JP4768889B1 - Image pickup device and manufacturing method thereof - Google Patents

Abstract

An image pickup device that is fine and easy to manufacture and a method of manufacturing the same are provided.
A hard mask material film is formed on a semiconductor substrate, and a recess is formed in a region immediately below the opening on the upper surface of the semiconductor substrate. Next, by implanting impurities into the imaging region A using the hard mask material film as a mask, the p-type region 4 is formed immediately below the recess 2c. Further, the trench 14 is formed by further processing the recess 2c in the processing region B. Then, the semi-embedded insulating film 5 and the STI 7 are formed by embedding an insulating material in the recess 2c and the trench 14, and the hard mask material film is removed. Next, electrodes 8a and 8b are formed so as to run over the semi-buried insulating film 5 and the STI 7, respectively, and impurities are implanted into the imaging region A using the electrode 8a and the semi-buried insulating film 5 as a mask, whereby the semiconductor substrate 2 The n-type region 3 constituting the photodiode is formed in a region in contact with the p-type region 4 in FIG.
[Selection] Figure 1

Description

  The present invention relates to an image pickup device and a manufacturing method thereof, and more particularly to an image pickup device in which a part between elements is separated by a semiconductor region and a manufacturing method thereof.

  In general, element isolation in a semiconductor element is performed by an STI (Shallow Trench Isolation) method in which a silicon substrate is etched to form a trench and an insulating film is embedded in the trench. However, when this STI method is applied to an imaging device (hereinafter referred to as “imaging device”) such as a CMOS (Complementary Metal Oxide Semiconductor) image sensor, the following problems occur. .

  That is, if the photodiodes of the imaging device are separated from each other by STI, damage occurs when the silicon substrate is etched, stress is applied when an insulating film is embedded in the trench, and crystal defects are introduced into the silicon substrate. End up. As a result, the unpaired electron pair possessed by the crystal defect becomes a carrier, and a white defect is generated in the image. In order to prevent this, it is necessary to wrap the STI with a well (inversion layer), but in this case, the area of the photodiode is reduced by the margin of the well. As a result, the number of saturated electrons at the time of photoelectric conversion decreases, and the pixel characteristics deteriorate, for example, the sensitivity decreases. This problem becomes particularly apparent as the pixel pitch is reduced.

  Under such a background, as a technique for providing sufficient element isolation tolerance while suppressing deterioration of pixel characteristics, a technique of applying element isolation by a mesa isolation method to an imaging device is being studied. Mesa isolation is a method in which a semiconductor region is formed between elements to perform PN isolation, and an insulating film is provided on the semiconductor region. For example, Non-Patent Document 1 discloses a technique of using both STI isolation and mesa isolation in a CMOS image sensor.

  However, in the technique described in Non-Patent Document 1, since the height of the insulating film for mesa isolation and the height of the insulating film for STI do not match, the difficulty of the subsequent process increases and the device can be miniaturized. There is a problem that it becomes difficult.

Kazuichiroh Itonaga, and et. Al., "A High-Performance and Low-Noise CMOS Image Sensor with an Expanding Photodiode under the Isolation Oxide", 2005 IEEE 0-7803-9269-8

  An object of the present invention is to provide an image pickup device that is fine and easy to manufacture, and a method for manufacturing the same.

  According to one aspect of the present invention, there is provided an imaging device provided with an imaging region for converting incident light into an electrical signal, and a processing region for processing the electrical signal, the semiconductor substrate and an upper layer of the semiconductor substrate A first conductivity type region formed in a portion and having a conductivity type of the first conductivity type; formed in an upper layer portion of the semiconductor substrate; and in contact with the first conductivity type region; A second conductivity type region which is a different second conductivity type, and a semi-embedding provided in a region immediately above the second conductivity type region, a lower portion embedded in the semiconductor substrate, and an upper portion protruding from the upper surface of the semiconductor substrate An insulating film, an element isolation film having a lower portion embedded in the semiconductor substrate, an upper portion protruding from the upper surface of the semiconductor substrate, and a lower surface positioned below the lower surface of the semi-buried insulating film; The second formed in the upper layer part of the conductivity type region And a transistor whose source / drain regions are in contact with the second conductivity type region and the semi-buried insulating film, wherein the second conductivity type region and the semi-buried insulating film are Separating a first conductivity type region from a region opposite to the first conductivity type region as viewed from the second conductivity type region and in contact with the second conductivity type region; Constitutes a photodiode provided in the imaging region, the element isolation film separates elements provided in the processing region, and the position of the lower surface of the semi-buried insulating film is the position of the inversion layer In the impurity concentration profile in the depth direction, it is below the position where the impurity concentration takes the maximum value, and in the impurity concentration profile in the depth direction of the source / drain region, below the position where the impurity concentration takes the maximum value. Ri, in the impurity concentration profile in the depth direction of the first conductivity type region, an image capturing device, wherein the impurity concentration is higher than the position where the maximum value is provided.

  According to another aspect of the present invention, there is provided an imaging region for converting incident light into an electrical signal, and a method for manufacturing an imaging device provided with a processing region for processing the electrical signal. A step of forming a hard mask material film; a step of forming an opening in the hard mask material film by etching; and a step of forming a recess immediately below the opening on the upper surface of the semiconductor substrate; and the hard mask material Etching using the film as a mask to further remove a part of the bottom surface of the recess to form a trench; and implanting impurities using the hard mask material film as a mask to form the recess in the semiconductor substrate Forming a second conductivity type region directly under the region, in the recess and in the opening provided in the region directly above, and in the trench And a step of embedding an insulating material in the opening provided immediately above the region, and removing the hard mask material film so that the lower portion is embedded in the semiconductor substrate and the upper portion protrudes from the upper surface of the semiconductor substrate. Forming a buried insulating film, forming an element isolation film having a lower portion buried in the trench and an upper portion protruding from the upper surface of the semiconductor substrate; and implanting impurities using the semi-buried insulating film as a mask A step of forming a first conductivity type region in a region in contact with the second conductivity type region of the semiconductor substrate; and a step of forming a second conductivity type inversion layer in an upper layer portion of the first conductivity type region; Forming a transistor whose source / drain regions are in contact with the second conductivity type region and the semi-buried insulating film, wherein the first conductivity type region is provided in the imaging region. In the step of separating the elements provided in the processing region and forming the inversion layer, the element isolation film has an impurity concentration in an impurity concentration profile in the depth direction of the inversion layer. The position where the maximum value of the impurity concentration in the impurity concentration profile in the depth direction of the source / drain region in the step of forming the transistor In the step of forming the first conductivity type region above the bottom surface of the recess, the position where the impurity concentration in the impurity concentration profile in the depth direction of the first conductivity type region takes the maximum value is determined from the bottom surface of the recess. Also provided is a method for manufacturing an image pickup device, characterized in that the image pickup device is also located below.

  ADVANTAGE OF THE INVENTION According to this invention, the image pick-up device which is fine and easy to manufacture, and its manufacturing method are realizable.

