JPH04102372A - Image sensor array - Google Patents

Abstract

PURPOSE:To improve performance by providing a photoconductive film of polycrystalline silicon having N-type impurity concentration, hydrogen concentration and crystal grain diameter of specified values, and a photosensor and a driving circuit consisting of TFT. CONSTITUTION:A photoconductive film of N-type impurity concentration in poly-Si film of 10<16> to 10<20>atoms/cm<3>, hydrogen concentration of 10<19> to 10<22> atoms/cm<3> and crystal grain diameter of 200Angstrom or more, a photosensor consisting of TFT and a driving circuit consisting of TFT are provided. Poly-Si 2 which becomes an active layer of TFT is formed on a quartz substrate 1 and a gate oxide film 3 of TFT is formed through heat oxidation. A gate electrode 4, a poly-Si resistor 32 and a light conducting film 31 are formed and P<+> ion is injected to the film 31. A photoresist 47 is provided, and P<+> ion is injected and activated. An NSG film 5 is formed, hydrogen plasma treatment is carried out and an Al electrode 52 and an Al light screening layer 53 are formed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image sensor array, and particularly to a life-sized image sensor array.

This image sensor is useful as a document reading sensor array for fax machines and the like.

[Prior art]

Photoconductive films using amorphous silicon are well known, but polycrystalline silicon (hereinafter referred to as Poly
-5i) film has a low carrier density;
Due to its low photoconductivity, it is not used as a photoconductive film.

Although the amorphous Si film has high photoconductivity and is advantageous as a photoconductive film, it has low heat resistance. JP-A No. 60-64467), which features an equal-size image sensor array that integrates both the 3i T F T) as a drive circuit section, and P
o1y-5i T FT After the high-temperature process for creating the T section is completed, a photoelectric conversion section made of an amorphous Si film must be manufactured, which unavoidably increases the number of steps.

〔the purpose〕

The present invention aims to increase the light output of the photoconductive film (Patent Application No. 1-138021) proposed by the present inventor, which has a high photoconductivity in the Po1y-5i film, when used as an optical sensor. The purpose is to increase the width and improve performance.

In addition, the present invention provides an optical sensor with improved output and a Po1y
It is an object of the present invention to provide an image sensor array, particularly a 1x image sensor array, which is combined with a drive circuit consisting of -5i TFT.

〔composition〕

Impurities (P, B, As,
etc.), unlike the case of single-crystal Si, if the concentration exceeds a certain level (e'x, 10"atoms/
AI? It is well known that the conductivity increases rapidly in the above cases.

This increase in electrical conductivity is a phenomenon in which carrier density increases exponentially with respect to an increase in impurity concentration, and is a property unique to Po1y-5i based on crystal grain boundaries.

However, as a result of intensive research into the photoconductivity of the Po1y-5i film, the present inventor found that the factors that determine the conductivity characteristics of the Po1y-5i film are the concentration of N-type impurities as impurities, the hydrogen content, and the concentration of the Po1y-3i film. They discovered that the Po1y-5i film can be used as a photoconductive film only when these factors satisfy specific values.

In Japanese Patent Application No. 1-138021, the present inventor proposed that (i) the concentration of 73N-type impurity in the Poly-3i film is 10" to 102a atoms/ci, preferably 1017 to 102a, particularly preferably 10 ” ~1
0” atoms/cnl, (ii) Po1y-
The hydrogen concentration in the 5i film is 10” to 10” atoms/a
7, preferably 5 X 10" to 5 X 10" at
oms/a&.

We have proposed a photoconductive film and an image sensor array using the same, characterized in that the crystal grain size of (ni) Poly-5i is 200 Å or more, preferably SOO-10 μm.

The present inventor further improved the invention of Japanese Patent Application No. 1-138021 and endeavored to improve the optical output, and as a result, the present invention was achieved.

That is, in the present invention, the N-type impurity concentration in the polycrystalline silicon film is 10"-1020 atoms/j, and the hydrogen concentration is 1.
A photoconductive film made of polycrystalline silicon having a crystal grain size of 200 Å or more and a photoconductive film having a crystal grain size of 200 Å or more, and an optical sensor made of a polycrystalline silicon thin film transistor for amplifying its output. The present invention relates to an image sensor array characterized by having a drive circuit made of polycrystalline silicon thin film transistors.

The thickness of the photoconductive film is usually 500 Å or more, and the thicker the film is, the more desirable it is in order to increase the light absorption efficiency.

Among the conditions for the Po1y-5i film in the photoconductive film,
The crystal grain size is the result of evaluation using a transmission electron microscope 1i (TEM), and the concentration of N-type impurities and hydrogen content are the values determined using a secondary ion mass spectrometer (SIMS). .

Hydrogen in the Po1y-5i film in the photoconductive film has the effect of increasing the lifetime of photocarriers and the effect of making the effect of only grain boundaries on photocarriers more apparent.

