# Patent

## Title
Method of forming self-aligned contacts and local interconnects

## Abstract

A method for simultaneous formation of a self-aligned contact of a core region and a local interconnect of a peripheral region of an integrated circuit includes etching a cap dielectric layer to simultaneously form a hole in the core region and a trench in the peripheral region of the cap dielectric layer, etching a dielectric layer to simultaneously form a hole in the core region and a trench in the peripheral region of the dielectric layer of the dielectric layer, etching a liner layer simultaneously on a shoulder of sidewall spacers associated with the hole and with the trench of the dielectric layer without etching the liner layer at a bottom area of the hole and the trench, performing an oxygen flushing to remove polymer residues, and etching simultaneously through the liner layer that lines the bottom area of the hole and the trench.

## Background
CROSS-REFERENCES TO RELATED APPLICATION
The present application is a Continuation of U.S. application Ser. No. 11/174,147, filed on Jul. 1, 2005, which is incorporated herein by reference in its entirety as if set forth in full.


BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of fabricating semiconductor devices, and more particularly to forming self-aligned contacts and local interconnects of semiconductor devices.
2. Description of the Related Art
In recent years, the size of integrated circuit devices continues to decrease resulting in considerable increase of the packing densities for these devices. The performance of the integrated circuit devices also improves as a result while the manufacture costs have gone down as well.
However, the performance of denser integrated circuit devices could drop when smaller process parameters are used. Accordingly, the issue of maintaining or controlling the precision of contact windows is particularly important as the density of integrated circuit devices continues to increase for future generations of these devices. This etching control issue is even more critical for integrated circuit devices with multiple polysilicon layers. Therefore, a so-called self-aligned contact (SAC) process which can reduce contact area is developed to deal with this issue.
Various SAC processes exist today. For example, U.S. Pat. No. 6,271,081 to Kinoshita et al. (the entire disclosure of which is herein incorporated by reference) provides a method of forming self-aligned contacts and local interconnects using self-aligned local interconnects. Referring now more particularly to FIGS. 1A-1D, there are illustrated the cross sectional views of the SAC process disclosed by Kinoshita et al. The figures show a portion of the core region 104 and also a portion of the peripheral region 106 in which an IC device such as a flash memory is built. FIG. 1A shows a portion of a partially completed dual gate flash memory device after a dielectric layer is deposited according to the prior art. The multi-layer stacked gate structure 110 of the core region 104 is formed on a semiconductor substrate 102. The multi-layer stacked gate structure 110 comprises a gate dielectric layer 112 of a material such as an oxide or nitride, a floating gate layer 114, an interpoly dielectric layer 116, a control gate layer 118, a gate silicide layer 120, and a cap dielectric layer 122. In the peripheral region 106, the multi-layer stacked gate structure only comprises a gate dielectric layer 112, a polysilicon gate layer 118, a gate silicide layer 120, and a cap dielectric layer 122. Sidewall spacers 130 and a liner layer 131 are formed on the sidewalls of the multi-layer stacked gate structure to protect the structure from over etching and short circuit. A common source 142 is formed between two multi-layer stacked gate structures and drains 144 are also formed in the semiconductor substrate 102 and spaced apart from the common source by channel regions 146. In order to decrease the contact resistance and thus to increase the operational speed of the IC device, source/drain suicides 129 are formed. Thereafter, a dielectric layer 132 is formed over the entire semiconductor substrate surface.
FIG. 1B shows the simultaneously forming of the source/drain contact 162 and interconnect contact opening 163 by using a photoresist pattern 166 as a mask. Then, FIG. 1C shows the reopening of the interconnect contact 165 alone by using a second photoresist pattern 168 as a mask to remove a portion of the cap dielectric layer 122 and expose the polysilicon gate layer 118 in the peripheral region 106. After the removal of the second photoresist mask, FIG. 1D shows a metal layer being deposited and planarized to complete the formation of both the SAC contact 170 and the interconnect contact 171.
From the above description, one of ordinary skills in the art can readily see that a lot of photolithography and etching steps are needed to complete the formation of both the SAC contact and the interconnect contact for a semiconductor device. These additional steps significantly increase the complexity and cost for mass-production.