1 is a cross-sectional view illustrating a semiconductor device according to a first embodiment of the invention. 10A to 10C are process cross-sectional views illustrating the method for manufacturing a semiconductor device according to the first embodiment. (A) And (b) is process sectional drawing which illustrates the manufacturing method of the semiconductor device which concerns on 1st Embodiment. (A) And (b) is process sectional drawing which illustrates the manufacturing method of the semiconductor device which concerns on 1st Embodiment. (A) And (b) is process sectional drawing which illustrates the manufacturing method of the semiconductor device which concerns on 1st Embodiment. (A) And (b) is process sectional drawing which illustrates the manufacturing method of the semiconductor device which concerns on 1st Embodiment. (A) And (b) is process sectional drawing which illustrates the manufacturing method of the semiconductor device which concerns on the comparative example of 1st Embodiment. (A) And (b) is process sectional drawing which illustrates the manufacturing method of the semiconductor device which concerns on the comparative example of 1st Embodiment. FIG. 6 is a cross-sectional view illustrating a semiconductor device according to a second embodiment of the invention. 10A to 10C are process cross-sectional views illustrating a method for manufacturing a semiconductor device according to the second embodiment. FIG. 6 is a plan view illustrating a semiconductor device according to a second embodiment of the invention. FIG. 12 is a plan view illustrating the imaging region illustrated in FIG. 11. It is sectional drawing by the A-A 'line shown in FIG. It is sectional drawing by the B-B 'line shown in FIG. It is sectional drawing by the C-C 'line shown in FIG. It is sectional drawing by the D-D 'line shown in FIG. FIG. 12 is a cross-sectional view schematically illustrating an imaging region and a processing region illustrated in FIG. 11. FIG. 5 is a graph illustrating impurity concentration profiles of a light receiving region, an inversion layer, and a source / drain region, with the horizontal axis representing the depth direction position and the vertical axis representing the impurity concentration. FIG. 6 is a graph illustrating an impurity concentration profile in a region immediately below a semi-buried insulating film, with the horizontal axis representing the position in the depth direction and the vertical axis representing the impurity concentration. (A) is a top view which illustrates one pixel in the CMOS image sensor which concerns on the comparative example of 2nd Embodiment, (b) is sectional drawing by the EE 'line shown to (a), (C) is a top view which illustrates one pixel in the CMOS image sensor which concerns on 2nd Embodiment, (d) is sectional drawing by the FF 'line shown to (c).

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First, a first embodiment of the present invention will be described.
FIG. 1 is a cross-sectional view illustrating a semiconductor device according to this embodiment.
The semiconductor device 1 according to the present embodiment is, for example, an imaging device.

  As shown in FIG. 1, in the semiconductor device 1 according to the present embodiment, a semiconductor substrate 2 is provided. The semiconductor substrate 2 is provided with an N-channel MOSFET (Metal Oxide Semiconductor Field Effect Transistor) (hereinafter referred to as “NMOS”), and an imaging region for converting incident light into an electrical signal. A and an NMOS and a P-channel type MOSFET (hereinafter referred to as “PMOS”) are provided, and a processing area B for processing an electric signal output from the imaging area A is set.

  In a part of the upper layer portion of the semiconductor substrate 2 in the imaging region A, an n-type region 3 (first conductivity type region) constituting a photodiode is formed. In addition, a p-type region 4 (second conductivity type region) and a semi-buried insulating film 5 constituting mesa isolation are provided in another part of the upper layer portion of the semiconductor substrate 2. The semi-buried insulating film 5 is provided immediately above the p-type region 4. The lower part of the semi-buried insulating film 5 is buried in the semiconductor substrate 2, and the upper part of the semi-buried insulating film 5 protrudes from the upper surface 2 a of the semiconductor substrate 2. That is, the lower surface 5 b of the semi-buried insulating film 5 is located below the upper surface 2 a of the semiconductor substrate 2, and the upper surface 5 a of the semi-buried insulating film 5 is located above the upper surface 2 a of the semiconductor substrate 2. For example, in the example shown in FIG. 1, mesa isolation is provided at two locations, and the p-type region 4 and the semi-buried insulating film 5 constituting one mesa isolation are in contact with the n-type region 3. As a result, the p-type region 4 and the semi-buried insulating film 5 are the n-type region 3 in the semiconductor substrate 2 and the region opposite to the n-type region 3 when viewed from the p-type region 4. That is, the region 20 corresponding to the region immediately below the electrode 8a in the upper layer portion of the semiconductor substrate 2 is separated.

  On the other hand, the processing region B is provided with the NMOS and the PMOS as described above, and the PMOS channel region 6 is formed in a part of the upper layer portion of the semiconductor substrate 2 in the region B. On the other hand, a pair of STIs 7 are embedded as element isolation films. The STI 7 separates the PMOS provided with the channel region 6 from other transistors formed on the semiconductor substrate 2, and is located higher than the upper end of the channel region 6 and lower than the lower end of the channel region 6. It is formed to a low position. That is, the upper surface 7 a of the STI 7 is located above the upper surface 2 a of the semiconductor substrate 2. Further, the lower surface 7 b of the STI 7 is located below the lower end portion of the channel region 6 and is located below the lower surface 5 b of the semi-buried insulating film 5.

  An electrode 8 a is provided on the semiconductor substrate 2 so as to run over the semi-buried insulating film 5. In order to insulate the electrode 8a from the n-type region 3, the thickness of the semi-buried insulating film 5 is a certain thickness or more. In addition, an electrode 8b is provided so as to ride on the STI 7. A gate insulating film 2g is formed in a portion between the semiconductor substrate 2 and the electrode 8a or 8b where the semi-buried insulating film 5 or the STI 7 is not provided. Furthermore, an interlayer insulating film 9 is provided on the semiconductor substrate 2 so as to cover the electrodes 8a and 8b. Contacts 10a and 10b are formed in the interlayer insulating film 9 so as to be connected to the electrodes 8a and 8b, respectively. An upper wiring layer (not shown) is provided on the interlayer insulating film 9.

Next, a method for manufacturing the semiconductor device 1 according to this embodiment will be described.
2 (a) to (c), FIGS. 3 (a) and (b), FIGS. 4 (a) and (b), FIGS. 5 (a) and (b), and FIGS. 6 (a) and (b). These are process cross-sectional views illustrating a method for manufacturing a semiconductor device according to this embodiment.

  First, as shown in FIG. 2A, a hard mask material film 11 is formed on the entire surface of the semiconductor substrate 2, and a resist pattern 12 is formed thereon. The semiconductor substrate 2 and the hard mask material film 11 are formed of, for example, silicon (Si) and silicon nitride (SiN), respectively. At this time, in the resist pattern 12, openings 12a are formed in the regions A and B, respectively.

  Next, as shown in FIG. 2B, dry etching is performed using the resist pattern 12 as a mask. Thus, the hard mask material film 11 is removed over the entire region in the thickness direction in the region immediately below the opening 12a of the resist pattern 12, and the upper layer portion of the semiconductor substrate 2 is also removed. As a result, an opening 11 a is formed in the hard mask material film 11, and a recess 2 c is formed in a region directly below the opening 11 a on the upper surface 2 a of the semiconductor substrate 2. Thereafter, the resist pattern 12 is removed.

  Next, as shown in FIG. 2C, a resist pattern 13 is formed on the hard mask material film 11 so as to cover the region A and expose the region B. Then, dry etching is performed using the resist pattern 13 and the hard mask material film 11 as a mask. Thereby, the bottom surface of the recess 2c of the semiconductor substrate 2 is further removed in the region B, and the trench 14 is formed. Thereafter, the resist pattern 13 is removed.

  Next, as shown in FIG. 3A, a resist pattern 15 is formed on the hard mask material film 11 so as to cover the region B and expose the region A. Then, acceptors are implanted using the resist pattern 15 and the hard mask material film 11 as a mask. As a result, the p-type region 4 is formed in the region immediately below the opening 11a in the region A in the semiconductor substrate 2, that is, in the region immediately below the recess 2c. Thereafter, the resist pattern 15 is removed.

  Next, as shown in FIG. 3B, an insulating material 16 is deposited on the entire surface. At this time, the insulating material 16 is also embedded in the recess 2 c in the region A and in the trench 14 in the region B. Next, the insulating material 16 is subjected to a planarization process such as CMP (Chemical Mechanical Polishing) to expose the hard mask material film 11.

