JP2015099840A - Method of manufacturing solid-state imaging element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a solid-state imaging element in which unevenness is prevented from occurring in an output image by flattening step portions having a plurality of different depths.SOLUTION: A substrate 1 includes a plurality of step portions 12 having different depths around a photoelectric conversion element array to be mounted, and a coated film 13 of a photosensitive resin composition is formed on the substrate 1. In a portion through which an exposure light 10 irradiated to the plurality of step portions 12 transmits, a photomask 9 has an exposure amount adjustment region 11 whose operation ratio is adjusted in accordance with the depth of the plurality of step portions 12 and in which a patterned coated film 13a corresponding to the adjusted operation ratio can be formed. Following a development step, the upper surfaces of the plurality of step portions 12 having a plurality of different depths are leveled.

Description

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

Conventionally, as a method for manufacturing a solid-state imaging device, first, a photoelectric conversion element is provided for each solid-state imaging device on a substrate having a size capable of forming a predetermined number of solid-state imaging devices, and bonding pads and scribe lines are provided around the photoelectric conversion device. A method is known in which an undercoat layer, a color filter array, an overcoat layer, and a microlens array are formed on the substrate.
However, this method includes a step of sequentially applying each of the materials for forming the undercoat layer, the color filter array, the overcoat layer, and the microlens array to the entire surface of the wafer by a spin coat method or the like. There is a possibility that unevenness of the coating film (hereinafter, also referred to as coating unevenness) may occur due to a stepped portion such as a pad and a scribe line. Such coating unevenness causes image unevenness when captured.

As a countermeasure against this coating unevenness, a method of selectively filling recesses such as scribe lines with a photosensitive polymer material has been proposed in the past, and is one effective means for improving coating unevenness (Patent Document 1). . In order to further reduce the level difference, it has also been proposed to fill a polymer material in a recess in a scribe line and a recess in a field region and heat and melt the resin (Patent Document 2). Further, a method has been proposed in which a scribe line is at least partially filled with a resist material, or the entire substrate other than the bonding pad and its vicinity is covered (Patent Document 3).

Japanese Patent No. 2786647 Japanese Patent No. 2892865 US Pat. No. 6,956,253

However, although the means for selectively filling the concave portion of the substrate using the photosensitive polymer material described in Patent Document 1 is an effective means, there are various stepped portions having different depths on the substrate. Therefore, there is a problem that it is difficult to effectively fill all the stepped portions in every photolithography process.
Further, in the method described in Patent Document 2, if there is a large difference in depth between the scribe line recesses and the field region recesses, it is difficult to flatten both, leaving room for improvement. .
Further, the method described in Patent Document 3 can flatten a step of a scribe line having a certain depth, but has a problem that a step of a portion having a different depth such as a bonding pad still remains.
An object of the present invention is to provide a method of manufacturing a high-quality, high-yield solid-state imaging device at a low cost by making it possible to flatten a plurality of step portions having different depths by a single patterning process. There is to do.

In the method for manufacturing a solid-state imaging device, the present inventors apply a photosensitive resin composition on a substrate having a plurality of step portions having different depths around the photoelectric conversion element array, and the depth of the step portion. The step of exposing the photosensitive resin composition through a photomask with the aperture ratio adjusted accordingly, the step of developing the exposed photosensitive resin composition to remove unnecessary portions, and the substrate after development are heated to sensitize It has been found that a plurality of step portions having different depths can be planarized at a time by having the step of melting the conductive resin composition, and the present invention has been completed.
That is, the present invention includes a step of applying a photosensitive resin composition on a substrate on which a photoelectric conversion element array is mounted to form a coating film of the photosensitive resin composition, and applying the photosensitive resin composition via a photomask. In a method for manufacturing a solid-state imaging device, including a step of exposing a film, and a step of developing the coating film after exposure to remove unnecessary portions,
The substrate has a plurality of step portions having different depths around a photoelectric conversion element array to be mounted;
In the photomask, the aperture ratio is adjusted in accordance with the depth of the plurality of step portions at a portion through which the exposure light irradiated to the plurality of step portions is transmitted, and a patterned coating film corresponding to this is formed. In the manufacturing method, after the development step, the coating film remaining on the substrate is heat-cured, and at that time, with respect to a plurality of step portions having different depths, The present invention further relates to a method for manufacturing a solid-state imaging device, further comprising a step of leveling an upper surface of the patterned coating film by melting.
Further, as a preferred aspect of the present invention, the exposure amount adjustment region is arranged so that the light transmitting portion and the light shielding portion are adjacent to each other, and has a checkered pattern, a striped pattern, or a repetitive pattern of a lattice pattern. The present invention relates to a method for manufacturing the solid-state imaging device.
More specifically, the present invention relates to the method for manufacturing the solid-state imaging device, wherein the plurality of stepped portions are stepped portions in a scribe line and stepped portions in a bonding pad.
Further, the present invention provides a photomask used for exposure of a coating film of a photosensitive resin composition on a substrate in the production of a solid-state imaging device, and a plurality of different depths around the photoelectric conversion element array on which the substrate is mounted. A photomask having an exposure adjustment region in which the aperture ratio is adjusted for a portion through which exposure light irradiated to the stepped portion is transmitted, and in particular,
The said exposure amount adjustment area | region is related with the said photomask which is arrange | positioned so that a translucent part and a light-shielding part may mutually adjoin, and has a repetitive pattern of a checkered pattern, a striped pattern, or a lattice pattern.

