JP2005236325A - Method for manufacturing solid-state image sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a solid-state image sensor, in which the dynamic range is wide, and the properties such as blooming tolerance, read-out voltage and smear can be improved. <P>SOLUTION: The solid-state image sensor is manufactured in which ion-implantation forming an impurity diffusion region 13 constituting a sensor part 2 is carried out at an angle of 7° to 45° from the wafer normal of a semiconductor wafer forming the solid-state imaging device. The ion-implantation process is divided to two or more processes, in which the direction inclined from the wafer normal is respectively in the reverse direction of the charge transfer direction of a transfer register 6. The width W<SB>1</SB>of the impurity diffusion region 13 is formed wider than the width of a positive charge storage region 17 in the charge transfer direction of the transfer register 6. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for manufacturing a solid-state imaging device.

In a CCD solid-state imaging device which is a kind of solid-state imaging device, a sensor portion is constituted by a photodiode formed by performing impurity diffusion by ion implantation in a semiconductor region.
Conventionally, the ion implantation process for forming the sensor portion of the CCD image pickup device has been performed only once from the viewpoint of improving work efficiency.

However, with the recent miniaturization of CCD solid-state imaging devices, finer adjustments of sensor characteristics, such as sensor pattern, blooming resistance, and readout voltage, have been required.
Moreover, the diameter of the wafer has been increased in order to reduce the cost. For this reason, the degree of demand for increasing the uniformity of manufacturing within the wafer surface and the stability of each lot is becoming stricter.

  In response to such a demand, the conventional sensor unit forming process by simple one-time ion implantation can no longer cope.

  In order to solve the above-described problems, in the present invention, a solid-state imaging device having a large dynamic range, improved blooming resistance, read voltage, smear, and the like is controlled by controlling an ion implantation process for forming a light receiving portion. A method for manufacturing a solid-state imaging device to be manufactured is provided.

According to the method for manufacturing a solid-state imaging device of the present invention, an impurity diffusion region constituting a sensor unit is formed in a semiconductor region, a transfer register for transferring signal charges is formed along each column of the sensor unit, and an impurity is formed. A method of manufacturing a solid-state imaging device having a positive charge accumulation region formed on the surface of a diffusion region, wherein ion implantation for forming an impurity diffusion region constituting a sensor unit is performed on a semiconductor wafer forming a solid-state imaging device The ion implantation process is performed at an angle of 7 ° or more and 45 ° or less from the normal, and the ion implantation process is performed in two or more ion implantation processes in which directions inclined from the wafer normal are opposite to each other in the charge transfer direction of the transfer register. In other words, the width of the impurity diffusion region is formed larger than the width of the positive charge storage region in the charge transfer direction of the transfer register.
According to the method for manufacturing a solid-state imaging device of the present invention, an impurity diffusion region constituting a sensor unit is formed in a semiconductor region, a transfer register for transferring signal charges is formed along each column of the sensor unit, and an impurity is formed. A method of manufacturing a solid-state imaging device having a positive charge accumulation region formed on the surface of a diffusion region, wherein ion implantation for forming an impurity diffusion region constituting a sensor unit is performed on a semiconductor wafer forming a solid-state imaging device The ion implantation process is performed at an inclination of 7 ° or more and 45 ° or less from the normal, and the directions inclined from the wafer normal are opposite to each other in a direction perpendicular to the charge transfer direction of the transfer register. The ion diffusion process is performed separately, and the width of the impurity diffusion region is formed larger than the width of the positive charge accumulation region in the direction orthogonal to the charge transfer direction of the transfer register.

According to the above-described manufacturing method of the present invention, the ion implantation step for forming the sensor portion is inclined by 7 ° or more and 45 ° or less from the normal to the wafer, and the ion implantation is performed twice or more in opposite directions to each other. The impurity diffusion region can be formed by extending horizontally in the inclined direction.
In addition, the electrical characteristics can be controlled by performing the ion implantation process in two or more opposite directions.
When ion implantation is performed twice in the opposite direction, the impurity diffusion region is widened on both sides, so that the sensor portion can be formed wider and the amount of charge handled can be increased.

  According to the above-described present invention, since the impurity diffusion region is widened, the amount of charge handled is increased and the dynamic range is widened.

Hereinafter, embodiments of the solid-state imaging device of the present invention will be described with reference to the drawings.
FIG. 1 is a view of an embodiment of a solid-state imaging device according to the present invention, and in this example, an imaging region, that is, an effective pixel region of a CCD solid-state imaging device as viewed from above. 2 The transfer electrode pattern is shown so that it can be seen.

