JP2599726B2 - Light receiving device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a light receiving device for photoelectric conversion,
In particular, the present invention relates to a light receiving device suitable for, for example, a long imaging device.

[Problems to be Solved by Conventional Technology and Invention] Conventionally, a light receiving device is formed on a semiconductor substrate such as a CCD by using a diffusion process. In that case, the size is at most within the range of the semiconductor substrate, and it is difficult to obtain a long sensor array. In addition, when the light receiving device is to be formed on another substrate for systemization, a separately manufactured semiconductor sensor chip must be pasted on the system substrate, which involves many steps and lowers the alignment accuracy. .

On the other hand, a light-receiving device using amorphous silicon (a-Si) has been developed as a method for freely selecting a substrate. However, a transistor using a-Si has poor characteristics and has a problem in terms of high-speed operation.

Recently, as one means to solve it, a sensor
The transistor part is made of polycrystalline silicon (poly-
A method using Si) has been proposed (Japanese Unexamined Patent Publication No.
-126666). However, in this method, poly-Si
Since an a-Si sensor is formed after a normal IC process is used to form a transistor, there is a problem that the number of steps is increased and the cost is increased.

As described above, in the conventional example, it is difficult to configure a low-cost and high-performance light receiving device on a substrate other than a semiconductor.

[Means for Solving the Problems] The present invention relates to a light receiving device having a semiconductor layer formed on an insulating surface of a substrate and an insulating layer provided on the semiconductor layer; A first semiconductor region of the first conductivity type connected thereto and a second semiconductor of a second conductivity type different from the first conductivity type contacting the first semiconductor region with a bonding surface intersecting the insulating surface. A third semiconductor region of the second conductivity type and the second semiconductor region as a source and a drain, and a fourth semiconductor region of the first conductivity type between the source and the drain. A field effect transistor having a gate provided over the channel region with the insulating layer interposed therebetween; and a field effect transistor provided over the second semiconductor region with the insulating layer interposed therebetween while avoiding the junction surface. Having a storage gate and SUMMARY exists in the light receiving device characterized by and.

Here, the desired area is an area determined according to the purpose, use, and standard of the device. Further, the lateral type means that the first type semiconductor region and the second type semiconductor region constituting the photosensor are joined perpendicularly to the surface.

[Operation] According to the present invention, the sensitivity can be improved by using a photodiode having a junction surface crossing the substrate surface as a photosensor. Further, since the storage gate is provided only on the source (drain) avoiding the junction surface, the amount of charge stored in the source (drain) region can be increased. Furthermore, by providing a storage gate by crossing the junction surface of the photodiode with the substrate,
Even if a polycrystalline semiconductor thin film is used, it is possible to obtain sufficient sensitivity, responsiveness, and signal charge amount.

Embodiment 1 Embodiment 1 FIG. 1 is a perspective view of a light receiving device according to Embodiment 1 of the present invention, and FIG.
The figure is an equivalent circuit diagram of the device of FIG.

In FIG. 1, an n-type or i-type semiconductor thin film 2 is provided on a substrate 1. When the light receiving device is a substrate incident type, a transparent substrate such as quartz or glass is used as the substrate 1. The first semiconductor thin film uses polycrystalline Si or single crystal Si. As polycrystalline Si (poly-Si),
Poly-Si having a particle size of 50 nm or less deposited by a low pressure CVD method using a normal silane gas (SiH ₄ ) may be used, but the present applicant has proposed in Japanese Patent Application Nos. 62-73629 and 62-73630. The large particle size poly-Si is preferable for obtaining a high-performance light receiving device. As the single crystal Si, a recrystallized single crystal by laser annealing or a flattened single crystal grown by a single crystal growth method using a micro SiH ₄ pattern on SiO ₂ as a seed can be used. The large particle size poly-Si is most suitable for the present embodiment because the forming method is easy. The large grain size poly-Si will be described later in detail. The film thickness is determined in consideration of spectral sensitivity, and is about 1 μm.

Now, in the n-type or i-type semiconductor thin film thus provided, p-type impurities such as boron are diffused in predetermined regions 4, 24, and 14 until reaching the substrate. As a method of spreading,
BBr leaving the SiO ₂ or Si ₃ N ₄ film as a diffusion mask on the region 3 of the n-type or i-type semiconductor thin film where the impurities do not diffuse.
Gas diffusion by ₃ or the like, diffusion from a BSG film, and diffusion by ion implantation using a resist mouse are used.

