JP2014011228A - Optical device, optical scanner, and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical device that has a metal pad formed thereon, formed by cleavage, has good yield, and can be manufactured at low costs.SOLUTION: Provided is an optical device that is formed by cleaving to separate one semiconductor substrate, and includes a light-emitting unit formed on the substrate, and electrode pads electrically connected with electrodes of the light-emitting unit. An outside end part of the electrode pad has a shape in which a thickness in the outside end part is gradually reduced toward the outside.

Description

  The present invention relates to an optical device, an optical scanning device, and an image forming apparatus.

  In an optical device such as a semiconductor laser, a plurality of chips are simultaneously formed on a single wafer, and these are separated and packaged to form individual optical devices. Chip separation is mainly performed by a dicing method or a scribe method. The dicing method is a method of cutting along a dicing line by rotating a rotating blade mixed with diamond powder at a high speed. The scribe method is a method in which a scribe line (straight scratches, separation grooves) is formed on a substrate surface with a diamond cutter, and a break blade is pressed from the back side of the substrate to cleave.

  When the dicing method is used, water is used for cooling and washing away the cutting waste during cutting. For this reason, in order to avoid the generation of a large amount of sewage, chips are often separated by cleaving using a scribing method.

An outline of the cleaving process is as follows.
(1) A dicing film is attached to the back surface of the wafer on which a plurality of optical devices are formed.
(2) Affix this dicing film to a metallic ring.
(3) A scribe line is formed on the surface of the wafer in two directions orthogonal to each other using a diamond pen.
(4) A protective sheet is attached to the surface of the wafer. This protective sheet is coated with silicone as an antistatic agent and a release agent.
(5) The wafer is placed with the protective sheet side down on the receiving blades arranged at an interval smaller than twice the interval (separation pitch) between the scribe lines. At this time, the scribe line is positioned at the center of the receiving blade interval.
(6) The blade of the ceramic cutter is pressed from behind the scribe line, and a predetermined amount (hereinafter referred to as “cut depth”) is pressed to open the wafer.
(7) The other scribe lines are similarly cleaved to divide the wafer into a plurality of strip-shaped pieces. This is called “primary opening”.
(8) Each of the plurality of pieces is cleaved by a scribe line and divided into individual optical devices. This is called "secondary opening".
(9) Remove the protective sheet.
(10) Using a dilator warmed to about 50 ° C., the dicing film is uniformly stretched in all directions of 360 degrees to separate the plurality of optical devices from each other.

  In recent years, in many technical fields such as optical communication and optical recording, interest in surface-emitting semiconductor lasers (vertical-cavity surface-emitting lasers; Vertical-Cavity Surface-Emitting Lasers) is increasing. This is because the VCSEL has a lower threshold current and lower power consumption than the edge-emitting semiconductor laser, and a circular light spot can be easily obtained. It has many advantages such as easy integration.

  For example, Patent Document 1 includes a substrate including a semiconductor layer on the surface, a post structure formed on the substrate, and a plurality of protrusions formed separately on the substrate. A VCSEL having the same height as the post structure is disclosed.

  Some VCSELs make use of their characteristics to form a laser array in which multi-channel laser oscillation units such as 32 channels and 40 channels are integrated, but in that case the chip outline is as large as about 1 mm square, In order to prevent wafer cracking in the manufacturing process, the thickness of the wafer is often as thick as 200 μm or more.

  The inventors have been developing a method for efficiently separating an optical device having a large chip outer shape and a large wafer thickness, such as the VCSEL, with good yield by cleaving. And while advancing development, the inventors discovered a phenomenon in which silicone on the surface of the protective sheet adheres to the end of a metal pad (electrode pad) having a thickness of about 1 μm in the optical device when cleaving an optical device of about 1 mm square. The silicone adhering to the end of the metal pad moved to the surface of the metal pad and the light emitting surface in the subsequent process, and the manufacturing yield was lowered.

  FIG. 1 shows a photomicrograph (plan view) of silicone adhered to a metal pad. As shown in FIG. 1, it can be seen that the silicone adheres as if it was scraped off at the end of the metal pad.

  It has also been confirmed that the adhesion of silicone to the metal pad tends to occur at the end away from the scribe line to be cleaved in both the primary cleaving and the secondary cleaving.

  By the way, adhesion of foreign matter made of silicone from the protective sheet on the chip has problems in the following two points. One is that the light output decreases when the foreign matter moves on the chip surface to cover the light opening. The other is that when silicon adheres to the metal pad, wire bonding becomes poor. The foreign matter may move on the chip, and may cause poor adhesion during wire bonding, so it is not preferable that the foreign object is on the chip surface as well as the metal pad.

  Therefore, the present invention has been made in view of the above, and in an optical device such as a surface-emitting laser having a metal pad or the like, particularly a surface-emitting laser array having a plurality of light-emitting portions, An object of the present invention is to provide an optical device which can be manufactured at a low cost with a high yield by reducing the adhesion of foreign substances.

  According to one aspect of the present invention, in an optical device that is separated and formed by cleaving a single semiconductor substrate, a light emitting portion formed on the substrate and an electrode electrically connected to the electrode in the light emitting portion The outer end portion of the electrode pad has a shape such that the thickness at the outer end portion gradually decreases toward the outside.

  According to another aspect of the present invention, in an optical device that is separated and formed by cleaving a single semiconductor substrate, a light emitting portion formed on the substrate, an electrode in the light emitting portion, The electrode pad is electrically connected, and the outer end portion of the electrode pad is formed so as to have a round cross-sectional shape.

