JPH098266A - Manufacture of on-chip lens - Google Patents

Abstract

PURPOSE: To provide a manufacturing method by which an on-chip lens having such an excellent shape that can improve the sensitivity of a CCD image pickup element can be manufactured. CONSTITUTION: At the time of etching back an organic macromolecular material layer 12 which is an on-chip lens material layer together with a reflow resist pattern 13a, plasma etching is performed by using a mixed gas of O2 and Cl2 . Therefore, the dependence on incident angle of the sputtering yield of incident ions is reduced and an on-chip lens 14 is prevented from becoming abnormal is shape.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing an on-chip lens, and more particularly, to a method of manufacturing an on-chip lens for improving the light receiving sensitivity of a sensor unit such as a solid-state image pickup device.

[0002]

2. Description of the Related Art CCD (Charge Coupled)
Solid-state image sensors such as devices are roughly divided into area sensors used for video cameras and camera-integrated video tape recorders, and line sensors used for facsimiles and bar code readers. Has become an indispensable device for the electronic eyes of. There is a strong demand for miniaturization and high resolution of the CCD, and the occupied area per unit pixel is reduced with the progress of high integration, and at the same time, the opening area of the sensor portion is also being reduced.

Due to the reduction of the opening area of the sensor section,
Since the amount of light taken into the sensor section is insufficient, it has become difficult to secure a sufficient amount of photo-induced charges to secure an S / N ratio. Therefore, an on-chip lens is a structure adopted in view of the requirements of satisfying both the characteristics of high integration and high sensitivity. A schematic sectional view in the vertical register direction of a CCD image pickup device adopting an on-chip lens will be described with reference to FIG. By forming a first-layer polysilicon gate 3 and a second-layer polysilicon gate 4 on a semiconductor substrate 1 made of silicon or the like and performing ion implantation and activation heat treatment by self-alignment using these gate electrodes as a mask, the sensor unit 2 To form. Next, aluminum is deposited on the entire surface, and the light shielding layer 5 is formed by opening the upper portion of the sensor portion. The opening plane shape of the light shielding layer is, for example, 1.5 μm × 2.5 μm
Is a rectangle. After that, a protective layer 6 of Si ₃ N ₄ or the like is formed on the entire surface, and the step formed by the first-layer polysilicon gate 3 and the second-layer polysilicon gate 4 is filled to form a flattening layer 7 made of acrylic resin or the like. Then, the color filter layer 8 is further formed. After that, the on-chip lens 14 is formed so as to be located above the sensor unit 2. With this structure, the incident light condensed by the on-chip lens 12 is condensed on the sensor unit 2, and the utilization efficiency of the incident light can be improved several times or more.

As a method of manufacturing the on-chip lens 14, as disclosed in Japanese Patent Application Laid-Open No. 1-10666 filed by the applicant of the present application, an organic polymer material layer is formed on the color filter layer 8 to form an organic film. After the resist pattern is selectively formed on the polymer material layer, heat treatment is applied to reflow the resist pattern to form a reflow resist pattern having a surface shape forming a part of a substantially spherical surface. At this stage, the shape of the on-chip lens is fixed,
For the reasons described below, the reflow resist pattern and the organic polymer material layer are both etched back, the reflow resist pattern is etched off, and the shape of the reflow resist pattern is transferred to the organic polymer material layer that is the on-chip lens material layer, and turned on. The chip lens 14 is completed.

The reason why the reflow resist pattern is not directly used as an on-chip lens is that the lower color filter layer 8 is not thermally discolored and can be reflowed at, for example, 180 ° C. or lower, and it is added in a wire bonding or resin molding process in a post-treatment process. This is because it is difficult to select a resist material having the property of not reflowing at a temperature of about 150 ° C. Even if a resist material that can be reflowed in a narrow temperature range of 150 ° C. to 180 ° C. can be selected, the actual process window is narrow in terms of temperature control, and it is difficult to use. Therefore, a resist material having excellent low temperature reflow properties and an organic polymer material layer having excellent heat resistance and optical characteristics are individually selected and used.

