US20080119112A1

US20080119112A1 - Set-up method for cmp process

Info

Publication number: US20080119112A1
Application number: US11/766,225
Authority: US
Inventors: Jae-won Choi
Original assignee: Samsung Electronics Co Ltd
Current assignee: Samsung Electronics Co Ltd
Priority date: 2006-11-21
Filing date: 2007-06-21
Publication date: 2008-05-22
Also published as: KR100827698B1

Abstract

A method of performing a chemical mechanical polishing (CMP) process is disclosed and includes; detecting a removal rate profile for a material layer formed on a wafer, converting the detected material layer removal rate profile into a condition effect profile for a predetermined section of the wafer, monitoring the converted condition effect profile, simulating the condition effect profile by defining input control parameters in response to the monitoring of the converted effect profile, applying the input control parameters as one or more process set-up conditions, as required by the monitored condition effect profile, and performing polishing and conditioning according to the input process set-up conditions.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of Korean Patent Application No. 10-2006-0114901, filed Nov. 21, 2006, the subject matter of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to a set-up method and apparatus for performing a chemical mechanical polishing (or planarization) (CMP) process. More particularly, the invention relates to a set-up method and apparatus capable of detecting a film removal rate for wafer being conditioned, directly monitoring a simulation result while setting up processing conditions in accordance with a condition profile, and/or regulating the profile so as to realize a desired condition effect profile by selectively changing various process conditions.
2. Description of the Related Art
Contemporary semiconductor devices are formed by a complex fabrication process involving the sequential application of specific processes variously related, for example, to the masking, etching, cleaning, and conditioning of a target wafer, as well as the deposition material layers on the wafer. As semiconductor devices have increased in their integration density of constituent components and layers, multi-level structures have emerged as one way of incorporating more components per unit surface area.
The use of multi-level structures has been particularly beneficial in the layout of multi-layer wiring structures which allow increased integration density and miniaturization of the overall device. However, the proper formation of multi-level structures requires intermediate planarization of a base layer before the formation of overlying structures.
One conventional class of planarization processes is referred to a chemical mechanical polishing or planarization or “CMP”. CMP processes are characterized by their ability to remove material(s) from the upper surface of a wafer by the combined action of chemical reaction(s) and mechanical polishing. The chemical reaction is caused by introduction of an appropriate solvent or reactive chemical solution (e.g., a slurry) to the wafer's surface. The mechanical polishing is introduced via an applied frictional force.
Conventional CMP processes may thus be seen as a minute machining technology applied to various material layers and components (e.g., interlayer insulation layers, metal plugs, multi-layer wiring structures, etc.) formed on a wafer surface. Application of a CMP process to a target wafer is typically intended to selectively or globally reduce the vertical profile (i.e., uniformly planarize) of the irregularities in the surface in anticipation of preparing a flat uniform surface to receive a next layer. Hence, uniformity of the resulting polished surface is a very important measure of a CMP process's effectiveness.
On the other hand, the effect rate of material removal (i.e., the “removal rate”) provided by a CMP process is also a very important consideration. Too slow a removal rate will extend wafer processing periods. Too fast a removal rate may result in damage to the wafer's surface. Change in the removal rate of a CMP process may be expressed as a “removal rate profile.” A particular removal rate profile may be expressed in relation to a radial distance from the center of the wafer.
Various set up processes, and related set up equipment and techniques may be used to optimize the application of a CMP process to a target wafer. Both the removal rate and removal rate profile may be defined as part of the overall set up process associated with a CMP process.
Long experience has shown that the removal rate of a CMP process will vary according to the conditioning state of one or more polishing pads used in the CMP process. That is, the material removal rate for a given wafer surface will vary with the use of polishing pads having different roughness.
FIGS. 1 and 2 are related side view and a plan view showing application of a typical CMP process.
A turntable 10 having a polishing pad 12 attached to its upper surface is rotated as a wafer W held by a wafer carrier 20 is pressed against it. The frictional effect of this rotation and vertical pressing polishes the surface of wafer W. Additionally, a conditioner 30 holding a conditioning disc 32 is provided on the other side of polishing pad 12 opposite to the position of wafer carrier 20. A slurry 40 and ultra-pure water are injected onto polishing pad 12 at a point between wafer carrier 20 and conditioner 30.
Wafer carrier 20 and conditioner 30 are typically rotated in the same direction as polishing pad 12. Wafer carrier 20 and conditioner 30 may be swept radially and/or linearly over polishing pad 12. In other words, wafer carrier 20 is assumed to move from center to edge over polishing pad 12 as conditioner 30 moves simultaneously from edge to center. In this manner, the wafer W may be polished while polishing pad 12 is being simultaneously conditioned. The conditioning of polishing pad 12 is controlled by the application of conditioning disc 32 attached to conditioner 30.
Wafer W and conditioning disc 32 perform sweep movement in the same direction by wafer carrier 20 and conditioner 30 in order to perform the polishing and the conditioning, thereby preventing collision between wafer carrier 20 and conditioner 30.
Application of the conventional CMP process will also be effected by the nature of the wafer surface being polished. For example, where the wafer surface includes a highly non-uniform film deposited by a previously applied process the removal rate profile for the CMP process relative to the film will vary with its radial position relative to the center of wafer W.
FIG. 3 is a graph illustrating removal rate profiles for a conventional CMP process applied to portions of a wafer as a function of radial position. As shown in the graph, the removal rate is relatively high at a mid-radial position between the wafer center and edge.
The variable polishing effects associated with non-uniform film thickness and changing removal rate profiles have historically been compensated for by the skills of an experienced process engineer or technician. His/her experience in such matters allows for set up calibrations and process variations in an applied CMP process sufficient to preclude serious problems. These types of custom changes may be made to standard recipe parameters in order to optimize performance. However, this optimization approach requires the periodic intervention of an experienced engineer, and the resulting set-up process is inconvenient and takes too long, thereby lowering the processing yields.

