JP2005347518A - Method of manufacturing solid-state imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing solid-state imaging apparatus by which light receiving openings and transfer electrodes having excellent shape accuracy can be formed and a readout voltage can be maintained at a low level and, at the same time, transfer efficiency can be secured and, in addition, the occurrence of smear can be prevented. <P>SOLUTION: In the method of manufacturing a solid-state imaging apparatus provided with the transfer electrodes having single-layer structures, sacrificial layer patterns 6 are formed along the charge transferring direction v and electrode material layers 7 are formed by burying the layers 7 among the sacrificial layer patterns 6 in a state where the patterns 6 are exposed. Then stripe-like dividing grooves 9 extended in the direction perpendicular to the charge transferring direction v are formed in the electrode material layer 7, so that the grooves 9 may reach the patterns 6 and the transfer electrodes 7a are formed by dividing the electrode material layer 7 with the dividing grooves 9 and sacrificial layer patterns 6. Thereafter, the light receiving openings exposing light receiving areas are formed by removing the sacrificial layer patterns 6. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for manufacturing a solid-state imaging device, and more particularly to a method for manufacturing a solid-state imaging device having a drive electrode having a single layer structure.

  With the demand for downsizing and increasing the number of pixels of a solid-state imaging device, the size of pixels has been reduced. In order to prevent a decrease in sensitivity due to the miniaturization of the pixel size, it is important to increase the ratio of the amount of light incident on the light receiving unit with respect to the amount of incident light, that is, the light collection rate. For this reason, it is advantageous to change the transfer electrode structure from a two-layer structure to a single-layer structure. That is, in the two-layer structure in which the end portions of the adjacent transfer electrodes are in a laminated state, the amount of light incident on the light receiving portion is reduced due to the “deletion” of incident light in the laminated portion. On the other hand, in the single layer structure without a laminated portion, the height of the transfer electrode can be kept low, so that the scatter of the incident light can be suppressed, and the amount of incident light to the light receiving portion is increased correspondingly to increase the light collection rate. It can be done.

  The plan view of FIG. 7, the A-A ′ sectional view, and the B-B ′ sectional view thereof show the procedure for forming the transfer electrode having such a single layer structure. First, as illustrated in FIG. 7A, the conductive layer 102 is formed over the substrate 101 covered with the gate insulating film, and then the mask pattern 103 is formed over the conductive layer 102. Thereafter, the conductive layer 102 is etched from above the mask pattern 103. As a result, as shown in FIG. 7B, the light receiving opening 104 and the separation groove 105 are formed in the conductive layer 102. Then, a plurality of transfer electrodes 102 a formed by separating the conductive layer 102 in the charge transfer direction v are formed by the light receiving openings 104 and the separation grooves 105.

  In addition to this, the following method has been proposed as shown in the plan view of FIG. 8 and its A-A ′ and B-B ′ sectional views. First, as shown in FIG. 8A, a conductive layer 102 is formed on a substrate 101 covered with a gate insulating film, and then the conductive layer 102 is etched by etching from a mask pattern not shown here. A separation groove 105 is formed in After that, as shown in FIG. 8B, an insulating film 106 is buried in the isolation trench 105 to be flattened, and an isolation portion 106 is formed by embedding the insulating film 106 in the isolation trench 105. Next, as shown in FIG. 8 (3), a light receiving opening 107 is formed in the conductive layer 102 by etching from a mask pattern not shown here, and the separation portion 106 and the light receiving opening 107 form a charge. A plurality of transfer electrodes 102a formed by separating the conductive layer 102 in the transfer direction v are formed (see Patent Document 1 below).

JP 2002-299597 A

  However, each manufacturing method described above has the following problems. That is, in the method of forming transfer electrodes in a batch by a single etching as described with reference to FIG. 7, the convex corners a of the transfer electrode 102a have a round shape as shown in FIG. easy. As shown in FIG. 7A, when the mask pattern 103 in the case where the transfer electrode is formed by etching is formed by lithography, the convex corner a of the mask pattern 103 becomes a land shape. This is also due to the fact that the etchant is likely to be locally excessively supplied to the convex corner a even in the etching from the mask pattern 103, and the rounding of the convex corner a further proceeds. Yes.