In the method for manufacturing a solid-state imaging device of the present invention, since a plurality of step portions having different depths are effectively flattened, for example, a thermosetting resin solution for forming an undercoat layer, a resist solution for forming a color filter, and When a positive resist for forming a microlens shape is applied, coating unevenness does not occur, and it is possible to manufacture a high-quality image pickup device with no unevenness in the output image with a high yield.
In addition, it is possible to effectively flatten a plurality of stepped portions in a single patterning process, and it is possible to manufacture a high-quality image sensor with no unevenness in captured images at a low cost and with a high yield.

FIG. 1 is a diagram illustrating a substrate on which a solid-state imaging device is mounted. FIG. 2 is an enlarged view showing the solid-state imaging device mounted on the substrate and the periphery thereof. FIG. 3 is a diagram for explaining a flattening method aiming at elimination of the level difference of the scribe line, FIG. 3 (a) is a diagram showing a state at the time of exposure, and FIG. 3 (b) is a diagram after development processing. It is a figure which shows a state. 4A and 4B are diagrams for explaining a planarization method aiming at elimination of the level difference of the bonding pad, FIG. 4A is a diagram showing a state at the time of exposure, and FIG. 4B is a diagram after development processing. It is a figure which shows a state. FIG. 5A is a schematic diagram (left diagram) showing an exposure adjustment region when the aperture ratio is 50%, and a schematic diagram (right diagram) showing an enlarged repeating unit of the light transmitting part and the light shielding part. 5B is a schematic diagram (left diagram) showing an exposure adjustment region when the aperture ratio is 28%, and a schematic diagram (right diagram) showing an enlarged repeating unit of the light transmitting portion and the light shielding portion. FIG. 5C is a schematic diagram (left diagram) showing an exposure adjustment region when the aperture ratio is 72%, and a schematic diagram showing an enlarged repeating unit of the light transmitting part and the light shielding part. Yes (right figure). FIG. 6 is an enlarged view for explaining the method according to the present invention for the stepped portion of the substrate and the vicinity thereof, and FIG. 6A is a diagram showing a state when the positive photosensitive resin composition is exposed. 6 (b) is a diagram showing a state after the development processing, and FIG. 6 (c) is a diagram showing a state after the heat treatment. FIG. 7 is an enlarged view for explaining the method according to the present invention for the stepped portion of the substrate and its vicinity, in which the exposure amount is reduced as compared with the case of FIG. 6, and FIG. 7 (a) is a positive photosensitive resin. It is a figure which shows the state at the time of exposing a composition, FIG.7 (b) is a figure which shows the state after image development processing, FIG.7 (c) is a figure which shows the state after heat processing. FIG. 8 is a diagram showing results when patterning and heat treatment of a positive photosensitive resin composition are performed using various photomasks having different aperture ratios.

