JP2671151B2 - Semiconductor device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a semiconductor device, and more particularly to a charge transfer device.

(Prior Art) In recent years, a video camera incorporating a solid-state imaging device has been widely used. Among them, the mainstream of solid-state imaging devices is the interline transfer CCD.
(Hereinafter referred to as "IT-CCD").

FIG. 3 shows a cross section of a conventional IT-CCD. In FIG. 3, 31 is an N-type substrate, 32 is a P layer, 33 is a photoelectric conversion element, 34 is a vertical transfer CCD transfer channel, and 35 is a vertical transfer C.
CD transfer gate, 36 is a read transfer channel,
The transfer channel 34 and the read-out transfer channel 36 are regions in which charges are controlled by the transfer gate 35, and thus are active regions of the solid-state image sensor. 37 is a separating part.

Next, the operation of the above conventional example will be described. The signal charge generated by the light incident on the photoelectric conversion element 33 is accumulated in the photoelectric conversion element 33 and is sent to the transfer channel 34 through the read transfer channel 36 by applying the pulse voltage to the transfer gate 35. Then the transfer channel
It is transferred through 34 in the direction perpendicular to the paper surface.

(Problems to be Solved by the Invention) By the way, in the above-described conventional configuration, the vertical transfer CCD including the transfer channel 34 and the transfer gate 35, the read transfer channel 36, the photoelectric conversion element 33, and the separation of the adjacent pixel are separated. One unit pixel is composed of the section 37, and the size of this unit pixel is determined by the optical system of the element and the number of pixels. That is, the above four elements must be included in a fixed size. However, with the recent trend toward higher resolution, deterioration of element characteristics due to the reduction of the area of each element has become unavoidable. One of them is a decrease in sensitivity due to the reduction of the photoelectric conversion element 33,
There are problems such as a decrease in the maximum transfer charge amount (a decrease in the saturation charge amount, a decrease in the dynamic range) due to the reduction of the transfer channel 34.

The present invention is to solve the above conventional problems,
By reducing the area of the transfer channel without reducing the transfer charge amount, the area of the photoelectric conversion element can be increased conversely to realize a charge transfer device with improved sensitivity of the element. is there.

(Means for Solving the Problem) The present invention provides a semiconductor device in which a convex portion extends in a certain direction in a partial region of the surface of a semiconductor layer, in which the upper surface and both side surfaces are convex portions formed of (100) crystal planes. And an electrode formed via an insulating film so as to extend over the upper surface and both side surfaces of the convex portion, and by applying a voltage to this electrode,
The electric charge is transferred in the convex portion in a certain direction.

Further, the present invention provides a semiconductor device in which a convex portion is formed in a partial region of the surface of a semiconductor layer of one conductivity type, in which photoelectric conversion of a conductivity type opposite to that of the semiconductor layer formed near the convex portion of the surface of the semiconductor layer is performed. A region, at least a transfer channel region of a conductivity type opposite to the semiconductor layer formed on the upper surface of the convex portion, and an insulating film formed so as to extend from the transfer channel region to both side surfaces of the convex portion and the photoelectric conversion region. And an electrode.

Further, in the present invention, the upper surface and both side surfaces of the convex portion are composed of (100) crystal planes.

(Operation) According to the present invention, when the upper surface and the three side surfaces of the convex portion in which a partial region of the surface of the semiconductor layer is vertically projected are made into (100) crystal planes, the convex portion and the insulating film are separated from each other. The interface level is minimized, the charge transfer efficiency is maximized, and the three surfaces of the convex portion become the active region. In other words, the active region becomes three-dimensional, so that the area of the active region is smaller than the conventional one. The size of the semiconductor device can be reduced as compared with a planar device, and the entire semiconductor device can be miniaturized.

Further, when the electrode is formed over the three surfaces of the convex portion, when a voltage is applied to this electrode, the effect of forming a depletion layer from the upper surface of the convex portion and the effect of forming a depletion layer from both side surfaces of the convex portion are provided. Overlap each other, depletion of the convex portion can be performed at a lower voltage than that of a conventional planar electrode. In other words, since the charge transfer channel can be easily formed in the convex portion and the transfer charge amount can be increased, Since the convex portion can be formed thin without reducing the saturated charge amount and the dynamic range, the integration degree of the semiconductor device can be improved.

(Embodiment) FIG. 1 shows a general schematic configuration of an embodiment of the present invention. In FIG. 1, 10 is a P-type substrate, 11 is an N-type buried channel, 12 is a main surface of the P-type substrate 10, 13 is a surface perpendicular to the main surface 12, and 14 is parallel to a vertical surface 13. The surface. Here, the main surface 12, the surface 13 and the surface 14 are crystallographically equivalent surfaces. In an actual device, an insulating film such as an oxide film is formed around the transfer channel 11 by a thermal oxidation process or the like, and a transfer gate made of a polycrystalline silicon film or the like is formed thereon.

