Polishing apparatus and polishing method

Abstract

A polishing apparatus is used for polishing and planarizing a substrate such as a semiconductor wafer on which a conductive film such as a copper (Cu) layer or a tungsten (W) layer is formed. The polishing apparatus includes a polishing table having a polishing surface, a motor for rotating the polishing table, a top ring for holding a substrate and pressing the substrate against the polishing surface, a film thickness measuring sensor disposed in the polishing table for scanning a surface of the substrate, and a computing device for processing signals of the film thickness measuring sensor to compute a film thickness of the substrate.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing a polishing apparatus according to an embodiment of the present invention;

FIG. 2 is a plan view of the polishing apparatus shown in FIG. 1;

FIGS. 3A and 3B are graphs showing examples of output signals from an eddy current sensor shown in FIG. 1; and

FIG. 3C is a graph showing an example of signals after correction of the output signals shown in FIG. 3B.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A polishing apparatus according to an embodiment of the present invention will be described below with reference to FIGS. 1 through 3C. In FIGS. 1 through 3C, the same or corresponding members or elements are denoted by the same reference numerals and will not be described repetitively.

FIG. 1 is a schematic view showing a polishing apparatus according to an embodiment of the present invention. As shown in FIG. 1, the polishing apparatus comprises a polishing table 12 having a polishing pad 10 serving as a polishing surface mounted thereon, and a top ring 14 for holding a semiconductor wafer W and pressing the semiconductor wafer W against the polishing pad 10 of the polishing table 12. The polishing table 12 is coupled to a motor 16 and is rotatable about its axis as shown by an arrow A in FIG. 1.

The top ring 14 is connected to a motor (not shown) and a lifting/lowering cylinder (not shown). Thus, the top ring 14 is movable vertically and rotatable about its own axis as indicated by the arrows B and C in FIG. 1. With such an arrangement, the top ring 14 can press the semiconductor wafer W against the polishing pad 10 under a desired pressure while being rotated.

The top ring 14 is coupled to a top ring shaft 18, and has an elastic pad 20 made of polyurethane or the like on a lower surface thereof. The top ring 14 has a guide ring 22 disposed around a lower outer peripheral portion of the top ring 14 for retaining the semiconductor wafer W against dislodgement from the top ring 14. A polishing liquid supply nozzle 24 is disposed above the polishing table 12 for supplying a polishing liquid Q onto the polishing pad 10.

As shown in FIG. 1, an eddy current sensor 30 serving as a film thickness measuring sensor for measuring a thickness of a film formed on a semiconductor wafer W is embedded in the polishing table 12. The eddy current sensor 30 is electrically connected to a controller 40 by a connection cable 32 extending through the polishing table 12, a table support shaft 12a, and a rotary connector (or slip ring) 34 mounted on the lower end of the table support shaft 12a.

The controller 40 is composed of a computer comprising a storage device 40a for storing data from the eddy current sensor 30 and other data and a computing device 40b for computing a film thickness of the semiconductor wafer W by processing output signals from the eddy current sensor 30. The storage device 40a has a predetermined program therein, and this program is loaded in a central processing device 40c of the computer, and thus a representative value generating device 40d, a correction device 40e, a film thickness computing device 40f, and the like (described later) are constituted. The controller 40 is connected to a display device 42.

FIG. 2 is a plan view of the polishing apparatus shown in FIG. 1. As shown in FIG. 2, the eddy current sensor 30 is positioned so as to pass across a center C_W of the semiconductor wafer W which is held by the top ring 14 and is being polished. The polishing table 12 has a center C_T about which it is rotated. While the eddy current sensor 30 is moving below the semiconductor wafer W, the eddy current sensor 30 can continuously detect a film thickness of a conductive film such as a copper layer or a barrier layer of the semiconductor wafer W along an arcuate path L.

With the polishing apparatus thus constructed, the semiconductor wafer W held on the lower surface of the top ring 14 is pressed against the polishing pad 10 on the upper surface of the polishing table 20 which is rotated. At this time, the polishing liquid Q is supplied onto the polishing pad 10 from the polishing liquid supply nozzle 24. Thus, the semiconductor wafer W is polished with the polishing liquid Q being present between the lower surface, being polished, of the semiconductor wafer W and the polishing pad 10.

During polishing, the eddy current sensor 30 passes through immediately below the lower surface of the semiconductor wafer W each time the polishing table 12 makes one revolution. As described above, because the eddy current sensor 30 is positioned so as to pass across the center Cw of the semiconductor wafer W along the arcuate path L, the eddy current sensor 30 can continuously detect the film thickness of the semiconductor wafer W along the arcuate path L located on the lower surface of the semiconductor wafer W while the eddy current sensor 30 is moving below the semiconductor wafer W.

