JP2005005561A - Manufacturing method of semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To form an oxide film to desired regions with different thickness without the need for a process. <P>SOLUTION: A plurality of grooves 107, 108 with at least two kinds of depths are formed to a silicon substrate 103. The silicon substrate 103 is oxidized until the regions between the grooves 107, 108 of the silicon substrate 103 become the oxide film 109, and the inside of the grooves 107, 108 is buried with the oxide film 109. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for forming a silicon oxide film. The present invention relates to a semiconductor element, a photodiode, and a solar cell using a silicon oxide film as an element isolation film, an integrated circuit using the semiconductor element as a part thereof, and an integrated circuit including the photodiode or solar cell as a component. The present invention can be applied to the manufacture of information terminal devices such as digital cameras and mobile phones.
[0002]
[Prior art]
A conventional technique will be described with reference to FIG. In the method of manufacturing a semiconductor device described in Patent Document 1, the first thermal oxide film 12, the silicon nitride film 13, and the NSG film 14 are patterned on the silicon substrate 11 (FIG. 8A), and the silicon nitride film 15 and the NSG are patterned. After the film 16 is deposited, anisotropic etching is performed on the NSG film 16 (FIG. 8B). Next, a side wall 16 ′ is formed by an NSG film (FIG. 8C), and the silicon nitride film 15 is selectively etched using the side wall 16 ′ as a mask. Next, by removing the NSG films 14 and 16 ′, a sidewall 15 ′ made of a silicon nitride film is formed (FIG. 8D). Further, selective oxidation is performed in a steam atmosphere to grow a field oxide film 17 (FIG. 8E). Subsequently, only the silicon nitride film 15 ′ serving as a sidewall is selectively removed (FIG. 8F), and selective oxidation is performed again to form a final field oxide film 17 (FIG. 8G). )). Thereafter, the silicon nitride film 13 and the first thermal oxide film 12 are removed (FIG. 8H).
[0003]
FIG. 9 shows a manufacturing process of an image sensor according to the prior art. As is well known, an image sensor processes a pinned photodiode or a valid photodiode as a light sensing element and a photogenerated charge generated by the pinned photodiode into an electrical signal. For a plurality of MOS transistors. FIG. 9 shows only the region where the photodiode is formed.
[0004]
First, an element isolation film 301 is formed on a P-type silicon substrate (P-sub) 304 by a normal STI (Shallow Trench Isolation) process. Next, an N-type impurity layer 303 is formed inside the substrate by performing low-concentration high-energy N-type ion implantation using an ion implantation mask (not shown) in which the regions 3a and 3b in which the photodiodes are formed are opened. Then, high-concentration low-energy P-type ion implantation is performed to form a P-type impurity layer 302 under the substrate surface. FIG. 9 shows this state. Thereafter, a pinned photodiode comprising a P-type silicon substrate / N-type impurity layer / P-type impurity layer is formed by impurity diffusion by a thermal process.
[0005]
A pinned photodiode has various advantages over photodiodes having other structures such as a source / drain PN junction structure or a MOS capacitor structure. One of the advantages is that the depth of the depletion layer can be increased, so that the ability to convert incident photons into electrons, that is, photocharge generation efficiency is high. More specifically, in the pinned photodiode having the PNP junction structure, the N region (N-type impurity chamber 303) is completely depleted, and two P regions (P-type impurity chamber 302 and P-type are interposed through the N region). Since the depletion layer is also formed in the silicon substrate 304), the depth of the depletion layer is increased, so that the photocharge generation efficiency can be improved. In addition, the light sensitivity is extremely excellent.
[0006]
[Patent Document 1]
JP-A-62-190852 (Fig. 9)
[0007]
[Problems to be solved by the invention]
However, in the conventional method shown in FIG. 8, only an oxide film having the same thickness can be formed in all regions except the bird's beak region. Therefore, when forming oxide films with different film thicknesses in different regions, it is necessary to newly add photolithography, etching, and oxidation steps, which complicates the process.
[0008]
A similar problem exists in the image sensor manufacturing method according to the prior art described with reference to FIG. This will be described in detail below. A leakage current (LKG) is generated between the pinned photodiodes of adjacent unit pixels below the element isolation film 301. In order to prevent this leakage current, the element isolation film 301 may be excessively deep. However, in order to make the element isolation film 301 excessively deep, an element isolation manufacturing process for the photodiode region is required in addition to the element isolation manufacturing process for the MOS transistor region, which necessitates additional process steps.
