# Patent

## Title
Oxygen-rich layers underlying BPSG

## Abstract

An integrated circuit structure and a method of forming the same are provided. The method includes providing a surface; performing an ionized oxygen treatment to the surface; forming an initial layer comprising silicon oxide using first process gases comprising a first oxygen-containing gas and tetraethoxysilane (TEOS); and forming a silicate glass over the initial layer. The method may further include forming a buffer layer using second process gases comprising a second oxygen-containing gas and TEOS, wherein the first and the second process gases have different oxygen-to-TEOS ratio.

## Background
This application is a divisional of U.S. patent application Ser. No. 11/803,437, entitled “Oxygen-Rich Layers Underlying BPSG,” filed on May 15, 2007, which application is incorporated herein by reference.


TECHNICAL FIELD
This invention relates generally to integrated circuits, and more particularly to the formation of dielectric layers underlying boron and/or phosphorous containing silicate glass.
BACKGROUND
In modern integrated circuits, semiconductor devices are formed on semiconductor substrates, and are connected through metallization layers. The metallization layers are interconnected to the semiconductor devices through contact plugs. Also, external pads are connected to the semiconductor devices through the contact plugs.
The metallization layers are separated from each other by dielectric layers. Further, the metallization layers are separated from active devices by an inter-layer dielectric (ILD). Conventionally, the dielectric layers, particularly the ILDs, are often formed of boronphosphosilicate glass (BPSG).
FIG. 1 illustrates a conventional structure. Transistors 4, which include gates 16 and source/drain regions 14, are formed at the surface of semiconductor substrate 2. Inter-layer dielectric (ILD) 10 is formed on transistors 4. Contact plugs 6 are formed in ILD 10 to electrically connect source and drain regions 14 and gates 16 to metal lines 7 in metallization layer 8. Typically, the formation of contact plugs 6 includes forming openings in ILD 10, and then filling the openings with tungsten plugs. A single damascene process is then performed to form metallization layer 8.
With the down-scaling of integrated circuits, the formation of ILD 10 experiences shortcomings. Due to the increase in the aspect ratio of the gaps between transistors 4, the gap filling of ILD 10 becomes increasingly difficult. Particularly, at the top corners 18 of the gate structures, BPSG tends to be deposited faster than in the middle region between gates 16, hence void 11 may be generated. This situation becomes worse in integrated circuits formed using 90 nm technology or below. Also, boron and phosphorous tend to accumulate in the bottom portions of the BPSG ILD 10. In the etching of ILD 10 for forming contact openings, lateral etching may result in the bottom portions of the BPSG ILD 10. In addition, boron and phosphorous may penetrate into devices, resulting the electrical property shift and even the failure of the devices.
Accordingly, what is needed in the art is a new dielectric structure and formation methods for solving the above-discussed problems.
SUMMARY OF THE INVENTION
In accordance with one aspect of the present invention, a method for forming an integrated circuit structure includes providing a surface; performing an ionized oxygen treatment to the surface; forming an initial layer comprising silicon oxide using first process gases comprising a first oxygen-containing gas and tetraethoxysilane (TEOS); and forming a silicate glass over the initial layer.
In accordance with another aspect of the present invention, a method of forming an integrated circuit structure includes providing a semiconductor substrate; forming an initial layer over the semiconductor substrate using process gases comprising first oxygen-containing gas and a first TEOS, wherein a flow rate of the first oxygen-containing gas and a flow rate of the TEOS have a first ratio; forming a buffer layer over the initial layer using process gases comprising a second oxygen-containing gas and TEOS, wherein a flow rate of the second oxygen-containing gas and a flow rate of the TEOS have a second ratio, and wherein the first ratio is substantially greater than the second ratio; and forming a boronphosphosilicate glass (BPSG) layer over the buffer layer.
In accordance with yet another aspect of the present invention, a method of forming an integrated circuit structure includes providing a semiconductor substrate and forming a transistor at a top surface of the semiconductor substrate. The step of forming the transistor includes forming a gate stack on the semiconductor substrate; forming a gate spacer on a sidewall of the gate stack; forming a source/drain region adjacent the gate stack; and forming a source/drain silicide region on the source/drain region. The method further includes providing ionized ozone to activate exposed surfaces of materials over the semiconductor substrate; blanket forming an initial layer on the exposed surfaces using process gases comprising a first oxygen-containing gas and TEOS, wherein a flow rate of the first oxygen-containing gas and a flow rate of the TEOS have a first ratio of greater than about 8; forming a buffer layer on the initial layer using process gases comprising a second oxygen-containing gas and TEOS, wherein a flow rate of the second oxygen-containing gas and a flow rate of the TEOS have a second ratio of less than about 3; and forming an inter-layer dielectric (ILD) layer comprising BPSG, wherein the buffer layer is between and adjoining the initial layer and the ILD layer.
In accordance with yet another aspect of the present invention, an integrated circuit structure includes a semiconductor substrate; an initial layer comprising a first silicon oxide over the semiconductor substrate, wherein the first silicon oxide has a first oxygen-to-silicon atomic ratio; a silicate glass over the initial layer; and a buffer layer comprising a second silicon oxide between and adjoining the initial layer and the silicate glass, wherein the second silicon oxide has a second oxygen-to-silicon atomic ratio substantially less than the first oxygen-to-silicon atomic ratio.
In accordance with yet another aspect of the present invention, an integrated circuit structure includes a semiconductor substrate and a transistor. The transistor includes a gate stack on the semiconductor substrate; a gate spacer on a sidewall of the gate stack; a source/drain region adjacent the gate stack; and a source/drain silicide region on the source/drain region. The integrated circuit structure further includes an initial layer comprising a first TEOS oxide over the semiconductor substrate and the transistor; a buffer layer comprising a second TEOS oxide on the initial layer, wherein the first TEOS oxide comprises more oxygen than the second TEOS oxide; and a BPSG on the buffer layer, wherein the buffer layer is between and adjoins the initial layer and the BPSG.
The advantageous features of the present invention include improved gap filling ability of dielectric layers and reduced lateral etching in the dielectric layer.



