JP2000127023A - Polishing method for semiconductor and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable flattening working having high accuracy, high efficiency and low cost without generating working damage by making it possible to exchange the edge of a blade of a dress tool and to adjust the height of the edge of the blade. SOLUTION: On a dressing part 200 for dressing, a small-sized throw away tip 201 is mounted with a screw 202. It is desirable that a plurality of these small-sized throw away tips 201 are provided so as to improve dynamic balance at the time of rotation. As a result, an exchanging work at the time of maintenance becomes easy. Because the small-sized throw-away tips 201 are easy to fix with a dressing tool because the throw-away tips 201 are large, falling of the throw away tips 201 can be prevented and clutch becomes difficult to be generated. Further, because the small-sized throw away chips 201 can be adjusted in height with the screws 202, changes in cutting location can be prevented in sizing dressing and stable dressing can be performed for a long period.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for flattening a wafer surface pattern by polishing used in a process of manufacturing a semiconductor integrated circuit, and more particularly, to a high-precision, high-efficiency, and inexpensive flattening without causing processing damage. The present invention relates to a processing method for forming the same and a processing apparatus therefor.

[0002]

2. Description of the Related Art A semiconductor manufacturing process includes a number of process steps. First, a wiring process as an example of a process to which the present invention is applied will be described with reference to FIG. FIG. 1 (a)
Shows a cross-sectional view of the wafer on which the first-layer wiring is formed. Wafer substrate 1 on which transistor portion is formed
Is formed on the surface thereof, and a wiring layer 3 of aluminum or the like is provided thereon. Since a hole is formed in the insulating film 2 to form a junction with the transistor, the portion 3 'of the wiring layer is slightly dented.

In a second wiring step shown in FIG. 1B, an insulating film 4 and a metal aluminum layer 5 are formed on the first layer, and a photoresist layer 6 for exposure is used to form a wiring pattern on the aluminum layer. To adhere.

Next, as shown in FIG. 1C, a circuit pattern is exposed and transferred onto the photoresist 6 using a stepper 7. In this case, if the surface of the photoresist layer 6 is uneven, the concave portion and the convex portion 8 on the photoresist surface will not be simultaneously focused as shown in the figure, and this will be a serious obstacle of poor resolution.

[0005] In order to solve the above-mentioned problems, a flattening process of the substrate surface as described below is performed. After the processing step of FIG. 1A, as shown in FIG. 1D, after the insulating layer 4 is formed, the insulating layer 4 is polished by a method described later so as to be flat to the level 9 in FIG. Obtain the state of e). Thereafter, a metal aluminum layer 5 and a photoresist layer 6 are formed.
Exposure is performed with a stepper as shown in FIG. In this state, since the resist surface is flat, the problem of the poor resolution does not occur.

FIG. 2 shows a conventional chemical mechanical polishing method for planarizing the insulating film pattern. The polishing pad 11 is stuck on the surface plate 12 and rotated. This polishing pad is, for example, a product obtained by slicing urethane foam resin into a thin sheet shape and forming the same. Depending on the type of workpiece and the degree of surface roughness to be finished, various materials and fine surface structures are selected and used. Divide.

On the other hand, the wafer 1 to be processed is fixed to a wafer holder 14 via an elastic holding pad 13.
A load is applied to the surface of the polishing pad 11 while rotating the wafer holder 14, and a polishing slurry 15 is further supplied onto the polishing pad 11, whereby the projections of the insulating film 4 on the wafer surface are polished and removed, and are planarized.

When polishing an insulating film such as silicon dioxide, colloidal silica is generally used as a polishing slurry. Colloidal silica is obtained by suspending fine silica particles having a diameter of about 30 nm in an aqueous alkali solution such as potassium hydroxide.
Compared to mechanical polishing using only abrasive grains, there is a feature that a significantly higher processing efficiency and a smooth surface with less processing damage can be obtained.

As described above, a method of processing while supplying a polishing slurry between a polishing pad and a workpiece is widely known as a free abrasive polishing technique, but has three major problems. I have.

The first problem is that the pattern cannot be sufficiently flattened depending on the type of the pattern and the state of the step. Generally, patterns on a semiconductor wafer are formed from patterns having various dimensions and steps.

