JP2006108441A - Etching method for compound semiconductor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method by which an AlGaInP system semiconductor layer and the other semiconductor layers can be respectively etched at relatively close etching speed by using an easily handleable etchant, and also, a smooth surface can be obtained after etching. <P>SOLUTION: The AlGaInP system semiconductor layer and the other semiconductor layers are etched by using the etchant made of an acid solution including a halogen oxygen acid ion. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for etching a compound semiconductor layer used for a light emitting element or the like.

  A semiconductor material made of an AlGaInP-based compound semiconductor can emit light from red to green, and thus has been conventionally used in light-emitting elements and light-receiving elements such as light-emitting diodes and semiconductor lasers. It is widely used for field effect transistors because of its high speed. In addition, AlGaInP-based compound semiconductors with a low Al composition exhibit strong resistance to etching solutions. Therefore, device isolation during chip formation, ridge formation and groove formation for current confinement layer formation of semiconductor lasers, and evaluation of multilayer structures When performing surface layer etching for the purpose of etching, it is often used as an etching stop layer in combination with an AlGaInP-based compound semiconductor having a high Al composition or a compound semiconductor other than an AlGaInP-based compound semiconductor.

A conventional ridge waveguide semiconductor laser is manufactured, for example, by the steps shown in FIGS. This process will be described with a specific example. First, a clad layer 302 made of n- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P having a thickness of 1.2 μm and a thickness of 60 nm are formed on an n-GaAs substrate 301 by MOCVD. Of (Al _0.5 Ga _0.5 ) _0.5 In _0.5 P guide layer 303, 5 nm thick Ga _0.5 In _0.5 P quantum well layer 304, and 5 nm thick (Al _0.5 Ga _0.5 ) _0.5 In _0.5 P barrier layer 305. Multiple quantum well active layer 306 of formula 4, first clad layer 307 made of p- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P with a thickness of 0.25 μm, etching made of p-Ga _0.5 In _0.5 P with a thickness of 5 nm Stop layer 308, second cladding layer 309 made of p- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P with a thickness of 0.7 μm, oxidation suppression layer 31 made of p-Ga _0.5 In _0.5 P with a thickness of 50 nm By sequentially laminating 0, a compound semiconductor layer having a double hetero structure is formed. Next, the second cladding layer 309 and the oxidation suppression layer 310 on the etching stop layer 308 are formed in a ridge shape, and the block layer 312 made of n-GaAs and the contact layer 313 made of p-GaAs are grown by MOCVD again. To do.

  In forming the ridge shape in this manufacturing process, a selective etching solution having a higher etching rate for the second cladding layer 309 than the etching stop layer 308 is used. For example, sulfuric acid (98% by weight) heated to about 60 ° C. (Patent Document 1: Japanese Patent Laid-Open No. 63-20835) or hydrochloric acid-water etching solution (Non-Patent Document 1: JW Lee et. Al., Solid-State Electronics 38 (1995) 1871) has been used conventionally. However, since the heated sulfuric acid has a high viscosity, there is a problem that if this is used as an etching solution, tailing occurs at the ridge bottom portion, and a sharp ridge shape cannot be obtained. Further, when a hydrochloric acid-water based etching solution is used, there is a problem that surface roughness occurs and it is difficult to obtain a smooth surface.

In the ridge waveguide semiconductor laser described above, the oxidation suppression layer 310 having substantially the same composition as the etching stop layer 308 is present on the second cladding layer 309. For this reason, almost the same layer as the layer for stopping the ridge formation etching must be etched at the initial stage of the ridge formation. Although it is possible to etch the oxidation-inhibiting layer with a sulfuric acid or hydrochloric acid-water-based etching solution heated to about 60 ° C., it is possible to etch slowly, but if there is a distribution of the film thickness of the oxidation-inhibiting layer in the wafer plane, As a result, a difference occurs in the time required to reach the second cladding layer having a high Al composition, so that the etching unevenness of the second cladding layer itself becomes remarkable. A hydrochloric acid-acetic acid-hydrogen peroxide etching solution having a relatively high etching rate for p-GaInP has also been proposed (Non-Patent Document 2: JR Flemish et. al., J. Electrochem. Soc., 140 (1993)). 844) has a problem that it is difficult to handle because it has an odor due to acetic acid, and the etching rate is highly time-dependent because chlorine is generated by the reaction between hydrochloric acid and hydrogen peroxide. As another system, a hydrochloric acid-phosphoric acid based etchant is also known. However, when the second cladding layer having a high Al composition is reached, the etching rate is explosively increased, and toxic phosphine (PH ₃ ) is very toxic. There is a problem that the etching surface becomes extremely rough with the occurrence.

