True color image by modified microlens array

An image sensor array includes a substrate having at least three image sensors located therein. The image sensor array also includes a blue filter positioned proximate to the first image sensor; a green filter proximate to the second image sensor; and a red filter proximate to the third image sensor A first microlens is positionally arranged with the blue filter and the first image sensor; a second microlens is positionally arranged with the green filter and the second image sensor; and a third microlens is positionally arranged with the red filter and the third image sensor. The first microlens has a larger effective area than the second microlens, and the second microlens has a larger effective area than the third microlens.

BACKGROUND

The present disclosure relates generally to image sensor arrays and, more specifically, to an image sensor array utilizing a modified microlens array.

Image sensor arrays widely employ in various technologies, including charged coupling device (CCD) image sensors and complimentary metal-oxide-semiconductor (CMOS) image sensors. In general, CCD, CMOS, and other types of image sensor arrays transform a light pattern (i.e., an image) into an electric charge pattern. Image sensor arrays generally include polymer or dielectric microlenses. The microlenses are often arranged in a microlens array, with each microlens in the array being similarly sized and shaped.

In many applications, a selection of wavelengths/colors is received by the image sensor array. For example, red, green, and blue pixels (filtered image sensor elements) are often used in many imaging systems such as a digital camera. It is noted that different photo response sensitivities exist between the different colored pixels. This is inherently the case due to the different wavelengths of the different colors. In continuation of the present example, one pixel's sensitivity to blue light is less than another pixel's sensitivity to green light, which is less than yet another pixel's sensitivity to red light. It is desired to have these sensitivities (for blue, green, and red, in the present example) similar each other, thereby obtaining a more “true color” image.

Accordingly, what is needed in the art is an improved image sensor array, pixel, and method of creating same.

DETAILED DESCRIPTION

Referring toFIG. 1, one embodiment of a semiconductor chip100includes a substrate110and image sensors120formed therein. In the present embodiment, the substrate110is a silicon substrate, but in other embodiments the substrate may comprise such things as germanium or diamond. It is understood that front-side and back-side illumination image sensors can benefit from the present invention, with the substrate110appropriately configured. For the sake of further example, front-side illumination configuration will be further described.

The substrate110may also comprise a compound semiconductor such as silicon carbide, gallium arsenic, indium arsenide, and/or indium phosphide. The substrate110may comprise an alloy semiconductor such as silicon germanium, silicon germanium carbide, gallium arsenic phosphide, and/or gallium indium phosphide. The substrate110may include an epitaxial layer. For example, the substrate may have an epitaxial layer overlying a bulk semiconductor. Further, the substrate may be strained for performance enhancement. For example, the epitaxial layer may comprise semiconductor materials different from those of the bulk semiconductor such as a layer of silicon germanium overlying a bulk silicon, or a layer of silicon overlying a bulk silicon germanium formed by a process such as selective epitaxial growth (SEG). Furthermore, the substrate110may comprise a semiconductor-on-insulator (SOI) structure. For example, the substrate may include a buried oxide (BOX) layer formed by a process such as separation by implanted oxygen (SIMOX). The substrate110may comprise a p-type doped region and/or an n-type doped region. The doping may be implemented by a process such as ion implantation. The substrate110may comprise lateral isolation features to separate different devices formed on the substrate. In the present embodiment, the image sensors120are photodiodes diffused or otherwise formed in the substrate110and separated by shallow trench isolation (STI) regions125.

Aspects of the present disclosure are applicable and/or readily adaptable to image sensor arrays employing various types of devices, including charged coupling device (CCD) and complimentary metal-oxide-semiconductor (CMOS) image sensor applications (e.g., active-pixel sensors), among others. As such, the image sensors120may comprise conventional and/or future-developed image sensing devices.