For example, in the case of a semiconductor memory device,
As shown in FIG. 3A, one chip is roughly divided into four blocks. Of these, inside the four blocks, fine memory cells are regularly and densely formed, and are called memory mat portions 16. A peripheral circuit 17 for accessing the memory cell is formed at a boundary between the four memory mats. In the case of a typical dynamic memory, the size of one chip is about 7 mm × 20 mm, and the width of the peripheral circuit is about 1 mm.

FIG. 3 shows a cross section AA 'of the chip.
As shown in (b), the average height of the memory mat section 16 is about 0.5 to 1 μm higher than the average height of the peripheral circuit section 17.
When the insulating film 4 having a thickness of about 1 to 2 μm is formed on such a step pattern, the cross-sectional shape 31 of the surface portion substantially reflects the step shape of the underlying pattern.

In the step of flattening the semiconductor wafer, the insulating film 4 on the wafer surface is desired to be flattened as shown by a one-dot chain line 32. In general, a soft polyurethane foam resin, which is widely used for this purpose, is used. When the polishing pad 11L is used, the polishing rate is not planarized because the polishing rate has pattern dependency. That is, as shown in FIG. 4, when a soft polishing pad 11L is used, the polishing pad surface shape is deformed as shown by a solid line 30 in the figure due to a polishing load. A load concentrates on a fine pattern having a size on the order of μm, so that flattening and polishing is performed in a short time. However, a pattern having a large size on the order of mm is applied as a distributed load, and the polishing rate is reduced. As a result, the cross-sectional shape after polishing becomes as shown by the wavy line 34 in the figure, and the level difference: d remains as before.

In order to improve the flattening function, the polishing pad may be made harder. In this case, however, there arises a problem of processing damage described later and a new problem of an increase in processing unevenness in a wafer surface. The cause of the increase in processing unevenness that occurs when using the hard pad is not yet scientifically elucidated, but the abrasive grains supplied on the polishing pad surface are captured by the fine structure on the polishing pad surface, and the processing target substrate and The cause is considered that the probability of entering between fluctuates.

For use in the semiconductor wiring process, the unevenness is required to be ± 5% or less. At present, the upper limit of the hardness of the polishing pad is a Young's modulus of about 10 kg / mm ² . For this reason, a semiconductor device having a large and small pattern from the order of mm to the order of μm, such as a memory device, cannot be expected to have a sufficient flattening effect. It is limited to semiconductor products that do not include, for example, logic LSIs.

A second problem in the flattening technique using the loose abrasive method is that the running cost is high. This is due to the low use efficiency of the polishing slurry in the free abrasive polishing method. That is, it is necessary to supply a polishing slurry such as colloidal silica at a rate of several hundred cc / min or more for ultra-smooth polishing without generating polishing scratches, but most of the polishing slurry does not contribute to actual processing. Will be eliminated. The price of high-purity slurries for semiconductors is extremely expensive, and the polishing slurries determine most of the cost of the flattening polishing process.

The third problem, the short life of the polishing pad, is caused by dressing work on the surface of the polishing pad. At present, it is necessary to replace the polishing pad every about 500 wafers.

As a solution to the above-mentioned drawback of flattening by loose abrasive polishing, the concept of flattening by fixed abrasive polishing is disclosed in PCT / JP95 / 01814.

This new flattening technique is characterized in that a special grindstone 20 whose hardness is optimally controlled is used in place of the conventional polishing pad in the polishing apparatus shown in FIG. Specifically, the elastic modulus of the grindstone 20 is 5 to 500 kg /
and mm ^2, from 1/10 compared to the conventional general grindstone 1/10
On the contrary, the hardness is 5 to 50 times as high as the hardness of a hard polishing pad made of a hard foamed polyurethane or the like conventionally used for the purpose of the present invention.

FIG. 5 shows the structure of a grindstone used in the above technique. As the type of the abrasive grains 21, silicon dioxide, cerium oxide, alumina oxide, and the like are preferable, and the particle diameter is 0.01 to
With a thickness of about 1 μm, good working efficiency can be obtained without generating scratches. It is said that the resin 22 for binding these abrasive grains is preferably a high-purity organic resin such as a phenol-based or polyester-based resin. After kneading the abrasive grains with the binding resin, an appropriate pressure is applied to solidify, and if necessary, a treatment such as heat curing is applied. In the above-mentioned manufacturing method, the type of the binder resin, and the hardness of the grindstone formed by the applied pressure can be controlled.
It is set to be 500 kg / mm ² .