When manufacturing a ridge waveguide type semiconductor laser, a contact layer made of an As-based compound may be stacked on the oxidation suppression layer and etched to form a ridge structure. Etching solutions for As-based compounds such as GaAs and AlGaAs are relatively well known, and various etching solutions including those containing acid and hydrogen peroxide have been reported. However, almost no etching solution has been reported that can simultaneously etch the As-based compound semiconductor layer and the AlGaInP-based compound semiconductor layer containing Al. With the above-mentioned hydrochloric acid-acetic acid-hydrogen peroxide system, it is possible to etch an AlGaAs system by controlling the composition of the etching solution, but there is a problem that it is difficult to handle as an etching solution as described above. is doing.
JP 63-20835 A (Claims) JW Lee et.al., Solid-State Electronics 38 (1995) p1871 JR Flemish et. Al., J. Electrochem. Soc., 140 (1993) 844

  In the prior art, it is difficult to etch a layer having a low Al composition particularly in an AlGaInP-based compound semiconductor, and there is no etching solution that can be used easily. In addition, there is no suitable etching solution when etching is performed on a multilayer film including an AlGaInP-based semiconductor and another semiconductor (for example, an AlGaAs-based semiconductor).

The present invention has been made in view of such problems.
The first object of the present invention is to generate phosphine and the like at a relatively close etching rate in a region including one or more AlGaInP-based semiconductor layers and one or more AlGaAs-based semiconductor layers using an etching solution that can be easily handled. It is an object of the present invention to provide a method that can be etched without etching, and that a smooth surface can be obtained after etching.

  A second object of the present invention is to provide a method capable of accurately forming a pattern shape necessary for a laser structure by further performing selective etching after performing the etching of the first object.

A first object of the present _{invention, (Al X1 Ga 1-X1} ) Y1 In 1-Y1 P (0 ≦ X1 <1,0 ≦ Y1 ≦ 1) on the first semiconductor layer made of (Al _X2 Ga _{1- X2} ) _{Y2In1 -Y2P} (0 <X2≤1, 0 <Y2≤1, X1 <X2) and a second semiconductor layer ( _{AlX3Ga1 -X3} ) _{Y3In1 -Y3P} ( _0≤X3 ) In the method for etching a compound semiconductor sequentially including a third semiconductor layer composed of <1, 0 <Y3 ≦ 1, X3 <X2), an etching solution composed of an acidic solution containing halogen oxyacid ions is used. And a method of etching a compound semiconductor, wherein a part of the second semiconductor layer is removed by etching.

A first object of the present _{invention, (Al X1 Ga 1-X1} ) Y1 In 1-Y1 P (0 ≦ X1 <1,0 ≦ Y1 ≦ 1) on the first semiconductor layer made of (Al _X2 Ga _{1- X2} ) _{Y2In1 -Y2P} (0 <X2≤1, 0 <Y2≤1, X1 <X2), a second semiconductor layer, ( _{AlX3Ga1 -X3} ) _{Y3In1 -Y3P} ( _0≤X3 ) In a method for etching a compound semiconductor, which sequentially includes a third semiconductor layer composed of <1, 0 <Y3 ≦ 1, X3 <X2) and a fourth semiconductor layer composed of Al _X4 Ga _1-X4 As (0 ≦ X4 ≦ 1). Also achieved by an etching method of a compound semiconductor, characterized in that a part of the fourth semiconductor layer, the third semiconductor layer and the second semiconductor layer is removed by etching using an etching solution comprising an acidic solution containing a halogen oxygenate ion. It was done.

  The etching solution used for achieving the first object preferably contains hydrochloric acid and / or sulfuric acid together with halogen acid ions. The etching solution preferably contains a complexing agent capable of forming a water-soluble complex ion with at least one group III element constituting the compound semiconductor.

  The second object of the present invention is to remove portions of the third semiconductor layer and the second semiconductor layer by etching in the above method (if there is a fourth semiconductor layer, the fourth semiconductor layer, the third semiconductor layer, and the second semiconductor layer). The second semiconductor layer on the first semiconductor layer is etched by using a selective etching solution having high selectivity between the first semiconductor layer and the second semiconductor layer after etching a part of the semiconductor layer. This is achieved by a method of etching a compound semiconductor, characterized in that is removed.

  The selective etching solution used for achieving the second object preferably contains oxycarboxylic acid and / or dicarboxylic acid together with hydrochloric acid. The selective etching solution preferably contains at least one organic acid selected from the group consisting of tartaric acid, citric acid, malic acid, glycolic acid, malonic acid, and lactic acid.

  In the etching method of the present invention, etching is carried out at an almost constant speed using an acidic solution containing halogen oxygen acid ions, and no highly toxic phosphine or the like is generated, and the surface of the compound semiconductor layer is kept smooth after etching. be able to. Further, according to the etching method of the present invention, etching with high selectivity can be performed on the etching stop layer, so that a structure necessary for the light emitting element can be stably realized with a good shape.

  Hereinafter, the etching method of the present invention will be described in detail. The description of the constituent elements described below may be made based on typical embodiments of the present invention, but the present invention is not limited to such embodiments. In the present specification, a numerical range represented by using “to” means a range including numerical values described before and after “to” as a lower limit value and an upper limit value.