SUMMARY OF THE INVENTION

Embodiments of the invention provide a set-up method and apparatus for a CMP process that are capable of monitoring a removal rate profile. Related conditioning effects may be regulated to ensure a desired removal rate profile while visually monitoring a simulation process so that desired condition effect distribution may be produced by applying various control parameters.
In one embodiment, the invention provides a method of performing a chemical mechanical polishing (CMP) process, comprising; detecting a removal rate profile for a material layer formed on a wafer, converting the detected material layer removal rate profile into a condition effect profile for a predetermined section of the wafer, monitoring the converted condition effect profile, simulating the condition effect profile by defining input control parameters in response to the monitoring of the converted effect profile, applying the input control parameters as one or more process set-up conditions, as required by the monitored condition effect profile, and performing polishing and conditioning according to the input process set-up conditions.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a side view showing application of a conventional CMP process;

FIG. 2 is a plan view related to FIG. 1;

FIG. 3 is a graph showing removal rate profiles for portions of a wafer polished using a conventional CMP process;

FIG. 4 is a plan view showing a movement orbit of a conditioning disc during a process;

FIG. 5 is a graph showing movement orbits of a wafer and a conditioning disc in a polishing pad;

FIG. 6 is a block diagram showing a control flow according to the present invention; and

FIG. 7 is a graph showing a condition effect distribution between the center and an edge of a wafer according to the present invention.

