JP4682449B2 - Chemical mechanical polishing method and chemical mechanical polishing apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a chemical mechanical polishing (CMP) method useful for polishing a thin plate-like workpiece such as a semiconductor wafer or a glass plate for LCD, and an apparatus used for the method.
[0002]
[Prior art]
CMP is used as a planarization technique for a semiconductor wafer in a semiconductor device manufacturing process and a glass plate in an LCD panel manufacturing process.
[0003]
FIG. 7 is a schematic sectional view of a conventional CMP apparatus 1. The apparatus includes a surface plate 2 having a rotation mechanism, a polishing pad 3 fixed on the surface plate 2 with a double-sided tape or the like, and a polishing head 5 that holds an object to be polished 4 such as a semiconductor wafer. An adsorption film 6 is provided as an adsorption holding material and a buffer material on the holding surface of the polishing object 5 of the polishing head 5, and the polishing object 4 does not come off the polishing head 5 on the outer periphery of the polishing head 5. For this purpose, a retainer ring 7 is provided.
[0004]
In the vicinity of the polishing head 5, a polishing agent supply line 10 for supplying a slurry-like polishing agent 9 onto the polishing pad 3 is provided.
[0005]
At the time of polishing, the polishing head 5 is lowered by the cylinder 8 while rotating the surface plate 2 and rotating the polishing head 5 holding the workpiece 4 while supplying the polishing agent 9 from the polishing agent supply line 10 to the polishing pad 3. After the object to be polished 4 comes into contact with the polishing pad 3, the object to be polished 4 is further pressed against the polishing pad 3 to perform polishing.
[0006]
As shown in FIG. 8, the polishing pad 3 is conspicuous so as to have an infinite number of pointed protrusions 11 having a height h of about 1 to 2 mm. During polishing, the abrasive grains 12 contained in the polishing agent 9 are pointed. The abrasive grains 12 and the pointed protrusions 11 are pressed against the polishing surface of the object to be polished 4 and polished.
[0007]
Since the pointed convex portion 11 of the polishing pad 3 is worn away by polishing and the polishing surface of the polishing pad 3 is flattened, the area of the polishing pad 3 in contact with the workpiece 4 is increased. It becomes difficult to press the workpiece 4 with the force of the period. In addition, the polishing debris of the polishing pad 3 is clogged in the recesses between the pointed protrusions 11, or the polishing debris accumulated in the recesses between the pointed protrusions 11 scratches the polishing surface of the workpiece 4. Cause it to occur.
[0008]
Therefore, the CMP apparatus 1 is provided with a dresser unit 20 that performs dressing (that is, a process of shaving the polished surface of the worn polishing pad 3 and correcting its surface state). The dressing is performed by pressing the dresser unit 20 against the polishing pad 3 while rotating similarly to the polishing head 5 at the time of polishing or separately from the polishing.
[0009]
The dresser unit 20 includes a dresser 21 and a support portion 22 thereof. For example, as shown in FIG. 9, the dresser 21 is configured by concentrically fixing diamond particles 25 on a base metal 24 attached on a SUS plate 23 by Ni vapor deposition.
[0010]
[Problems to be solved by the invention]
However, in the conventional CMP method, since dressing is often insufficient in general, scratches are likely to occur on the polished surface of the workpiece 4. When scratches are generated on the semiconductor wafer by CMP, problems such as breakdown of the gate electrode and dielectric breakdown of the insulating film formed on the scratches are caused, and the yield of the semiconductor device is remarkably reduced.
[0011]
For this, it is conceivable to perform dressing excessively. However, if dressing is excessively performed, the life of the polishing pad 3 is shortened, so that the cost of CMP is high.
[0012]
An object of the present invention is to reduce scratches and prevent the life of a polishing pad from becoming excessively short when performing CMP in order to solve the conventional problems as described above.