[0009]
Therefore, an object of the present invention is to provide a method of forming two or more oxide films having different thicknesses in a desired region without adding steps such as a photolithography step and an oxidation step.
[0010]
[Means for Solving the Problems]
According to a first aspect of the present invention, in the method for manufacturing a semiconductor device in which oxide films having different thicknesses are formed on a silicon substrate, a step of forming a plurality of grooves having at least two types of depths in the silicon substrate; The silicon substrate is oxidized until the region between the grooves of the silicon substrate becomes an oxide film, and the inside of the groove is filled with the oxide film, and the thickness varies depending on the depth of the at least two kinds of grooves. And a step of obtaining a film. A method of manufacturing a semiconductor device is provided.
[0011]
The silicon substrate is oxidized on both sides of individual grooves of different depths. As a result, all the regions between the grooves of the silicon substrate are oxidized. In addition, since the volume of silicon constituting the substrate is increased by about 2 times due to oxidation, the oxidized silicon advances into the groove and fills the groove. Therefore, a thick oxide film is formed in a region where a deep groove is formed, while a thin oxide film is formed in a region where a shallow groove is formed, and oxide films having different thicknesses are formed simultaneously.
[0012]
According to the method of the first aspect, it is possible to manufacture oxide films having different thicknesses without adding a process such as a photolithography process and an oxidation process, thereby reducing the manufacturing process and reducing the cost. .
[0013]
Oxide films having different thicknesses can be formed in desired regions of the silicon substrate by setting the position where the groove is provided and the depth of the groove. That is, in the step of forming the plurality of grooves, a groove having a depth corresponding to the thickness of the oxide film in the region is formed in the region of the silicon substrate where the oxide film is to be formed.
[0014]
As described above, the volume of silicon is approximately doubled by oxidation. However, if the groove does not completely fill even if the oxidized silicon advances inside, an oxide film is deposited in the remaining recess without being filled. You can do it. That is, the second aspect of the present invention is a method of manufacturing a semiconductor device in which oxide films having different thicknesses are formed on a silicon substrate, and a step of forming a plurality of grooves having at least two types of depths in the silicon substrate. Etching the silicon substrate until the region between the grooves of the silicon substrate becomes an oxide film, depositing an oxide film inside the plurality of grooves, and etching the oxide film inside the grooves And a step of backing. A method for manufacturing a semiconductor device is provided.
[0015]
Different oxide films can be formed in a desired region of the silicon substrate by setting the position where the groove is provided and the depth of the groove. That is, in the step of forming the plurality of grooves, a groove having a depth corresponding to the thickness of the oxide film in the region is formed in the region of the silicon substrate where the oxide film is to be formed.
[0016]
Specifically, the step of forming the plurality of grooves includes a step of patterning a resist, an oxidation resistant film formed on the silicon substrate using the resist as a mask, and a step of etching the silicon substrate. The step of patterning the resist includes a step of exposing using a phase shift mask. Finer processing is possible, and the element can be miniaturized.
[0017]
The step of etching the oxidation-resistant film and the silicon substrate is performed with N of 5% to 15%. ₂ It is preferable that an etching gas containing the above is used and a groove corresponding to the thickness of the oxide film is formed by one etching. By forming grooves having different depths by one etching, the number of etching steps can be minimized. In order to form grooves having different depths, for example, the width of the exposed region of the silicon substrate in the resist may be varied.
[0018]
The step of oxidizing the silicon substrate is performed, for example, under a temperature condition of 1100 ° C. or higher and 1400 ° C. or lower. With such temperature conditions, stress acting on the silicon substrate during oxidation can be relaxed and uniform oxidation can be achieved.
[0019]
The oxide film is used as an element isolation film, for example. Since oxide films having different thicknesses are formed in desired regions without any positional deviation, it is not necessary to consider an alignment margin in design, so that an element isolation film can be formed in a fine region.
[0020]
It is preferable to manufacture a semiconductor element using the element isolation film. By manufacturing a semiconductor element using a fine element separation film, the semiconductor element can be miniaturized.
[0021]
It is preferable to manufacture an integrated circuit using the semiconductor element. If an integrated circuit is manufactured using the semiconductor element, an integrated circuit with a high degree of integration can be produced.
