Production method for solid imaging device

Details Production method for solid imaging device Production method for solid imaging device

2003-05-05

2004-06-08

Smith, Matthew (Department: 2825)

Semiconductor device manufacturing: process

Gettering of substrate

C438S060000, C438S075000, C438S473000, C438S476000, C438S477000, C438S526000, C257S215000, C257S227000, C148S033200

Reexamination Certificate

active

06746939

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a method of producing a solid-state imaging device having a buried getter sink layer formed by introducing a substance of a congener of an element of a semiconductor substrate, such as carbon, to a silicon substrate, on which a crystal growth layer is formed, and a solid-state imaging element is formed in and on the crystal growth layer.
Particularly, the present invention relates to a method of producing a solid-state imaging device wherein white defects are reduced by improving a gettering capability of a buried getter sink layer for gathering impurities which contaminate the crystal growth layer to areas other than element formation regions.
As a semiconductor substrate for being formed a semiconductor element, generally a CZ substrate grown by the CZ (Czochralski) method, an MCZ substrate grown by the MCZ (Magnetic field Czochralski) method, and an epitaxial substrate wherein an epitaxial layer is formed on a surface of the CZ substrate or MCZ substrate, etc. are often used.
Particularly, the epitaxial substrate and the MCZ substrate are mainly used for a solid-state imaging device so as to reduce unevenness of image contrast caused by dopant concentration inhomogeneities (dopant striations). Among the above, the epitaxial substrate indicates a substrate provided in advance with an element formation layer (hereinafter, referred to as an epitaxial layer) formed by crystal growth. The epitaxial substrates are capable of reducing series resistance of a lower part than the epitaxial layer by using a low resistance substrate in its formation and/or by forming a low resistance buried region prior to the crystal growth. Therefore, when using the epitaxial substrate, a drive voltage for bringing a desired change of energy barrier height in an element and an application voltage to a substrate are reduced, which is advantageous to a reduction of power consumption. Accordingly, a solid-state imaging device using an epitaxial substrate is expected to be in wider use in the future.
The Chemical Vapor Deposition (CVD) is used as a practical method for forming a silicon epitaxial substrate. The CVD is performed by the hydrogen reduction method using SiCl
4
or SiHCl
3
as a source gas, or the pyrolysis method using SiH
2
Cl
2
or SiH
4
as a source gas.
Reactions of using the above main four kinds of source gases are indicated below.
(Hydrogen Reduction Method)
SiCl
4
+2H
2
→Si+4HCl  (1)
SiHCl
3
+H
2
→Si+3HCl  (2)
(Pyrolysis Method)
SiH
2
Cl
2
→Si+2HCl  (3)
SiH
4
→Si+2H
2
  (4)
From the above, a substrate formed by using SiHCl
3
as a source gas is mainly used for solid-state imaging element because the source gas is inexpensive and suitable to formation of a thick epitaxial layer of a high growing speed, etc.
However, even in a case of forming an epitaxial substrate by using any of the above source gases, a large amount of contaminating impurities, particularly metal impurities or heavy metal impurities, are mixed in during formation of the epitaxial layer. Accordingly, when forming a solid-state imaging element by using the epitaxial substrate, the metal impurities, etc. contained in the substrate cause an increase of a dark-current of the solid-state imaging element and white defects (white spots in the dark) arises much in the solid-state imaging element. Therefore, characteristics and yield thereof decline.
Stainless (SUS) based parts in a bell jar of the epitaxial growth apparatus and piping of a source gas are considered as sources to generate heavy metal impurities. When a chloride (Cl) gas is included in the source gas, the gas is decomposed at the time of epitaxial growing to generate hydrogen chloride (HCl). It is considered that as a result that the HCl corrodes the SUS based parts, metal chlorides are taken into the source gas and further into the epitaxial layer.
Also, prior to forming the epitaxial layer, a HCl gas is intentionally introduced to lightly etch off the surface of the silicone substrate on an object of cleaning the same in some cases, but the HCl is also a part of reasons of corroding the SUS based parts, etc.
Therefore, when forming a solid-state imaging element by using an epitaxial substrate, some kind of gettering technique is necessary for removing metal impurities mixed in as explained above. As the gettering technique, there are the Intrinsic Gettering (IG) by which an oxide of oxygen and silicon included in the silicon substrate is deposited only inside the substrate to be used as a getter sink and the Extrinsic Gettering (EG) by which polycrystalline silicon or concentrated phosphorous (P) regions, etc. is formed on the back surface of the substrate and a getter sink is formed by using a strain stress with silicon. However, neither of the above methods was sufficiently capable as a gettering method and was not able to sufficiently reduce white defects caused by a dark-current of a solid-state imaging element.
To reduce the white defects as above, the present inventors have proposed a technique of, for example, performing ion implantation of a congener element of a silicone substrate, such as carbon, on one surface of the substrate by a doze of 5×10
13
ions/cm
2
or more and forming an epitaxial layer of silicon on its surface in the Japanese Unexamined Patent Publication No. 6-338507.
According to the method, white defects of a solid-state imaging device is reduced to ⅕ or less comparing with that in the case of an epitaxial substrate using a conventional gettering method.
FIG. 1
shows a reduction of white defects of the solid-state imaging device according to the method described in the Japanese Unexamined Patent Publication No. 6-338507, wherein the number of white defects was standardized by assuming the number of white defects when not performing ion implantation to be 1. As shown in
FIG. 1
, by performing ion implantation of carbon, white defects widely reduce when a doze of carbon is 5×10
13
ions/cm
2
or so and further reduce when a doze of carbon is 5×10
13
ions/cm
2
or more, for example, raised to 5×10
14
ions/cm
2
.
Note that when a doze of carbon exceeds 5×10
15
ions/cm
2
, the crystallinity of a mirror surface of the substrate and a silicon epitaxial layer grown thereon are reduced.
From the above, in the Japanese Unexamined Patent Publication No. 6-338507, there is described that a range of 5×10
13
to 5×10
15
ions/cm
2
is preferable as a doze of carbon.
However, along with the solid-state imaging devices getting highly sensitive, a further reduction of white defects has been desired and a necessity of further improvement of the above conventional method has risen.
SUMMARY OF THE INVENTION
The present invention was made in consideration of the above problem and has as an object thereof to provide a method of producing a solid-state imaging device to reduce white defects caused by a dark-current by effectively bringing out an ability of gettering contaminating impurities mixed in during formation of a crystal growth layer for forming a solid-state imaging element, for example, for a buried gettering layer formed by introducing carbon to a silicon substrate.
To attain the above object, according to a first aspect of the present invention, there is provided a method of producing a solid-state imaging device, including the steps of forming a buried getter sink layer by introducing to a semiconductor substrate a substance of a second element which is a congener of a first element composing the semiconductor substrate, forming a crystal growth layer by crystal growing the substance of the first element on a surface of the semiconductor substrate, and forming a solid-state imaging element in and on the crystal growth layer at a lower temperature than that in the case of forming an extrinsic getter sink layer by introducing a substance of a third element of a different group from the first element to a back surface of the semiconductor sub

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