[0006]

When the shape of the reflow resist pattern is transferred to the organic polymer material layer which is the on-chip lens material layer, anisotropic etching using O ₂ is performed. At the same time, isotropic etching due to O ^* (oxygen radical), that is, undercut is likely to occur. Therefore, if an etching condition with a high sputter property in which the incident ion energy is increased is adopted with the intention of accurately transferring the pattern, the phenomenon that the cross-sectional shape of the organic polymer material layer after etching back becomes a triangle due to the relationship of the sputtering yield. Occurs. This problem will be described with reference to FIG.

First, as shown in FIG. 3A, the base substrate 11
Organic polymer material layer 1 which is the material of the on-chip lens
2 is formed, and a reflow resist pattern 13a is further formed. The reflow resist pattern 13a has a substantially spherical surface shape that is the original shape of the on-chip lens.

FIG. 3B shows a state in which the shape of the reflow resist pattern 13a is transferred to the organic polymer material layer 12 by etching back the entire surface from this state by strongly anisotropic ionic etching using O ₂ gas. Show. As shown in the figure, the surface shape of the reflow resist pattern 13a is not accurately transferred to the organic polymer material layer 12 after the etch back, and the cross-sectional shape becomes an abnormal on-chip lens 14a having a triangular shape. The case can be seen. As described above, the reason for the abnormal shape is that the sputtering yield changes depending on the angle formed by the surface of the reflow resist pattern 13a and O ⁺ which is vertically incident on the substrate to be etched, and the specific incident angle portion is preferentially etched. It is thought to be because.
When the on-chip lens 14a having an abnormal shape is formed, the incident light does not normally converge on the sensor portion, and the purpose of improving the photosensitivity of the CCD cannot be achieved.

An object of the present invention is to solve the above-mentioned problems of the prior art. That is, an object of the present invention is to provide a method for manufacturing an on-chip lens that allows the surface shape of a reflow resist pattern to be accurately transferred onto an organic polymer material layer.

[0010]

The method for manufacturing an on-chip lens of the present invention comprises a step of forming a resist pattern on an organic polymer material layer, a step of reflowing the resist pattern to form a reflow resist pattern, In a method for forming an on-chip lesbian, which includes a step of etching back both a reflow resist pattern and the organic polymer material layer to remove the reflow resist pattern and transferring the surface shape of the reflow resist pattern to the organic polymer layer. The etch back step is a step of performing plasma etching using a mixed gas containing a gas capable of generating an oxygen chemical species and a gas capable of generating a halogen chemical species other than a fluorine chemical species. To do. The gas capable of generating a halogen-based chemical species other than the fluorine-based chemical species described here is a gas capable of generating a chlorine-based chemical species such as Cl ₂ or HCl, or a bromine-based chemical species such as HBr or Br _2. Gas which can generate iodine-based chemical species such as HI.

In a preferred embodiment of the present invention, the gas capable of generating halogen-based chemical species other than fluorine-based chemical species is
It is a gas that can generate free sulfur in plasma under discharge dissociation conditions. As such gas,
S ₂ F having an X / S ratio (X represents a halogen element) of less than 6
₂ , sulfur fluoride gas such as SF ₂ , SF ₄ , S ₂ F ₁₀ , sulfur chloride gas such as S ₂ Cl ₂ , S ₃ Cl ₂ , and SCl ₂ , and S ₂ Br ₂ , S ₃ Br ₂ , Examples thereof include sulfur bromide-based gas such as SBr ₂ . Since SF _{6 which} is a general fluorinated sulfur gas has an X / S ratio of 6, it is excluded.

[0012]

In the etch back step of transferring the surface shape of the reflow resist pattern onto the organic polymer material layer which is the on-chip lens material layer, a gas capable of generating oxygen-based chemical species and a fluorine-based gas are used as etching gas. It is characterized in that plasma etching is performed using a mixed gas containing a gas that can generate a halogen-based chemical species other than the chemical species.

The present inventor has previously disclosed a technique of plasma etching using an O ₂ / Cl ₂ mixed gas in order to prevent side etching in patterning a lower layer resist of a multilayer resist mask, as disclosed in Japanese Patent Laid-Open No. 2-244625. It was disclosed in Japanese Patent Application Laid-Open No. 4-7829. The purpose of this prior application is to form a resist pattern having vertical side walls, but the present invention is based on the fact that when this technique was applied to the transfer of a resist pattern having a spherical shape, an unexpectedly good result was obtained.