[0022]
It is preferable to manufacture a photodiode using the element isolation film. If a photodiode is manufactured using the element isolation film, the number of manufacturing steps such as an oxidation step and an etching step can be reduced, and the cost can be reduced.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
[0024]
(First embodiment)
A semiconductor device manufacturing method (a method of forming a silicon oxide film) according to the first embodiment of the present invention will be described with reference to FIG.
[0025]
First, as shown in FIG. 1A, a semiconductor substrate (silicon substrate) 103 is provided with a silicon oxide film 102 (thickness of 10 to 20 nm in this embodiment) and a silicon nitride film 101 (thickness in this embodiment). 100 to 200 nm) are sequentially formed.
[0026]
Next, as shown in FIG. 1B, the silicon nitride film 101 in the regions 106 and 105 where the trenches (see reference numerals 107 and 108 in FIG. 1C) are formed using photolithography and etching techniques. The silicon oxide film 102 is selectively removed, and the surface of the semiconductor substrate 103 is partially exposed. In the present embodiment, the width of the exposed region is about 0.18 to 0.22 μm in the region 106 and 0.11 to 0.13 μm in the region 105. Further, the width of the region 104 remaining without removing the silicon nitride film 101 and the silicon oxide film 102 is about 0.10 to 0.12 μm. The photolithography process will be described in detail later.
[0027]
Next, using the silicon nitride film 101 as a mask, the semiconductor substrate 103 is etched using an etching condition that allows more etching of a portion with a large exposed area than a portion with a small exposed area. As shown in FIG. 1C, under this etching condition, the semiconductor substrate 103 is etched deeper in the region 106 where the exposed width of the substrate surface is larger than in the region 105 where the exposed width is small. As a result, grooves (trench) 108 and 107 having different depths are formed in the semiconductor substrate 103. In the present embodiment, the depth of the deep groove 108 is about 1.0 to 1.2 μm, and the depth of the shallow groove 107 is about 0.3 to 0.5 μm. Details of the etching process including the above etching conditions will be described later.
[0028]
Next, as shown in FIG. 1D, the inner walls of the grooves 107 and 106 are oxidized in an oxidizing atmosphere using the silicon nitride film 101 as an oxidation resistant film, and about 0.09 to 0.11 μm of silicon oxide is formed on these inner walls. A film or a thermal oxide film (hereinafter simply referred to as an oxide film) is formed. An oxide film having a thickness of about 0.09 to 0.11 μm is formed on both sides of the trenches 107 and 108. In the region between the trenches 107 and the region between the trenches 107 and 108, all the silicon constituting the semiconductor substrate 103 is oxidized. The Further, since the volume of silicon constituting the semiconductor substrate 103 is approximately doubled by oxidation, the oxidized silicon advances from the inner wall into the grooves 107 and 108, and the grooves 107 and 108 disappear. Due to the oxidation of the region between the grooves 107 and 108 and the entry of oxidized silicon into the grooves 107 and 108, the grooves 108 and 107 having a width of about 0.18 to 0.22 μm or less are all oxide films. Buried. That is, a thick oxide film 109a having a film thickness of about 1.1 to 1.3 μm is formed in a region where the deep groove 108 is formed, and a film thickness of about 0.1 mm is formed in a region where the shallow groove 107 is formed. A thin oxide film 109b having a thickness of 4 to 0.6 μm is formed.
[0029]
Next, as shown in FIG. 1E, the silicon oxide film, the silicon nitride film 101, and the silicon oxide film 102 on the surface of the silicon nitride film 101 formed by the oxidation process are removed. Through the above steps, oxide films 109 having different thicknesses (having two kinds of thicknesses) are formed on the semiconductor substrate 103.
[0030]
In this embodiment, thermal oxide films having different thicknesses can be formed by performing the photolithography process, the etching process, and the oxidation process only once. Therefore, two or more thermal oxide films having different film thicknesses can be formed without going through many complicated steps, and the cost can be reduced.
[0031]
Further, since the positions of the thick oxide film 109a and the thin oxide film 109b are determined in one photolithography process, no alignment shift occurs unlike in the case of using two photolithography processes. For this reason, when the oxide film formed according to the present embodiment is used for element isolation or the like, the element can be miniaturized.
[0032]
Furthermore, since the oxide films 109a and 109b having different thicknesses are thermal oxide films, the selectivity at the time of etching in the subsequent process is good.
[0033]
Furthermore, since the oxide films 109a and 109b having different thicknesses are thermal oxide films, they are highly reliable, unlike the films formed by the CVD method, and are optimal for element isolation. It becomes possible to form.