  Next, as shown in FIG. 4A, wet etching is performed on the entire surface, and the portion of the insulating material 16 embedded in the upper portion of the opening 11a is removed. At this time, the insulating material 16 remains in the lower part of the recess 2c and in the opening 11a immediately above it, and in the trench 14 and in the lower part of the opening 11a immediately above it, and the semi-buried insulating film 5 and the STI 7 respectively. Become. The semi-buried insulating film 5 is formed immediately above the p-type region 4. Further, since the semi-buried insulating film 5 and the STI 7 are formed by removing the insulating material 16 by the same wet etching process, the height of the upper surface 5a of the semi-buried insulating film 5 and the height of the upper surface 7a of the STI 7 Are substantially identical. Thereafter, the hard mask material film 11 is removed. Thereby, the upper part of the semi-buried insulating film 5 and the upper part of the STI 7 protrude from the upper surface 2 a of the semiconductor substrate 2.

  Next, as shown in FIG. 4B, the channel region 6 is formed in the region B between the STIs 7 in the region B and on the upper layer side of the lower surface 7b. The PMOS including the channel region 6 is separated from the surroundings by the STI 7. Thereafter, a gate insulating film 2g is formed on the exposed portion of the upper surface 2a of the semiconductor substrate 2 by thermal oxidation.

  Next, as shown in FIG. 5A, a conductive material is deposited on the entire surface of the semiconductor substrate 2 to form a conductive film 18. At this time, the conductive film 18 is continuously formed so as to cover the gate insulating film 2g, the semi-buried insulating film 5 and the STI 7, and the shape of the upper surface 18a of the conductive film 18 is a protruding portion of the semi-buried insulating film 5. And the shape reflects the protruding portion of STI7. That is, the region directly above the semi-buried insulating film 5 and the region directly above the STI 7 on the upper surface 18a are convex with the same dimensions with respect to the surroundings.

  Next, as shown in FIG. 5B, the conductive film 18 is selectively removed by photolithography, so that the region immediately above the region 20 between the semi-buried insulating films 5 and the region 20 in the semi-buried insulating film 5. In the region directly above the side portion, the region immediately above the channel region 6 and the region immediately above the portion on the channel region 6 side in the STI 7. Thus, the electrode 8a is formed so as to run over the semi-buried insulating film 5, and the electrode 8b is formed so as to run over the STI 7.

  Next, as illustrated in FIG. 6A, a resist pattern 19 is formed on the semiconductor substrate 2 so as to cover the region B and expose the region A. Then, a donor is implanted using the resist pattern 19, the electrode 8 a and the semi-buried insulating film 5 as a mask, and the n-type region 3 is formed in a part of the upper layer portion of the semiconductor substrate 2 in the region A. At this time, the n-type region 3 is formed so as to be in contact with the p-type region 4 formed immediately below the half-buried insulating film 5 by a self-alignment process using the half-buried insulating film 5 as a mask. Thereafter, the resist pattern 19 is removed.

  Next, as shown in FIG. 6B, an insulating material is deposited on the semiconductor substrate 2, and an interlayer insulating film 9 is formed so as to cover the semi-buried insulating film 5, the STI 7, and the electrodes 8a and 8b. At this time, the shape of the upper surface 9a of the interlayer insulating film 9 is a shape reflecting the shapes of the electrodes 8a and 8b. That is, the region directly above the electrodes 8a and 8b on the upper surface 9a has a convex shape with substantially the same dimensions with respect to the surroundings.

  Next, as shown in FIG. 1, a planarization process such as CMP is performed to planarize the upper surface 9 a of the interlayer insulating film 9. Then, the interlayer insulating film 9 is processed by photolithography to form contact holes in the regions directly above the electrodes 8a and 8b, and after depositing a conductive material on the entire surface, the contact holes are formed by planarizing by CMP. Embed conductive material. Thereby, contacts 10a and 10b are formed. At this time, the contact 10a is connected to the electrode 8a, and the contact 10b is connected to the electrode 8b. Thereafter, an upper wiring layer (not shown) is formed on the interlayer insulating film 9. Thereby, the semiconductor device 1 is manufactured.

Next, the effect of this embodiment is demonstrated.
As shown in FIG. 1, in the semiconductor device 1 according to this embodiment, the interface between the n-type region 3 and the p-type region 4 is a pn junction surface. As a result, the n-type region 3 is separated from the region 20 by the p-type region 4 and the semi-buried insulating film 5. Further, the semi-buried insulating film 5 also insulates the n-type region 3 from the electrode 8a. On the other hand, the PMOS including the channel region 6 is separated from other elements formed on the semiconductor substrate 2 by the STI 7. In this embodiment, since the lower part of the semi-buried insulating film 5 is buried in the semiconductor substrate 2, the semi-buried insulating film 5 is necessary for the characteristics of the semiconductor device 1 and the manufacturing process of the semiconductor device 1. The amount of protrusion of the semi-buried insulating film 5 can be suppressed while providing a sufficient thickness. As a result, the height of the upper surface 5a of the semi-buried insulating film 5 and the height of the upper surface 7a of the STI 7 can be made substantially the same. In one example, with reference to the upper surface 2a of the semiconductor substrate 2, the height of the upper surface 5a of the semi-buried insulating film 5 and the height of the upper surface 7a of the STI 7 are both 20 nm (nanometers).

  Since the semi-buried insulating film 5 does not protrude greatly from the upper surface 2a of the semiconductor substrate 2, and the height of the upper surface 5a and the height of the upper surface 7a are substantially the same, in the process shown in FIG. When the conductive film 18 that covers the semi-buried insulating film 5 and the STI 7 is formed on the semi-buried insulating film 5, the semi-buried insulating film 5 on the upper surface 18 a of the conductive film 18 does not have to be formed excessively thick. The region corresponding to the region directly above does not protrude greatly from the periphery thereof, and is substantially equal to the height of the region corresponding to the region immediately above STI 7. Thereby, the thickness of the conductive film 18 becomes substantially uniform in the entire semiconductor device 1 and the upper surface 18a becomes substantially flat.

  Since the thickness of the conductive film 18 becomes substantially uniform and the upper surface 18a becomes substantially flat, the process for forming the electrodes 8a and 8b from the conductive film 18 is facilitated in the step shown in FIG. 5B. That is, since the thickness of the conductive film 18 becomes substantially uniform, the timing for ending the etching of the conductive film 18 is substantially the same between the periphery of the electrode 8a and the periphery of the electrode 8b. Moreover, the thickness of the electrode 8a and the thickness of the electrode 8b can be made substantially equal. Further, since the upper surface 18a is planarized, a resist pattern used for processing the conductive film 18 can be formed thin, and the electrodes 8a and 8b can be formed finely.

  Since the thicknesses of the electrodes 8a and 8b are substantially equal to each other, when the interlayer insulating film 9 is formed in the step shown in FIG. 6B, the upper surface 9a is directly above the semi-buried insulating film 5. The height of the area corresponding to the area and the height of the area corresponding to the area immediately above the STI 7 are substantially equal to each other. Accordingly, when viewed macroscopically, the height of the upper surface 9a is substantially equal in the region A and the region B, and the upper surface 9a is substantially flat in the entire semiconductor device 1. As a result, in the step shown in FIG. 1, the planarization process such as CMP on the upper surface 9a is facilitated. Further, it is not necessary to form the interlayer insulating film 9 before the planarization process excessively thick, so that the manufacturing cost can be reduced. Furthermore, since the upper surface 9a becomes flat, a resist pattern used for processing the interlayer insulating film 9 can be formed thin, and the contacts 10a and 10b can be formed finely. As a result, the fine semiconductor device 1 can be easily manufactured together with the miniaturization of the electrodes 8a and 8b.

Next, a comparative example of this embodiment will be described.
7A and 7B and FIGS. 8A and 8B are process cross-sectional views illustrating a method for manufacturing a semiconductor device according to this comparative example.

