JP2004264489A - Lens forming method - Google Patents

Abstract

An object of the present invention is to provide a lens forming method capable of accurately transferring a lens shape of a resist mask to a lens material layer thereunder without flattening a shoulder portion or a crown portion of the lens.
A lens forming step of forming a lens-shaped resist mask on a lens material layer, etching back of the resist mask and the lens material layer by dry etching, and transferring the resist mask shape to the lens material layer. Wherein the dry etching is performed while setting the gas pressure in the reaction chamber accommodating the lens material layer and the resist mask to a plurality of values.
[Selection] Fig. 10

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a lens forming method for forming a lens that collects light.
[0002]
[Prior art]
Generally, in order to improve photoelectric conversion efficiency, a solid-state imaging device includes a lens that collects external light to a light receiving unit (photoelectric conversion unit) that generates signal charges according to the amount of incident light. The lens is formed using a transparent insulating film such as a silicon nitride film or an organic resin, and is formed on, for example, wiring, an interlayer insulating film, a color filter, and a planarizing layer sequentially stacked on a substrate including a light receiving unit. It is formed. As a method for forming this lens, a transfer etching method has been conventionally proposed in Patent Document 1.
[0003]
In the transfer etching method, a resist mask is selectively formed on a lens material layer to be a lens, and heat treatment is applied to deform (reflow) each of the resist masks into a lens shape. Then, the resist mask and the lens material layer are etched using a reactive ion etching (RIE) method, which is a kind of dry etching, to remove the resist mask and change the shape of the resist mask to the lens material layer. This is a method of forming a lens by transferring the image to a lens.
[0004]
[Patent Document 1]
JP-A-64-10666
[Problems to be solved by the invention]
However, in the conventional lens forming method as described above, in the reactive ion etching step, when the gas pressure in the reaction chamber accommodating the substrate on which the lens material layer and the resist mask are laminated is 133 Pa or less, the gas is generated by plasma discharge. The irradiated ions are irradiated on the substrate in a substantially vertical direction. Therefore, the ion density of the shoulder portion of the resist mask where the surface to be etched is oblique to the ion irradiation direction becomes low, and the top of the resist mask where the surface to be etched is positioned substantially perpendicular to the ion irradiation direction. The ion density becomes high. Therefore, when transfer etching is performed on the lens material layer under such conditions, a lens having a flat top is formed as shown in FIG.
[0006]
On the other hand, when the gas pressure in the reaction chamber is higher than 133 Pa, the probability of collision between ions generated by the plasma discharge increases, and the ions are scattered and irradiated onto the substrate. As a result, the ion density at the top of the resist mask becomes low. Therefore, if transfer etching is performed on the lens material layer under such conditions, a mountain-shaped lens having a flat shoulder is formed as shown in FIG.
[0007]
SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the conventional technology, and does not flatten the shoulder or crown of the lens. It is an object of the present invention to provide a method for forming a lens that can be accurately transferred to a material layer.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the lens forming method of the present invention includes a mask forming step of forming a lens-shaped resist mask on a lens material layer,
A dry etching step of performing dry etching on the resist mask and the lens material layer, and transferring a shape of the resist mask to the lens material layer to form a lens;
A lens forming method having
The dry etching step includes:
The dry etching is performed while setting a gas pressure in a reaction chamber accommodating the lens material layer and the resist mask to a plurality of values.
[0009]
At this time, the gas pressure is changed from the low pressure at which the ions generated in the reaction chamber are irradiated in a direction substantially perpendicular to the lens material layer, the ions generated in the reaction chamber are scattered and the lens material is scattered. The pressure may be shifted to a high pressure applied to the layer,
It is preferable to change the gas pressure from 67 Pa to 200 Pa or more.
[0010]
Further, the gas pressure when forming the shoulder of the lens and the gas pressure when forming the crown of the lens may be set to different values,
The gas pressure when forming the shoulder of the lens is 67 Pa to 133 Pa,
It is preferable that the gas pressure when forming the top of the lens is 133 Pa to 333 Pa.
