TW201501280A - Photodiode structure - Google Patents

Abstract

A photodiode structure includes a first-type substrate, a second-type doped well and a second-type doped region is formed in the first-type substrate. An isolation layers is disposed on the peripheral of the second-type doped well without contact in between. The second-type doped region is formed in the second-type doped well and is extended on the surface of the second-type doped well. A protective layer covers the first-type substrate. A contact conductor thread through the protective layer which includes a contact layer and a conductive strip. The contact layer is formed on the opposite side of the conductive strip and in contact with and connected to the second-type doped region.

Description

Photodiode

The present invention relates to an image sensing element, and more particularly to an improvement of a photodiode image sensing element.

A complementary metal oxide semiconductor image sensor mainly utilizes an active pixel matrix or an image sensor cell array including photodiode elements, and the two arrays can image an incident image. Light energy is converted into digital data. A conventional image sensor cell includes a photodiode that senses light intensity, and an adjacent transistor.

Other additional components associated with the peripheral region of the transistor include a control and signal processing circuit and peripheral logic circuitry to form a photodiode-type CMOS image sensor. Therefore, in order to reduce the manufacturing cost and the complexity of the process, the circuit around the diode complementary MOS image sensing element and the transistor of the image sensing element in the main area are formed in the same process step.

However, the above methods often cause the influence of poor transistor electrical properties of the image sensing elements in the main light sensing region. More specifically. At the interface between the semiconductor and the oxide layer, due to the Si dangling bond defect, surface recombination centers are generated to reduce the minority carrier life cycle of the device and cause leakage current. When a self-aligned telluride (Silicide, Self-aligned Silicidation) is formed in the gate and drain/source regions of a peripheral circuit (for example, a CMOS logic circuit), the self-aligned germanide is also formed in the photodiode. The surface of the component will deepen this defect. In this way, the image sensing element will generate unnecessary dark current (dark Current), in turn, reduces the ratio of signal/to-noise ratio (S/N or SNR), affecting the quality of the sensor device.

With the advancement of semiconductor process technology, the complementary metal oxide semiconductor (COMS, Complementary Metal Oxide Semiconductor) component process technology has become more and more obvious in terms of component reduction and high precision, and is used as insulation between components. The shallow trench isolation process (STI, Shallow Trench Isolation) has become more and more important. In conventional photodiode elements, defects located at the interface between the isolation layer and the active region surrounding the photodiode element may cause dark current, while being located around or adjacent to the side surface of the photodiode. The dangling button also causes dark current. That is to say, in the absence of incident light, around the interface portion of the photodiode, dangling bonds conforming to the grain boundary of the surface physics theory, when the charge carriers move at the interface, some carriers It will be randomly captured and then released in this order, resulting in dark currents resulting in reduced image quality and dynamic range of the image captured by the image sensor.

In order to solve the problem that the isolation layer of the conventional photodiode element is caused by the high stress causing the leakage current of the adjacent N-type well region, the present invention provides a photodiode by layout. The design is such that the isolation layer is separated from the well area by a certain distance.

A photodiode includes a first type substrate, a second type doping well disposed in the first type substrate, and a second type doping region formed in the second type doping well. The first type substrate has an isolation region as an isolation element of the photodiode, and the isolation region does not contact the second type doping well. Wherein, a protective layer is formed on the upper surface of the first type substrate, and the protective layer covers the second type doping well and the second type doping area. A contact conductor includes a contact layer and a conductive strip, and a contact layer is formed at a lower end of the conductive strip. The contact guiding system penetrates the protective layer and is in contact with and electrically connected to the second type doped region through the contact layer at the lower end.

Compared with the prior art, in the photodiode of the present invention, the isolation region is not in contact with the second type doping well to avoid dark current interference which may be caused by interface defects between the isolation layer and the active region.

The above described objects, features, and advantages of the present invention will become more apparent and understood.