Solid-state image sensors represented by CCD and CMOS are widely used as image input devices in video cameras, surveillance cameras, digital still cameras, mobile phones, smartphones, etc., and are photoelectric conversion elements formed two-dimensionally on a substrate. The light incident by the array is converted into an electrical signal, and the generated electrical signal is output.
FIG. 1 schematically shows a substrate 1 on which a solid-state imaging element is formed. A large number of solid-state imaging elements are separated on a substrate by scribe lines 3.
FIG. 2 is an enlarged view of a portion of the solid-state imaging device 2 formed on the substrate 1, and a plurality of bonding pads 5 are formed surrounding the photoelectric conversion element array portion 4. Line 3 surrounds.
By the way, in order to colorize the solid-state imaging element, a color filter is formed on the photoelectric conversion element 2 via an undercoat layer, and further, on the upper part of the color filter array, in order to improve the condensing rate of incident light. A microlens is formed through the overcoat layer.
If the undercoat layer, the color filter array, the overcoat layer, and the microlens array are not formed uniformly in the photoelectric conversion region, the output image may be uneven.
There are many types of unevenness such as a forehead shape, a shading shape, and a streak shape, which cause a reduction in the quality and yield of the element.
These unevennesses are caused by the thermosetting resin solution for forming the undercoat layer, the dye-containing resist (so-called color resist) for forming the color filter, the thermosetting resin solution for forming the overcoat layer, or the transparent photosensitivity. This often occurs when either the resin solution or the positive resist for forming the microlens shape is not uniformly applied.
In other words, since these resin solutions and resist solutions are formed by spin coating, they rarely occur if the substrate before application of each resin solution or resist solution is completely flat. Since there are step portions due to various structures such as the scribe line 3, the bonding pad 5, the field oxide film, and the metal wiring, it causes non-uniformity (coating unevenness) in the coating film.
Conventionally, in order to prevent the occurrence of such coating unevenness, a method of filling the stepped portion with the photosensitive polymer material as described above has been proposed, but the substrate has a plurality of stepped portions having different depths. In this case, it was difficult to flatten all the steps.
For example, in FIG. 3, a step (A part) 8 of a bonding pad having a width of 40 μm and a depth of 1.5 μm surrounding the photoelectric conversion element array 4 and a step of a scribe line having a width of 80 μm and a depth of 3.5 μm (B part) FIG. 3A is a diagram for explaining a planarization method aiming at elimination of the scribe line step (B portion) 7 in a wafer (substrate 1) having a scribe line 7. FIG. 3A shows a scribe line step (B portion). 3) shows a state when the negative photosensitive resin composition coating film 6 coated on the wafer (substrate 1) so as to be filled with 7 is exposed with exposure light 10 using a photomask 9, and FIG. ) Shows the state after the development.
As shown in FIG. 3 (b), in this case, the coating film 6a of the negative photosensitive resin composition after development does not fit in the step (A portion) 8 of the bonding pad which is a smaller step portion, On the contrary, there is a problem that the step (A portion) 8 of the bonding pad becomes convex.
On the other hand, FIG. 4 shows a diagram for explaining a planarization method aiming at elimination of the step (A part) 8 of the bonding pad in the same substrate as that shown in FIG. 3, and FIG. When the negative photosensitive resin composition coating film 6 applied on the wafer (substrate 1) so that the step (A part) 8 of the bonding pad is filled is exposed with the exposure light 10 using the photomask 9. The state is shown, and FIG. 4B shows the state after the development. On the contrary, when the film thickness of the coating film 6 of the negative photosensitive resin composition is adjusted so that the step (A part) 8 of the bonding pad does not become convex as shown in FIG. There exists a problem that the level | step difference (B part) 7 of a scribe line is not fully embedded with the coating film 6a of a type photosensitive resin composition.
These problems can be avoided by patterning the bonding pad step (A portion) 8 and the scribe line step (B portion) 7 separately using different photomasks. In this case, there is a problem that the manufacturing process becomes long and the manufacturing cost increases.
On the other hand, the present invention is a substrate having a plurality of step portions having different depths by collectively filling a plurality of step portions having different depths with a photosensitive resin composition in an amount capable of flattening. It is possible to flatten at once.
Although not shown in FIGS. 3 and 4, for example, in the solid-state imaging device 2, a peripheral circuit region for processing a signal output from the photoelectric conversion element is provided around the photoelectric conversion element array 4. A multilayer wiring layer having a plurality of wirings is formed on the upper or lower portion of the wirings via an interlayer insulating film or the like.
Further, the bonding pad 5 for electrical connection with the outside is usually disposed at the bottom of the step 8 (A portion) of the bonding pad.

In the present invention, the coating film of the photosensitive resin composition applied on the substrate having a plurality of step portions having different depths is selected according to the depth of the step portion at the portion through which the exposure light irradiated to the step portion is transmitted. Then, exposure is performed through a photomask having an exposure amount adjustment area in which the aperture ratio is adjusted.
Here, the aperture ratio means the ratio of the area of the light-transmitting part to the total area of the light-transmitting part and the light-shielding part in a specific exposure region of the photomask, and is defined by Equation 1.
Aperture ratio (%) = (area of light transmitting part / area of light transmitting part + area of light shielding part) × 100 Equation 1
Usually, a photomask (also referred to as a reticle when the exposure apparatus is a stepper) is a known method, for example, a light shielding film made of chromium or the like (hereinafter also referred to as a chromium film) is formed on a quartz substrate, and a photolithography process. And a portion of the chromium film to be transmitted is removed by an etching process.
In this step, since the chromium film in the region to be exposed is completely removed by etching, the aperture ratio of the portion to be exposed is usually 100% according to the above definition.
On the other hand, the photomask used in the present invention is manufactured so that the aperture ratio becomes a value between 0% and 100% in the exposure amount adjustment region which is at least a part of the region to be exposed.
In order to set the aperture ratio to a value between 0% and 100%, a certain area of the chromium film in the region to be exposed may be left on the photomask without being etched away.
For example, a light-transmitting part and a light-shielding part are arranged adjacent to each other in a specific exposure area, thereby forming a checkered repetitive pattern, and changing the areas of the light-transmitting part and the light-shielding part in the repetitive pattern. It becomes possible to control the aperture ratio.
As an example, FIG. 5 shows a schematic diagram showing the exposure adjustment region 11 and a schematic diagram showing an enlarged repeating unit of the light transmitting part 11a and the light shielding part 11b. FIG. 5A is a schematic diagram (left diagram) showing the exposure adjustment region 11 when the aperture ratio is 50%, and a schematic diagram (right diagram) showing an enlarged repeating unit of the light transmitting portion 11a and the light shielding portion 11b. FIG. 5B is a schematic diagram (left diagram) showing the exposure adjustment region 11 when the aperture ratio is 28%, and an enlarged repeating unit of the light transmitting portion 11a and the light shielding portion 11b. FIG. 5C is a schematic diagram (left diagram) showing an exposure amount adjustment area 11 when the aperture ratio is 72%, and repetition of the light transmitting portion 11a and the light shielding portion 11b. It is a schematic diagram which expands and shows a unit (right figure).

