TW201818534A - Back-illuminated image sensor structure and method for fabricating back-illuminated image sensor structure - Google Patents

Abstract

A backside illumination image sensor structure includes multiple photodiodes disposed in a substrate, an interlayer dielectric layer directly disposed on the substrate and a metal routing directly disposed on the interlayer dielectric layer. The metal routing includes a top barrier layer, a patterned bottom barrier layer directly disposed on the interlayer dielectric layer to define at least one opening region corresponding to the multiple photodiodes and a metal layer which covers the patterned bottom barrier layer and the at least one opening region as well as is covered by the top barrier layer.

Description

Back-illuminated image sensor structure and method for manufacturing back-illuminated image sensor structure

The present invention generally relates to a back-illuminated (BSI) image sensor structure and a method for manufacturing the back-illuminated image sensor structure. In particular, the present invention is directed to a back-illuminated image sensor structure having a metal layer as a highly reflective layer in a metal winding, and a patterned bottom barrier layer arranged in the metal winding as the case requires, and A method of manufacturing these back-illuminated image sensor structures.

For a back-illuminated complementary metal-oxide-semiconductor image sensor (CIS), the photosensitive element (ie, the photodiode) is located in silicon with a thickness in the range of several microns (about 2-5 microns). The thickness of the silicon substrate is suitable for detecting wavelengths in the visible range (around 400-700 nm). However, for near-infrared light sources or infrared light sources, the photodiodes in silicon are too superficial to absorb most photons. The quantum efficiency of superficial sensors is therefore too low.

An obvious solution is to increase the thickness of the silicon so that deeper photodiodes can be implanted. However, the small pixel spacing of this solution is difficult in terms of current technology, because narrow dopants cannot be deep enough. Typically, a million electron volt (MeV) level of implantation energy is needed to create hundreds of nanometers of narrow enough pixels to isolate pixels.

In view of this, the present invention therefore proposes a back-illuminated (BSI) image sensor structure, which has an exposed high-reflectivity metal layer and serves as a high-reflective layer in metal windings to solve the aforementioned problems , And a method for manufacturing such a back-illuminated image sensor structure. In addition, if necessary, a patterned bottom barrier layer may be provided in the metal winding.

The metal layer with high reflectivity can assist near-infrared light or infrared light. Because of its longer running distance, it is more effectively absorbed by the photodiode, which increases the quantum efficiency of the back-illuminated image sensor. In particular, the method for manufacturing a back-illuminated image sensor structure of the present invention has the advantage of being compatible with the current standard complementary metal-oxide-semiconductor (CMOS) process.

In a first aspect, the present invention first provides a back-illuminated image sensor structure. The back-illuminated image sensor structure of the present invention includes a substrate, a plurality of photodiodes, an interlayer dielectric layer, and a metal wire. A plurality of photodiodes are located in the substrate. The interlayer dielectric layer is directly on the substrate. The metal winding is directly on the interlayer dielectric layer and is composed of a metal layer and a top barrier layer. A metal layer with high reflectivity is located on the interlayer dielectric layer and directly contacts the interlayer dielectric layer. The top barrier layer covers the metal layer.

In one embodiment of the present invention, the reflectivity of the metal layer is higher than 80% for a given light having a wavelength greater than 600 nm.

In another embodiment of the present invention, the metal layer is selected from the group consisting of silver, copper, gold, and aluminum.

In a second aspect, the present invention provides another back-illuminated image sensor structure. The back-illuminated image sensor structure of the present invention includes a substrate, a plurality of photodiodes, an interlayer dielectric layer, and a metal wire. A plurality of photodiodes are located in the substrate. The interlayer dielectric layer is directly on the substrate. The metal winding is directly on the interlayer dielectric layer and includes a metal layer, a patterned bottom barrier layer and a top barrier layer. The patterned bottom barrier layer is directly on the interlayer dielectric layer to define at least one open area corresponding to at least one of the plurality of photodiodes. The metal layer covering the patterned bottom barrier layer and the at least one open area is covered by the top barrier layer.

In an embodiment of the present invention, a metal layer is filled in at least one of the opening regions and is located directly above at least one of the plurality of photodiodes.

In another embodiment of the present invention, at least one open area is square or circular.

In another embodiment of the present invention, the metal layer has a higher reflectance than the patterned bottom barrier layer.

In another embodiment of the present invention, the patterned bottom barrier layer is selected from the group consisting of titanium and titanium nitride.

