JP4195556B2 - Photoelectric conversion film manufacturing method, photoelectric conversion film manufacturing apparatus, and imaging device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing a photoelectric conversion film, a photoelectric conversion film manufacturing apparatus, and an image sensor that are used in a solid-state image sensor such as a charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS) image sensor.
[0002]
[Prior art]
As a photoelectric conversion film of a conventional ultra-high sensitivity television camera, “High-sensitivity HARP tube using avalanche multiplication a-Se photoconductive film” (TV magazine, Tanioka, Yamazaki, Shitara, Taketoshi, Kawamura, Hirai Takasaki, Kumouchi: Vol. 44, No. 8, pp. 1074-1083 (1990).), Mainly amorphous selenium (a-Se) has been used. The amorphous selenium photoelectric conversion film has a small dark current, and a quantum efficiency exceeding 1 is achieved by avalanche multiplication of a signal charge generated by applying a high electric field. This photoelectric conversion film is called a HARP (High-gain Avalanche Rushing amorphous Photoconductor) film, and a high-sensitivity HARP image pickup tube camera using this HARP film has been realized.
[0003]
Here, in order to realize a more compact and robust high-sensitivity camera using a HARP film, it is necessary to solidify the HARP imaging tube. To that end, the charge is multiplied at a lower voltage than that of amorphous selenium. A new photoelectric conversion film that can be used is required.
[0004]
For example, in Japanese Patent Laid-Open No. 2001-007381, a photoelectric conversion film made of silicon crystal grains (silicon nanocrystals) having a diameter of several nanometers whose silicon surface is covered with an insulating film such as a silicon oxide film is manufactured. This film is expected to be a high-sensitivity photoelectric conversion film because the nanocrystal is composed of single-crystal silicon with a high “impact ionization rate” that is an index of the probability of avalanche multiplication more easily than amorphous selenium. . In addition, according to Appl. Surf. Sci. 146, 371 (1999). (N. Koshida, X. Sheng, and, T. Komoda), in silicon nanocrystals, charges are nano-wired while tunneling through the silicon oxide film repeatedly. It is known that the electric charge eventually becomes a high energy state because it conducts ballistically without being scattered in the crystal. For this reason, in the silicon nanocrystal film, charge avalanche multiplication may occur at a lower voltage than the silicon single crystal.
[0005]
Here, a photoelectric conversion film manufactured by using the method for manufacturing a silicon nanocrystal film proposed in Japanese Patent Laid-Open No. 2001-007381 will be described with reference to the drawings.
[0006]
FIG. 1 is a cross-sectional view of an example of a conventional photoelectric conversion film using silicon nanocrystals.
[0007]
In FIG. 1, a silicon oxide film is formed on a silicon substrate, and silicon nanocrystals covered with the silicon oxide film are further deposited on the silicon oxide film.
[0008]
In FIG. 1, signal charges generated by an electric field are sent to a silicon substrate while tunneling between adjacent silicon nanocrystals through silicon nanocrystals covered with a silicon oxide film.
[0009]
[Problems to be solved by the invention]
However, in the method for producing a silicon nanocrystal film proposed in Japanese Patent Laid-Open No. 2001-007381, the arrangement of silicon nanocrystals in the film thickness direction is disordered as shown in FIG. Therefore, the photogenerated signal charge must be conducted while tunneling between adjacent silicon nanocrystals arranged randomly. For this reason, there is a problem that the external extraction efficiency of the signal charge is poor. In addition, if the arrangement of the silicon nanocrystals is disordered, there may be a large variation in the distance between the silicon nanocrystals.
[0010]
The present invention has been made in view of the above points, and is a method for producing a photoelectric conversion film characterized by improving the external extraction efficiency of signal charges and reducing the avalanche multiplication starting voltage of signal charges An object of the present invention is to provide an imaging device.
[0011]
[Means for Solving the Problems]
In order to solve the above problems, the present invention employs means for solving the problems having the following characteristics.