  In this comparative example, after forming the hard mask material film 11 and the resist pattern 12 on the semiconductor substrate 2 as shown in FIG. 2A, the resist pattern 12 is masked as shown in FIG. 7A. As shown in FIG. At this time, only the hard mask material film 11 is etched, and the semiconductor substrate 2 is not etched. That is, the recess 2c (see FIG. 2B) is not formed in the semiconductor substrate 2.

Next, processing similar to the processing shown in FIGS. 2C to 4B is performed. As a result, as shown in FIG. 7B, the non-embedded insulating film 105 is formed in the region A, and the PMOS including the STI 7 and the channel region 6 is formed in the region B. Unlike the semi-buried insulating film 5 (see FIG. 5A), the non-buried insulating film 105 is not buried in the semiconductor substrate 2 and is entirely located on the upper surface 2a of the semiconductor substrate 2. is doing. For this reason, the height of the upper surface 105a of the non-buried insulating film 105 is higher than the height of the upper surface 7a of the STI 7. In one example, with reference to the upper surface 2a of the semiconductor substrate 2, the height of the upper surface 105a of the non-buried insulating film 105 is 60 nm, the height of the upper surface 7a of the STI 7 is 20 nm, and a difference of 40 nm occurs. When the conductive film 18 is formed on the semiconductor substrate 2 in this state, the height of the region corresponding to the region directly above the non-buried insulating film 105 on the upper surface 18a of the conductive film 18 is the region corresponding to the region directly above STI7. Higher than the height of. In the above example, the height difference d ₁ is about 40 nm.

  Next, a process similar to the process shown in FIG. 5B is performed to pattern the conductive film 18. As a result, as shown in FIG. 8A, electrodes 8a and 8b are formed on the non-buried insulating film 105 and the STI 7, respectively. At this time, the upper surface of the electrode 8a is higher than the upper surface of the electrode 8b. Next, as shown in FIG. 6A, a donor is implanted using the resist pattern 19, the electrode 8a, and the non-embedded insulating film 105 (see FIG. 8A) as a mask. Thereby, the n-type region 3 is formed in the region A.

Next, as illustrated in FIG. 8B, an interlayer insulating film 9 is formed on the semiconductor substrate 2 so as to cover the non-buried insulating film 105 and the STI 7. At this time, the height of the region corresponding to the region directly above the non-buried insulating film 105 on the upper surface 9a of the interlayer insulating film 9 is higher than the height of the region corresponding to the region immediately above the STI 7. In the above example, the height difference _{d 2} is about 40 nm.

  In the present comparative example, as described above, in the step shown in FIG. 7B, the height of the region corresponding to the region directly above the non-buried insulating film 105 on the upper surface 18a of the conductive film 18 is in the region directly above the STI 7. It becomes higher than the height of the corresponding region. For this reason, when the conductive film 18 is etched to form the electrodes 8a and 8b, the timing at which the etching should be finished differs between the periphery of the electrode 8a and the periphery of the electrode 8b. As a result, if sufficient etching is performed so that no conductive material residue is generated around the electrode 8a, overetching occurs around the electrode 8b, and the shape of the electrode 8b deteriorates. On the other hand, when the etching end timing is matched with the electrode 8b, a residue is generated around the electrode 8a. Moreover, since etching cannot be performed with high accuracy, it is difficult to form the electrodes 8a and 8b finely.

In this comparative example, in the step shown in FIG. 8B, the height of the region corresponding to the region directly above the non-buried insulating film 105 on the upper surface 9a of the interlayer insulating film 9 corresponds to the region directly above the STI 7. It becomes higher than the height of the area. Thereby, when viewed macroscopically, the height of the upper surface 9a in the region A is higher than the height of the upper surface 9a in the region B. As a result, even when subjected to a planarization process such as CMP the interlayer insulating film 9, it is difficult to eliminate the height difference d ₂ of the top surface 9a between the regions A and B.

If the height difference remains on the upper surface 9a, the difficulty of the subsequent processes increases. For example, the difficulty of CMP for the conductive material film when forming the contacts 10a and 10b in the interlayer insulating film 9 is increased, and the conductive material remains. Further, fine photolithography becomes difficult, and the contacts 10a and 10b cannot be formed finely. Meanwhile, in order to minimize the difference in height d ₂ of the top surface 9a, when forming a thick interlayer insulating film 9, the low height of the semiconductor device becomes difficult. Thus, in this comparative example, it is difficult to miniaturize the semiconductor device as compared with the first embodiment described above.

Next, a second embodiment of the present invention will be described.
FIG. 9 is a cross-sectional view illustrating a semiconductor device according to this embodiment.
As shown in FIG. 9, in the semiconductor device 21 according to the present embodiment, in addition to the configuration of the semiconductor device 1 (see FIG. 1) according to the first embodiment described above, the lower part of the semi-buried insulating film 5, That is, the buffer insulating film 22 is provided so as to cover the portion embedded in the semiconductor substrate 2. The buffer insulating film 22 is formed of an insulating material different from that of the semi-buried insulating film 5. For example, the semi-embedded insulating film 5 is formed of silicon oxide (SiO ₂ ) deposited by HDP-CVD (High Density Plasma Chemical Vapor Deposition) method, and is a buffer insulating film. 22 is formed of silicon nitride (SiN). Other configurations in the present embodiment are the same as those in the first embodiment.

  In the present embodiment, since the buffer insulating film 22 is provided between the semi-buried insulating film 5 and the semiconductor substrate 2, stress generated between the semi-buried insulating film 5 and the semiconductor substrate 2 is relieved. be able to. For example, when silicon oxide is deposited by HDP-CVD to form the semi-buried insulating film 5, a large tensile stress is generated inside the semi-buried insulating film 5. On the other hand, when the buffer insulating film 22 is formed of silicon nitride, compressive stress is generated inside the buffer insulating film 22. Thereby, the tensile stress inside the semi-buried insulating film 5 and the compressive stress inside the buffer insulating film 22 cancel each other. As a result, the stress concentration at the corner of the semi-buried insulating film 5 is relaxed, and the characteristics of the semiconductor device 21 can be made better and stable. Operations and effects other than those described above in the present embodiment are the same as those in the first embodiment described above.

Next, a method for manufacturing the semiconductor device 21 according to the present embodiment will be described.
10A to 10C are process cross-sectional views illustrating the method for manufacturing a semiconductor device according to this embodiment.
The semiconductor device manufacturing method according to this embodiment will be described below with reference to the semiconductor device manufacturing method according to the first embodiment.

  First, the steps shown in FIGS. 2A to 2C are performed. That is, the hard mask insulating film 11 is formed on the semiconductor substrate 2, and the recess 2c and the trench 14 are formed using this as a mask. As a result, as shown in FIG. 10A, a hard mask insulating film 11 is provided on the semiconductor substrate 2, and a recess 2c and a trench 14 are formed immediately below the opening 11a of the hard mask insulating film 11. A body is made. At this time, the hard mask insulating film 11 is not formed inside the recess 2 c and the trench 14.

  Next, as shown in FIG. 10B, the hard mask insulating film 11 is removed. After that, as shown in FIG. 10C, a hard mask material film 23 is again deposited on the entire upper surface of the semiconductor substrate 2. The hard mask material film 23 is formed of silicon nitride (SiN) and has a thickness corresponding to the protruding height from the upper surface 2a of the semiconductor substrate 2 in the STI 7 (see FIG. 9). At this time, the hard mask material film 23 is formed not only on the semiconductor substrate 2 but also on the inner surface of the recess 2 c and the inner surface of the trench 14.

  Next, the steps shown in FIGS. 3A to 7B are performed. At this time, the hard mask material film 23 is used instead of the hard mask material film 11 in the first embodiment. As a result, as shown in FIG. 9, the hard mask material film 23 remaining in the recess 2 c and in the trench 14 becomes the buffer insulating film 22, and the semiconductor device 21 is manufactured.

