JP2017010999A - Solid-state image pickup element and manufacturing method for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an imaging element having small dark current and high sensitivity by enhancing flatness of the interface between an n-type semiconductor layer and a chalcopyrite semiconductor (hereinafter referred to as CIGS) film, etc. when a CIGS film or a crystal selenium film is formed.SOLUTION: A method of manufacturing a solid-state image pickup device in which a CIGS film 2 made of crystal selenium is formed above a signal readout circuit substrate 1 for performing signal readout processing, first forms the CIGS film 2 above a dummy film formation substrate 11 having surface flatness, bonds a front-side surface of the signal reading circuit board 1 to the upper surface of the CIGS film 2 to form a conjugate, next, removes the film-formed substrate 11 from the conjugate, and laminates at least an n-type semiconductor layer 3 and a transparent conductive film 4 in this order on the surface of the conjugate from which the film-forming substrate 11 has been removed, thereby manufacturing a solid-state image pickup device 10.SELECTED DRAWING: Figure 1

Description

The present invention relates to a solid-state imaging device and a method for manufacturing the same, and particularly to a compound semiconductor film having a chalcopyrite structure in a photoelectric conversion portion, such as a CIGS film (Cu and In or Ga or both, S or Se or both, And a manufacturing method thereof.

  In recent years, the resolution of solid-state imaging devices has been increased, and the area of the photoelectric conversion unit has been reduced accordingly, and the problem of a decrease in light receiving sensitivity has become apparent. As a technique for solving this problem, a conventional technique having a structure in which light is irradiated from the back surface of a CMOS solid-state imaging device is known (see Non-Patent Document 1).

  However, the purpose of this method is to increase the arrival rate of light to the photoelectric conversion unit, and it does not exceed the light receiving sensitivity based on the quantum efficiency and light absorption coefficient which are the physical properties of Si used for the material of the photoelectric conversion unit. Can not. Therefore, in order to solve the problem of reduction in light receiving sensitivity due to further higher resolution in the future, it is indispensable to develop a method using a material that exceeds Si in terms of quantum efficiency and light absorption coefficient in the photoelectric conversion unit.

Such materials are mainly classified into organic materials (see Non-Patent Document 2) and inorganic materials. As inorganic materials, CIGS (see Non-Patent Document 3) which is a mixed crystal of CuInSe ₂ and CuGaSe ₂ is used. cSe (see Non-Patent Document 4) is known.

  In particular, the CIGS described above has excellent quantum efficiency, light absorption coefficient, and stability, and is expected as a material for a photoelectric conversion part of a future solid-state imaging device. Even when the film thickness is thin, light can be sufficiently absorbed, so that a high internal electric field can be applied even when the applied voltage is low. This enables carrier multiplication operation in the film, resulting in higher sensitivity. Application of CIGS to a solid-state imaging device was proposed in 1993 (see Non-Patent Document 5), and research into practical application is currently underway for applications in vehicles, crime prevention, and biometric authentication (Non-Patent Document 5). Reference 6).

A solid-state imaging device using CIGS and a manufacturing method thereof according to the prior art will be described with reference to FIG.
For example, as shown in FIG. 4B, the image pickup element is provided with a CIGS film 102 on a substrate 101 provided with a signal readout circuit composed of CMOS, and further includes an n-type semiconductor layer 103 and a transparent conductive film. (ITO layer) 104 is provided.

  Further, the manufacturing method of the solid-state imaging device according to the prior art is, for example, a method of manufacturing in the order of FIGS. 4A and 4B, and on the signal readout circuit substrate 101 on which the signal readout circuit is formed, The CIGS film 102 is formed by sputtering or vapor deposition, and then the n-type semiconductor layer 103 and the transparent conductive film 104 are sequentially formed by sputtering or vapor deposition.

S. Iwabuchi, Y. Maruyama, Y. Ohgishi, M. Muramatsu, N. Karasawa and T. Hirayama, ISSCC 2006 Dig. Tech. Papers, 1171 (2006). Hayashi, Masayuki, Eijiho Technical Report, 37 (40), 5 (2013). Kenji Kikuchi, S. Imura, K. Miyakawa, H. Ohtake, M. Kubota and E. Ohta, Sensors and Acutuators A: Physical, 224, 24 (2015). S. Imura, K. Kikuchi, K. Miyakawa, H. Ohtake and M. Kubota, Appl. Phys. Lett. 104, 242101 (2014). K. Tanaka, M. Kosugi, F. Ando, T. Ushiki, H. Usui and K. Sato, Jpn. J. Appl. Phys., 32 (32-33), 113 (1993). O.Matsushima, K.Miyazaki, M.Takaoka, T.Maekawa, H.Sekiguchi, H.Fuchikami, M.Moriwake, H.Takasu, S.Ishizuka, K.Sakurai, A. Yamada, and S.Niki, IEDM Tech.Dig., 267 (2008).