  According to the present invention, in an optical device such as a surface-emitting laser having a metal pad or the like, light that can be manufactured with high yield and low cost by reducing adhesion of foreign matter to the metal pad during cleaving. A device can be provided.

Explanatory drawing for explaining adhesion of silicone Structure diagram of surface emitting laser which is an optical device according to the first embodiment Process chart of laser chip manufacturing method (1) Process chart of laser chip manufacturing method (2) Process chart of laser chip manufacturing method (3) Process chart of laser chip manufacturing method (4) Process chart of laser chip manufacturing method (5) Process chart of laser chip manufacturing method (6) Explanatory drawing of electrode pads in laser chip (1) Explanatory drawing of electrode pad in laser chip (2) Illustration of electrode pad shape in laser chip Explanatory drawing of the mask used when forming the electrode pad of the optical device in 1st Embodiment Explanatory drawing (1) of the electrode pad of the laser chip which is an optical device in 1st Embodiment Explanatory drawing (2) of the electrode pad of the laser chip which is an optical device in 1st Embodiment Process chart of laser chip manufacturing method (7) Illustration of dicing film and metal ring Illustration of scribe line Illustration of protective sheet Illustration of the receiving blade Explanatory drawing in opening process (1) Explanatory drawing in the opening process (2) Explanatory diagram of silicone adhesion mechanism (1) Explanatory drawing of silicone adhesion mechanism (2) Explanatory drawing of silicone adhesion mechanism (3) Explanatory drawing of silicone adhesion mechanism (4) Explanation of why silicone does not adhere to chip A Main part enlarged view in FIG. Explanatory drawing of movement amount Δl of protective sheet Explanatory drawing of the relationship between the cutting depth, the movement amount Δl of the protective sheet and the adhesion of the protective sheet Explanatory drawing of the relationship between the space | interval L in a receiving blade, the movement amount (DELTA) l of a protection sheet, and the contact | adhesion power of a protection sheet Explanatory drawing (1) of the reason why silicone does not adhere in the first embodiment Explanatory drawing of the reason why silicone does not adhere in the first embodiment (2) Explanatory drawing (3) of the reason why silicone does not adhere in the first embodiment Explanatory drawing of the laser chip in the first embodiment Explanatory drawing of the arrangement | sequence of the several light emission part of the laser chip in 1st Embodiment Configuration diagram of laser printer in second embodiment The block diagram of the optical scanning device in 2nd Embodiment Configuration diagram of laser printer in third embodiment

  The form for implementing this invention is demonstrated below. In addition, about the same member etc., the same code | symbol is attached | subjected and description is abbreviate | omitted.

[First Embodiment]
(Structure of surface emitting laser)
A surface emitting laser which is an optical device in the present embodiment will be described. As shown in FIG. 2, the surface emitting laser that is an optical device in this embodiment includes a substrate 101, a buffer layer 102, a lower semiconductor DBR 103, a lower spacer layer 104, an active layer 105, an upper spacer layer 106, and an upper semiconductor DBR 107. , Contact layer 109, protective film 111, p-side electrode 113, n-side electrode 114, and the like. FIG. 2 is a cross-sectional view of the surface emitting laser according to the present embodiment. In addition, the optical device in the present embodiment, that is, the one in which the above-described surface emitting laser is formed may be referred to as a laser chip.

  The substrate 101 is an n-GaAs single crystal substrate.

  The buffer layer 102 is laminated on the + Z side surface of the substrate 101 and is a layer made of n-GaAs.

The lower semiconductor DBR 103 is stacked on the + Z side of the buffer layer 102, and includes a low refractive index layer made of n-Al _0.9 Ga _0.1 As and a high refractive index made of n-Al _0.3 Ga _0.7 As. It has 40.5 pairs of layers. 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 T of the layer is T = 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, and includes a quantum well layer composed of three layers of Al _0.12 Ga _0.88 As and a barrier layer composed of four layers of Al _0.3 Ga _0.7 As. Is an active layer having a triple quantum well structure.

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.

  A portion composed of the lower spacer layer 104, the active layer 105, and the upper spacer layer 106 is also called a resonator structure, and the thickness thereof is set to be an optical thickness of one wavelength. 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 as to obtain a high stimulated emission probability.

The upper semiconductor DBR 107 is laminated on the + Z side of the upper spacer layer 106, and has a low refractive index layer made of p-Al _0.9 Ga _0.1 As and a high refractive index made of p-Al _0.3 Ga _0.7 As. It has 25 pairs of layers. Between each refractive index layer, in order to reduce electrical resistance, a composition gradient layer is provided in which the composition is gradually changed from one composition to the other composition. Each refractive index layer is set to have an optical thickness of λ / 4 including 1/2 of the adjacent composition gradient layer.

  One of the low refractive index layers in the upper semiconductor DBR 107 is provided with a current confinement layer 108 made of p-AlAs. The current confinement layer 108 includes a selective oxidation region 108a that is selectively oxidized in the peripheral portion and a current confinement region 108b that is not oxidized in the central portion.

  The insertion position of the current confinement layer 108 is a position corresponding to the third node from the active layer 105 in the standing wave distribution of the electric field.

  The contact layer 109 is stacked on the + Z side of the upper semiconductor DBR 107 and is a layer made of p-GaAs.