[0011]
The lens material layer is
It may be a transparent insulating film,
Preferably, it is a silicon nitride film or an organic resin.
[0012]
In the lens forming method as described above, in the dry etching step, by performing dry etching while setting the gas pressure in the reaction chamber to a plurality of values, the irradiation direction of ions generated in the reaction chamber to the resist mask, It can be changed appropriately according to the shape.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, the present invention will be described with reference to the drawings.
[0014]
1 to 4 are side sectional views schematically showing manufacturing steps of the lens forming method of the present invention.
[0015]
In the lens forming method of the present embodiment, first, as shown in FIG. 1, a silicon nitride film 2 serving as a lens is formed on a semiconductor substrate 1 by using a well-known plasma CVD (Chemical Vapor Deposition) method, a low pressure CVD method, or the like. I do.
[0016]
Subsequently, after depositing a resist film on the silicon nitride film 2 and patterning the resist film into a desired shape using a known photolithography technique, the resist film is subjected to a heat treatment to deform the resist film to form a lens-shaped resist. A mask 3 is formed. In this embodiment, an example in which a lens is formed on the semiconductor substrate 1 is shown. However, instead of the semiconductor substrate 1, for example, an organic material such as PGMA (polyglycidyl methacrylate), PMMA (polymethyl methacrylate), or polyimide is used. A resin may be used. When an organic resin is used as the substrate, the surface of the substrate may be planarized by using a well-known CMP (Chemical Mechanical Polishing) method, and then the silicon nitride film 2 may be formed thereon.
[0017]
Next, the resist mask 3 and the silicon nitride film 2 are etched by using a well-known reactive ion etching method, thereby removing the resist mask 3 and transferring the shape of the resist mask 3 to the silicon nitride film 2 to form a lens. To form For the etching process, for example, a well-known parallel plate type RIE etching device is used.
[0018]
In the present embodiment, in the initial stage of the start of the transfer etching, the gas pressure in the reaction chamber of the RIE etching apparatus is set to 133 Pa or less (for example, 67 Pa), and the ions 4 generated by the plasma discharge as shown in FIG. Irradiation in a direction substantially perpendicular to 1 forms the shoulder of the lens. Then, the gas pressure in the reaction chamber is gradually increased to 133 Pa or more (preferably 200 Pa or more). When the gas pressure in the reaction chamber is set to 133 Pa or more as described above, the collision probability of ions generated by plasma discharge increases, and the ions 4 are scattered and radiated to the semiconductor substrate 1 as shown in FIG. . Therefore, each of the shoulder portion and the top portion of the lens transferred to the silicon nitride film 2 does not become flat, and is formed into a lens shape as shown in FIG.
[0019]
According to the lens forming method of the present embodiment, by performing reactive ion etching while setting the gas pressure in the reaction chamber to a plurality of values, the irradiation direction of ions generated in the reaction chamber to the resist mask 3 can be changed. Since the shape can be appropriately changed according to the shape, the shape of the resist mask 3 can be accurately transferred to the underlying silicon nitride film 2 (lens material layer). Therefore, it is possible to obtain a high-quality lens in which the shoulder and the crown are not flat.
[0020]
【Example】
Next, an embodiment of the lens forming method of the present invention will be described using a solid-state imaging device as an example.
[0021]
FIG. 5 is a side sectional view showing the structure of a solid-state imaging device including a lens formed by the lens forming method of the present invention.
[0022]
As shown in FIG. 5, the solid-state imaging device has a configuration including a light receiving unit 7 that generates a signal charge according to the amount of incident light near the surface of the semiconductor substrate 1. The light receiving unit 7 is provided for each of a plurality of pixels arranged in a lattice shape, and each pixel is separated by an element isolation region 6 provided near the surface of the semiconductor substrate 1. Note that an active element (not shown) is generally formed on the semiconductor substrate 1 together with the light receiving section 7.