In another embodiment of the present invention, the metal layer is selected from the group consisting of silver, copper, gold, and aluminum.

In a third aspect, the present invention provides a method for forming a back-illuminated image sensor structure. First, a substrate is provided. The substrate has a plurality of photodiodes, and an interlayer dielectric layer is directly on the substrate. Second, a metal layer is formed on the interlayer dielectric layer and directly contacts the interlayer dielectric layer to define a metal winding. After that, a top barrier layer is formed to cover the metal layer.

In one embodiment of the present invention, the metal layer is selected from the group consisting of silver, copper, gold, and aluminum.

In another embodiment of the present invention, before forming the metal layer, the method further includes forming a patterned bottom barrier layer. The patterned bottom barrier layer is located directly on the interlayer dielectric layer to define at least one open area corresponding to at least one of the plurality of photodiodes, so that the metal layer is located between the patterned bottom barrier layer and the interlayer dielectric layer. Touch the two directly and touch them to fill at least one open area.

In another embodiment of the present invention, the metal layer has a higher reflectance than the patterned bottom barrier layer.

In another embodiment of the present invention, at least one open area is square or circular.

In another embodiment of the present invention, the patterned bottom barrier layer is selected from the group consisting of titanium and titanium nitride.

In a first aspect, the present invention provides a method for forming a back-illuminated image sensor structure. FIG. 1 to FIG. 8 illustrate a feasible method for forming a back-illuminated image sensor structure according to the present invention. The back-illuminated image sensor structure of the present invention, in particular, has a metal winding having an image sensor exposed in a substrate, and in the presence of a highly reflective metal layer in the metal winding, it helps to promote incident light to be imaged Absorbed by the sensor.

First, referring to FIG. 1, a substrate 110 is provided. The substrate 110 is a semiconductor material, such as doped silicon, undoped silicon, or a combination thereof. In addition, a plurality of photodiodes 120 are constructed in the substrate 110, and an interlayer dielectric layer 130 is directly on the substrate 110 and the plurality of photodiodes 120 to cover the substrate 110 and the plurality of photosensitive Diode 120 is both. Each photodiode 120 includes a contact pad 121 for electrical connection to a circuit (not shown) in a subsequent step. The photodiode 120 is a photosensitive element, such as a back-illuminated complementary metal-oxide semiconductor image sensor. The thickness of the substrate can be in the range of 2 micrometers to 5 micrometers.

The interlayer dielectric layer 130 is an insulating material, such as silicon oxide, silicon nitride, or a combination thereof. Both the interlayer dielectric layer 130 and the photodiode 120 can be manufactured in a conventional manner, so the manufacturing process is not described in detail here.

Next, referring to FIG. 2, a plurality of contact plugs 131 are formed in the interlayer dielectric layer 130. Each contact plug 131 corresponds to a lower contact pad 121 and directly contacts the contact pad 121. For example, first, a plurality of contact holes (not shown) are formed in the interlayer dielectric layer 130. Next, a conductive material is filled in each contact hole (not shown) to obtain a contact plug 131. Since both the contact hole (not shown) and the contact plug 131 can be manufactured in a conventional manner, the manufacturing process is not described in detail here.

Continuing, referring to FIG. 4, if necessary, a bottom barrier layer 141 is formed on the interlayer dielectric layer 130. Forming a bottom barrier layer 141 as needed may be used to increase the adhesion between the interlayer dielectric layer 130 and a metal layer (not shown). The bottom barrier layer 141 may be a titanium-containing material, such as titanium, titanium nitride, or a combination thereof, as required, and has a thickness of several hundred Angstroms (Å). The bottom barrier layer 141 as required may be made by a printing method, a deposition method, or an etching method. FIG. 3 to FIG. 4 illustrate the formation of the bottom barrier layer 141 as required by an etching method.

First, referring to FIG. 3, a whole bottom barrier layer 141 ′ is formed to cover the interlayer dielectric layer 130. Secondly, referring to FIG. 4, the bottom barrier layer 141 ′ is patterned by an etching method to form a patterned bottom barrier layer 141, and an opening area 142 corresponding to a plurality of photodiodes below is defined. Each of the opening regions 142 may be a polygon (eg, a rectangle, a square, an octagon, etc.), an oval, a circle, or any other specific shape. If the patterned bottom barrier layer 141 is manufactured by a printing method or a deposition method, the patterned bottom barrier layer 141 can be prepared in one step, so the steps shown in FIG. 3 can be omitted.