Another SAC process has been proposed to address this issue by opening both the SAC contact and the interconnect contact at the same time. For example, U.S. Pat. No. 5,668,065 to Chen-Hsi Lin (the entire disclosure of which is herein incorporated by reference) provides a method of simultaneously forming silicide-based self-aligned contacts and local interconnects. Referring now more particularly to FIGS. 2A-2C, there are illustrated the cross sectional views of the SAC process disclosed by Lin. The figures show a portion of the core region and also a portion of the peripheral region in which a MOSFET IC device is built. FIG. 2A shows a first photoresist pattern 244 formed to define source/drain contacts and interconnect contacts. The gates 220 of the IC device are formed on a semiconductor substrate 210. The gate structure comprises a gate dielectric layer 222, a polysilicon gate layer 224, a tungsten silicide layer 226, and a cap dielectric layer 228. Sidewall spacers 230 and a liner layer 232 such as a thin oxide layer are formed on the sidewalls of the gate structure to protect the structure from over etching and short circuit. A common source 214 is formed between two gate structures, and drains 212 are also formed in the semiconductor substrate and spaced apart from the common source by channel regions. The liner layer 232 is also formed over a field oxide isolation region 216. Thereafter, the source/drain SAC contact opening and interconnect contact opening are simultaneously formed using a photoresist pattern 234 as a mask.
FIG. 2B shows a cross-sectional view of the IC substrate in which an amorphous silicon layer 240 is formed and etched by using a second photoresist pattern 244 as a mask to remove the exposed portion of the amorphous layer and liner layer. After the second photoresist pattern is removed, FIG. 2C shows the forming of a silicide layer 250 in both the source/drain SAC contact 252 and the interconnect contact.
However, this approach can not be used in a high speed operation device if interlayer dielectric (ILD) thickness difference occurs between the core region and the peripheral region as described in FIG. 1D. Therefore, there is still a need for a process which can effectively solve the above-mentioned problems of the prior art.
SUMMARY OF THE INVENTION
The present invention is directed to solve these and other disadvantages of the prior art. A method of forming self-aligned contacts of a core region and local interconnects of a course region of a peripheral region of a semiconductor device is disclosed. This is achieved by the etching step having high selectivity with respect to a dielectric layer and sidewall spacers of the semiconductor device.
One aspect of the present invention contemplates a method for formation of a self-aligned contact of a core region and a local interconnect of a peripheral region of an integrated circuit. The method includes the steps of etching a cap dielectric layer to form a hole and a trench of the cap dielectric layer, etching a dielectric layer to form a hole and a trench of the dielectric layer of the dielectric layer, etching a liner layer on a shoulder of sidewall spacers associated with the hole and with the trench of the dielectric layer without etching the liner layer at a bottom area of the hole and the trench, performing an oxygen flushing to remove polymer residues, and etching through the liner layer that lines the bottom area of the hole and the trench.
Another aspect of the present invention provides a method of fabricating a semiconductor device on a semiconductor substrate. The method comprising the steps of forming a gate structure on the semiconductor substrate, forming sidewall spacers around the gate structures, forming a silicon nitride (SiN) liner layer over the semiconductor substrate, forming a dielectric layer over the semiconductor substrate, forming a photoresist pattern to define a hole associated with at least one self-aligned contact and a trench associated with a local interconnect opening, and etching the dielectric layer and the SiN liner layer and sidewall spacers before etching the portion of the SiN liner layer that lines a bottom area of the hole and the trench to form at least one self-aligned contact and local interconnect opening.
Another aspect of the present invention provides a method of fabricating a semiconductor device on a semiconductor substrate. The method comprising the steps of forming sidewall spacers around a gate-structure on the semiconductor substrate in a core region and around a gate-structure in a peripheral region on the semiconductor substrate, thereby forming a hole and a trench respectively, forming a silicon nitride (SiN) liner layer and a dielectric layer on the substrate, and etching the dielectric layer and the SiN liner layer on the sidewall spacers before etching a portion of the SiN liner layer that lines a bottom area of the hole and the trench to form a self-aligned contact and a local interconnect opening.
Yet another aspect of the present invention provided a method of fabricating a semiconductor device on a semiconductor substrate. The method comprising the steps of forming sidewall spacers around a gate-structure on the semiconductor substrate in a core region and around a gate-structure in a peripheral region on the semiconductor substrate, thereby forming a hole in a source region of the substrate and a trench in a drain region of the substrate, respectively, forming a silicon nitride (SiN) liner layer and a dielectric layer on the substrate, and etching the dielectric layer and the SiN liner layer on the sidewall spacers before etching a portion of the SiN liner layer that lines a bottom area of the hole and the trench to form a self-aligned contact in the source region and a local interconnect opening in the drain region.



BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings are included to provide a further understanding of the present invention, and are incorporated in and constitute a part of the description to this invention. The drawings illustrate embodiments of the present invention, and together with the description, serve to explain the principles of the present invention. There is shown:
FIG. 1A illustrates a portion of a partially completed dual gate flash memory device after a dielectric layer is deposited according to the prior art;
FIG. 1B illustrates the simultaneous forming of the source/drain contact and interconnect contact by using a photoresist pattern as a mask according to the prior art;
FIG. 1C illustrates the forming only the interconnect contact by using a second photoresist pattern as a mask in the peripheral region according to the prior art;
FIG. 1D illustrates a metal layer being deposited and planarized to complete the formation of both the SAC contact and the interconnect contact according to the prior art;
FIG. 2A illustrates a portion of a partially completed memory device after a first photoresist pattern is formed to define source/drain contacts and interconnect contacts according to the prior art;
FIG. 2B illustrates a cross-sectional view of the IC substrate in which an amorphous silicon layer is formed and etched by using a second photoresist pattern as a mask according to the prior art;
FIG. 2C illustrates the forming of a silicide layer in both source/drain SAC contact and the interconnect areas according to the prior art;
FIG. 3A illustrates a portion of a partially completed semiconductor device according to an embodiment of the present invention;
FIG. 3B illustrates a portion of a partially completed semiconductor device after self-aligned contact and local interconnect opening photoresist patterns are formed according to an embodiment of the present invention;
FIG. 3C illustrates a portion of a partially completed semiconductor device after initial etching steps are performed to form a self-aligned contact and local interconnect openings according to an embodiment of the present invention; and
FIG. 3D illustrates a portion of a partially completed semiconductor device after self-aligned contact and local interconnect openings are formed according to an embodiment of the present invention.