  In the convex corner portion a shaped in a round shape in this way, the interval between the transfer electrodes 102a is widened, so that the width between the transfer electrodes 102a is maintained at a predetermined interval (substantial transfer width). Becomes a factor that reduces transfer efficiency. Further, the transfer electrode 102a portion beside the light receiving opening 104 also serves as a read gate, but the width of the read gate is locally narrowed by rounding the convex corner portion a. This makes it difficult to keep the read voltage low. Further, when ion implantation is performed using the transfer electrode 102a as a mask, there is a problem in that variations occur in the ion implantation region and the charge readout characteristics vary.

  On the other hand, as described with reference to FIG. 8, in the method of forming the light receiving opening 107 after forming the separating portion 106 for separating the transfer electrode 102a, the convex corner portion of the transfer electrode 102a as described above is round. However, since it is necessary to reliably separate the transfer electrodes 102 a by the separating portion 106 and the light receiving opening 107, the end portion of the separating portion 106 protrudes into the light receiving opening 107. For this reason, the substantial opening shape of the light receiving opening 107 is deteriorated, and the incident light is likely to be scattered at the protruding end portion of the separating portion 106 into the light receiving opening 107. In addition, when a light shielding film having a light receiving opening is provided in a state of covering the transfer electrode 102a and the separation part 106, the projecting width of the light shielding film part covering the separation part 106 is reduced, and the lower part of the transfer electrode 102a from this part. It is easy for light to be directly incident on the light source, which also causes smear.

  Therefore, the present invention provides a solid-state imaging device capable of forming a light receiving aperture and a transfer electrode with good shape accuracy, thereby maintaining a readout voltage low, ensuring transfer efficiency, and preventing smear. An object is to provide a manufacturing method.

  In order to achieve such an object, the present invention is a method for manufacturing a solid-state imaging device including a transfer electrode having a single-layer structure, and is characterized as follows. First, in the first step, a sacrificial layer pattern is formed on the substrate along the charge transfer direction. Next, in the second step, an electrode material layer is embedded between the sacrificial layer patterns with the sacrificial layer pattern exposed. Thereafter, in the third step, stripe-shaped separation grooves extending in a direction perpendicular to the charge transfer direction are formed in the electrode material layer in a state extending between the sacrifice layer patterns, and the separation grooves and the sacrifice layer patterns are formed. A transfer electrode is formed by separating the electrode material layer.

  In the manufacturing method described above, a transfer electrode formed by separating the electrode material layer is obtained by forming a stripe-like separation groove in the electrode material layer embedded between the sacrificial layer patterns. For this reason, the transfer electrode formed by patterning the electrode material layer can be obtained without subjecting the electrode material layer to pattern etching using a mask having convex corners. Therefore, the round shape of the convex corner portion generated by pattern etching using the mask having the convex corner portion does not occur in the obtained transfer electrode. Then, a transfer electrode having a single layer structure is obtained in which the adjacent electrodes are maintained at a predetermined distance up to the end reaching the sacrificial layer pattern. In addition, when the light receiving region is arranged beside the transfer electrode, the space between the transfer electrode and the light receiving region is maintained at a predetermined distance to the end of the transfer electrode.

  Further, by removing the sacrificial layer pattern after forming the transfer electrode, an opening having the same shape as the sacrificial layer pattern can be obtained. Therefore, by forming the sacrificial layer pattern in an island shape that covers the light receiving region, the sacrificial layer pattern is removed to obtain a light receiving opening having the same shape as the island shape of the sacrificial layer pattern. Thus, no protrusion is formed in the light receiving opening, and when the light shielding film having the light receiving opening is provided so as to cover the transfer electrode, the extending width of the light shielding film becomes uniform at the periphery of the light receiving opening. .

