# Patent

## Title
Method of enabling alignment of wafer in exposure step of IC process after UV-blocking metal layer is formed over the whole wafer

## Abstract

A method of enabling alignment of a wafer in at least one exposure step of an integrated circuit process after a UV-blocking metal layer is formed over the whole wafer covering a patterned upmost metal layer of the integrated circuit is described, wherein the wafer has an edge portion where a composite dielectric layer corresponding to the dielectric layers of the integrated circuit is formed. The method includes forming a cavity in the composite dielectric layer over the edge portion of the wafer in the patterning process of the upmost metal layer, such that an alignment mark is formed after the UV-blocking metal layer is formed.

## Background
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an integrated circuit process and a resulting structure. More particularly, this invention relates to a method of enabling alignment of a wafer in at least one exposure step of an integrated circuit (IC) process after a UV-blocking metal layer is formed over the whole wafer, to an IC process incorporating the step of the above method, and to a wafer structure resulting from a part of the above process.
2. Description of the Related Art
In the fabricating process of an integrated circuit sensitive to UV-light, such as a non-volatile memory operated by carrier injection and removal, a UV-blocking metal layer is usually formed over the whole wafer after the passivation layer covering the upmost metal layer is formed. The openings exposing the bonding pads in the upmost metal layer are formed through the UV-blocking metal layer and the passivation layer.
FIGS. 1A and 1B illustrate a two-photo process in the prior art for defining the openings above the bonding pads of a non-volatile memory after a UV-blocking layer is formed screening the zero alignment mark on the wafer.
Referring to FIG. 1A, a wafer 100 including dies 102 and an edge portion 104 is provided, wherein only one die 102 is shown for simplicity. Each die 102 includes a periphery circuit area 106 and an array area 108, with a circuit of a non-volatile memory and the accompanying dielectric layers 120 thereon. The edge portion 104 is formed with a zero alignment 110 thereon, and is screened in the deposition of any conductive layer to be defined into a portion of the circuit so that only the dielectric layers 120 are formed thereon as a composite dielectric layer. An upmost metal layer, which includes bonding pads 130a within the periphery circuit area 106 and other upmost metal patterns 130b, has been formed on the dielectric layers 120, wherein only one bonding pads 130a is shown for simplicity. A passivation layer 140 has been formed over the whole wafer 100 covering the upmost metal layer, and a UV-blocking metal layer 150 has been formed over the whole passivation layer 140.
In the first stage of the two-photo process, a photoresist layer 160 is formed over the whole wafer 100, and then a portion thereof above the edge portion 104 is exposed and removed in subsequent development. The UV-blocking layer 150 thus exposed is then removed in an etching step 162 making the zero alignment mark 110 under the transparent layers 120 and 140 optically detectable.
After the photoresist layer 160 is removed, a water-resistant layer 170 is formed over the whole wafer 100 covering the remaining UV-blocking metal layer 150a. A photoresist layer 180 is formed over the whole wafer 100 and exposed by a photomask 10 to form an exposed region 180a over each bonding pad 130a. Because the zero alignment mark 110 under the transparent layers 120 and 140 is optically detectable, the wafer 100 can be aligned using an optical method based on the zero alignment mark 110 in the exposure using the photomask 10. After the exposed region 180a is removed in subsequent development, the photoresist layer 180 is used as an etching mask to form an opening through the a water-resistant layer 170, the UV-blocking metal layer 150 and the passivation layer 140 above the bonding pad 130a. 
The above partial removal process for the UV-blocking metal layer 150 as shown in FIG. 1A needs an extra photomask, and the coating, exposure, development and so forth of the photoresist layer consume much time.
SUMMARY OF THE INVENTION
In view of the foregoing, this invention provides a method of enabling alignment of a wafer in at least one exposure step of an integrated circuit process after a UV-blocking metal layer is formed over the whole wafer.
This invention also provides an integrated circuit process that incorporates the step of the above method of this invention and thereby allows the wafer to be aligned in an exposure step after the UV-blocking metal layer is formed over the whole wafer.
This invention also provides a wafer structure that can be formed with a part of the above integrated circuit process of this invention.
In the method of enabling alignment of a wafer in at least one exposure step of an integrated circuit process after a UV-blocking metal layer is formed over the whole wafer of this invention, the UV-blocking metal layer covers the patterned upmost metal layer of the integrated circuit and the wafer has an edge portion where a composite dielectric layer corresponding to the dielectric layers of the integrated circuit is formed. The method includes forming a cavity in the composite dielectric layer over the edge portion of the wafer in the patterning process of the upmost metal layer, such that an alignment mark is formed after the UV-blocking layer is formed.
The integrated circuit process of this invention is applied to a wafer over which an upmost metal layer has been formed, wherein the wafer has an edge portion where a composite dielectric layer corresponding to the dielectric layers of the integrated circuit is formed. The upmost metal layer is patterned into a patterned one including bonding pads, while a cavity is simultaneously formed in the composite dielectric layer over the edge portion of the wafer. A passivation layer is then formed over the whole wafer, and a UV-blocking metal layer is formed over the whole passivation layer, wherein the cavity, the passivation layer and the UV-blocking metal layer result in an alignment mark. Openings are formed at least in the passivation layer over the bonding pads, wherein the alignment mark is utilized to align the wafer.
The wafer structure of this invention includes a plurality of dies, an edge portion where a composite dielectric layer corresponding to the dielectric layers of an integrated circuit is disposed, a passivation layer and a UV-blocking metal layer. Each die has the integrated circuit formed thereon, wherein the integrated circuit includes an upmost metal layer that includes bonding pads. A cavity is formed in the composite dielectric layer over the edge portion. The passivation layer is over the whole wafer covering the upmost metal layer, and the UV-blocking metal layer on the passivation layer covering the edge portion and at least a portion of each of the dies. The cavity, the passivation layer and the UV-blocking metal layer result in an alignment mark.
By utilizing the method of this invention, a new alignment mark can be formed on the wafer edge portion with a zero alignment mark after the UV-blocking metal layer is formed, so that the wafer can be aligned in a subsequent exposure step even though the UV-blocking metal layer entirely screens the zero alignment mark.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.



BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1A and 1B illustrate a two-photo process in the prior art for defining the openings above the bonding pads of a non-volatile memory after a UV-blocking metal layer is formed screening the zero alignment mark.
FIGS. 2A and 2B illustrate a non-volatile memory process according to a first embodiment of this invention, wherein FIG. 2A illustrates how to enable alignment of the wafer after the UV-blocking layer is formed screening the zero alignment mark.
FIG. 3 depicts an additional patterning step for the UV-blocking metal layer in a non-volatile memory process according to a second embodiment of this invention.



DESCRIPTION OF THE PREFERRED EMBODIMENTS
It is noted that the following two embodiments are intended to further explain this invention but are not to restrict the scope of this invention. Though the integrated circuit exemplified in each of the embodiments is a non-volatile memory of charge-trapping type operated by carrier injection and removal, this invention can be applied to the fabricating process of any other integrated circuit which is sensitive to UV-light and requires a UV-blocking metal layer formed thereover.
First Embodiment
FIGS. 2A and 2B illustrate a non-volatile memory process according to the first embodiment of this invention, wherein FIG. 2A illustrates how to enable alignment of the wafer after the UV-blocking layer is formed screening the zero alignment mark.
Referring to FIG. 2A, a wafer 200 including a plurality of dies 202 and an edge portion 204 is provided, wherein the wafer 200 is possibly a single-crystal silicon wafer and only one die 202 is shown for simplicity. Each die 202 includes a periphery circuit area 206 and an array area 208, with the circuit of a non-volatile memory except the upmost metal layer and corresponding dielectric layers 220 thereon. The edge portion 204 is formed with a zero alignment mark 210 thereon, and is screened in the deposition of any conductive layer to be defined into a portion of the circuit so that only the dielectric layers 220 are formed thereon to be a composite dielectric layer.
An unpatterned upmost metal layer as the precursor of the layers 230a and 230b in FIG. 2A, which may be an aluminum layer of 3000 to 12000 angstroms thick, is deposited over the dies 202. A patterned photoresist layer 232 having the patterns of the upmost metal layer to be defined and having an opening 234 therein over the edge portion 204 of the wafer 200 is formed over the wafer 200. An etching step 236 is conducted using the photoresist layer 232 as a mask to define the unpatterned upmost metal layer into a patterned one, which includes bonding pads 230a in the periphery circuit area 206 and other upmost metal patterns 230b, and simultaneously form a cavity 238 in the dielectric layers 220 as a composite dielectric layer, wherein only one bonding pad 230a is shown for simplicity.
In certain embodiments, the etching rate of the dielectric layers 220 is about 1⁄3 of the etching rate of the upmost metal layer, so that the cavity 238 can be formed deeply enough to result in an effective alignment mark later.
Referring to FIG. 2B, after the bonding pads 230a, the metal patterns 230b and the cavity 238 are formed, the photoresist layer 232 is removed. A passivation layer 240 is formed over the whole wafer 200 covering the bonding pads 230a and the metal patterns 230b. The passivation layer 240 may include polyamide or an epoxy resin, and the thickness thereof may range from 10000 Å to 20000 Å. A UV-blocking metal layer 250, such as a tungsten or AlCu layer, is then formed over the whole wafer 200, so as to prevent the memory cells from being irradiated by UV-light and injected with electrons. The thickness of the UV-blocking metal layer 250 may range from 3000 Å to 8000Å.
The passivation layer 240 is formed in a manner such that the topography of the surface of the dielectric layer 220 is substantially retained, making the passivation layer 240 also have a cavity therein over the cavity 238. The UV-blocking metal layer 250 is formed substantially conformal to the surface of the passivation layer 240, so that a new alignment mark 256 is formed after the UV-blocking metal layer 250 is formed. Although the alignment mark 256 is above the zero alignment mark 210 in the figure, the former may alternatively be not above the latter if only the data of the preset location of the alignment mark 256 is stored in the wafer alignment system.