BRIEF DESCRIPTION OF THE DRAWINGS
For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:
FIG. 1 illustrates a conventional semiconductor structure having an inter-layer dielectric comprising boronphosphosilicate glass, wherein a void is formed; and
FIGS. 2 through 7 are cross-sectional views of intermediate stages in the manufacturing of an embodiment of the present invention.



DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
The making and using of the presently preferred embodiments are discussed in detail below. It should be appreciated, however, that the present invention provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative of specific ways to make and use the invention, and do not limit the scope of the invention.
A novel method for forming dielectric layers is provided. The intermediate stages of manufacturing a preferred embodiment of the present invention are illustrated. The variations of the preferred embodiment are then discussed. Throughout the various views and illustrative embodiments of the present invention, like reference numbers are used to designate like elements.
FIGS. 2 though 7 illustrate cross-sectional views of an embodiment of the present invention. Referring to FIG. 2, substrate 20 is provided. Substrate 20 is preferably a semiconductor substrate, which may include single-crystalline semiconductor materials such as silicon, or compound materials comprising commonly used group III, group IV and group V elements.
Transistors 100 and 200 are formed at the surface of substrate 20. Transistor 100 includes gate dielectric 124, gate electrode 126, gate spacers 128, source/drain regions 134 and silicide regions 130. Similarly, transistor 200 includes gate dielectric 224, gate electrode 226, gate spacers 228, source/drain regions 234 and silicide regions 230. Shallow trench isolation (STI) regions 22 may be formed to isolate semiconductor devices.
In an embodiment, STI regions 22 are formed of dielectric materials, such as high-density plasma (HDP) oxides, plasma enhanced oxides, thermal reacted oxides, and the like. Gate spacers 128 and 228 are also formed of dielectric materials, such as oxides, nitrides, oxynitrides, and the like. In the preferred embodiment, gate spacers 128 and 228 each include a silicon nitride layer on a liner oxide. Silicide regions 130 and 230 may comprise metal silicides or metal germano-silicides, wherein the metals in silicide regions 130 and 230 may include cobalt, nickel, platinum, palladium, tantalum, ruthenium, tungsten, and combinations thereof.
Referring to FIG. 3, etch stop layer (ESL) 24 is formed over substrate 20 transistors 100 and 200. In an embodiment, ESL 24 includes silicon nitride. In other embodiments, ESL 24 includes other commonly used dielectric materials, such as silicon oxynitride, silicon oxycarbide, silicon carbide, and the like. A thickness T1 of ESL 24 is preferably less than about 600 Å, and more preferably between about 200 Å and about 600 Å.
In alternative embodiments, ESL 24 is omitted, and the subsequently formed initial layer, buffer layer and inter-layer dielectric (ILD) are formed directly on transistors 100 and 200, and other active or passive devices (not shown), which may include resistors, capacitors, and the like. For simplicity, in subsequently discussed drawings, ESL 24 is not shown.
Referring to FIG. 4, the exposed surfaces of the structures formed in the preceding steps are treated in an oxygen-containing gas. In the preferred embodiment, the oxygen-containing gas contains O3 (ozone). Alternatively, the oxygen-containing gas contains O2 or a combined gas of ozone and O2. A radio frequency (RF) power is applied, which breaks the bonds of the oxygen-containing gas and results in ionized oxygen, or an oxygen-containing plasma. The RF power needs to be low to avoid the bombardment to the exposed surfaces. Alternatively, a remote plasma of the oxygen-containing gas is used to activate the exposed surfaces, wherein the remote plasma is generated in a separate chamber and introduced into the chamber where the substrate 20 is located. In an exemplary embodiment, the RF power is less than about 100 watts, and the oxygen-containing gas has a flow rate of between about 5000 sccm and about 10000 sccm.