Alternatively, if the adhesion between the interlayer dielectric layer 130 and the metal layer (not shown) thereon is not critical, the steps shown in FIGS. 3 to 4 can also be skipped. Therefore, the following steps will be continued.

Then, a metal layer 143 is formed. The metal layer 143 is formed as a circuit and a reflective layer. The reflectivity of the metal layer 143 is higher than that of the patterned bottom barrier layer 141. For example, for a wavelength of 850 nanometers, the 80% reflectance of aluminum is greater than the 60% reflectance of TiN or the 58% reflectance of Ti. The material of the metal layer 143 may be selected from the group consisting of silver, copper, gold, and aluminum. The metal layer 143 can be filled with a deposition method to form a plurality of open regions 142. The thickness of the metal layer 143 is variable according to circumstances. For example, for a technology node of 0.13 μm to 0.18 μm, the thickness of the metal layer 143 may be 0.2 μm to 0.3 μm.

Continuing, referring to FIG. 5 or FIG. 5A, a whole metal layer 143 ′ is formed on the interlayer dielectric layer 130. If the patterned bottom barrier layer 141 is present, as shown in FIG. 5, the entire metal layer 143 ′ formed will cover both the patterned bottom barrier layer 141 and the interlayer dielectric layer 130. At the same time, the entire metal layer 143 ′ formed directly contacts the patterned bottom barrier layer 141 and directly contacts the interlayer dielectric layer 130 through the opening region 142. Otherwise, if the patterned bottom barrier layer 141 does not exist, as shown in FIG. 5A, the entire metal layer 143 'formed will only cover the underlying interlayer dielectric layer 130 and directly contact the interlayer dielectric. Layer 130.

After that, referring to FIG. 6 or FIG. 6A, a top barrier layer 145 is formed and is located on the metal layer 143. The top barrier layer 145, similar to the bottom barrier layer 141 ', may be another one-piece layer and a titanium-containing material, such as titanium, titanium nitride, or a combination thereof. The top barrier layer 145 may have a thickness (Å) of several hundred Angstroms, and is made by a printing method or a deposition method. For example, a whole piece of the top barrier layer 145 is prepared by a deposition method to cover the metal layer 143.

If a patterned bottom barrier layer 141 is present, as shown in FIG. 6, the entire top barrier layer 145 formed will be positioned on the metal layer 143 and directly contact the metal layer 143 at the same time. FIG. 6 illustrates an example in which the metal layer 143 is sandwiched between the patterned bottom barrier layer 141 and the top barrier layer 145. Otherwise, if the patterned bottom barrier layer 141 does not exist, as shown in FIG. 6A, the entire top barrier layer 145 formed will be positioned on the metal layer 143 and directly contact the metal layer 143 at the same time. . FIG. 6A illustrates an example in which the metal layer 143 is sandwiched between the interlayer dielectric layer 130 and the top barrier layer 145.

Next, referring to FIG. 7 or FIG. 7A, the metal layer 143, the patterned bottom barrier layer 141, and the top barrier layer 145 are patterned together to define a metal winding 149. The metal wire 149 can be formed by using an etching method with the help of an etching mask (not shown). If the patterned bottom barrier layer 141 is present, as shown in FIG. 7, the metal layer 143, the patterned bottom barrier layer 141, and the top barrier layer 145 are patterned together to form a metal winding 149, and The metal layer 143 becomes a circuit in the metal winding 149, and is also referred to as M1 (the first order of the metal winding). FIG. 6 illustrates that the metal layer 143, the patterned bottom barrier layer 141, and the top barrier layer 145 are patterned together, and become an example of metal windings 149 having the same pattern.

Otherwise, if the patterned bottom barrier layer 141 does not exist, as shown in FIG. 7A, the metal layer 143 and the top barrier layer 145 are patterned together to define a metal winding 149, and the metal layer 143 becomes the circuit in metal winding 149, also known as M1 (first order of metal winding). FIG. 6A illustrates that only the metal layer 143 and the top barrier layer 145 are patterned together to form an example of the metal winding 149 having the same pattern. In either case, the interlayer dielectric layer 130 serves as an etch stop layer to obtain a back-illuminated image sensor structure.

Then, for example, referring to FIG. 8, another dielectric layer called an intermetal dielectric layer 150 is formed to cover the metal windings 149 and fill in the pattern of the metal windings 149 to help form M2 (metal Winding second order). Therefore, a plurality of through holes 151 are formed in the inter-metal dielectric layer 150 and serve as an electrical connection between the first stage of the metal winding and the second stage of the metal winding. Therefore, after the second stage of the metal winding is formed on the intermetal dielectric layer 150 and the plurality of through holes 151, a back-illuminated image sensor structure with multiple groups of metal winding stages is obtained. The second stage of metal winding is similar to the first stage of metal winding, and may also include another metal layer, another patterned bottom barrier layer and another top barrier layer as required.

