Method for manufacturing CMOS image sensor having microlens therein with high photosensitivity

The method for manufacturing a CMOS image sensor is employed to prevent bridge phenomenon between adjacent microlenses by employing openings between the microlenses. The method includes the steps of: preparing a semiconductor substrate including isolation regions and photodiodes therein obtained by a predetermined process; forming an interlayer dielectric (ILD), metal interconnections and a passivation layer formed on the semiconductor substrate in sequence; forming a color filter array having a plurality of color filters on the passivation layer; forming an over-coating layer (OCL) on the color filter array by using a positive photoresist or a negative photoresist; forming openings in the OCL by patterning the OCL by using a predetermined mask; and forming dome-typed microlenses on a patterned OCL.

FIELD OF THE INVENTION

The present invention relates to a method for manufacturing a semiconductor device; and, more particularly, to a method for manufacturing a complementary metal oxide semiconductor (CMOS) image sensor having microlenses therein with a high photosensitivity by forming openings between the microlenses.

DESCRIPTION OF THE PRIOR ART

As is well known, an image sensor is a semiconductor device converting an optical image to an electrical signal. Among various types of the image sensors, a charged coupled device (CCD) image sensor uses a plurality of metal-oxide-silicon (MOS) capacitors therein so that charge carriers are stored and transferred by the MOS capacitors. Meanwhile, a complementary MOS (CMOS) image sensor is a semiconductor device that converts an optical image to an electrical signal using a CMOS manufacturing technology, which employs a switching scheme of an MOS transistor for transportation of photo-electric charges from a photodiode to an output node as well as detection of an output signal at the output node.

The CCD image sensor has many demerits that complicated operation methods, high power consumption and a number of mask processes are required. Furthermore, it is very difficult to make a signal processing circuit integrated into a CCD chip. Accordingly, in order to overcome such demerits, many developments for the CMOS image sensor have been recently ensued using a submicron CMOS manufacturing technique. The CMOS image sensor creates a picture by detecting signals from the photodiode and the MOS transistors in a unit pixel. The use of a CMOS manufacturing technique can reduce power consumption compared with a CCD. Furthermore, while it is necessary to perform about 30 to 40 mask processes for manufacturing the CCD image sensor, the method for manufacturing the CMOS image sensor requires only about 20 mask processes, thereby simplifying the manufacturing process. Since an image signal processing circuit can be integrated together with light-sensing elements in one chip, the CMOS image sensor is highlighted as a next generation image sensor.

As well known, to embody color images in an image sensor, a color filter array is arranged over a pixel array, wherein color filter array usually includes an organic material that only transmits light with a specific wavelength band. For example, a blue color filter transmits light with the blue wavelength band and shields light with other wavelength band. The color filter array includes generally three colors of red, green and blue, or those of yellow, magenta and cyan.

The CMOS image sensor includes a pixel array for sensing the lights and accumulating photocharges and a logic circuit for processing the signal from the pixel array. In order to improve the photosensitivity of the CMOS image sensor, there have been proceeded endeavors to increase the area ratio of the photosensitive parts in the unit pixel, i.e., a fill factor. However, there are fundamentally limits in such endeavors, because the logic circuit parts can not be completely eliminated and thus, the photosensitive part has a limited area. Accordingly, in order to increase the photosensitivity, light-collecting technique has been researched. Using this technique, the pathways of the incident lights projected on the regions other than the photosensitive parts are changed, whereby much light is collected in the photosensitive parts. For collecting much more lights effectively, the image sensor employs microlenses on the color filter array.

There is provided inFIG. 1a cross sectional view setting forth a conventional method for manufacturing the CMOS image sensor having microlenses therein.

InFIG. 1, the conventional method for manufacturing the CMOS image sensor begins with preparing a semiconductor substrate110obtained by a predetermined process. Isolation regions112are formed in the semiconductor substrate110, thereby defining an active region and a field region. In each unit pixel, there is formed a corresponding photodiode114for converting an incident light to photocharges. For the sake of convenience, transistors required for the unit pixel is not depicted in the drawings.

