Image sensor and method of fabricating the same

An image sensor includes a semiconductor substrate, a photodiode formed in the semiconductor substrate, a first impurity region formed in the semiconductor substrate spaced from the photodiode, a second impurity region formed in the semiconductor substrate spaced from the first impurity region, a first gate formed over the semiconductor substrate between the photodiode and the first impurity region, a second gate formed over the semiconductor substrate between the first impurity region and the second impurity region, a spacer formed over the fourth impurity region and a first sidewall of the second gate, and an insulating film formed over the photodiode, the first gate, the first impurity region and a second sidewall and a portion of the uppermost surface of the second gate.

The present application claims priority under 35 U.S.C. §119 to Korean Patent Application No. 10-2007-0118338 (filed on Nov. 20, 2008), which is hereby incorporated by reference in its entirety.

BACKGROUND

An image sensor is a semiconductor device which converts an optical image into an electrical signal, and is largely divided into a charge coupled device (CCD) and a complementary metal oxide silicon (CMOS) image sensor (CIS). The CMOS image sensor has a photodiode and a MOS transistor formed within a unit pixel and is adapted to implement an image by sequentially detect electrical signals of each unit pixel using a switching method.

SUMMARY

Embodiments relate to an image sensor and a method of fabricating the same which can maximize reliability of the image sensor by minimizing the occurrence of defects caused by etching on surfaces of a photodiode and an impurity region of the image sensor.

Embodiments relate to an image sensor that may include at least one of the following: a semiconductor substrate having a photodiode including a first impurity region and a second impurity region, a first gate formed on and/or over the semiconductor substrate between the photodiode and the first impurity region, a second gate formed on and/or over the semiconductor substrate between the first impurity region and the second impurity region, a spacer formed on and/or over a sidewall of the second gate in the second impurity region, and an insulating film formed on and/or over the photodiode region, the first gate, and the first impurity region.

Embodiments relate to a method of fabricating an image sensor that may include at least one of the following: forming a first gate and a second gate on and/or over a semiconductor substrate; and then forming a photodiode including a first impurity region and a second impurity region in the semiconductor substrate on and/or over which the first and second gates are formed; and then forming a first oxide film on and/or over the semiconductor substrate on and/or over which the first and second gates are formed, and then forming a first nitride film pattern on and/or over the first oxide film of the second impurity region; and then forming a second oxide film on and/or over the first oxide film on and/or over which the first nitride film pattern is formed; and then forming a first oxide film pattern and a second oxide film pattern on the photodiode, the first gate, and the first impurity region by performing a first etch process, and then forming a spacer on and/or over a sidewall of the second gate on the second impurity region.

Embodiments relate to a method of fabricating an image sensor that may include at least one of the following: simultaneously forming a first gate and a second gate over a semiconductor substrate; and then forming a photodiode including a first impurity region and a second impurity region in the semiconductor substrate; and then simultaneously forming a third impurity region formed in the semiconductor substrate spaced from the photodiode and a fourth impurity region formed in the semiconductor substrate spaced from the third impurity region; and then sequentially forming a first oxide film and a first nitride film over the semiconductor substrate including the first and second gates and the third and fourth impurity regions; and then forming a first nitride film pattern over a portion of the first oxide film formed over the fourth impurity region, a first sidewall of the second gate and a portion of the uppermost surface of the second gate; and then forming a second oxide film over a remaining portion of the first oxide film; and then simultaneously forming a first oxide film pattern and a second oxide film pattern over the photodiode, the first gate, the third impurity region, a second sidewall of the second gate and a portion of the uppermost surface of the second gate while also forming a spacer over the fourth impurity region and on the first sidewall of the second gate.

Embodiments relate to an apparatus that may include at least one of the following: a semiconductor substrate; a photodiode formed in the semiconductor substrate; a first impurity region formed in the semiconductor substrate spaced from the photodiode; a second impurity region formed in the semiconductor substrate spaced from the first impurity region; a first gate formed over the semiconductor substrate between the photodiode and the first impurity region; a second gate formed over the semiconductor substrate between the first impurity region and the second impurity region; a spacer formed over the fourth impurity region and a first sidewall of the second gate; and an insulating film formed over the photodiode, the first gate, the first impurity region and a second sidewall and a portion of the uppermost surface of the second gate.