Each time the polishing table 12 makes one revolution, the eddy current sensor 30 scans the lower surface of the semiconductor wafer W one time, and the representative value generating device 40d in the controller 40 generates representative values from signals obtained by the eddy current sensor 30. According to the present embodiment, the arcuate path L on the semiconductor wafer W is divided into a plurality of zones (for example, five zones), and a representative value of the output signals of the eddy current sensor 30 is generated in each zone. The operating conditions are set such that the size of each zone is larger than the size of the die, and a plurality of dies and regions between the adjacent two dies are included in each zone. Since the semiconductor wafer W is divided into a plurality of zones, a polishing state and a film thickness of the semiconductor wafer W can be obtained in each zone during polishing. Thus, process analysis can be performed on the basis of the obtained data including the polishing state and the film thickness.

For example, it is assumed that signals as shown in FIG. 3A are obtained in a certain zone by the eddy current sensor 30, a representative value is generated from the obtained signals by the representative value generating device 40d in the controller 40. Specifically, the representative value generating device 40d in the controller 40 obtains the minimum value V_min of signal values in the certain zone, and a representative value Vo is obtained by adding a predetermined correction value Vc to the minimum value V_min. The equation is given as follows:

Vo=V _min +Vc

It is desirable that the correction value Vc is determined so as to be effective in reducing noise on the basis of noise period, the size of die of the semiconductor wafer W, patterns of the semiconductor wafer W depending on the position of the die, and polishing conditions such as a rotational speed of the top ring 14 or a rotational speed of the polishing table 12.

In this manner, after the representative value Vo is generated in each zone by the representative value generating device 40d in the controller 40, when the eddy current sensor 30 scans the lower surface of the semiconductor wafer W one time at the time of the subsequent rotation, output signals from the eddy current sensor 30 are corrected on the basis of the representative value Vo. Specifically, it is assumed that signals shown by a solid line in FIG. 3B is obtained at the time of the subsequent rotation of the polishing table 12, the correction device 40e in the controller 40 outputs the representative value Vo when the obtained signals are larger than the representative value Vo, and outputs signals from the eddy current sensor 30 as they are when the obtained signals are smaller than the representative value Vo. Thus, signals as shown in FIG. 3C are outputted from the correction device 40e.

Next, the film thickness computing device 40f in the controller 40 computes a film thickness of the semiconductor wafer W on the basis of the signals outputted from the correction device 40e. For example, the signals shown in FIG. 3C are integrated, and a film thickness corresponding to the integral value is calculated. Thus, according to the present embodiment, output signals of the eddy current sensor 30 generated at the current rotation are corrected on the basis of output signals of the eddy current sensor 30 generated during rotation of the polishing table 12 one time ago. That is, a value obtained by adding a predetermined correction value to the minimum value of signals generated during rotation of the polishing table 12 one time ago is used as a representative value (threshold value), and signals (voltage) larger than the representative value are cut and only signals smaller than the representative value are employed. Thus, any effect of the metal layer as an underlying layer on output signals of the eddy current sensor can be eliminated.

Specifically, as the output signals from the eddy current sensor are smaller, the effect caused by noise or pattern of the semiconductor wafer W becomes smaller. Further, as polishing of the semiconductor wafer W progresses, values of output signals tend to be smaller gradually. Therefore, the above-mentioned representative value is used as a threshold value, and signals larger than the representative value are judged as noise and are cut. Thus, any effect of noise or interconnect pattern of the underlying layer can be reduced. As a result, the polishing state of the interconnect layer can be grasped exactly, and the end point of the polishing can be detected stably.

In the above example, the representative value generating device 40d in the controller 40 generates the above representative value from signals of the eddy current sensor 30 generated during rotation of the polishing table 12 one time ago. However, the generation of the representative value is not limited to this example, and a representative value may be generated from signals of the eddy current sensor 30 generated during rotation of the polishing table 12 several times ago. Further, the correction value Vc may be constant. Instead, a value obtained by multiplying the deference between the maximum value V_max and the minimum value V_min of the signals of the eddy current sensor 30 generated during rotation of the polishing table 12 one time ago (or several times ago) by a predetermined coefficient k may be taken as the above correction value Vc. The equations are given as follows:

Vc=k(V_max−V_min)

Vo=V _min +Vc=V _min +k(V_max−V_min)

Here, k is constant of less than 1, and it is desirable that k is determined so as to be effective in reducing noise on the basis of noise period, the size of die of the semiconductor wafer W, patterns of the semiconductor wafer W depending on the position of the die, and polishing conditions such as a rotational speed of the top ring 14 or a rotational speed of the polishing table 12.

Further, when the eddy current sensor 30 is positioned outside an area of the semiconductor wafer W, a value obtained by adding a predetermined value to the minimum value of signals of the eddy current sensor 30 within the area of the semiconductor wafer W or a value obtained by adding the minimum value to a value obtained by multiplying the deference between the maximum value and the minimum value by a predetermined coefficient may be taken as a hypothetical output signal. Specifically, only data generated when the eddy current sensor 30 scans the semiconductor wafer W is not outputted, but data generated in other time are replaced by the above value which is then outputted. Thus, data on the basis of real time of the polishing process can be outputted, and polishing operations such as feedback control can be easily adjusted.

Although the eddy current sensor is used as a film thickness measuring sensor in the present embodiment, the film thickness measuring sensor which can be used in the present invention is not limited to the eddy current sensor. For example, an optical sensor or a microwave sensor may be used as a film thickness measuring sensor.