In the present invention, after exposing the coating film of the photosensitive resin composition, unnecessary portions are removed by development, thereby corresponding to the pattern of the light transmitting portion and the light shielding portion formed in the exposure amount adjustment region of the photomask. A patterned coating film of the photosensitive resin composition is formed inside the step.
The pattern of this patterned coating film is heat-sealed by subsequent heating and the upper surface thereof is leveled, and a hot melt of the photosensitive resin composition is formed.
When the hot melt of the photosensitive resin composition fills the stepped portion with an amount that does not exceed the surface of the substrate (the portion without the stepped portion), the stepped portion is flattened.
In order to flatten each level difference part, it is necessary to optimize the amount of the patterned photosensitive resin composition so that the hot melt of the photosensitive resin composition becomes an amount capable of flattening the level difference part. Therefore, it is necessary to adjust the ratio of the light transmitting portion and the light shielding portion in the exposure amount adjustment area of the photomask for each depth of the stepped portion.
In addition, as for the repetitive pattern formed on the photomask, a lattice pattern, a striped pattern, etc. can be conveniently used at the time of designing the photomask in addition to the checkered pattern, but it is not always necessary to be a repetitive pattern.
However, in the case where the pattern of the photosensitive resin composition after development formed inside the stepped portion is isolated from the adjacent pattern, it means that the adjacent patterns are fused in the heating process after development. It is preferable that the distance between adjacent patterns is not too large, and it is preferable to design the pattern of the light transmitting part and the light shielding part of the photomask so that the maximum distance between adjacent patterns is approximately 6 μm or less, preferably 4 μm or less.

The photosensitive resin composition used in the present invention is required to have the following two characteristics, but is not particularly limited as long as it has these characteristics.
1. The pattern of the coating film of the photosensitive resin composition after development is thermally deformed in a subsequent heating step, and is fused with an adjacent pattern, so that the unevenness after development becomes substantially flat.
2. The hot melt of the photosensitive resin composition after the heating step is insoluble in a general organic solvent.
Examples of the resin that can satisfy both of the above requirements 1 and 2 include a positive photosensitive resin composition containing, as essential components, an alkali-soluble resin, a naphthoquinonediazide compound, and a thermosetting agent.

As the alkali-soluble resin, those used in this kind of field can be used. For example, a novolak resin, a vinyl polymer having a phenolic hydroxy group (for example, p-hydroxyphenylethyl methacrylate copolymer, p-hydroxystyrene copolymer), a condensation resin of polyhydric phenol and aldehyde or ketone, a copolymer of N- (p-toluenesulfonyl) methacrylamide and methyl methacrylate, and the like. These resins can also be used in combination.
As the novolak resin, cresol / formaldehyde resin (for example, m-cresol / formaldehyde resin, m-, p-mixed cresol / formaldehyde resin, cresol and condensation resin of m- or p-alkylphenol and formaldehyde), polyhydric phenol and ketone As the condensation resin, a resin obtained by polycondensation of pyrogallol and acetone (hereinafter referred to as pyrogallol-acetone resin) is preferably used. These alkali-soluble resins preferably have a weight average molecular weight of 1500 or more in consideration of applicability.