DESCRIPTION OF THE PREFERRED EMBODIMENTS
The invention disclosed herein is directed to a fabricating process flow for forming self-aligned contacts and local interconnects of a semiconductor device. The drawing figures illustrate a partially completed flash memory device as an exemplary application of the present invention. In the following description, numerous details are set forth in order to provide a thorough understanding of the present invention. It will be appreciated by one skilled in the art that variations of these specific details are possible while still achieving the results of the present invention. In other instances, well-known processing steps are not described in detail in order not to unnecessarily obscure the present invention.
Referring now more particularly to FIG. 3A, there is shown a portion of a partially completed semiconductor device according to an embodiment of the present invention. The figures show a portion of a core region 310 and also a portion of a peripheral region 330 in which the semiconductor device is built.
First, a multi-layer stacked gate structure of the core region 310 and also of the peripheral region 330 is simultaneously formed on a semiconductor substrate 300. The formation of the multi-layer stacked gate structure comprises growing a gate dielectric layer (not shown), and sequentially depositing a floating gate layer 304, an interpoly dielectric layer (not shown), a control gate layer 306, a gate silicide layer 308, and a cap dielectric layer 312. Thereafter, the multi-layer stacked gate structure is patterned by conventional photolithography and etching techniques.
In one embodiment, the semiconductor device is a non-volatile memory such as a flash, EPROM, or EEPROM. However, other types of memory devices or logic devices can also work by utilizing the process disclosed by the present invention. The gate dielectric layer is a thin layer of oxide with a thickness between 50 to 100 angstroms. The floating gate layer 304 is typically a polysilicon layer formed by the conventional chemical vapor deposition (CVD) process. The interpoly dielectric layer is a thin layer of oxide-nitride-oxide (ONO). The control gate layer 306 is another CVD formed polysilicon layer. The gate silicide layer 308 is typically a layer of tungsten silicide (WSi). And the cap dielectric layer 312 is a layer of silicon nitride (Si3N4) with a thickness between 1000 to 2000 angstroms.
Next, spacers 314 are formed on the sidewalls of the gates, and a thin liner layer 316 is also formed over the entire semiconductor substrate 300. Then, source/drain regions 318 are formed to complete the multi-layer stacked gate structure as shown in FIG. 3A.
In one embodiment, the sidewall spacers 314 are typically made of silicon nitride (SiN) and anisotropically etched by the conventional technique. The source/drain regions 318 which are typically formed by ion implantation technique, are preferably doped with arsenic (As75) or phosphorus (p31) impurities, with an implantation dose of about 2E15 to 5E16 cm−2, and an implantation energy of 30 to 80 KeV. Lightly doped drain (LDD) region can be formed to improve the operational speed of the IC. The liner layer 316 also uses silicon nitride (SiNx) formed by the LPCVD technique with a thickness between 100 to 200 angstroms as an etch stop layer of the self-aligned contact (SAC) process.
Referring now more particularly to FIG. 3B, there is shown a portion of a partially completed semiconductor device after a self-aligned contact and a local interconnect opening photoresist patterns are formed according to an embodiment of the present invention. A dielectric layer is first formed over the entire semiconductor substrate. Thereafter, self-aligned contact and local interconnect opening photoresist patterns are formed.
In one embodiment, the dielectric layer comprises three dielectric layers of a boronphosphosilicate glass (BPSG) 320, tetra-ethyl-ortho silicate (TEOS) 322 and silicon oxynitride (SiON) cap layer 324 from bottom to top as shown in FIG. 3B. The BPSG layer 320 is usually formed by an atmosphere CVD (APCVD) technique with a thickness of about 3000 to 8000 angstroms. The TEOS layer 320 is usually formed by a plasma CVD (PECVD) technique with a thickness of about 1000 to 3000 angstroms. The silicon oxynitride (SiON) cap layer 324 is usually used as an anti-reflection coating (ARC) layer with a thickness of about 500 to 1000 angstroms. However, a single dielectric layer or a double dielectric layers can also work. The SAC contact opening 315 and local interconnect contact opening 335 photoresist pattern are formed by the conventional photolithography technique.
Referring now to FIG. 3C, there is shown a portion of a partially completed semiconductor device after a self-aligned contact and a local interconnect are formed according to an embodiment of the present invention.
This etching step is one of the key points of the present invention. The self-aligned contact and local interconnect opening are formed by the etching recipe of the present invention. In one embodiment, the etching is achieved by a five step etching recipe disclosed herein. The first step is etching the silicon oxynitride (SiON) cap layer 324 and the TEOS layer 322. The etching recipe uses a source power of 800 watts, a bias power of 400 watts, and the etchant comprises CF4 at a flow rate of 60 sccm, Ar at a flow rate of 270 sccm, and O2 at a flow rate of 10 sccm, all for 40 seconds. The second step is a main step comprising etching the BPSG layer 320 and stopping at approximately the level of the shoulder of the sidewall spacers 314. The etching recipe which has a higher selectivity of BPSG to SiN uses a source power of 1400 watts, a bias power of 1100 watts, and the etchant comprises C4F6 at a flow rate of between 10 to 13 sccm, Ar at a flow rate of between 200 to 300 sccm, and O2 at a flow rate of 10 sccm, all for 45 seconds. Most preferably, the etchant comprises C4F6 at a flow rate of 10 sccm, and Ar at a flow rate of 300 sccm. The third step is an over etch step which etches the remaining BPSG layer 320 and the SiNx liner layer 316 on the sidewall spacers 314 and stops on the SiN sidewall spacers 314 and the liner layer 316 at the bottom area of the trench and hole. The etching recipe uses a source power of 1400 watts, a bias power of 1100 watts, and the etchant comprises C4F6 at a flow rate of between 10 to 13 sccm, Ar at a flow rate of between 200 to 300 sccm, and O2 at a flow rate of 10 sccm, all for 60 seconds. Most preferably, the etchant comprises C4F6 at a flow rate of 11 sccm, Ar at a flow rate of 300 sccm. The fourth step is an O2 flush step which removes the polymer residue at the bottom of the openings. The etching recipe uses a source power of 400 watts, a bias power of 200 watts, and the etchant comprises Ar at a flow rate of 250 sccm, and O2 at a flow rate of 10 sccm, both for 10 seconds. Finally, as illustrated in FIG. 3D, the fifth step is a through etch step which etches through the remaining SiNx liner layer 316 at the bottom of the trench and hole. The etching recipe uses a source power of 300 watts, a bias power of 100 watts, and the etchant comprises Ar at a flow rate of 850 sccm, CH3F at a flow rate of 50 sccm, and O2 at a flow rate of 300 sccm, all for 40 seconds. According to the present invention, the etching rate in the core (hole) region is about 8000 angstroms/minute, and the etching rate in the peripheral (trench) region is about 7900 angstroms/minute.
In this way, the etching rates are substantially the same in both the core (hole) and peripheral (trench) regions. Therefore, the self-aligned contacts and local interconnect openings can be formed without the problems of the prior arts.
Referring again to FIG. 3D, after the self-aligned contact and local interconnect opening are formed according to an embodiment of the present invention, the photoresist pattern is removed by the conventional stripping technology. The self-aligned contact and local interconnect opening are then filled by a conductive metal layer 340 and are planarized. The fabricating method of forming self-aligned contacts and local interconnects according to the present invention thus achieves its goal of reducing masking and etching steps
While the invention has been particularly shown and described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention.