(Method for manufacturing surface emitting laser)
Next, a method for manufacturing the surface emitting laser in the present embodiment will be briefly described. As described above, a structure in which a plurality of semiconductor layers are stacked over the substrate 101 is also referred to as a “stacked body” for convenience.

(1) First, as shown in FIG. 3, the stacked body is crystal-grown by metal organic chemical vapor deposition (MOCVD) method or molecular beam epitaxy (MBE) method. To make. Specifically, a buffer layer 102, a lower semiconductor DBR 103, a lower spacer layer 104, an active layer 105, an upper spacer layer 106, an upper semiconductor DBR 107 including a current confinement layer 108, and a contact layer 109 are stacked on the substrate 101. . Here, when the stacked body is formed by the MOCVD method, trimethylaluminum (TMA), trimethylgallium (TMG), and trimethylindium (TMI) are used as the group III material, and the group V material is Phosphine (PH ₃ ) and arsine (AsH ₃ ) are used. Further, carbon tetrabromide (CBr ₄ ) is used as a p-type dopant material, and hydrogen selenide (H ₂ Se) is used as an n-type dopant material.

  (2) Next, a plurality of portions to be light emitting portions on the surface of the laminate are masked with square resist patterns each having a side of 25 μm. Further, the peripheral region in each laser chip is also masked with a resist pattern so as not to be etched.

(3) Next, as shown in FIG. 4, a mesa structure (denoted as “mesa” for convenience is described) by performing etching using the resist pattern as a mask by an ECR etching method using Cl ₂ gas. ). Here, the etching is performed so that the bottom surface of the etching is located in the lower spacer layer 104.

  (4) Next, the photomask is removed.

  (5) Next, as shown in FIG. 5, the laminate is heat-treated in water vapor. As a result, in the current confinement layer 108, Al (aluminum) contained in the current confinement layer 108 is selectively oxidized from the outer peripheral portion of the mesa to form the selective oxidation region 108a, and is not oxidized in the central portion. The current confinement region 108b is formed by the region. As a result, a so-called oxidized constriction structure that can limit the drive current path of the light emitting unit to only the central part of the mesa is formed, and the non-oxidized current confinement region 108b becomes a current passing region (current injection region). Become. In this way, for example, a substantially square current passing region having a width of about 4 μm is formed.

  (6) Next, as shown in FIG. 6, a protective layer 111 made of SiN is formed by using a chemical vapor deposition (CVD) method.

  (7) Next, an etching mask for opening a window for the p-side electrode contact is formed on the top of the mesa serving as the laser light emission surface.

  (8) Next, as shown in FIG. 7, the protective layer 111 is etched with BHF to open a window for the p-side electrode contact.

  (9) Next, the mask is removed.

  (10) Next, a square resist pattern having a side of 10 μm is formed in a region (emission region) serving as a light emitting portion on the upper part of the mesa, and vapor deposition of a p-side electrode material is performed. As the electrode material on the p side, a multilayer film made of Ti / Pt / Au is used. At this time, the p-side electrode material is deposited on the electrode pad and the wiring member at the same time.

  (11) Next, as shown in FIG. 8, the p-side electrode 113 is formed by removing the electrode material deposited in the region to be the light emitting portion by lift-off. On the upper surface of the mesa, the region surrounded by the p-side electrode 113 formed in this way is the emission region. At this time, as shown in FIGS. 9 and 10, the electrode pad 150, the wiring member 155, and the like are simultaneously formed. The electrode pad 150 formed at this time has a thickness of about 1 μm. FIG. 9 shows a portion including the electrode pad 150 and the wiring member 155 formed in this step, and FIG. 10 is a top view of what is shown in FIG.

  By the way, as shown in FIG. 11, when the electrode pad 150 is formed by lift-off, the outer end portion of the electrode pad 150 has a shape with a sharp corner. FIG. 11 is an enlarged view of a region surrounded by an alternate long and short dash line 9A in FIG.

  Therefore, in the present embodiment, as shown in FIG. 12, the thickness gradually increases near the end of the electrode pad 150 (the end of the electrode pad 150 on the side far from the scribe line to be cleaved). Etching is performed after the resist pattern 160 having the thin film thickness gradient region 161 is formed. The film thickness gradient region 161 in the resist pattern 160 having such a film thickness gradient region 161 can be formed by exposing with an exposure apparatus using a photomask called a gradation mask.

  The gradation mask used here is a photomask provided with a gradation region composed of a pattern having a scale less than the resolution limit of light. Depending on the area ratio between the portion with the pattern and the portion without the pattern, The amount of transmitted light is adjusted. Since the size of the pattern in the gradation area is below the light resolution limit, the shape of the pattern in the gradation area of the photomask is not reflected in the resist pattern, and the exposure amount of the photoresist is reduced. Can be adjusted. Therefore, the thickness of the resist pattern to be formed can be adjusted. In this manner, a resist pattern 160 having a film thickness gradient region 161 having a cross-sectional shape as shown in FIG. 12 can be formed by exposure and development by an exposure apparatus using a gradation mask as a photomask.

  After such a resist pattern 160 is formed, when the resist pattern 160 is sputter-etched by reverse sputtering mode of the sputtering apparatus or argon plasma by the RIE apparatus, a thin part of the resist pattern 160, that is, a thin part of the film thickness gradient region 161 is obtained. First, the surface of the electrode pad 150 is exposed, and thereafter, the electrode pad 150 is gradually sputter-etched. Therefore, the shape of the electrode pad 150 gradually decreases at the end of the electrode pad 150 (the end of the electrode pad 150 on the side far from the scribe line to be cleaved), that is, before etching. The electrode pad 150 can be formed so as to have a cross-sectional shape substantially the same as the cross-sectional shape of the resist pattern 160 having the thickness gradient region 161. At this time, the light emission surface of the surface emitting laser has a thick resist pattern 160 and is protected, so there is no damage due to etching.