  As shown in FIG. 1, the CCD solid-state imaging device 1 includes a vertical transfer register having a CCD structure on one side of each sensor unit row in which sensor units 2 constituting a plurality of pixels are arranged in a matrix in the imaging region. 6 is formed. Reference numeral 3 denotes an opening of the sensor unit 2. The vertical transfer register 6 includes two vertical transfer electrodes that transfer signal charges from the sensor unit 2 via a read gate unit, that is, a first vertical transfer electrode 4 and a second vertical transfer electrode 5. The direction of arrow a in FIG. 1 is the vertical transfer direction.

  The direction along the line AB in FIG. 1 is the horizontal transfer direction (the horizontal transfer part is not shown), and a cross section on the line AB is shown in FIG. Further, the direction along the line CD is the vertical transfer direction (because it is the direction in which the charge actually moves, so it will be referred to as the forward direction hereinafter), and a cross section along the line CD is shown in FIG.

For example, a first p-type semiconductor well region 12 serving as an overflow barrier is formed in a semiconductor substrate 11 made of n-type silicon, and the n-type constituting the light receiving unit 2 is formed in the first p-type semiconductor well region 12. An impurity diffusion region 13 and a read gate portion 14, an n-type transfer channel region 15 constituting the vertical transfer register 6, and a pixel separation portion (a p-type channel stop region is formed if necessary) 16 are formed. Yes.
A p-type positive charge storage region 17 is formed above the n-type impurity diffusion region 13, and a second p-type semiconductor well region 18 is formed below the n-type transfer channel region 15. The p-type semiconductor well region 12, the n-type impurity diffusion region 13, and the p-type positive charge accumulation region 17 constitute a sensor unit 2 that is a so-called HAD (Hole Accumulated Diode) sensor.

A gate insulating film 19 is formed on the surface of the semiconductor substrate 11 on which the first p-type semiconductor well region 12 is formed, and a read gate portion 14, a transfer channel region 15, and a channel stop region are formed through the gate insulating film 19. A first vertical transfer electrode 4 and a second vertical transfer electrode 5 are formed on 16.
Only the second vertical transfer electrode 5 is formed in the cross section on the line AB, and the second vertical transfer electrode 5 is formed on the first vertical transfer electrode 4 via the interlayer insulating film 20 in the CD cross section. The transfer channel region 15, the gate insulating film 19 and the vertical transfer electrodes 4 and 5 constitute a vertical transfer register 6.

Then, an interlayer insulating film 20 is formed so as to cover these vertical transfer electrodes 4 and 5, and a light shielding film 21 made of a metal such as Al is formed thereon, and the upper and side surfaces of the vertical transfer electrodes 4 and 5 are covered. An opening 3 is formed in the light shielding film corresponding to the light receiving portion.
Further, a passivation film 22 made of a transparent insulating film such as an oxide film is formed so as to cover the whole, and a planarizing film 23 made of a transparent insulating film such as glass is formed thereon. An on-chip color filter 24 is formed on the planarized surface of the planarizing film 23, and an on-chip lens 25 is formed on the top.

In this example, in particular, the width W ₁ of the impurity diffusion region 13 constituting the sensor unit 2 is set to the impurity in the case of normal ion implantation in one direction as shown in the comparative example of FIG. 9 (cross-sectional view in the vertical transfer direction). than the width _{W 2} of the diffusion region 13 is formed larger.

The opening 3 of the sensor unit 2 is set by the pattern of the opening 3 of the light shielding film 6, but the actual charge accumulation amount is determined by the distribution of impurity elements forming the sensor unit 2 in the semiconductor substrate 11.
In this example, the charge accumulation amount of the entire sensor unit is increased by increasing the width W ₁ of the impurity diffusion region 13, that is, by forming the sensor unit 2 widely.
As a result, the dynamic range of the CCD solid-state imaging device 1 can be increased.

Thus, the width W ₁ of the impurity diffusion regions, in order to form the normal vertical direction of the large than the width W ₂ of the impurity diffusion region when the ion implantation, as described below, inclined to the vertical transfer forward An ion implantation step inclined in a direction opposite to the ion implantation step and the vertical transfer direction may be performed.

Next, the manufacturing method of the solid-state image sensor of this invention is demonstrated.
Usually, when an ion implantation method is used for n-type dopant implantation for forming a sensor portion, it is at least 5 ° with respect to the wafer normal (ie, a line perpendicular to the surface of the semiconductor wafer) to suppress channeling. It is generally applied by tilting and rotating by 20 ° or more from the crystal axis.