  The naphthoquinone diazide compound is 1,2-naphthoquinone diazide sulfonic acid ester, and is not particularly limited, but the following sulfonic acid esters of polyphenols are preferably used. 2,3,4-trihydroxybenzophenone-1,2-naphthoquinonediazide-4-sulfonic acid ester, 2,3,4-trihydroxybenzophenone-1,2-naphthoquinonediazide-5-sulfonic acid ester, 4,4′-tetrahydroxybenzophenone-1,2-naphthoquinonediazide-4-sulfonic acid ester, 2,3,4,4′-tetrahydroxybenzophenone-1,2-naphthoquinonediazide-5-sulfonic acid ester, 3, 4,5,2 ′, 4′-pentahydroxybenzophenone-1,2-naphthoquinonediazide-4-sulfonic acid ester, 1,1,3-tris (2,5-dimethyl-4-hydroxyphenyl) -3-phenyl Propane-1,2-naphthoquinonediazide-4-sulfonic acid ester, 1,1,3-tri (2,5-Dimethyl-4-hydroxyphenyl) -3-phenylpropane-1,2-naphthoquinonediazide-5-sulfonic acid ester, 4,4 '-[1- [4- [1- [4-hydroxyphenyl] ] -1-methylethyl] -1-methylethyl] phenyl] ethylidene] bisphenol-1,2-naphthoquinonediazide-4-sulfonic acid ester, 4,4 ′-[1- [4- [1- [4-hydroxy] Phenyl] -1-methylethyl] -1-methylethyl] phenyl] ethylidene] bisphenol-1,2-naphthoquinonediazide-5-sulfonic acid ester, 2,2,4-trimethyl-7,2 ′, 4′-tri Hydroxyflavan-1,2-naphthoquinonediazide-4-sulfonic acid ester, 2,2,4-trimethyl-7,2 ′, 4′-trihydroxy Flavan-1,2-naphthoquinone diazide-5-sulfonic acid ester, 1,1,1-tri (p-hydroxyphenyl) ethane-1,2-naphthoquinone diazide-4-sulfonic acid ester, 1,1,1-tri (P-Hydroxyphenyl) ethane-1,2-naphthoquinonediazide-5-sulfonic acid ester. These 1,2-naphthoquinone diazide sulfonic acid esters can be used alone or in combination of two or more.

The thermosetting agent is not particularly limited, and a conventional thermosetting agent can be used.
Also, in the negative photosensitive resin composition, for example, those having a relatively low molecular weight after exposure / development can satisfy the requirements 1 and 2 by adding a thermosetting agent.

  Furthermore, the photosensitive resin composition used in the present invention may contain other components as necessary as long as the effects of the present invention are not impaired. Other components include, for example, rheology modifiers, pigments, dyes, storage stabilizers, antifoaming agents, adhesion promoters, surfactants or solubilizers such as polyphenols and polycarboxylic acids. Can be mentioned.

There is no restriction | limiting in particular as an organic solvent used for the photosensitive resin composition used by this invention, Various solvents, such as ester, alcohols, ethers, and ketones, can be used individually or in mixture. Can be used. The solvent is appropriately selected depending on the characteristics of various coating apparatuses. Solvents include alcohols such as methanol, ethanol and 2-propanol, ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone, ethers such as diethyl ether, dibutyl ether and dioxane, ethyl acetate, isobutyl acetate, ethylene glycol monoacetate , Esters such as propylene glycol monoacetate and dipropylene glycol monoacetate, ethylene glycol monoalkyl ethers, diethylene glycol monoalkyl ethers, propylene glycol monoalkyl ethers, dipropylene glycol monoalkyl ethers, ethylene glycol dialkyl ethers, Propylene glycol dialkyl ethers, diethylene glycol dimethyl ether, diethylene glycol Diethylene glycol dialkyl ethers of ethyl ethers, dipropylene glycol dialkyl ethers such as dipropylene glycol dimethyl ether and dipropylene glycol diethyl ether, ethylene glycol monoalkyl ether acetates, propylene glycol monoalkyl ether acetates, diethylene glycol monoalkyl ether Examples include acetates and dipropylene glycol monoalkyl ether acetates.

When the photosensitive resin composition is applied to the substrate in the present invention, a conventional apparatus such as a spin coater, natural roll coater, reverse roll coater, gravure roll coater, screen printing machine, curtain coater, air spray, bar coater. A knife coater, a brush, a dip coating machine or the like can be used.
In the present invention, the film thickness of the coating film of the photosensitive resin composition needs to be at least thick enough to fill the stepped portions on the substrate such as scribe lines and electrode pads.

Next, the substrate coated with the photosensitive resin composition is pre-baked using a conventional apparatus such as a hot plate or an oven. The pre-baking conditions are not particularly limited as long as the photosensitive resin composition and the substrate do not deteriorate, and the temperature and time are not particularly limited. The heating temperature and the heating time are adopted.
The obtained substrate is exposed by irradiating active energy rays through the above-described photomask using a high pressure mercury lamp, an ultrahigh pressure mercury lamp, a xenon lamp, a metal halide lamp, or the like.