The semiconductor chip100includes a passivation layer130. The passivation layer130may comprise silicon nitride (e.g., Si3N4), silicon oxynitride (e.g., SixNyOz), silicon oxide, silicon dioxide, and/or other materials. The passivation layer130may be substantially optically transparent, and may be formed by chemical vapor deposition (CVD), physical vapor deposition (PVD), atomic layer deposition (ALD), spin-on coating, and/or other processes. In one embodiment, the passivation layer130has a thickness ranging between about 1 μm and about 50 μm. The passivation layer130may further comprise a multilayer interconnect structure formed therein. The multilayer interconnect may include metal lines for lateral connections and via/contact features for vertical connections. The metal lines and via/contact features may be configured such that the image sensors120may not be blocked thereby from incident light. The passivation layer130may have a multilayer structure such as a layer having the multilayer interconnects embedded therein and a layer to protect the underlying interconnects and the substrate.

The semiconductor chip100includes a dielectric layer140. The dielectric layer140may comprise silicon nitride, silicon oxynitride, silicon oxide, silicon dioxide, and/or other materials. The dielectric layer140may also comprise a low-k dielectric layer having a dielectric constant less than or equal to about 3.9. The dielectric layer140may be formed by CVD, PVD, ALD, spin-on coating, and/or other processes. In furtherance of the present embodiment, the dielectric layer140includes a multilayer structure including a planarization layer, a color filter layer, and/or a spacer layer. The dielectric layer140may be formed by a method described above and may be substantially planar, possibly the result of chemical-mechanical-polishing (CMP). Different color filters may be positioned such that the incident light is directed thereon and there through. In one embodiment, such color-transparent layers may comprise a polymeric material (e.g., negative photoresist based on an acrylic polymer) or resin. The color filter layer may comprise negative photoresist based on an acrylic polymer including color pigments. The spacer layer is formed to adjust the distance between the overlying microlens array and the underlying image sensors120. In one embodiment, the dielectric layer140has a thickness ranging between about 0.2 μm and about 50 μm.

A layer of photoresist150is formed over the semiconductor chip100using a method such as spin-on coating. The layer of photoresist150may be pre-baked. The photoresist layer may then be exposed to a light source300through a photo mask200, wherein the photo mask200is specially designed according to the present disclosure. It is understood that in the present embodiment, microlenses are formed from the photoresist150. In other embodiments, one or more intermediate layers can be provided and patterned by the photoresist150, and these layer(s) can be used to form the microlenses.

Referring toFIG. 2, three different microlenses are formed, designated with the reference numeral155r(for red),155g(for green), and155b(for blue). It is understood that the drawings and present disclosure are simplified to better illustrate the various embodiments of the present invention. As shown in the figure, the three microlenses (collectively referenced155) have different effective areas, in the following order:effective area of microlens155b>microlens155g>microlens155r. Also, in the present embodiment, there is a gap160between the red microlens155rand the green microlens155g, and there is no gap165between the green microlens155gand the blue microlens155b. The gap160may prevent portions of the incident light from being accurately directed toward the underlying image sensor120. Various techniques can be used to obtain the different sized microlenses155, as discussed in greater detail below.

Referring toFIG. 3, in one embodiment, optical proximity correction (OPC) is applied to the mask200to make changes in the respective geometries of the microlenses155. In the present example, the mask200is shown having four areas identified as B, GI, G2, and R, which correspond to blue, green, green, and red pixels on the substrate100(FIGS. 1-2). Correspondingly, microlens images205,210,215, and220are provided to in the areas B, G1, G2, and R, respectively. The microlens images205,210, and220also correspond to the microlenses155b,155g, and155r, respectively, ofFIG. 2.

Referring also toFIG. 4, using OPC, features can be applied to one or more of the mask microlens images205-220to produce desired alterations to the microlenses155. The vertical axis shows a photo response. The horizontal axis shows the wavelength of the light being provided to the various pixels, including a blue band405, a green band410, and a red band420. For the sake of comparison, two conventional photo responses are shown, a first response430for a standard pixel element corresponding to the wavelength, and a second response440for a thin backend (backside illuminated) pixel element corresponding to the wavelength. As can be seen, the photo response for the various wavelengths are such that:
blue 405<green 410<red 420.