After forming the isolation regions112and the photodiodes114, an interlayer dielectric (ILD)116is formed on the semiconductor substrate110. Thereafter, metal interconnections118are formed on predetermined locations of the ILD116in consideration of the underlying photodiodes114so that the incident light projected on the photodiodes114is not shielded by the existence of the metal interconnections118.

Following a formation of the metal interconnections118, a passivation layer129is formed over the resultant structure including the metal interconnections118for protecting a device from moisture and a scratch during post manufacturing processes.

Subsequently, color filter array122having a red, a green and a blue color filters is formed directly on the passivation layer120by using a typical method. Alternatively, after a planarized layer (not shown) is formed on the passivation layer120, the color filter array122can be formed on the planarized layer. Each color filter is formed in a corresponding unit pixel for transmitting only a color with a predetermined wavelength band among a plurality of waves in the incident light. Herein, the color filter array122uses an exemplary dyed photoresist or a photoresist containing pogment.

While forming the color filter array122, boundaries between the color filters are overlapped each other so as to form micro-steps therebetween. In order to form microlenses, however, an underlying layer on which microlenses will be formed should be planarized. Thus, an over coating layer (OCL)124is formed on the color filter array122for providing a planarized surface by using the photoresist material.

Afterward, a microlens layer is formed on the OCL124by using a method such as a spin on coating. Thereafter, the microlens layer is patterned into a predetermined configuration by using a predetermined mask, thereby forming a rectangular microlens correspondent to each unit pixel.

Finally, a thermal flow process is carried out to convert the rectangular microlenses to dome-typed microlenses128, as shown inFIG. 1.

In the CMOS image sensor, as the dome-typed microlenses128are wider and wider, much more lights are concentrated in the photodiodes114to enhance a photosensitivity. However, as the dome-typed microlenses128are wider, it causes a problem that there may be happened a bridge phenomenon (‘A’) between the adjacent microlenses128during the thermal flow process. That is, according to the conventional method for manufacturing the CMOS image sensor having the microlenses therein, overflowed substances are collected between adjacent microlenses128during the flow process so that end portions of the dome-typed microlenses128cling together. Accordingly, such a bridge phenomenon (‘A’) incurs a poor photosensitivity of the CMOS image sensor. Moreover, since the dome-typed microlenses128are not aligned uniformly within an area of a corresponding unit pixel, it deteriorates an optical property in the long run.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide a method for manufacturing a complementary metal oxide semiconductor (CMOS) image sensor having microlenses therein with an enhanced photosensitivity and an optical property by introducing openings between the microlenses.

In accordance with a first aspect of the present invention, there is provided a method for manufacturing a complementary metal oxide semiconductor (CMOS) image sensor having microlenses therein, the method including the steps of: a) preparing a semiconductor substrate including isolation regions and photodiodes therein obtained by a predetermined process; b) forming an interlayer dielectric (ILD), metal interconnections and a passivation layer formed on the semiconductor substrate in sequence; c) forming a color filter array having a plurality of color filters on the passivation layer; d) forming an over-coating layer (OCL) on the color filter array by using a positive photoresist; e) forming openings in the OCL by patterning the OCL by using a binary mask, wherein the binary mask has coated portions and uncoated portions, the uncoated portions being disposed above boundaries between the color filters; and f) forming dome-typed microlenses on a patterned OCL.

In accordance with a second aspect of the present invention, there is provided a method for manufacturing a complementary metal oxide semiconductor (CMOS) image sensor having microlenses therein, the method including the steps of: a) preparing a semiconductor substrate including isolation regions and photodiodes therein obtained by a predetermined process; b) forming an ILD, metal interconnections and a passivation layer formed on the semiconductor substrate in sequence; c) forming a color filter array having a plurality of color filters on the passivation layer; d) forming an OCL on the color filter array by using a negative photoresist; e) forming openings in the OCL by patterning the OCL by using a binary mask, wherein the binary mask has coated portions and uncoated portions, the coated portions being disposed above boundaries between the color filters; and f) forming dome-typed microlenses on a patterned OCL.