[0034]
In this embodiment, the grooves 107 and 108 having two types of depth are formed by etching, but three or more types of oxide films having different thicknesses are formed by forming grooves having three or more types of depth. be able to. If three types of photoresists are patterned at the same time, three types of films having different thicknesses can be formed in a desired region without deviation.
[0035]
In addition, although the oxide films 109a and 109b having different thicknesses are thermal oxide films, since the regions on both sides of the grooves 107 and 108 are formed by oxidation, an increase in volume due to oxidation can be released into the grooves 107 and 108. it can. Therefore, the stress acting on the oxide films 109a and 109b can be reduced.
[0036]
Furthermore, as will be described in detail later, in the present embodiment, since the oxidation is performed under a temperature condition of 1200 ° C., the silicon edge portion can be rounded. As a result, when an electric current is passed through the semiconductor substrate 103, electrolytic concentration in the silicon edge portion can be suppressed.
[0037]
Furthermore, in this embodiment, two types of line width patterns are formed in the photolithography process, but three or more types of thicknesses are formed by forming a pattern having three or more types of line widths, etching, and oxidizing. An oxide film can be formed. Further, the thickness of each oxide film can be controlled by changing the etching and oxidation conditions.
[0038]
Furthermore, in this embodiment, the oxide films 109a and 109b having different thicknesses are adjacent to each other and have a continuous two-stage structure. However, the masks are provided so that the regions 105 and 106 are arranged at positions separated from each other. Is designed, an oxide film having a thickness can be formed in each of a plurality of separated regions. In this case, the oxide film has a discontinuous structure.
[0039]
In this embodiment, the width of the thicker oxide film 109a is narrower than the width of the thinner oxide film 109b. However, the width of the thicker oxide film 109a is made wider than that of the thinner oxide film 109b by adding a pattern corresponding to the region 106 on the mask and optimizing the etching and oxidation conditions. You can also.
[0040]
In the present invention, the etching of the silicon nitride film 101 and the silicon oxide film 102 located in the regions 106 and 105 and the etching of the semiconductor substrate 103 are separate processes. However, these etchings may be performed as one step.
[0041]
Next, the photolithography process in this embodiment will be described. In this photolithography process, it is necessary to simultaneously process two or more types of line widths, and one of the line widths is preferably as fine as possible. However, it is not easy to form a pattern including a line width less than half of the exposure wavelength used in the photolithography process. In this embodiment, since lithography is performed using a KrF excimer laser stepper, processing of 0.12 μm or less is difficult. Therefore, in order to process the finer line width, a shifter that reverses the phase of light by 180 ° is arranged on the exposure mask. This shifter is a shifter that does not contain chrome and draws out contrast at the edge of the shifter. On the other hand, only chrome is arranged in the mask region in order to process the non-fine line width. A KrF excimer laser stepper was used, and the exposure conditions were N.P. When A = 0.65 and σ = 0.3, a resist pattern having two widths of about 0.18 to 0.22 μm and about 0.11 to 0.13 μm can be formed. A pattern having a region 104 as shown in b) is formed.
[0042]
As described above, according to the photolithography process of this embodiment, it is possible to form two types of silicon nitride films 101 having different widths in a fine region.
[0043]
In the present embodiment, a phase shift mask in which only the shifter exists in the shifter using portion is used as the exposure mask. However, a phase shift mask such as a Levenson type, a halftone type, and an edge enhancement type may be used as an exposure mask, and these may be used in combination.
[0044]
In addition, as another reso- rphy method for forming a continuous fine pattern as in this embodiment, it is preferable to use annular illumination. By using this annular illumination, the resolution for a continuous pattern is improved in order to suppress diffraction of light through the mask. The ratio of the light shielding part of the annular illumination is greatly effective from 1/2 or more. Of these, about 2/3 is preferable.
[0045]
The exposure machine is not limited to the KrF excimer laser stepper, and may be any apparatus that can process a pattern having a desired line width.
[0046]
Next, the etching process in this embodiment will be described. In this etching process, it is necessary to perform two or more kinds of depth etching by one etching. In this embodiment, the RIE etching method is used. In detail, in order to cause a deposition effect in the etched portion, about 5 to 15% N in HBr ₂ Etching gas to which is added is used. N ₂ O instead of ₂ You may add about 5 to 15%. The pressure in the etching chamber is 15 to 40 mTorr. By using an etching gas having such a component, in the region 105 where the opening width is narrow, the etching is stopped due to the influence of deposition or the etching rate is lowered when the etching proceeds to some extent. On the other hand, in the region 106 with the wide opening width, the etching further proceeds even if the etching in the region 105 with the small opening width is stopped. As a result, as shown in FIG. 1C, the etching depth can be varied for each of the regions 105 and 106.