At this time, if the principal surfaces 12, 13 and 14 are not crystallographically equivalent, even if the same thermal oxidation step is performed, the oxide film thickness formed on each surface will not be equal. Also, the effective mass and the mobility are not equal. Therefore, even if the surface 13 and the surface 14 other than the main surface 12 are formed, they do not function effectively.

However, such a problem can be solved by constructing these planes with crystallographically equivalent planes. Especially,
In a MOS device, these planes are (10
0) or a crystallographically equivalent surface.

FIG. 2 is a diagram showing a cross section of a structure of an actual element according to an embodiment of the present invention. In FIG. 2, 21 is an N-type substrate, 22 is a P layer, 23 is a photoelectric conversion element, 24 is a transfer channel of a vertical transfer CCD, 25 is a transfer gate, 26 is a read transfer channel, and 27 is a separation section. Next, an example configured in this way will be described. In Figure 2, the transfer channel
With the 24, the same cross-sectional area as the transfer channel 34 of the conventional example can be realized with a much smaller upper area.
Is surrounded by the gate 25 in three directions, the voltage required for depleting the channel due to the two-dimensional effect is lower than that in the case where the transfer gate 25 is in contact only in one direction. Therefore, the impurity concentration of the transfer channel 24 can be increased, and the maximum transfer charge amount can be increased accordingly.

Further, since the read transfer channel 26 is formed on the surface perpendicular to the substrate surface, the upper area is unnecessary. Therefore, these areas can be greatly reduced, and the photoelectric conversion element is correspondingly reduced.
Since the area of 23 can be enlarged, the sensitivity can be improved.

In order to effectively produce these effects, as described in the explanation of FIG. 1, the three faces of the transfer channel 24 facing the transfer gate 25 are crystallographically equivalent faces. is necessary.

Further, in this embodiment, the transfer channel 24 has a shape projecting from the semiconductor substrate, but conversely, in a device in which the side surface of a so-called trench structure in which the semiconductor substrate is recessed in a groove shape is used as the transfer channel, the same applies. It is valid.

Further, since the present embodiment is a solid-state image sensor, an N-type substrate is used, but a P-type substrate may be used as a general charge transfer element as shown in FIG.

Further, it goes without saying that it is generally effective not only for the charge transfer element but also for an element suitable for the gist of the present invention.

(Effect of the Invention) As described above, according to the present invention, when the upper surface and the three side surfaces of the convex portion in which a partial region of the surface of the semiconductor layer is vertically protruded are (100) crystal planes, The level of the interface between the convex portion and the insulating film is minimized, the charge transfer efficiency is maximized, and the three surfaces of the convex portion become active regions. In other words, the active region becomes three-dimensional. There is an effect that the area of the active region is reduced as compared with the conventional planar type, and the entire semiconductor device can be downsized.

Further, according to the present invention, when the electrode is formed over the three surfaces of the convex portion, when a voltage is applied to this electrode, the effect of forming a depletion layer from the upper surface of the convex portion and the depletion from both side surfaces of the convex portion are achieved. The effect of forming a layer overlaps, and the depletion of the convex portion can be performed at a lower voltage than that of the conventional planar electrode. In other words, the charge transfer channel can be easily formed on the convex portion and the transfer charge amount can be increased. As a result, it is possible to form the protrusions in a fine shape without reducing the saturated charge amount and the dynamic range, and thus it is possible to improve the integration degree of the semiconductor device.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic structure of an embodiment of the present invention, FIG. 2 is a sectional view of a structure of an actual element of an embodiment of the present invention, and FIG. 3 is a sectional view of a conventional IT-CCD. 10 ... P-type substrate, 11 ... N-type and buried transfer channel, 12 ... P-type substrate main surface, 13 ... Plane perpendicular to main surface,
14 …… A plane parallel to the vertical plane, 21,31 …… N-type substrate, 22,32…
… P layer, 23,33 …… photoelectric conversion element, 24,34 …… transfer channel, 25,35 …… transfer gate, 26,36 …… read-out transfer channel, 27,37 …… separator.

Claims (3)

(57) [Claims] 1. A semiconductor device in which a convex portion extends in a certain direction in a partial region of a surface of a semiconductor layer, wherein the upper surface and both side surfaces are (100) crystal planes, and the upper surface of the convex portion. And an electrode formed via an insulating film so as to extend over both side surfaces, and by applying a voltage to the electrode, charges are transferred in the convex portion in the certain direction. A semiconductor device characterized by the following. 2. A semiconductor device in which a convex portion is formed in a partial region of the surface of a semiconductor layer of one conductivity type, wherein the semiconductor layer has a conductivity type opposite to that of the semiconductor layer formed in the vicinity of the convex portion of the surface of the semiconductor layer. A photoelectric conversion region, at least a transfer channel region of a conductivity type opposite to the semiconductor layer formed on the upper surface of the convex portion, and extending from the transfer channel region to both side surfaces of the convex portion and the photoelectric conversion region. An electrode formed through an insulating film. 3. The semiconductor device according to claim 2, wherein the upper surface and both side surfaces of the convex portion are (100) crystal planes.