(Etching solution)
First, the “etching solution comprising an acidic solution containing halogen oxygenate ions” (hereinafter also referred to as “etching solution of the present invention”) used in the etching method of the present invention will be described.
The halogen oxygenate ion used here is a hypohalite ion containing a monovalent positive ion halogen element, a halite ion containing a trivalent positive ion halogen element, and a pentavalent positive ion halogen. Examples thereof include a halogenate ion containing an element and a perhalogenate ion containing a halogen element of a 7-valent positive ion.

  Halogen oxyacid ions may be any of hypohalous acid, halous acid, halogen acid and perhalogen acid ions, but halogen acid ions are less prone to decomposition than hypohalous acid and halous acid. It is stable, easy to weigh, and reacts faster than perhalogen acid. For this reason, it is preferable to use a halogen acid ion as the halogen oxygen acid ion.

Examples of the halogenate ion include chlorate ion (ClO ₃ ⁻ ), bromate ion (BrO ₃ ⁻ ), iodate ion (IO ₃ ⁻ ), and the like. Among them, it is preferable to use chlorate ions or iodate ions in which the salt is likely to be water-soluble, and it is more preferable to use iodate ions with mild reactivity. The halogenate ion may be in the form of an acid bonded to hydrogen, but may be in the form of a salt bonded to K, Na or the like.

  When the halogen oxyacid ion concentration in the etching solution is too large, the surface after etching becomes rough, and when it is too small, the etching becomes insufficient. Therefore, the halogen oxygenate ion concentration in the etching solution of the present invention is preferably 0.0001 to 1 mol / l, and preferably 0.003 to 0.1 mol / l.

The etching solution of the present invention may contain only the halogen oxygenate ions as long as it is an acidic solution, but preferably contains a reagent that makes the solution acidic. The acidic reagent to be contained is not particularly limited as long as it can make the solution acidic. For example, inorganic acids such as HCl, HF, H ₂ SO ₄ , HNO ₃ , H ₃ PO ₄ , citric acid, tartaric acid, etc. The organic acid can be used. When mixed with a halogen oxygenate ion, it is preferable to select and use an acidic reagent having a redox potential that does not reduce the halogen of the halogen oxygenate ion, and it is further preferable to use HCl and / or H ₂ SO _4. preferable.

Further, a second semiconductor layer made of (Al _X2 Ga _{1 -X2} ) _Y2 In _{1 -Y2} P (0 <X2 ≦ 1, 0 <Y2 ≦ 1, X1 <X2), (Al _X3 Ga _1-X3 ) _Y3 In _A third semiconductor layer made of _1-Y3 P (0 ≦ X3 <1, 0 <Y3 ≦ 1, X3 <X2) and a fourth semiconductor layer made of Al _X4 Ga _1-X4 As (0 ≦ X4 ≦ 1) are both included. In the case of etching, it is preferable to select an acid that does not greatly differ in speed from layer to layer.

  When the etching solution of the present invention exhibits strong acidity, group III elements such as Al, Ga, and In are easily dissolved in the solution, but on the other hand, halogen oxygen acids are difficult to dissolve. As a result, the number of dissociated halogen oxygenate ions decreases, and sufficient etching may not be obtained. On the other hand, when the etching solution shows weak acidity, etching is easy because there are a large number of halogen oxygenate ions, but the solubility of the group III element in the solution is reduced, and as a result etching proceeds. It may be difficult. Therefore, the acid used to maintain the etching solution of the present invention is acidic, when the aqueous solution containing the halogen oxygen acid ion is acidic, the acid reagent is not added and only the halogen oxygen acid is added. Even when used, the acid concentration is preferably 0.001 to 25 mol / l or less, and more preferably 0.001 to 10 mol / l.

  When an acid is used, it is preferable to dissociate the acid in the solution as much as possible in order to maintain a low pH value. Since the dissociation constant of the acid changes due to the presence of halogen oxygen acid, it cannot be expressed in pH as it is, but when a binary solution consisting of an acid not containing halogen oxygen acid and water is prepared, the acid The pH value of is preferably -1.5 to 4, more preferably -1 to 3. In addition, when a fine adjustment of pH is required, a small amount of alkaline solution can also be added.

  As a solvent for the etching solution, water can be generally used, but from the viewpoint of preventing mixing of impurities, it is preferable to use filtered water, purified water, distilled water, or the like. An alcohol solvent such as ethyl alcohol or glycerin can also be used.

  Group III elements contained in compound semiconductors are generally difficult to dissolve. For this reason, it is preferable that the etching solution contains a complexing agent capable of forming a water-soluble complex ion with at least one group III element contained in the compound semiconductor to help dissolve the group III element. Specifically, it is preferable to contain a complexing agent capable of forming a water-soluble complex ion with Al, Ga and In. By containing the complexing agent, a complex ion of a group III element is stably present in the etching solution, so that stable etching is possible.

  The content of the complexing agent in the etching solution may be larger than the amount of forming a water-soluble complex ion with the group III element contained in the semiconductor, preferably 100 times or more of the group III element content. It is preferable.