The treatment activates the exposed surfaces, resulting in the exposed surfaces to have greater electro negativity, and hence the bondability of the exposed surfaces is improved. Accordingly, the treatment is referred to as a surface activation process. The treatment also causes an increase in the number of precursor nucleation sites. In FIG. 4, O* is used to symbolize the nucleation sites with increased electro negativity. With the combination of improved bondability and increased number of precursor nucleation sites, the exposed surfaces have a greater and a more uniform ability to bond with the subsequently formed oxide layer. Such an improvement is particularly advantageous for the surfaces comprising different materials, such as oxides, nitrides, metal silicides, and the like, as is illustrated in FIG. 4. The bondability difference between different materials is accordingly reduced.
Referring to FIG. 5, initial layer 30, which is preferably performed using a chemical vapor deposition (CVD) method, is formed. In the preferred embodiment, the process gases for forming initial layer 30 include an oxygen-containing gas, which includes O2, O3, or the combinations thereof, and tetraethoxysilane (TEOS). The reaction of the oxygen-containing gas and TEOS results in the formation of TEOS oxide (silicon oxide). Preferably, the flow rate of the oxygen-containing gas and the flow rate of TEOS have a ratio (referred to as oxygen-to-TEOS ratio hereinafter) of greater than about eight. In an exemplary embodiment, the oxygen-containing gas has a flow rate of between about 1000 sccm and about 5000 sccm, while TEOS has a flow rate of between about 100 mgm and about 300 mgm. The resulting initial layer 30 may have a thickness of between about 5 nm and about 20 nm. The formation of initial layer 30 is preferably performed at elevated temperatures, for example, between about 300° C. and about 500° C. However, the reaction may also be plasma-assisted.
Advantageously, the TEOS oxide with a high oxygen-to-TEOS ratio has a high electro negativity, and is highly polarized, so that it can form strong bonds with the underlying surfaces. Combined with the greater and more uniform electro negativity of the underlying surfaces, the strong bonds of TEOS oxide result in improved gap filling ability and improved conformity of the subsequently gap filling materials. In the embodiment wherein ESL 24 (refer to FIG. 3) is formed, due to the fact that ESL 24 will have corners 25, which will adversely affect the gap filling of the subsequently formed ILD layer, the activation is still beneficial.
FIG. 5 also illustrates the formation of buffer layer 32, which may also be formed using chemical vapor deposition (CVD). In the preferred embodiment, buffer layer 32 is formed by introducing the same types of process gases as used in the formation of initial layer 30, for example, an oxygen-containing gas, which may be O2, O3, or the combinations thereof, and TEOS. In a more preferred embodiment, the formation of initial layer 30 and buffer layer 32 may be in-situ formed in the same reaction chamber, with no vacuum break therebetween. Preferably, the oxygen-to-TEOS ratio for forming buffer layer 32 is less than about three. In an exemplary embodiment, the oxygen-containing gas has a flow rate of between about 30 sccm and about 100 sccm, while TEOS has a flow rate of between about 100 mgm and about 500 mgm sccm. The resulting buffer layer 32 may have a thickness of between about 10 nm and about 50 nm. Similar to the formation of initial layer 30, the reaction may be performed thermally and/or with plasma.