In accordance with a third aspect of the present invention, there is provided a method for manufacturing a complementary metal oxide semiconductor (CMOS) image sensor having microlenses therein, the method including the steps of: a) preparing a semiconductor substrate including isolation regions and photodiodes therein obtained by a predetermined process; b) forming an ILD, metal interconnections and a passivation layer formed on the semiconductor substrate in sequence; c) forming a color filter array having a plurality of color filters on the passivation layer; d) forming an OCL on the color filter array by using a negative photoresist; e) forming openings in the OCL by patterning the OCL by using a phase shifted mask (PSM), wherein the PSM has a 0° phase and a 180° phase, boundaries between the 0° phase and the 180° phase being disposed above boundaries between the color filters; and f) forming dome-typed microlenses on a patterned OCL.

In accordance with a fourth aspect of the present invention, there is provided a method for manufacturing a complementary metal oxide semiconductor (CMOS) image sensor having microlenses therein, the method including the steps of: a) preparing a semiconductor substrate including isolation regions and photodiodes therein obtained by a predetermined process; b) forming an ILD, metal interconnections and a passivation layer formed on the semiconductor substrate in sequence; c) forming a first OCL, color filters, a second OCL and a third OCL on the passivation layer sequentially; d) patterning the third OCL into a preset configuration, thereby forming openings and a patterned third OCL; and e) forming dome-typed microlenses by carrying out a flow process.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

There are provided inFIGS. 2 to 6cross sectional views and a plane view setting forth a method for manufacturing a complementary metal oxide semiconductor (CMOS) image sensor in accordance with preferred embodiments of the present invention.

Referring toFIGS. 2A to 2D, there are shown cross sectional views setting forth a method for manufacturing a CMOS image sensor having microlenses therein in accordance with a first preferred embodiment of the present invention.

InFIG. 2A, a first inventive method for manufacturing the CMOS image sensor begins with preparing a semiconductor substrate210obtained by a predetermined process. Isolation regions212are formed in the semiconductor substrate210, thereby defining an active region and a field region. In each unit pixel, there is formed a corresponding photodiode214for converting an incident light to photocharges. For the sake of convenience, transistors required for the unit pixel are not depicted in the drawings.

After preparing the semiconductor substrate210, an interlayer dielectric (ILD)216is formed on the semiconductor substrate210. Thereafter, metal interconnections218are formed on predetermined locations of the ILD216in consideration of underlying photodiodes214so that the incident light projected on the photodiodes214is not shielded by the existence of the metal interconnections218.

Following the formation of the metal interconnections218, a passivation layer220is formed over the resultant structure including the metal interconnections218for protecting a device from moisture and a scratch during post processes.

Subsequently, a color filter array222having three kinds of color filters is formed for transmitting only colors with predetermined wavelength bands among a plurality of waves in the incident light. Herein, the color filter array222is generally formed by using a dyed photoresist or a photoresist containing pogment, of which boundaries are overlapped each other so as to form micro-steps therebetween. In order to form microlenses228A, however, an underlying layer on which the microlenses228A will be formed should be planarized. Thus, an over-coating layer (OCL)224is formed on the color filter array222by using a positive photoresist correspondent to a post binary mask, for providing a planarized surface.

Thereafter, the mask226is prepared by making use of a conventional binary mask having uncoated portions226A and coated portions226B, wherein the uncoated portions226A are disposed above boundaries of the color filters. The coated portions226B are situated above the color filters which are coated with chromium (Cr). Herein, the uncoated portions226A have widths (d1) of less than a maximum resolution and preferably, the widths of the uncoated portions226A are less than about 0.2 μm in the first preferred embodiment of the present invention. Since the mask226has the uncoated portions226A, it is possible to adjust critical dimensions (CD) of openings205and depths of the openings205by controlling the dose amount.