  Further, the cross-sectional shape of the electrode pad 150 formed in this way depends on the cross-sectional shape of the resist pattern 160, although it is necessary to consider the selection ratio between the electrode pad 150 and the resist pattern 160. Therefore, in consideration of this selection ratio, the electrode pad 150 having a desired shape can be formed by forming the cross-sectional shape of the resist pattern 160 so that the electrode pad 150 has a desired shape. Thereafter, the resist pattern 160 is removed with an organic solvent or the like.

  As a result, as shown in FIG. 13, the electrode pad 150a having a rounded and rounded cross section at the outer end 151a and the thickness at the outer end 151b as shown in FIG. The electrode pad 150b can be formed in such a shape that gradually becomes thinner toward the outside. As described above, in this embodiment, the shape of the outer end portion of the electrode pad 150 is formed to be a desired shape by controlling the degree of gradation of the gradation mask in the photomask.

  (12) Next, as shown in FIG. 15, after polishing the back side of the substrate 101 to a predetermined thickness (for example, about 200 μm), the n-side electrode 114 is formed. Here, the n-side electrode 114 is a multilayer film made of AuGe / Ni / Au.

  (13) Next, 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 portion, and a plurality of laser chips are formed on the substrate 101. In addition, a structure in which a plurality of laser chips are formed on the substrate 101 is referred to as a “chip forming substrate 200” for convenience. In the chip formation substrate 200, the surface on the p-side electrode 113 side (+ Z side) is referred to as the front surface, and the surface on the n-side electrode 114 side (−Z side) is referred to as the back surface.

  (14) Next, as shown in FIG. 16, the dicing film 210 is attached to the back surface of the chip forming substrate 200. The dicing film 210 is a vinyl chloride film having a thickness of 75 μm, and an acrylic pressure-sensitive adhesive is uniformly applied to a thickness of 10 μm on one surface thereof.

  (15) Next, the dicing film 210 is attached to a metal ring 212 having an outer diameter of 6 inches.

  (16) Next, as shown in FIG. 17, scribe lines are formed on the surface of the chip forming substrate 200 in the X-axis direction and the Y-axis direction using a diamond pen in the gap between adjacent laser chips. Here, the scribe lines are formed at equal intervals in both the X-axis direction and the Y-axis direction, and this interval is referred to as a separation pitch w.

  (17) Next, as shown in FIG. 18, a protective sheet 214 is attached to the surface of the chip forming substrate 200. This protective sheet 214 is a PET film having a thickness of 25 μm. An antistatic agent is applied to the surface of the protective sheet 214 on the chip forming substrate 200 side, and silicone is further applied thereon as a release agent. If the antistatic agent is not applied, static electricity of 200 V or more is generated, and the laser chip may be electrostatically broken. In addition, since the protective sheet 214 has no adhesiveness, it is attached and fixed to the adhesive surface of the dicing film 210.

  (18) Next, as shown in FIG. 19, the chip forming substrate 200 is placed on the receiving blade 220 having a groove narrower than twice the separation pitch w, and the scribe line to be opened is the center of the groove of the receiving blade 220. It is placed so that it is located at.

  (19) Next, as shown in FIG. 20, a ceramic cutter blade 230 is pressed from directly behind the scribe line to be cleaved. The laser chip on the −X side of the scribe line to be cleaved is referred to as chip A, and the laser chip on the + X side of the scribe line to be cleaved is referred to as chip B.

  (20) Next, the cutter blade 230 is pushed in a predetermined amount to open the chip forming substrate 200. In the following, the pushing amount of the cutter blade 230 is referred to as “cut depth”.

  (21) Next, in the same manner, primary cleavage and secondary cleavage are performed on all scribe lines.

  (22) Next, the protective sheet 214 is peeled off.

  (23) Next, using the dilator warmed to about 50 ° C., the dicing film 210 is uniformly stretched in all directions of 360 degrees. As a result, the plurality of laser chips are separated from each other.

  (24) Next, the plurality of laser chips are individually peeled off from the dicing film 210.

  Thereafter, a laser chip, that is, a surface emitting laser according to the present embodiment can be manufactured through several subsequent processes.

  By the way, as described above, the inventors of the present invention have a phenomenon in which silicone on the surface of the protective sheet adheres to the end of an electrode pad having a thickness of about 1 μm (hereinafter referred to as “silicone”) when cleaving an optical device of about 1 mm square. "Attachment phenomenon"). And the inventors estimated the generation | occurrence | production mechanism of a silicone adhesion phenomenon as follows.

  When the cutter blade 230 is pushed in from the back surface, the chip forming substrate 200 is deformed by the pushing load. At this time, a compressive stress is generated on the back surface of the chip forming substrate 200, and a tensile stress is generated on the surface of the chip forming substrate 200. The tensile stress is concentrated at the bottom of the scribe line to be cleaved.

  Further, when the cutter blade 230 is pushed in and the tensile stress at the bottom becomes equal to or higher than the tensile strength of the substrate 101, a crack occurs at the bottom. This crack immediately proceeds to the back surface of the chip forming substrate 200.