After going through the above steps, a back-illuminated image sensor structure suitable for a long-wavelength light source (greater than 600 nm) can be obtained. Please refer to FIG. 7 or FIG. 7A. FIG. 7 shows that the patterned bottom barrier layer 141 is present. FIG. 7A shows that the patterned bottom barrier layer 141 does not exist.

The back-illuminated image sensor structure 101 and the back-illuminated image sensor structure 102 include a substrate 110, a plurality of photodiodes 120, an interlayer dielectric layer 130, and a metal wire 149, respectively. The back-illuminated image sensor structure 101 or the back-illuminated image sensor structure 102 further includes an inter-metal dielectric layer 150, a plurality of through holes 151, and a second stage of metal winding (M2).

The substrate 110 is a semiconductor material, such as doped silicon, undoped silicon, or a combination thereof. The thickness of the substrate can range from about 2-5 microns. The plurality of photodiodes 120 are built in the substrate 110. Each photodiode 120 includes a contact pad 121 that is exposed to the outside of the substrate 110 and is electrically connected to the previous metal winding 149 via a contact plug 131. The photodiode 120 is a photosensitive element, such as a back-illuminated complementary metal-oxide semiconductor image sensor. The interlayer dielectric layer 130 is directly on the substrate 110 to cover both the substrate 110 and the plurality of photosensitive diodes 120. The interlayer dielectric layer 130 is an insulating material, such as silicon oxide, silicon nitride, or a combination thereof.

The metal winding 149 is directly above the interlayer dielectric layer 130. In the back-illuminated image sensor structure 101, the metal winding 149 includes a metal layer 144, a patterned bottom barrier layer 141, and a top barrier layer 145. The patterned bottom barrier layer 141 is positioned directly on the interlayer dielectric layer 130 to define a plurality of opening regions 142 corresponding to the plurality of photodiodes 120, so that the opening regions 142 are located in the positive positions of the plurality of photodiodes 120. Up. Each of the opening regions 142 may be a polygon (eg, a rectangle, a square, an octagon, etc.), an oval, a circle, or any other specific shape. The patterned bottom barrier layer 141 serves as an adhesion layer between the interlayer dielectric layer 130 and the metal layer thereon, and may be a titanium-containing material, such as titanium, titanium nitride, or a combination thereof. The metal layer 143 that covers both the patterned bottom barrier layer 141 and the interlayer dielectric layer 130 also fills the plurality of opening regions 142. The metal layer 143 functions as a circuit and a reflection layer. The reflectivity of the metal layer 143 is higher than that of the patterned bottom barrier layer 141. For example, for a wavelength of 850 nanometers, the 80% reflectance of aluminum is greater than the 60% reflectance of TiN or the 58% reflectance of Ti. Therefore, the material of the metal layer 143 may be selected from silver, copper, gold, and aluminum. A group of people.

The metal layer 143 is further covered by the top barrier layer 145. The top barrier layer 145 is similar to the bottom barrier layer 141, and may also be another adhesive layer, such as a titanium-containing material, such as titanium, titanium nitride, or a combination thereof. The metal layer 143, the patterned bottom barrier layer 141, and the top barrier layer 145 as needed form a metal winding 149 together.

The metal winding 149 is a first-order metal winding in the back-illuminated image sensor structure 101 or the back-illuminated image sensor structure 102, also referred to as M1, and is patterned so that the metal layer 143 serves as a back-illuminated The circuit in the image sensor structure 101 or the back-illuminated image sensor structure 102. In the metal winding 149, there is a metal layer 143 having a higher reflectivity than the patterned bottom barrier layer 141, and faces and passes through the opening region 142 corresponding to the plurality of photodiodes 120 below.

As shown in FIG. 9, in the back-illuminated image sensor structure 101, the exposed metal layer 143, that is, the metal layer 143 that is not blocked by the patterned bottom barrier layer 141, assists the plural below. Each photodiode 120 collects more reflected incident light from the back surface 109, so that the quantum efficiency of the photodiode 120 with respect to a long-wavelength light source, such as a wavelength greater than 600 nm, can be improved.