Afterward, referring toFIG. 2B, since the OCL224uses the positive photoresist, the OCL224under the uncoated portions226A of the mask226is patterned into a predetermined shape and the OCL224under the coated portions226B is left intact on the contrary, thereby forming the openings205and a patterned OCL224A. Meanwhile, it is not necessary to form the wide and the deep openings205for preventing a bridge phenomenon during a post flow process. Thus, it is sufficient to form the small openings205having the widths less than the maximum resolution for preventing a bridge phenomenon. That is, in the first preferred embodiment, the openings205can be formed with the widths in the range of about 0.1 μm to about 0.2 μm by controlling the dose amount. After formation of the openings205, a curing process is carried out for hardening the patterned OCL224A.

Subsequently, referring toFIG. 2C, a microlens layer is formed on the patterned OCL224A and the openings205by employing a material such as a silicon oxide-based photoresist with a high optical transmittance property. Then the microlens layer is patterned into a predetermined configuration so as to form rectangular microlenses228. It is noted that the rectangular microlens228should be formed with a predetermined width in consideration of a post flow process. That is, the width of the rectangular microlens226should be smaller than the width of the patterned OCL224A between the openings205.

Finally, referring toFIG. 2D, the flow process is carried out, thereby forming dome-typed microlenses228A. Herein, overflowed substances215detached from the rectangular microlenses228during the flow process are collected in the openings205, whereby a bridge phenomenon between the adjacent microlenses228A are effectively prevented. Moreover, since there is no bridge phenomenon, it is possible to enlarge the microlenses as wide as possible so that a photosensitivity of the CMOS image sensor can be enhanced without increasing a manufacturing cost because of using the conventional binary mask as the mask226.

Referring toFIGS. 3A to 3D, there are provided cross sectional views setting forth a method for manufacturing a CMOS image sensor having microlenses therein in accordance with a second preferred embodiment of the present invention.

InFIG. 3A, a second method for manufacturing the CMOS image sensor begins with preparing a semiconductor substrate310obtained by a predetermined process. Since the processes for forming isolation regions312, photodiodes314, an ILD316, metal interconnections318, a passivation layer320and color filter array322are same to those of the first embodiment, further description will be abbreviated herein.

After carrying out above processes, an OCL324of a negative photoresist is formed on the color filter array322for providing a planarized surface where microlenses will be formed. Thereafter, a mask326is prepared by making use of a conventional binary mask having coated portions326A and uncoated portions326B therein, wherein the coated portions326A are disposed above boundaries between the color filters322and the uncoated portions326B are situated above the color filters.

Subsequently, referring toFIG. 3B, the OCL324is patterned into a predetermined configuration by using the mask326. In detail, since the OCL324uses the negative photoresist in the second embodiment, portions of the OCL324under the coated portions326A of the mask326are patterned and the other portions of the OCL324under the uncoated portions326B are left intact, thereby forming openings305and a patterned OCL324A. After forming the openings305, a curing process is carried out for hardening the patterned OCL324A.

Following the formation of the openings305, referring toFIG. 3C, a microlens layer is formed on the patterned OCL324A and the openings305by employing a silicon oxide-based photoresist and is patterned into a predetermined configuration so as to form rectangular microlenses328. It is noted that the rectangular microlens328should be formed with a predetermined width in consideration of a post flow process. That is, the width of the rectangular microlens328should be smaller than the width of the patterned OCL324between the openings305.

Finally, referring toFIG. 3D, the flow process is carried out, thereby forming dome-typed microlenses328A. Herein, overflowed substances315detached from the rectangular microlenses328during the flow process are collected in the openings305, whereby a bridge phenomenon between the adjacent microlenses328A are effectively prevented like the first embodiment.

Referring toFIGS. 4A to 4D, there are provided cross sectional views setting forth a method for manufacturing a CMOS image sensor having microlenses therein in accordance with a third preferred embodiment of the present invention.

