JP2016143718A - Method of manufacturing infrared ray sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing an infrared ray sensor that can more stably form a semiconductor mesa formed on a compound semiconductor substrate with little dispersion.SOLUTION: A method of manufacturing an infrared sensor creates an epitaxial wafer 50 in which a compound semiconductor laminate part 11 formed of a lamination film of InSb or AlInSb is formed on a substrate 10 formed of GaAs, and a cap layer 16 formed of GaAs and having a film thickness of 1 to 20 nm is formed on the compound semiconductor laminate part 11, and performing etching processing on the epitaxial wafer 50 in a desired mesa-shape by wet etching.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a method for manufacturing an infrared sensor, and more particularly, to a method for manufacturing an infrared sensor including a semiconductor mesa.

  The infrared sensor has a pn junction surface made of a group III-V compound semiconductor such as indium antimonide (InSb) or aluminum indium antimonide (AlInSb). A method of manufacturing an infrared sensor having a barrier layer for suppressing a diffusion current is known (for example, see Patent Document 1). In this method, an n-type semiconductor layer, an i-type semiconductor layer, a barrier layer, and a p-type semiconductor layer made of a III-V group compound semiconductor are sequentially grown on a substrate, and these are wet-etched to form a semiconductor mesa. .

  By the way, in an infrared sensor having a semiconductor mesa, when the variation in the shape of the semiconductor mesa (hereinafter, sometimes referred to as “mesa shape”) increases, the variation in the upper area of the semiconductor mesa increases, and the variation in element resistance or the like. growing. As described above, since the element characteristics of the infrared sensor greatly depend on the mesa shape, it is important to stabilize the mesa shape in order to control variations in the element characteristics.

  In particular, when the semiconductor mesa is formed by wet etching, the mesa shape varies depending on the adhesion between the resist mask for etching and the semiconductor surface. Since the adhesion between the resist mask and the semiconductor surface varies greatly depending on the baking temperature of the resist mask, the oxidation state of the semiconductor surface, and the like, it is difficult to form a semiconductor mesa with little variation in the upper area.

JP 2007-81225 A JP 2014-72217 A

In order to solve the above-mentioned problems, studies have been made to suppress mesa shape variations due to wet etching by forming a cap layer made of the same material as the barrier layer on the upper part of the compound semiconductor stack (for example, Patent Documents). 2).
However, a semiconductor substrate and a wet etching method that can stabilize the mesa shape regardless of the presence or absence of a barrier layer are desired.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a method for manufacturing an infrared sensor capable of forming a semiconductor mesa formed on a compound semiconductor substrate with less variation in shape and more stably. And

  In order to achieve the above object, a method of manufacturing an infrared sensor according to an aspect of the present invention includes a compound semiconductor multilayer portion formed of a laminated film of InSb or AlInSb on a substrate made of GaAs, and the compound semiconductor multilayer portion. An epitaxial wafer having a cap layer having a thickness of 1 to 20 nm made of GaAs on the surface is prepared, and the epitaxial wafer is etched into a desired mesa shape by wet etching.

  According to the method for manufacturing an infrared sensor of one embodiment of the present invention, the semiconductor mesa formed on the compound semiconductor substrate can be formed more stably with less variation in shape.

It is sectional drawing which shows a mesa shape in case the adhesiveness of a resist mask and a compound semiconductor laminated part surface is weak. It is sectional drawing which shows a mesa shape in case the adhesiveness of a resist mask and a compound semiconductor laminated part surface is strong. It is sectional drawing which shows a mesa shape when the cap layer formed with the GaAs material was provided in the compound semiconductor laminated part surface. The figure which shows the main processes in the manufacturing method of the infrared sensor which concerns on embodiment. Sectional drawing which shows the manufacturing method of the infrared sensor which concerns on embodiment. Sectional drawing which shows the manufacturing method of the infrared sensor which concerns on embodiment. It is an electron micrograph of a mesa-shaped cross section when an InSb film having a GaAs cap layer (thickness: 20 nm) is wet etched. It is an electron micrograph of a mesa-shaped cross section when an InSb film having a GaAs cap layer (thickness: 1 nm) is wet-etched.

  Hereinafter, a mode for carrying out the present invention (referred to as the present embodiment) will be described. 1 to 3 are views schematically showing a cross section of a semiconductor mesa at the time of manufacturing an infrared sensor. FIG. 1 shows a cross section of a semiconductor mesa formed when the adhesion between a resist mask and a compound semiconductor stacked portion is relatively weak. FIG. 2 shows a cross section of the semiconductor mesa formed when the adhesion between the resist mask and the compound semiconductor stacked portion is relatively strong (stronger than the adhesion in FIG. 2). FIG. 3 shows a cross section of a semiconductor mesa formed when a gap layer is provided between the resist mask and the compound semiconductor stacked portion.