  Next, development processing is performed by a spray gun, a dipping method, a paddle method, or the like. In the present invention, for example, an alkaline aqueous solution is used for the development processing. Specific examples of the alkaline component of the alkaline aqueous solution include hydroxides of alkali metals such as lithium, sodium and potassium, inorganic bases such as carbonate, bicarbonate and phosphate, pyrophosphate, benzylamine and butylamine. Primary amines such as dimethylamine, dibenzylamine, secondary amines such as diethanolamine, tertiary amines such as trimethylamine, triethylamine, triethanolamine, cyclic amines such as morpholine, piperazine, pyridine, ethylenediamine, hexamethylene Polyamines such as diamine, tetraethylammonium hydroxide, trimethylbenzylammonium hydroxide, trimethylphenylbenzylammonium hydroxide, ammonium hydroxides such as choline, trimethylsulfonium hydroxide, Ethyl methyl sulfonium hydroxide, sulfonium hydroxide such as dimethyl benzyl sulfonium hydroxide, and a mixed solution of buffer and these alkali components. One or a mixture of two or more of these is used, and tetraethylammonium hydroxide (hereinafter also referred to as TMAH) is preferably used.

FIG. 6A shows the exposure amount adjustment in which the positive photosensitive resin composition is applied to the substrate 1 having the stepped portion 12 to form the coating film 13, and then the pattern of the light transmitting portion 11a and the light shielding portion 11b is formed. FIG. 6 (b) shows a state when the exposure light 10 is exposed through the photomask 9 having the area 11, FIG. 6 (b) shows a state after the development processing, and FIG. 6 (c) shows the heating. The figure showing the mode after processing is shown.
As shown in FIG. 6 (b), a positive-type photosensitive resin composition coating film 13a is formed inside the stepped portion 12 of the substrate 1 after development, and is shown in FIG. 6 (c). As described above, the patterned photosensitive resin composition pattern is thermally deformed and fused with the adjacent pattern in the subsequent heating process, and the upper surface is leveled and the positive photosensitive resin composition coating film is melted by heat. An object 13b is formed, and as a result, the stepped portion is flattened.
As heating conditions in this heating step, a heating temperature and a heating time appropriately selected from the range of a temperature of 50 ° C. to 300 ° C. and a time of 0.1 minutes to 60 minutes are employed.

The film thickness of the photosensitive resin composition inside the stepped portion after heat planarization is determined by the volume of the pattern after development and the curing shrinkage rate during heat curing.
Since the curing shrinkage is a value inherent to the photosensitive resin, the film thickness after heating and planarization is substantially controlled by the pattern volume after development.
As a means for controlling the pattern volume, the above-described photomask having an adjusted aperture ratio is used. However, in practice, the adjustment of the exposure amount can be used together for the purpose of tuning the film thickness after planarization.

For example, even when a positive photosensitive resin is used and the photomask aperture ratio is constant, if the exposure amount is increased, the pattern volume after development decreases, and as a result, the film thickness after planarization decreases. .
Similarly, if the exposure amount is decreased, the pattern volume after development increases, and as a result, the film thickness after planarization increases.
FIG. 7A shows a state in which a positive photosensitive resin composition is applied to the substrate 1 having the stepped portion 12 to form the coating film 13 and then exposed to the exposure light 10 with an increased exposure amount. FIG. 7B illustrates a state after the development processing, and FIG. 7C illustrates a state after the heat processing.
In this case, if the exposure amount is further reduced, the patterned positive photosensitive resin composition coating film 13a after development is developed to the stepped portion 12 as shown in FIG. 7B. As a result, the surface shape of the coating film 13a of the patterned positive photosensitive resin composition is only uneven by exposure, but even in this state, as shown in FIG. Since the hot melt 13b of the coating film of the conductive resin composition is formed and the stepped portion is flattened, the method of reducing the exposure dose matches the purpose of the present invention of controlling the pattern volume after development. It can be used as a means to increase the pattern volume after development.
Strictly speaking, the coating film of the stepped portion such as a scribe line does not have a constant film thickness over the entire surface of the stepped portion as shown in FIG. 6 and FIG. There is a tendency for the effective film thickness to increase in the vicinity of the edge of the step. That is, even in the step portion having the same depth, the film thickness of the coating film on the step portion may vary depending on whether the area of the step portion is large or small. Therefore, even if it is a stepped portion having the same depth, the stepped portion finally becomes smaller by finely adjusting the aperture ratio for the portion on the mask through which the exposure light irradiated to each stepped portion is transmitted. Can be flattened.