In an embodiment of the present invention, when the specific pixel layout does not allow the first order of metal winding, and is arranged to be large enough to provide sufficient space to reflect light, the second order of metal winding or higher order metal Winding, although far away from the silicon substrate, is still a candidate for reflecting incident light.

FIG. 10 is a top view of a back-illuminated image sensor. The metal wire 149 passing through the photodiode 120 has an opening area 142 corresponding to the photodiode 120. The opening regions 142 are respectively exemplified in a rectangular, octagonal, oval, or circular manner. The above description is only a preferred embodiment of the present invention, and all equivalent changes and modifications made in accordance with the scope of patent application of the present invention shall fall within the scope of the present invention.

101‧‧‧Back-illuminated image sensor structure

102‧‧‧Back-illuminated image sensor structure

109‧‧‧Back

110‧‧‧ substrate

120‧‧‧photodiode

121‧‧‧ contact pad

130‧‧‧ Interlayer dielectric layer

131‧‧‧contact plug

141‧‧‧ bottom barrier

141'‧‧‧ a whole piece of bottom barrier layer

142‧‧‧open area

143‧‧‧metal layer

143'‧‧‧ a whole piece of metal layer

145‧‧‧Top barrier layer

149‧‧‧ metal winding

150‧‧‧Intermetal dielectric layer

151‧‧‧through hole

M2‧‧‧ Metal winding second stage

FIG. 1 to FIG. 8 illustrate a feasible method for forming a back-illuminated image sensor structure according to the present invention. FIG. 5A shows a whole piece of metal layer covering only the underlying interlayer dielectric layer and directly contacting the interlayer dielectric layer. FIG. 6A illustrates that only the metal layer and the top barrier layer are patterned together, and become an example of metal windings having the same pattern. FIG. 7A shows that the metal layer and the top barrier layer are patterned together to define a metal winding, and the metal layer becomes a circuit in the metal winding. Figure 9 shows that in the back-illuminated image sensor structure, the exposed metal layer assists the plurality of photodiodes below to collect more reflected incident light from the back. FIG. 10 is a top view of the back-illuminated image sensor of the present invention.

Claims (12)

A back-illuminated image sensor structure includes: a substrate; a plurality of photodiodes located in the substrate; an interlayer dielectric layer directly on the substrate; and a metal winding Is directly on the interlayer dielectric layer and includes: a top barrier layer; a patterned bottom barrier layer directly on the interlayer dielectric layer to define at least one corresponding to the plurality of photodiodes At least one opening region; and a metal layer covering the patterned bottom barrier layer and the at least one opening region, and covered by the top barrier layer. For example, the back-illuminated image sensor structure of claim 1, wherein the at least one opening area is filled with the metal layer and is located directly above at least one of the plurality of photodiodes. For example, the back-illuminated image sensor structure of claim 1, wherein the at least one opening area is a polygon, an ellipse, or a circle. For example, the back-illuminated image sensor structure of claim 1, wherein the metal layer has a higher reflectivity than the patterned bottom barrier layer. For example, the back-illuminated image sensor structure of claim 1, wherein the patterned bottom barrier layer is selected from the group consisting of titanium and titanium nitride. For example, the back-illuminated image sensor structure of claim 1, wherein the metal layer is selected from the group consisting of silver, copper, gold, and aluminum. A method for forming a back-illuminated image sensor structure, comprising: providing a substrate having a plurality of photodiodes located in the substrate, and having an interlayer dielectric layer directly on the substrate; Forming a metal layer on the interlayer dielectric layer and directly contacting it to define a metal winding; and forming a top barrier layer to cover the metal layer. If the method of claim 7 forms a back-illuminated image sensor structure, the metal layer is selected from the group consisting of silver, copper, gold and aluminum. If the method of claim 7 forms a back-illuminated image sensor structure, before forming the metal layer, the method further includes: forming a patterned bottom barrier layer directly on the interlayer dielectric layer to define a plurality of At least one opening area of at least one of the photodiodes, so that the metal layer is located on both the patterned bottom barrier layer and the interlayer dielectric layer and directly contacts both to fill the at least one opening area in. For example, the method of claim 9 for forming a back-illuminated image sensor structure, wherein the metal layer has a higher reflectance than the patterned bottom barrier layer. If the method of claim 9 forms a back-illuminated image sensor structure, the at least one open area is a polygon, an ellipse or a circle. If the method of claim 9 forms a back-illuminated image sensor structure, the patterned bottom barrier layer is selected from the group consisting of titanium and titanium nitride.