JP2968971B2 - Image sensor and manufacturing method thereof - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an image sensor used in an optical reading device and the like, and a method for manufacturing the same.

(Prior art)

In the conventional typical image sensor manufacturing process, the photosensitive layer of the optical sensor portion was formed after the transistor portion was formed. (This is because the characteristics of amorphous silicon change at a high temperature of 300 ° C. or higher.) For this reason, it is necessary to avoid the thermal history of the transistor formation step, and the photosensitive layer must be formed after the transistor formation step.) Therefore, a very large number of steps are required in addition to the number of steps for forming the optical sensor section. This will be described with reference to FIG.

FIG. 1A shows a step of forming a thin film transistor (TFT) active layer, in which a polycrystalline silicon (Poly-Si) layer 2 as a TFT active layer is formed on an insulating substrate 1. (2)
In this step, a gate oxide film (SiO ₂ film) 3 and a gate electrode 4 made of Poly-Si are formed on the Poly-Si layer 2. (3) is a step of implanting ions into the source / drain regions and activating them. (4) The interlayer insulating film 5
And a step of forming a contact hole 6 are shown. (5) is a step of forming a wiring electrode (corresponding to a lower electrode of an optical sensor) 7; (6) is a step of forming an a-Si layer (sensor photosensitive layer) 8 having a photoelectric conversion function; 7) is a step of forming the optical sensor portion by etching. (8) is a process for forming the contact hole 9 in the optical sensor unit, and (9) is a process for forming the electrode 10 in the optical sensor unit.

As described above, in the conventional type, the thin film transistor section and the optical sensor section must be formed separately, which not only increases the number of steps but also increases the number of resists and masks used for etching. (1), (2),
The steps (4), (5), (7), (8), and (9) are required, and a total of seven sheets are required.

FIG. 2 shows a typical configuration example of a photodiode using amorphous silicon formed in the steps (6) and (7) of FIG. In this case, the lower electrode 7, P-i
Four masks are required to form the -N photodiode (sensor photosensitive layer) 8, the interlayer insulating layer 5, and the upper electrode 10, respectively. This not only increases the cost but also inevitably lowers the reliability due to an increase in constraints in each step.

〔Purpose〕

An object of the present invention is to reduce the number of processes and reduce the number of masks used, thereby achieving cost reduction and maintaining high product reliability.

[Configuration] A first aspect of the present invention is an image sensor including a thin film transistor portion and an optical sensor portion provided on the same insulating substrate,
(A) The thin film transistor section includes a transistor active layer, a gate oxide film, a gate electrode formed of a polycrystalline silicon layer on the substrate, and a wiring electrode formed of a metal layer in contact with the transistor active layer. The optical sensor unit includes a lower electrode made of a polycrystalline silicon layer formed on the substrate, an interlayer insulating layer formed thereon except for a part of the lower electrode, and a metal formed thereon. And the lower electrode formed of a polycrystalline silicon layer and the metal layer in contact with the lower electrode form a Schottky diode,
(C) The polycrystalline silicon layer of the thin film transistor portion and the polycrystalline silicon layer of the optical sensor portion are made of the same material.

The second aspect of the present invention is that (a) after forming a polycrystalline silicon layer on an insulating substrate, other portions are removed by etching while leaving the active layer of the thin film transistor portion, and (b) a portion on the active layer After a gate oxide film is formed on the substrate, a polycrystalline silicon layer for forming a lower electrode of the light sensor unit and a gate electrode of the thin film transistor unit is formed on the optical sensor unit on the substrate and the gate oxide film. After forming an electrode and the gate electrode, and (c) forming an insulating layer on the entire surface,
A contact hole is formed at a necessary portion, and (d) a metal layer is further provided on the entire surface, and a Schottky diode is formed by the polycrystalline silicon layer forming the lower electrode of the optical sensor portion and the metal layer portion in contact with the polycrystalline silicon layer. The present invention also relates to a method for manufacturing an image sensor, comprising the steps of: performing etching for forming a wiring electrode of a thin film transistor portion with a metal layer in contact with an active layer of the thin film transistor portion.

FIG. 3 (a) shows a reference configuration example of a photoelectric conversion element using a Schottky diode, and FIG. 3 (b) shows a configuration example of a photoelectric conversion element using a Schottky diode obtained by the method of the present invention.

In (a), a P ⁺ layer of Poly-Si is used as a lower electrode 7 and also serves as a wiring electrode. And non-doped Poly-Si (i
This is an example in which a bond is formed between the layer 8 and the Schottky metal 11. In (b), a metal 11 having a Schottky property is formed on the lower electrode / wiring electrode 7 as a base layer. This configuration is such that the Schottky metal 11 also serves as the upper electrode 10 and the TFT-side (or signal-reading-side) wiring electrode, and is the simplest photoelectric conversion element.