As described above, according to the method for manufacturing a solid-state imaging device of the present invention, a stepped portion can be flattened even if the substrate has a plurality of stepped portions having different depths.
On the thus flattened substrate, an undercoat layer, a color filter array, an overcoat layer, a microlens array, and the like are sequentially formed by a known method to manufacture a solid-state imaging device.
For example, first, an undercoat layer is formed by applying and heating a thermosetting resin solution for forming an undercoat layer on the flattened surface of the substrate.
Thereafter, the color filter is formed by performing coating, exposure, development, baking, and the like of a dye-containing resist (so-called color resist) for forming a color filter for each of red (R), green (G), and blue (B). After forming the array, a thermosetting resin solution or a transparent photosensitive resin solution for forming an overcoat layer is applied and heated or exposed to form an overcoat layer.
Subsequently, a positive resist for forming a microlens shape is applied, exposed, developed, and reflowed to form a microlens array.
At this time, since the step portions such as the scribe line and the bonding pad are flattened, the formed undercoat layer, color filter array, overcoat layer, and resist film for forming the microlens are formed with uniform thicknesses, respectively. can do.
Therefore, the solid-state imaging device manufactured according to the manufacturing method of the present invention can reduce the occurrence of unevenness in the output image, and can improve the quality and yield of the solid-state imaging device.
In addition, the above-mentioned hot melt existing inside the step can be removed by a conventional method using chemicals, dry etching, or the like at a stage after forming the microlens, if necessary. In particular, at the step of the bonding pad, it is desirable to remove the hot melt from the viewpoint of establishing an electrical connection between the bonding pad and the outside.

  Hereinafter, as an example of step portions having different depths, a step (A portion) of a bonding pad having a width of 40 μm and a depth of 1.5 μm surrounding a photoelectric conversion array as shown in FIGS. A specific method for flattening a substrate having a scribe line step (B portion) of 80 μm depth and 3.5 μm by the method of the present invention will be described, but the present invention is not limited thereto.

<Example 1>
PMR-NT2 (a positive photoresist sold by Fuji Pharmaceutical Co., Ltd. as a positive photosensitive resin composition on the substrate, a naphthoquinone diazide photosensitive agent and a thermosetting agent on a polystyrene-based alkali-soluble resin. Was pre-baked at 90 ° C. for 90 seconds, and then exposed to 125 mJ / cm ² with an i-line stepper (NSR-2205i9c manufactured by Nikon Corporation).
At this time, the portion of the photomask that exposes the A portion is a repetitive checkered pattern with an aperture ratio of 28% and a pitch of 2.0 μm, the portion of the photomask that exposes the B portion has an aperture ratio of 0% (entire light shielding) Portions other than the portion B and the portion B were 100% aperture ratio (entire transmission).
Next, development processing was performed with 0.43% TMAH aqueous solution for 60 seconds, rinsed with pure water for 20 seconds, and then spin-dried to remove moisture.
Next, an entire exposure (400 mJ / cm ² ) using an i-line stepper (NSR-2205i9c)
After performing bleaching treatment), heat treatment was performed for 5 minutes on a 220 ° C. hot plate. By this heat treatment, the uneven pattern surface formed in the A portion by the development became flat.
When the level difference between A and B was measured with a stylus type level gauge on the basis of the substrate surface (the portion having no level difference on the substrate surface), the results were as follows.
Part A: Maximum height 0.2 μm Maximum depth −0.1 μm
Part B: Maximum height -0.4μm Maximum depth -0.8μm
Maximum level difference 0.2μm-(-0.8μm) = 1.0μm

  Next, FOC-07M (acrylic thermosetting undercoat material sold by Fuji Pharmaceutical Co., Ltd.) was applied to the substrate with the flattened grooves at 1500 rpm, followed by a curing treatment at 180 ° C. for 5 minutes. Later, when the wafer was visually observed, a uniform film without coating unevenness was formed.

<Example 2>
Although planarization was performed using PMR-NT2 as in Example 1, the coating rotation speed of PMR-NT2 was 800 rpm.
In addition, the photomask for the portion that exposes the A portion is a repetitive checkered pattern with an aperture ratio of 38% and a pitch of 2.0 μm, and the photomask for the portion that exposes the B portion is a checkerboard with an aperture ratio of 18% and a pitch of 2.0 μm The portions other than the A portion and B portion where the pattern is repeated have an aperture ratio of 100% (entire transmission).
After the heat treatment at 220 ° C., the step difference between the A part and the B part was measured with a stylus type step system, which was as follows.
Part A: Maximum height 0.2μm Maximum depth 0μm
Part B: Maximum height -0.2μm Maximum depth -0.4μm
Maximum level difference 0.2μm-(-0.4μm) = 0.6μm

  Next, FOC-07M (acrylic thermosetting undercoat material sold by Fuji Pharmaceutical Co., Ltd.) was applied to the substrate with the flattened grooves at 1500 rpm, followed by a curing treatment at 180 ° C. for 5 minutes. Later, when the wafer was visually observed, a uniform film without coating unevenness was formed.