## Claims

1. A method for formation of a contact and a local interconnect of an integrated circuit, comprising the steps of:
etching a cap dielectric layer to form a hole and a trench of the cap dielectric layer;
etching a dielectric layer to form a hole and a trench of the dielectric layer of the dielectric layer;
etching a liner layer on a shoulder of sidewall spacers associated with the hole and with the trench of the dielectric layer without etching the liner layer at a bottom area of the hole and the trench;
performing an oxygen flushing to remove polymer residues; and
etching through the liner layer that lines the bottom area of the hole and the trench.

2. The method of claim 1, wherein the etching of the dielectric layer and the etching of the liner layer have a high selectivity with respect to the dielectric layer and the sidewall spacers.

3. The method of claim 1, wherein the cap dielectric layer includes silicon oxynitride (SiON) and tetra-ethyl-ortho silicate (TEOS).

4. The method of claim 1, wherein the dielectric layer includes boronphosphosilicate glass (BPSG).

5. The method of claim 1, wherein the sidewall spacers include silicon nitride (SiN).

6. The method of claim 1, wherein the etching of the dielectric layer includes an etchant comprising Ar, C4F6, and O2.

7. The method of claim 6, wherein the etching of the dielectric layer includes an etchant comprising Ar at a flow rate between 200 to 300 sccm, and C4F6 at a flow rate between 10 to 13 sccm.

8. The method of claim 1, wherein the etching of the liner layer includes an etchant-comprising Ar, C4F6, and O2.

9. The method of claim 8, wherein the etching of the liner layer includes an etchant comprising Ar at a flow rate between 200 to 300 sccm, and C4F6 at a flow rate between 10 to 13 sccm.