However, the surface planarity of the chalcopyrite semiconductor film such as CIGS or the cSe film formed is not good. Figure 2 shows a scanning electron microscope (SEM).
(FIG. 2 shows the state of the CIGS film according to the embodiment of the present invention, but the CIGS film according to the prior art is also in the same state) is there). As is clear from FIGS. 2A and 2B, the CIGS film 102 is a polycrystalline film, and since fine grains are aggregated, the planarity on the film surface is low.
For this reason, the planarity of the interface between the CIGS film 102 (or a p-type semiconductor layer such as a cSe film) and the n-type semiconductor layer 103 also decreases due to the unevenness of the CIGS film 102 serving as a base, and the CIGS film Large irregularities exist at the pn interface of the pn junction photodiode formed by the n-type semiconductor layer 103 and the n-type semiconductor layer 103. As a result, the photodiode characteristics such as the dark current value and the sensitivity are greatly deteriorated.
Note that it is conceivable that the surface roughness of the CIGS film 102 is improved by directly cutting the irregularities on the surface of the CIGS film 102. In this case, however, the photoelectric conversion surface is cracked and the photoelectric conversion characteristics are greatly improved. It will deteriorate.

  The present invention has been made to solve these problems. When a chalcopyrite semiconductor such as CIGS or crystalline selenium (hereinafter referred to as a CIGS film or the like) is formed, the CIGS film or the like and the n-type are formed. It is an object of the present invention to provide a solid-state imaging device capable of realizing an imaging device with high darkness and high sensitivity by improving the planarity of the interface of the semiconductor layer, and a manufacturing method thereof.

In order to achieve the above object, the solid-state imaging device and the manufacturing method thereof of the present invention are configured as follows.
That is, the manufacturing method of the solid-state imaging device of the present invention,
In a method for manufacturing a solid-state imaging device, a p-type semiconductor layer made of chalcopyrite semiconductor or crystalline selenium is formed above a signal readout circuit board provided with a signal readout circuit section for performing signal readout processing.
First, the p-type semiconductor layer is formed on the upper surface of a dummy base body having surface flatness, and the surface of the signal readout circuit board is bonded to the upper surface of the p-type semiconductor layer to form a bonded body. Forming,
Next, the base body is removed from the joined body, and at least an n-type semiconductor layer and a transparent conductive film are stacked in this order on the surface of the joined body on which the removed base body is in contact. A solid-state imaging device is manufactured.

Moreover, it is preferable that the chalcopyrite semiconductor constituting the p-type semiconductor layer is made of CIGS (a compound semiconductor containing Cu and / or In and / or Ga and / or S and / or Se).
The base body is preferably made of a material selected from Si, Ge, sapphire, and glass.

Further, in the step of removing the base body from the joined body, a first grinding stage in which the speed of cutting the base body in the thickness direction is high and a second grinding stage in which the speed of cutting the base body in the thickness direction is low. It is preferable to carry out in order.
Further, in the step of bonding the front side surface of the signal readout circuit substrate provided with the signal readout circuit unit to the upper surface of the p-type semiconductor layer, a planarization process is performed on the upper surface of the p-type semiconductor layer as a pretreatment. Is preferred.

Furthermore, a solid-state imaging device manufactured by any one of the above-described solid-state imaging device manufacturing method,
Above the signal readout circuit board, at least a p-type semiconductor layer made of chalcopyrite semiconductor or crystalline selenium, an n-type semiconductor layer and a transparent conductive film are provided in this order,
The flatness (average surface roughness) of the interface between the p-type semiconductor layer and the n-type semiconductor layer is 5 nm or less.
The solid-state image sensor can be a CMOS.

  When forming a p-type semiconductor layer that is a photoelectric conversion film, particularly a CIGS film, in the manufacturing process of a solid-state imaging device, when trying to form a CIGS film or the like above a signal readout circuit board (especially a CMOS substrate) The signal circuit portion attached to the semiconductor substrate is damaged by heat during the film forming process of the CIGS film or the like.

Therefore, in the manufacturing method of the solid-state imaging device of the present invention, the film transfer technology (Layer Transfer technology)
) Is used to solve such problems.

  In other words, this film transfer technology forms a high-quality CIGS film on a dummy substrate that can be subjected to a high temperature by applying a sufficiently high temperature and reads the original signal on the CIGS film. Since the circuit board is bonded and the dummy board is removed thereafter, it is possible to avoid a situation in which the signal circuit portion attached to the board is damaged by the heat during the film forming process of the CIGS film or the like.