DESCRIPTION OF EMBODIMENTS

Embodiments of the invention will now be described with reference to the accompanying drawings. Throughout the drawings and written description like reference numerals indicate like or similar elements.
Embodiments of the invention are directed to an improved class of CMP processes useful in the planarizing of a wafer surface (e.g., one or more material layers formed on wafer surface). As noted above, the quality and effect of a particular CMP process is directly related to the frictional effect imparted by the constituent polishing pad upon the wafer surface. Experience has shown that over time the frictional effects imparted by the polishing pad are reduced, unless the polishing pad is continually conditioned (i.e., the roughness or surface quality of the polishing pad is maintained).
With reference again to FIG. 1, wafer carrier 20 fixing wafer W is positioned to one lateral side of polishing pad 12 and conditioner 30 is positioned to the opposite lateral side. Conditioning disc 32 attached to conditioner 30 may be conventional in its composition (e.g., an abrasive pad including diamond grit). The conditioning effect provided by conditioning disc 32 increases the roughness of the working surface of polishing pad 12 while compensating for any irregular wear. In addition, any foreign matter or contaminates trapped on polishing pad 12 may be removed by conditioning. As a result of conditioning, the desired polishing efficiency (e.g., rate of material removal) provided by the CMP process may be maintained.
Of additional note, the respective size of polishing pad 12 and conditioning disc 32 are usually determined by the particular equipment used to implement the CMP. That is, CMP equipment usually specifies a particular size(s) of polishing pad 12 and/or conditioning disc 32. Fortunately, these sizes are commonly assigned by accepted convention or existing industry standards.
As illustrated by FIGS. 2 and 4, conditioning disc 32, along with wafer carrier 20, rotates in sympathy with turntable 10. In the example shown in FIG. 2, the fixed lateral position of conditioning disc 32 relative to polishing pad 12 allows only partial conditioning of polishing pad 12. However, as shown by the example of FIG. 4, as conditioning disc 32 is moved laterally across polishing pad 12 more of polishing pad 12 may be conditioned. Additionally, the lateral movement of wafer carrier 20 across polishing pad 12 mitigates the tendency towards uneven pad wear. Thus, wafer carrier 20 holding wafer W and conditioning disc 32 sweep radially (i.e., laterally from the center of polishing pad 12) across polishing pad 12 to effect both polishing and conditioning operations.
Vertical pressure down through the arm holding wafer carrier 20 adjusts the polishing friction between wafer W and polishing pad 12. Similarly, the conditioning effect provided by conditioning disc 32 is a product of its vertical forcing into polishing pad 12. Both the polishing and conditioning operations may be defined in advance by determining certain CMP parameters such as vertical pressure, relative surface compositions, etc.
These parameters will be established in view of the characteristics of the material layer being polished, as well as related conditioning requirements. That is, the nature of the material layer (e.g., a CVD deposited material layer), its homogeneous or non-homogenous composition, its overall uniformity. etc., must be taken into account.
For example, the thickness of a deposited material layer generally varies with radial position across a wafer surface. See, FIG. 3, wherein the subject material layer varies in its positional removal rate from center C to edge E of wafer W, (i.e., rising in a mid-radial position and then falling again at the edge portion E).
FIG. 5 is a graph showing respective rotational movements for wafer W and conditioning disc 32 across polishing pad 12 during a conventional CMP process. As may be seem from FIG. 5, the movement of wafer W and conditioning disc 32 from the center to the edge of polishing pad 12 is shown for a lateral sweeping movement during a predetermined time period (e.g., 6 to 12 seconds) across polishing pad 12. During this lateral sweeping movement, wafer W moves from center to edge of polishing pad 12 and back. Simultaneously, disc 32 moves from edge to center and returns.
Since the diameter of wafer W is larger than the diameter of conditioning disc 32, the movement path of wafer W occurs mostly within the radial length of polishing pad 12. From FIG. 5, it can be seen that conditioning disc 32 partially overlaps the movement path of wafer W, but the overlapping path portions vary with sweep time. As a result, since the movement path of conditioning disc 32 providing the conditioning effect and the movement path of wafer carrier 20 holding wafer W providing the polishing effect are different, degree of polishing will vary between portions of wafer W over time even with proper conditioning. (Compare, for example, the polishing effects at the center of wafer W and the edge of wafer W).
FIG. 6 is a block diagram summarizing a CMP process control method according to an embodiment of the invention. This method is able to mitigate the irregular polishing effects provided by conventional CMP processes as discussed above.
According to the illustrated embodiment, a material layer removal rate profile is detected for a given material layer using empirical or statistical modeling (1). This detected material removal rate profile is then converted into a conditioning effect profile to be applied to wafer W (2). The application of the conditioning effects provided by the conditioning effects profile is then monitored for utility (3). This may be done, for example, by visual inspection.
FIG. 7 is a graph showing an exemplary conditioning effect distribution between the center and edge of a wafer being polished using an embodiment of the invention. As shown in FIG. 7, since the wafer W shows a predetermined distribution of film removal rates according to the distribution of the deposited film, the condition effects applied to portions from the center to the edge has a predetermined distribution. In other words, the condition effects applied to the portions from the center to the edge of the wafer W have a predetermined pattern, and the condition effect profile is monitored using visual inspection. However, FIG. 7 shows condition effect profiles for two cases where CMP process conditions are different.
It can be seen that the condition effect distributions between the center and the edge of the wafer W can be different in the two cases. Therefore, if the CMP process condition is carefully regulated, the condition effect can be controlled more actively. That is, since the condition effect distributions are different according to the process conditions, the condition effect distribution of the wafer W can be changed by properly regulating the process condition so as to control the material layer removal rate for wafer W.
Consequently, various process conditions causing a change of the condition effect for the CMP process are parameters capable of being actively controlled during the polishing of wafer W. The parameters affecting the condition effect include, for example, the rotational speed of the polishing pad, the rotational speed of the conditioning disc, the sweep speed and the movement condition of the conditioning disc, the rotational speed of the wafer, the sweep speed and the movement condition of the wafer, and the distance between the conditioning disc and the wafer. Besides, there are other “input control parameters” that may be adjusted in order to follow a defined polishing simulation that takes into account various process conditions (4).
For example, the condition effects determined when the rotational speed of the polishing pad is changed in view of the size of a target wafer being polished, by the nature of the polishing pad and/or conditioning disc and when the rotational speed of the conditioning disc and/or the rotational speed of the wafer is changed are all quite different. Further, if the rotational speed of the wafer or the conditioning disc is changed, while the rotational speed of the polishing pad is maintained constant, or if they are both changed, the condition effect can be much changed.
The movement speeds, (i.e. the sweep speeds of the conditioning disc across the wafer) may be also an important parameter greatly influencing the condition effect of the wafer. Separately from the sweep speed, itself, the condition effect may be also changed in accordance with the regularity of the sweep speed during the sweep operation.
The condition effect shows a completely different form according to whether the conditioning disc and the wafer are moved at constant speeds across a sweep distance, whether they are moved at different speeds in certain sections, and whether they are stopped for a short while in a predetermined section and are moved again. Therefore, the condition effect can be freely changed by carefully regulating the sweep speed of wafer W and conditioning disc 32 together with their movement condition either separately or simultaneously.
Further, the condition effect can be changed by regulating the distance between the wafer W and the conditioning disc 32. The condition effect of the required wafer can be realized by selectively or simultaneously regulating the parameters. On the other hand, although the condition effect of the wafer W can be changed by a setting condition such as a pressure by which the wafer W or the conditioning disc 32 is pressed on the polishing pad 12, in addition to the above-mentioned parameters, it can be realized sufficiently only by the above-mentioned parameters.
In one aspect of the illustrated embodiment any change in the condition effect may be visually confirmed in relation to one or more changes in the input control parameters and further in view of a desired simulation result (5)
Therefore, if the CMP process is performed after the monitoring result of the initial condition effect to the finally monitored condition effect is confirmed, the process condition is set up by the input control parameters for realization of the final condition effect (6) and the process result having the required condition effect profile can be obtained.
In other words, the material layer removal rate can be improved and the film removal rate profile can be easily regulated by making the change values of the variously input parameters the set up condition of the CMP process, in order to realize the condition effect distribution with reference to the initially monitored condition effect distribution.
Especially, if the polishing and the conditioning are performed according to the input process condition while visually monitoring the simulation result (7), the condition effect profile may be regulated to achieve a desired pattern and can provide the convenience of an accurate and easy work.
The illustrated embodiment of the invention recognizes that according to existing industry standards, the diameter of conditioning disc 32 is usually about one fifth (⅕) to one third (⅓) that of wafer W. That is, although it is required to accelerate the rotational speed or the sweep speed of the conditioning disc 32 on the polishing pad 12 as the diameter of the conditioning disc 32 is reduced, since the material layer removal rate profile of the wafer can be divided into a plurality of regions to be carefully regulated, a more precise CMP polishing process may be provided.
Those of ordinary skill in the art will recognize that foregoing embodiment is but one example of other embodiments defined within the scope of the present invention. The present invention is not limited to only the illustrated embodiment.