  In the conventional mesa pattern forming method, a resist mask is applied to the semiconductor surface of the compound semiconductor laminated portion made of a laminate of InSb or AlInSb, and baked. After forming a mask pattern by a photolithography process, a mesa pattern is formed. Wet etching is performed. At this time, if the adhesion between the semiconductor layer surface of the compound semiconductor multilayer portion and the resist mask 218 is weak, the etchant easily penetrates into the gap between the resist mask 218 and the semiconductor layer surface of the compound semiconductor multilayer portion. Etching of the surface of the semiconductor layer easily proceeds. For this reason, as shown in FIG. 1, the mesa angle θ, which is an angle between the substrate 210 and the semiconductor mesa 211a formed by wet etching the compound semiconductor stacked portion, becomes small. Conversely, if the adhesion between the semiconductor layer surface of the compound semiconductor stack and the resist mask 218 is strong, the etchant will not easily penetrate into the gap between the resist mask 218 and the surface of the compound semiconductor stack. For this reason, the etching of the surface of the semiconductor layer of the compound semiconductor stack is difficult to proceed, and the mesa angle θ of the semiconductor mesa 211a is increased as shown in FIG. For example, when the adhesion at the time of forming the semiconductor mesa 211a shown in FIG. 2 is stronger than the adhesion at the time of forming the semiconductor mesa 211a shown in FIG. 1, the mesa angle θ shown in FIG. It becomes larger than the angle θ.

  The adhesion between the semiconductor layer surface of the compound semiconductor multilayer portion made of an InSb or AlInSb laminate and the resist mask is easily affected by the oxidation state of the semiconductor surface of the compound semiconductor multilayer portion, the application of the resist mask, and the baking conditions, and further wet. Due to the influence of etchant agitation during etching, the mesa shape varies greatly.

  In the infrared sensor manufacturing method of the present embodiment, a compound semiconductor laminated portion formed of a laminated film of InSb or AlInSb on a GaAs substrate (GaAs substrate), and a film thickness of 1 on the surface of the compound semiconductor laminated portion. An epitaxial wafer having a cap layer made of GaAs having a thickness of ˜20 nm is prepared, and this epitaxial wafer is etched into a desired mesa shape by wet etching.

  The epitaxial wafer before wet etching is provided with a cap layer made of a GaAs material at the top of the compound semiconductor stack. This cap layer completely protects the surface (that is, the upper surface) of the InSb or AlInSb compound semiconductor laminated portion located immediately below the cap layer. Therefore, the resist mask formed before wet etching is in close contact with the surface of the cap layer. As a result, the etching of the surface of the semiconductor layer of the compound semiconductor stack formed of InSb or AlInSb is determined by the bond between the surface of the semiconductor layer and the cap layer, and the adhesion between the semiconductor layer surface of the compound semiconductor stack and the resist mask. It does not depend on.

  The cap layer is formed continuously with the formation of the InSb or AlInSb compound semiconductor stack 11 by a semiconductor film forming apparatus typified by a molecular beam epitaxy (MBE) apparatus or a MOCVD (Metal Organic Chemical Vapor Deposition) apparatus. Done. Therefore, the bond between the surface of the semiconductor layer of InSb or AlInSb and the cap layer formed of the GaAs material is extremely stable, and stable etching is possible. Thereby, the variation in the shape of the semiconductor mesa formed by etching the compound semiconductor stacked portion is reduced. As shown in FIG. 3, since the semiconductor mesa 11a having the cap layer 16a made of GaAs at least in the manufacturing stage has a small variation in shape, the mesa angle θ of the semiconductor mesa 11a formed under the same manufacturing conditions is determined between the elements. The variation of becomes smaller and almost constant.

Hereinafter, the manufacturing method of the infrared sensor of this embodiment is demonstrated in detail using drawing.
<Embodiment>
FIG. 4 is a diagram showing main steps in the method of manufacturing the infrared sensor according to the embodiment of the present invention. FIG. 5 is a cross-sectional view showing the manufacturing method of the infrared sensor in the order of steps.

[Formation of compound semiconductor laminate]
In step S10 shown in FIG. 4, an n-type semiconductor layer 12, an i-type semiconductor layer 13, a p-type semiconductor layer 15 and a cap layer 16 made of InSb or AlInSb are formed on a substrate 10 as shown in FIG. It is a lamination process of laminating in this order.