When plasma etching is performed using an O ₂ / Cl ₂ mixed gas, reaction products mainly composed of CCl _x are simultaneously deposited on the pattern side surface of the resist mask and the layer to be etched, and incident ions and It is possible to protect the pattern from radical attack and prevent side etching and shape abnormality. Carbon in this reaction product is supplied from the resist pattern, but when the layer to be etched is an organic polymer material layer, it is also directly supplied from the layer to be etched. On the other hand, in the case of etch back using the conventional O ₂ gas alone, the reaction product is CO 2.
And CO ₂ do not deposit on the substrate to be etched and have no effect of protecting the pattern of the resist mask and the layer to be etched. Therefore, the reflow resist pattern cannot maintain the initial surface shape due to the above-described sputtering yield, and the cross-section of the reflow resist pattern is formed into a triangular shape. As a result, the cross-sectional shape of the on-chip lens formed is also an abnormal shape. Become.

According to the present invention, however, the surface of the reflow resist pattern is protected by the fact that the reaction product mainly composed of CCl _x is deposited in competition with etching,
Only a specific incident angle portion is not preferentially etched. Therefore, it is possible to accurately transfer the surface shape of the substantially spherical surface to the organic polymer material layer. The deposited reaction product may be CBr _x depending on the type of halogen-based species.
Or CI _x , but in any case, it is the same as CCl _{x in} that it has the effect of improving the resistance to ion incidence.

When a gas capable of generating free sulfur in plasma under discharge dissociation conditions is used as a gas capable of generating a halogen-based chemical species other than a fluorine-based chemical species, CC
Since sulfur deposition can be used in addition to l _{x and the} like, the pattern protection effect is further enhanced, and accurate pattern transfer is possible. It should be noted that at the same time with this sulfur-based gas, N ₂ and N ₂ H ₄
Alternatively, when N-based gas such as NF ₃ is used together, deposition of polythiazyl (SN) _x can be utilized, and in this case, a higher pattern protection effect can be obtained. Since these sulfur materials are sublimable, effective deposition can be expected when the temperature of the substrate to be etched is controlled to about room temperature or lower. On the contrary, if the substrate to be etched is heated to 90 ° C. or higher for sulfur and 150 ° C. or higher for polythiazil in a reduced pressure atmosphere, it is possible to remove contamination and particles without leaving the substrate to be etched.

[0017]

Embodiments of the present invention will be described below with reference to the accompanying drawings. It should be noted that the same reference numerals are given to the same components as those in FIG. 3 referred to in the description of the prior art.

Example 1 This example is an example in which an organic polymer material layer, which is an on-chip lens material layer, was etched back using an O ₂ / Cl ₂ mixed gas, and this will be described with reference to FIG. As shown in FIG. 1A, a novolac resist OFPR-800 is used as an example of the organic polymer material layer 12 on the base substrate 11.
Is spin coated and heat cured. The organic polymer material layer 12 only needs to be a material satisfying heat resistance and optical characteristics, and does not require photosensitivity or reflow characteristics. Next, TSMR-V3, which is a novolac-based resist, is spin-coated on the organic polymer material layer 12 as an example, and exposed.
The resist pattern 13 is formed by developing. The material of the resist pattern may be another material as long as it has photosensitivity and reflowability. The base substrate 11 has the semiconductor substrate 1 to the color filter layer 8 formed therein, which will be described with reference to FIG. 2 showing a schematic sectional view of the CCD image pickup device in the vertical register direction. Therefore, the resist pattern 13 is selectively patterned immediately above the sensor unit 2.

Next, as shown in FIG. 1 (b), 160 ° C.
Post-baking is performed to reflow the resist pattern 13 to form a reflow resist pattern 13a having a substantially spherical and gentle surface shape. This temperature does not cause discoloration of the color filter layer.