[0047]
As described above, in this embodiment, since the grooves 108 and 107 having two or more depths can be formed by one etching process, the process can be reduced and the cost can be reduced.
[0048]
In this embodiment, there are two types of opening widths in the regions 105 and 106 where the semiconductor substrate 103 is exposed. However, if an exposed region having three or more types of opening widths is provided, the etching depth is set to three or more types. Can be divided. In this case, three or more types of oxide films can be formed in the next oxidation step.
[0049]
Further, as a method of changing the etching depth corresponding to the opening width of the exposed region, a micro-rotating effect that occurs during RIE etching can be used. Also in this case, the pattern having a small etching area has a low etching rate, so that the etching depth can be varied as shown in FIG. Also, the etching depth can be divided by using the inverse micro-rotating effect. However, in this case, the etching rate for a pattern with a small etching area becomes high, so the design of the exposure mask needs to be changed.
[0050]
Further, in the etching process of this embodiment, grooves having different depths are formed by one etching as described above. However, in the state before etching the semiconductor substrate 103 shown in FIG. 1B, the photolithography process is performed again so that one of the exposed regions of the semiconductor substrate is covered with a resist pattern and not covered with the resist pattern. Etching is performed in two steps, such as removing the resist after etching the exposed areas, then covering the exposed areas (grooves) that have already been etched with the resist, and etching the unexposed areas. Thus, grooves having different depths can be formed. In this case, it is not necessary to change the opening width of the exposed region of the semiconductor substrate 103 in accordance with the etching depth.
[0051]
Although the etching is divided into two times, the photolithography process can be performed only once. First, in the state of FIG. 1B before the silicon substrate is etched, the photolithography process is performed again, so that one of the exposed regions is covered with a resist pattern, and the exposed region not covered with the resist pattern is etched. The resist is stripped later. The process up to this point is the same as the above method. Next, etching is performed using the patterned oxidation resistant film as a mask. In this case, since etching is performed twice in one exposed region and etching is performed only once in the other exposed region, a groove having two depths can be formed. Also in this case, it is not necessary to change the opening width of the exposed region of the semiconductor substrate 103 in accordance with the etching depth.
[0052]
Next, the oxidation process will be described. This oxidation step is the most important step in the present invention. The purpose of the oxidation step is listed below.
[0053]
・ Equally oxidize both side wall, corner and edge while relaxing stress generated during oxidation.
[0054]
-All the silicon located between adjacent grooves is oxidized by simultaneously oxidizing the semiconductor substrate on both sides of each adjacent groove.
[0055]
Complete filling of the individual grooves with silicon that has been increased in volume by oxidation.
[0056]
In the oxidation process of this embodiment, oxidation was performed for 1 hour in a high-temperature dry oxygen atmosphere at 1200 ° C. Oxidation treatment under such conditions oxidizes silicon between the grooves 107 and 108 while achieving the above object, and shapes of the grooves 107 and 108 before oxidation (the original shape before oxidation shown in FIG. 1C) As shown in FIG. 1D, two types of oxide films 109a and 109b having different thicknesses can be formed simultaneously.
[0057]
As described above, the oxidation temperature in the oxidation step of the present embodiment is 1200 ° C., but the oxidation temperature may be 800 ° C. or higher and 1400 ° C. or lower. From the viewpoint of uniform oxidation while relaxing the stress, the oxidation temperature is preferably as high as possible, specifically 1100 ° C. or higher and 1400 ° C. or lower.
[0058]
Since the oxidation rate is also an important point for determining the shape after oxidation, it may be important to adjust the oxidation rate by diluting oxygen with argon gas or the like.
[0059]
As a method of activating stress relaxation, NF that acts as a catalyst for oxidation action ₃ It is preferable to add about 50 ppm to the oxygen atmosphere. As another method of stress relaxation, 0.5% or more and 20% H ₂ O may be added to oxygen. But H ₂ If the amount of O added is large, the oxidation rate becomes high, stress relaxation is not sufficiently performed, and an oxide film having a desired shape may not be formed.