[0012]
According to a first aspect of the present invention, in a photoelectric conversion film manufacturing method for manufacturing a photoelectric conversion film having a silicon crystal, an insulating film such as a silicon oxide film having a thickness capable of tunneling a signal charge on a silicon substrate. A silicon crystal film is formed using the covered silicon single crystal grains, and the silicon oxide film on the surface of the silicon single crystal grains is terminated with Si—OH bonds , and the silicon single crystal grains are formed. To function as a crystal nucleus generation site of a crystal grain, and form a silicon single crystal grain to be deposited next so as to come into contact with one silicon single crystal grain among a plurality of silicon single crystal grains already deposited. Thus, a film in which silicon single crystal grains are aligned and arranged in the film thickness direction is manufactured.
[0013]
According to the first aspect of the present invention, it is possible to improve the external extraction efficiency of signal charges and reduce the avalanche multiplication starting voltage of signal charges. Further, since the silicon crystal grains can be aligned in the film thickness direction, variation in the distance between the silicon crystals can be reduced, and charges can be conducted efficiently.
[0016]
According to a second aspect of the present invention, in the formation step, the silicon substrate is thermally oxidized at a high temperature, and the surface of the silicon single crystal grains is thermally oxidized at a low temperature, and then the sample is held in the atmosphere of air, water vapor or hydrogen radical. The silicon crystal grains are aligned in the film thickness direction by terminating a predetermined silicon oxide film on the surface of the silicon single crystal grains with a Si—OH bond.
[0017]
According to the second aspect of the invention, since the silicon crystal grains can be aligned in the film thickness direction, variation in the distance between the silicon crystals can be reduced, and charges can be conducted efficiently.
[0018]
The invention described in claim 3 is characterized in that, in the forming step, an additional band offset is formed in the signal charge traveling direction by controlling the size of the silicon single crystal grains.
[0019]
According to the third aspect of the invention, impact ionization is more likely to occur, and the avalanche multiplication start voltage of the silicon crystal film can be reduced.
[0020]
According to a fourth aspect of the present invention, in a photoelectric conversion film manufacturing apparatus for manufacturing a photoelectric conversion film having a silicon crystal, an insulating film such as a silicon oxide film having a thickness capable of tunneling a signal charge on a silicon substrate. A silicon crystal film is formed by using the covered silicon single crystal grains, and the formation section terminates the silicon oxide film on the surface of the silicon single crystal grains with Si—OH bonds, and these are formed on the silicon single crystal grains. To function as a crystal nucleus generation site of a crystal grain, and form a silicon single crystal grain to be deposited next so as to come into contact with one silicon single crystal grain among a plurality of silicon single crystal grains already deposited. Thus, a film in which silicon single crystal grains are aligned and arranged in the film thickness direction is manufactured.
[0022]
According to a fifth aspect of the invention, in the formation portion, the silicon substrate is thermally oxidized at a high temperature, and the surface of the silicon single crystal grains is thermally oxidized at a low temperature, and then the sample is held in an atmosphere of air, water vapor, or hydrogen radical. The silicon crystal grains are aligned in the film thickness direction by terminating a predetermined silicon oxide film on the surface of the silicon single crystal grains with a Si—OH bond.
[0023]
The invention described in claim 6 is characterized in that, in the forming portion, an additional band offset is formed in the traveling direction of the signal charge by controlling the size of the silicon single crystal grain.
[0024]
According to the invention described in claims 4 to 6 , it is possible to provide a photoelectric conversion film manufacturing apparatus suitable for the photoelectric conversion film manufacturing method according to any one of claims 1 to 3 .
[0025]
The invention described in claim 7 is an image pickup device using a photoelectric conversion film manufactured by the photoelectric conversion film manufacturing apparatus according to any one of claims 4 to 6 .
[0026]
DETAILED DESCRIPTION OF THE INVENTION
The present invention makes it possible to efficiently conduct and accelerate photogenerated signal charges by an external electric field by arranging silicon crystal grains (silicon crystals) whose surfaces are covered with a silicon oxide film in alignment in the film thickness direction. Thus, the main objective is to improve the external extraction efficiency of the signal charge and to reduce the avalanche multiplication start voltage of the signal charge.
[0027]
Next, embodiments of the present invention will be described with reference to the drawings.
[0028]
FIG. 2 is a diagram of an example of a process for producing a silicon nanocrystal film in the present invention.
