JPH0685310A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To reduce the leakage current from a photodiode. CONSTITUTION:A channel stopper layer 13 is formed on a silicon substrate 11. A titanium film 14 is formed thereon using a photoresist layer 15 as a mask. An n-type diffusion layer 12 is formed by ion implantation. Thereafter, the titanium film 14 is selectively left. An oxide film 18 is formed, and a heat treatment is performed. The titanium film 14 is turned into a titanium silicide layer 17 through the heat treatment.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor device, and more particularly to reduction of leakage current of a photodiode used in a solid-state image pickup device.

[0002]

2. Description of the Related Art When forming a silicon photodiode that converts light into electric charges, the lattice structure is discontinuous on the silicon surface. Because of this, there are many surface states and production-recombination centers. At these energy levels, the generated recombination current increases and becomes a dark current, resulting in deterioration of characteristics. Therefore, a method of forming a hole accumulation layer of the opposite conductivity type (P ⁺ layer) on the surface of the silicon photodiode (N type) so that the depletion region of the photodiode does not reach the silicon surface is generally used. For example, Yuji Kiuchi: Basics and applications of image sensors,
p. 154 (1991), Nikkan Kogyo Shimbun.

A conventional example will be described below with reference to the drawings. FIG. 4 is a diagram illustrating a manufacturing process of a conventional example. Figure 4
In the figure, 1 is a P-type silicon substrate, 2 is an N-type diffusion layer, 3
Is a channel stop layer, 4 is a 100 nm-thick oxide film,
Reference numeral 5 is a 1.0 μm thick photoresist layer, 6 is a phosphorus ion beam, 7 is a boron ion beam, and 8 is a hole storage layer.

In FIG. 4A, a P-type silicon substrate 1
A channel stop layer 3 of a P-type region for a channel stopper is formed thereon by implanting boron with an acceleration energy of 40 keV and an implantation dose of 1 × 10 ¹³ cm ^-2 . A relatively thin concentration N-type diffusion layer 2 for forming a photodiode is selectively formed on the oxide film 4 which is a thermal oxide film having a thickness of 100 nm and the photoresist layer 5 by using a phosphorus ion beam 6. The ion implantation conditions at this time are acceleration energy of 200.
It is performed with keV and an injection amount of 2 × 10 ¹³ cm ⁻² . Next, FIG.
In (b), the boron beam 7 is used to form a P-type hole accumulation layer 8 having a relatively high concentration. Ion implantation conditions at this time are: acceleration energy 35 keV, implantation amount 1 × 10 ^14.
Do it in cm ^-2 . The reason for forming the hole storage layer 8 is that the photodiode reversely biases the P-type silicon substrate 1 and the N-type diffusion layer 2 and uses them in a depleted state. The depleted region reaches the interface between the N-type diffusion layer 2 and the oxide film 4. N
At the interface between the type diffusion layer 2 and the oxide film 4, the lattice structure is discontinuous, and there are many interface states and generation-recombination centers that are sources of dark current. For this reason, the hole accumulation layer 8 is provided between the N-type diffusion layer 2 and the oxide film 4 because the depletion state of the N-type diffusion layer 2 is extended to the interface between the N-type diffusion layer 2 and the oxide film 4. This is to prevent the area of.

[0005]

[Problems to be Solved by the Invention] However, boron
The hole accumulation layer 8 formed by the beam 7 is 1 × 10
¹⁷cm^-3The concentration of boron exceeds. For this reason,
Crystal defects occur, which may cause a new leakage current.
Become. In this way, the characteristics of the photodiode are degraded.
Had the problem.

[0006]

In order to solve the above problems, a method of manufacturing a semiconductor device according to the present invention comprises a first conductivity type silicon substrate or a silicon substrate having a first conductivity type well. A step of introducing a second conductivity type impurity to form a photodiode, and a step of depositing a refractory metal on the surface of the silicon substrate of the photodiode.
A step of siliciding the refractory metal by heat treatment is provided.

Further, rapid heat annealing in an inert gas is used for the heat treatment.

[0008]

According to the present invention, a refractory metal is deposited on the surface of the photodiode by the above-described method, and heat treatment is performed to form a silicided region, so that the depleted region of the N-type diffusion layer of the photodiode is removed. It is possible to stop at the silicided regions and not reach the silicon / oxide interface where many interface states and production-recombination centers are present. This can prevent the influence of the dark current generated at the silicon / oxide film interface from reaching the N-type depletion layer region of the photodiode.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram for explaining the manufacturing process of the first embodiment of the present invention. In FIG. 1, 11 is a P-type silicon substrate, 12 is an N-type diffusion layer, 13 is a channel stop layer, 1
4 is a 10 nm thick titanium film, 15 is a 1.0 μm thick photoresist layer, 16 is a phosphorus ion beam, 17 is a 15 nm thick titanium silicide layer, and 18 is 100 n thick.
m oxide film.