At this time, the P ⁺ portion 4 of the photosensor 7 and the source portion 24 and the drain portion 14 of the MOS-FET 8 are formed simultaneously. In the photosensor 7, the P ⁺ portion 4 and the n-type or i-type portion 3 are arranged in a stripe pattern to constitute a horizontal P ⁺ -n photodiode. In a horizontal photodiode, since there is no high-concentration layer on the surface of the n-type or i-type region, carriers generated on the surface by short-wavelength light can be used as a photocurrent without recombination immediately. High spectral sensitivity (blue side). Large particle size mentioned above
Also in poly-Si, a larger photocurrent can be obtained if the stripe pitch is as small as possible in consideration of the diffusion length of the carrier.

In the MOS-FET 8, P ⁺ source / drain regions 14 and 24 are formed with an n-type or i-type channel region 13 interposed therebetween, and a gate 6 is provided via a gate film 5 of about 100 nm. The gate film is preferably a thermal oxide film of a semiconductor thin film in terms of characteristics, but from the viewpoint of cost, an SiO ₂ film formed by low-pressure CVD,
A Si ₃ N ₄ film formed by plasma CVD or the like is preferable. The gate is formed by depositing poly-Si or a-Si or aluminum, and then forming the first gate.
As shown in the figure, patterning is performed with a width having a margin enough to overlap the source / drain region on the channel portion 13. In FIG. 1, contacts and wiring are omitted.

As is clear from the equivalent circuit of FIG. 2, the light receiving device constructed in this embodiment can switch the output from the high-sensitivity photodiode 7 by the high-speed MOS-FET 8,
High-speed reading is possible even if a large number of sensor arrays are formed.

When an i-type layer is used as the semiconductor layer, it is preferable that the channel region is lightly channel-doped with an n-type impurity.

Next, a method of forming the above-described large grain poly-Si film will be described in detail.

FIG. 7 is a view conceptually showing a process of growing a large grain polycrystalline film on the SiO ₂ deposition surface 71.

7 (A) shows a stage where a growth nucleus is formed, FIG. 7 (B) shows a stage where the nucleus grows into an island shape and comes into contact with each other, and FIG. Indicates the stage at which Since the density of the nuclei in FIG. 7 (A) greatly depends on the interaction between the flying atoms and the deposition surface,
It greatly depends on deposition conditions such as gas type, pressure and temperature.

In the case of forming a silicon (Si) nuclei the Si ₃ N ₄ film or SiO ₂ film in FIG. 8 shows changes in nucleation density (N _D) in the case where the deposition condition parameters picked addition ratio of HCl . Si ₃ N
_Four films were formed by low pressure chemical vapor deposition (LPCVD), Si
The O ₂ film is formed by a normal pressure chemical vapor deposition method. Using a reaction gas of SiH ₂ Cl ₂ as a source gas and H ₂ as a carrier gas, under a reduced pressure (H150 Torr) at a composition ratio of SiH ₂ Cl ₂ : HCl: H ₂ = 1.2: x: 100 (1 / min) The reaction is.
The temperature of the substrate (deposition surface) at that time is 950 ° C. In the figure, S
N _D of i ₃ N ₄ film 81, the N _D of the SiO ₂ film is 82. As is clear from the figure, the nucleation density shows a specific value depending on the deposition surface, but more than that, it greatly changes depending on the flow rate ratio (mixing ratio) of HCl, indicating that it can be controlled by HCl. Therefore, HCl can be said to be a nucleation density control gas.

FIG. 9 shows the relationship between the amount of HCl and the average particle size. In this, for example, a nucleation density of 10 ⁷ / c is obtained, and an HCl flow rate of 1.
After deposition for 30 minutes under the condition of 11 / min, the average particle size in the film surface was 3
Polycrystalline silicon having a large grain size such as μm was obtained. Since the average particle diameter is inversely proportional to the 乗 power of the nucleation density, the nucleation density may be controlled to about 10 ⁸ / c or less in order to make the average particle diameter in the film plane 1 μm or more.

However, on the other hand, when the nucleation density is significantly reduced, non-uniformity of the particle size occurs. This is because the internuclear distance cannot be ignored with respect to the diffusion length of silicon atoms on the deposition surface together with statistical variations. In the experiment, the practical range of the actual semiconductor device was a nucleation density of 10 ⁶ / c or more, that is, an average particle size of 10 μm or less.

