# Patent

## Title
Interconnect structure and method for semiconductor device

## Abstract

An interconnect method in a semiconductor device may include a step of examining various regions of an inter layer dielectric to identify regions having high densities or concentrations of trench features. A cap insulator layer may be added to the dielectric to assist in outgassing of absorbed impurities from the dielectric, but may be removed from the high density areas to allow the lower density areas to increase outgassing. The lower density areas may then compensate for increased outgassing on the high density areas due to the trench features, and may result in an overall device with a more stable dielectric constant across the device.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims priority to, and is a divisional of, U.S. patent application Ser. No. 11/356,146, filed Feb. 17, 2006, hereby incorporated by reference herein as to its entirety.


BACKGROUND
Semiconductor manufacturing processes operate on a very small scale, where the tiniest amount of impurity in a semiconductor wafer can render the device inoperable. For this reason, there is a need for improved manufacturing methods that can help reduce the appearance and effects of impurities. Some such methods involve highly-filtered clean rooms, to help ensure that unwanted particulates are removed from the interior environment. While such filtering systems are beneficial, they are far from perfect, and there remain various types of impurities that can still exist in the filtered clean room. When such impurities remain in the clean room, they may unfortunately be absorbed by the semiconductor wafers and devices during the manufacturing process, leading to undesired results.
FIG. 1 illustrates a basic example of a semiconductor device during a manufacturing process that may experience such undesired results. In the process, circuit components are formed on a substrate, such as an interlayer (or interlevel) dielectric (ILD) 100. Components are formed by creating trenches 101 in the ILD 100, where the trenches are filled with different conductive/insulating/semiconductive materials to form interconnections, transistor elements, etc. of a semiconductor circuit. When the ILD 100 is manufactured in an environment having impurities, such as water moisture and ammonia particles, those impurities may be absorbed by the ILD 100. The absorption of such particles into the ILD 100 may have the undesired effect of lowering the dielectric constant (k) of the device(s) created on the ILD 100.
Manufacturing processes may include some steps, such as annealing, that may allow the ILD 100 to outgas some of the absorbed impurities. However, this outgassing might not occur uniformly. For example, ILD 100 may include some portions 102 that are relatively densely populated with trenches, while other portions 103 are more isolated, and not as densely populated. These portions experience different amounts of outgassing. In the denser portion 102, more outgassing can occur because of the larger surface area of the ILD 100 exposed by the trenches (e.g., the side walls of the trenches that extend into the ILD 100, and create additional surface area). In the less dense portion 103, less outgassing can occur because there is a smaller exposed surface area due to there being fewer trenches.
This imbalance in outgassing can lead to a variation in the ILD 100's dielectric constant (k) across portions of the device. Such variation can make it more difficult to reliably design and construct semiconductor devices, and it would be an advance in the art if this imbalance could be reduced and/or minimized.
SUMMARY
This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.
In some aspects, a semiconductor device manufacturing method may include steps of depositing a cap insulator layer on an inter layer dielectric, forming trenches in the dielectric, and identifying high and low density regions based on a concentration of trenches in the regions. Regions having higher densities of trenches, or trench densities that exceed a predetermined cutoff value, may have their cap insulator layers removed, so that the cap insulator layers remain only on the low density regions.
Interconnect material, such as barrier layers and/or seed metals, may be deposited in the trenches to form interconnects on the resulting device. In some aspects, and depending on the metals involved, a damascene process may be used for the deposition.
In some aspects, the removal may be performed after the interconnect material is deposited. This removal may be performed using chemical mechanical polishing, and by adjusting polishing rates over different regions of the inter layer dielectric. In other aspects, the removal may be performed before interconnect material is added to the trenches, such as by a photoresist etching process. A subsequent chemical mechanical polishing to remove unwanted interconnect material may be performed without having to adjust different polishing rates over different regions of the dielectric.
To determine whether a region has a high or low trench density, the surface area of a region may be compared with the surface area occupied by trenches in the region, and a resulting percentage may be compared against a predetermined cutoff value defining high and/or low density regions.
These and other features will be described in greater detail below.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates a basic example of a semiconductor manufacturing process.
FIGS. 2a-d illustrate steps in a semiconductor manufacturing process.
FIGS. 3a-e illustrate steps in an alternative semiconductor manufacturing process.