<Comparative example>
As in Example 1, planarization was performed using PMR-NT2. The coating rotation speed of PMR-NT2 was 1500 rpm.
At this time, both the photomask aperture ratios of the portions exposed to the A portion and the B portion were set to 0% (entire light shielding), and the other portions were set to an aperture ratio of 100% (full surface transmission).
After the heat treatment at 220 ° C., the step between the A part and the B part was measured with a stylus type step meter, and the results were as follows.
Part A: Maximum height 1.0 μm Maximum depth 0.4 μm
Part B: Maximum height -0.4μm Maximum depth -0.8μm
Maximum step 1.0μm − (− 0.8μm) = 1.8μm

  Next, FOC-07M (acrylic thermosetting undercoat material sold by Fuji Pharmaceutical Co., Ltd.) was applied to the substrate with the flattened grooves at 1500 rpm, followed by a curing treatment at 180 ° C. for 5 minutes. Later, when the wafer was visually observed, several thin radial coating irregularities were observed on the wafer.

In addition, using a photomask having a different aperture ratio, a change in film thickness when patterning and heat treatment of a positive photoresist (positive photosensitive resin composition) was evaluated.
<Example 3>
Patterning of positive photoresist (positive photosensitive resin composition) and 220 ° C. for 5 minutes using photomasks with an aperture ratio of 64%, 59%, 55%, 50%, 28%, 23% and 19%, respectively. The heat treatment was performed.
The photomask used in this example is a checkered pattern or a lattice pattern with a pitch of 2.0 um, and the type of positive photosensitive resin composition, its application conditions, and exposure conditions are the same as those in Example 2. did.
FIG. 8 shows the SEM image of the pattern shape of the photosensitive resin composition after development, the SEM image of the cross section after development and after heat treatment, and the ratio of the film thickness after heat treatment to the coating film thickness.
The uneven pattern after development is flattened by the heat treatment, and the film thickness is 64%, 59%, 55%, 50%, 28%, 23%, and 19%, respectively, after the development. 14%, 16%, 21%, 24%, 57%, 63% and 70% with respect to the film thickness, and it can be seen that the film thickness after planarization can be controlled by the aperture ratio of the photomask.

  The present invention is used in an industry for manufacturing a solid-state imaging device.

DESCRIPTION OF SYMBOLS 1 Substrate 2 Solid-state image sensor 3 Scribe line 4 Photoelectric conversion element array 5 Bonding pad 6 Negative photosensitive resin composition coating film 6a Negative photosensitive resin composition coating film 7 Step of scribe line (Part B) )
8 Bonding pad step (Part A)
DESCRIPTION OF SYMBOLS 9 Photomask 10 Exposure light 11 Exposure amount adjustment area 11a Translucent part 11b Light-shielding part 12 Step part 13 Coating film 13a of positive type photosensitive resin composition Patterned coating film 13b of positive type photosensitive resin composition Positive type Hot melt of coating film of photosensitive resin composition

Claims (5)

A step of applying a photosensitive resin composition on a substrate on which a photoelectric conversion element array is mounted to form a coating film of the photosensitive resin composition, a step of exposing the coating film of the photosensitive resin composition through a photomask And, in the method for producing a solid-state imaging device, including a step of developing the coating film after exposure to remove unnecessary portions,
The substrate has a plurality of step portions having different depths around a photoelectric conversion element array to be mounted;
In the photomask, the aperture ratio is adjusted in accordance with the depth of the plurality of step portions at a portion through which the exposure light irradiated to the plurality of step portions is transmitted, and a patterned coating film corresponding to this is formed. In the manufacturing method, after the development step, the coating film remaining on the substrate is heat-cured, and at that time, with respect to a plurality of step portions having different depths, A method for producing a solid-state imaging device, further comprising a step of leveling an upper surface of the patterned coating film by melting.   2. The solid-state imaging device according to claim 1, wherein the exposure amount adjustment region has a repetitive pattern of a checkered pattern, a striped pattern, or a lattice pattern in which the light transmitting part and the light shielding part are arranged adjacent to each other. Manufacturing method.   3. The method for manufacturing a solid-state imaging device according to claim 1, wherein the plurality of stepped portions include a stepped portion in a scribe line and a stepped portion in a bonding pad.   In manufacturing a solid-state imaging device, a photomask used for exposure of a coating film of a photosensitive resin composition on a substrate is irradiated to a plurality of steps having different depths around the photoelectric conversion element array on which the substrate is mounted. The photomask which has the exposure amount adjustment area | region where the aperture ratio was adjusted about the site | part which the exposure light which transmits. The exposure amount adjustment area has a repetitive pattern of a checkered pattern, a striped pattern, or a lattice pattern in which the light transmitting part and the light shielding part are arranged adjacent to each other.
The photomask according to claim 4.