It is a figure which shows the manufacturing method of the solid-state image sensor which concerns on embodiment of this invention. It is an electron micrograph which shows the state of the surface (A) and cross section (B) of the CIGS film | membrane of the solid-state image sensor which concerns on embodiment of this invention. It is a graph which shows the evaporation amount of each vapor deposition substance in a vapor deposition process in each process of small process ad. It is a figure which shows the manufacturing method of the solid-state image sensor concerning a prior art.

Hereinafter, a solid-state imaging device and a manufacturing method thereof according to an embodiment of the present invention will be described with reference to the drawings.
First, a solid-state imaging device according to an embodiment and a manufacturing method thereof will be described with reference to FIG.

<Embodiment>
As shown in FIG. 1D, the solid-state imaging device 10 according to the present embodiment includes a signal readout circuit substrate 1 provided with a signal readout circuit unit, a CIGS film (p-type semiconductor layer) 2, an n-type semiconductor layer 3, and The transparent conductive film 4 is laminated in this order.

Here, a voltage is applied to the CIGS film 2 between the back electrode and the transparent electrode of the solid-state imaging device 10.
CIGS is included in the chalcopyrite semiconductor _{(e.g., CuIn 1-x Ga x Se} 1-y S y , etc.),
In the present invention, the same effect can be obtained even if it is replaced by crystalline selenium (hereinafter referred to as cSe). Here, _x in CuIn _1-x Ga _x Se _1-y S _y is 0 to 1 (0 ≦ x ≦ 1), and y is 0 to 1.
It can take a value within the range of (0 ≦ y ≦ 1).
In the following description, the part described for the CIGS film 2 can be basically replaced with cSe, and the same effect can be obtained.

The n-type semiconductor layer 3 is a layer that blocks (suppresses) the injection of holes from the transparent conductive film 4 to the CIGS film 2. For example, gallium oxide (Ga ₂ O ₃ ), which is a wide-gap n-type semiconductor, is used. Consists of.

  The transparent conductive film 4 is made of, for example, an ITO (Indium Oxide: Sn 10 wt%) film. The ITO film is formed on the n-type semiconductor layer 3 by sputtering or vapor deposition. The transparent conductive film 4 is used as a positive electrode. The transparent conductive film 4 may be another metal thin film such as a thin film made of gold.

Next, each step of FIGS. 1A to 1D is a step that is sequentially performed in order to manufacture such a solid-state imaging device 10. It is shown.
This manufacturing method will be conceptually described. A CIGS film 2 is formed on a film-forming substrate 11 with good flatness, and the surface of the signal readout circuit substrate 1 is bonded onto the CIGS film 2, and the film is formed in this state. The dark current can be reduced by using the surface of the CIGS film 2 with good flatness, which is peeled off from the substrate 11 and in contact with the film formation substrate 11, as a base for forming the n-type semiconductor layer 3. In addition, the solid-state imaging device 10 having high sensitivity can be obtained.

The average surface roughness Ra of the polycrystalline thin film of CIGS or cSe is, for example, several tens of nanometers, and the planarity can be improved by adding a predetermined additive, but the average surface roughness Ra is still It can only be as small as 8 nm.
On the other hand, the average surface roughness Ra of the flat glass substrate is, for example, 0.1 to 0.2 nm (such as EAGLE-XG manufactured by Corning), and at least according to the manufacturing method of this example using this as an underlayer, The average surface roughness Ra can be 5 nm or less. Furthermore, the average surface roughness Ra is considered to be 1 nm or less, for example.

(1) Step 1
First, a film-forming substrate 11 having good flatness made of Si, Ge, sapphire, glass or the like is prepared as a dummy substrate. For example, a substrate having a substrate size of 4 inches square and a thickness of 400 μm can be used. Since the dummy substrate is finally removed, the impurity concentration and p-type / n
Content conditions such as any of the types are unquestioned.

  Next, the CIGS film 2 included in the chalcopyrite semiconductor can be formed on the film formation substrate 11 by, for example, multi-source deposition (such as a three-step method) or sputtering, and the film thickness is, for example, , About 0.2 to 3 μm.

An example of the vapor deposition process when CIGS (film thickness 1μm) is formed by the multi-source vapor deposition method described above is shown in FIG.
Shown in
That is, the multi-source deposition method is a method in which each material of Cu, In, Ga, and Se is individually filled in a crucible, heated and evaporated to form a film on a substrate.