Next, a third embodiment of the present invention will be described.
The semiconductor device according to this embodiment is a CMOS image sensor.
FIG. 11 is a plan view illustrating a semiconductor device according to this embodiment.
FIG. 12 is a plan view illustrating the imaging region shown in FIG.
13 is a cross-sectional view taken along line AA ′ shown in FIG.
14 is a cross-sectional view taken along line BB ′ shown in FIG.
15 is a cross-sectional view taken along the line CC ′ shown in FIG.
16 is a cross-sectional view taken along the line DD ′ shown in FIG.
FIG. 17 is a cross-sectional view schematically illustrating the imaging region and the processing region shown in FIG.

  As shown in FIG. 11, in the CMOS image sensor 31 according to the present embodiment, an imaging region 32 that converts incident light into an electrical signal is provided at the center of the silicon substrate 40. Further, a processing area 33 for processing the electrical signal output from the imaging area 32 is provided around the imaging area 32. In the processing area 33, a peripheral circuit area 34 that extracts an electrical signal from the imaging area 32 is provided in a frame-like area surrounding the imaging area 32. Further, an image processing circuit area 35 that performs image processing based on an electrical signal is provided on one side of the peripheral circuit area 34 in the processing area 33, and an image is displayed on the other side of the peripheral circuit area 34. An image compression circuit area 36 to be compressed is provided.

  As shown in FIG. 12, in the imaging region 32, a plurality of pixels 41 are arranged in a matrix as viewed from above. One cell 42 is constituted by four pixels 41 arranged in two rows and two columns. Each pixel 41 belonging to one cell 42 is provided with, for example, red, green, blue, and blue color filters 82 (see FIG. 17). Hereinafter, in this embodiment, for convenience of explanation, the arrangement direction of the pixels 41 is defined as an X direction and a Y direction.

  Each pixel 41 is provided with a photodiode 43 that converts incident light into electric charge. Each pixel 41 is provided with a transfer gate 44. The transfer gate 44 is disposed at one corner of the pixel 41, and its shape is a parallel hexagon in which three corners are cut off from a right triangle along the corner of the pixel 41. In the imaging region 32, the pixel 41 in which the transfer gate 44 is arranged in the corner portion on the + X + Y side and the pixel 41 in which the transfer gate 44 is arranged in the corner portion on the + X−Y side are along the X direction and the Y direction. Are alternately arranged.

  The pixels 41 are separated by a barrier region 45 formed in a lattice shape. Among regions corresponding to lattice points in the barrier region 45, a rectangular reset gate 46 is provided in a region including a region directly above a region corresponding to a lattice point not close to the corner portion where the transfer gate 44 is disposed. Yes. A rectangular amplifier gate 47 is provided at a position separated from the reset gate 46 by a distance of less than one pixel in the −X direction. Further, a U-shaped mesa isolation region 48 is formed along the portion extending in the X direction in the barrier region 45 so as to surround the reset gate 46 and the amplifier gate 47. The U-shape of each mesa separation region 48 opens in the −X direction.

  As shown in FIGS. 12 to 16, in the CMOS image sensor 31, an n-type epitaxial layer 50 is formed on a p-type silicon substrate 40 containing boron (B). The silicon substrate 40 and the epitaxial layer 50 constitute a semiconductor substrate. A gate oxide film 52 is formed on the epitaxial layer 50. The photodiode 43, the barrier region 45, and the mesa isolation region 48 described above are formed in the epitaxial layer 50. On the other hand, the transfer gate 44, the reset gate 46, and the amplifier gate 47 described above are disposed above the epitaxial layer 50 and the gate oxide film 52.

  The photodiode 43 includes an n-type light receiving region 43n (first conductivity type region) formed in the upper layer portion of the epitaxial layer 50, and a p-type inversion layer 43p formed in the outermost layer portion of the light receiving region 43n. Has been. When light enters the light receiving region 43n, an electric charge is generated. The inversion layer 43p is a layer that suppresses the generation of excessive charges on the surface of the light receiving region 43n.

  As described above, the barrier region 45 is a region that separates the pixels 41 from each other. The barrier region 45 is formed by connecting an implantation layer (ion implantation layer) formed by ion implantation of boron from the surface side and a diffusion layer formed by diffusion of boron from the silicon substrate 40. Has been. That is, each pixel 41 is surrounded in a bowl shape by the barrier region 45 and the silicon substrate 40. However, the barrier region 45 is not exposed on the surface of the epitaxial layer 50, and a p-type pixel well 51 is formed between the barrier region 45 and the surface of the epitaxial layer 50. In addition, the p-type well 53 is included in the edge of the transfer gate 44 that is close to the barrier region 45, that is, in a region including a region directly below the edge that does not face the photodiode 43 belonging to the same pixel 41. Is formed.

  A pixel well 51 is disposed immediately below the reset gate 46 in the epitaxial layer 50 and serves as a channel region. In addition, a pair of n-type source / drain regions 55 are formed at positions sandwiching the channel region in the X direction, and an n-type extension region 56 is formed around the source / drain regions 55. . The extended region 56 has a lower donor concentration and a smaller depth than the source / drain region 55. Similarly, a pixel well 51 is also arranged in a region immediately below the amplifier gate 47 to form a channel region, and a source / drain region 55 and an extension region 56 are formed on both sides in the X direction. Furthermore, a p-type channel layer 57 is formed in the outermost layer of the epitaxial layer 50 and immediately below the transfer gate 44. As a result, a transistor structure is realized immediately below each gate.

The mesa isolation region 48 is a region that is disposed on both sides of the mesa isolation region 48 and isolates the regions that are in contact with the mesa isolation region 48. Specifically, the photodiode 43 is separated from the transistor structure formed immediately below each gate. It is an area to do. That is, the mesa isolation region 48 separates the photodiode 43 and the pixel well 51 as shown in FIG. 15, and separates the photodiode 43 and the source / drain region 55 as shown in FIG. In the mesa isolation region 48, a p-type region (second conductivity type region) 58 into which, for example, boron is implanted is formed in the epitaxial layer 50, and a semi-buried insulation is formed immediately above the p-type region 58. A film 59 is formed. The lower part of the half buried insulating film 59 is buried in the epitaxial layer 50, and the upper part of the half buried insulating film 59 protrudes from the upper surface of the epitaxial layer 50. The semi-buried insulating film 59 is made of, for example, silicon oxide (SiO ₂ ).

On the other hand, as shown in FIG. 17, the processing region 33 is provided with an analog circuit and a digital circuit, and a CMOS 61 is formed in a part of the digital circuit. In the CMOS 61, a P-channel MOSFET (PMOS) 62 and an N-channel MOSFET (NMOS) 63 are provided, and an STI 64 is provided around the PMOS 62 and the NMOS 63. Thereby, the PMOS 62 and the NMOS 63 are separated from each other and from the surroundings by the STI 64. The STI 64 is made of, for example, silicon oxide (SiO ₂ ). The height of the upper surface of the STI 64 is substantially equal to the height of the upper surface of the semi-buried insulating film 59. In one example, the protruding amounts of the semi-buried insulating film 59 and the STI 64 from the epitaxial layer 50 are both 20 nm.

  In the PMOS 62, an N well 66 is formed in the upper layer portion of the epitaxial layer 50, and a pair of p-type source / drain regions 67 separated from each other are formed in the upper layer portion of the N well 66. An n-type channel region 68 is formed between the drain regions 67. A gate insulating film 69 and a gate electrode 70 are provided on the epitaxial layer 50 and immediately above the channel region 68, and side walls 71 are provided on the sides of the gate electrode 70.

  On the other hand, in the NMOS 63, a P well 72 is formed in the upper layer portion of the epitaxial layer 50, and a pair of n-type source / drain regions 73 spaced apart from each other are formed in the upper layer portion of the P well 72. A p-type channel region 74 is formed between the source / drain regions 73. A gate insulating film 75 and a gate electrode 76 are provided on the epitaxial layer 50 and immediately above the channel region 74, and a side wall 77 is provided on the side of the gate electrode 76.