The substrate to be etched shown in FIG. 1 (b) is set on the substrate stage of a substrate bias application type ECR plasma etching apparatus. As an example, the reflow resist pattern 13a and the organic polymer material layer 12 are both formed under the following plasma etching conditions. Etch back. O ₂ flow rate 40 sccm Cl ₂ flow rate 10 sccm Gas pressure 1.3 Pa Microwave power supply power 1500 W (2.45 GHz) Substrate bias power supply power 200 W (13.56 MHz) Substrate temperature 0 ° C. Reflow resist in this etching process CCl _x , which is a reaction product of the pattern 13a or the organic polymer material layer 12 and Cl ₂ , is reflow resist pattern 13a.
Surface of organic polymer layer 1 being patterned
2 was deposited on the surface of No. 2 to effectively prevent shape anomalies due to sputtering of incident ions. Base substrate 11 for etch back
The process was completed before the color filter layer on the surface was exposed, and as a result, the on-chip lens 14 in which the surface shape of the reflow resist pattern 13a was accurately transferred was formed. The etching rate was 500 nm / min.

According to this embodiment, it is possible to stably manufacture an on-chip lens having a good surface shape by adopting the etch back condition using Cl ₂ / O ₂ mixed gas.

Example 2 This example is an example in which an organic polymer material layer which is an on-chip lens material layer is etched back using an O ₂ / HBr mixed gas. This will be described again with reference to FIG. Since the substrate to be etched shown in FIG. 1B used in this embodiment is the same as that in the first embodiment, duplicate description will be omitted.

The substrate to be etched shown in FIG. 1B is set on the substrate stage of a substrate bias application type ECR plasma etching apparatus, and as an example, the reflow resist pattern 13a and the organic polymer material layer 12 are etched under the following plasma etching conditions. Back. O ₂ flow rate 40 sccm HBr flow rate 10 sccm Gas pressure 1.3 Pa Microwave power supply power 2000 W (2.45 GHz) Substrate bias power supply power 250 W (13.56 MHz) Substrate temperature 0 ° C. Reflow resist pattern in this etching process 13a or the organic polymer material layer 12 and CBr _x which is a reaction product of HBr with the surface of the reflow resist pattern 13a or the organic polymer material layer 12 being patterned.
It was deposited on top and effectively prevented shape anomalies due to incident ion sputtering. CBr _x is the CCl _{x of the} previous example
The ion implantation resistance was higher, and abnormal sputtering did not occur even when the substrate bias was increased as compared with Example 1. The etch back is completed before the color filter layer on the surface of the base substrate 11 is exposed, and as a result, the reflow patterning 13a is performed.
The on-chip lens 14 in which the surface shape of (1) was accurately transferred was formed. The etching rate was 700 nm / min, which was higher than that in Example 1.

According to this embodiment, by adopting the etch-back condition using HBr / O ₂ mixed gas, it is possible to manufacture an on-chip lens having a good surface shape stably and with high throughput.

Example 3 This example is an example in which an organic polymer material layer which is an on-chip lens material layer is etched back by using an O ₂ / S ₂ Cl ₂ mixed gas, and this is referred to FIG. 1 again. explain. Since the substrate to be etched shown in FIG. 1B used in this embodiment is the same as that in the first embodiment, duplicate description will be omitted here.

The substrate to be etched shown in FIG. 1 (b) is set on the substrate stage of a substrate bias application type ECR plasma etching apparatus, and as an example, the reflow resist pattern 13a and the organic polymer material layer 12 are etched under the following plasma etching conditions. Back. O ₂ flow rate 40 sccm S ₂ Cl ₂ flow rate 10 sccm Gas pressure 1.3 Pa Microwave power supply power 2500 W (2.45 GHz) Substrate bias power supply power 350 W (13.56 MHz) Substrate temperature 0 ° C. In this etching process, Since a mixed gas containing S ₂ Cl ₂ is used, the reflow resist pattern 1
3a and CCl _x which is a reaction product of chlorine with the organic polymer material layer 12 and sulfur generated by dissociation of S ₂ Cl ₂ are on the surface of the reflow resist pattern 13a or on the organic polymer material layer 12 being patterned. Deposited on the
The shape abnormality due to the sputtering of incident ions was extremely effectively prevented. These mixed deposition films have extremely high ion incidence resistance, and abnormal sputtering did not occur even when the substrate bias was further increased than in Example 2. The etch back was completed before the color filter layer on the surface of the base substrate 11 was exposed, and as a result, the on-chip lens 14 in which the surface shape of the reflow resist pattern 13a was accurately transferred was formed. The etching rate was 800 nm / min, which was higher than that in Example 2.

