JPH03181139A - Charge transfer device - Google Patents

Abstract

PURPOSE:To maintain a required channel stop function even if the size of a channel stop region is reduced by making impurity concentration at a part of the channel stop region on contact with charge transfer region lower than that of the parts. CONSTITUTION:A channel stop region formed on the surface of a p-type semiconductor substrate 1 consists of a p-type channels stop region 6 at a part in contact with an n-well region 2 being a charge transfer region and a p<+>-type channel stop region 3 self-aligned with the region 6, where impurity concentration is higher than that of the region 6. Thus the n-well region 2 is free from influence of crystal defects caused in the p<+>-type channel stop region 3 so that the impurity concentration of the p<+>-type channel stop region 3 can be sufficiently high as well as a required channel stop function can be maintained even if the size is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a charge transfer device, and particularly to the structure of a channel stop region that defines a charge transfer region of a charge transfer device.

[Prior Art] A cross-sectional view of a conventional buried channel type charge transfer device is shown in FIG. As shown in the figure, a p-type semiconductor substrate 1
An n-well region 2 constituting a charge transfer region is provided in the surface region of the
A + type channel stop region 3a is arranged. Furthermore, a gate electrode 5 is provided on the surface of the semiconductor substrate via a gate oxide film 4 so as to cover the n-well region 2 .

In a charge transfer device having such a structure, by sequentially applying appropriate transfer pulses to the plurality of gate electrodes 5, a potential depression (potential well) formed in the n-well region 2 is sequentially moved. Signal charges input into the n-well region can be moved along with the movement of the potential well. In this case, in the p+ type channel stop region 3a, since this region is a region doped with p-type impurities at a high concentration, a voltage of the level applied to the gate electrode 5 has no potential on the surface of this region. No dents occur. Therefore, the charge transfer region can be electrically isolated from other regions by the p+ type channel stop region 3a.

[Problems to be Solved by the Invention] In solid-state imaging devices and the like that use multiple charge transfer devices in parallel, there is a need to increase the density of the devices in order to improve resolution. In this case, it is necessary to reduce the width of the charge transfer region and to reduce the channel stop region. Therefore, in order to reduce the size of the channel stop region without reducing the channel stop function, the impurity concentration in the region must be increased. However, as the impurity concentration of the channel stop region is increased, crystal defects are induced, which deteriorates the characteristics of the device due to an increase in leakage current, an increase in noise signals, and the like.

Furthermore, increasing the concentration of the channel stop region results in a decrease in the effective channel width of the charge transfer region.

The reason for this is that, as shown in the substrate surface potential diagram of FIG. 6, the potential on both sides of the n-well region is raised by the p+ type channel stop region. This is because the potential of the area is raised further and the well formed there becomes shallower.

The ratio of the effective channel width to this n-well region is n
It decreases as the width of the well region is reduced. Therefore, as described above, when the width of the n-well region is reduced due to the increase in the density of devices, the channel stop region will be strongly affected by the high concentration, the effective channel width will decrease, and the charge The transferable charge amount of the transfer device decreases.

[Means for Solving the Problems] The charge transfer device of the present invention includes a channel stop region formed on the surface of a semiconductor substrate, and a channel region (charge transfer region) separated by the channel stop region. The stop region is composed of a portion with a relatively low impurity concentration that contacts the charge transfer region and a portion with a high impurity concentration other than that portion.

[Example] Next, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a sectional view showing one embodiment of the present invention. In this figure, the same reference numerals are given to the parts common to the parts of the conventional example shown in FIG. 5, and therefore redundant explanation will be omitted. The difference between this embodiment and the conventional example is that the channel stop region formed on the surface of the semiconductor substrate has a p-type channel stop region 6 in contact with an n-well region 2, which is a charge transfer region, and a self-contained region with respect to this region. The point is that it has a double structure with the p+ type channel stop region 3 having a higher impurity concentration than this region which is formed in alignment.

Next, the manufacturing method of this example will be explained with reference to FIGS. 2(a) to 2(f).

First, as shown in FIG. 2(a), a thin silicon oxide M7 with a thickness of about 50 nm is formed on the surface of the p-type semiconductor substrate 1.
A silicon nitride film 8 is grown thereon to a thickness of 1100 nm. The silicon nitride film 8 is patterned so that the location where the channel stop is to be formed is opened, and boron is applied at a dose of 5 to 10
A p-type channel stop region 6 is formed by implanting ions of about 1012/-.

Next, as shown in FIG. 2(b), a silicon oxide film 9 with good coverage is formed to a thickness of 1100 nm using high temperature and low pressure chemical vapor deposition.
grow to a certain extent. Next, by etching the silicon oxide film 9 using an anisotropic RIE method, sidewall silicon oxide M is formed on the sidewall of the silicon nitride film 8 as shown in FIG. 2(c).
9 a is formed. In this state, boron is further ion-implanted at a dose of about 5 to 10.times.10"/ad to form p+ type channel stop region 3.

Next, a silicon oxide film 10 is grown to a thickness of about 200 nm,
On the other hand, if etching is performed using the RIE method, the second
As shown in Figure (e), silicon oxide films 9a and 10 can be embedded between the patterns of silicon nitride film 8.