[0029]
In FIG. 2, after cleaning the single crystal silicon substrate first, a silicon oxide film having a thickness of about 1 nm capable of charge tunneling conduction is formed on the silicon substrate surface by high temperature thermal oxidation at about 1000 ° C. ((1)) . Next, a silicon nanocrystal is produced on this ((2)). Silicon nanocrystals can be produced using a low pressure chemical vapor deposition (LP-CVD) method. In this method, silicon nanocrystals are formed in a self-organized manner on the silicon oxide film by stopping the supply of silane gas as a deposition material at the initial stage of silicon film deposition. Thereafter, the surface of the silicon nanocrystal is thermally oxidized in an oxygen atmosphere at a temperature lower than the oxidation temperature of the substrate surface (for example, about 600 ° C.) to form a silicon oxide film of about 1 nm ((3)).
[0030]
Next, when the sample is held in the atmosphere of air, water vapor, or hydrogen radical, only the silicon oxide film on the surface of the silicon nanocrystal formed at a low temperature becomes the Si—OH bond termination (4). According to Mat. Res. Soc. Symp. Proc. 452, 234 (1997). (K. Nakagawa, M. Fukuda, S. Miyazaki and M. Hirose) It is known to function as an outbreak site. Therefore, when silicon nanocrystals are deposited again by LP-CVD, silicon nanocrystals are not formed on the silicon oxide film that has been thermally oxidized at high temperature, but nanocrystals are formed only on silicon nanocrystals that have been thermally oxidized at low temperature. Will be. As a result, the silicon nanocrystals are aligned in the film thickness direction ((5)).
[0031]
By repeating the above processes (3) to (5), a silicon nanocrystal film in which a plurality of silicon nanocrystals are aligned as shown in (6) in FIG. 2 can be produced.
[0032]
FIG. 3 is a diagram of an example of the formed photoelectric conversion film in the present invention.
[0033]
In FIG. 3, compared with FIG. 1 described above, the silicon nanocrystals are aligned in the film thickness direction, so that when the signal charges are tunneled, variation in the distance between the silicon nanocrystals is reduced, and the efficiency is improved. Therefore, the external extraction efficiency of the signal charge can be improved.
[0034]
Here, when the silicon nanocrystal film of FIG. 3 is used as a photoelectric conversion film, when the thickness of the silicon oxide film is 3 nm or more, signal charge tunneling hardly occurs, and thus the quantum conversion efficiency is adversely affected.
[0035]
In addition, when the thickness is 1 nm or less, the quantum confinement effect becomes weak, and it becomes difficult to control the band gap by the crystal size described later. For this reason, the silicon oxide film thickness is desirably 1 to 3 nm.
[0036]
In the manufacturing method described above, the position of the crystal nucleation site of the silicon nanocrystal is controlled by the difference in silicon oxide film formation temperature between the silicon substrate surface and the silicon nanocrystal surface. The lower the thermalization temperature of a silicon oxide film, the easier it is to form Si—OH bonds (functioning as crystal nucleation sites) on the surface of the silicon oxide film, but the oxidation rate becomes extremely slow at 600 ° C. or lower. Therefore, it becomes impractical. Accordingly, the thermal oxidation temperature of the portion where the silicon nanocrystal is to be formed, that is, the surface of the silicon nanocrystal, is about 600 ° C.
[0037]
On the other hand, when the silicon oxide film is heated to about 950 ° C. or higher, it becomes a dense and high-quality film, and the Si—OH bond termination is hardly formed on the surface. Therefore, it is desirable that the oxidation temperature of the portion where the silicon nanocrystal is not formed, that is, the silicon substrate surface, is 950 ° C. or higher.
[0038]
Furthermore, in order to use the silicon nanocrystal film as a photoelectric conversion film, it is necessary to have a sufficient thickness to absorb light. In the experiments so far, photoelectric conversion characteristics have been obtained with samples having 15 or more layers of silicon nanocrystals, but a thickness of 1 micron (μm) or more is desirable in order to obtain sufficient light absorption characteristics. .
[0039]
Next, an embodiment using the present invention will be described with reference to the drawings.
[0040]
FIG. 4 is a diagram of an example of a photoelectric conversion film using the present invention.
[0041]
In FIG. 4, the photoelectric conversion film includes an Al electrode 40, a heavily doped n-type c-Si substrate (n ⁺ layer) 41, silicon carbide (a-SiC _x : O) (n-type) 42, silicon The nanocrystal film 43, a hydrogenated amorphous silicon carbide (p-type) 44, and a transparent electrode 45 are formed. The wide band gap silicon carbide (a-SiC _X : O) 42 to which an n-type impurity is added as a hole blocking layer may be silicon oxide (SiO _X N _Y ), SiO ₂ or the like.