100‧‧‧Photoelectric diode

102‧‧‧First type substrate

103‧‧‧Contact conductor

104‧‧‧Protective layer

105‧‧‧ upper surface

106‧‧‧Isolated area

107‧‧‧PN connection interface

109‧‧‧ Vacant Zone

118‧‧‧Type 2 doping well

119‧‧‧Second-type doped area

120‧‧‧Contact layer

121‧‧‧ Conductive strip

212‧‧‧ interval zone

213‧‧‧ Passivation layer

214‧‧‧Transparent conductive oxide layer

215‧‧‧Polysilicon layer

216‧‧‧electrode

1 is a top view of a photodiode according to an embodiment of the present invention; FIG. 2 is a cross-sectional view taken along line AA of FIG. 1 and illustrating a distribution of elements thereof; and FIG. 3 is a cross-sectional view of a photodiode according to an embodiment of the present invention; FIG. 4 is a schematic cross-sectional view showing a photodiode according to an embodiment of the present invention. FIG.

Please refer to Figure 1 and Figure 2. 1 is a top view of a photodiode according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view taken along line A-A of FIG. 1. The photodiode 100 of the present invention includes a first type substrate 102, a second type doping well 118, a second type doping region 119, a depletion region 109, a PN junction interface 107, an isolation region 106, a contact layer 120, and a contact conductor 103. And a protective layer 104. The first type substrate 102 has an upper surface 105 as a light incident surface. The second type doping well 118 is disposed in the first type substrate 102, and the first type substrate 102 and the second type doping well 118 adjacent to the junction area form a PN connection interface 107. A second type doping region 119 is formed in the second type doping well 118 and extends from the surface of the second type doping well 118 to be exposed on the surface of the second type doping well 118.

In one embodiment, the first type substrate 102 is a P-substrate and the second type doping well 118 is an N-type well. The second type doping region 119 is disposed on the surface of the second type doping well 118 as a relatively high concentration N-type doping region.

The above-mentioned depletion area 109 is an area included by a broken line in the figure, and the area is first The type substrate 102 is defined adjacent to the area around the PN junction interface 107 adjacent to the second type doping well 118.

The first type substrate 102 has an isolation region 106 therein as an isolation element of the photodiode 100 and does not contact the second type doping well 118. In detail, between the isolation region 106 and the second doping region 119 of the present invention, there is a spacer 212, which is a partial region of the coverage area of the depletion region 109, and the internal structure of the spacer 212 is The internal composition of the depletion zone 109 is the same. Therefore, in accordance with an embodiment of the present invention, a photodiode 100 is provided that isolates the isolation region 106 from the second doped region 119, that is, the isolation region 106 does not interact with the first type substrate 102 and the second type doping well. 118 is in contact with the PN connection interface 107 of the adjacent region, and the isolation region 106 forms a limitation of the side diffusion range of the depletion region 109. The isolation region 106 may be composed of a material selected from the group consisting of tantalum nitride or hafnium oxide, and the isolation layer formed by local oxidation (LOCOS), shallow trench isolation (STI), and field oxidation region (FOX). .

The upper surface 105 of the first type substrate 102 is formed with a protective layer 104 covering the second type doping well 118 and the second type doping area 119. The upper surface 105 of the first type substrate 102 is further formed with a contact conductor 103. The contact conductor 103 includes a contact layer 120 and a conductive strip 121. The contact layer 120 is formed at the other end of the conductive strip 121. When the contact conductor 103 penetrates the protective layer 104 and contacts the second type doping region 119, the contact layer 120 passing through the lower end of the conductive strip 121 is in contact with and electrically connected to the second type doping region 119.

Therefore, when the surface 105 of the second type doping well 118 absorbs photons, most of the free electron-hole pairs in the depletion region 109 begin to absorb the energy of the photons, and at the same time separate the electrons and holes from the electron-holes. And the current is generated. The isolation region 106 is used to define the current generated by the current generating region and is then guided to the CMOS circuit via the contact conductor 103 disposed on the second doping region 119.