  An interlayer insulating film 80 is provided on the epitaxial layer 50 throughout the imaging region 32 and the processing region 33, and metal wirings 81 are embedded in the interlayer insulating film 80 in multiple stages. However, the metal wiring 81 is not disposed in the region immediately above the photodiode 43 in the imaging region 32. A color filter 82 is provided immediately above the photodiode 43 on the interlayer insulating film 80. Further, an overcoat layer 83 is provided on the interlayer insulating film 80 and the color filter 82, and a microlens 84 is provided in a region immediately above the photodiode 43 on the overcoat layer 83.

Next, the embedding depth of the semi-buried insulating film 59 will be described.
FIG. 18 is a graph illustrating the impurity concentration profiles of the light receiving region, the inversion layer, and the source / drain region, with the horizontal axis representing the depth direction position and the vertical axis representing the impurity concentration. In the horizontal axis of FIG. 18, the position of the upper surface of the epitaxial layer 50 is set as a reference (0 μm).
As shown in FIGS. 16 and 18, the embedding depth of the semi-buried insulating film 59, that is, the position of the lower surface of the semi-buried insulating film 59 satisfies the following three requirements (1) to (3). It is preferable.

(1) The lower surface of the semi-buried insulating film 59 is positioned below the position where the acceptor concentration takes the maximum value (hereinafter referred to as “inversion layer depth”) in the acceptor concentration profile in the depth direction of the inversion layer 43p. To do. In the example shown in FIG. 18, the inversion layer depth is about 20 nm.
(2) The lower surface of the semi-buried insulating film 59 has a position where the impurity concentration has a maximum value in the impurity concentration profile in the depth direction of the source / drain region 55 adjacent to the semi-buried insulating film 59 (hereinafter referred to as “SD”). It is located below the depth). In the example shown in FIG. 18, the SD depth is about 30 nm.
(3) The lower surface of the semi-buried insulating film 59 is located above the position where the donor concentration takes the maximum value (hereinafter referred to as “PD depth”) in the donor concentration profile in the depth direction of the light receiving region 43n. . In the example shown in FIG. 18, the PD depth is about 200 nm.

  Hereinafter, the reason for the above requirements will be described.

Regarding (1) As described above, since the position of the upper surface of the semi-buried insulating film 59 is substantially coincident with the position of the upper surface of the STI 64, the lower surface of the semi-buried insulating film 59 is positioned above the inversion layer depth. As a result, the semi-buried insulating film 59 becomes thin. Thereby, when ion plantation (implantation) is performed using the semi-buried insulating film 59 as a mask and the inversion layer 43p is formed, impurities penetrate the semi-buried insulating film 59. As a result, charge leakage occurs from the photodiode 43 toward the transistor structure, and color mixing tends to occur.

Regarding (2) Similar to (1) above, when the lower surface of the semi-buried insulating film 59 is positioned above the SD depth of the source / drain region 55, the semi-buried insulating film 59 becomes thin. As a result, when implantation is performed using the semi-buried insulating film 59 as a mask and the source / drain regions 55 are formed, impurities penetrate the semi-buried insulating film 59. As a result, the element isolation resistance deteriorates.

In order to confirm this phenomenon, a semi-buried insulating film 59 having an upward protrusion amount of 20 nm from the upper surface of the epitaxial layer 50 and having different burying depths is formed. The source / drain region 55 was formed by performing implantation using the 59 and the amplifier gate 47 as a mask. And the leakage current in a pn junction surface was measured. The measurement results are shown in Table 1. Further, after the measurement, the semi-buried insulating film 59 was peeled off, and the impurity concentration introduced immediately below the semi-buried insulating film 59 was measured. The results are shown in FIG.
FIG. 19 is a graph illustrating an impurity concentration profile in the region immediately below the semi-buried insulating film, with the horizontal axis representing the depth direction position and the vertical axis representing the impurity concentration. In the horizontal axis of FIG. 19, the position of the lower surface of the semi-buried insulating film is taken as a reference (0 nm).

As shown in FIG. 19, when the burying depth of the semi-buried insulating film 59 is 0 nm, that is, when the entire thickness of the semi-buried insulating film 59 is 20 nm, Impurities of up to about 1 × 10 ¹⁵ cm ⁻³ were introduced. On the other hand, when the buried depth of the semi-buried insulating film 59 is 50 nm, that is, when the thickness of the entire semi-buried insulating film 59 is 70 nm, the maximum is directly below the half-buried insulating film 59. Impurities were introduced only at about 1 × 10 ¹¹ cm ⁻³ , which was about 1 / 10,000 when the embedding depth was 0 nm. Further, when the buried depth of the semi-buried insulating film 59 is 200 nm, that is, when the total thickness of the semi-buried insulating film 59 is 220 nm, a maximum of 1 × 10 6 is provided directly below the half-buried insulating film 59. Impurities were introduced only at about ⁸ cm ⁻³ .

  Thus, when the buried depth of the semi-buried insulating film 59 is 0 nm and 20 nm shallower than the SD depth, the impurities implanted to form the source / drain regions cause the semi-buried insulating film 59 to be formed. The leakage current occurred in the pn junction surface of the source / drain region. On the other hand, when the buried depth of the semi-buried insulating film 59 is 50 nm and 200 nm, which are deeper than the SD depth, the impurities hardly penetrate the semi-buried insulating film 59 and almost no leak current is generated. I did not. Therefore, the lower surface of the semi-buried insulating film 59 is preferably positioned below the SD depth of the source / drain region 55 adjacent to the semi-buried insulating film 59.

Regarding (3) When the lower surface of the semi-buried insulating film 59 is positioned below the PD depth, the portion with the highest impurity concentration in the photodiode 43 is eroded by the semi-buried insulating film 59 and can be used for photoelectric conversion. The amount of impurities is greatly reduced. As a result, the sensitivity of the pixel is lowered.

In order to confirm this phenomenon, an optical simulation was performed. In this simulation, a semi-buried insulating film 59 in which the protrusion amount from the upper surface of the epitaxial layer 50 is 20 nm and the buried depths are different from each other and a photodiode 43 having a PD depth of 200 nm are assumed. Then, the number Q _sat of electrons generated by photoelectric conversion when light enters the photodiode was calculated. The results are shown in Table 2. Table 2 also shows the reduction rate of the number of electrons Q _{sat based on} the case where the embedding depth is zero.

When the burying depth of the semi-buried insulating film 59 reached the PD depth of 200 nm, the number of electrons Q _sat decreased significantly. As described above, by forming the semi-buried insulating film 59 to the PD depth, the portion having the highest impurity concentration in the photodiode 43 is eroded by the semi-buried insulating film 59 and can be used for photoelectric conversion. This is because the amount was greatly reduced. Conversely, if the lower surface of the semi-buried insulating film 59 does not reach the PD depth, the number of electrons required for photoelectric conversion will not be extremely reduced. Therefore, the lower surface of the semi-buried insulating film 59 is preferably positioned above the PD depth of the light receiving region 43n.

  As described above, the embedding depth of the semi-buried insulating film 59 is not preferable whether it is too shallow or too deep, and there is a suitable range. In other words, it is preferable that the height of the upper surface of the semi-buried insulating film 59 is made equal to the height of the upper surface of the STI 64 so that the impurities implanted when forming the inversion layer and the source / drain regions do not penetrate. In addition, it is preferable to set the depth so as not to erode a portion having a high impurity concentration in the photodiode. Specifically, the position of the lower surface of the buried insulating film 59 is preferably a position that satisfies the above (1) to (3). The inversion layer depth, PD depth, and SD depth described above are substantially the same during impurity implantation and after device completion. This is because, even if impurities are diffused due to thermal history, the peak of the profile is broad, but the peak position does not change.