The reduced oxygen-to-TEOS ratio results in the greater hardness of buffer layer 32. Advantageously, the greater percentage of TEOS in buffer layer 32 results in a relatively silicon-rich oxide, and hence more potential bonds (since each silicon atom has four vacancy sites). Since the subsequently formed boronphosphosilicate glass (BPSG) includes boron and phosphorous, which tend to have dangling bonds, the increased number of silicon atoms in buffer layer 32 may form more bonds with the boron and phosphorous atoms, and thus the adhesion between buffer layer 32 and the overlying BPSG increases. The adhesion between initial layer 30 and buffer layer 32 is satisfactory because of the similarity of these two layers. Therefore, buffer layer 32 acts as an excellent adhesion layer to bond together initial layer 30 and the subsequently formed BPSG layer.
A further advantageous feature of buffer layer 32 is that it acts as a penetration stop layer (PSL), preventing boron and phosphorous in the overlying BPSG from penetrating into the underlying devices, which may result in the electrical property shift of the underlying devices.
As a result of the above-discussed process steps, in initial layer 30, the TEOS oxide is relatively oxygen rich with a first oxygen-to-silicon atomic ratio, while in buffer layer 32, the TEOS oxide is relatively silicon rich with a second oxygen-to-silicon atomic ratio. Preferably, a ratio of the first oxygen-to-silicon atomic ratio to the second oxygen-to-silicon atomic ratio is greater than about 8.
Next, ILD layer 34 is deposited on buffer layer 32, preferably by a CVD process, as is illustrated in FIG. 6. ILD layer 34 may be formed by introducing TEOS, a phosphorus-containing source, and a boron-containing source into a processing chamber along with an oxygen-containing gas. The resulting ILD layer 34 includes BPSG. An example of the phosphorus-containing source is tri-methyl-phosphate (TMPO). An example of the boron-containing source is tri-methyl-borate (TMB). In an exemplary embodiment, ILD layer 34 has a thickness of between about 200 nm and about 1200 nm. Alternatively, ILD layer 34 may include other types of silicate glasses, such as boron silicate glass or phosphosilicate glass. One skilled in the art will realize the respective precursors and the formation methods.
FIG. 7 illustrates the formation of contacts 36 used for connecting transistors 100 and 200 to the lowest metallization layer 40 (commonly referred to as M1). As is known in the art, to form contacts 36, contact openings are first formed by etching ILD 34. Metallic materials, such as tungsten, are then filled into the contact openings. Metallization layer 40, which includes metal lines 38 in dielectric layer 42, is then formed, preferably by a single damascene process.
Experiment results have shown that the embodiments of the present invention can effectively prevent lateral etching and the formation of voids. The samples having initial layers formed with oxygen-to-TEOS ratios less than about eight exhibit voids. However, similar samples formed using similar techniques, except that the oxygen-to-TEOS ratios are greater than eight, exhibited no noticeable voids. In other experiments, the samples having buffer layers formed with oxygen-to-TEOS ratios greater than three, the CESL exhibits lateral etching. However, similar samples, except the buffer layers were formed with oxygen-to-TEOS ratios less than three, showed no lateral etching.
In the embodiments discussed in the preceding paragraphs, although BPSG is used to form ILD, which underlies the lowest metallization layer, one skilled in the art will realize the teaching of the present invention is readily available for the formation of other dielectric layers, such as inter-metal dielectric layers, which are formed between metallization layers. Further, the formation of initial layer 30 and buffer layer 32 not only improves the ILD formation over transistors, the ILD formation on other devices and materials, such as resistors, capacitors, etch stop layers, and the like, also benefit from the improved conformity, adhesion, and penetration prevention ability.
Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, and composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed, that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.