  The complex stability constant of the complexing agent is not particularly limited as long as it is 1 or more, but is preferably 3 or more. Here, the complex stability constant is, for example, the value of K = − ([A] [X] / [AX]) in a complex composed of AX, when the ionic state is not taken into consideration and expressed as AX = A + X. Say. A complex stability constant of 1 or more is preferable because it is stably present in the solvent as a complex ion.

  The complexing agent is not particularly limited as long as it can generally form a water-soluble complex ion with a group III element. Examples of the complexing agent include, for example, polyfunctional carboxylic acid capable of forming a water-soluble complex ion with Al, Ga, In and the like, an ethylenediaminetetraacetic acid-based compound (EDTA), and the like. Examples of the polyfunctional carboxylic acid include tartaric acid, citric acid, glycolic acid and the like. These complexing agents may be used alone or in combination of two or more.

(Selective etchant)
In a preferred embodiment of the etching method of the present invention, (Al _X1 Ga _1-X1 ) _Y1 In _1-Y1 P (0 ≦ X1 <1, 0 ≦ Y1 ≦ 1, X1 <X2) separately from the above etching solution. A selective etching solution having high selectivity between the first semiconductor layer and the second semiconductor layer made of (Al _X2 Ga _{1 -X2} ) _Y2 In _{1 -Y2} P (0 <X2 ≦ 1, 0 <Y2 ≦ 1) Also used. The selective etching solution has a property that the etching rate of the second semiconductor layer is faster than the etching rate of the first semiconductor layer.

  As the selective etching solution, a mixed solution of hydrochloric acid and organic acid is preferably used. As the organic acid, it is preferable to use oxycarboxylic acid and / or dicarboxylic acid. Specifically, tartaric acid, citric acid, malic acid, glycolic acid, succinic acid, malonic acid, and lactic acid are preferable, and tartaric acid and citric acid are preferable. More preferred.

As a composition of the selective etching solution, in the case of a mixed solution of 35% hydrochloric acid and lactic acid, the volume ratio is preferably 1: 1 to 5, and more preferably 1.5 to 4. Further, in the case of a mixed solution of 35% hydrochloric acid and 20% by weight to 50% by weight of oxycarboxylic acid and / or dicarboxylic acid (excluding lactic acid), the volume ratio is preferably 1: 1-5. More preferably, it is 1.5-4.
If the amount of oxycarboxylic acid and / or dicarboxylic acid is too large, the etching time becomes long and it becomes difficult to determine the end point of etching, and the pattern shape may be disturbed. In addition, if the amount of oxycarboxylic acid and / or dicarboxylic acid is too small, the amount of hydrochloric acid in the etching solution is relatively increased and the etching rate is increased, so that the time for the etching stop layer to function is reduced, and the film thickness is reduced in the semiconductor layer. When there is a distribution, etching unevenness may occur.

  Furthermore, an oxidizing agent such as 5% by weight or less of hydrogen peroxide may be mixed in the selective etching solution with respect to the weight of the selective etching solution in order to improve the etching surface property. However, since hydrochloric acid and a large amount of oxidizing agent are accompanied by generation of chlorine, it is desirable to mix them with the composition or less.

  Furthermore, it may be diluted with ultrapure water or the like while the relative amounts of hydrochloric acid and oxycarboxylic acid and / or dicarboxylic acid are fixed.

(Etching method)
The etching method of the present invention is performed using the above etching solution.
The compound semiconductor to be etched is (Al _X2 Ga _1-X1 ) _Y1 In _1-Y1 P (0 ≦ X1 <1, 0 ≦ Y1 ≦ 1) on the first semiconductor layer (Al _X2 Ga _{1- X2} ) _{Y2In1 -Y2P} (0 <X2≤1, 0 <Y2≤1, X1 <X2) and a second semiconductor layer ( _{AlX3Ga1 -X3} ) _{Y3In1 -Y3P} ( _0≤X3 ) The third semiconductor layer sequentially includes <1, 0 <Y3 ≦ 1, X3 <X2). As long as it has the said structure consisting of a 1st semiconductor layer, a 2nd semiconductor layer, and a 3rd semiconductor layer, you may have another compound semiconductor layer. For example, a fourth semiconductor layer made of Al _X4 Ga _{1 -X4} As (0 ≦ X4 ≦ 1) may be further provided on the third semiconductor layer. In addition, under the first semiconductor layer, there may be a material or a layer that a normal semiconductor laser or the like such as a substrate, a clad layer, or an active layer has. These materials and layers can be freely selected as long as they do not unduly hinder the practice of the present invention.