10. A method of fabricating a semiconductor device on a semiconductor substrate, comprising the steps of:
forming a gate structure on the semiconductor substrate;
forming sidewall spacers around the gate structures;
forming a silicon nitride (SiN) liner layer over the semiconductor substrate;
forming a dielectric layer over the semiconductor substrate;
forming a photoresist pattern to define a hole associated with at least one self-aligned contact and a trench associated with a local interconnect opening; and
etching the dielectric layer and the SiN liner layer before etching the portion of the SiN liner layer that lines a bottom area of the hole and the trench to form at least one self-aligned contact and local interconnect opening.

11. The method of claim 10, wherein the etching has a high selectivity with respect to the dielectric layer and the sidewall spacers.

12. The method of claim 10, wherein the semiconductor device includes a non-volatile memory.

13. The method of claim 12, wherein the non-volatile memory includes a flash memory.

14. The method of claim 12, wherein the gate-structure includes a multi-layered gate structure.

15. The method of claim 10, wherein the dielectric layer includes silicon oxynitride (SiON), tetra-ethyl-ortho silicate (TEOS), and boronphosphosilicate glass (BPSG).

16. The method of claim 10, wherein the sidewall spacer layer includes silicon nitride (SiN).

17. The method of claim 10, wherein the etching includes an etchant comprising Ar, C4F6, and O2.

18. The method of claim 17, wherein the etching includes an etchant comprising Ar at a flow rate between 200 to 300 sccm, and C4F6 at a flow rate between 10 to 13 sccm both for about 45 seconds.

19. The method of claim 18, wherein the etching further includes an etchant comprising Ar at a flow rate between 200 to 300 sccm, and C4F6 at a flow rate between 10 to 13 sccm both for about 60 seconds.

20. A method of fabricating a semiconductor device on a semiconductor substrate, comprising the steps of:
forming sidewall spacers around a gate-structure on the semiconductor substrate in a core region and around a gate-structure in a peripheral region on the semiconductor substrate, thereby forming a hole and a trench respectively;
forming a silicon nitride (SiN) liner layer and a dielectric layer on the substrate; and
etching the dielectric layer and the SiN liner layer on the sidewall spacers before etching a portion of the SiN liner layer that lines a bottom area of the hole and the trench to form a self-aligned contact and a local interconnect opening.

21. The method of claim 20, wherein the etching has a high selectivity with respect to the dielectric layer and the sidewall spacers.

22. The method of claim 20, wherein the semiconductor device includes a non-volatile memory.

23. The method of claim 22, wherein the non-volatile memory includes a flash memory.

24. The method of claim 22, wherein the gate-structure includes a multi-layered gate structure.

25. The method of claim 20, wherein the dielectric layer includes silicon oxynitride (SiON), tetra-ethyl-ortho silicate (TEOS), and boronphosphosilicate glass (BPSG).

26. The method of claim 20, wherein the sidewall spacer layer includes silicon nitride (SiN).

27. The method of claim 20, wherein the etching includes an etchant comprising Ar, C4F6, and O2.

28. The method of claim 20, wherein the etching includes an etchant comprising Ar at a flow rate between 200 to 300 sccm, and C4F6 at a flow rate between 10 to 13 sccm both for about 45 seconds.

29. The method of claim 28, wherein the etching further includes an etchant comprising Ar at a flow rate between 200 to 300 sccm, and C4F6 at a flow rate between 10 to 13 sccm both for about 60 seconds.

30. A method of fabricating a semiconductor device on a semiconductor substrate, comprising the steps of:
forming sidewall spacers around a gate-structure on the semiconductor substrate in a core region and around a gate-structure in a peripheral region on the semiconductor substrate, thereby forming a hole in a source region of the substrate and a trench in a drain region of the substrate, respectively;
forming a silicon nitride (SiN) liner layer and a dielectric layer on the substrate; and
etching the dielectric layer and the SiN liner layer on the sidewall spacers before etching a portion of the SiN liner layer that lines a bottom area of the hole and the trench to form a self-aligned contact in the source region and a local interconnect opening in the drain region.