  As an example, as shown in FIG. 21, when a load P is applied from the back side of the scribe line to be cleaved, the portion of the protective sheet 214 immediately above the receiving blade is applied to the chip forming substrate 200 with a force of P / 2. It will be pressed. In other words, the portion of the protective sheet 214 immediately above the receiving blade is pressed more tightly against the chip forming substrate 200 than any other portion, and is in close contact therewith.

  When the cutter blade 230 is further pushed in this state, the protective sheet 214 is also pushed down as shown in FIG. 22, and the protective sheet 214 moves.

  As a result, for example, in the chip B, as shown in FIG. 23 and FIG. 24, the end of the electrode pad 150 on the side far from the scribe line to be cleaved ( However, unlike the present embodiment, in the case of a shape with sharp corners, it is considered that the silicone corresponding to the amount of movement of the protective sheet 214 is scraped off.

  Thereafter, when the protective sheet 214 is removed, a part of the silicone remains on the laser chip as shown in FIG.

  On the other hand, the end of the electrode pad 150 on the side close to the scribe line to be cleaved, that is, the inner end opposite to the outer end is immediately after cleaving, as shown in FIGS. It becomes free with respect to the protective sheet 214, and the adhesion force of the protective sheet 214 is reduced. Accordingly, it is considered that the silicone does not adhere to the inner end portion of the electrode pad 150.

  Next, the adhesion force between the protective sheet 214 and the chip forming substrate 200 will be examined in detail, and this adhesion force will be estimated.

The cleaving process is considered to be a central concentrated load problem in simple support beams at both ends in terms of material mechanics. Assuming that the cross-sectional shape of the object to which the load P is applied is a rectangle, the breaking load Pmax is obtained by the following equation (1).

Pmax = (2bh ² / 3L) σ (1)

Here, b is the width of the cleavage plane, which is the maximum diameter of the substrate 101 in the case of primary cleavage, and the length of the side of the laser chip in the case of secondary cleavage. h is the height of the open surface, L is the groove interval in the receiving blade 220, and σ is the tensile strength of this object.

In the case of secondary cleaving, L = 2b, so that the above equation (1) can be expressed as the following equation (2).

^{Pmax = (h 2/3)} σ ...... (2)

At the time of opening, the breaking load Pmax obtained by the above formula (1) or (2) is applied to the chip forming substrate 200, and a force of Pmax / 2 acts on the protective sheet on the receiving blade 220 in the -Z direction. Become.

  As an example, in the case where a plurality of 1.2 mm square laser chips are formed on a 3 inch GaAs wafer (h = 240 μm), the adhesion between the chip forming substrate and the protective sheet during cleaving is estimated. Note that 138 Mpa is used as the tensile strength σ of GaAs. Further, the interval L in the receiving blade 220 is 2 mm.

  It is estimated that the maximum breaking load (when b = wafer radius) at the primary cleavage is 200 N (20.4 Kg), and the breaking load at the secondary cleavage is 2.65 N (270 g). That is, a load of about 135 g per one laser chip is applied at the time of primary cleaving and secondary cleaving, and the protective sheet 214 and the chip forming substrate 200 are in close contact with each other.

  Next, in order to estimate the amount of movement of the protective sheet 214, first, the amount of pressing of the cutter blade 230, that is, the cut depth D is examined.

The amount of deflection d when the center load P is applied to the simple support beams at both ends is obtained by the following equation (3). Here, E is Young's modulus. 83 GPa is used as the Young's modulus E of GaAs.

d = PL ³ / 4Ebh ³ (3)

When the expression (3) in the above is modified, the following expression (4) is obtained.

P = 4 dbh ³ E / L ³ (4)

When the bending amount d in each hex opening is obtained from the breaking load Pmax in the primary hex opening and the secondary hex opening, d = 4.5 μm in the primary hex opening (b = 76.2 mm), and the secondary hex opening (b = 1.2 mm), d = 3.8 μm.

  Even if a 3-inch wafer is bent by about 5 μm, it is predicted that it will open. However, since stress concentration actually occurs on the scribe line, it is considered that the scribe line is cleaved with a bending amount smaller than the estimated bending amount.

  In order to set the actual cut depth D, the difference in parallelism between the cutter blade 230 and the chip forming substrate 200, the thickness variation in the dicing film 210 to which the chip forming substrate 200 is attached, the thickness of the wafer It is necessary to consider in-plane variations, in-plane variations in the thickness of the protective sheet 214, and the like.

  The parallelism between the cutter blade 230 and the chip forming substrate 200 is 20 μm, the thickness of the dicing film 210 is 85 μm (of which 10 μm is an adhesive layer), the variation is ± 10 μm, the thickness of the protective sheet 214 is 25 μm, and the variation is ± 10. If it is%, a cut depth of about 50 μm or more is required to ensure cleavage. Further, considering the mechanical accuracy of the cleaving device, the cut depth D is selected to be about 80 μm.

  In other words, in order to stably open the folds, an overdrive of 20 times or more than the amount of bending required for rip opening is required. As a result, as shown in FIG. 28, the chip forming substrate 200 and the protective sheet 214 are pushed down by the cutter blade 230 even after the cleavage, and the movement amount Δl of the protective sheet 214 increases.

  Here, the movement amount Δl of the protective sheet 214 was calculated using the following equation (5).

Δl = 2Dh / L (5)

From equation (5) above, as shown in FIG. 29, in order to reduce the amount of movement of the protective sheet 214, the cut depth D is made shallow, and the thickness h of the chip forming substrate 200 is made thin. Is effective.