A preferable range of X1 of (Al _X1 Ga _{1 -X1} ) _Y1 In _{1 -Y1} P constituting the first semiconductor layer is 0 ≦ X1 ≦ 0.7, and a more preferable range is 0 ≦ X1 ≦ 0.5. A more preferable range is 0 ≦ X1 ≦ 0.3. A preferred range for Y1 is 0 <Y1 ≦ 1, a more preferred range is 0.3 ≦ Y1 <1, and a further preferred range is 0.4 ≦ Y1 ≦ 0.8.
A preferable range of (Al _X2 Ga _{1 -X2} ) _Y2 In _{1 -Y2} P constituting the second semiconductor layer is 0.3 ≦ X2 ≦ 1, and a more preferable range is 0.5 ≦ X2 ≦ 1, A preferred range is 0.6 ≦ X2 ≦ 1. A preferred range for Y2 is 0 <Y2 <1, a more preferred range is 0.3 ≦ Y2 ≦ 0.7, and a further preferred range is 0.4 ≦ Y2 ≦ 0.6.

A preferable range of X3 of (Al _X3 Ga _{1 -X3} ) _Y3 In _{1 -Y3} P constituting the third semiconductor layer is 0 ≦ X3 ≦ 0.9, and a more preferable range is 0 ≦ X3 ≦ 0.5. A more preferable range is 0 ≦ X3 ≦ 0.3. A preferred range for Y3 is 0 <Y3 <1, a more preferred range is 0.3 ≦ Y3 ≦ 0.9, and a further preferred range is 0.4 ≦ Y3 ≦ 0.7.
A preferable range of X4 of Al _X4 Ga _{1 -X4} As constituting the fourth semiconductor layer is 0 ≦ X4 ≦ 0.9, a more preferable range is 0 ≦ X4 ≦ 0.7, and a further preferable range is 0 ≦ X4 ≦ 0.4.

X2 must be greater than X1. A preferred range of the difference between X2 and X1 is 0.2 <X2-X1, a more preferred range is 0.4 <X2-X1, and a further preferred range is 0.5 <X2-X1.
X2 must be greater than X3. A preferable range of the difference between X2 and X3 is 0.2 <X2-X3, and a more preferable range is 0.3 <X2-X3.

  The second semiconductor layer may completely cover the first semiconductor layer or may partially cover it. Similarly, the third semiconductor layer may completely cover the second semiconductor layer or may partially cover the fourth semiconductor layer, and the fourth semiconductor layer completely covers the third semiconductor layer. It may be present or partially covered. Further, a part of the third semiconductor layer and a part of the fourth semiconductor layer may be formed directly on the first semiconductor layer, and a part of the fourth semiconductor layer is formed directly on the second semiconductor layer. May be. Details of these structures are appropriately determined according to the use and purpose of use of the compound semiconductor to be etched.

  Etching can usually be performed by immersing the entire object to be etched in an etching solution or supplying the etching solution to the entire object by spraying. The etching solution is usually supplied to the etching reaction field by stirring with a stirrer or circulating with a motor.

  According to the method of the present invention, the third semiconductor layer and the second semiconductor layer which are not protected can be etched by performing etching using an etching solution made of an acidic solution containing halogen oxygenate ions. it can. In the case where the fourth semiconductor layer is formed in the third semiconductor layer, the fourth semiconductor layer can also be etched. Here, the expression “together etching” includes the case where the etching of the fourth semiconductor layer proceeds simultaneously with the etching of the third semiconductor layer and the second semiconductor layer, and the case where the third semiconductor layer is etched after the etching of the fourth semiconductor layer. And the case where the etching of the second semiconductor layer proceeds.

  According to the method of the present invention, each semiconductor layer can be etched at a relatively close etching rate as compared with the conventional method. In particular, since the etching rate of the third semiconductor layer having a low Al composition and the etching rate of the second semiconductor layer having a high Al composition are close to each other, etching unevenness and surface roughness that have been problems in the prior art are effectively suppressed. be able to. Even in the case where the fourth semiconductor layer containing As exists, the etching rate of the fourth semiconductor layer is relatively close to the etching rate of the second semiconductor layer and the third semiconductor layer. Roughness can be suppressed as well. Therefore, according to the method of the present invention, uniform etching can be performed over the entire etching region, and a smooth surface can be obtained after etching.

  In the present invention, a part of the second semiconductor layer is etched with an etching solution made of an acidic solution containing a halogen oxygenate ion. The part here refers to 0.01 to the total thickness of the second semiconductor layer. It is preferably 80%, more preferably 0.1 to 50%, and further preferably 1 to 30%.

It is preferable to further etch the second semiconductor layer with a selective etching solution after the etching with an etching solution made of an acidic solution containing halogen oxygenate ions. As described above, the selective etching solution has a feature that the etching rate of the second semiconductor layer is higher than the etching rate of the first semiconductor layer. For this reason, the second semiconductor layer is selectively etched, and after the etching, the first semiconductor layer having a smooth surface having no etching residue appears. By performing such selective etching, a pattern shape necessary for the laser structure can be accurately formed.
In consideration of the etching shape and the time during which the etching stop layer functions, the etching rate in the present invention is preferably 50 to 5000 nm / min, and more preferably 100 to 2000 nm / min.

