as the image carrier. However, the image carrier may be an image forming apparatus using a silver salt film. 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 similar to a developing process in a normal silver salt photographic process. Then, it can be transferred to photographic paper by the same process as the printing process in the ordinary 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.

  Further, an image forming apparatus using a color developing medium (positive photographic paper) that develops color by the heat energy of a beam spot as an image carrier may be used. In this case, a visible image can be directly formed on the image carrier by optical scanning.

  As mentioned above, although the form which concerns on implementation of this invention was demonstrated, the said content does not limit the content of invention.

41 n-GaAs substrate 42 Lower reflector 43 Lower spacer layer 44 Multiple quantum well layer 45 Upper spacer layer 46 Selective oxide layer 46a Oxide region 46b Current confinement region 47 Upper reflector 48 Mesa structure region 49 Electrode pad region 51 First dielectric Body layer 52 Second dielectric layer 53 Upper electrode 54 Lower electrode

JP 2001-156395 A

Claims (10)

A lower reflector formed by alternately laminating semiconductor films of different refractive indexes on the surface of a semiconductor substrate;
On the lower reflector, an active layer made of a semiconductor material;
On the active layer, a selective oxidation layer in which a current confinement structure is formed by oxidizing a partial region of a semiconductor material;
An upper reflecting mirror formed by alternately laminating semiconductor films having different refractive indexes on the selective oxide layer;
A lower electrode is connected to the semiconductor substrate, and an upper electrode is connected to the upper reflector, and a current is passed between the upper electrode and the lower electrode, whereby a laser is perpendicular to the surface of the semiconductor substrate. In surface emitting semiconductor lasers that emit light,
Forming the mesa structure region and the electrode pad region by etching the upper reflecting mirror, the selective oxidation layer, and the active layer;
In the mesa structure region and the electrode pad region, a first dielectric layer and a second dielectric layer are formed, and the second dielectric layer formed in the electrode pad region is A surface emitting semiconductor laser characterized in that the surface emitting semiconductor laser is formed in a narrower region than the first dielectric layer. In the portion where the laser beam is emitted in the mesa structure region, the first region including only the first dielectric layer or the second dielectric layer, the first dielectric layer, and the second dielectric A second region laminated with the layer;
Either one of the first region and the second region has a film thickness that strengthens light of the wavelength of the laser beam, and the other has a film thickness that weakens light of the wavelength of the laser beam. The surface emitting semiconductor laser according to claim 1. The first dielectric layer and the second dielectric layer have a wavelength emitted by the surface-emitting semiconductor laser as λ, a refractive index of a material constituting the first dielectric layer is n1, and the first dielectric layer When the refractive index of the material constituting the dielectric layer 2 is n2,
The film thickness of the first dielectric layer is λ / 4 × n1, and the film thickness of the second dielectric layer is λ / 2 × n2, or
The film thickness of the first dielectric layer is λ / 2 × n1, and the film thickness of the second dielectric layer is λ / 4 × n2. Surface emitting semiconductor laser.   4. The surface emitting semiconductor laser according to claim 1, wherein the first dielectric layer formed in the electrode pad region is divided into a plurality of regions. . A step of laminating a lower reflecting mirror, an active layer, a selective oxidation layer in which a current confinement structure is formed by oxidizing a part of a semiconductor material, and an upper reflecting mirror on a surface of a semiconductor substrate; ,
Forming a first dielectric layer on the upper reflector;
Forming the mesa structure region and the electrode pad region by etching the active layer, the selective oxidation layer, and the upper reflecting mirror after forming the first dielectric layer;
Forming the second dielectric layer in the mesa structure region and the electrode pad region;
Forming an upper electrode on the mesa structure region and forming a lower electrode on the back surface of the semiconductor substrate;
Have
The method of manufacturing a surface-emitting type semiconductor laser, wherein the first dielectric layer formed in the electrode pad region is narrower than a region where the second dielectric layer is formed.   In the step of forming the first dielectric layer, the first dielectric layer formed in the electrode pad region forms the first dielectric layer, and then the first dielectric layer. 6. The method of manufacturing a surface-emitting type semiconductor laser according to claim 5, wherein the first dielectric layer is divided into a plurality of regions by etching.   5. A surface-emitting laser array element, wherein a plurality of surface-emitting semiconductor lasers according to claim 1 are arranged on the same semiconductor substrate. An optical scanning device that scans a surface to be scanned with a light beam,
A light source unit comprising the surface emitting laser array element according to claim 7;
Deflecting means for deflecting the light beam from the light source unit;
A scanning optical system for condensing the light beam deflected by the polarizing means on the surface to be scanned;
An optical scanning device comprising: At least one image carrier;
9. The optical scanning device according to claim 8, wherein the at least one image carrier scans a light beam including image information;
An image forming apparatus comprising:   The image forming apparatus according to claim 9, wherein the image is a color image.

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