JPH0613594A - Solid-state image pick-up device - Google Patents

Abstract

PURPOSE:To make difficult the movement of heavy metallic iron and the like, trapped in a silicon substrate, in the silicon substrate. CONSTITUTION:A recess 14 is formed on the rear surface of a solid-state image pick-up device 11 and adhesive agent 12 is applied on the inside of the recess 14 to bond the device 11 to a package 13. The adhesive agent 12 pulls the solid-state image pick-up device 13 toward the rear surface after heat treatment since the thermal expansion coefficient of the adhesive agent is smaller than a silicon substrate. Accordingly, the surface of the solid-state image pick-up device 11 becomes concave physically and is compressed and, simultaneously, the lattice spacing of silicon atoms is decreased whereby the potential between silicon atoms is increased and it is effective to restrain the movement of heavy metallic ion and the like.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state image pickup device.

[0002]

2. Description of the Related Art A conventional solid-state image pickup device and a method for manufacturing the same will be described with reference to the drawings.

FIG. 3 is a sectional view for explaining the mold state of the solid-state image pickup device. In FIG. 3, the package 1
The solid-state image pickup device 3 is adhered to the upper surface by using the adhesive 2.

Next, FIG. 4 is a sectional view of a conventional solid-state image pickup device. In FIG. 4, a P-type well region 5, an N-type impurity layer 6 of the light receiving portion and an N-type of the charge transfer portion are formed on the surface of the N-type semiconductor substrate 4.
The mold well layer 7 is formed. Polycrystalline silicon 9 is formed on the N-type well layer 7 of the charge transfer portion via a gate insulating film 8, and a silicon oxide film 10 is formed above the polycrystalline silicon 9. Further, a light shielding film 11 is formed so as to prevent incident light from leaking into portions other than the N-type impurity layer 6 of the light receiving portion, and a protective film 12 is formed thereon.

[0005]

However, in the above solid-state image pickup device, the solid-state image pickup device 3 is packaged in the package 1.
After adhering to, the heat treatment is performed to dry the adhesive 2. However, since the thermal expansion coefficient of the solid-state imaging device 3 is smaller than that of the adhesive 2, the surface of the solid-state imaging device 3 has a convex warped shape. For this reason, the interstitial distance on the surface of the silicon semiconductor becomes large and the interlattice potential becomes small. Therefore, when diffusion is performed, heavy metal ions such as Fe ions already trapped in the semiconductor substrate easily move in the silicon semiconductor. Will be able to spread to. In the solid-state imaging device 3, when heavy metal ions are present at the PN junction of the light receiving portion formed by the N-type semiconductor substrate 4 and the P-type well region 5,
Even when the light is completely blocked, the heavy metal ions act as recombination centers, and the dark current locally increases. Dark current is a kind of thermally generated leakage current. In particular, when a dark subject is photographed, it becomes an image with white scratches, and the S / N ratio thereof is significantly reduced.

[0006]

In order to solve the above-mentioned problems of the prior art, a solid-state image pickup device of the present invention comprises a light-receiving portion in which a main surface of a one-conductivity type semiconductor substrate is provided with a region of the opposite conductivity type. At least a charge transfer section for reading out the signal charge generated in the light receiving section and transferring the signal charge, and a transfer electrode provided above the charge transfer section are provided, and a recess is formed on the surface opposite to the main surface of the semiconductor substrate. And at least one or more.

[0007]

According to the present invention, by adopting the above-mentioned constitution, the surface of the silicon substrate of the solid-state image pickup device can be warped in a concave shape even after the adhesive heat treatment. Therefore, by physically compressing the surface of the silicon semiconductor substrate, the interstitial distance of silicon can be shortened, and diffusion of heavy metal ions trapped in the silicon substrate to the surface of the silicon substrate can be significantly reduced. it can.

[0008]

1 is a sectional view showing a solid-state image pickup device according to an embodiment of the present invention. In FIG. 1, 11 is a solid-state imaging device, 12 is an adhesive, 13 is a package, and 14 is a recess formed on the back surface of the solid-state imaging device 11.

The solid-state image pickup device 11 is adhered onto the package 11 by using an adhesive 12 applied inside the recess 14 on the back surface of the solid-state image pickup device 11. Since the adhesive 12 has a thermal expansion coefficient smaller than that of the silicon substrate on which the solid-state imaging device 11 is configured after the heat treatment, the solid-state imaging device 11 is pulled below the solid-state imaging device 11 (direction of arrow in FIG. 1). Therefore, the substrate surface of the solid-state imaging device 11 is physically concave.

Next, a method of manufacturing a solid-state image pickup device according to an embodiment of the present invention will be described with reference to FIG.

As shown in FIG. 2A, a CVD protective film 22 is formed on the surface of the silicon substrate 21 of the solid-state image pickup device.

After that, as shown in FIG. 2B, a pattern for forming holes is formed by a photoresist 23 on the back surface of the silicon substrate 21 of the solid-state image pickup device.

Next, as shown in FIG. 2C, wet etching is performed with a mixed solution of hydrofluoric acid and nitric acid to form the recess 24.
To form. Then, the photoresist 23 is removed.
This makes it possible to realize a solid-state imaging device in which the recess 24 is formed on the back surface of the silicon substrate 21.

[0014]

As described above, according to the present invention, by forming a recess on the back surface of the silicon substrate of the solid-state image pickup device, the surface of the silicon substrate can be made concave even after bonding. Therefore, the distance between the silicon lattices is shortened, diffusion of heavy metal ions in the silicon substrate to the vicinity of the PN junction photodiode can be significantly suppressed, and a local dark current can be significantly reduced. Can be provided.

[Brief description of drawings]

FIG. 1 is a sectional view of a solid-state imaging device according to an embodiment of the present invention.

FIG. 2 is a process sectional view showing a method of manufacturing a solid-state imaging device according to an embodiment of the present invention.

FIG. 3 is a cross-sectional view of a conventional solid-state imaging device in a molded state.

FIG. 4 is a sectional view of a conventional solid-state imaging device.

[Explanation of symbols]

 11 solid-state imaging device 12 adhesive 13 package 14 recess

Claims (1)

[Claims] 1. A light receiving portion having a region of opposite conductivity type on a main surface of a semiconductor substrate of one conductivity type, a charge transfer portion for reading signal charges generated in the light receiving portion and transferring the signal charges, and the charge. A solid-state imaging device comprising at least a transfer electrode provided above a transfer section, and having at least one recess on the surface opposite to the main surface of the semiconductor substrate.