  After performing the selective etching, a compound semiconductor layer or a functional layer having a specific composition can be appropriately stacked in order to obtain a compound semiconductor having a desired function. For example, a semiconductor laser or the like can be manufactured by appropriately forming a contact layer, an electrode, or the like as described in Examples described later. Such subsequent steps can be appropriately selected and determined within the knowledge of those skilled in the art.

  Hereinafter, the present invention will be described in more detail with reference to specific examples including examples. The materials, reagents, ratios, operations, and the like shown in the following examples can be appropriately changed without departing from the spirit of the present invention. Therefore, the scope of the present invention is not limited to the specific examples shown below.

(Reference Example 1)
First, etching solutions A1 to A3 and B1 to B3 were prepared by the following procedure.
Etching solution A1 containing 0.01 mol / l of iodic acid was prepared by adding 0.5277 g of iodic acid (HIO ₃ ) to 53 ml of 35% hydrochloric acid and diluting with water to make 300 ml as a whole. . Similarly, after adding 0.5277 g of iodic acid (HIO ₃ ) to 39 ml of 35% hydrochloric acid, the whole is diluted with water to 300 ml, whereby the etching solution A2 containing 0.01 mol / l of iodic acid is added. Was prepared. Similarly, after adding 0.5277 g of iodic acid (HIO ₃ ) to 16 ml of 35% hydrochloric acid, the whole is diluted with water to 300 ml, whereby an etching solution A3 containing 0.01 mol / l of iodic acid is added. Was prepared.

An etching solution B1 containing 0.03 mol / l of iodic acid was prepared by adding 1.5832 g of iodic acid (HIO ₃ ) to 53 ml of 35% hydrochloric acid and diluting with water to make a total of 300 ml. . Similarly, 1.5832 g of iodic acid (HIO ₃ ) was added to 39 ml of 35% hydrochloric acid, and then diluted with water to make a total of 300 ml, whereby etching solution B2 containing 0.03 mol / l of iodic acid was added. Was prepared. Similarly, 1.5832 g of iodic acid (HIO ₃ ) was added to 16 ml of 35% hydrochloric acid, and then diluted with water to make a total of 300 ml, whereby etching solution B3 containing 0.03 mol / l of iodic acid was used. Was prepared.

Next, a compound semiconductor sample was prepared and etched according to the following procedure.
Using MOCVD, a p-GaAs layer is grown on a GaAs substrate, a p-Ga _0.5 In _0.5 P layer is grown on another GaAs substrate, and p- (Al _{0.7 is} grown on another GaAs substrate. A total of three types of compound semiconductor samples were prepared by crystal growth of a Ga _0.3 ) _0.5 In _0.5 P layer. The thickness of the crystal-grown layer was 1000 nm. When each of the formed compound semiconductor layers was etched at 23 ° C. for 90 seconds using the etching solutions A1, A2, A3, B1, B2, and B3, there was no etching residue or reaction deposit. An etched surface was formed. The etching rate is as shown in FIG. 1, and it was confirmed that it changed depending on the amount of iodic acid (HIO ₃ ) to be added without depending on the type of compound semiconductor.

(Comparative Example 1)
An etching solution in which 98 wt% sulfuric acid was heated to 60 ° C. was prepared, and the same three types of compound semiconductor samples as in Reference Example 1 were etched. Although the etching surface was smooth, as shown in FIG. 2, the etching rate clearly decreased with p-Ga _0.5 In _0.5 P, and was almost impossible to etch with p-GaAs.

(Comparative Example 2)
An etching solution in which 35% hydrochloric acid and ultrapure water were mixed at a volume ratio of 1: 1 was prepared, and etching was performed on the same three types of compound semiconductor samples as in Reference Example 1. As shown in FIG. 2, a clear difference in the etching rate is recognized depending on the type of compound semiconductor as in Comparative Example 1, and in the case of p- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P, the surface after etching is It was rough.

(Reference Example 2)
Using sulfuric acid instead of hydrochloric acid in Reference Example 1 and adding 0.642 g, 1.926 g and 3.21 g of potassium iodate, respectively, and diluting with water to make 300 ml of the whole, potassium iodate 0 Etching solutions containing 0.01 mol / l, 0.03 mol / l, and 0.05 mol / l were prepared.

  Etching was performed on the same three types of compound semiconductor samples as in Reference Example 1 using each etching solution. As a result, it was confirmed that a smooth etching surface free from etching residues and reaction deposits was formed. The etching rates were about 40 nm / min, 160 nm / min, and 280 nm / min.

(Reference Example 3)
After adding 0.5277 g of iodic acid (HIO ₃ ) to 39 ml of 35% hydrochloric acid, add 50 g of citric acid and dilute with water to make a total of 300 ml. An etching solution was prepared.

  Using this etching solution, the same three types of compound semiconductor samples as in Reference Example 1 were etched. As a result, it was confirmed that a smoother etching surface was formed as compared with the case of using the etching solution of Reference Example 1 having the same acid amount and the same iodic acid amount.