According to the present embodiment, by adopting the etch back condition using the S ₂ Cl ₂ / O ₂ mixed gas, it is possible to stably manufacture an on-chip lens having a very good surface shape and a high throughput. Is. As described above, if N ₂ gas is further added to the S ₂ Cl ₂ / O ₂ mixed gas, the deposition of polythiazyl can be utilized, and the effect of preventing shape abnormality is further enhanced.

Although the present invention has been described with reference to the three examples, the present invention is not limited to these examples. For example, if the resist pattern is composed of a two-layer resist pattern and an upper layer resist having a good resolution and a lower layer resist having an excellent reflow property are used in combination, it is possible to cope with miniaturization of the on-chip lens. The etchback method using the mixed gas of the present invention is extremely effective also in the etchback of such a fine on-chip lens.

A substrate bias application type ECR plasma etching apparatus has been exemplified as the plasma etching apparatus.
Even an etching apparatus such as a parallel plate type RIE apparatus, a magnetron RIE apparatus, an inductively coupled plasma etching apparatus or a helicon wave plasma etching apparatus can be preferably used.

Besides, the structure of the CCD image pickup device is not limited to the illustrated one. The method of manufacturing an on-chip lens of the present invention can be applied not only to CCDs but also to various OEICs using a microlens made of an organic polymer material layer or a diffraction grating.

[0031]

As is apparent from the above description, according to the method for manufacturing an on-chip lens of the present invention, the surface shape of the reflow resist pattern can be accurately transferred to the organic polymer material layer, and the on-shape having an excellent shape can be obtained. Since it becomes possible to stably manufacture the chip lens, it is possible to contribute to improvement in sensitivity and reliability of the CCD image pickup device.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view illustrating a method for manufacturing an on-chip lens according to Examples 1 to 3 to which the present invention is applied,
(A) is a state where a resist pattern is formed on an organic polymer material layer, (b) is a state where a reflow resist pattern is formed by heat melting the resist pattern, (c) is a reflow resist pattern and an organic polymer material layer Are both etched back to form an on-chip lens.

FIG. 2 is a schematic sectional view in the vertical register direction of a CCD image pickup element adopting an on-chip lens.

3A and 3B are schematic cross-sectional views illustrating a conventional method for manufacturing an on-chip lens, where FIG. 3A is a state in which a reflow resist pattern is formed on an organic polymer material layer, and FIG. This is a state in which an on-chip lens having an abnormal shape is formed by etching back the molecular material layers together.

[Explanation of symbols]

 1 Semiconductor Substrate 2 Sensor Part 3 First Layer Polysilicon Gate 4 Second Layer Polysilicon Gate 5 Light Shielding Layer 6 Protective Layer 7 Flattening Layer 8 Color Filter Layer 11 Base Substrate 12 Organic Polymer Material Layer 13 Resist Pattern 13a Reflow Resist Pattern 14 On-chip lens 14a On-chip lens with abnormal shape

Claims (2)

[Claims] 1. A step of forming a resist pattern on an organic polymer material layer, a step of reflowing the resist pattern to form a reflow resist pattern, and a step of etching back both the reflow resist pattern and the organic polymer material layer. Then, in the method for forming an on-chip lesbian having a step of removing the reflow resist pattern and transferring the surface shape of the reflow resist pattern to the organic polymer layer, the etch back step generates oxygen-based chemical species. Method for producing an on-chip lens, which is a step of performing plasma etching using a mixed gas containing a gas that can generate a halogen-based chemical species other than a fluorine-based chemical species. 2. The gas capable of generating halogen-based chemical species other than fluorine-based chemical species is a gas capable of generating free sulfur in plasma under discharge dissociation conditions. On-chip lens manufacturing method.