In addition, a water-resistant layer 270 may optionally be formed over the whole wafer 200 after the UV-blocking layer 250 is formed. The water-resistant layer 270 may include silicon oxynitride (SiON) or silicon nitride (SiN), and may have a thickness of 4000 Å to 9000Å.
A photolithography process is then conducted, wherein a photoresist layer 280 is formed over the whole wafer 200 and then exposed with a photomask 10 to form an exposed region 280a over the bonding pad 230a. Since a new alignment mark 256 is formed after the UV-blocking metal layer 250 is formed, the wafer 200 can be aligned using an optical method based on the alignment mark 256 in the above exposure step. The exposed region 280a will be removed in later development to form a corresponding opening in the photoresist layer 280.
Then, an opening is formed through the water-resistant layer 270, UV-blocking metal layer 250 and the passivation layer 240 using the patterned photoresist layer 280 as a mask, as indicated by the dashed lines in FIG. 2B that also show the border of the resulting opening. When no water-resistant layer is formed on the UV-blocking metal layer 250, the opening is formed through the UV-blocking layer 250 and the passivation layer 240 only.
The process after the patterned photoresist layer 280 is removed can be any one known in the prior art. For example, a spacer is preferably formed on the sidewall of the resulting opening to prevent the bonding pads 230a from electrically connecting with each other via the conductive UV-blocking layer 250, and a gold wire or a solder ball is then bonded onto each bonding pad 230a exposed in the resulting openings.
Since a new alignment mark is formed on the wafer edge portion with a zero alignment mark after the UV-blocking metal layer is formed, the wafer can be aligned in the exposure step for defining the openings above the bonding pads even after the UV-blocking metal layer is formed screening the zero alignment mark.
Second Embodiment
FIG. 3 depicts an additional patterning step for the UV-blocking metal layer in a non-volatile memory process according to the second embodiment of this invention.
The process of the second embodiment is similar to that of the first one, except that the UV-blocking metal layer 250 over the periphery circuit area 206 of each die 202 is removed. The removal can be done directly after the UV-blocking metal layer 250 is formed, in an etching step 310 that uses a patterned photoresist layer 300 exposing the periphery circuit area 206 of each die 202 as a mask.
In cases where each memory cell is disposed with a charge-trapping layer like an ONO composite layer to store data, the photomask for defining the patterned photoresist layer 300 may be the one for removing the charge-trapping layer 213 in the periphery circuit area 206. In such a case, the gate dielectric layer 217 of the transistors in the periphery circuit area 206 is formed after the charge-trapping layer 213 in the periphery circuit area 206 is removed.
After the photoresist layer 300 is removed, as in the case of the first embodiment shown in FIG. 2B, a water-resistant layer may be further formed over the whole wafer 200 covering the remaining UV-blocking layer 250a. A lithography process is then conducted using the same photomask 10 to form an opening through the passivation layer 240, or through the water-resistant layer and the passivation layer 240 as a water-resistant layer is further form, over each bonding pad 230a in the periphery circuit area 206. Since there is no UV-blocking metal layer in the periphery circuit area 206, no spacer has to be formed on the sidewall of each opening exposing a bonding pad 230a to prevent electrical short.
It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention covers modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.