The Schottky metal may be anything that has a junction with each of the P, i, and N layers. For example, in (b), Poly-Si
When a P layer is used for the layer 7, Al, Ti, Ni, Cr, Cu, or the like is preferable. When an N-type semiconductor layer is used as an underlayer, Au, Pt, P
d, Sn, etc. are preferred. Further, for the i-layer, the Schottky metal may be changed according to the interface state, particle size, and the like at that time. Further, in FIG. 3 (a), the poly-Si layer 8 is on the base and the Schottky metal 11 is formed on the upper part, but it goes without saying that the function is not changed even if the upper and lower sides are reversed. Also, transparent electrodes such as SnO ₂ and ITO are not metals, but they are conductors similar to metals.
Since the metal forms a Schottky junction with Poly-Si, it is apparent from the function that the metal also includes these transparent electrode materials.

The incident direction of light as a sensor can be from the glass side or from the opposite side. In particular, when light is incident from the Schottky metal side, the thickness is preferably 100 to 500 °. In the case of incidence from the Poly-Si side, the thickness of the Poly-Si is preferably 1000 ° to 1 μm.

FIG. 4 shows an example of a sensor / TFT integrated formation process in the present invention. 2A shows a TFT active layer 2 formed on a substrate 1. FIG.
The gate electrode 4 for the TFT and the lower electrode 7 of the optical sensor portion have just been formed by using -Si. (C) shows a state in which an interlayer insulating layer 5 is provided thereon and contact holes are formed at necessary places. (D) Schottky metal 11 and upper electrode
10 has just been formed. In this case, only four masks are used.

〔Example〕

An active layer 2 is formed on a quartz substrate 1 by forming Poly-Si of 1000 ° by LPCVD. The conditions at this time are SiH ₄ 100%, 600 ° C,
0.1 torr. Processing of the active layer is SF ₆ 100%, dry etching is performed at 0.1 torr. Thereafter, a gate oxide film 3 of about 1000 ° C. is formed under DryO _{2 at} 1000 ° C. for 2 hours, and then a poly-Si layer having a thickness of only 4000 ° is formed under the same conditions as described above. Thereafter, P ⁺ is implanted with 90Kev4E15 by implantation, and activation is performed at 900 ° C. for 30 minutes. The insulating layer 5 is made of LPH by SiH ₄ / O ₂ = 80/2
About 5000 ° of SiO ₂ is formed at 0 sccm. Then CHF ₃ / O ₂ =
The contact hole is formed by dry etching at 76/4 sccm and 0.05 torr. Light etching by HF is performed if necessary. Thereafter, an Au deposited film 11 is formed by an electron beam to form a Schottky diode of about 2000 °. Thereafter, unnecessary portions of the Au are etched under the conditions of plasma etching using Ar plasma to complete the product of the present invention.

〔effect〕

By employing the configuration of the present invention, the number of steps is reduced, and as a result, cost reduction, improvement in yield, and higher precision are realized.

[Brief description of the drawings]

1 to 3 show a manufacturing process of a conventional image sensor, FIG. 2 shows one configuration example of a conventional photodiode using amorphous silicon, and FIG. 3 (a) shows a reference configuration example. (B) shows a configuration example of the present invention. 4th
(A)-(d) show the manufacturing process of the image sensor of the present invention. 1: Insulating substrate, 2: TFT active layer 2 ': Sensor photosensitive layer, 3: Gate oxide film 4: Gate electrode, 5: Interlayer insulating layer 6: Contact hole, 7: Wiring electrode (lower electrode) 8: Sensor photosensitive Layer, 9: contact hole 10: electrode (upper electrode), 11: Schottky metal layer

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁶ , DB name) H01L 27/146 H01L 29/786 H01L 31/108

Claims (2)

(57) [Claims] 1. An image sensor comprising a thin film transistor portion and an optical sensor portion on the same insulating substrate, wherein:
The thin film transistor section includes a transistor active layer, a gate oxide film, a gate electrode formed of a polycrystalline silicon layer, and a wiring electrode formed of a metal layer in contact with the transistor active layer on the substrate, and The sensor section includes a lower electrode made of a polycrystalline silicon layer formed on the substrate, an interlayer insulating layer formed thereon except for a part of the lower electrode, and the metal layer formed thereon. And (C) the polycrystalline silicon layer of the thin film transistor section and the photosensor, wherein the lower electrode composed of a polycrystalline silicon layer and the metal layer in contact with the lower electrode form a Schottky diode. Wherein the polycrystalline silicon layers of the portions are made of the same material. (A) after forming a polycrystalline silicon layer on an insulating substrate, etching to remove the remaining portion except for the active layer of the thin film transistor portion; and (b) forming a gate on a portion of the active layer. After forming the oxide film, a polycrystalline silicon layer for forming a lower electrode of the photosensor portion and a gate electrode of the thin film transistor portion is formed on the photosensor portion on the substrate and the gate oxide film. After the gate electrode is formed, (c) an insulating layer is formed on the entire surface, a contact hole is formed at a required position, and (d) a metal layer is further provided on the entire surface to form a lower electrode of the optical sensor unit. A Schottky diode is formed by the polycrystalline silicon layer and the metal layer portion in contact with the polycrystalline silicon layer, and the metal electrode in contact with the active layer of the thin film transistor portion has a metal electrode in contact with the thin film transistor portion. Method of manufacturing an image sensor that performs etching for, that consists of the steps of the features.