Claims

1. A method of performing a chemical mechanical polishing (CMP) process, comprising:

detecting a removal rate profile for a material layer formed on a wafer;

converting the detected material layer removal rate profile into a condition effect profile for a predetermined section of the wafer;

monitoring the converted condition effect profile;

simulating the condition effect profile by defining input control parameters in response to the monitoring of the converted effect profile;

applying the input control parameters as one or more process set-up conditions, as required by the monitored condition effect profile; and

performing polishing and conditioning according to the input process set-up conditions.

2. The set-up method according to claim 1, wherein the material layer removal rate profile for the wafer is defined in part by the thickness distribution of the material layer across the surface of the wafer.

3. The set-up method according to claim 1, wherein the input control parameters are related to a simulation established to regulate at least one of the rotational speed of a polishing pad, rotational speed of a conditioning disc, sweep speed of the conditioning disc and movement condition of the conditioning disc, rotational speed of the wafer, sweep speed of the wafer and movement condition of the wafer, and distance between the conditioning disc and the wafer.

4. The set-up method according to claim 3, wherein the input control parameters are defined in relation to the rotational speed of the polishing pad, rotational speed of the conditioning disc, sweep speed and the movement condition of the conditioning disc, rotational speed of the wafer, sweep speed and the movement condition of the wafer, and distance between the conditioning disc and the wafer.

5. The set-up method according to claim 1, wherein the material layer removal rate profile for the wafer is divided into a plurality of regions, and wherein the polishing and conditioning are monitored and regulated in relation to each one of the plurality of regions.