[0023]
A first wiring 8 patterned into a desired shape using polysilicon or the like on the semiconductor substrate 1 and a first BPSG (Boro-Phospho Silicated Glass) film having an opening on the light receiving section 7 and the like. Is formed, and a second wiring 10 patterned into a desired shape using Al (aluminum) or the like is formed on the first interlayer insulating film 9.
[0024]
Further, on the first interlayer insulating film 9, a second interlayer insulating film 12 made of a SiO ₂ film formed by a plasma CVD method or the like, a third wiring 13 patterned into a desired shape using Al or the like. A third interlayer insulating film 15 made of a SiO ₂ film formed by a plasma CVD method or the like, and a fourth wiring 16 patterned into a desired shape by using Al or the like are sequentially formed corresponding to the circuit pattern. You.
[0025]
The first wiring 8 and the second wiring 10 are connected via a first through hole 11 provided in the first interlayer insulating film 9, and the second wiring 10 and the third wiring 13 are The third wiring 13 and the fourth wiring 16 are connected via a second through hole 14 provided in the second interlayer insulating film 12, and are connected to a third through hole provided in the third interlayer insulating film 15. The connection is made via a hole 17. These interlayer insulating films and wirings do not need to have the four-layer structure shown in FIG. 5, but may have a structure of three layers, two layers, one layer, or four or more layers.
[0026]
On the third interlayer insulating film 16, a protective film 18 made of a SiO ₂ film formed by a plasma CVD method or the like is formed so as to cover the third wiring 16. An inner lens 19 formed by the lens forming method and a first planarization layer 20 made of an organic film or the like are formed.
[0027]
On the first flattening film 20, a color filter 21 for separating incident light corresponding to each pixel is formed. The color filter 21 is formed using, for example, a photoresist containing pigments of three primary colors of red (R), green (G), and blue (B). On the color filter 21, a second flattening layer 12 made of a light-transmitting organic film or the like is formed.
[0028]
In such a configuration, a method of manufacturing the solid-state imaging device according to the present embodiment will be described next with reference to FIGS.
[0029]
6 to 9 are side sectional views showing a manufacturing procedure of a solid-state imaging device to which the lens forming method of the present invention is applied in order of steps. FIG. 6 is a graph showing a relationship with the graph.
[0030]
In the present embodiment, first, as shown in FIG. 6, a first wiring 8, a first interlayer insulating film 9, a second wiring 10, a second interlayer insulating After sequentially forming the film 12, the third wiring 13, the third interlayer insulating film 15, the fourth wiring 16, and the protection film 18, the surface of the protection film 18 is planarized by the CMP method.
[0031]
Subsequently, as shown in FIG. 7, a silicon nitride film 2 serving as an inner lens 19 is formed on the protective film 18 by a plasma CVD method or a low pressure CVD method, and then, as shown in FIG. 2, a resist film is formed, and the resist film is selectively patterned using a photolithography technique. Further, the resist film is deformed by heat treatment to form a lens-shaped resist mask 3.
[0032]
Next, as shown in FIG. 9, the resist mask 3 and the silicon nitride film 2 are etched by reactive ion etching to remove the resist mask 3 and transfer the shape of the resist mask 3 to the silicon nitride film 2 to form a lens. To form At this time, in this embodiment, as shown in FIG. 10, transfer etching is performed while changing the gas pressure in the reaction chamber from 67 Pa to 333 Pa. That is, in the initial stage of the start of the reactive ion etching, the gas pressure is set to 67 Pa to mainly form the shoulder portion of the inner lens 19, and then the gas pressure is gradually increased to 333 Pa to mainly set the inner lens. Form the 19 crowns.
[0033]
Finally, a first flattening film 20 made of an organic film or the like, a color filter 21, and a second flattening layer 22 made of an organic film or the like are sequentially formed to form the solid-state imaging device shown in FIG. .