  As described above, according to the method for manufacturing a solid-state imaging device of the present invention, it is possible to obtain a transfer electrode having a single layer structure in which the distance between adjacent electrodes is maintained at a predetermined distance across the end. For this reason, the charge transfer efficiency by the transfer electrode can be ensured. In addition, when a light receiving region is provided on the side of the transfer electrode, the distance between the transfer electrode and the light receiving region is maintained at a predetermined distance from the transfer electrode to the end of the transfer electrode. Can be kept low. Furthermore, the light-receiving opening obtained by removing the island-shaped sacrificial layer pattern covering the light-receiving region is formed in the same shape as the island-shaped sacrificial layer pattern, and the overhang width of the light-shielding film covering the transfer electrode becomes uniform. Further, it is possible to prevent the occurrence of smear due to light leakage under the transfer electrode.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a plan view illustrating an example of a substrate configuration of a solid-state imaging device. Hereinafter, a method for manufacturing the solid-state imaging device according to the embodiment will be described with reference to FIG. 2 and the subsequent figures correspond to a plan view of the enlarged portion a in FIG. 1, a cross-sectional view taken along line A-A ′, and a cross-sectional view taken along B-B ′.

  First, as shown in FIG. 1, a semiconductor substrate 1 made of, for example, n-type single crystal silicon is prepared. Then, a p-well diffusion layer (not shown) is formed in the surface layer of the semiconductor substrate 1, and an n-type vertical transfer region 2 in which impurities are diffused in the surface layer, a high-concentration p + -type channel stop diffusion layer 3, and Form. Each vertical transfer region 2 extends along the charge transfer direction (vertical transfer direction v) on the side of the light receiving region 1b set in a matrix on the imaging region 1a of the substrate 1. The channel stop diffusion layer 3 is disposed adjacent to one side of the vertical transfer region 2 and a part thereof extends toward the opposing vertical transfer region 2 between the light receiving regions 1b. In addition, the horizontal transfer area 4 and the read area 4 ′ along the horizontal transfer direction h are formed as necessary.

  As described above, after each region is formed on the surface layer of the semiconductor substrate 1, the gate insulating film 5 is formed on the semiconductor substrate 1, as shown in FIG. The gate insulating film 5 is made of, for example, an ONO (Oxide / Nitride / Oxide) film in which a silicon oxide film, a silicon nitride film, and a silicon oxide film are stacked in this order. Then, a sacrificial layer pattern 6 is formed on the gate insulating film 5. The sacrificial layer pattern 6 is formed in a pattern so as to cover the respective light receiving regions 1b shown in FIG. 1 and is vertical with a predetermined interval between the channel stop diffusion layer 3 and the vertical transfer region 2. Arranged in a matrix on the gate insulating film 5 along the transfer direction v.

  The sacrificial layer pattern 6 is made of a material film that is resistant to etching of the electrode material layer to be formed next, such as silicon oxide, and has a film thickness that is equal to or greater than the film thickness of the transfer electrode formed by the electrode material layer. It shall be formed. The sacrificial layer pattern 6 is formed by depositing the above-described material film such as silicon oxide by atmospheric pressure CVD, plasma CVD, or another method appropriately selected, and then masking the resist pattern (not shown). This is performed by etching this material film. After this etching is completed, a step of removing the resist pattern used for the mask is performed.

  Next, as shown in FIG. 2B, an electrode material layer 7 is embedded between the sacrificial layer patterns 6. In this case, first, an electrode material layer 7 made of polysilicon or the like is formed by, for example, a CVD method so as to cover the sacrificial layer pattern 6, and the electrode material layer 7 is planarized until the sacrificial layer pattern 6 is exposed. The planarization process of the electrode material layer 7 is performed by, for example, a CMP method. Thereby, the electrode material layer 7 is embedded between the sacrifice layer patterns 6 at the same height as the sacrifice layer pattern 6.

  Next, as shown in FIG. 3 (1), a strip-like resist pattern 8 extending in the horizontal direction is formed on the plane constituted by the sacrificial layer pattern 6 and the electrode material layer 7. This resist pattern 8 has a slit extending in the horizontal direction above the sacrificial layer pattern 6 arranged in the vertical transfer direction v, and in the horizontal direction across the sacrificial layer pattern 6 arranged in the horizontal direction. Suppose that it is a strip | belt shape provided with the slit extended in this.

