JP4331386B2 - Manufacturing method of quantum well type infrared sensor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a manufacturing method of a quantum well type infrared sensor, and more particularly, etching processability in an infrared sensor using infrared absorption by a transition between a sub-level generated in a multiple quantum well and a continuous band at the bottom of a conduction band. It is related with the manufacturing method of the quantum well type | mold infrared sensor characterized by the multiple quantum well layer for improving this.
[0002]
[Prior art]
Conventionally, photodiode arrays using HgCdTe have been used as infrared detectors for detecting infrared rays in the vicinity of the 10 μm band, but in recent years, as an alternative to such HgCdTe-based infrared detectors, large crystallinity with good crystallinity has been used. Quantum well-type infrared sensor that uses a GaAs-based semiconductor, which is easy to obtain an area substrate, and makes it possible to detect infrared rays in the vicinity of the 10 μm band by utilizing light absorption by transition between sub-levels in multiple quantum wells ( QWIP: Quantum Well Infrared Photodetector has attracted attention.
[0003]
Here, a conventional quantum well infrared sensor (QWIP) will be described with reference to FIG.
FIG. 8A is a schematic cross-sectional view of a conventional QWIP. First, an MQW layer 44 is used as a photosensitive layer on an n ⁺ -type GaAs lower contact layer 42 serving as a common electrode layer. A plurality of infrared sensor elements are provided, and the n-type GaAs upper contact layer 45 of each infrared sensor element is provided with irregularities for forming an irregular reflection structure, and Au is reflected through a partially provided ohmic electrode 47. An electrode 48 is provided.
[0004]
Note that an i-type InGaP layer 41 and an n-type InGaP layer 43 serving as etching stopper layers are provided above and below the n ⁺ -type GaAs lower contact layer 42 for reasons of the manufacturing process, and the other of the i-type InGaP layer 41 is provided. An antireflection film 52 is provided on the surface, and infrared rays 53 are incident through the antireflection film.
[0005]
Each infrared sensor element is provided with an irregular reflection structure composed of irregularities and an Au reflecting electrode 48 so that incident infrared rays incident substantially perpendicularly from the n ⁺ -type GaAs lower contact layer 42 side are easily absorbed by the MQW layer 44. Incident infrared rays are deflected in an oblique direction by the irregular reflection structure.
[0006]
An infrared detection array is configured by arranging such infrared sensor elements in a one-dimensional array or a two-dimensional array, and a common bias for each infrared sensor element is passed through an ohmic electrode 47 in contact with the n-type InGaP layer 43. In addition, the output from each infrared sensor element is taken out from the In bump 51 provided in each infrared sensor element.
[0007]
In such a quantum well-type infrared sensor, carriers confined in the quantum well, in this case, electrons are excited by infrared rays 53, and the band on the conduction band side of the i-type AlGaAs barrier layer constituting the MQW layer 44 is obtained. In order to increase the light absorption efficiency in the quantum well, the n-type GaAs well layer constituting the MQW layer 33 is increased in doping concentration to increase the light absorption efficiency in the quantum well. The carrier concentration in the well, that is, the electron concentration may be increased.
[0008]
However, when an AlGaAs / GaAs quantum well system is used, there is a problem that the sensitivity of infrared rays having a short wavelength of 5 μm or less is lowered.
That is, in order to absorb a short wavelength of 5 μm or less, a transition between the ground level formed in the quantum well and the lower end of the conduction band is used, but the energy gap between the conduction bands of AlGaAs and GaAs, That is, since there is an upper limit in the difference ΔE _C at the lower end of the conduction band, the absorption efficiency is lowered.
[0009]
FIG. 8B is a band diagram on the conduction band side of the MQW layer 44. When an AlGaAs / GaAs quantum well system is used, the energy gap ΔE _{C is set} to 0.25 eV or more. I can't.
[0010]
Therefore, in order to absorb a short wavelength of 5 μm or less, an attempt is made to use InGaAs having a large electron affinity χ instead of GaAs as the well layer, and to further increase the difference ΔE _C at the lower end of the conduction band with AlGaAs. Yes.
[0011]
FIG. 8C is a band diagram on the conduction band side of the AlGaAs / InGaAs quantum well system, and the conduction band energy gap ΔE _C is larger than that in the case of using the AlGaAs / GaAs quantum well system. Thereby, sufficient sensitivity can be given to a wavelength of 5 μm or less.