On the other hand, in the method for manufacturing a solid-state imaging device according to the present invention, as shown in FIG. 3 and FIG. On the other hand, ion implantation is performed with an inclination of 7 ° to 45 °.
If the angle is less than 7 °, the effect of tilting and ion implantation is not sufficient, and if it exceeds 45 °, the light shielding film 21 and the like are partially blocked, so that neither is preferable.
At this time, the angle formed by the tilt direction with respect to the vertical transfer direction (C → D in FIG. 1) is determined by blooming resistance, that is, resistance to leakage of signal charges to adjacent pixels, and electrical characteristics such as readout.

  For example, in FIG. 5 showing a plan view of the vicinity of the sensor unit, when implantation is performed at an angle of 7 ° with respect to the normal line of the wafer from the pixel separation unit 16 to the readout gate unit 14 (arrow A), it is parallel to the vertical transfer direction. The blooming resistance is reduced by about 0.5 V as compared with the case where implantation is performed with an inclination of 7 ° with respect to the wafer normal (arrow B), and 7% with respect to the wafer normal from the read gate portion 14 toward the channel stop region 16. ° Decrease by about 1 V compared to the case of tilted injection (arrow C).

  That is, the impurity diffusion region 13 is formed on the side of the read gate portion 14 below the transfer electrodes 4 and 5 by implanting at an angle of 7 ° with respect to the wafer normal from the pixel separation portion 16 toward the read gate portion 14 (arrow A). Can be widely implanted to adjust the substantial read gate length.

  As described above, the ion implantation angle of the dopant forming the sensor unit 2 is used as a control parameter for obtaining a desired balance of characteristic values in a trade-off relationship such as blooming, readout, substrate applied voltage at the time of imaging, and smear. be able to.

  Conventionally, fine blooming characteristics are adjusted in the vertical transfer direction in a single ion implantation process to the extent that a significant difference is obtained in terms of manufacturing non-uniformity and instability (about 0.5 V as described above). Only the direction parallel to the vertical transfer direction or only the direction perpendicular to the vertical transfer direction is performed, and although the position of the impurity diffusion region 13 of the sensor unit 2 may be shifted, its size is almost unchanged. When the magnitude (depth) of the sensor potential is the same, the saturation charge amount is almost unchanged.

  If the saturation charge amount is large, the dynamic range also increases. However, if the sensor potential is to be increased (deep) in order to increase the saturation charge amount, the impurity concentration must be increased, that is, the dose amount in ion implantation must be increased. . However, increasing the dose increases the crystal defect density and increases the number of so-called white scratches.

Therefore, in the embodiment shown in FIGS. 1 to 3, as a means for increasing the dynamic range without increasing the number of white scratches, ion implantation for forming the sensor unit 2 is performed in a direction parallel to the vertical transfer direction. Thus, in the opposite directions, the ion implantation process is divided into about half doses in each of the two ion implantation steps.
As a result, as shown in FIG. 3, the impurity diffusion region 13 of the sensor unit 2 is enlarged as compared with the above-described comparative example of FIG. The balance of electrical characteristics such as blooming resistance may be adjusted by fine adjustment of the planar pattern, and the saturation charge amount can be increased and the dynamic range can be expanded without increasing the number of white scratches.

  In order to exert this effect, it is inclined by 7 ° or more from the normal line of the wafer so that the effect of narrowing the pixel separating portion 16 (see FIG. 3) between the adjacent sensor portions 2 in the vertical direction can be sufficiently obtained. Is required.

  In addition, when it is difficult to completely adjust electrical characteristics such as blooming resistance by fine pattern adjustment, vertical transfer as shown by the arrows in FIG. It is also possible to set the injection from an intermediate angle such as a direction rotated 45 ° horizontally from the direction.

On the other hand, for example, when ions are implanted twice with the same dose in the opposite directions in the horizontal direction, the impurity diffusion region 13 is expanded in the horizontal direction as shown in FIG. The amount can be increased and the dynamic range can be expanded.
In this case, since the widths of the readout gate unit 14 and the pixel separation unit 16 are further changed, characteristics such as readout characteristics and blooming resistance are also changed. Conditions such as the tilt angle of ion implantation are set to such an extent that the change in these characteristics causes no problem in the solid-state imaging device.

  In addition, the ion implantation process can be divided into three or more operations such as a vertical transfer forward direction, a reverse direction, and a direction from the readout gate portion to the pixel separation portion, that is, a direction perpendicular to the vertical transfer direction.