  Then, as shown in FIG. 3 (2), by using the resist pattern 8 as a mask and selectively etching the electrode material layer 7 with respect to the sacrificial layer pattern 6, a separation groove 9 is formed in the electrode material layer 7. To do. The separation grooves 9 formed in this way are arranged between the sacrificial layer patterns 6 arranged in the horizontal direction, and are arranged between the sacrificial layer patterns 6 arranged in the vertical transfer direction v. Then, a transfer electrode 7 a formed by separating the electrode material layer 7 in the vertical transfer direction v by the separation groove 9 and the sacrificial layer pattern 6 is formed. Note that, after the etching is completed, a step of removing the resist pattern 8 is performed.

  Thereafter, as shown in FIG. 4A, a resist pattern 10 having a shape that exposes the sacrificial layer pattern 6 and covers the separation groove 9 is formed on the transfer electrode 7a. The resist pattern 10 preferably has a shape in which the sacrificial layer pattern 6 is completely exposed and the separation groove 9 is completely covered.

  Next, as shown in FIG. 4B, the sacrificial layer pattern 6 is selectively removed by etching from above the resist pattern 10. As a result, the light receiving opening 11 is formed by exposing the gate insulating film 5 in the light receiving region (see FIG. 1) on the side of the transfer electrode 7a while protecting the gate insulating film 5 at the bottom of the separation groove 9 with the resist pattern 10. In this etching, when the sacrificial layer pattern (6) to be etched is made of silicon oxide, the silicon oxide film on the uppermost layer of the gate insulating film 5 of the ONO structure serving as a base is also etched away. Therefore, the etching is stopped in the silicon nitride film constituting the intermediate layer of the gate insulating film 5 having the ONO structure.

  The etching removal of the sacrificial layer pattern (6) described above forms the resist pattern 10 if only the sacrificial layer pattern (6) can be selectively removed without affecting the gate insulating film 5. You may carry out without doing. In this case, in particular, the thickness (configuration) of the gate insulating film 5 at the bottom of the separation groove 9 between the transfer electrodes 7a is kept the same as the thickness (configuration) of the gate insulating film 5 under the transfer electrodes 7a. The sacrificial layer pattern (6) is preferably removed by etching.

  After the above, as shown in FIG. 5, an oxide film 12 is formed on the surface layer of the transfer electrode 7a by an oxidation process (for example, a thermal oxidation method), and the isolation trench 9 is filled with the oxide film 12. Further, an oxide film (not shown) is also formed on the surface layer of the silicon nitride film constituting the surface of the gate insulating film 5 exposed at the bottom surface of the light receiving opening 11. In this step, an insulating film made of silicon oxide or silicon nitride may be formed to such an extent that the inside of the isolation trench 9 is filled by a CVD method or the like without depending on the oxidation treatment.

  Next, as shown in FIG. 6, the sensor portion 13 is formed on the surface layer of the semiconductor substrate 1 at the bottom of the light receiving opening 11 by ion implantation using the transfer electrode 7 a covered with the oxide film 12 as a mask. For example, the sensor unit 13 includes a high concentration p + type diffusion layer on an n type diffusion layer. Then, as shown in the cross-sectional view CC ′ (horizontal direction cross-sectional view) in the plan view, the sensor unit 13 formed in this way becomes a reading region between the n-type vertical transfer region 2. The distance is maintained and the high-concentration p + type channel stop diffusion layer 3 is provided.

  After the above, although not shown here, a light shielding film having an opening that covers the transfer electrode 17a and exposes the light receiving opening 11a through the oxide film 12 is formed, and further, on-chip as necessary. A solid-state imaging device is completed by forming lenses and color filters.