[0012]
9 is an explanatory diagram of the correlation between ΔE _C and the detection wavelength. In the case of an Al _0.25 Ga _0.75 As / GaAs quantum well, ΔE _C ≈0.2 eV, and the detection wavelength is about 8.4 μm. Become.
Further, as is apparent from the figure, it is understood that ΔE _C needs to be 0.3 eV or more in order to provide sensitivity to a short wavelength of 5 μm or less.
[0013]
[Problems to be solved by the invention]
However, when InGaAs is used as the well layer, there is a problem that the etching rate becomes very low in the dry etching process when forming the element isolation grooves 49 for arraying, and the process controllability is extremely deteriorated. is there.
[0014]
That is, in such a dry etching process, a reactive gas containing Cl is generally used, but in a system containing In, In and Cl react with each other, and InCl _x having a low vapor pressure is formed on the processing surface. This is because it is formed.
[0015]
Therefore, an object of the present invention is to improve the process controllability in the dry etching process.
[0016]
[Means for Solving the Problems]
Here, means for solving the problems in the present invention will be described with reference to FIG.
1A is a cross-sectional view of the main part of the quantum well infrared sensor, and FIG. 1B is a band diagram on the conduction band side of the quantum well layer.
1A and 1B, in order to achieve the above object, in the present invention, the well layer 2 constituting the multiple quantum well layer 1 is provided as a barrier layer constituting the multiple quantum well layer. dry the energy gap Delta] E _c of the conduction band with used GaAsNSb composition comprising a 0.3EV～0.5EV, that when the array of separating the multiple quantum well layer 1, using a reactive gas containing Cl of It has the process of etching the multiple quantum well layer 1 by an etching.
[0017]
In this way, by using GaAsN or GaAsNSb as the well layer 2, the energy gap ΔE _C in the conduction band between the well layer 2 and the barrier layer 3 can be set to 0.3 to 0.5 eV. The sensitivity to infrared rays 8 having a wavelength shorter than 5 μm can be increased, and in the dry etching process of the multiple quantum well layer 1, the reactive gas containing Cl is used to process at the same etching rate as GaAs. Can do.
[0018]
In particular, by using GaAs NSb, the difference Δa of the lattice constant a from GaAs can be made 0.1% or less, that is, Δa / a can be made 0.1% or less, while maintaining substantially the same ΔE _C. Thereby, the well layer 2 can be lattice-matched to the growth substrate or the barrier layer 3.
[0019]
In the present invention, Al _x Ga _1-x As (0 ≦ x ≦ 1) is used as the barrier layer 3 constituting the multiple quantum well layer 1.
[0020]
In this way, by using Al _x Ga _1-x As (0 ≦ x ≦ 1) as the barrier layer 3, ΔE _C for the well layer 2 made of GaAsN or GaAsNSb can be increased.
[0021]
The present invention is characterized in that an irregular reflection structure is provided in the contact layer 6 in contact with the multiple quantum well layer 1.
[0022]
In this way, by providing an irregular reflection structure, for example, an irregular reflection structure using the unevenness and the reflection electrode 7, the irregularly reflected incident infrared ray 8 is incident on the multiple quantum well layer 1 from an oblique direction. A transition or a transition between the sub-level 4 and the continuous band 5 can be efficiently performed.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
Here, the QWIP of the embodiment of the present invention will be described with reference to FIGS. 2 to 7. First, the manufacturing process of the QWIP will be described with reference to FIGS.
2A. First, on the semi-insulating GaAs substrate 11, by an MOVPE method (metal organic vapor phase epitaxy), an i-type GaAs buffer layer 12 and an i-type InGaP layer 13 serving as an etching stopper layer are used. Lower n ⁺ -type GaAs having a thickness of 0.5 to 3.0 μm, for example, 2.0 μm and a carrier concentration of 1 × 10 ^{17 to} 5 × 10 ¹⁸ cm ⁻³ , for example, 1 × 10 ¹⁸ cm ⁻³ Contact layer 14, n-type InGaP layer 15 serving as an etching stopper layer, GaAs NSb-based MQW layer 16, and a thickness of 1.0 to 3.0 μm, for example, 1.0 μm, and a carrier concentration of 1 × 10 ¹⁷ to An n-type GaAs upper contact layer 17 of 5 × 10 ¹⁸ cm ⁻³ , for example, 2 × 10 ¹⁷ cm ⁻³ is epitaxially grown sequentially.