  When the thickness h of the chip forming substrate 200 is 240 μm, the cut depth D is 80 μm, and the distance L between the receiving blades is 2 mm, the movement amount Δl of the protective sheet 214 is predicted to be about 19 μm.

  In FIG. 30, the adhesion force F of the protective sheet 214 and the amount of movement Δl are calculated when the cut depth D is 80 μm, the thickness h of the chip forming substrate 200 is 240 μm, and the distance L between the receiving blades is changed. Results are shown.

  From the above consideration, the mechanism of the silicone adhesion phenomenon is summarized as follows: (1) When cleaving, the cut depth D increases, and the adhesion force F of the protective sheet 214 to the chip forming substrate 200 increases, thereby protecting Movement of the sheet 214 occurs. (2) Immediately after opening the claw, due to overdrive of the cutter blade 230, the adhesion force and the movement amount l of the protective sheet 214 are further increased, and the silicone is scraped off the outer end portion of the electrode pad 150.

  In order to reduce the adhesion of silicone to the outer end portion of the electrode pad 150, (A) the amount of overdrive of the cutter blade 230 is reduced, and (B) the adhesion force F of the protective sheet 214 at the time of opening is opened. It is possible to make it smaller.

  As a method for reducing the amount of overdrive (A) and a method for reducing the amount of movement of the protective sheet 214, a method of reducing the thickness h of the chip forming substrate 200 is effective. There is a disadvantage that the rate of occurrence increases.

  Therefore, in the present embodiment, as a method of reducing the adhesion force F in (B) above, the outer end portion of the electrode pad 150 has a round shape with a rounded cross-sectional shape, or an outer end portion. Is formed so as to have a shape in which the thickness gradually decreases toward the outside. By forming the electrode pad 150 so as to have such a shape, silicone does not adhere to the outer end portion of the electrode pad 150, and it is possible to reduce the phenomenon that the electrode pad 150 is scraped off.

  Next, in the optical device according to the present embodiment, the reason why silicone or the like that is a part of the protective sheet 214 does not adhere to the outer end portion of the electrode pad 150 at the time of cleaving will be described.

  As described above, when the force from the receiving blade 220 is applied to the protective sheet 214, unlike the present embodiment, when the outer end portion of the electrode pad 150 has a shape that stands up, the protective sheet As 214 moves, the silicone is pressed against the outer edge, resulting in scraping of the silicone.

  However, as in the present embodiment, the outer end portion 151 of the electrode pad 150 has a rounded cross-sectional shape and the thickness at the outer end portion 151 gradually decreases toward the outside. 31 to 32, when the protective sheet 214 is moved to the outer end 151 of the electrode pad 150, the silicone flows slidably as shown in FIGS. Therefore, when the protective sheet 214 is removed as shown in FIG. 33, part of the silicone does not remain on the laser chip.

  Note that the outer end portion 151 of the electrode pad 150 is limited to a round shape with a rounded cross section, or a shape in which the thickness at the outer end portion 151 gradually decreases toward the outside. In short, the shape of the outer end portion 151 of the electrode pad 150 may be a shape that allows the silicone to slide without being caught when the protective sheet 214 is pressed, and is a sharp shape that scrapes off the silicone. If you are not doing.

(Surface emitting laser array)
Next, a laser chip on which a surface emitting laser array that is an optical device in the present embodiment is formed will be described. As shown in FIG. 34, a plurality of surface emitting laser arrays are formed on the laser chip 300, and the 32 light emitting units 140 arranged in a two-dimensional manner and the periphery of the 32 light emitting units 140 are arranged. And has 32 electrode pads 150 corresponding to the respective light emitting portions 140. In addition, each electrode pad 150 is electrically connected to the corresponding light emitting unit 140 by the wiring member 155. The light emitting unit 140 corresponds to the surface emitting laser described above.

  In the present specification, the light emission direction from each light emitting unit is described as a Z-axis direction, and two directions orthogonal to each other in a plane perpendicular to the Z-axis direction are described as an X-axis direction and a Y-axis direction.

  As shown in FIG. 35, the 32 light emitting units 140 are arranged at the interval d2 in the Y-axis direction, but when all the light emitting units 140 are orthogonally projected onto a virtual line parallel to the Y-axis direction. In addition, they are arranged so that the intervals between the light emitting portions are equal ("d1" in FIG. 35). In the present specification, the “light emitting portion interval” refers to the distance between the centers of two light emitting portions.

  Here, each light emitting unit is a vertical resonator type VCSEL having an oscillation wavelength of 780 nm. That is, the laser chip 300 shown in FIG. 34 is a so-called VCSEL array chip. 2 described above is a cross-sectional view of the light emitting unit 140 in FIG. 35 cut along a plane parallel to the XZ plane.

  As described above, according to the laser chip 300 according to the present embodiment, the 32 light emitting units 140 formed on one substrate and the p-side electrode 113 in the 32 light emitting units 140 are electrically connected. 32 electrode pads 150 connected to each other are provided.

  Then, the electrode pad 150 that may cause a silicone adhesion phenomenon in the cleaving step has a side length close to the cleaved portion in the plan view as shown in FIG. It is set to be longer than the dimension w1 in the direction parallel to the portion.

  In this case, even when the thickness h of the chip forming substrate 200 is thicker than before, the adhesion of the protective sheet 214 can be reduced, and silicone adheres to each electrode pad in the cleaving step. Can be reduced. As a result, the manufacturing yield can be improved. That is, the unit price of the laser chip 300 can be lowered.

