Metal treatment – Barrier layer stock material – p-n type
Reexamination Certificate
1999-04-01
2002-02-05
Chaudhuri, Olik (Department: 2814)
Metal treatment
Barrier layer stock material, p-n type
C438S017000, C438S143000, C438S473000, C257S048000
Reexamination Certificate
active
06344092
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an epitaxial semiconductor substrate, manufacturing method thereof, manufacturing method of a semiconductor device and manufacturing method of a solid-state imaging device.
2. Description of the Related Art
As semiconductor substrates for manufacturing semiconductor devices, CZ substrates grown by CZ (Czochralski) method, MCZ substrates grown by MCZ (magnetic field Czochralski) method, and epitaxial substrates having epitaxial layers made on those substrates are often used generally.
As semiconductor substrates for solid-state imaging devices, epitaxial substrates and MCZ substrates are mainly used to reduce uneven image contrast caused by uneven dopant concentration, i.e., striation. Among them, epitaxial substrates can be made to include a low-resistance region (buried region or low-resistance substrate) under epitaxial layers for forming a device, they are effective for progressing low-voltage driving and low power consumption of solid-state imaging devices. Therefore, their wider use is still expected.
For manufacturing silicon (Si) epitaxial substrates, chemical vapor deposition (CVD) is currently used as a practical method, and four kinds of source gases are mainly used therefor. That is, hydrogen reduction process uses SiCl
4
, or SiHCl
3
, and reaction occurring there is expressed as follows.
SiCl
4
. . . SiCl
4
+2H
2
→Si+4HCl
SiHCl
3
. . . SiHCl
3
+H
2
→Si+3HCl
Thermal decomposition method uses SiH
2
Cl
2
or SiH
4
, and reaction occurring there is expressed as follows.
SiH
2
cl
2
. . . SiH
2
Cl
2
Si+2HCl
SiH
4
. . . SiH
4
Si+2H
2
Among these four kinds of source gases, SiHCl
3
is inexpensive, grows fast, and is suitable for growth of a thick epitaxial layer. And it is most used for manufacturing Si epitaxial substrates for solid-state imaging devices.
However, whichever one of those source gases is used, Si epitaxial substrates have a high impurity concentration, especially metal impurity such as heavy metal impurity, which undesirably mixes in during deposition of the epitaxial layer. Therefore, so-called white defects due to a dark current of a solid-state imaging device cannot be reduced sufficiently, and this makes characteristics and the production yield poor.
Possible sources of metal impurities such as heavy metal impurities are stainless steel (SUS) members in a bell jar of an epitaxial growth apparatus and source material gas pipes, among others. It is assumed that, if a source gas contains a chlorine (Cl) gas, for example, it decomposes and produces HCl during growth, this corrodes stainless steel members to produce a chloride of a metal, the metal chloride is captured into the source gas, and the metal impurity is caught into the epitaxial layer. In some cases, HCl gas is intentionally introduced into a bell jar to lightly etch off the surface of a Si substrate prior to epitaxial growth of layers, and this is also a cause of corrosion of stainless steel members.
Therefore, when a Si epitaxial substrate is used to fabricate a solid-state imaging device, some gettering technique is necessary for removing metal impurities. As such gettering technique, there are, for example, intrinsic gettering for precipitating over-saturated oxygen in the Si substrate exclusively within the substrate and using it as the getter sink, and extrinsic gettering for making a polycrystalline Si film or a region doped with high-concentrated phosphorus (P) on the bottom surface of the Si substrate and utilizing a distortion stress caused thereby to make a getter sink. None of them, however, had sufficient ability to remove metal impurities from a Si epitaxial substrate, and could not sufficiently reduce white defects of solid-state imaging devices.
Taking the above matters into account, the Inventor previously proposed a method for manufacturing a Si epitaxial substrate by implanting carbon into one of the surfaces of an Si substrate by a dose amount of 5×10
13
cm
−2
or higher and thereafter stacking an Si epitaxial layer thereon (Japanese Patent Laid-Open Publication No. hei 6-338507). According to the method, since a getter sink assumed to be a compound of carbon and oxygen in the substrate can powerfully getter metal impurities, etc. mixed into the epitaxial layer, white defects of solid-state imaging devices could be reduced to ⅕ as compared with Si epitaxial substrates made by using conventional gettering method.
To control impurities (especially metal impurities) mixing into epitaxial layers under growth, conventionally used were (1) a method for observing pits or crystal defects in epitaxial layers after growth, (2) a method for quantitatively measuring heavy metal impurities on the surface of an epitaxial layer or in a substrate bulk by atomic absorption spectrometry, inductively coupled plasma mass spectrometry (ICP-MS), or neutron activation analysis, (3) a method for conducting electric measurement such as lifetime measurement on the entirety of an epitaxial substrate by microwaves, and so on.
Among these methods, control of impurities by microwave lifetime measurement needs no pre-treatment, and gets a result quickly and easily. Therefore, microwave lifetime measurement is used widely. With regard to such, the Applicant also proposed a method for reducing white defects of solid-state imaging devices by using a Si epitaxial substrate having a lifetime whose ratio relative to the lifetime of the Si substrate before deposition of the epitaxial layer is larger than a predetermined value (Japanese Patent Laid-Open Publication No. hei 9-139408).
However, in the Si epitaxial substrate treated by carbon gettering, since the getter sink behaves as a center of electron-hole recombination, there is the problem that the measured lifetime does not reflect the amount of impurities mixing into the epitaxial layer under growth. To date, therefore, instead of measuring the life time of a Si epitaxial substrate treated by carbon gettering, the lifetime was measured from a monitor substrate prepared by forming the epitaxial layer on a Si substrate of the same batch but not treated by carbon gettering, and the result was used to evaluate the quality of the Si epitaxial substrate.
However, even among Si epitaxial substrate made in the same batch, a difference among the substrates is inevitable. Therefore, although there is a correlation to an extent between the lifetime measured from the monitor substrate and white defects of solid-state imaging devices manufactured by using Si epitaxial substrates treated by carbon gettering, the correlation is not satisfactory. It is therefore actually difficult to evaluate white defects of solid-state imaging devices, i.e., degree of impurity contamination of Si epitaxial substrates by heavy metal impurities, for example, and accurately know their acceptabiity from the result of measurement of lifetime using a monitor substrate. Furthermore, a wafer-by-wafer type has become the main current of epitaxial devices made by processing a semiconductor substrate as large as 8 inches or more in diameter, and the degree of impurity contamination varies from one sheet of the semiconductor substrate to another. Therefore, measurement of the lifetime using a monitor substrate has become almost meaningless.
In light of the above there is a strong demand for a technique which enables direct measurement of lifetime of a Si epitaxial substrate itself treated by carbon gettering, and can determine acceptability of the Si epitaxial substrate precisely and quickly.
OBJECTS AND SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide an epitaxial semiconductor substrate and its manufacturing method which enables precise and quick determination of acceptability of the epitaxial semiconductor substrate treated by carbon gettering.
Another object of the invention is to provide a method for manufacturing a semiconductor device capable of precisely and quickly determining acceptability of an epitaxial semicondu
Chaudhuri Olik
Kananen Ronald P.
Peralta Ginette
Rader & Fishman & Grauer, PLLC
LandOfFree
Epitaxial semiconductor substrate, manufacturing method... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Epitaxial semiconductor substrate, manufacturing method..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Epitaxial semiconductor substrate, manufacturing method... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2969501