Embodiments relate to an image sensor that may include at least one of the following: a semiconductor substrate; a photodiode including a first impurity region and a second impurity region formed in the semiconductor substrate; a third impurity region formed in the semiconductor substrate spaced from the first impurity region and the second impurity region; a fourth impurity region formed in the semiconductor substrate spaced from the third impurity region; a first gate formed over the semiconductor substrate between the photodiode and the third impurity region; a second gate formed over the semiconductor substrate between the third impurity region and the fourth impurity region; a spacer formed over the fourth impurity region and a first sidewall of the second gate; and an insulating film formed over the photodiode, the first gate, the third impurity region and a second sidewall and a portion of the uppermost surface of the second gate.

DESCRIPTION

Although reference is made to the example drawings of a structure regarding a CMOS image sensor (CIS), embodiments are not limited to the CMOS image sensor, but can be applied to all image sensors including a CCD image sensor.

As illustrated in exampleFIG. 1, first gate25and second gate26are formed on and/or over semiconductor substrate10in which isolation film5is formed. Isolation film5can be formed by forming a trench in semiconductor substrate10and gap-filling the trench with insulating material. Semiconductor substrate10can be a high-concentration p++type silicon substrate and have a low-concentration p-type epitaxial layer formed thereon and/or thereover. This can increase the depletion region of a photodiode significantly and deeply due to the existence of the low-concentration p-type epitaxial layer, and therefore, can increase the ability of the photodiode for collecting optical charges. When the high-concentration++type substrate is provided under the p-type epitaxial layer, optical charges are recombined before the optical charges diffuse into neighboring unit pixels. Accordingly, random diffusion of the optical charges can be reduced and a change in the transfer function of the optical charges can be decreased.

First gate25is formed of first oxide film pattern21and first polysilicon pattern23. Second gate26is formed of second oxide film pattern22and second polysilicon pattern24. First gate25and second gate26can be formed at the same time by forming a first oxide film and a first polysilicon film on and/or over semiconductor substrate10and then performing a first etching process. First gate25can become a transfer gate and second gate26can become a reset gate. While embodiments illustrate that first gate25and second gate26are formed from polysilicon, it is not limited thereto. For example, first gate25and second gate26can be formed of a metal silicide film.

As illustrated in exampleFIG. 2, first photoresist pattern19is formed on and/or over semiconductor substrate10including isolation film5, first gate25and second gate26. A first ion implantation process and a second ion implantation process are then performed to thereby form photodiode14. Photodiode14can be formed to include first impurity region12is formed by performing the first ion implantation process using first photoresist pattern19as a mask and second impurity region13is then formed by performing the second ion implantation process. First impurity region12can be formed by injecting an n-type impurity and second impurity region13can be formed by injecting a p-type impurity. First impurity region12, second impurity region13and semiconductor substrate10come in contact with one another and may operate as a PNP photodiode.

As illustrated in exampleFIG. 3, after first photoresist pattern19is removed, second photoresist pattern29is formed on and/or over semiconductor substrate10including isolation film5, photodiode14and first gate25. A third ion implantation process is then carried out in order to form third impurity region16in semiconductor substrate10between first gate25and second gate26and fourth impurity region18in semiconductor substrate10. Third impurity region16and fourth impurity region18can be formed by injecting an n-type impurity. Third impurity region16can operate as a floating diffusion region. Optical charges generated from photodiode14are transmitted to third impurity region16by first gate25and then transmitted to a circuit unit. Second gate26can discharge the optical charges stored in third impurity region16in order to detect a next signal.