[0034]
By performing transfer etching while changing the gas pressure in the reaction chamber from 67 Pa to 333 Pa at the time of reactive ion etching as in the present embodiment, a solid with a high-quality in-layer lens whose shoulder and top are not flattened An imaging device can be obtained.
[0035]
【The invention's effect】
Since the present invention is configured as described above, the following effects can be obtained.
[0036]
In the dry etching process, by performing dry etching while setting the gas pressure in the reaction chamber to a plurality of values, the irradiation direction of ions generated in the reaction chamber to the resist mask can be appropriately changed according to its shape. Therefore, the shape of the resist mask can be accurately transferred to the lens material layer, and a high-quality lens in which the shoulder and the crown are not flattened can be obtained.
[Brief description of the drawings]
FIG. 1 is a side sectional view schematically showing a manufacturing process of a lens forming method of the present invention.
FIG. 2 is a side sectional view schematically showing a manufacturing process of the lens forming method of the present invention.
FIG. 3 is a side sectional view schematically showing a manufacturing process of the lens forming method of the present invention.
FIG. 4 is a side sectional view schematically showing a manufacturing process of the lens forming method of the present invention.
FIG. 5 is a side sectional view showing a structure of a solid-state imaging device including a lens formed by the lens forming method of the present invention.
FIG. 6 is a side sectional view showing a manufacturing procedure of the solid-state imaging device to which the lens forming method of the present invention is applied in the order of steps.
FIG. 7 is a side sectional view showing a manufacturing procedure of the solid-state imaging device to which the lens forming method of the present invention is applied in the order of steps.
FIG. 8 is a side sectional view showing a manufacturing procedure of the solid-state imaging device to which the lens forming method of the present invention is applied in the order of steps.
FIG. 9 is a side sectional view showing a manufacturing procedure of the solid-state imaging device to which the lens forming method of the present invention is applied in the order of steps.
FIG. 10 is a graph showing a relationship between an etching time set during a reactive ion etching process and a gas pressure in a reaction chamber.
FIG. 11 is a side sectional view showing an example of a lens shape formed by a conventional lens forming method.
FIG. 12 is a side sectional view showing another example of a lens shape formed by a conventional lens forming method.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 semiconductor substrate 2 silicon nitride film 3 resist mask 4 ions 6 element isolation region 7 light receiving section 8 first wiring 9 first interlayer insulating film 10 second wiring 11 first through hole 12 second interlayer insulating film 13 Third wiring 14 Second through hole 15 Third interlayer insulating film 16 Fourth wiring 17 Third through hole 18 Protective film 19 In-layer lens 20 First planarizing layer 21 Color filter 22 Second planar Layer

Claims (8)

A mask forming step of forming a lens-shaped resist mask on the lens material layer,
A dry etching step of performing dry etching on the resist mask and the lens material layer, and transferring a shape of the resist mask to the lens material layer to form a lens;
A lens forming method having
The dry etching step includes:
A lens forming method for performing the dry etching while setting a gas pressure in a reaction chamber accommodating the lens material layer and the resist mask to a plurality of values. The gas pressure is irradiated from the low pressure at which ions generated in the reaction chamber are irradiated in a direction substantially perpendicular to the lens material layer. 2. The method according to claim 1, wherein the pressure is changed to a high pressure. 3. The lens forming method according to claim 2, wherein the gas pressure is changed from 67 Pa to 200 Pa or more. The lens forming method according to claim 1, wherein the gas pressure when forming the shoulder of the lens and the gas pressure when forming the crown of the lens are set to different values. The gas pressure when forming the shoulder of the lens is 67 Pa to 133 Pa,
5. The lens forming method according to claim 4, wherein the gas pressure when forming the crown of the lens is 133 Pa to 333 Pa. The lens material layer,
2. The method according to claim 1, wherein the lens is a transparent insulating film. The lens material layer,
7. The method according to claim 6, wherein the lens is a silicon nitride film. The lens material layer,
7. The method according to claim 6, wherein the lens is an organic resin.

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