Next, the taper angle of the semi-buried insulating film 59 will be described.
As shown in FIG. 16, the direction is parallel to the upper surface of the epitaxial layer 50, the direction is from the outer edge of the semi-buried insulating film 59 toward the center, and the direction is parallel to the side surface of the semi-buried insulating film 59. When the angle formed by the downward direction is a taper angle θ, the taper angle θ is preferably 73 to 90 °. When the taper angle θ exceeds 90 °, the bottom of the recess formed on the upper surface of the epitaxial layer 50 becomes wider than the opening, making it difficult to bury the insulating material.

  On the other hand, when the taper angle θ is less than 90 °, the cross-sectional shape of the semi-buried insulating film 59 is a trapezoidal shape with the upper side being long and the lower side being short, and the film thicknesses at both ends of the semi-buried insulating film 59 are reduced. Therefore, when forming diffusion regions (for example, the source / drain regions 55 shown in FIG. 14 or the light receiving regions 43n shown in FIG. 16) using the semi-buried insulating film 59 as a mask, these diffusion regions are formed. The donor to be injected penetrates through both end portions of the semi-buried insulating film 59. As a result, the penetrating donor cancels out the action of the acceptor contained at both ends of the p-type region 58, and the effective width of the p-type region 58 is narrowed. If the taper angle θ is less than 73 °, the effective width of the p-type region 58 becomes too narrow, and the leakage current flowing through the p-type region 58 becomes large. For this reason, it becomes difficult to sufficiently separate both sides by the p-type region 58. In one example, when the width of the upper end portion of the semi-buried insulating film 59 is 0.16 μm and the thickness is 55 nm, if the taper angle θ is less than 73 °, The width becomes less than 0.12 μm, and the leakage current flowing through the p-type region 58 increases.

Next, the operation of the CMOS image sensor 31 according to this embodiment will be described.
When light enters the imaging region 32 from the outside of the CMOS image sensor 31, this light is collected by the microlens 84, passes through the overcoat layer 83, passes through the color filter 82, and the wavelength is selected, and interlayer insulation is performed. The light passes through the film 80 and enters the photodiode 43. As a result, charges are generated and accumulated in the light receiving region 43n.

  Then, when the circuit in the peripheral circuit region 34 drives the transfer gate 44, the charge accumulated in the light receiving region 43n is formed in the region immediately below the amplifier gate 47 through the channel layer 57 (see FIG. 13). It is transferred to the transistor structure and read out as an electrical signal. Further, when the circuit in the peripheral circuit region 34 drives the reset gate 46, the charge is erased. The electrical signal read by the amplifier gate 47 is processed by the processing region 33. That is, the image data is input to the image processing circuit area 35 via the peripheral circuit area 34 and subjected to image processing. Thereafter, the data is compressed in the image compression circuit area 36 and output from the CMOS image sensor 31.

Next, a method for manufacturing the CMOS image sensor 31 according to this embodiment will be described.
The characteristic part of the manufacturing method of the CMOS image sensor 31 is the same as that of the semiconductor device manufacturing method according to the first embodiment described above. That is, after forming the epitaxial layer 50 on the silicon substrate 40, a hard mask material film (not shown) is formed on the epitaxial layer 50. The hard mask material film is formed of, for example, silicon nitride (SiN). Next, etching is selectively performed to form openings in the region where the mesa isolation region 48 is to be formed in the hard mask material film and the region where the STI 64 is to be formed, and the epitaxial layer 50 in the region immediately below the opening is formed. A recess is formed on the upper surface. Then, the recess of the processing region 33 is further processed using the hard mask material film as a mask to form a trench.

  Next, an acceptor such as boron is implanted into the imaging region 32 using the hard mask material film as a mask, thereby forming the p-type region 58. Next, an insulating material such as silicon oxide is deposited on the entire surface and etched back by wet etching to embed the semi-buried insulating film 59 in the recess of the imaging region 32 and to form the STI 64 in the trench of the processing region 33. Buried. Thereby, the protruding amount of the semi-buried insulating film 59 can be suppressed, and the height of the upper surface of the semi-buried insulating film 59 can be made substantially equal to the height of the upper surface of the STI 64.

  Thereafter, other components in the CMOS image sensor 31 are produced by a normal method. In this process, by receiving a donor such as phosphorus (P) into the epitaxial layer 50 using the semi-buried insulating film 59 as a mask, the photodiode 43 receives light in a self-aligned manner in a region in contact with the p-type region 58. A step of forming the region 43n is also included. The transfer gate 44, reset gate 46 and amplifier gate 47 in the imaging region 32, and the gate electrode 70 and gate electrode 76 in the processing region 33 are formed by processing the same polysilicon film.

  At this time, since the height of the upper surface of the semi-buried insulating film 59 is low and is substantially the same as the height of the upper surface of the STI 64, the transfer gate is operated according to the same principle as that described in the first embodiment. 44, the reset gate 46, the amplifier gate 47, the gate electrode 70, and the gate electrode 76 can be easily formed, and the heights of the upper surfaces of these gates can be made substantially the same. In addition, the height of the upper surface of the interlayer insulating film 80 can be made substantially the same between the imaging region 32 and the processing region 33. Thereby, the difficulty of CMP for the interlayer insulating film 80 is reduced, and a fine structure can be easily formed. The CMOS image sensor 31 is manufactured by the above method.

Next, the effect of this embodiment is demonstrated.
In the present embodiment, the photolithography 43 and the transistor structure are separated by the mesa isolation region 48. Thereby, compared with the case where this isolation | separation is performed by STI, the area required for isolation | separation can be reduced. As a result, since the area of the photolithography 43 can be increased, the number of saturated electrons at the time of photoelectric conversion is increased and the sensitivity is improved. Thereby, pixel characteristics are improved.

Hereinafter, this effect will be described in detail.
FIG. 20A is a plan view illustrating one pixel in a CMOS image sensor according to a comparative example of this embodiment, and FIG. 20B is a cross-sectional view taken along line EE ′ shown in FIG. (C) is a top view which illustrates one pixel in the CMOS image sensor which concerns on this embodiment, (d) is sectional drawing by the FF 'line | wire shown in (c).

  As shown in FIGS. 20A and 20B, in the comparative example of this embodiment, the photodiode 43 and the peripheral transistor structure are separated by the STI 107. In this case, crystal defects are introduced into the silicon substrate along with the formation of the STI 107 and unpaired electron pairs are generated. Therefore, the STI 107 needs to be enclosed by the pixel well 51. As a result, the area of the photodiode 43 is reduced by the margin of the pixel well 51.

  On the other hand, as shown in FIGS. 20C and 20D, in this embodiment, the photodiode 43 and the surrounding transistor structure are composed of a p-type region 58 and a semi-buried insulating film 59. They are separated by a mesa separation structure 48. Further, since the p-type region 58 is thinly formed not only in the region directly under the semi-buried insulating film 59 but also on the side (not shown), the semi-buried insulating film 59 is thinly wrapped by the p-type region 58. Can do. As a result, it is possible to prevent the crystal defects introduced into the silicon substrate accompanying the formation of the semi-buried insulating film 59 from affecting the photoelectric conversion by the photodiode 43. For this reason, unlike the comparative example described above, it is not necessary to arrange the pixel well 51 on the photodiode 43 side of the mesa isolation structure 48, and the area of the photodiode 43 can be increased correspondingly. Thereby, the number of saturated electrons at the time of photoelectric conversion increases, and the sensitivity improves. As a result, the performance of the CMOS image sensor 31 is improved.