[0060]
As described above, the oxidation step can be performed by various methods. However, since they are affected by the shape of the grooves formed by the photolithography process and the etching process, the damage given to the semiconductor substrate by the etching, etc., optimization including all the processes is very important.
[0061]
In this embodiment, a silicon nitride film is used as an oxidation resistant film, but the present invention can be implemented as long as it has oxidation resistance.
[0062]
By using the oxide film formed by the method of this embodiment as element isolation, oxide films having different thicknesses are formed in desired regions without positional deviation, so it is necessary to consider the alignment margin in design. Disappear. For this reason, element isolation can be formed in a fine region. Further, by using the present invention, it is possible to manufacture oxide films having different thicknesses without adding photolithography, etching, and oxidation processes, so that the manufacturing processes are reduced and the cost can be reduced.
[0063]
If the semiconductor device is manufactured by using the oxide film formed as a fine device isolation by the method of this embodiment, the semiconductor device can be miniaturized.
[0064]
Further, by using a miniaturized semiconductor element manufactured by such a method, an integrated circuit with a high degree of integration can be manufactured.
[0065]
Furthermore, if the element isolation formed by the method of the present embodiment is used as the element isolation of the solar cell, the manufacturing process is reduced and the cost can be reduced.
[0066]
(Second Embodiment)
Next, a second embodiment of the present invention will be described.
[0067]
Due to the shape of the groove after etching and some process restrictions, a portion of the groove may not be filled with an oxide film even if the oxidation step (see FIG. 1D) is executed. The second embodiment provides a method for completely filling all trenches with an oxide film in such a case.
[0068]
The processes up to the photolithography process, the etching process, and the oxidation process are the same as those in the first embodiment. That is, after forming the silicon oxide film 202 and the silicon nitride film 201 on the semiconductor substrate 210 (see FIG. 1A), an exposed region of the semiconductor substrate 210 corresponding to the trench is formed by a photolithography process (FIG. 1 ( b)). Subsequently, grooves having different depths are formed by an etching process (see FIG. 1C). Further, the semiconductor substrate 210 is oxidized by an oxidation process.
[0069]
FIG. 2A shows the semiconductor substrate 210 at the end of the oxidation process. In the portion corresponding to the thin oxide film 209b, the inside of the groove is completely filled with the oxide film. However, in the portion corresponding to the thick oxide film 209a, a space or recess 203 that is not filled with the oxide film remains. In this embodiment, the depth of the recess 203 is 0.1 μm.
[0070]
Next, 0.2 μm of silicon oxide film 204 is deposited in the recess 203, and the recess 203 is filled with the silicon oxide film 204. Since the width of the recess 203 is 0.1 μm, the silicon oxide film 204 protrudes from the surface of the semiconductor substrate 210.
[0071]
The silicon oxide film 204 is etched back to the vicinity of the surface of the semiconductor substrate 210 by RIE etching which is anisotropic etching as shown in FIG.
[0072]
Next, as shown in FIG. 2C, the silicon oxide film, the silicon nitride film 201, and the oxide film 202 on the surface of the silicon nitride film 101 formed by the oxidation process are removed.
[0073]
Through the above steps, oxide films 209a and 209b having different thicknesses are formed as in the first embodiment.
[0074]
In this embodiment, the silicon oxide film 204 is volumed and etched back, but a polysilicon film may be deposited and oxidized after the etch back.
[0075]
For etch back, other than the RIE etching method, for example, a chemical mechanical polishing method (CMP) may be used. In this embodiment, a silicon nitride film is used as an oxidation resistant film, but the present invention can be implemented as long as it has oxidation resistance. The etching method for dividing the depth of the groove may be a method for dividing two or more different depths. However, the shape after etching and the damage to the silicon substrate are greatly affected during oxidation in the post-process, so optimization including all of them is necessary. For photolithography, it is preferable to use a phase shift mask or annular illumination, but the method is not limited to this method, as long as patterning with a desired dimension is possible. Other points of the second embodiment are the same as those of the first embodiment.
[0076]
(Third embodiment)
Next, a third embodiment of the present invention will be described with reference to FIGS. In the third embodiment, the present invention is applied to an image sensor manufacturing method.