  In the present embodiment, the n-type semiconductor layer 12, the i-type semiconductor layer 13, and the p-type semiconductor layer 15 are collectively referred to as a compound semiconductor stacked portion 11. Hereinafter, the stacked body formed up to the cap layer 16 on the compound semiconductor stacked portion 11 is referred to as an epitaxial wafer 50. The cap layer 16 is additionally formed on the uppermost layer of the compound semiconductor stacked portion 11, but the other stacking order of the compound semiconductor stacked portion 11 is as long as the i-type semiconductor layer is sandwiched between the n-type semiconductor layer and the p-type semiconductor layer. There is no restriction on the stacking order. In this example, the pin type semiconductor laminated structure constituting the infrared sensor is taken as an example. However, even in the process of forming the photoconductor type infrared sensor with a single layer or laminated film made of InSb or AlInSb, the following mesa shape is used. The effect of stabilizing is not changed.

The compound semiconductor stacked portion 11 and the cap layer 16 can be formed on the substrate 10 by a semiconductor film forming apparatus typified by an MBE apparatus or an MOCVD apparatus. As the substrate 10, for example, a substrate made of a GaAs semiconductor is used.
In the case where the compound semiconductor layer is formed using the MBE method, as shown in FIG. 4, step S10 can be performed as in steps S1 and S2 below.

  First, in step S <b> 1, the n-type semiconductor layer 12 is grown on the substrate 10. The n-type semiconductor layer 12 is made of, for example, n-type InSb (n-InSb) containing a known n-type dopant. Next, the i-type semiconductor layer 13 is grown on the n-type semiconductor layer 12. The i-type semiconductor layer 13 is made of an intrinsic semiconductor layer, for example, made of InSb, but may be doped. Further, a p-type semiconductor layer 15 made of, for example, p-type InSb (p-InSb) containing a known p-type dopant is grown on the i-type semiconductor layer 13.

  Next, in step S <b> 2, a cap layer 16 made of GaAs is grown on the p-type semiconductor layer 15. The cap layer 16 made of GaAs has a significantly different etching rate from InSb and AlInSb. A GaAs material that is an As-based compound semiconductor is a material that has a stronger bonding force between elements than that of InSb and AlInSb, which are Sb-based compound semiconductors, and is difficult to be etched. For this reason, GaAs is a material suitable for forming a stable protective layer on the surface of the compound semiconductor stacked portion 11.

  If the cap layer 16 is too thick, it will be difficult to remove GaAs if it is necessary to remove it in a later step. On the other hand, if the thickness of the cap layer 16 is too thin, the effect of surface protection cannot be obtained. For this reason, the thickness of the cap layer 16 may be 1 to 20 nm, and may be 2 to 10 nm.

  The next step S20 is a mask forming step for forming a resist mask 18 on the cap layer 16 of the epitaxial wafer 50, as shown in FIG. The resist mask 18 is a mask layer for forming a semiconductor mesa by wet-etching the compound semiconductor stacked portion 11. The pattern of the resist mask 18 is formed so as to leave the resist in a region where a semiconductor mesa is to be formed and remove the resist from other regions using, for example, a photolithography technique.

In the next step S30, as shown in FIG. 5C, the compound semiconductor multilayer portion 11 is wet-etched using the resist mask 18, thereby forming the semiconductor mesa 11a including the compound semiconductor multilayer portion on the substrate 10. This is a mesa formation process. As the etchant used at this time, for example, a mixed solution of hydrochloric acid, hydrogen peroxide and water is used. In the mesa formation process, the cap layer 16, the p-type semiconductor layer 15, the i-type semiconductor layer 13, and the n-type semiconductor layer 12 are wet-etched in this order. The semiconductor mesa 11a includes an etched cap layer 16a, an etched p-type semiconductor layer 15a, an etched i-type semiconductor layer 13a, and an etched n-type semiconductor layer 12a.
After forming the semiconductor mesa 11a, the resist mask 18 is removed with an organic solvent or the like.

[Formation of wiring layer]
In this embodiment, for example, as shown in FIG. 6A, a plurality of semiconductor mesas 11a formed by the above-described manufacturing method are formed simultaneously on the same substrate 10. Then, as shown in FIG. 6B, the adjacent semiconductor mesas 11a are separated by using a photolithography technique and an etching technique. For example, the adjacent semiconductor mesas 11a are separated from each other by removing a part of the n-type semiconductor layer 12a in the region between the adjacent semiconductor mesas 11a. At this time, the cap layer 16 may be removed. For removing the cap layer 16, for example, a dry etching method such as a RIE (Reactive Ion Etching) method is used. When the cap layer 16 does not affect the contact with the electrode, the cap layer 16 may be left as it is.

Next, as illustrated in FIG. 6B, an insulating film 21 is deposited on the substrate 10. The insulating film 21 is a silicon oxide film (SiO ₂ ), for example, and is formed using, for example, a CVD (Chemical Vapor Deposition) method. Next, using photolithography technique and etching technique, a part of the insulating film 21 located immediately above the cap layer 16 is removed, and a contact hole 23a having the cap layer 16 as a bottom surface is formed. Further, when forming the contact hole 23a, a part of the insulating film 21 located immediately above the n-type semiconductor layer 12a is removed, and a contact hole 23b having the n-type semiconductor layer 12a as a bottom surface is formed.