In this multi-source vapor deposition method, the substrate temperature is set to 350 to 400 ° C. in the small step a (initiated by opening the shutter of the vapor deposition flow) in this step 1, and In, Ga, and Se (crucible temperature) Irradiates the deposition substrate 11 with a deposition flow of 880 ° C. for In, 1000 ° C. for Ga, and 210 ° C. for Se for 12 minutes.
Next, in the small step b, the deposition temperature of Cu and Se (crucible temperature is 1150 ° C. for Cu and 210 ° C. for Se) is irradiated for 8 minutes while raising the substrate temperature to 450 ° C.
Next, in a small step c, the vapor deposition flow of In, Ga, and Se (crucible temperature is 860 ° C. for In, 975 ° C. for Ga, and 210 ° C. for Se) is irradiated again for 2 minutes.
Finally, in the small step d (finished by the operation of closing the deposition flow shutter), the deposition flow of Se (crucible temperature Se 170 ° C.) is continued for about 30 minutes while lowering the substrate temperature to 200 ° C. or less. Irradiate.

  In the CIGS film 2 formed in this way, as shown in FIG. 1A, the surface formed on the film formation substrate 11 (the upper surface in FIG. 1A) is uneven. However, the surface on the opposite side of the CIGS film 2 (the lower surface in FIG. 1A: the interface on the film formation substrate 11 side) is a transfer of the good flatness of the surface of the film formation substrate 11 and is high. It has flatness.

(2) Step 2
Next, as shown in FIG. 1B, the CIGS film 2 is bonded to a signal readout circuit board 1 provided with a signal readout circuit. At this time, it is desirable to planarize the surface of the CIGS film 2 in order to improve the bonding strength between the CIGS film 2 and the signal readout circuit board 1. As the planarization treatment, plasma treatment using a rare gas such as Ar, Kr, or Xe, ion beam treatment, high-speed atomic beam treatment, buff polishing, CMP, or the like can be used. For example, when the planarization process is performed by plasma treatment using Ar gas, the surface can be planarized by performing the process for 10 minutes or more under the conditions of power of RF300W, pressure of 60Pa, and flow rate of 100sccm.

  When the CIGS film 2 and the signal readout circuit board 1 are joined, the surfaces of the CIGS film 2 and the signal readout circuit board 1 are opposed to each other using a pressurizing device or the like. Pressurize. At this time, in order to improve the bonding strength, it is preferable to apply a pressure of at least 1 MPa, preferably 5 MPa or more.

Next, it heats in the state which applied the said pressurization. The heating temperature is at least 100 ° C. or higher, desirably 200 ° C. or higher. However, in order not to deteriorate the performance of the signal readout circuit due to heating,
It is necessary to set the heating temperature to 400 ° C. or lower.
The pressurizing time is at least 5 minutes or more, preferably 60 minutes or more.

(3) Process 3
Next, as illustrated in FIG. 1C, the film formation substrate 11 is removed from the bonded body in which the CIGS film 2 and the signal readout circuit substrate 1 are bonded. For removal of the film formation substrate 11, an appropriate one of various mechanical or chemical methods can be selected and used according to the material constituting the film formation substrate 11. For example, in the case of using Si as a material of the deposition substrate 11, it can be carried out using an etching by grinding and XeF ₂ with a diamond wheel.

In the grinding process, it is preferable to perform two-stage grinding in order to reduce damage to the joint.
That is, in the first grinding process, for example, grinding is performed at a wheel rotation speed of 3000 rpm and a grinding speed of 5 μm / sec. When the remaining thickness of the film formation substrate 11 becomes 100 μm or less, the grinding is stopped.

Next, in the second grinding process, the number of revolutions is maintained in the state of the first grinding process, the grinding speed is reduced to 0.5 μm / sec, and the remaining thickness of the film formation substrate 11 is 30 μm. Stop grinding when the level is reached. In this way, when the substrate is ground until the substrate thickness is considerably reduced, the two-step grinding is used to reduce the grinding speed, so that the grinding time is shortened and the grinding is excessively caused to damage the joint portion. The fear can be prevented.

Next, the remaining film formation substrate 11 is completely removed using XeF ₂ . Since XeF ₂ has a very large selection ratio with respect to the CIGS film and the cSe film, the situation where the CIGS film 2 is etched even if the Si deposition substrate 11 made of XeF ₂ is removed is prevented. Can do.
For example, in the case of a Si substrate having a substrate size of 20 mm square and a thickness of 30 μm, the Si substrate can be completely removed by repeating the etching cycle of 30 sec 75 times with a pressure of 400 Pa.