DETAILED DESCRIPTION
FIG. 2a illustrates an example ILD 100, which can be of any dielectric substance(s), such as silicon oxycarbide (SiCOH), CxHy, etc. The figure illustrates two portions of a semiconductor device, where a portion shown on the left will have a higher density of trenches than the portion shown on the right. A cap insulator 201 may be deposited on the ILD 100 using any desired deposition technique (e.g., vapor deposition, sputtering, etc.). The cap insulator 201 may be of any desired substance that can absorb undesired impurities. For example, tetraethoxysilane (TEOS) or silicon oxycarbide (SiCOH) can be used as the cap insulator 201 substance.
When the cap insulator 201 has been deposited, various trenches 202 may then be formed on the ILD 100 as needed to create the various circuit components, such as line interconnects. The trenches may be formed using any desired process, such as photoresist etching and/or other lithography. The trenches may then be lined 203 with a barrier material (such as a metal, like titanium nitride (TiN), tantalum nitride (TaN), titanium (Ti) and tantalum (Ta)), and a metal or other conductive material 204, such as copper (Cu), aluminum (Al), or silver (Ag), which may be deposited using any desired technique, such as by first applying a seed layer of the conductive material 204.
The ILD 100 design may be examined to identify portions of the ILD 100's surface that have a higher concentration of trenches, and portions of the ILD 100's surface that have a lower concentration of trenches. This may be done in a variety of ways. For example, the following calculation may be performed to calculate a percentage identifying the amount of trench surface area occupying a given portion of the ILD 100:




  
    S
    RATIO
  
  =
  
    
      S
      TRENCH
    
    
      S
      PORTION
    
  




In this example, SPORTION refers to the original (e.g., before trenches were formed) surface area of a portion of the ILD 100 being examined, STRENCH refers to the surface area of the ILD 100 occupied by trench structures in the portion of the ILD 100 under consideration, and SRATIO refers to a percentage of the portion's surface area that is occupied by trench structures. The portion referred to above can be defined in any way, such as dividing the surface of the ILD 100 into a grid (e.g., 1 square micrometer, 100 square micrometers, etc.) of portions, each having its own SRATIO.
The SRATIO for a particular portion may then be compared with a predetermined cutoff value for high- and/or low-density portions. For example, a high density cutoff value of 50% may be defined, meaning those portions whose ratios are equal to or greater than 50% are considered high density. Additionally or alternatively, a low-density cutoff value of 30% may be defined, so that portions whose ratios are less than 30% are considered low density. Other values may be used for either of these ratios, depending on designer's choice (e.g., high-density cutoff values of 40%, 60%, etc. and low-density cutoff values of 20%, 25%, etc.).
Variations to the above can also be made to accomplish the same result. For example, the calculated ratio can identify the remaining exposed ILD 100 surface area after trench formation, as opposed to the amount of occupied surface area. The calculations can also take into account the depths of the trenches, such as by adding in the side wall surface area after calculating an amount of remaining original surface area of ILD 100.
Using one or more of these calculations, certain portions of the ILD 100 may be designated as high density portions 101a, and other portions are designated as low density portions 101b. When the high density 101a and low density 101b portions have been identified, they may be treated differently in the manufacturing process. As shown in FIG. 2d, chemical mechanical polishing (CMP) may be applied to remove unwanted portions of the barrier metal liner 203 and conductive material 204. This polishing may be controlled to be different for various portions of the semiconductor device so that different amounts of cap insulator 201 are removed, depending on whether a portion is a high or low density portion. In the FIG. 2d example, cap insulator layer 201 is completely removed from high density region 101a, but the layer 201 remains, or is preserved, in the low density region 101b. This CMP can be controlled in a number of ways. For example, polishing rates for the two regions may be adjusted with respect to one another by adjusting the slurry type used for each region, or the down force used in each region.
The cap insulator layer 201 material absorbs certain impurities from the ILD 100, such as the water and ammonia particles mentioned above. Accordingly, impurities that were previously absorbed into the ILD 100 at the low density region 101b may be pulled out of the low density region 101b by the remaining cap insulator layer 201. The cap insulator layer 201 may also help prevent the absorption of additional impurities into the ILD 100 from sources external to the semiconductor device. By having this cap insulator layer 201 at the low density region 101b, but not in the high density region 101a, the low density region 101b will be able to outgas additional impurities to compensate for the increased outgassing that the high density region 101a experienced. As a result, a more uniform distribution of impurities may be achieved in the ILD 100 between areas of different densities, reducing the variation in dielectric constant (k) among different portions of the device.
FIGS. 3a-e illustrate many of the same process steps shown in FIGS. 2a-2d, but with some variation. FIGS. 3a and 3b are the same as FIGS. 2a and 2b, although after the trenches 202 are formed in FIG. 3b, a step of etching may be performed to remove the cap insulator layer 201 from areas of the ILD 100 that are designated as high density. This etching may be accomplished, for example, by using masking and photoresist techniques to remove the appropriate portion of the cap insulator layer 201. As shown in FIG. 3c, the cap insulator layer 201 is completely removed from the surface of the ILD 100 at the high density area 101a, but remains on the surface at the low density area 101b. Then, as shown in FIGS. 3d and 3e, the liner 203 and conductive material (e.g., metal) 204 may be deposited and polished down using CMP, as described above with respect to FIGS. 2c and 2d, respectively. In this example, the amount of CMP used in the process between FIGS. 3d and 3e may be the same as between the high and low density regions, avoiding the need for adjusting different polishing rates in the different regions.
Other variations to these methods are also possible, as the techniques and structures described thus far are merely examples of the various features described herein. For example, the step of determining which portions are high and low density need not occur at the specific steps described above, and can instead occur at any time during the manufacturing process (e.g., at the initial design stage, during manufacture but before trenches are formed, etc.). Additionally, although the examples described above refer to particular types of deposition and/or removal processes, and particular examples of materials, these are merely examples, and the present application is not limited to those specific examples. As another example, the initial cap insulator layer 201 need not be deposited onto the high density portion 101a at all, and instead the layer 201 may be selectively deposited onto just the low density portion 101b. 
Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.