[0077]
Using the method of the first embodiment, an element isolation region 401 surrounding the pinned photodiode region is formed. That is, after the silicon oxide film 412 and the silicon nitride film 411 are formed on the semiconductor substrate 404, an exposed region of the semiconductor substrate 404 corresponding to the groove is formed by a photolithography process. Subsequently, as shown in FIG. 3, grooves 437 and 438 having different depths are formed by an etching process. Further, the semiconductor substrate 404 is oxidized by an oxidation process, the region between the trenches 437 and 438 is oxidized, and the trenches 437 and 438 are filled with silicon whose volume is increased by oxidation, and an element isolation region (hereinafter referred to as a trench) 401 made of an oxide film. Form. The trench 401 has two types of depth, and the deeper trench 401b is deeper than an N-type impurity layer 403, which will be described later, and has a shape surrounding it. On the other hand, the shallower trench 401a is formed at the same depth as the trench formed in the CMOS transistor. Further, the depth of the deeper trench 401b is determined in consideration of the depth of the N-type impurity layer 403 of the pinned photodiode. To cut off the leakage current, the depth of the N-type impurity layer 403 is as much as possible. It is preferable that the depth is deeper.
[0078]
Next, as shown in FIG. 5, high-concentration low-energy P-type ion implantation is performed to form a P-type impurity layer 402 at the lower surface of the substrate. Further, low-concentration high-energy N-type ion implantation is performed to form an N-type impurity layer 403 inside the substrate. Thereafter, a pinned photodiode composed of P-type silicon substrate / N-type impurity layer / P-type impurity layer is formed by impurity diffusion by a thermal process.
[0079]
In the image sensor manufactured by the method of the present embodiment, since the trench 401 formed in the semiconductor substrate 404 exists in the boundary region of the pinned photodiode, the leakage current between adjacent pinned photodiodes is suppressed or prevented. The Rukoto. Further, since the STI process is not used for manufacturing the trench 401, the cost can be reduced.
[0080]
As shown in FIG. 5 above, in the third embodiment, deep trenches 401b are provided on both sides of the shallow trench 401a. However, by improving the shape of the trench 501 as shown in FIG. 6 and providing the deep trench 501b at the center of the shallow trench 501a, the ratio of the element isolation region can be reduced, so that the cells can be further miniaturized. Furthermore, the cost can be reduced. In FIG. 6, reference numeral 502 denotes a P-type impurity layer, 503 denotes an N-type impurity layer, and 504 denotes a P-type semiconductor substrate.
[0081]
Further, as shown in FIG. 7, only the deep trench 601 may be formed in the photodiode region without forming a shallow trench. In this case, only a shallow trench is formed in the COMS transistor formation region. With this configuration, in the photodiode formation region, the ratio of the element isolation formation region is further reduced to further miniaturize the cell, thereby reducing the cost. In FIG. 7, reference numeral 602 denotes a P-type impurity layer, 603 denotes an N-type impurity layer, and 604 denotes a P-type semiconductor substrate.
[0082]
A high-performance and inexpensive electronic camera is manufactured by mounting the photodiode manufactured by the manufacturing method of the third embodiment, which can suppress the leakage current and reduce the cost, as part of the electronic camera component. It becomes possible to do.
[0083]
Furthermore, by mounting the inexpensive electronic camera on an information terminal device such as a mobile phone or a notebook computer, an information terminal device such as an inexpensive mobile phone or a notebook computer can be manufactured.
[0084]
【The invention's effect】
As is apparent from the above description, according to the semiconductor manufacturing method of the present invention, a plurality of grooves having at least two types of depths are formed in a silicon substrate, and a region between these grooves becomes an oxide film, Further, by oxidizing the silicon substrate until the inside of the groove is filled with an oxide film, or filling the recess remaining in the groove after oxidation with oxide film deposition and etching back, photolithography, oxidation process, etc. Without adding a process, oxide films having different thicknesses can be formed on the silicon substrate. Therefore, the cost can be reduced by reducing the number of manufacturing processes.
[Brief description of the drawings]
1A and 1B are schematic views showing a manufacturing process by a method for manufacturing a semiconductor device according to a first embodiment of the present invention, wherein FIG. 1A shows a substrate structure after formation of an oxidation resistant film and a silicon oxide film, and FIG. (C) shows the substrate structure after forming a groove in the silicon substrate, (d) shows the substrate structure after the oxidation step, (e) ) Shows the substrate structure after removing the oxidation resistant film and the oxide film.
FIGS. 2A and 2B are schematic views showing a manufacturing process by a method for manufacturing a semiconductor device according to a second embodiment of the present invention, wherein FIG. 2A shows a substrate structure after an oxidation process, and FIG. The substrate structure after etching back is shown, and (c) shows the substrate structure after removing the oxidation resistant film and the oxide film.