(4) Step 4
Next, as shown in FIG. 1D, an n-type semiconductor layer 3 and a transparent conductive film 4 are formed on the CIGS film 2.
The n-type semiconductor layer 3 has a function of preventing (suppressing) injection of holes from the transparent conductive film 4 to the CIGS film 2, for example, gallium oxide (Ga ₂ O ₃ ) which is a wide gap n-type semiconductor. Consists of. Ga ₂ O ₃ is used as a target material, and a film is formed by sputtering. The substrate temperature in film formation 400 ° C. from room temperature, the oxygen partial pressure P _D, 0 Pa <preferably set to P _D <1 Pa, the range of.

The transparent conductive film 4 is made of, for example, an ITO (Indium Oxide: Sn 10 wt%) film. The transparent conductive film 4 is formed on the n-type semiconductor layer 3 by sputtering or vapor deposition.
The transparent conductive film 4 is used as a positive electrode. Further, as the transparent conductive film 4, other metal thin films such as a gold thin film can be used.

  The solid-state imaging device 10 manufactured in this way can be provided with the characteristics that the dark current is small and the sensitivity is high.

<Modification>
The solid-state imaging device and the manufacturing method thereof according to the present invention are not limited to those of the above-described embodiment, and various other modes can be changed. For example, in the above embodiment, the CIGS film 2 (or cSe layer), the n-type semiconductor layer 3 and the transparent conductive film 4 are provided in this order above the signal readout circuit board 1. Further, another layer may be provided between the n-type semiconductor layer 3 and the transparent conductive film 4 or above the transparent conductive film 4. Further, the n-type semiconductor layer 3 may include a buffer layer.

Further, the film formation substrate 11 may not be made of Si but is preferably removable by etching.
As the film formation substrate 11, as described above, the film formation substrate 11 having good flatness made of Si, Ge, sapphire, glass, or the like can be used. The whole of the film formed by sputtering or the like of metal such as high-quality Si or Al may be handled as a dummy substrate. However, it is necessary that the entire surface formed by depositing a metal such as amorphous Si or Al has a good flatness on the film formation surface.
In this case, the entire metal film such as amorphous Si or Al formed on the surface of the film formation substrate 11 is peeled off from the CIGS film 2 (or cSe layer) as a dummy substrate.

  The electrode attached to the signal readout circuit board 1 has an advantage that it is not oxidized if it is an Au electrode, but other electrodes such as an In electrode can also be used.

1, 101 Signal reading circuit board 2, 102 CIGS film (p-type semiconductor layer)
3, 103 n-type semiconductor layer 4, 104 transparent conductive film 11 deposition substrate

Claims (7)

In a method for manufacturing a solid-state imaging device, a p-type semiconductor layer made of chalcopyrite semiconductor or crystalline selenium is formed above a signal readout circuit board provided with a signal readout circuit section for performing signal readout processing.
First, the p-type semiconductor layer is formed on the upper surface of a dummy base body having surface flatness, and the surface of the signal readout circuit board is bonded to the upper surface of the p-type semiconductor layer to form a bonded body. Forming,
Next, the base body is removed from the joined body, and at least an n-type semiconductor layer and a transparent conductive film are stacked in this order on the surface of the joined body on which the removed base body is in contact. A method of manufacturing a solid-state image sensor, comprising producing a solid-state image sensor.   The chalcopyrite semiconductor constituting the p-type semiconductor layer is made of CIGS (a compound semiconductor containing Cu and / or In and / or Ga, and / or S and / or Se). A method for producing a solid-state imaging device according to 1.   The method of manufacturing a solid-state imaging device according to claim 1, wherein the base body is made of a material selected from Si, Ge, sapphire, and glass.   In the step of removing the base body from the joined body, a first grinding stage in which the base body is sharpened in the thickness direction and a second grinding stage in which the base body is shaved in the thickness direction are performed in this order. The manufacturing method of the solid-state image sensor of any one of Claims 1-3 characterized by the above-mentioned.   5. The planarization process is performed on the upper surface of the p-type semiconductor layer as a pretreatment in the step of bonding the upper surface of the signal readout circuit board to the upper surface of the p-type semiconductor layer. The manufacturing method of the solid-state image sensor of any one of these. A solid-state imaging device manufactured by the method for manufacturing a solid-state imaging device according to any one of claims 1 to 5,
Above the signal readout circuit board, at least a p-type semiconductor layer made of chalcopyrite semiconductor or crystalline selenium, an n-type semiconductor layer and a transparent conductive film are provided in this order,
A solid-state imaging device, wherein flatness (average surface roughness) of an interface between the p-type semiconductor layer and the n-type semiconductor layer is 5 nm or less. The solid-state imaging device according to claim 6, comprising a CMOS.