  Next, a metal film is deposited above the substrate 10 so as to fill the contact holes 23a and 23b. This metal film is formed using, for example, a vapor deposition method or a sputtering method. Then, the metal film is partially removed by using a photolithography technique and an etching technique. As a result, the wiring layer 25 is formed as shown in FIG. For example, the wiring layer 25 allows the cap layer 16 exposed in the contact hole 23a of one semiconductor mesa 11a among the adjacent semiconductor mesas, and the n-type semiconductor layer 12a exposed in the contact hole 23b of the other semiconductor mesa 11a. Is connected. Thereby, the several semiconductor mesa 11a is connected in series, for example, and a single infrared sensor is comprised. Thereafter, an insulating protective film 27 is deposited on the substrate 10 by using, for example, a CVD method. This protective film 27 prevents the wiring layer 25 and the semiconductor mesa 11a from coming into contact with moisture or the like. Through the above steps, the infrared sensor 100 including a plurality of semiconductor mesas 11a is completed.

<Effect of embodiment>
The embodiment of the present invention has the following effects.
Since the semiconductor mesa having a uniform shape is formed on the epitaxial wafer, the variation in the upper area of the semiconductor mesa is small, and an infrared sensor having uniform characteristics such as element resistance can be formed on the same epitaxial wafer. In addition, since the cap layer formed of a GaAs material can be stably formed, variation in characteristics of the infrared sensor between the epitaxial wafers can be reduced.
Further, when the manufacturing method of the infrared sensor according to the present embodiment is used, a semiconductor mesa can be stably formed with little variation even when there is no barrier layer.

Example 1
A semi-insulating GaAs substrate (substrate surface orientation (100)) is epitaxially grown with a thickness of 1 μm using MBE, and then a GaAs cap layer is grown on InSb with a thickness of 20 nm. Formed. A resist mask was formed on the epitaxial wafer by photolithography, and wet etching was performed using an etchant mixed at a volume ratio of hydrochloric acid: water: hydrogen peroxide = 170: 440: 30 to form a semiconductor mesa. FIG. 7 shows the result of confirming the cross section of the formed semiconductor mesa with an electron microscope. As shown in FIG. 7, InSb under the cap layer showed a stable mesa shape.

(Example 2)
A semi-insulating GaAs substrate (substrate surface orientation (100)) is epitaxially grown with a thickness of 1 μm using MBE, and then a GaAs cap layer is grown on InSb with a thickness of 1 nm. Formed. A resist mask was formed on the epitaxial wafer by photolithography, and wet etching was performed using an etchant mixed at a volume ratio of hydrochloric acid: water: hydrogen peroxide = 170: 440: 30 to form a semiconductor mesa. The result of confirming the cross section of the formed semiconductor mesa with an electron microscope is shown in FIG. As shown in FIG. 8, InSb under the cap layer showed a stable mesa shape.

(Comparative example)
An epitaxial wafer was formed by epitaxially growing InSb to a thickness of 1 μm on a semi-insulating GaAs substrate (substrate surface orientation (100)) using the MBE method. The surface oxide film of this epitaxial wafer was removed with 1N dilute hydrochloric acid. A resist mask was formed on this epitaxial wafer by photolithography, and wet etching was performed using an etchant mixed at a volume ratio of hydrochloric acid: water: hydrogen peroxide = 170: 440: 30. Since the adhesion between InSb and the resist mask was low and a part of the resist mask was peeled off during etching, stable etching could not be performed.

  The above embodiment exemplifies an apparatus for embodying the technical idea of the present invention, and the technical idea of the present invention specifies the material, shape, structure, arrangement, etc. of the component parts. Not. The technical idea of the present invention can be variously modified within the technical scope defined by the claims described in the claims.

10, 210 Substrate 11 Compound semiconductor stack 11a, 211a Semiconductor mesa 12, 12a n-type semiconductor layer 13, 13a i-type semiconductor layer 15, 15a p-type semiconductor layer 16, 16a cap layer 18, 218 resist mask 21 insulating film 23a, 23b Contact hole 25 Wiring layer 27 Protective film 50 Epitaxial wafer 100 Infrared sensor

Claims (2)

An epitaxial wafer in which a compound semiconductor laminated portion formed of a laminated film of InSb or AlInSb on a GaAs substrate and a cap layer made of GaAs and having a thickness of 1 to 20 nm is formed on the surface of the compound semiconductor laminated portion. ,
An infrared sensor manufacturing method, wherein the epitaxial wafer is etched into a desired mesa shape by wet etching. The method for manufacturing an infrared sensor according to claim 1, wherein the etchant is a mixed solution of hydrochloric acid, water, and hydrogen peroxide.