In the third preferred embodiment of the present invention, there is used a phase shifting mask (PSM) instead of the conventional binary mask in order to increase resolution. In general, the light passing through the PSM has 0° phase or 180° phase so that there is happened a destructive interference between 0° phase and 180° phase, i.e., zero light intensity, thereby improving resolution and depth of focus (DOF) in optical lithography.

InFIG. 4A, a third method for manufacturing the CMOS image sensor begins with preparing a semiconductor substrate410obtained by a predetermined process. Since the processes for forming isolation regions412, photodiodes414, an ILD416, metal interconnections418, a passivation layer420and a color filter array422are same to those of the first and the second embodiments, further descriptions will be abbreviated herein.

After carrying out above processes, an OCL424is formed on the color filter array422for providing a planarized layer where microlenses will be formed. Herein, the OCL424uses a negative photoresist.

Subsequently, referring toFIG. 4B, the OCL424is patterned into a predetermined configuration by using the PSM426. That is, since light intensity is about zero at around boundaries of 0° phase and 180° phase, portions of the OCL424under the boundaries are patterned and the other portions of the OCL424are left intact so that openings405and a patterned OCL424A are formed. After forming the openings405, a curing process is carried out for hardening the patterned OCL424. The third embodiment employs the PSM426so as to form much more delicate openings405with the width in the range of about 0.03 μm to about 0.1 μm, thereby maximizing the width of the microlens in comparison with the first and the second embodiments making use of the binary mask.

Following the formation of the openings405, referring toFIG. 4C, a microlens layer is formed on the patterned OCL424and the openings405by employing a material such as a silicon oxide-based photoresist and is patterned into a predetermined configuration so as to form rectangular microlenses428. It is noted that the rectangular microlens428should be formed with a predetermined width in consideration of a post flow process. That is, the width of the rectangular microlens428should be smaller than the width of the patterned OCL424A between the openings405.

Finally, referring toFIG. 4D, the flow process is carried out so as to form dome-typed microlenses428A. Herein, overflowed substances415detached from the rectangular microlenses428produced during the flow process are collected in the openings405, whereby a bridge phenomenon between the adjacent microlenses428A are effectively prevented.

Referring toFIGS. 5A to 5E, there are provided cross sectional views setting forth a method for manufacturing a CMOS image sensor having microlenses therein in accordance with a fourth preferred embodiment of the present invention.

InFIG. 5A, the fourth method for manufacturing the CMOS image sensor begins with preparing a semiconductor substrate510obtained by a predetermined process. Then, since the processes for forming isolation regions512, photodiodes514, an ILD516, metal interconnections518and a passivation layer520are same to those of the first, the second and the third embodiments, further descriptions are abbreviated herein. Furthermore, MOS transistors required in the CMOS image sensor are not depicted in the drawings for the sake of convenience.

After carrying out the above processes, a first OCL521such as a photoresist material is formed on the passivation layer520with the thickness of about 6,500 Å, for providing a planarized surface where a color filter array522will be formed.

Thereafter, the color filter array522is formed on a top face of the first OCL521. In the fourth preferred embodiment, since the color filter array522is formed on the planarized layer, i.e., the first OCL521, it is possible to form the color filter array522uniformly in comparison with the first, the second and the third embodiments.

Following the formation of the color filter array522, a curing process is carried out for about three minutes at about 220° C., in order to prevent an inter-reaction and a chemical attack which may be happened between materials in the color filter array522.

Thereafter, a second OCL523is formed on the color filter array522with the thickness of about 5,000 Å in order to overcome a problem of the steps formed between boundaries of the color filters and to provide a planarized surface where a third OCL will be formed. Afterward, a third OCL is formed with the thickness ranging from about 1,400 Å to about 1,600 Å on the second OCL523and then, is patterned into a predetermined configuration by using a predetermined mask such as a binary mask, a PSM or the like, thereby forming openings505and a patterned third OCL524. It is noted that the deposition thickness of the third OCL is determined by considering the depths of the openings505for preventing the bridge phenomenon between adjacent microlenses. Herein, the openings505have widths of about 0.4 μm to about 0.6 μm. In addition, the widths of the openings505are smaller than those of the patterned third OCL524in consideration of forming microlenses thereon, as shown inFIG. 5A.