As shown in FIG. 8, the nucleation density of the SiO ₂ film is about two orders of magnitude smaller than that of the Si ₃ N ₄ film, and a polycrystalline film having a large grain size is easily obtained.

FIG. 10 shows the pressure dependence of the average particle size. The condition is HCl
Except for 1.11 / min, it is the same as FIG. The decompression has the effect of reducing the nucleation density and making the distribution of nuclei uniform to make the particle size uniform. Other conditions in FIG. 10 include SiH ₂ Cl ₂ :
HCl: H ₂ = 1.2: 1.1: 100 (1 / min), temperature 960 ° C, deposition time 3
0 minutes. In particular, the effect of reduced pressure increases sharply below 200 Torr.

FIG. 11 shows the temperature dependence of the average grain size and the deposited film thickness.
Other deposition conditions are as follows: SiH ₂ Cl ₂ : HCl: H ₂ = 1.2: 1.0: 100 (1: mi
n), pressure 150 Torr, deposition time 30 minutes. The average particle size is
It increases as the temperature becomes lower than 1000 ° C. However, as can be seen from the curve of the deposited film thickness, the growth rate was reduced to 850 ° C.
, The growth rate becomes almost zero. Therefore, the lower limit is determined by this growth rate. Of course, the higher the temperature, the better the crystallinity of each crystal grain, so that an appropriate temperature can be selected according to the specifications of the device.

So far, SiH ₂ Cl ₂ gas has been described as a source gas, but the same tendency is exhibited even when other Si-based source gases such as SiHCl ₂ , SiH ₂ , SiCl ₄ are used. Other than silicon, trimethylgallium (TMG) and arsine (AsH
_If the mixing ratio of ₃ ) of 60: 1 is used, it can be applied to compound semiconductors such as GaAs. Also in this case, the carrier gas
It is H ₂ and can be deposited at a temperature of 600 ° C. or higher and 10 to 20 Torr.

Cl ₂ other than HCl as a nucleation density control gas,
A gas system that reacts with a semiconductor material such as F ₂ , CCl ₄ , and CCl ₂ F ₂ can be used.

The large particle size Poly-
The surface of the Si film is polished by mechanochemical polishing and p-type
When the MOS-FET was fabricated, the hole mobility was about
A MOS-FET having a higher performance than ordinary poly-Si of 70 cm ² / V · sec was obtained.

As described above, in this embodiment, since the horizontal photodiode is used, the photosensitivity of short wavelength is high, and the high-concentration diffusion region (P ⁺ ) of the photodiode is directly used as the drain region of the MOS-FET. Thus, a light receiving device capable of transmitting a minute photocurrent without loss due to wiring and requiring very few diffusion steps was obtained.

Second Embodiment FIG. 3 is a plan view showing a second embodiment of the present invention, FIG. 4 is a sectional view of the device of FIG. 3, and FIG. 5 is an equivalent circuit diagram of the device of FIG.

In FIG. 3, p-type boron is applied to the n-type semiconductor thin film 2 with the sensor region 4, the source / drain regions 14, 24 and M
The P ⁺ type region is formed by simultaneously diffusing into the OS capacitance region 34. Then, after forming a gate film, the gate 16 of the MOS capacitance and the gate 6 of the MOS-FET are changed to n ⁺ -poly
-Si or n ⁺ -a-Si. Reference numeral 12 denotes a wiring contact.

In the present embodiment, as shown in the equivalent circuit of FIG. 5, since there is a capacitor 9 for accumulating a photocurrent, it is suitable for a sensor array of a system in which a minute photocurrent is temporarily stored and read out in a time series. Further, in this embodiment, the P ⁺ region 4 of the sensor, the P ⁺ region 34 of the MOS capacitor, and the drain region 14 of the MOS-FET are common diffusion regions, so that wiring work and leakage are reduced, and the area is effectively utilized. Can be. Therefore, the yield is good and the advantage in manufacturing is great.

In the embodiments described above, the case where the sensor array is used is not specifically shown, but basically the devices shown in FIGS. 1 and 3 may be arranged in parallel. However, in that case, the sensor n
Since it is necessary to electrically insulate except for the mold region 3, it is necessary to separate the semiconductor thin film from an adjacent element by etching or the like.

In the description so far, the n-type and the p-type are compatible. However, the i-type layer is used as a low concentration layer.

Third Embodiment FIGS. 6 (a) to 6 (d) are cross-sectional views showing the steps of a third embodiment of the present invention.