  In the above description, the case where the laser chip 300 has 32 light emitting units has been described. However, the present invention is not limited to this. For example, the laser chip 300 may have 40 light emitting units.

  In the above description, the case where the oscillation wavelength of the light emitting unit is in the 780 nm band has been described. However, the present invention is not limited to this. The oscillation wavelength of the light emitting unit may be changed according to the characteristics of the photoreceptor.

  In addition, the laser chip 300 which is an optical device in the present embodiment 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, or 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.

[Second Embodiment]
Next, a second embodiment will be described. The present embodiment is a laser printer 1000 which is an image forming apparatus using the optical device in the first embodiment. Based on FIG. 36, the laser printer 1000 in the present embodiment will be described. The laser printer 1000 according to this embodiment includes an optical scanning device 1010, a photosensitive drum 1030, a charging device 1031, a developing roller 1032, a transfer charger 1033, a charge eliminating unit 1034, a cleaning unit 1035, a toner cartridge 1036, a paper supply roller 1037, A paper 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, and a printer control device 1060 that comprehensively controls each of the above units 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 printer control device 1060 includes a CPU, a program described in a code decipherable by the CPU, a ROM storing various data used for executing the program, a RAM as a working memory, an analog, An AD conversion circuit for converting data into digital data is included. The printer control device 1060 controls each unit in response to a request from the host device, and sends image information from the host device to the optical scanning device 1010.

  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 is rotated in the direction indicated by the arrow X in FIG.

  The charging device 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. The charging device 1031 → the developing roller 1032 → the transfer charger 1033 → the discharging unit 1034 → the cleaning unit 1035 are arranged in the order of rotation of the photosensitive drum 1030.

  The charging device 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 device 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.

  Toner cartridge 1036 stores toner, and this toner is supplied to 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 toner-attached image (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. 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 is removed returns to the position facing the charging device 1031 again.

  Next, the optical scanning device 1010 will be described with reference to FIG. As shown in FIG. 37, the optical scanning device 1010 includes a light source 1114, a coupling lens 1115, an aperture plate 1116, a cylindrical lens 1117, a reflection mirror 1118, a polygon mirror 1113, a first scanning lens 1111a, and a second scanning lens 1111b. , And a scanning control device (not shown). These are assembled at predetermined positions of the optical housing 1130. The light source 1114 includes the optical device according to the first embodiment.

  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 1115 converts the light beam emitted from the light source 1114 into substantially parallel light.

  The aperture plate 1116 has an aperture and defines the beam diameter of the light beam that has passed through the coupling lens 1115.

  The cylindrical lens 1117 forms an image of the light beam that has passed through the opening of the aperture plate 1116 in the vicinity of the deflection reflection surface of the polygon mirror 1113 via the reflection mirror 1118 in the sub-scanning corresponding direction.

  The optical system arranged on the optical path between the light source 1114 and the polygon mirror 1113 is also called a pre-deflector optical system. In the present embodiment, the pre-deflector optical system includes a coupling lens 1115, an aperture plate 1116, a cylindrical lens 1117, and a reflection mirror 1118.

  The polygon mirror 1113 is made of a regular hexagonal columnar member having a low height, and six deflecting reflecting surfaces are formed on the side surface. The polygon mirror 1113 deflects the light beam from the reflection mirror 1118 while rotating at a constant speed around an axis parallel to the sub-scanning corresponding direction.

  The first scanning lens 1111 a is disposed on the optical path of the light beam deflected by the polygon mirror 1113.

  The second scanning lens 1111b is disposed on the optical path of the light beam that passes through the first scanning lens 1111a. Then, the light beam that has passed through the second scanning lens 1111b is irradiated onto the surface of the photosensitive drum 1030 to form a light spot. This light spot moves in the longitudinal direction of the photosensitive drum 1030 as the polygon mirror 1113 rotates. That is, the photosensitive 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 1113 and the photosensitive drum 1030 is also called a scanning optical system. In this embodiment, the scanning optical system includes a first scanning lens 1111a and a second scanning lens 1111b. Even if at least one folding mirror is disposed on at least one of the optical path between the first scanning lens 1111 a and the second scanning lens 1111 b and the optical path between the second scanning lens 1111 b and the photosensitive drum 1030. Good.

  In this embodiment, since the light source 1114 has the optical device in the first embodiment, the optical scanning apparatus 1010 can reduce the cost without degrading the accuracy of the optical scanning. .

  In addition, since the laser printer 1000 includes the optical scanning device 1010, the cost can be reduced without degrading the image quality.

  In the above embodiment, the case of the laser printer 1000 as the image forming apparatus has been described. 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.

  For example, the medium may be a printing plate known as CTP (Computer to Plate). That is, the optical scanning device 1010 is also suitable for an image forming apparatus that forms a printing plate by directly forming an image on a printing plate material by laser ablation.

  For example, the medium may be so-called rewritable paper. For example, a material described below is applied as a recording layer on a support such as paper or a resin film. Then, reversibility is imparted to color development by thermal energy control by laser light, and display / erasure is performed reversibly.

  There are a transparent cloudy type rewritable marking method and a color developing / erasing type rewritable marking method using a leuco dye, both of which can be applied.