The crystal grain size is determined based on the change in conductivity with respect to impurity concentration based on the crystal grain boundaries (as long as the change in conductivity with respect to impurity concentration is within a range that shows a tendency specific to Poly-5i, the larger the grain size, the higher the sensitivity to light.

Poly-5i film formation is done by LP-CVD, AP-CVD
It can be produced by any method such as plasma CVD, sputtering, or vacuum evaporation, or by crystallizing amorphous Si or by using a laser beam or an electron beam.
It may also be produced by melt recrystallization of 5i. However, since the crystal grain size and hydrogen content vary depending on the manufacturing method,
Control is required by selecting film forming conditions (temperature, reaction gas, pressure, annealing, etc.) and film forming method.

Next, N-type impurities (P, As) are added to the Po1y-5i film.

etc.), there are two methods for introducing impurities into the film, using a reaction gas or compound containing certain impurities during the film formation process, and a method of introducing impurities after film formation (diffusion, ion implantation, etc.). ).

The concentration of impurities can be controlled by selecting film forming conditions such as the concentration, flow rate, temperature, and pressure of 1 reaction gas when mixed during film forming, and by controlling the concentration of the diffusion source when introduced after film forming. The conditions such as the ion implantation dose, the diffusion temperature, etc. may be selected.

Po1y containing N-type impurity prepared by the above method
The hydrogen content of the -5i film varies significantly depending on its fabrication process. When the hydrogen content is high, hydrogen atoms can be reduced from the Po1y-5i film by annealing at 400° C. or higher.

On the other hand, when the hydrogen content is low, it is introduced into the Po1ySi film by ion implantation, hydrogen plasma treatment, thermal diffusion from a film containing hydrogen (plasma SiN film), or the like.

In the case of ion implantation, a set amount of hydrogen atoms can be introduced into the Po1y-5i film by controlling the dose and implantation energy, but it is necessary to anneal at a temperature of about 400° C. after implantation. When hydrogen plasma treatment is used, the hydrogen content is adjusted by adjusting conditions such as plasma power, heating temperature, and treatment time. In addition, plasma SiN
When hydrogen diffusion from the film is used, the amount of hydrogen in the plasma SiN film and the diffusion conditions (temperature, time, etc.)
Control the hydrogen content of the y-5i film.

〔Example〕

This will be explained in detail below using examples.

Production example (1) Poly-
5i film is formed. The film forming conditions were a temperature of 630° C., a reaction gas of SiH, 145 sec, a pressure of 0.12 Torr, and a film thickness of 2000 mm. This Po1y-5i film was implanted with P'''' ions at a varying dose at an energy of 60 keVIL, and P+ ions were implanted at a dose of I x 10''1 ons/ci into the region where a coplanar electrode for evaluation was to be formed later. conduct and activate (9oO℃, 3
0 minutes in N2 atmosphere). Po1y after activation
-5i had a grain size of 500.

Next, 3000 NSG films were stacked on the Po1y-5i film, and hydrogen plasma treatment was performed. NSG film is Po1y
This is to prevent plasma damage to the -5i film, and the LP-CVD method (temperature 430°C1C15iH4
80se, 02120SCCII, pressure 0.2 Torr
) was used to form a film. Hydrogen plasma treatment uses Rf power
1,611/a#, temperature 350℃, H2100sec+
++, and the pressure was 0.5 Torr. Po1y-
The amount of hydrogen in the 5i film was 2×10” atoms #j.

After hydrogen plasma treatment, the NSG film was removed, an AQ coplanar electrode was formed, and dark conductivity and photoconductivity were evaluated. In evaluating photoconductivity, light was irradiated from above the Poly-5i film, the wavelength was 550 nm, and the light intensity was 500 μw/d.
It is.

Figure 1 shows the evaluation results.

It can be seen that the photoconductivity is about two orders of magnitude larger than the dark conductivity in the range of phosphorus concentration from 5×10 17 to 10” atoms/al.

From the above, it can be seen that the photoconductivity of the Po1y-5i film is significantly improved by controlling the phosphorus concentration in the film.

(2) Three types of Po1y-5i films A, B, on a quartz substrate,
form C.

Po1y-5illA was produced under the same conditions as production example (1).
The film was formed by the P-CVD method. Po1y-
5i film B was formed from amorphous Si by the LP-CVD method.

It was crystallized by thermal annealing at 600° C. for 10 hours. At this time, the film forming conditions for amorphous Si are at a temperature of 5
40°C, reaction gas Si8.200sec, pressure 0.
It is 2 Torr. Poly-5i [C is Poly-
The 5i film A was made amorphous by implanting Si''' ions, and then recrystallized by thermal annealing at 600°C for 50 hours.
eV 2.5X101Sions/cd and 130keV
The test was carried out under the conditions of 2.5 x 101sions/ad.

Next, P0 ion implantation, activation, NSC film lamination, hydrogen plasma treatment, and electrode formation were performed on these Po1y-5i films A, B, and C under the same conditions as in Production Example (1).

Po1y-5ill A, B examined after activation
, each grain size of C is 500 and 2800, respectively.
1.0. It was um.