[0013]
[Means for Solving the Problems]
In the method of performing CMP while performing dressing, the inventor of the present invention (i) wear of the polishing pad is caused exclusively by dressing, (ii) the amount of grinding per unit time of the polishing pad by dressing, and the object to be polished. (Iii) Therefore, data on the amount of grinding per unit time of the polishing pad and the number of scratches generated on the object to be polished are accumulated in advance. Based on the data, find the optimum grinding amount per unit time of the polishing pad to reduce the number of scratches, and adjust the dressing conditions to achieve such grinding amount and perform chemical mechanical polishing (Iv) In particular, as a method of adjusting the dressing conditions in this case, the scratch on the polishing pad can be reduced. It was found that adjusting the pressing force of the hose was effective.
[0014]
That is, the chemical mechanical polishing method of the present invention, the data of the generation number of scratches occurring in an object to be polished grinding amount per unit of polishing pad time and by its chemical mechanical polishing in-chemical mechanical polishing the collected previously determined grinding amount per unit time of the optimal polishing pad to reduce scratches, chemical mechanical polishing a polishing pad mounted in order to perform, loaded thickness of the polishing pad, wherein By measuring the height of the pointed protrusions formed on the surface of the polishing pad and the distribution of the pointed protrusions, the shape of the polishing pad is measured, a wafer is mounted on the polishing pad, and the polishing pad while performing dressing that presses the dresser, using said polishing pad and chemical mechanical polishing the surface of the wafer, and then measuring the shape of the polishing pad, the chemical machine In polishing, grinding amount per unit of polishing pad time obtained based on the measurement of the shape of the polishing pad made before and after chemical mechanical polishing the surface of the wafer, previously obtained While adjusting the dressing conditions so as to take the optimum value of the amount of grinding per unit time of the polishing pad, while mounting the object to be polished for main processing on the polishing pad, and performing dressing that presses the dresser against the polishing pad, The surface of the object to be polished is chemically and mechanically polished using the polishing pad .
[0015]
The chemical mechanical polishing apparatus of the present invention includes a polishing pad, a surface plate for fixing the polishing pad, a polishing head holding a workpiece, to press the workpiece to the polishing pad, the polishing a dresser dressing the pad, the thickness of the polishing pad, the height of the tip projecting portion formed on the surface of the polishing pad, and by measuring the distribution of the pointed protrusions, the shape of the polishing pad a polishing pad shape measuring means for measuring the polishing pad shape measuring the polishing pad of the unit of the polishing pad time obtained based on the measurement of the shape of by means takes place before and after chemical mechanical polishing the surface of the wafer The dressing condition is such that the grinding amount per unit takes the optimum value of the grinding amount per unit time of the polishing pad that has been determined in advance to reduce scratches generated on the workpiece. Adjust, and a pressure adjusting means for adjusting the pressing force of the dresser against the polishing pad, while performing dressing that presses the dresser to the polishing pad, it is retained in the polishing head with a polishing pad In addition, the surface of the workpiece to be processed is chemically and mechanically polished .
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the drawings. In addition, in each figure, the same code | symbol represents the same or equivalent component.
[0017]
FIG. 1 is an overall configuration diagram of an embodiment of a CMP apparatus according to the present invention. This CMP apparatus 1A generally includes a polishing unit 100, a dresser unit 20 that performs dressing in the polishing unit 100, a pad shape measuring unit 200 that measures the shape of the polishing pad in the polishing unit 100, a cleaning of an object to be polished after CMP, A cleaning unit 300 that performs drying, a chemical solution supply unit 400 that supplies a cleaning chemical solution such as HF and NH ₃ used in the cleaning unit 300, and an object to be polished are sequentially loaded from the cassette 500, and the polishing unit 100, the cleaning unit 300, and the cassette 500 are loaded. It is composed of a transport unit 600 that unloads the motor.
[0018]
As in the conventional CMP apparatus, the polishing unit 100 includes a surface plate 2 having a rotation mechanism, a polishing pad 3 fixed on the surface plate 2 with double-sided tape or the like, and a polishing head for holding an object to be polished such as a semiconductor wafer. 5 is provided. The polishing head 5 rotates about a shaft 5a and is vertically movable. In the vicinity of the polishing head 5, a polishing agent supply line 10 for supplying a slurry-like polishing agent supplied from the polishing agent supply unit 700 onto the polishing pad 3 is provided.