FIG. 3 is a schematic diagram showing a substrate structure after an oxidation step in a photodiode manufacturing method according to a third embodiment of the present invention.
FIG. 4 is a schematic diagram showing a substrate structure after removing an oxidation-resistant film and an oxide film in a photodiode manufacturing method according to a third embodiment of the present invention.
FIG. 5 is a schematic view showing a substrate structure after formation of a P-type impurity layer and an N-type impurity layer in a photodiode manufacturing method according to a third embodiment of the present invention.
FIG. 6 is a schematic diagram showing another example of element isolation of a photodiode.
FIG. 7 is a schematic diagram showing another example of element isolation of a photodiode.
FIGS. 8A to 8H are schematic views showing manufacturing steps according to a conventional method for manufacturing a semiconductor device. FIGS.
FIG. 9 is a schematic view showing element isolation of a conventional photodiode.
[Explanation of symbols]
101 Silicon nitride film
102 Silicon oxide film
103 Silicon substrate
104 Remaining silicon nitride film and silicon oxide film
105 Small exposed part of silicon substrate
106 Large exposed portion of silicon substrate
107 Shallow groove
108 Deep Groove
109 Thermal oxide films with different thickness
201 Silicon nitride film
202 Silicon oxide film
203 Groove that could not be filled
204 Embedded oxide film
301 Silicon oxide film
302 P-type impurity layer
303 N-type impurity layer
304 P-type silicon substrate
3a Resist mask opening during implantation
3b resist mask opening during implantation
401 Silicon oxide film
402 P-type impurity layer
403 N-type impurity layer
404 P-type silicon substrate
501 Silicon oxide film
502 P-type impurity layer
503 N-type impurity layer
504 P-type silicon substrate
601 Silicon oxide film
602 P-type impurity layer
603 N-type impurity layer
604 P-type silicon substrate

Claims (11)

In a method for manufacturing a semiconductor device in which oxide films having different thicknesses are formed on a silicon substrate,
Forming a plurality of grooves having at least two depths in the silicon substrate;
The silicon substrate is oxidized until the region between the grooves of the silicon substrate becomes an oxide film and the inside of the groove is filled with the oxide film, and the thickness differs according to the depth of the at least two kinds of grooves. A method for manufacturing a semiconductor device, comprising: obtaining an oxide film. 2. The step of forming the plurality of grooves includes forming a groove having a depth corresponding to the thickness of the oxide film in the region of the silicon substrate where the oxide film is to be formed. The manufacturing method of the semiconductor device as described in any one of. In a method for manufacturing a semiconductor device in which oxide films having different thicknesses are formed on a silicon substrate,
Forming a plurality of grooves having at least two depths in the silicon substrate;
Oxidizing the silicon substrate until a region between the grooves of the silicon substrate becomes an oxide film;
Depositing an oxide film inside the plurality of grooves;
And a step of etching back the oxide film inside the groove. The step of forming the plurality of grooves forms a groove having a depth corresponding to the thickness of the oxide film in the region of the silicon substrate in which the oxide film is formed. The manufacturing method of the semiconductor device as described in any one of. The step of forming the plurality of grooves includes a step of patterning a resist, and a step of etching the oxidation resistant film formed on the silicon substrate and the silicon substrate using the resist as a mask,
5. The method of manufacturing a semiconductor device according to claim 1, wherein the step of patterning the resist includes a step of exposing using a phase shift mask. 6. In the step of etching the oxidation resistant film and the silicon substrate, an etching gas containing 5% or more and 15% or less of N ₂ is used, and a groove corresponding to the thickness of the oxide film is formed by one etching. 5. The method of manufacturing a semiconductor device according to claim 1, wherein the method is a semiconductor device manufacturing method. The method for manufacturing a semiconductor device according to claim 1, wherein the step of oxidizing the silicon substrate is performed under a temperature condition of 1100 ° C. or higher and 1400 ° C. or lower. The method of manufacturing a semiconductor device according to claim 1, wherein the oxide film is used as an element isolation film. 9. The method of manufacturing a semiconductor device according to claim 8, wherein a semiconductor element is manufactured using the element isolation film. The method for manufacturing a semiconductor device according to claim 9, wherein an integrated circuit is manufactured using the semiconductor element. The method of manufacturing a semiconductor device according to claim 8, wherein a photodiode is manufactured using the element isolation film.

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