## Claims

1. A method of enabling alignment of a wafer in at least one exposure step of an integrated circuit process after a UV-blocking metal layer is formed over the whole wafer covering a patterned upmost metal layer of the integrated circuit, wherein the wafer has an edge portion where a composite dielectric layer corresponding to dielectric layers of the integrated circuit is formed, the method comprising:
forming a cavity in the composite dielectric layer over the edge portion of the wafer in a patterning process of the upmost metal layer, such that an alignment mark is formed when the UV-blocking metal layer is formed.

2. The method of claim 1, wherein
the patterned upmost metal layer includes a plurality of bonding pads,
a passivation layer is formed over the whole wafer before the UV-blocking metal layer is formed, and
the at least one exposure step comprises an exposure step for defining openings in the UV-blocking metal layer and the passivation layer over the bonding pads.

3. The method of claim 2, wherein the integrated circuit comprises a non-volatile memory.

4. The method of claim 3, wherein
each of a plurality of dies on the wafer includes a peripheral circuit area and an array area, wherein the bonding pads are within the peripheral circuit area,
the at least one exposure step further comprises an exposure step in a patterning process for removing a portion of the UV-blocking metal layer over the peripheral circuit area of each of the dies, and
the openings are defined in the passivation layer only.

5. The method of claim 2, wherein a water-resistant layer is further formed over the whole wafer covering the UV-blocking metal layer before the openings are formed, and the openings are formed through the water-resistant layer.

6. The method of claim 5, wherein the water-resistant layer comprises silicon oxynitride (SiON) or silicon nitride (SiN).

7. The method of claim 1, wherein a zero alignment mark is formed on the edge portion of the wafer, and the alignment mark formed after formation of the UV-blocking metal layer is or is not above the zero alignment mark.

8. The method of claim 1, wherein the UV-blocking metal layer comprises tungsten or AlCu.

9. An integrated circuit process applied to a wafer over which an upmost metal layer has been formed, wherein the wafer has an edge portion where a composite dielectric layer corresponding to dielectric layers of the integrated circuit is formed, comprising:
patterning the upmost metal layer into a patterned one that includes bonding pads and simultaneously forming a cavity in the composite dielectric layer over the edge portion of the wafer;
forming a passivation layer over the whole wafer;
forming a UV-blocking metal layer over the whole passivation layer, wherein the cavity, the passivation layer and UV-blocking metal layer result in an alignment mark;
forming openings in the UV-blocking metal layer and the passivation layer over the bonding pads, wherein the alignment mark is utilized to align the wafer.

10. The integrated circuit process of claim 9, further comprising:
forming a water-resistant layer over the whole UV-blocking metal layer before the openings are formed,
wherein the openings are formed through the water-resistance layer, the UV-blocking metal layer and the passivation layer.

11. The integrated circuit process of claim 9, wherein the integrated circuit comprises a non-volatile memory.

12. The integrated circuit process of claim 11, wherein each of dies on the wafer includes an array area and a peripheral circuit area and the bonding pads are within the peripheral circuit area, further comprising:
removing a portion of the UV-blocking metal layer over the peripheral circuit area of each of the dies after the UV-blocking metal layer is formed but before the openings are formed,
wherein the openings are formed in the passivation layer only.

13. The integrated circuit process of claim 12, further comprising:
forming a water-resistant layer over the whole wafer after the portion of the UV-blocking metal layer is removed but before the openings are formed,
wherein the openings are formed through the water-resistance layer and the passivation layer.

14. The integrated circuit process of claim 13, wherein the water-resistant layer comprises silicon oxynitride (SiON) or silicon nitride (SiN).

15. The integrated circuit process of claim 9, wherein a zero alignment mark is formed on the edge portion of the wafer, and the alignment mark resulting from the cavity, the passivation layer and the UV-blocking metal layer is or is not above the zero alignment mark.

16. The integrated circuit process of claim 9, wherein the UV-blocking metal layer comprises tungsten or AlCu.