[0042]
In FIG. 4, a wide band gap silicon carbide (a-SiC _X : O) in which an n-type impurity is added as a hole blocking layer on a heavily doped n-type c-Si substrate (n ⁺ layer) 41 ( n-type) 42 is formed, and an additive-free silicon nanocrystal film 43 is formed thereon as a photoelectric conversion layer. Here, in order to give sensitivity to the visible light region, the silicon nanocrystal film 43 has a band gap of 1.7 eV or more (the silicon nanosize corresponds to 10 nm or less), which is the same as that of hydrogenated amorphous silicon. desirable. Further, a hydrogenated amorphous silicon carbide layer added with a p-type impurity as an electron blocking layer is formed thereon (the composition ratio is adjusted so that the band gap is about 2.5 eV which is a value capable of transmitting visible light) 44. Finally, an ITO film is formed as the transparent electrode 45.
[0043]
Here, the silicon nanocrystal has a feature that an optical bandgap can be controlled by its size. For example, it is known that when the silicon nanocrystal size is changed from 10 nm to 1 nm, the optical band gap changes from about 1.7 eV to about 2.6 eV.
[0044]
In the silicon nanocrystal production method of the present invention, the silicon nanocrystal size can be easily controlled by appropriately adjusting the deposition time and deposition temperature of the silicon nanocrystal.
[0045]
Therefore, as described in Japanese Patent Application Laid-Open No. 2001-007381, the band gap of the silicon nanocrystal is increased by a gradient by controlling the crystal size, and then the band gap is reduced by abruptly reducing the band gap. It can be formed in the thickness (electric field) direction.
[0046]
The above example will be described with reference to the drawings.
[0047]
FIG. 5 is an example of a nanosilicon layer having an energy band structure inclined in the film thickness direction.
[0048]
In the structure of FIG. 5, the size of the silicon nanocrystals is sequentially reduced from the light incident side (about 10 nm → 6 nm → 3 nm → 1 nm) and the band gap is increased in a tilted manner, and then the silicon nanocrystal size is increased again. By sequentially reducing the size, a large offset is formed in the conduction band edge energy between adjacent silicon nanocrystals.
[0049]
Since the traveling signal charges (electrons) can acquire additional energy corresponding to the conduction band offset at a point where the band gap suddenly decreases, impact ionization is more likely to occur. As a result, the avalanche multiplication starting voltage of the silicon nanocrystal film is further reduced.
[0050]
Here, FIG. 6 shows an example of the silicon nanocrystal film having the energy band structure described above.
[0051]
As shown in FIG. 6, a silicon nanocrystal film composed of silicon nanocrystals aligned in the film thickness direction can conduct and accelerate signal charges more efficiently than a conventional silicon nanocrystal film in which silicon nanocrystals are randomly arranged. Thus, the quantum conversion efficiency of the photoelectric conversion film can be improved, and the avalanche multiplication starting voltage of the signal charge can be reduced.
[0052]
Next, a second embodiment using the present invention will be described with reference to the drawings.
[0053]
FIG. 7 is a diagram of an example of a cold cathode light emitting device using the present invention.
[0054]
The cold cathode light emitting device of FIG. 7 includes an Al electrode 40, a silicon substrate (n ⁺ type) 41, a silicon carbide (n type) 42, a silicon nanocrystal film 43, a fluorescent film 70, and a transparent electrode 45. Is formed.
[0055]
In FIG. 7, since the silicon nanocrystal grains have a size of about 1 to 10 nm, as shown in FIG. 7, when an electric field is applied to the silicon nanocrystal film 43, the silicon nanocrystal grains are aligned at the tips of the silicon nanocrystals aligned in the electric field direction. The electric field is concentrated and electrons are easily released into the vacuum. In silicon nanocrystals, it is known that charges are conducted ballistically, and the energy of emitted electrons increases. Therefore, it is possible to use the low-pressure fluorescent film 70. Also in FIG. 7, since the silicon nanocrystal grains are aligned in the film thickness direction, signal charges can be efficiently conducted / accelerated, so that light can be efficiently emitted through the fluorescent film 70 and the glass substrate 71.