Although copper is used as an interconnect forming material in the present embodiment, aluminum, tungsten, aluminum alloy or tungsten alloy can be also used as an interconnect forming material in the present invention.

Although certain preferred embodiments of the present invention have been shown and described in detail, it should be understood that various changes and modifications may be made therein without departing from the scope of the appended claims.

Claims

1. A polishing apparatus comprising: a polishing table having a polishing surface;a motor for rotating said polishing table;a top ring for holding a substrate and pressing the substrate against said polishing surface;a film thickness measuring sensor disposed in said polishing table for scanning a surface of the substrate; anda computing device for processing signals of said film thickness measuring sensor to compute a film thickness of the substrate; said computing device comprising:a representative value generating device for generating a representative value from signals of said film thickness measuring sensor generated during the previous rotation of said polishing table;a correction device for outputting said representative value when values of said signals of said film thickness measuring sensor are larger than said representative value, and outputting said signals of said film thickness measuring sensor when values of said signals of said film thickness measuring device are smaller than said representative value; anda film thickness computing device for computing said film thickness of the substrate from the signals outputted from said correction device.

2. The polishing apparatus according to claim 1, wherein a plurality of dies are formed on the substrate, and said computing device is configured to divide scanning data on the substrate obtained by said film thickness measuring sensor into a plurality of zones having a size larger than said die and to compute said film thickness of the substrate by processing said signals of said film thickness measuring sensor in each of said plurality of zones on the substrate using said representative value generated in each of said plurality of zones by said representative value generating device.

3. The polishing apparatus according to claim 1, wherein said representative value generating device generates said representative value from said signals of said film thickness measuring sensor generated during rotation of said polishing table one time ago.

4. The polishing apparatus according to claim 1, wherein said representative value generating device obtains said representative value by adding a predetermined correction value to the minimum value of said signals of said film thickness measuring sensor within a certain period of time.

5. The polishing apparatus according to claim 4, wherein said representative value generating device obtains said predetermined correction value by multiplying the deference between the maximum value and the minimum value of said signals of said film thickness measuring sensor within said certain period of time by a predetermined coefficient.

6. The polishing apparatus according to claim 1, wherein said film thickness measuring sensor comprises at least one of an eddy current sensor, an optical sensor and a microwave sensor.

7. The polishing apparatus according to claim 1, wherein said film thickness measuring sensor comprises an eddy current sensor.

8. A polishing method for polishing a substrate by pressing the substrate against a polishing surface on a rotating polishing table, the polishing method comprising: scanning the substrate by a film thickness measuring sensor disposed in said polishing table;generating a representative value from signals of said film thickness measuring sensor generated during the previous rotation of said polishing table;outputting said representative value when values of said signals of said film thickness measuring sensor are larger than said representative value, and outputting said signals of said film thickness measuring sensor when values of said signals of said film thickness measuring device are smaller than said representative value; andcomputing a film thickness of the substrate from the outputted signals.

9. The polishing method according to claim 8, wherein scanning data on the substrate obtained by said film thickness measuring sensor is divided into a plurality of zones having a size larger than a die formed on the substrate; and said film thickness of the substrate is computed by processing said signals of said film thickness measuring sensor in each of said plurality of zones on the substrate using said representative value generated in each of said plurality of zones.

10. The polishing method according to claim 8, wherein said representative value is generated from said signals of said film thickness measuring sensor generated during rotation of said polishing table one time ago.

11. The polishing method according to claim 8, wherein said representative value is obtained by adding a predetermined correction value to the minimum value of said signals of said film thickness measuring sensor within a certain period of time.

12. The polishing method according to claim 11, wherein said predetermined correction value is obtained by multiplying the deference between the maximum value and the minimum value of said signals of said film thickness measuring sensor within said certain period of time by a predetermined coefficient.

13. The polishing method according to claim 8, wherein said film thickness measuring sensor comprises at least one of an eddy current sensor, an optical sensor and a microwave sensor.

14. The polishing method according to claim 8, wherein said film thickness measuring sensor comprises an eddy current sensor.

15. A film thickness measuring program for measuring a film thickness of a substrate on the basis of signals of a film thickness measuring sensor disposed in a polishing table for use in a polishing apparatus for polishing the substrate by pressing the substrate against a polishing surface on the polishing table, the film thickness measuring program making a computer function as: means for obtaining a representative value by adding a predetermined correction value to the minimum value of said signals of said film thickness measuring sensor generated during rotation of said polishing table one time ago within a certain period of time;means for outputting said representative value when values of said signals of said film thickness measuring sensor are larger than said representative value, and outputting said signals of said film thickness measuring sensor when values of said signals of said film thickness measuring device are smaller than said representative value; andmeans for computing said film thickness of the substrate from the outputted signals.

16. The film thickness measuring program according to claim 15, wherein said predetermined correction value comprises a value obtained by multiplying the deference between the maximum value and the minimum value of said signals of said film thickness measuring sensor by a predetermined coefficient.