Further, the distribution of the dose amount of the ion implantation in the case of dividing into two times is not half, for example, 2/3 dose amount in the vertical transfer forward direction (C → D in FIG. 1) and reverse direction (D in FIG. 1). If a dose amount of 1/3 is distributed to C), a potential gradient in the forward transfer forward direction in the light receiving unit 2 as shown in the plan view of FIG. 8A and the PP diagram of FIG. 8A in FIG. 8B. And the sensor potential center slightly approaches the vertical transfer forward direction (D side in FIG. 1). Then, since reading is performed by the electrode on the vertical transfer forward direction side, that is, the second transfer electrode 5, the applied voltage required for reading is lower than that of the conventional structure.
In this way, a new function of adjusting electrical characteristics can be obtained by distributing the dose of ion implantation twice or more.

In addition, according to the manufacturing method of the present invention, by further setting and changing each condition of the ion implantation inclination angle, the angle from the vertical transfer direction, and the dose distribution in a plurality of regions in the wafer surface, respectively. In addition, it is possible to absorb the in-wafer distribution of the electrical characteristics, and it is possible to absorb the change with time of the state of the manufacturing apparatus.
That is, for example, by adjusting the conditions by performing feedback such as reducing the angle of the implantation direction on the semiconductor wafer surface by 20 ° from the previous time and adjusting these conditions, it is possible to stabilize the manufacturing and improve the uniformity within the wafer surface. Can do.

  The present invention is not limited to the above-described examples, and various other configurations can be taken without departing from the gist of the present invention.

It is a schematic block diagram (plan view) of the Example of the solid-state image sensor by this invention. It is sectional drawing in AB of FIG. It is sectional drawing in CD of FIG. It is a figure explaining the direction of ion implantation. It is a figure explaining the direction of ion implantation. It is a figure explaining the direction of ion implantation. It is sectional drawing of the horizontal direction of the other Example of the solid-state image sensor by this invention. It is a block diagram of the further another Example of the solid-state image sensor by this invention. It is A top view. 8B is a potential diagram of the light receiving section in the P-P ′ cross section of FIG. 8A. It is sectional drawing of the vertical transfer direction of the solid-state image sensor of the comparative example which formed the sensor part with the normal ion implantation method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 CCD solid-state image sensor, 2 Sensor part, 3 Opening, 4 1st transfer electrode, 5 2nd transfer electrode, 6 Vertical transfer register, 11 Semiconductor substrate, 12 1st p-type semiconductor well area | region, 13 Impurity diffusion area | region, 14 Read gate portion, 15 transfer channel region, 16 pixel separation portion, 17 positive charge accumulation region, 18 second p-type semiconductor well region, 19 gate insulating film, 20 interlayer insulating film, 21 light shielding film, 22 passivation film, 23 flat Chemical film, 24 on-chip color filter, 25 on-chip lens, 30 semiconductor wafer, 31 wafer radiation, I ion implantation direction, width of W ₁ and W ₂ impurity diffusion regions

Claims (2)

An impurity diffusion region constituting a sensor unit is formed in the semiconductor region,
A transfer register for transferring signal charges is formed along each column of the sensor unit,
A method of manufacturing a solid-state imaging device in which a positive charge accumulation region is formed on the surface of the impurity diffusion region,
Ion implantation for forming an impurity diffusion region constituting the sensor unit is performed by inclining by 7 ° or more and 45 ° or less from a wafer normal line of a semiconductor wafer forming the solid-state imaging device,
The ion implantation process is performed in two or more ion implantation processes in which directions inclined from the normal to the wafer are opposite to each other in the charge transfer direction of the transfer register, respectively.
A method of manufacturing a solid-state imaging device, wherein the width of the impurity diffusion region is formed larger than the width of the positive charge accumulation region in the charge transfer direction of the transfer register. An impurity diffusion region constituting a sensor unit is formed in the semiconductor region,
A transfer register for transferring signal charges is formed along each column of the sensor unit,
A method of manufacturing a solid-state imaging device in which a positive charge accumulation region is formed on the surface of the impurity diffusion region,
Ion implantation for forming an impurity diffusion region constituting the sensor unit is performed by inclining by 7 ° or more and 45 ° or less from a wafer normal line of a semiconductor wafer forming the solid-state imaging device,
The ion implantation step is performed in two or more ion implantation steps in which directions inclined from the normal to the wafer are opposite to each other in a direction perpendicular to the charge transfer direction of the transfer register,
A method of manufacturing a solid-state imaging device, wherein the width of the impurity diffusion region is formed larger than the width of the positive charge storage region in a direction orthogonal to the charge transfer direction of the transfer register.

Images