[0019]
In the CMP apparatus 1A, as the polishing pad 3, a known polishing pad having innumerable pointed protrusions 11 as shown in FIG. 8 can be used.
[0020]
As shown in FIG. 2, the dresser unit 20 is configured by attaching a rotatable dresser 21 shown in FIG. 9 to a support portion 22 that is movable in the radial direction of the polishing pad 3, and polishing the dresser 21. A pressure adjustment mechanism that adjusts the pressing force to the pad 3 is provided.
[0021]
The pad shape measuring unit 200 is one of the characteristic configurations of the CMP apparatus 1A. The pad shape measuring unit 200 is configured by attaching a dial gauge 201 as a pad shape measuring means to the support portion 22 of the dresser unit 20. The shape of the polishing pad 3 is measured when the surface plate 2 is stationary. As this measuring method, for example, first, the support portion 22 is moved in the radial direction of the polishing pad 3 to move the dial gauge 201 onto the center of the polishing pad 3, and the radial direction from the center toward the outer periphery of the polishing pad 3. The measurement is performed by measuring the position of the surface of the polishing pad 3 with the dial gauge 201 and calculating the average of each measurement point as necessary.
[0022]
FIG. 3 is a process diagram for carrying out the method of the present invention using this CMP apparatus 1A. First, the dressing pressing force when performing CMP while performing dressing with a predetermined pressing force in advance using this CMP apparatus 1A, the grinding amount per unit time of the polishing pad at that time, and generated on the object to be polished The relationship between the number of scratches of a predetermined size or more and various CMP conditions (polishing pad type, dresser type, dresser rotation number, dresser pressing force, surface plate rotation number, polishing head pressing force) , The number of revolutions of the polishing head, the film type of the object to be polished, etc.), and the optimum grinding amount per unit time of the polishing pad is determined under the CMP conditions. As an optimum grinding amount, for example, a single layer urethane foam is used as a polishing pad, and other CMP conditions are dresser load 6 lbf (26.7 N), dresser rotation speed 87 rpm, polishing head load 5 lbf (22.3 N), and polishing. When the head rotation speed is 93 rpm and the platen rotation speed is 90 rpm, the speed can be 45 to 55 μm / hr. Also, as the polishing pad, a stud pad made of foamed urethane and a flexible pad on the base is used. However, when other CMP conditions are the same as those described above, it can be set to 30 to 35 μm / hr.
[0023]
Next, the pad shape measurement unit 200 is used to perform pad shape measurement for examining the film thickness of the polishing pad 3, the height of the tip protrusions formed on the surface of the polishing pad 3, and the distribution of the tip protrusions.
[0024]
Next, a dummy wafer is mounted on the polishing head 5, CMP processing is performed while dressing with a predetermined pressing force (preliminary processing), and then pad shape measurement is performed again.
[0025]
From the measurement of the pad shape before and after this pretreatment, the grinding amount per unit time of the polishing pad 3 in this pretreatment is obtained, and this value matches the previously obtained optimum grinding amount per unit time of the polishing pad. If it is determined that the pressure is not within the optimum value, the pressing force of the dresser unit 20 against the polishing pad 3 is appropriately adjusted and the preliminary process is performed again. Thus, the pressing force of the dresser unit 20 is adjusted until the grinding amount per unit time of the polishing pad 3 matches the optimum value. The amount of grinding of the polishing pad 3 depends solely on the dressing conditions and hardly depends on whether or not the object to be polished is mounted on the polishing head 5, so that it is not possible to mount a dummy wafer on the polishing head 5 in the preliminary process. Although not necessary, the finish of the polished surface after the CMP process of the original object is affected by the polishing temperature, so that the temperature during the preliminary process is matched with the temperature of the CMP process of the original object. In addition, it is preferable to use a dummy wafer in the preliminary process.