  The transparent cloudy type is a polymer thin film in which fine particles of fatty acid are dispersed. When heated to 110 ° C. or higher, the resin expands due to melting of the fatty acid. Thereafter, when cooled, the fatty acid becomes supercooled and remains in a liquid state, and the expanded resin solidifies. Thereafter, the fatty acid solidifies and shrinks to become polycrystalline fine particles, and voids are formed between the resin and the fine particles. Light is scattered by this gap and appears white. Next, when heated to an erasing temperature range of 80 ° C. to 110 ° C., the fatty acid partially melts, and the resin thermally expands to fill the voids. If it cools in this state, it will be in a transparent state and an image will be erased.

  The rewritable marking method using a leuco dye utilizes a reversible color development and decoloration reaction between a colorless leuco dye and a developer / decolorant having a long-chain alkyl group. When heated by laser light, the leuco dye and the developer / decolorant react to develop color, and when rapidly cooled, the colored state is maintained. Then, when it is slowly cooled after heating, phase separation occurs due to the self-aggregating action of the long-chain alkyl group of the developer / decolorant, and the leuco dye and developer / decolorizer are physically separated and decolored.

  In addition, when the medium is exposed to ultraviolet light, it develops in C (cyan) and is decolored by visible R (red) light, and when exposed to ultraviolet light, it develops in M (magenta). A photochromic compound that is decolored by G (green) light, a photochromic compound that develops color when exposed to ultraviolet light (Y) and is decolored by visible B (blue) light. It may be a so-called color rewritable paper provided on the body.

  This is a method of expressing full color by controlling the color density of the three types of materials that develop color in Y, M, and C by the time and intensity of applying R, G, and B light once it is made black by applying ultraviolet light. However, if the strong light of R, G, and B is continuously applied, all three types can be decolored to become pure white.

  Such an apparatus that imparts reversibility to color development by light energy control can also be realized as an image forming apparatus including an optical scanning device similar to the above-described embodiment.

  Further, an image forming apparatus using a silver salt film as an 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.

[Third Embodiment]
Next, a third embodiment will be described. The present embodiment is a color printer 2000 including a plurality of photosensitive drums.

  Based on FIG. 38, the color printer 2000 in the present embodiment will be described. The color printer 2000 in this embodiment 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 (photosensitive drum M1, charging device M2, developing device M4, cleaning unit M5, and transfer device M6) and yellow station (photosensitive drum Y1, charging device Y2, developing device Y4, cleaning unit Y5, And transfer device Y6) and optical scanning device 2010 Includes a transfer belt 2080, a fixing unit 2030.

  Each photoconductor drum rotates in the direction of the arrow in FIG. 38, 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 provided with the optical device according to the first embodiment for each color. Thus, the same effect as that of the optical scanning device 1010 in the second embodiment can be obtained. In addition, since the color printer 2000 includes the optical scanning device 2010, it is possible to obtain the same effect as the laser printer 1000 in the second embodiment.

  In the color printer 2000, color misregistration may occur due to a manufacturing error or a position error of each component. Even in such a case, color misregistration can be reduced by selecting a light emitting unit to be lit.

  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.

101 Substrate 102 Buffer layer 103 Lower semiconductor DBR
104 Lower spacer layer 105 Active layer 106 Upper spacer layer 107 Upper semiconductor DBR
108 current confinement layer 108a selective oxidation region 108b current confinement region 109 contact layer 111 protective film 113 p-side electrode 114 n-side electrode 140 light-emitting portion 150 electrode pad 150a, 150b electrode pad 151 outer end portion 151a, 151b outer end portion 155 wiring member 160 Resist pattern 161 Thickness inclined region 200 Chip forming substrate 210 Dicing film 212 Metal ring 214 Protective sheet 220 Receiving blade 230 Cutter blade 1000 Laser printer (image forming apparatus)
1010 Optical scanning device 2000 Color printer (image forming apparatus)

JP 2004-319553 A Japanese Patent Laid-Open No. 11-40884

Claims (9)

In an optical device that is separated and formed by cleaving one semiconductor substrate,
A light emitting part formed on the substrate;
An electrode pad electrically connected to the electrode in the light emitting portion;
Have
The optical device according to claim 1, wherein the outer end portion of the electrode pad has a shape such that the thickness at the outer end portion gradually decreases toward the outside. In an optical device that is separated and formed by cleaving one semiconductor substrate,
A light emitting part formed on the substrate;
An electrode pad electrically connected to the electrode in the light emitting portion;
Have
The outer end of the electrode pad is formed to have a round cross-sectional shape.   The optical device according to claim 1, wherein the outer end portion is an end portion of the electrode pad on a side far from a scribe line when cleaving.   The optical device according to claim 1, wherein the light emitting unit is a surface emitting laser.   The outer end is formed by performing etching after forming the electrode pad, forming a resist pattern having a thickness gradient region where the region where the outer end is formed is formed thinly. The optical device according to claim 1, wherein the optical device is provided. A plurality of the light emitting portions are formed,
6. The optical device according to claim 1, wherein a plurality of the electrode pads are formed corresponding to the light emitting part. An optical scanning device that scans a surface to be scanned with light,
A light source comprising the optical device according to claim 1;
A light deflector for deflecting light from the light source;
A scanning optical system for condensing the light deflected by the light deflection unit on the surface to be scanned;
An optical scanning device comprising: An image carrier;
The optical scanning device according to claim 7, wherein the image carrier is scanned with light modulated according to image information.
An image forming apparatus comprising:   9. The image forming apparatus according to claim 8, wherein there are a plurality of image carriers, and the image information is multicolor color information.