As illustrated in exampleFIG. 5, first nitride film pattern34is formed by performing a second etch process on nitride film32. First nitride film pattern34is formed on and/or over a portion of second oxide film31formed on and/or over a sidewall and a portion of the uppermost surface of second gate26and also fourth impurity region18. First nitride film pattern34is formed by forming third photoresist pattern39on and/or over the portion of second oxide film31formed on and/or over the sidewall and the portion of the uppermost surface of second gate26and also fourth impurity region18and then performing a second etching process removing a portion of nitride film32formed on and/or over photodiode14, first gate25and third impurity region16can be removed. The second etch process can be performed using a dry etch or wet etch process. Removal of a portion of nitride film32formed on and/or over isolation film5, photodiode14, first gate25, third impurity region16and a sidewall and a portion of the uppermost surface of second gate26is to facilitate the subsequent formation of a contact in third impurity region16and also prevent the a decrease in sensitivity of photodiode14due to nitride film32.

As illustrated in exampleFIG. 6, after third photoresist pattern39is removed, third oxide film36is formed on and/or over second oxide film31and first nitride film pattern34. Accordingly, an oxide-nitride-oxide (ONO) stacked film that includes second oxide film31, first nitride film pattern34, and third oxide film36is formed on and/or over fourth impurity region18. Second oxide film31and third oxide film36are stacked on and/or over photodiode14, first gate25and third impurity region16a sidewall and a portion of the uppermost surface of second gate26.

As illustrated in exampleFIG. 7, a third etching process is performed in order to form spacer40on a sidewall of second gate26and fourth impurity region18. Spacer40can be formed by forming a fourth photoresist pattern49on and/or over isolation film5, photodiode14, first gate25, third impurity region16and the other sidewall and the other portion of the uppermost surface of second gate26and then performing the third etch process. The third etch process is performed using an anisotropic etch process. Through the third etch process, fifth oxide film pattern51, sixth oxide film pattern56and spacer40are formed at the same time. Spacer40can include third oxide film pattern41, second nitride film pattern44and fourth oxide film pattern46formed on and/or over the sidewall of second gate26and fourth impurity region18through the third etch process. Thus, only fifth oxide film pattern51and sixth oxide film pattern56remain on and/or over isolation film5, photodiode14, first gate25, third impurity region16and the other sidewall and the other portion of the uppermost surface of second gate26. Since fourth photoresist pattern49is formed over isolation film5, photodiode14, first gate25, third impurity region16and the other sidewall and the other portion of the uppermost surface of second gate26, photodiode14and third impurity region16are not etched so that damage thereto due to etching can be prevented. Particularly, fourth photoresist pattern49prevents damage to photodiode14and third impurity region16during etching that would otherwise cause the dark characteristic of the semiconductor device is influenced, thereby degrading the device. In accordance with embodiments, fourth photoresist pattern49is formed on and/or over photodiode14and third impurity region16so that such damage thereto can be prevented.

As illustrated in exampleFIG. 8, fourth photoresist pattern49is removed. Accordingly, fifth oxide film pattern51and sixth oxide film pattern56are formed on and/or over semiconductor substrate10including isolation film5, photodiode14, first gate25and a sidewall and portion of the uppermost surface of second gate26. Spacer40can be formed only on and/or over the other sidewall of second gate26and fourth impurity region18. A metal line layer, a color filter array, and one or more corresponding micro lenses can be formed on and/or over semiconductor substrate10. Such an image sensor and the method of fabricating the same in accordance with embodiments can prevent damage due to etching on the photodiode and a floating diffusion region and therefore prevent degradation of a device due to a dark characteristic.

The image sensor in accordance with an embodiment includes semiconductor substrate10in which photodiode14including third impurity region16and fourth impurity region18are formed. First gate25includes first oxide film pattern21and first polysilicon pattern23and is formed on and/or over semiconductor substrate10between photodiode14and third impurity region16. Second gate26includes second oxide film pattern22and second polysilicon pattern24and is formed on and/or over semiconductor substrate10between third impurity region16and fourth impurity region18. Spacer40includes third oxide film pattern41, nitride film pattern44and fourth oxide film pattern46and is formed on and/or over the other sidewall of second gate26and fourth impurity region18. Fifth oxide film pattern51and sixth oxide film pattern56are formed on and/or over at least isolation film5, photodiode14, first gate25, third impurity region16and the other sidewall and a portion of the uppermost surface of second gate26. Third impurity region16can serve as a floating diffusion region.