[0026]
Further, in this method, the adjustment of the pressing force of the dresser unit 20 described above is performed as one of the adjustment methods of the dressing conditions for matching the grinding amount per unit time of the polishing pad 3 to the optimum value. As other methods for adjusting the dressing conditions, the rocking width and rocking speed of the dresser unit 20 that rocks in the radial direction of the polishing pad 3 may be adjusted, and the surface plate 2, the polishing head 5, and the dresser. You may adjust each rotation speed, pressing force, etc. of the unit 20. FIG.
[0027]
Further, in the pad shape measurement, if it is found that the variation in the radial direction of the polishing pad 3 exceeds the predetermined range (for example, within 10 μm), the film thickness of the polishing pad 3 or the height of the pointed protrusion is uniform. Therefore, the swing speed of the dresser unit 20 may be varied for each predetermined region in the radial direction of the polishing pad 3 when adjusting the dressing conditions.
[0028]
After adjusting the dressing conditions as described above, CMP of the original object to be polished is performed while dressing (main body processing). In the main body processing, CMP is performed on a predetermined number of objects to be polished (for example, 25 to 50 semiconductor wafers).
[0029]
For the object to be polished in the main body, the number of scratches on the polishing surface is measured, and the relationship between the measured number of scratches and the grinding amount per unit time of the polishing pad in the main body processing is described above. It is preferable to accumulate as one of the data of the relationship between the amount of grinding per unit time and the number of scratches generated on the workpiece.
[0030]
After performing the predetermined number of main body treatments, the pretreatment and the shape measurement of the polishing pad 3 before and after the pretreatment are performed in the same manner as described above to obtain the grinding amount per unit time of the polishing pad, and the value is optimum. The dressing conditions are adjusted so that the value becomes the value, and then the main body processing is resumed.
[0031]
When CMP is performed as described above, the grinding amount per unit time of the polishing pad polished by dressing becomes an optimum value that does not cause scratches on the object to be polished by adjusting the pressing force of the dresser unit against the polishing pad. Therefore, the generation of scratches on the object to be polished can be remarkably reduced, and dressing is not excessively performed, so that the life of the polishing pad can be extended. Further, the arrival of the life of the polishing pad can be monitored by measuring the pad shape.
[0032]
Further, in contrast to the aspect of the present invention in which the pressing force of the dresser unit is adjusted every time a predetermined number of main body processes are performed, in the conventional CMP method, it is possible to change the pressing force of the dresser unit once set during the main body processing. Not done. However, when the height of the pointed convex portion of the polishing pad is lowered due to wear, the optimum pressure of the dresser changes. For this reason, as in this embodiment, it is effective in reducing scratches to readjust the pressing force of the dresser unit every time a predetermined number of main body processes are performed.
[0033]
The present invention can take various aspects. For example, instead of the pad shape measuring unit 200 described above, as shown in FIG. 4, the dial gauge 201 can be moved in the radial direction of the polishing pad 3 to an independent stand 202 outside the surface plate 2. It may be attached.
[0034]
Further, as the pad shape measuring means, instead of the dial gauge 201, as shown in FIG. 5, a laser type or optical line displacement meter 203 is attached directly above the surface plate 2, and the pad shape measuring means is provided. Without moving the polishing pad 3 in the radial direction, the thickness in the radial direction of the polishing pad 3 or the height of the tip protrusion may be measured at a time.
[0035]
In addition, the pressure adjusting mechanism provided in the dresser unit 20 and the pad shape measuring unit 200 are connected to an arithmetic control device such as a personal computer, and the arithmetic control device uses the polishing pad based on the measurement data obtained by the pad shape measuring unit 200. The grinding amount per unit time is automatically calculated, the grinding amount is compared with a predetermined set value, and the pressing force of the dresser on the polishing pad is automatically adjusted so that the grinding amount takes the predetermined set value. It may be adjusted.