[0024]
In this case, the GaAs NSb-based MQW layer 16 includes, for example, an i-type Al _0.25 Ga _0.75 As barrier layer having a thickness of 50 nm and an n-type having a thickness of 5.5 nm and a carrier concentration of 2 × 10 ¹⁷ cm ⁻³ . GaAs _0.95 N _0.01 Sb _0.04 well layers are alternately deposited so that there are 20 n-type GaAs _0.95 N _0.01 Sb _0.04 well layers.
In this case, the i-type Al _0.25 Ga _0.75 As barrier layer does not tunnel electrons between adjacent n-type GaAs _0.95 N _0.01 Sb _0.04 well layers, and only the ground level is formed in the quantum well. So that it is sufficiently thick.
[0025]
2B. Next, using the resist pattern 18 as a mask, a recess 19 having a depth of, for example, 0.6 μm is formed in the n-type GaAs upper contact layer 17 in order to form an irregular reflection structure in each infrared sensor element. To do.
[0026]
Next, referring to FIG. 3C, after removing the resist pattern 18, an SiON film 20 is provided on the entire surface, and an opening for forming a common electrode is formed in the SiON film 20 by an ordinary photolithography process. A contact opening 21 reaching the n-type InGaP layer 15 is formed by performing wet etching using the film 20 as a mask.
[0027]
In this case, by using HF + H ₂ O ₂ + H ₂ O as an etchant, the n-type InGaP layer 15 serves as an etching stopper layer to selectively etch GaAs, AlGaAs, and GaAsNSb, and the surface of the n-type InGaP layer 15 The etching stops automatically at.
[0028]
Next, referring to FIG. 3D, after removing the SiON film 20, a new SiON film 22 is provided on the entire surface, and the SiON film 22 of the common electrode forming part and sensor electrode forming part is formed using a resist pattern (not shown). After selectively removing and then partially providing an ohmic electrode 23 made of Au.Ge/Ni, an Au reflective electrode 24 is provided to selectively form a common electrode and a sensor electrode.
[0029]
Next, referring to FIG. 4E, after removing the resist pattern (not shown), a new photoresist is applied, and a resist mask (not shown) having an opening corresponding to the element isolation trench 25 is provided. By performing dry etching using the resist mask as a mask, a part of the SiON film 22 is removed, and subsequently dry etching is performed using a Cl-based gas to thereby form the n-type GaAs upper contact layer 17 and the GaAs NSb-based MQW layer 16. Then, an element isolation trench 25 reaching the n-type InGaP layer 15 is formed.
[0030]
Note that SiCl ₄ + SF ₆ is used as the Cl-based gas in this case, but GaAsNSb has an etching rate comparable to that of GaAs with respect to such a Cl-based gas, so that the process controllability does not deteriorate.
[0031]
Next, after removing the resist pattern, a new SiON film 26 serving as a protective insulating film is deposited, and a part of the Au reflecting electrode 24 of the common electrode portion and sensor electrode portion is formed by a normal photolithography process. Then, an In bump 28 is formed by vapor deposition on the exposed portion through a Ti / Au film 27 that becomes a barrier layer and an adhesion improving layer.
[0032]
Next, referring to FIG. 5G, the semi-insulating GaAs substrate 11 and the i-type GaAs buffer layer 12 are selectively removed using HF + H ₂ O ₂ + H ₂ O as an etchant.
Since the i-type InGaP layer 13 in this case serves as an etching stopper layer, the etching automatically stops at the i-type InGaP layer 13.
Next, by providing the antireflection film 29 on the surface of the i-type InGaP layer 13, the basic configuration of QWIP is completed.
[0033]
In such QWIP, most of the infrared light incident from the direction perpendicular to the antireflection film 29 is transmitted without being absorbed by the GaAs NSb-based MQW layer 16, but provided on the surface of the n-type GaAs upper contact layer 17. The concave and convex structure formed by the concave portion 19 and the Au reflecting electrode 24 are irregularly reflected and deflected in an oblique direction, and again enter the GaAs NSb-based MQW layer 16 in an oblique direction. To be absorbed.
[0034]
Further, the oblique infrared rays transmitted without being absorbed by the GaAs NSb-based MQW layer 16 are totally reflected at the interface of the n-type InGaP layer 15 or the i-type InGaP layer 13 and enter the GaAs NSb-based MQW layer 16 again from the oblique direction. Will be absorbed.
In this case, the absorption wavelength band in the GaAs NSb-based MQW layer 16 is about 4 μm.