  According to the manufacturing method described above, as described with reference to FIG. 3B, the stripe-shaped separation grooves 9 are formed in the electrode material layer 7 embedded between the sacrificial layer patterns 6 covering the light receiving region. As a result, the transfer electrode 7a formed by separating the electrode material layer 7 in the vertical transfer direction v is obtained. For this reason, the transfer electrode 7a formed by patterning the electrode material layer 7 is obtained without subjecting the electrode material layer 7 to pattern etching using a mask having convex corners. Therefore, the obtained transfer electrode 7a does not have the round shape of the convex corners generated by the pattern etching using the mask having the convex corner portions.

  As a result, a transfer electrode 7a having a single-layer structure in which the adjacent transfer electrodes 7a are maintained at a predetermined interval up to the end reaching the sacrificial layer pattern 6 is obtained. Thereby, it is possible to ensure the charge transfer efficiency by the transfer electrode 7a. In addition, the distance between the transfer electrode 7a and the light receiving region on the side is maintained at a predetermined distance to the end of the transfer electrode 7a. It is possible to keep the charge readout voltage from the light receiving region to the transfer electrode low.

  Further, as described with reference to FIG. 4B, by removing the sacrificial layer pattern 6, the light receiving openings 11 having the same shape as the island shape of the sacrificial layer pattern 6 can be obtained. As a result, no projecting portion is formed in the light receiving opening 11, and when a light shielding film having an opening is provided in a state of covering the transfer electrode 7 a in a later step, the light shielding film is formed at the periphery of the light receiving opening 11. It is possible to make the overhang width uniform. As a result, it is possible to prevent smear due to light leakage under the transfer electrode 7a.

  In the above embodiment, the case where a resist pattern is used as a mask for pattern etching has been described. However, an inorganic mask formed using a resist pattern as a mask may be used as an etching mask. Furthermore, the sensor unit 13 is formed by ion implantation using the transfer electrode 7a as a mask. However, the sensor unit 13 may be formed before the transfer electrode 7a is formed.

  In the above embodiment, the manufacturing procedure of the present invention has been described focusing on the formation process of the transfer electrode (vertical transfer electrode) arranged in the imaging region, but the present invention is applied to the formation of the horizontal transfer electrode. It is also possible.

It is a figure (the 1) which shows the manufacturing method of embodiment. It is a figure (the 2) which shows the manufacturing method of embodiment. It is a figure (the 3) which shows the manufacturing method of embodiment. It is a figure (the 4) which shows the manufacturing method of embodiment. It is a figure (the 5) which shows the manufacturing method of embodiment. It is a figure (the 6) which shows the manufacturing method of embodiment. It is a figure which shows an example of the conventional transfer electrode formation. It is a figure which shows the other example of conventional transfer electrode formation.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Semiconductor substrate, 1b ... Light reception area | region, 5 ... Gate insulating film, 6 ... Sacrificial layer pattern, 7 ... Electrode material layer, 7a ... Transfer electrode, 9 ... Separation groove, 11 ... Light-receiving opening, 12 ... Oxide film, 20 * Solid-state imaging device, h: horizontal transfer direction (charge transfer direction), v: vertical transfer direction (charge transfer direction)

Claims (3)

A method of manufacturing a solid-state imaging device including a transfer electrode having a single layer structure,
A first step of forming a sacrificial layer pattern on the substrate along the charge transfer direction;
A second step of embedding and forming an electrode material layer between the sacrificial layer patterns with the sacrificial layer pattern exposed;
Striped separation grooves extending in a direction perpendicular to the charge transfer direction are formed in the electrode material layer in a state extending between the sacrifice layer patterns, and the electrode material is formed by the separation grooves and the sacrifice layer pattern. And a third step of forming a transfer electrode by separating the layers. A method for manufacturing a solid-state imaging device. In the manufacturing method of the solid-state imaging device according to claim 1,
After the third step, a fourth step of forming a light receiving opening exposing the light receiving region of the substrate by removing the sacrificial layer pattern is performed. In the manufacturing method of the solid-state imaging device according to claim 1,
A fourth step of removing the sacrificial layer pattern after the third step;
A method of manufacturing a solid-state imaging device, comprising: forming an oxide film on a surface layer of the transfer electrode by an oxidation process, and performing a fifth step of filling the separation groove with the oxide film.

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