[0036]
As the dresser unit, in addition to the type in which the dresser swings in the radial direction with respect to the polishing pad, the dresser has a sufficient size with respect to the radius of the polishing pad and swings in the radial direction of the polishing pad. You may use the thing of the type attached without it.
[0037]
【Example】
The CMP was performed on the semiconductor wafer using the CMP apparatus shown in FIG. In this case, a polishing pad having a diameter of 20 inches (50.8 cm) made of urethane foam was used, and the rotation speed of the surface plate was 95 rpm. A diamond dresser having a diameter of 4 inches (10.2 cm) was used and rotated at 93 rpm while swinging in the radial direction of the polishing pad. Model No. ID-C112P manufactured by Mitutoyo Corporation was used as the dial gauge. As an abrasive, silica-based slurry (Cabot, SS-25) was used and supplied at 150 ml / min.
[0038]
In CMP under this condition, data on the relationship between the grinding amount per unit time of the polishing pad and the number of scratches of the object to be polished was collected, and the optimum value of the grinding amount was determined in advance, and was 30 to 35 μm / hr. The optimum pressing force of the dresser for realizing this was 5.5 to 6.5 lbf (24.5 to 28.9 N). Therefore, the pressing force of the dresser is set to 6 lbf (26.7 N), and 800 semiconductor wafers (# 1 to # 800) are sequentially subjected to CMP processing as the main body processing, and the width or length generated in each semiconductor wafer after CMP is reduced. The number of scratches of 0.2 μm or more was measured. The results are shown in FIG. Note that the polishing pad was replaced four times as shown in FIG. 6 during the CMP process of 800 semiconductor wafers.
[0039]
For comparison, 800 semiconductor wafers (# 1 to # 800) are sequentially subjected to CMP as a main body treatment except that the pressing force of the dresser is set to 4 lbf (17.8 N), and each semiconductor wafer after CMP is subjected to CMP. The number of scratches with a generated width or length of 0.2 μm or more was measured. The results are shown in FIG.
[0040]
FIG. 6 shows that the number of scratches can be significantly reduced by performing CMP while adjusting the pressing force of the dresser so that the grinding amount of the polishing pad per unit time becomes the optimum value.
[0041]
【The invention's effect】
According to the present invention, when CMP is performed, scratches generated on an object to be polished can be remarkably reduced without excessively shortening the life of the polishing pad.
[Brief description of the drawings]
FIG. 1 is an overall configuration diagram of a CMP apparatus according to an embodiment.
FIG. 2 is a side view of a dresser unit to which a pad shape measuring unit is attached.
FIG. 3 is a process diagram of the CMP method of the example.
FIG. 4 is a side view of the vicinity of a dresser unit of a CMP apparatus to which a pad shape measuring unit is attached.
FIG. 5 is a side view of the vicinity of a dresser unit of a CMP apparatus to which a laser or optical line displacement meter is attached.
FIG. 6 is a relationship diagram between the number of objects to be polished and the number of scratches in main body processing.
FIG. 7 is a schematic sectional view of a conventional CMP apparatus.
FIG. 8 is a cross-sectional explanatory view of a polishing pad.
FIG. 9 is a schematic diagram of a dresser ((a) plan view, (b) side view).