[0035]
FIG. 6A is a band diagram on the conduction band side in the GaAs NSb-based MQW layer 16 in an unbiased state, and the AlGaAs barrier layer so that only the ground level 33 exists in the quantum well. The mixed crystal ratio and film thickness of 31 are controlled.
[0036]
6B, FIG. 6B shows that the n-type GaAs upper contact layer 17 becomes positive between the n ⁺ -type GaAs lower contact layer 14 and the n-type GaAs upper contact layer 17, for example, It is a band diagram by the side of the conduction band in the state where the voltage of 5.0V was applied.
[0037]
In this state, when the infrared ray 35 is incident on the GaAs NSb-based MQW layer from an oblique direction, the infrared ray 35 is absorbed by the transition between the ground level 33 and the continuous band 36 on the conduction band side, and excited by the continuous band 36. The electrons 34 are taken out through the n-type GaAs upper contact layer 17 as a photoinduced current 37.
[0038]
FIG. 7 is a diagram for explaining the correlation between the GaAs NSb composition and the detection wavelength. By using GaAs NSb as the well layer, ΔE _C is 0.2 to 0.65 eV with respect to the Al _0.25 Ga _0.75 As barrier layer. And can correspond to infrared rays of 8.4 to 3 μm.
For example, when the mixed crystal ratio of the AlGaAs barrier layer 31 is Al _0.25 Ga _0.75 As and the mixed crystal ratio of the GaAs NSb well layer 32 is GaAs _0.95 N _0.01 Sb _0.04 , ΔE _C ≈0.38 eV, which is about 4 μm. Sensitivity to infrared rays can be given.
[0039]
Although the embodiments of the present invention have been described above, the present invention is not limited to the configurations and conditions described in the embodiments, and various modifications can be made.
For example, in the above embodiment, the irregular reflection structure is formed by one irregularity, but the irregular reflection structure may be formed by more irregularities or complex irregularities, and further using a diffraction grating. You can do it.
[0040]
In the description of the above embodiment, since sensitivity to wavelengths shorter than the 5 μm band is a problem, the quantum level in the quantum well is assumed to be only the ground level, and the transition between the ground level and the continuous band is used. However, the present invention is not limited to the transition between the ground level and the continuous band.
That is, a multiple quantum well layer may be configured so that a plurality of quantum levels (sublevels) are formed in the quantum well, and a transition between sublevels may be used, or a higher quantum level and − Transitions between continuous bands may be used.
[0041]
In the above embodiment, the composition ratio of Sb is controlled so that the well layer is lattice-matched to the substrate or the barrier layer, and the difference Δa with respect to the lattice constant a of GaAs is Δa / a ≦ 0.1. However, the lattice matching is not necessarily required, and the well layer may be formed of GaAsN.
[0042]
That is, ΔE _C greatly depends on the N composition ratio of GaAsNSb and does not depend much on the Sb composition ratio. Therefore, GaAsN, for example, GaAs _0.99 N _0.01 may be used.
This GaAs _0.99 N _0.01 is Δa / a≈0.25% with respect to GaAs, but it is possible to grow a multiple quantum well crystal using such GaAsN.
[0043]
In the above embodiment, Al _0.25 Ga _0.75 As is used as the barrier layer. However, the barrier layer is not limited to such a mixed crystal ratio, and may be appropriately changed according to required characteristics. In extreme cases, GaAs may be used.
[0044]
In the above embodiment, the growth substrate is finally removed. However, it is not always necessary to remove the growth substrate, and the growth substrate may be used as an infrared sensor with the growth substrate remaining.
[0045]
Here, referring to FIG. 1 again, the supplementary note of the present invention will be described.
1A and 1B (Appendix 1) A quantum well infrared sensor using GaAsNSb as the well layer 2 constituting the multiple quantum well layer 1.
(Supplementary note 2) The quantum well infrared sensor according to supplementary note 1, wherein the composition ratio of the GaAs NSb is such that the difference in lattice constant from GaAs is 0.1% or less.
(Additional remark 3) The quantum well type infrared sensor characterized by using GaAsN as the well layer 2 which comprises the multiple quantum well layer 1. FIG.
(Supplementary Note 4) as a barrier layer 3 constituting the multiple quantum well layer 1, according to any one of _{Al x Ga 1-x As (} 0 ≦ x ≦ 1) Appendix 1 to 3, characterized in that using the Quantum well type infrared sensor.