## Claims

1. A semiconductor device, comprising:
a semiconductor layer;
an inter layer dielectric disposed on the semiconductor layer;
a first plurality of trenches in a first region of said inter layer dielectric, said first plurality of trenches having a first trench density;
a second plurality of trenches in a second region of said inter layer dielectric, wherein said second plurality of trenches has a second trench density smaller than the first trench density; and
a cap insulator layer disposed on said second region but not on said first region.

2. The semiconductor device of claim 1, wherein said cap insulator layer is SiCOH.

3. The device of claim 2, wherein said cap insulator layer is in direct contact with said inter layer dielectric.

4. The device of claim 3, wherein said cap insulator layer is configured to absorb an impurity from the inter layer dielectric.

5. The device of claim 3, wherein said cap insulator layer is configured to absorb impurities.

6. The device of claim 5, wherein said cap insulator layer is configured to absorb an impurity from the inter layer dielectric.

7. The device of claim 2, wherein said cap insulator layer is configured to absorb impurities.

8. The device of claim 7, wherein said cap insulator layer is configured to absorb an impurity from the inter layer dielectric.

9. The device of claim 2, wherein said cap insulator layer is configured to absorb an impurity from the inter layer dielectric.

10. The semiconductor device of claim 1, wherein said cap insulator layer is in direct contact with said inter layer dielectric.

11. The device of claim 10, wherein said cap insulator layer is configured to absorb impurities.

12. The device of claim 11, wherein said cap insulator layer is configured to absorb an impurity from the inter layer dielectric.

13. The device of claim 10, wherein said cap insulator layer is configured to absorb an impurity from the inter layer dielectric.

14. The semiconductor device of claim 1, wherein said second plurality of trenches are also formed in said cap insulator layer.

15. The device of claim 1, wherein said cap insulator layer is configured to absorb impurities.

16. The device of claim 15, wherein said cap insulator layer is configured to absorb an impurity from the inter layer dielectric.

17. The device of claim 1, wherein said cap insulator layer is configured to absorb an impurity from the inter layer dielectric.