Hereinafter, the steps will be described with reference to FIGS. 6 (a) to 6 (d).

A low-concentration n-type or i-type semiconductor layer is deposited on the transparent insulating substrate 1, a mask 30 for impurity diffusion or ion implantation is formed in a predetermined region, and a p-type mask is formed in a region not covered by the mask. Is diffused to form a p-type region (a). Next, the mask material is removed to form a gate oxide film 5, and a contact hole 31 is formed at a desired position in the n-type or i-type region (b). Next, a high-concentration n ⁺ -poly-Si or a-Si layer is deposited thereon and etched away leaving the contact portion 36 and the gate portion 6 (c). Next, an interlayer insulating film 10 is deposited on the entire surface, a second contact hole is opened, and an electrode 11 is formed (d).

During this time, the n-type impurity is diffused into the n-type or i-type region with a lower concentration than the p-type high concentration n ⁺ -poly-Si (or n ⁺ -a-Si) layer 36 to form the n ⁺ -type region 40. .

Through the above steps, a light receiving device with good ohmic contact was obtained. Further, in the related art, one extra high-concentration diffusion of the n-type layer is required. However, in the present embodiment, this is not necessary, and a highly reliable contact can be realized with a small number of steps.

[Effects of the Invention] As described above, according to the present invention, the sensitivity can be improved by using a photodiode having a junction surface crossing the substrate surface as a photosensor.

Further, since the storage gate is provided only on the source (drain) avoiding the junction surface, the amount of charge stored in the source (drain) region can be increased.

Furthermore, by providing the storage gate with the junction surface of the photodiode intersecting with the substrate, it is possible to obtain sufficient sensitivity, responsiveness, and signal charge even when using a polycrystalline semiconductor thin film.

[Brief description of the drawings]

FIG. 1 is a perspective view of a light receiving device according to a first embodiment of the present invention, FIG. 2 is an equivalent circuit diagram of the device of FIG. 1, FIG. 5 is a sectional view of the device of FIG. 3, FIG. 5 is an equivalent circuit diagram of the device of FIG. 3, FIGS. 6 (a) to 6 (d) are process sectional views of Embodiment 3 of the present invention, and FIG.
The figure is a conceptual diagram showing the state of crystal growth of large-grain poly-Si, FIG. 8 is a graph showing the effect of the nucleation density control gas on the nucleation density of large-grain poly-Si, and FIG. Particle size
FIG. 10 is a graph showing the effect of nucleation density control gas on the crystal grain size of poly-Si, FIG. 10 is a graph showing the effect of pressure on the crystal grain size of large-diameter poly-Si, and FIG. 11 is a large grain size.
5 is a graph showing the effect of temperature on the nucleation density of poly-Si. 1 ... an insulating substrate, 2 ... an n-type semiconductor thin film, 3, 13 ... a first type semiconductor region, 4, 14, 24 ... a second type semiconductor region, 5 ... a gate oxide film, 6 ... gate part of MOS-FET
7 ... Photo sensor section, 8 ... FET section, 9 ... Capacitance, 10
...... Interlayer insulating film, 11 ... Electrode, 12 ... Contact part for wiring, 16 ... Gate part of MOS capacitance, 30 ... Mask material, 31 ... Contact hole, 34 ... MOS capacitance area, 36 ... Contact part, 40 …… n ⁺ type region.

Claims (3)

(57) [Claims] 1. A light-receiving device having a semiconductor layer formed on an insulating surface of a substrate and an insulating layer provided on the semiconductor layer, wherein the light-receiving device has a first conductivity type connected to a wiring contact. A second semiconductor region different from the first conductivity type in contact with the first semiconductor region with a bonding surface crossing the insulating surface;
A photodiode having a second semiconductor region of a conductive type; a third semiconductor region of a second conductive type and the second semiconductor region as a source / drain; and a first conductive region between the source / drain. A field effect transistor having a gate provided on the channel region with the insulating layer interposed therebetween, and a fourth semiconductor region of the type serving as a channel region; A light receiving device, comprising: a storage gate provided via an insulating layer. 2. The semiconductor device according to claim 1, wherein said first semiconductor region and said second semiconductor region have a plurality of rectangular portions, which are arranged alternately. Light receiving device. 3. The light receiving device according to claim 1, wherein said semiconductor layer is made of polycrystalline silicon having a grain size of 0.5 μm or more.