(Supplementary note 5) The quantum well infrared sensor according to any one of supplementary notes 1 to 4, wherein an irregular reflection structure is provided in the contact layer 6 in contact with the multiple quantum well layer 1.
(Supplementary note 6) Any one of Supplementary notes 1 to 5, characterized in that either the transition between the sublevels 4 or the transition between the sublevel 4 and the continuous band 5 in the multiple quantum well layer 1 is used. The quantum well type infrared sensor according to claim 1.
[0046]
【The invention's effect】
According to the present invention, GaAsNSb or GaAsN is used as the well layer constituting the multiple quantum well layer, so that the process controllability of the etching process can be improved in a state where ΔE _C is increased. A quantum well infrared sensor having sensitivity to short-wave infrared light can be formed with high accuracy, and thus contributes to the practical application of a large-area highly integrated and high-resolution infrared solid-state imaging device.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of a basic configuration of the present invention.
FIG. 2 is an explanatory diagram of a manufacturing process up to the middle of QWIP according to an embodiment of the present invention.
FIG. 3 is an explanatory diagram of the manufacturing process up to the middle of FIG. 2 and subsequent drawings of the QWIP according to the embodiment of the present invention.
FIG. 4 is an explanatory diagram of a manufacturing process up to the middle of FIG. 3 and subsequent drawings of the QWIP according to the embodiment of the present invention.
FIG. 5 is an explanatory diagram of the manufacturing process of the QWIP according to the embodiment of the present invention after FIG. 4;
FIG. 6 is an explanatory diagram of QWIP detection operation according to the embodiment of this invention;
FIG. 7 is an explanatory diagram of a correlation between a GaAs NSb composition and a detection wavelength.
FIG. 8 is an explanatory diagram of conventional QWIP.
FIG. 9 is an explanatory diagram of a correlation between ΔE _C and a detection wavelength.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Multiple quantum well layer 2 Well layer 3 Barrier layer 4 Sublevel 5 Continuous band 6 Contact layer 7 Reflective electrode 8 Infrared 11 Semi-insulating GaAs substrate 12 i-type GaAs buffer layer 13 i-type InGaP layer 14 n ⁺ type GaAs lower contact layer 15 n-type InGaP layer 16 GaAs NSb-based MQW layer 17 n-type GaAs upper contact layer 18 resist pattern 19 recess 20 SiON film 21 contact opening 22 SiON film 23 ohmic electrode 24 Au reflective electrode 25 element isolation groove 26 SiON film 27 Ti / Au Film 28 In bump 29 Antireflection film 31 AlGaAs barrier layer 32 GaAs NSb well layer 33 Ground level 34 Electron 35 Infrared 36 Continuous band 37 Photo-induced current 41 i-type InGaP layer 42 n ⁺ -type GaAs lower contact layer 43 n-type InGaP layer 44 MQW layer 4 n-type GaAs upper contact layer 46 SiON film 47 ohmic electrode 48 Au reflective electrode 49 element isolation trenches 50 Ti / Au film 51 an In bump 52 antireflection film 53 infrared

Claims (5)

As the well layer constituting the multiple quantum well layer, GaAsNSb having a composition such that the energy gap ΔE _c of the conduction band with the barrier layer constituting the multiple quantum well layer is 0.3 eV to 0.5 eV is used. A method of manufacturing a quantum well infrared sensor, comprising: a step of etching the multiple quantum well layer by dry etching using a reactive gas containing Cl when separating the multiple quantum well layer into an array .   2. The method of manufacturing a quantum well infrared sensor according to claim 1, wherein the composition ratio of GaAs NSb is such that the difference in lattice constant with GaAs is 0.1% or less. As the well layer constituting the multiple quantum well layer , GaAsN having a composition such that the energy gap ΔE _c of the conduction band with the barrier layer constituting the multiple quantum well layer is 0.3 eV to 0.5 eV is used. A method of manufacturing a quantum well infrared sensor, comprising: a step of etching the multiple quantum well layer by dry etching using a reactive gas containing Cl when separating the multiple quantum well layer into an array . 4. The quantum well type according to claim ₁ , wherein Al _x Ga _1-x As (0 ≦ x ≦ 1) is used as a barrier layer constituting the multiple quantum well layer. 5. Infrared sensor manufacturing method.   5. The method for manufacturing a quantum well infrared sensor according to claim 1, wherein a diffuse reflection structure is provided in a contact layer in contact with the multiple quantum well layer.

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