In one example, in the comparative example shown in FIGS. 20A and 20B and in the present embodiment shown in FIGS. 20C and 20D, when the size and shape of the pixels are the same, in the comparative example, The area of the photodiode is 0.41 μm ² , and in the present embodiment, the area of the photodiode is 0.72 μm ² . That is, according to the present embodiment, the area of the photodiode can be increased about 1.76 times as compared with the comparative example.

  In the present embodiment, the mesa isolation structure and the STI are mixed. That is, as shown in FIG. 17, in the imaging region 32, the photodiode 43 and the surrounding transistor structure are separated by the mesa isolation structure 48, and in the processing region 33, elements such as the CMOS 61 are separated by the STI 64. Yes. Thereby, in the processing area 33, it is not necessary to change the conventional design rule and process, and a highly reliable device can be manufactured easily and at low cost.

  Then, by embedding the lower portion of the semi-buried insulating film 59 constituting the mesa isolation structure 48 in the epitaxial layer 50, while ensuring a necessary thickness in the semi-buried insulating film 59, the semi-buried insulating film 59 is formed. The height of the upper surface can be made substantially equal to the height of the upper surface of the STI 64. As a result, the CMOS image sensor 31 can be easily manufactured and miniaturized.

  In the present embodiment, a buffer insulating film may be formed around the semi-buried insulating film 59 as in the second embodiment described above. Thereby, the stress applied to the epitaxial layer 50 by the semi-buried insulating film 59 can be relaxed.

  In the first to third embodiments described above, the example in which the mesa isolation structure and the STI are mixed in one semiconductor device has been shown. However, the present invention is not limited to this, and only the mesa isolation structure is used. It may be provided. Even in this case, the area required for separation can be reduced, and the device can be miniaturized. Further, since the protruding amount of the semi-buried insulating film can be suppressed, the manufacturing becomes easy.

  While the present invention has been described with reference to the embodiments, the present invention is not limited to these embodiments. For example, those in which the person skilled in the art appropriately added, deleted, or changed the design of the above-described embodiments, or those in which the process was added, omitted, or changed the conditions are also included in the gist of the present invention. As long as it is provided, it is included in the scope of the present invention.

DESCRIPTION OF SYMBOLS 1 Semiconductor device, 2 Semiconductor substrate, 2a upper surface, 2c recessed part, 2g Gate insulating film, 3 n-type area | region, 4 p-type area | region, 5 Semi-buried insulating film, 5a upper surface, 5b lower surface, 6 channel area | region, 7 STI, 7a Upper surface, 7b lower surface, 8a, 8b electrode, 9 interlayer insulating film, 9a upper surface, 10a, 10b contact, 11 hard mask material film, 11a opening, 12 resist pattern, 12a opening, 13 resist pattern, 14 trench, 15 resist Pattern, 16 insulating material, 18 conductive film, 18a upper surface, 19 resist pattern, 20 region, 21 semiconductor device, 22 buffer insulating film, 23 hard mask material film, 31 CMOS image sensor, 32 imaging region, 33 processing region, 34 periphery Circuit area, 35 Image processing circuit area, 36 Image compression circuit area, 41 pixels, 42 43, 43 photodiode, 43n light receiving region, 43p inversion layer, 44 transfer gate, 45 barrier region, 46 reset gate, 47 amplifier gate, 48 mesa isolation region, 50 epitaxial layer, 51 pixel well, 52 gate insulating film, 55 source Drain region, 56 extended region, 57 channel layer, 58 p-type region, 59 semi-buried insulating film, 61 CMOS, 62 PMOS, 63 NMOS, 64 STI, 66 N well, 67 source / drain region, 68 channel region, 69 Gate insulating film, 70 Gate electrode, 71 Side wall, 72 P well, 73 Source / drain region, 74 channel region, 75 Gate insulating film, 76 Gate electrode, 77 Side wall, 80 Interlayer insulating film, 81 Metal wiring, 82 Color filter , 83 Overcoat layer, 84 Micro lens, 05 Non-buried insulating film, 105a upper surface, 107 STI, A, B _{area, d 1,} d ₂ height difference, theta taper angle

Claims (3)

An imaging area provided with an imaging area for converting incident light into an electrical signal, and a processing area for processing the electrical signal,
A semiconductor substrate;
A first conductivity type region formed in an upper layer portion of the semiconductor substrate and having a first conductivity type;
A second conductivity type region formed in an upper layer portion of the semiconductor substrate, in contact with the first conductivity type region, and having a second conductivity type different from the first conductivity type;
A semi-embedded insulating film provided directly above the second conductivity type region, a lower portion embedded in the semiconductor substrate, and an upper portion protruding from the upper surface of the semiconductor substrate;
An element isolation film having a lower part embedded in the semiconductor substrate, an upper part protruding from the upper surface of the semiconductor substrate, and a lower surface located below the lower surface of the semi-embedded insulating film;
A second conductivity type inversion layer formed in an upper layer portion of the first conductivity type region;
A transistor in which a source / drain region is in contact with the second conductivity type region and the semi-buried insulating film;
With
The second conductive type region and the semi-buried insulating film are the first conductive type region and a region opposite to the first conductive type region as viewed from the second conductive type region, and the second conductive type region. Separate the area that touches the mold area,
The first conductivity type region constitutes a photodiode provided in the imaging region,
The element isolation film separates elements provided in the processing region,
The position of the lower surface of the semi-buried insulating film is
In the impurity concentration profile in the depth direction of the inversion layer, below the position where the impurity concentration takes the maximum value,
In the impurity concentration profile in the depth direction of the source / drain region, below the position where the impurity concentration takes the maximum value,
An image pickup device, wherein the impurity concentration profile is above a position where the impurity concentration takes a maximum value in the impurity concentration profile in the depth direction of the first conductivity type region.   A direction parallel to the upper surface of the semiconductor substrate, the direction from the outer edge of the semi-buried insulating film toward the center, and a direction parallel to the side surface of the semi-buried insulating film and directed downward. The image pickup device according to claim 1, wherein an angle formed by is between 73 ° and 90 °. An imaging area for converting incident light into an electrical signal, and a method for manufacturing an imaging device provided with a processing area for processing the electrical signal,
Forming a hard mask material film on a semiconductor substrate;
Forming an opening in the hard mask material film by etching and forming a recess in a region directly below the opening on the upper surface of the semiconductor substrate;
Etching with the hard mask material film as a mask to further remove the bottom surface of some of the recesses to form a trench;
Forming a second conductivity type region in a region immediately below the recess in the semiconductor substrate by implanting impurities using the hard mask material film as a mask;
A step of embedding an insulating material in the opening provided in the recess and in a region immediately above the recess, and in the opening provided in the trench and a region immediately above the trench;
By removing the hard mask material film, the lower part is embedded in the semiconductor substrate, the upper part forms a semi-embedded insulating film protruding from the upper surface of the semiconductor substrate, and the lower part is embedded in the trench, Forming an element isolation film having an upper portion protruding from the upper surface of the semiconductor substrate;
Forming a first conductivity type region in a region of the semiconductor substrate in contact with the second conductivity type region by implanting impurities using the semi-buried insulating film as a mask;
Forming a second conductivity type inversion layer on an upper layer portion of the first conductivity type region;
Forming a transistor in which a source / drain region is in contact with the second conductivity type region and the semi-buried insulating film;
With
The first conductivity type region constitutes a photodiode provided in the imaging region,
The element isolation film separates elements provided in the processing region,
In the step of forming the inversion layer, the position where the impurity concentration in the impurity concentration profile in the depth direction of the inversion layer takes the maximum value is above the bottom surface of the recess,
In the step of forming the transistor, the position where the impurity concentration in the impurity concentration profile in the depth direction of the source / drain region takes the maximum value is above the bottom surface of the recess,
In the step of forming the first conductivity type region, a position where the impurity concentration in the impurity concentration profile in the depth direction of the first conductivity type region takes a maximum value is set below the bottom surface of the recess. For manufacturing an image pickup device.

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