Example 1
A cladding layer 302 made of n- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P having a thickness of 1.2 μm and a (Al _0.5 Ga _0.5 ) _0.5 In _0.5 P guide having a thickness of 60 nm are formed on the n-GaAs substrate 301 by MOCVD. A multi-quantum well active layer 306 having a number of wells of 4 consisting of a layer 303, a Ga _0.5 In _0.5 P quantum well layer 304 having a thickness of 5 nm, and an (Al _0.5 Ga _0.5 ) _0.5 In _0.5 P barrier layer 305 having a thickness of 5 nm, a thickness of 0 A first cladding layer 307 made of p- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P with a thickness of .25 μm, an etching stop layer 308 made of p-Ga _0.5 In _0.5 Pn with a thickness of 5 nm, and a p- (0.7 μm thickness of p- ( The second cladding layer 309 made of Al _0.7 Ga _0.3 ) _0.5 In _0.5 P and the oxidation-suppressing layer 310 made of p-Ga _0.5 In _0.5 P having a thickness of 50 nm are sequentially laminated to form a double heterostructure. A compound semiconductor layer was formed (FIG. 3A). Next, a SiNx protective film having a thickness of 100 nm was deposited on the surface of the double hetero substrate by plasma CVD, and then a large number of stripe-like SiNx protective films 311 were formed by photolithography (FIG. 3B).

An etching solution containing 0.01 mol / l of iodic acid was prepared by adding 0.5277 g of iodic acid (HIO ₃ ) to 39 ml of 35% hydrochloric acid and diluting with water to make the whole 300 ml. Using this etching solution, the striped SiNx protective film is used as an etching mask to etch FIG. 3B for 90 seconds, and all of the unprotected oxidation suppressing layer 310 and a part of the second cladding layer 309 are etched ( FIG. 3 (c)). The surface of the second cladding layer after the etching was smooth.

  An etching solution C1 was prepared by mixing 35% hydrochloric acid and 50% by weight citric acid in a volume ratio of 1: 3. Further, an etching solution C2 was prepared by mixing 35% hydrochloric acid, 50% by weight citric acid and 50% by weight tartaric acid in a volume ratio of 1: 2: 1. When the etching solution C1 or C2 was used to etch FIG. 3C for 3 minutes at 23 ° C., a ridge shape was formed using the striped SiNx protective film as an etching mask (FIG. 3D). When the etching stop layer was observed with a scanning electron microscope, it was confirmed that an extremely smooth surface with no etching residue on the etching stop layer was obtained when either of the etching solutions C1 and C2 was used.

(Example 2)
A clad layer made of n- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P with a thickness of 1.2 μm, an (Al _0.5 Ga _0.5 ) _0.5 In _0.5 P guide layer and a 5 nm thickness by MOCVD on an n-GaAs substrate A multi-quantum well active layer having 6 wells composed of a Ga _0.5 In _0.5 P quantum well layer and a (Al _0.5 Ga _0.5 ) _0.5 In _0.5 P barrier layer having a thickness of 5 nm, p- (Al _0.7 Ga having a thickness of 0.08 μm). _0.3 ) _0.5 In _0.5 P first cladding layer, 5 nm thick p-Ga _0.5 In _0.5 Pn etching stop layer, 0.5 μm thick p- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P By sequentially laminating the second cladding layer, the 10 nm thick p- (Al _0.2 Ga _0.8 ) _0.5 In _0.5 P oxidation inhibiting layer, and the 20 nm thick p-GaAs contact layer, a double hetero structure is obtained. Certain To form an object semiconductor layer. Next, an SiNx protective film having a thickness of 100 nm was deposited on the surface of the double hetero substrate by plasma CVD, and then a large number of stripe-like SiNx protective films were formed by photolithography.

An etching solution containing 0.03 mol / l of iodic acid was prepared by adding 1.5832 g of iodic acid (HIO ₃ ) to 39 ml of 35% hydrochloric acid and diluting with water to make a total of 300 ml. Using this etching solution, the compound semiconductor layer was etched at 23 ° C. for 50 seconds using the stripe-shaped SiNx protective film as an etching mask. As a result, all of the non-protected contact layer and oxidation suppression layer and part of the second cladding layer were obtained. Was removed by etching. The surface of the second cladding layer after the etching was smooth.

  An etching solution D1 was prepared by mixing 35% hydrochloric acid and 34% by weight malic acid in a volume ratio of 1: 3. Further, an etching solution D2 was prepared by mixing 35% hydrochloric acid and 40% by weight malic acid in a volume ratio of 1: 3. The compound semiconductor layer that has been etched to the middle of the second cladding layer with an iodic acid-based etchant is etched with the etchant D1 for 4 minutes and with the etchant D2 for 3 minutes. As a result, a ridge using the striped SiNx protective film as an etching mask A shape was formed. When the etching stop layer was observed with a scanning electron microscope, it was confirmed that an extremely smooth surface with no etching residue on the etching stop layer was obtained.