Referring to FIG. 2, since the isolation region 106 and the second doping region 119 are separately disposed, a spacer is formed between the isolation region 106 and the second doping region 119. 212. In an embodiment, the spacer 212 may have a width in the range of 50 um or more. As such, the isolation region 106 is not in contact with the second doping region 119, and the isolation region 106 can be prevented from being etched, chemical mechanical polishing (CMP), low pressure chemical vapor deposition (LPCVD), etc. The damage of the structure and the mechanical stress in the structure cause defects such as dislocation, resulting in an increase in lattice leakage current adjacent to the second type doping well 118.

Please refer to FIG. 3, which is used to illustrate the formation of the spacer region of FIG. In an embodiment of the invention, a passivation layer 213 is disposed after the isolation region 106 is formed in the first type substrate 102 and before the ion implantation is performed. The passivation layer 213 is disposed on the spacer 212 and the isolation region 106 as a mask for subsequent ion implantation, preventing impurities of the ion cloth value from entering the isolation region 106 and the second type of dopant. A space 212 between the miscellaneous zones 119. In this way, the contamination and destruction of the ion cloth value impurities in the dielectric material can be reduced, and the leakage current between the isolation region 106 and the second type doping region 119 is generated.

Please refer to Figure 2. The present invention provides a photodiode 100 having a protective layer 104 formed on the upper surface 105 of the first substrate 102. The protective layer 104 covers the second doping well 118 and the second doping region 119. The contact conductor 103 includes a contact layer 120 and a conductive strip 121 formed on the other end of the conductive strip 121. When the contact conductor 103 penetrates the protective layer 104 and contacts the second type doping region 119, the contact layer 120 passing through the lower end of the conductive strip 121 is in contact with and electrically connected to the second type doping region 119.

The contact layer 120 is a metal silicide layer formed by a salicide (Self-Aligned Silicidation) process, and various types of metals including titanium (Ti), cobalt (Co), and nickel can be used. Ni), palladium (Pd) or platinum (Pt), and alloys such as titanium/tungsten, titanium/molybdenum, cobalt/tungsten or cobalt/molybdenum.

In order to reduce the metal telluride on the surface of the photodiode 100, it becomes a leakage source and reduces the surface recombination center phenomenon. In one embodiment, the present invention provides a photodiode 100. The size of the contact layer 120 is such that it does not extend beyond the area defined by the lower surface of the contact conductor 103. borrow The metal halide contact layer 120, which is not covered by the contact conductor 103, is removed by the removal of the surface of the photodiode 100, that is, the portion of the metal halide contact layer 120 extending from the vertical projection of the contact conductor 103 is removed to reduce the leakage current effect formed by the contact layer 120.

In addition, since the absorption depth of the incident light in the photodiode is related to the wavelength of the incident light, the shorter wavelength light is absorbed by the surface portion of the photodiode, and the longer wavelength light has a deeper absorption depth ( Absorption path). The photodiode complementary gold-oxygen half-image sensing element senses the spectrum with infrared light (700-800 nm) as the best, and the best quantum efficiency has a wavelength of 850 nm. The spectral response curve increases as the wavelength of the light increases. Because the long-wavelength photon penetration depth is deeper, the conversion efficiency is improved near the PN junction interface 107 (the internal electric field of the PN junction interface 107 can be efficiently disassembled to absorb the photons). When the wavelength of the light is a short wavelength, it means that the absorbed light falls on the surface and is easily recombined to lower the responsiveness. Therefore, when the photodiode absorbs light having a short incident wavelength, such as blue light, it is re-combined due to surface absorption and generation of electron holes, and is used for a longer wavelength light source such as infrared light. A photodiode that primarily absorbs light energy causes some degree of interference.