Next, as shown in FIG. 2(f), the silicon nitride film 8 is removed with an etching solution that is highly selective to the silicon oxide film, the photoresist 11 is buttered, and phosphorous is ion-implanted. , an n-well region 2 is created.

Finally, the silicon oxide films 7.9a and 10 are removed with an etching solution, the gate oxide film 4 is formed by thermal oxidation, and the gate electrode 5 is formed, thereby obtaining the device shown in FIG.

As described above, since the p+ type channel stop region 3 is separated from the n-well region, it can be a region with a sufficiently high impurity concentration without being bothered by the problem of increased leakage current to the channel region. . therefore,
Even if the width of the p+ type channel stop region is reduced, the necessary channel stop function can be maintained. In that case, if the above manufacturing method is used, the width of the p+ type channel stop region 3 is regulated by the thickness of the sidewall silicon oxide film 9a, so it is possible to set it extremely finely to a dimension that is below the limit of lithography technology. can. Furthermore, according to the above manufacturing method, the n-well region 2 can be formed in self-alignment with the channel stop region 3.6, so its dimensions can be precisely controlled.

Further, in the charge transfer device having the above structure, the n-well region is p+
Since it is not in contact with the mold channel stop region, the effective channel width is not reduced.

FIG. 3 is a sectional view showing another embodiment of the present invention. In this embodiment, the p-type channel stop region 6a is formed deeply and forms the bottom of the tank surrounding the n-well region 2. Also in this embodiment, since the n-well region is in direct contact with the p+ type channel stop region 3, the same effects as in the previous embodiment can be achieved.

Next, the manufacturing method of this example will be explained with reference to FIGS. 4(a) to 4(d).

First, as shown in FIG. 4 (a), a thin silicon oxide film 7 is formed on the surface of the p-type semiconductor substrate 1 to a thickness of about 50 nm.
A silicon nitride film 8 is deposited thereon to a thickness of 1100 nm.

Silicon nitride film 8 is patterned to have openings at locations where the channel stop region and n-well region will be formed, ions are implanted, and then heat treatment is performed to form p-type channel stop region 6a.

Next, as shown in FIG. 4(b), the polysilicon film 12
is deposited to a thickness of 1100 nm and patterned so that it remains in the area where the n-well region is to be formed.

Next, as shown in FIG. 4(c), a sidewall silicon oxide film 9a is formed on the sidewalls of the silicon nitride film 8 and the polysilicon film 12 by depositing a silicon oxide film and anisotropic etching. Subsequently, using these films as a mask, boron ions are implanted to form p+ type channel stop region 3.

Next, as shown in FIG. 4(d), the silicon oxide film 10 is deposited and anisotropically etched to fill the gaps between the sidewall silicon oxide films with the silicon oxide film 10.Subsequently, the silicon nitride film 8 and Polysilicon film 12 is removed by wet etching, necessary areas are covered with photoresist 11, and ions are implanted to form n-well region 2.

If&, photoresist 11 and silicon oxide film 7.9
By removing portions a and 10 and forming a gate oxide film 4 and a gate electrode 5, the charge transfer device shown in FIG. 3 is obtained.

[Effects of the Invention] As explained above, the present invention provides a p-type channel stop region with a relatively low impurity concentration between the well region that forms the bottom of the charge transfer region of a charge transfer device and the p + type channel stop region. Since the well region is interposed, the well region is not affected by crystal defects generated in the p+ type channel stop region. Therefore, according to the present invention, the impurity concentration of the p+ type channel stop region can be made sufficiently high, and the necessary channel stop function can be maintained even if the size of the p + type channel stop region is reduced. Further, according to the present invention, since the effective channel width with respect to the well region does not decrease, a large amount of transferable charge can be ensured. Therefore, when the charge transfer device of the present invention is used in a solid-state image sensing device, it is possible to achieve high density and high image quality without increasing the chip area.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing one embodiment of the present invention, and FIG.
) to (f> are cross-sectional views for explaining the manufacturing process,
FIG. 3 is a sectional view showing another embodiment of the present invention, and FIG.
a) to (d) are cross-sectional views for explaining the manufacturing process, FIG. 5 is a cross-sectional view of a conventional example, and FIG. 6 is an explanatory view of its operation. 1...p-type semiconductor substrate, 2...n-well region,
3... P7 type channel stop region, 4... Gate oxide film, 5... Gate electrode, 6.6
a...p-type channel stop region, 7.9.10
...Silicon oxide film, 9a...Side wall silicon oxide film,
8... Silicon nitride film, 11... Photoresist, 12... Polysilicon film.

Claims (1)

[Claims] A charge transfer device in which a charge transfer region is provided in a semiconductor substrate of a first conductivity type surrounded by a channel stop region of a first conductivity type, and a charge transfer electrode is provided on the charge transfer region with an insulating film interposed therebetween. A charge transfer device, wherein the channel stop region has a lower impurity concentration in a portion in contact with the charge transfer region than in other portions of the channel stop region.