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1A ... CMP apparatus of Example, 2 ... Surface plate, 3 ... Polishing pad, 4 ... To-be-polished object, 5 ... Polishing head, 9 ... Polishing agent, 10 ... Abrasive supply line, 11 ... Point convex part, 12 ... Abrasive Grain, 20 ... dresser unit, 21 ... dresser

Claims (10)

Optimal polishing pad in order to collect data generation number of scratches occurring in an object to be polished to reduce the scratch grinding amount per unit time of the polishing pad in-chemical mechanical polishing and by its chemical mechanical polishing The amount of grinding per unit time is determined in advance ,
A polishing pad is mounted to perform chemical mechanical polishing, and the film thickness of the mounted polishing pad, the height of the tip protrusion formed on the surface of the polishing pad, and the distribution of the tip protrusion By measuring the shape of the polishing pad,
A wafer is attached to the polishing pad, and while performing dressing to press a dresser against the polishing pad, the surface of the wafer is chemically and mechanically polished using the polishing pad, and then the shape of the polishing pad is measured,
In the chemical mechanical polishing, the amount of grinding per unit time of the polishing pad obtained based on the measurement of the shape of the polishing pad performed before and after the chemical mechanical polishing of the surface of the wafer is dressing condition to take optimum values of the grinding amount per unit of polishing pad time had been determined by adjusting the,
The surface of the object to be processed is chemically and mechanically polished using the polishing pad while performing dressing for attaching the object to be processed to the polishing pad and pressing the dresser against the polishing pad. Chemical mechanical polishing method. The life of the polishing pad from the thickness of the polishing pad, the height of the tip protrusion formed on the surface of the polishing pad, and the shape of the polishing pad measured by measuring the distribution of the tip protrusion Detect
The chemical mechanical polishing method according to claim 1 . It said to take grinding amount is the optimum value per unit time of the polishing pad, a chemical mechanical polishing method according to claim 1 or 2, wherein dressing by adjusting the pressing force of the dresser against the polishing pad. While dressing the wafer as an object to be polished subjected to pretreatment for chemical mechanical polishing, based on the shape measurement of the polishing pad before and after pretreatment, determine the grinding amount per unit of polishing pad time in pretreatment , the grinding amount is obtained in advance to take optimum values of the grinding amount per unit of polishing pad time had been, chemical mechanical polishing method according to claim 1 or 2, wherein adjusting the dressing condition. Measure the shape of the polishing pad by measuring the film thickness of the polishing pad, the height of the tip protrusions formed on the surface of the polishing pad, and the distribution of the tip protrusions using a dial gauge. Do
The chemical mechanical polishing method according to claim 1 or 2. By measuring the film thickness of the polishing pad, the height of the tip protrusion formed on the surface of the polishing pad, and the distribution of the tip protrusion using a laser type or optical line displacement meter, Measure the shape of the polishing pad
The chemical mechanical polishing method according to claim 1 or 2. A polishing pad,
A platen for fixing the polishing pad,
Holding the object to be polished, a polishing head for pressing the workpiece to the polishing pad,
A dresser dressing on the polishing pad,
Polishing pad shape measuring means for measuring the shape of the polishing pad by measuring the film thickness of the polishing pad, the height of the tip protrusions formed on the surface of the polishing pad, and the distribution of the tip protrusions And
The amount of grinding per unit time of the polishing pad obtained based on the measurement of the shape of the polishing pad by the polishing pad shape measuring means performed before and after chemical mechanical polishing of the surface of the wafer is applied to the object to be polished. a pressure adjusting means for adjusting the dressing condition to assume an optimum value of the grinding amount per unit time of the polishing pad obtained in advance in order to reduce scratches caused to adjust the pressing force of the dresser against the polishing pad ,
With
A chemical mechanical polishing apparatus for performing chemical mechanical polishing on a surface of an object to be polished for processing held by the polishing head using the polishing pad while performing dressing for pressing the dresser on the polishing pad . Polishing pad life detecting means for detecting the life of the polishing pad from the shape of the polishing pad obtained by the polishing pad shape measuring means
With
The chemical mechanical polishing apparatus according to claim 7. The polishing pad shape measuring means includes a dial gauge, and using the dial gauge, the film thickness of the polishing pad, the height of the tip protrusion formed on the surface of the polishing pad, and the tip protrusion Measure the shape of the polishing pad by measuring the distribution
The chemical mechanical polishing apparatus according to claim 7 or 8. The polishing pad shape measuring means includes a laser-type or optical line-type displacement meter, and is formed on the thickness of the polishing pad and the surface of the polishing pad using the laser-type or optical line-type displacement meter. The shape of the polishing pad is measured by measuring the height of the tip protrusion and the distribution of the tip protrusion.
The chemical mechanical polishing apparatus according to claim 7 or 8.

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