The present invention is applied to a photodiode structure 100 that absorbs light energy mainly based on the long wavelength of infrared light by designing the protective layer 104. Referring to FIG. 4 , in an embodiment of the invention, the protective layer 104 is a stacked structure including a transparent conductive oxide layer 214 and a polysilicon layer 215 . The transparent conductive oxide layer 214 is disposed above the polysilicon layer 215 . The polysilicon layer 215 and the transparent conductive oxide layer 214 are electrically connected to the first type substrate 102, and the transparent current conductive oxide layer 214 and the polysilicon layer 215 absorb the photocurrent current generated by the short-wavelength incident light. The electrode 216 electrically connected to the polysilicon layer 215 is grounded. The transparent conductive oxide layer 214 and the polysilicon layer 215 are provided with a function of filtering out short-wavelength stray light.

The transparent conductive oxide layer 214 is a metal compound conductive film layer, and the preferred embodiment is an indium tin oxide (ITO, Indium Tin Oxide) conductive film layer.

The transparent conductive oxide layer 214 and the polysilicon layer 215 are stacked on top of each other. Around the contact conductor 103 and the upper surface 105 of the first type substrate 102, this area is an installation area of a spacer such as a conventional field oxide region (FOX). Long-wavelength light such as 850 nm infrared light has a depth of absorption of about 13 μm in the tantalum material, while the second type doping well 118 has a depth of only 2 μm (well ion cloth depth). Therefore, most of the long-wavelength light system falls in the first type substrate 102 which is not collected by the electric field outside the depletion region. The polysilicon layer 215 is disposed to have a deeper peak concentration of the original second type doping well 118, thereby enhancing the photon absorption efficiency of the long wavelength light having a deeper absorption depth in the second type doping well 118. (absorption efficiency).

While the present invention has been described in its preferred embodiments, the present invention is not intended to limit the invention, and the present invention may be modified and modified without departing from the spirit and scope of the invention. The scope of protection is subject to the definition of the scope of the patent application.

100‧‧‧Photoelectric diode

102‧‧‧First type substrate

103‧‧‧Contact conductor

104‧‧‧Protective layer

105‧‧‧ upper surface

106‧‧‧Isolated area

107‧‧‧PN connection interface

109‧‧‧ Vacant Zone

118‧‧‧Type 2 doping well

119‧‧‧Second-type doped area

120‧‧‧Contact layer

121‧‧‧ Conductive strip

212‧‧‧ interval zone

Claims (10)

A photodiode comprising: a first type substrate comprising an upper surface; a second type doping well disposed in the first type substrate, the first type substrate and the second type doped well phase The abutting surface region is a PN junction interface; a second type doping region is formed in the second type doping well and extends from a surface of the second type doping well; an isolation region is formed in the a first type of substrate, and not contacting the second type doping well; a protective layer formed on the upper surface and covering the second type doping region and the second type doping well; and a contact conductor, The protective layer is penetrated and includes a contact layer and a conductive strip, wherein the contact layer is formed at one end of the conductive strip and contacts and connects the second type doped region. The photodiode of claim 1, wherein the first type of substrate is a P-type substrate. The photodiode of claim 1, wherein the second doping well is doped at a relatively low concentration, and the second doped region is doped at a relatively high concentration. The photodiode of claim 1, wherein the contact layer is formed by a self-aligned metal deuteration process. The photodiode of claim 1, wherein the isolation region is tantalum nitride or hafnium oxide. The photodiode of claim 1, wherein the isolation region is a local oxide layer (LOCOS), a shallow trench isolation layer (STI) or a field oxide layer (FOX). The photodiode of claim 1, wherein the protective layer comprises a transparent conductive oxide layer (TCO) and a polysilicon layer, and the transparent conductive oxide layer is disposed above the polysilicon layer. The photodiode of claim 7, wherein the polycrystalline germanium layer has a thickness of 0.1 um. The photodiode of claim 7, wherein the polysilicon layer is electrically connected to the first type substrate. The photodiode of claim 1, wherein the contact conductor is a contact plug.