## Claims

1. A method of forming an integrated circuit structure, the method comprising:
performing an ionized oxygen treatment to an exposed surface, wherein the exposed surface comprises a surface of a metal silicide region using ionized ozone;
forming an initial layer comprising silicon oxide over and contacting the exposed surface, wherein the step of forming the initial layer is performed using first process gases comprising a first oxygen-containing gas and tetraethoxysilane (TEOS); and
forming a silicate glass over the initial layer.

2. The method of claim 1 further comprising, between the steps of forming the initial layer and the silicate glass, forming a buffer layer over and contacting the initial layer using second process gases different from the first process gases, wherein the buffer layer comprises silicon oxide, and wherein the buffer layer has a higher silicon concentration than the initial layer.

3. The method of claim 2, wherein the second process gases comprise a second oxygen-containing gas and TEOS, and wherein the first process gases have a first oxygen-to-TEOS ratio greater than a second oxygen-to-TEOS ratio of the second process gases.

4. The method of claim 3, wherein the first oxygen-to-TEOS ratio is greater than about 8, and the second oxygen-to-TEOS ratio is less than about 3.

5. The method of claim 2, wherein the first process gases and the second process gases comprise same types of gases, with at least one of the same types of gases in the first process gases having a first flow rate different from a second flow rate of the at least one of the same types of gases in the second process gases.

6. The method of claim 2, wherein the initial layer and the buffer layer are free from boron and phosphorous. one of the same types of gases in the second process gases.

7. The method of claim 1, wherein the step of performing the ionized oxygen treatment comprises:
introducing a treatment gas selected from the group consisting essentially of O2, O3, and combinations thereof; and
providing a radio frequency (RF) power to activate the treatment gas.

8. The method of claim 1, wherein the exposed surface further comprises surfaces of materials selected from the group consisting essentially of oxides, nitrides, oxynitrides, metal silicides, and combinations thereof.

9. The method of claim 1 further comprising:
forming a transistor comprising:
forming a gate stack on a semiconductor substrate;
forming a gate spacer on a sidewall of the gate stack; and
forming a source/drain region adjacent the gate stack; and
forming a source/drain silicide region on the source/drain region, wherein the exposed surface comprises a top surface of the source/drain silicide region and a sidewall of the gate spacer.

10. A method of forming an integrated circuit structure, the method comprising:
providing a substrate;
forming an initial layer over the substrate using process gases comprising a first oxygen-containing gas and a first tetraethoxysilane (TEOS), wherein a flow rate of the first oxygen-containing gas and a flow rate of the first TEOS have a first ratio;
forming a buffer layer over the initial layer using process gases comprising a second oxygen-containing gas and a second TEOS, wherein a flow rate of the second oxygen-containing gas and a flow rate of the second TEOS have a second ratio, and the first ratio is greater than the second ratio, and wherein the initial layer and the buffer layer are silicon oxide layers substantially free from boron and phosphorous, with the buffer layer being more silicon-rich than the initial layer; and
forming a boronphosphosilicate glass (BPSG) layer over the buffer layer.

11. The method of claim 10, wherein the first ratio is greater than about 8/3 of the second ratio.

12. The method of claim 10, wherein each of the first and the second oxygen-containing gases is selected from the group consisting essentially of O2, ozone, and combinations thereof.

13. The method of claim 10, wherein the first and the second oxygen-containing gases are ozone.

14. The method of claim 10 further comprising, before the step of forming the initial layer, performing an ionized oxygen treatment to an exposed metal silicide region at a top surface of the substrate, the ionized oxygen treatment including:
introducing a treatment gas selected from the group consisting essentially of O2, ozone, and combinations thereof; and
providing a radio frequency (RF) power to activate the treatment gas.

15. The method of claim 14, wherein the steps of introducing the treatment gas and providing the RF power are performed in a chamber separated from a chamber in which the substrate is located.

16. The method of claim 10 further comprising, before the step of forming the initial layer, performing the steps of:
forming a transistor comprising:
forming a gate stack on the substrate;
forming a gate spacer on a sidewall of the gate stack;
forming a source/drain region adjacent the gate stack; and
forming a source/drain silicide region on the source/drain region, wherein the initial layer is over and contacts a top surface of the source/drain silicide region and a sidewall of the gate spacer.

17. A method of forming an integrated circuit structure, the method comprising:
providing a semiconductor substrate;
forming a transistor at a top surface of the semiconductor substrate comprising:
forming a gate stack on the semiconductor substrate;
forming a gate spacer on a sidewall of the gate stack;
forming a source/drain region adjacent the gate stack; and
forming a source/drain silicide region on the source/drain region;

providing ionized ozone to activate exposed surfaces of the source/drain silicide region and the gate spacer;
after the step of providing ionized ozone to activate exposed surfaces, blanket forming a first silicon oxide layer on the exposed surfaces using process gases comprising a first oxygen-containing gas and a first tetraethoxysilane (TEOS); and
changing flow rates of the process gases used in the forming of the first silicon oxide layer to form a second silicon oxide layer, wherein same types of process gases are used for forming the first and the second silicon oxide layers, and wherein the second silicon oxide layer has a greater silicon percentage than the first silicon oxide layer.

18. The method of claim 17, wherein a flow rate of the first oxygen-containing gas and a flow rate of the first TEOS have a first ratio of greater than about 8.

19. The method of claim 17, wherein the process gases used in the forming of the seconds silicon oxide layer comprises a second oxygen-containing gas and a second TEOS, and wherein a flow rate of the second oxygen-containing gas and a flow rate of the second TEOS have a second ratio of less than about 3.