After forming the openings505, referring toFIG. 5B, a microlens layer528is formed over the resultant structure with the thickness in the range of about 5,500 Å to about 7,500 Å including the patterned third OCL524and the openings505. Herein, the microlens layer528employs a material such as silicon oxide-based photoresist with a high optical transmittance.

Thereafter, referring toFIG. 5C, the microlens layer528is patterned into a predetermined configuration, thereby forming rectangular microlenses528A on the patterned third OCL524, wherein the width of the rectangular microlens528A is relatively smaller than the width of the patterned third OCL524between the openings505in consideration of a post flow process. In the fourth embodiment, since there is the second OCL523beneath the third OCL, the color filter array522is not damaged during the formation of the openings505because the patterning process for forming the openings505is carried out till the top face of the second OCL523is exposed. Furthermore, it is possible to form each opening505with a uniform depth.

Subsequently, referring toFIG. 5D, a flow process is carried out in a stepper through a blank bleaching for converting the rectangular microlenses528A to dome-typed microlenses528B. During the blank bleaching, photo active compound (PAC) in the rectangular microlenses528A is dissolved by degrees, thereby decreasing coherent forces thereamong gradually. Here, the blank beaching process is carried out for about five minutes at about 150° C. In particular, a thermal process after the flow process can promote the flow process more and more.

After carrying out the flow process, there are formed the dome-typed microlenses528B as shown inFIG. 5E. During the flow process, overflowed substances515are collected in the openings505so that the bridge phenomenon between the adjacent microlenses is effectively prevented. Moreover, since the dome-typed microlenses528B are formed within the area of the patterned third OCL524, the dome-type microlenses528B are uniformly formed not being lopsided to one side of the patterned third OCL527.

Following the flow process, a curing process is carried out for about 5 minutes at about 200° C., for hardening the dome-typed microlenses528B.

Referring toFIG. 6, there is provided a schematic plane view setting forth an arrangement of each element in a unit pixel array of the CMOS image sensor in accordance with the fourth preferred embodiment.

InFIG. 6, it is easily understood that each element, i.e., each layer, is well aligned in the unit pixel array not being lopsided to one side thereof. In detail, the first OCL521has the same size to the second OCL523because the first and the second OCLs521,523are formed by using the same mask (not shown), wherein the color filter array522is formed vertically between the first OCL521and the second OCL523as described above. The color filter array522is disposed within the area of the first and the second OCLs521,523. Furthermore, the patterned third OCL524of an octagonal shape similar to the dome-typed microlenses528B is formed within the area of a corresponding color filter. In addition, the dome-typed microlenses528B are formed within the area of the patterned third OCL524. Accordingly, the fourth preferred embodiment provides an advantage that it is not difficult to measure the critical dimension (CD) of the dome-type microlenses528B because they are aligned only within the area of the patterned third OCL524.

As described above, in accordance with the preferred embodiments of the present invention, there are employed the openings in predetermined locations of the underlying OCL on which the microlenses will be formed so that it is possible to prevent the bridge phenomenon between the adjacent microlenses during the flow process, to thereby maximize the size of the microlens and reduce a chip size. Accordingly, much more lights passing through the microlenses are concentrated in the photodiode so that the CMOS image sensor has a good photosensitivity.

In addition, since the microlenses are formed within the area of the patterned OCL, the microlens has the uniform width and height. Therefore, each focal length of the light passing through each microlens becomes uniform, whereby increasing focused property to raise the image intensity.

While the present invention has been described with respect to the particular embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the scope of the invention as defined in the following claims.