In FIG. 1A, a P-type silicon substrate 1
A P-type channel stop layer 13 was implanted on the substrate 1 with boron at an acceleration energy of 40 keV and a dose of 1 × 10 ¹³ cm ^-2 .
Form. A titanium film 14 having a thickness of 10 nm is deposited on the photoresist layer 15 by the DC magnetron sputtering method. Next, the N type diffusion layer 12 having a relatively low concentration for selectively forming a photodiode is accelerated by using a phosphorus ion beam 16 at an acceleration energy of 200 keV and an implantation amount of 2 ×.
Formed at ¹³ cm ^-2 . Next, when the photoresist layer 15 is removed by fuming nitric acid cleaning, the titanium film 14 on the photoresist layer 15 is lifted off, and the titanium film 14 is selectively formed on the N-type impurity layer as shown in FIG. 1B. Remain. Then, as shown in FIG. 1C, a thermal oxide film 17 having a thickness of 100 nm is formed by performing a treatment at 1100 ° C. for 30 minutes in a dry oxygen atmosphere. At this time, at the same time, the titanium film 14 changes into a titanium silicide layer 17 having a thickness of 15 nm. At the boundary between the titanium silicide layer 17 and the oxide film 18, the lattice structure becomes discontinuous, and there are many interface states and generation-recombination centers. However, if the photodiode is
When a reverse bias is applied to the n-type silicon substrate 11 and the n-type diffusion layer 12 to use them in a depleted state, the n-type diffusion layer 12 is depleted up to the interface between the titanium silicide layer 17 and the oxide film 18. Since the region does not reach, it is not affected by the interface between the titanium silicide layer 17 and the oxide film 18.

FIG. 2 is a diagram for explaining the manufacturing process of the second embodiment of the present invention. In FIG. 2, 21 is a P-type silicon substrate, 22 is an N-type diffusion layer, 23 is a channel stop layer,
24 is a titanium film having a thickness of 10 nm, 25 is a thickness of 1.0 μm
Of photoresist layer 26 is a phosphorus ion beam.
Reference numeral 27 is a 12 nm thick titanium silicide layer, and 28 is a 100 nm thick oxide film.

In FIG. 2A, a P-type silicon substrate 2
A P-type channel stop layer 23 was implanted on the substrate 1 with boron at an acceleration energy of 40 keV and a dose of 1 × 10 ¹³ cm ^-2 .
Form. A titanium film 24 having a thickness of 10 nm is deposited on the photoresist layer 25 by the DC magnetron sputtering method. Next, the N type diffusion layer 22 having a relatively low concentration for selectively forming a photodiode is formed by using a phosphorus ion beam 26 with an acceleration energy of 200 keV and an implantation amount of 2 ×.
It is formed with 10 ¹³ cm ^-2 . Next, when the photoresist layer 25 is removed by fuming nitric acid cleaning, the photoresist layer 25 is removed.
The upper titanium film 24 is lifted off, and the titanium film 24 can be selectively left on the N-type impurity layer 22 as shown in FIG. 2B. Then, as shown in FIG.
By performing rapid thermal annealing (RTA) at 700 ° C. for 30 seconds in a nitrogen atmosphere, the titanium film 14 is changed to a titanium silicide layer 17 having a thickness of 12 nm. Thereafter, as shown in FIG. 2D, a 100 nm-thick thermal oxide film 17 is formed by performing a treatment at 1100 ° C. for 30 minutes in a dry oxygen atmosphere. The reason why the dark current decreases in the second embodiment is the same as in the first embodiment. However, as compared with the first embodiment, the thermal oxide film 28 is formed after the titanium silicide layer 27 is formed in advance. Therefore, the thermal oxide film 28 formed on the titanium silicide layer 27 is not mixed with titanium. A small amount of good quality oxide film can be obtained.

FIG. 3 shows data for improving the yield regarding the leakage current of the photodiode portion formed by using the first and second embodiments of the present invention. In FIG. 3, white circles indicate the case where a reverse bias of 5V is applied to the photodiode portion, and black circles indicate the case where a reverse bias of 20V is applied to the photodiode portion. The sample formed according to the present invention showed a significant improvement effect on the leakage current.

[0014]

As described above, according to the present invention,
The leakage current of the photodiode used in the solid-state image sensor can be reduced, and its practical effect is great.

[Brief description of drawings]

FIG. 1 is a cross-sectional view in order of steps of a method for manufacturing a semiconductor device according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view in order of the steps of a method for manufacturing a semiconductor device according to a second embodiment of the present invention.

FIG. 3 is a diagram showing a yield relationship in a leakage current of a photodiode according to the present invention.

4A to 4C are cross-sectional views in order of steps of a method for manufacturing a semiconductor device of a conventional example.

[Explanation of symbols]

 11 Silicon Substrate 12 Diffusion Layer 13 Channel Stop Layer 14 Titanium Film 15 Photoresist Layer 16 Phosphorus Ion Beam 17 Titanium Silicide Layer 18 Oxide Film

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display location H01L 27/08 331 B 9054-4M

Claims (3)

[Claims] 1. A step of forming a photodiode by introducing an impurity of a second conductivity type onto a silicon substrate of a first conductivity type or a silicon substrate having a well of the first conductivity type, and the silicon substrate of the photodiode. A method of manufacturing a semiconductor device, comprising: a step of depositing a refractory metal on a surface; and a step of silicidizing the refractory metal by heat treatment. 2. The method for manufacturing a semiconductor device according to claim 1, wherein a titanium film is deposited as the refractory metal. 3. The method for manufacturing a semiconductor device according to claim 1, wherein rapid thermal annealing in an inert gas is used for the heat treatment.