  In this embodiment, the contact layer, the oxidation suppression layer, and a part of the second cladding layer are etched in one step by using an etching solution containing halogen oxyacid ions. May be performed in two stages. For example, the contact layer is etched with an etching solution (such as phosphoric acid, hydrogen peroxide solution, ultrapure water mixture, tartaric acid and hydrogen peroxide solution, etc.) that can etch As-based compound semiconductors, and halogen oxygenate ions. It is also possible to perform two-stage etching that etches all of the oxidation suppression layer and a part of the second cladding layer using an etching solution containing

  In the first and second embodiments, a semiconductor laser having a ridge structure is manufactured. However, the present invention can be used to modify the method of the embodiment to make a groove structure using the present invention. A semiconductor laser can also be manufactured.

(Comparative Example 3)
In the same manner as in Example 1, using an etching solution prepared by mixing 35% hydrochloric acid and 85% phosphoric acid in a volume ratio of 1: 5 instead of the etching solution containing iodic acid used in Example 1. 3B is etched at 23 ° C. using the stripe-shaped SINx protective film as an etching mask, the oxidation suppression layer 310 is etched off after about 30 seconds, the second cladding layer 309 starts to be etched, and the surface of the semiconductor layer A large amount of air bubbles were generated from the surface, resulting in a highly uneven surface.

(Example 3)
98% sulfuric acid was used instead of the etching solution C1 or C2 used in Example 1, and this was heated to 60 ° C., and when FIG. 3C was etched for 4 minutes, the striped SiNx protective film was used as an etching mask. A ridge shape was formed. (FIG. 3 (d)). When observed with a scanning electron microscope, it was confirmed that a smooth surface having no etching residue was obtained on the etching stop layer. However, compared with Example 1, the ridge sidewall shape was gentle and the lower width of the second cladding layer 309 was widened.

  The etching method of the present invention etches at an almost constant speed using an acidic solution containing halogen oxygen acid ions, and is advantageous in that the etching solution is easy to handle and the surface of the compound semiconductor layer can be kept smooth after etching. Have Furthermore, according to the etching method of the present invention, since etching with high selectivity can be performed on the etching stop layer, a structure necessary for the light emitting element can be stably realized with a good shape. Therefore, the etching method of the present invention has high industrial applicability.

5 is a graph showing the etching rate with the etching solution of Reference Example 1. It is a graph which shows the etching rate by the etching liquid of the comparative example 1 and the comparative example 2. FIG. 1 is a diagram illustrating the structure and manufacturing process of a semiconductor laser according to Example 1. FIG.

Explanation of symbols

301 n-GaAs substrate 302 n-cladding layer 303 guide layer 304 well layer 305 barrier layer 306 multiple quantum well active layer 307 first cladding layer 308 etching stop layer 309 second cladding layer 310 oxidation suppression layer 311 SiNx film 312 block layer 313 Contact layer

Claims (7)

(Al _X1 Ga _{1 -X1} ) _Y1 In _{1 -Y1} P (0 ≦ X1 <1, 0 ≦ Y1 ≦ 1) on the first semiconductor layer (Al _X2 Ga _{1 -X2} ) _Y2 In _{1 -Y2} P ( A second semiconductor layer composed of 0 <X2 ≦ 1, 0 <Y2 ≦ 1, X1 <X2) and (Al _X3 Ga _1-X3 ) _Y3 In _1-Y3 P (0 ≦ X3 <1, 0 <Y3 ≦ 1, In the method for etching a compound semiconductor sequentially including a third semiconductor layer composed of X3 <X2), a part of the third semiconductor layer and the second semiconductor layer is etched using an etchant composed of an acidic solution containing halogen oxygen acid ions. A method for etching a compound semiconductor comprising removing the compound semiconductor. The compound semiconductor further includes a fourth semiconductor layer made of Al _X4 Ga _{1 -X4} As (0 ≦ X4 ≦ 1) on the third semiconductor layer, and an etching solution made of an acidic solution containing a halogen oxygenate ion The etching method according to claim 1, wherein the fourth semiconductor layer is also removed by etching.   3. The method for etching a compound semiconductor according to claim 1, wherein the etching solution contains hydrochloric acid and / or sulfuric acid together with a halogenate ion.   The compound semiconductor according to any one of claims 1 to 3, wherein the etching solution contains a complexing agent capable of forming a water-soluble complex ion with at least one group III element constituting the compound semiconductor. Etching method.   After removing portions of the third semiconductor layer and the second semiconductor layer by etching, etching is performed using a selective etching solution having high selectivity between the first semiconductor layer and the second semiconductor layer, whereby the first semiconductor layer is etched. The method of etching a compound semiconductor according to any one of claims 1 to 4, wherein the second semiconductor layer is removed.   6. The method for etching a compound semiconductor according to claim 5, wherein the selective etching solution contains oxycarboxylic acid and / or dicarboxylic acid together with hydrochloric acid.   The compound semiconductor according to claim 4 or 5, wherein the selective etching solution contains at least one organic acid selected from the group consisting of tartaric acid, citric acid, malic acid, glycolic acid, malonic acid, and lactic acid. Etching method.

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