Referring again toFIG. 3, OPC features are applied to increase the size of the blue microlens image205in a direction towards the green microlens images210and215. In the drawing ofFIG. 3, the features are graphically represented as a larger dotted box. It is understood that different features, or different shaped features, can be used for OPC, as is well known in the art and as dependent on the photolithography equipment being used. As a result, the corresponding microlenses are closer to each other. For example, inFIG. 2, the microlenses155b,155gare next to each other without a gap165therebetween. Similarly, OPC features (or the lack thereof) are applied to decrease the size of the red microlens image220in a direction away from the green microlens images210and215. As a result, the corresponding microlenses are further from each other. Referring again to the example inFIG. 2, the microlenses155g,155rhave a gap160therebetween. It is understood that various degrees of OPC can be applied to produce different amounts of gaps (or lack thereof) to achieve a desired result.

Referring again toFIG. 4, in the present example, a resulting photo response450is provided by the modified microlens images205-220of the mask200. As can be seen, the photo response at the blue wavelength405is improved, and is closer to that of the photo response at the green wavelength410and red wavelength420.

Referring now toFIG. 5, in another embodiment, the layout of microlens images205,210,215, and220(FIG. 3) are specifically modified in size and shape to accommodate for the differences in photo responses405,410, and420. Specifically, a ratio of the photo responses for blue:green:red is measured to be about 5:8:12, as shown by the first response430. It is understood that a different ratio may be obtained for the second response440or other response, as so determined. Accordingly, the size ratio of the blue microlens image205: green microlens image210,215: red microlens image220is also set to 5:8:12. As a result, a near-linear photo response460is provided across all of the pixel elements.

Thus, several different embodiments have been shown for implementing different features of the present invention. In one embodiment, a method is provided for making an image sensor array. The method includes providing a substrate having first and second image sensors located therein and forming first and second filters proximate to the first and second image sensors, respectively. First and second microlenses are formed proximate to the first and second filters, respectively, such that the first microlens has a larger effective area than the second microlens.

In some embodiments, the method further includes providing the substrate with a third image sensor located therein and forming a third filter proximate to the third image sensor. A third microlens is formed proximate to the third filter, such that the second microlens has a larger effective area than the third microlens.

In some embodiments, the first, second and third filters are configured to transmit blue, green, and red light, respectively.

In some embodiments, the steps of forming the three microlenses include utilizing a mask with different sized first, second and third areas corresponding to the first, second, and third microlenses, respectively. In some embodiments, at least one of the steps of forming the three microlenses includes utilizing optical proximity correction differently on first, second and third mask areas corresponding to the first, second, and third microlenses, respectively

In another embodiment of the present invention, an image sensor array is provided. The image sensor array includes a substrate having a plurality of image sensors located therein and a microlens layer. The microlens layer includes a plurality of microlenses located over the substrate, each of the plurality of microlenses including a substantially convex portion substantially aligned over a corresponding one of the plurality of image sensors. At least two of the microlenses of the microlens layer have different effective areas.

In another embodiment of the present invention, an image sensor array is provided. The image sensor array includes a substrate having at least three image sensors located therein. The image sensor array also includes a blue filter positioned proximate to the first image sensor; a green filter proximate to the second image sensor; and a red filter proximate to the third image sensor A first microlens is positionally arranged with the blue filter and the first image sensor; a second microlens is positionally arranged with the green filter and the second image sensor; and a third microlens is positionally arranged with the red filter and the third image sensor. The first microlens has a larger effective area than the second microlens, and the second microlens has a larger effective area than the third microlens.

In some embodiments, the three microlenses are formed utilizing a mask with different sized first, second and third areas corresponding to the first, second, and third microlenses, respectively.

In some embodiments, the three microlenses are formed utilizing optical proximity correction differently on at least one of the first, second and third mask areas corresponding to the first, second, and third microlenses, respectively.

In some embodiments, there is a gap between the second and third microlenses and no gap between the first and second microlenses.

The foregoing has outlined features of several embodiments so that those skilled in the art may better understand the detailed description that follows. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. For example, the microlenses155g,155r,155bare differently sized, as compared to each other, by using an advance ridge structure, as is disclosed in U.S. Ser. No. 11/064,452, which is hereby incorporated by reference. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions and alterations herein without departing from the spirit and scope of the present disclosure.