[0056]
Note that an image sensor with higher sensitivity can be provided by using the photoelectric conversion film manufactured in the present invention.
[0057]
【The invention's effect】
As described above, according to the present invention, a photoelectric conversion film manufacturing method, a photoelectric conversion film manufacturing apparatus, and a photoelectric conversion film manufacturing method characterized by improving signal charge external extraction efficiency and reducing the signal charge avalanche multiplication starting voltage, and An imaging device can be provided.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of an example of a conventional photoelectric conversion film using silicon nanocrystals.
FIG. 2 is a diagram showing an example of a production process of a silicon nanocrystal film in the present invention.
FIG. 3 is a diagram of an example of a formed photoelectric conversion film in the present invention.
FIG. 4 is a diagram of an example of a photoelectric conversion film using the present invention.
FIG. 5 is a diagram of an example of a nanosilicon layer having an energy band structure inclined in the film thickness direction.
FIG. 6 is a diagram of an example of a silicon nanocrystal film having an energy band structure inclined in the film thickness direction.
FIG. 7 is a diagram of an example of a cold cathode light emitting device using the present invention.
[Explanation of symbols]
40 Al electrode 41 Highly doped n-type c-Si substrate (n ⁺ layer)
42 Silicon Carbide (a-SiC _X : O) (n-type)
43 Silicon nanocrystal film 44 Hydrogenated amorphous silicon carbide (p-type)
45 Transparent electrode 70 Fluorescent film 71 Glass substrate

Claims (7)

In a photoelectric conversion film manufacturing method for manufacturing a photoelectric conversion film having a silicon crystal,
Forming a silicon crystal film using a silicon single crystal grain covered with an insulating film such as a silicon oxide film having a thickness capable of tunneling a signal charge on a silicon substrate;
In the forming step, the silicon oxide film on the surface of the silicon single crystal grains is terminated with Si-OH bonds, and these are made to function as crystal nucleus generation sites of the silicon single crystal grains, and the silicon single crystal grains to be deposited next are already deposited. A film in which silicon single crystal grains are aligned and arranged in the film thickness direction is formed by forming the silicon single crystal grains so as to be in contact with one of the silicon single crystal grains. A method for producing a photoelectric conversion film. In the forming step,
After the silicon substrate is thermally oxidized at a high temperature and the surface of the silicon single crystal grain is thermally oxidized at a low temperature, the sample is held in the atmosphere of air, water vapor or hydrogen radical, and a predetermined silicon oxide film on the surface of the silicon single crystal grain is formed on Si. by -OH coupling end, the photoelectric conversion film manufacturing method according to claim 1, wherein aligning the silicon crystal grains in the thickness direction. In the forming step,
3. The method for producing a photoelectric conversion film according to claim 1, wherein an additional band offset is formed in the traveling direction of the signal charge by controlling the size of the silicon single crystal grains. In a photoelectric conversion film manufacturing apparatus for manufacturing a photoelectric conversion film having a silicon crystal,
Using a silicon single crystal grain covered with an insulating film such as a silicon oxide film having a thickness capable of tunneling a signal charge on a silicon substrate;
The forming unit terminates the silicon oxide film on the surface of the silicon single crystal grain with a Si-OH bond, functions them as a crystal nucleus generation site of the silicon single crystal grain, and already deposits a silicon single crystal grain to be deposited next. A film in which silicon single crystal grains are aligned and arranged in the film thickness direction is formed by forming the silicon single crystal grains so as to be in contact with one of the silicon single crystal grains. A photoelectric conversion film manufacturing apparatus. In the formation part,
After the silicon substrate is thermally oxidized at a high temperature and the surface of the silicon single crystal grain is thermally oxidized at a low temperature, the sample is held in the atmosphere of air, water vapor or hydrogen radical, and a predetermined silicon oxide film on the surface of the silicon single crystal grain is formed on Si. 5. The photoelectric conversion film manufacturing apparatus according to claim 4 , wherein the silicon crystal grains are aligned in the film thickness direction by terminating the —OH bond. In the formation part,
6. The photoelectric conversion film manufacturing apparatus according to claim 4 , wherein an additional band offset is formed in the traveling direction of the signal charge by controlling the size of the silicon single crystal grains. An image sensor using a photoelectric conversion film manufactured by the photoelectric conversion film manufacturing apparatus according to claim 4 .

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