FIG. 2 shows the relationship between phosphorus concentration and (photoconductivity)/(dark conductivity) for each Po1y-5i film.

It can be seen that the larger the crystal grain size of the Po1y-5i film is, the larger the maximum value of (photoconductivity) dark conductivity) is, and the photoconductivity is improved.

(3) In the sample preparation process of production example (1), instead of hydrogen plasma treatment, H" ion implantation and activation (380°C, 30 minutes) were performed at varying doses to prepare the sample. did.

The photoconductivity with respect to the hydrogen concentration in the Po1y-5i film was determined first.
Shown in the table. It can be seen that the photoconductivity changes depending on the hydrogen concentration.

(Margin below) Table 1 Example 1 Figure 3 shows the wiring diagram of the image sensor of this example. The sensor section is made of Po1y-5i photoconductive film 31. Po1y-5i
It is composed of a low resistance 32 and an Nch-TF T 33.

This configuration is such that the gate voltage of the Nch-T F T 33 changes as the resistance value of the Po1y-5i photoconductive film 31 changes depending on the light intensity. Therefore, depending on the light intensity, Nch-T
The drive circuit part where the output of FT33 changes is Nch-TPT.
It is composed of an analog switch 34 and a shift register section 35.

An image sensor array was fabricated using the above basic circuit.

The manufacturing process of this image sensor array will be described below.

FIG. 4 shows the manufacturing process using one cross section of the image sensor array.

(a) Po1y- which becomes the active layer of TPT on the quartz substrate 1
Film formation of 5i 2 (LP-CVD method 630℃, 0.12T
A thin film of 1,100 orr) is patterned by photolithography and etched into an island shape.

(b) Poly-5i 2 is thermally oxidized to form a TPT gate oxide film 3 (dry oxidation method 1025°C thin film 8
00 people).

(c) Gate electrode 4 of TFT 33, Po1y-5i low resistance 32, P o 1. A Po1y-5i film that will become the y-Si photoconductive film 31 is formed (LP-CVD method at 630° C., film thickness: 3000 ml) and patterned. Furthermore, P
P1 ions are implanted into the o1y-3i photoconductive film 31 (I
E12ions/ad 80keV).

(d) Provide a photoresist 47 and implant P0 ions (4
E 151ons/al 80KeV) After removing the photoresist 47, it was activated (900°C 30°C).
), the TPT source/drain 48
, 49, Gate 4, Po1y-5i low resistance and Po1y
The resistance of the contact region (diffusion region) 50 of the Si photoconductive film is reduced.

(e) NSG film 5 is formed on the entire surface as an insulating film between the eyebrows (LP
-CVD method (430°C, film thickness: 4000 ml), followed by hydrogen plasma treatment to form a TFT.

Hydrogen electrons are introduced into the Po1y-5i photoconductive film.

(f) Open a contact hole, form an AQ film on the entire surface, and pattern it to form an AQ electrode 52 and an AQ light shielding layer 53.
form.

With the above process, Po1y-5i optical sensor and Po1y-
An image sensor array that integrates 5i TFTs can be manufactured.

In addition, since the conventional optical sensor part was an amorphous Si film (low heat resistance), the manufacturing process had to be set up after the production of the Po1y-5i TFT, and the total number of steps was very large.

〔effect〕

The present invention has the effects of the earlier patent application No. 1-138021,
In other words, since polysilicon film can now be used as a photoconductive film, the number of steps has been reduced compared to the conventional method of using amorphous silicon, which required many steps to make an image sensor array. can be reduced,
It is said that productivity has improved, and reliability has also improved because the steps are smaller.

In addition to the effects of the prior invention, the output of the photoconductive film could be significantly improved.

[Brief explanation of the drawing]

FIG. 1 shows the performance of the photoconductive film obtained in Production Example (1) of the present invention. Figure 2 shows the relationship between the concentration of phosphorus, which is an N-type impurity, and photoconductivity/dark conductivity.6 Figure 3 shows the wiring diagram of the image sensor according to the embodiment of the present invention, and Figures 4 (a) to (f) ) indicates the manufacturing process of the example. 1...M edge substrate 2...TFT active layer 3...
-Gate oxide film 4...Gate electrode 5...Interlayer insulating layer 31...Poly-5i photoconductive film 32-P
o1y-5i low resistance 33-Nch-TP T34・
・Analog switch 35...shift register section

Claims (1)

[Claims] 1. The N-type impurity concentration in the polycrystalline silicon film is 10^1^
6-10^2^0atoms/cm^3, hydrogen concentration is 1
A photoconductive film made of polycrystalline silicon with a crystal grain size of 200 Å or more and a polycrystalline silicon crystal grain size in the range of 0^1^9 to 10^2^2 atoms/cm^3 and a polycrystalline silicon to amplify its output. An image sensor array comprising an optical sensor made of a crystalline silicon thin film transistor and a drive circuit made of a polycrystalline silicon thin film transistor.