Cerium oxide abrasive grains having a particle size of 1 μm
When pure water is supplied as a polishing liquid to a grindstone manufactured by bonding with a phenol or polyester resin so as to be 100 kg / mm ^2, and a 1 μm-thick silicon dioxide film is processed using the polishing water, Processing speed: 0.3 ± 0.011 μm / min or less for all types of patterns with no occurrence and a pattern width of 10 mm to 0.5 μm
That is, an extremely good flattening performance is obtained. It is considered that the compatibility between the scratch-free processing and the excellent flattening performance is an effect that can be achieved for the first time by fixed abrasive processing using a grindstone having an optimized elastic modulus.

In the conventional loose abrasive processing, the wafer 50
Although the life of the polishing pad is about 0, the thickness of the grindstone can be reduced to several centimeters in the above-mentioned technology, and the life of the grindstone can be extended to about 15,000 wafer processing. This means that the replacement frequency of the polishing pad can be reduced to 1/30 from every day to every one month, which is a great advantage in a mass production site.

As described above, the flattening technique using a grindstone as a polishing tool has many advantages.
It has been found that when this is applied to a mass production line, a new problem occurs.

The first problem in the prior art is the problem of maintaining the flatness of the grinding wheel surface. Like conventional loose abrasive processing,
Even in the flattening technique using the above-mentioned grindstone, the grindstone surface is crushed as the wafer is polished, so that dressing of the grindstone surface is sometimes required. Heretofore, as this dressing method, a constant pressure load type scratching process which has a simple structure and a high dressing action has been used.

This is the same as the dressing method of the polishing pad used in the loose abrasive processing, and as shown in FIG.
A conditioning ring 42 in which diamond grains 41 of about 80 to # 400 are embedded
5 while applying an average surface pressure of about 00 to 300 g / cm ²
It slides at a relative speed of about 30 cm / s.

As a result, the edge of the diamond grain 41 scratches the surface of the grindstone evenly, so that the grindstone polished surface can be sharpened. However, when dressing the whetstone surface in the same manner as before, sometimes several tens of μm
In some cases, a crack 43 reaching a depth of m is generated, and the end of the crack is used as a trigger to break the end of the grindstone during the polishing process, eventually leading to the generation of a large scratch on the order of μm. Was.

It is presumed that the above-mentioned phenomenon is caused by the fact that the size of the diamond abrasive grains is as large as # 80 to # 400, that is, as large as 300 to 60 μm. This problem can be solved by reducing the diamond grain size, but in this case, it becomes difficult to fix the diamond abrasive grains to the base ring 42, and during the dressing operation, the diamond grains are peeled off and embedded in the grindstone surface. This causes scratching.

A second problem in the prior art is the problem of deterioration of the flatness of the grinding wheel surface. The conventional dressing method is based on the principle of scratching while pressing diamond abrasive grains into the grinding wheel surface with a constant load, and always applies a constant load to the conditioning ring regardless of changes in the height or inclination posture of the grinding wheel surface There is a need. Therefore, generally, as shown in FIG. 6, a load from an air cylinder or the like is applied to the conditioning ring 42 via the gimbal fulcrum 44. Therefore, if the hardness of the grindstone surface varies, or if the number of rotations of the conditioning ring deviates from the set value, the dress amount distribution in the grindstone radial direction becomes non-uniform, and as a result, the shape of the grindstone surface becomes a shallow beveled shape. Or the shape of Mt. Fuji. When the flatness of the whetstone surface is deteriorated in this way, processing unevenness occurs on the wafer surface to be processed, which becomes a serious defect.

A fixed size dress shown in FIG. 7 has been proposed to solve the above problem. Particle size # 50 to # 20
A small-diameter cup-shaped grindstone 101 having a diameter of 50 mm to which a large number of diamond grains of about 0 are fixed by first-come-first processing is driven by a spindle motor 102 and rotates at a high speed of 10,000 rpm.
The polished surface of the wafer polishing grindstone 20 rotating at a speed of about 10 rpm is dressed. Due to the high-speed rotation, the peripheral speed of the small-diameter cup-type grindstone 101 reaches approximately 20 m / s,
The grinding wheel surface can be dressed with sufficiently small roughness. In this case, the cut amount of the small-diameter cup-shaped grindstone 101 is on the order of μm, and is typically 1 μm.

The spindle motor 102 is a Z moving table 103
And is driven by a Z drive system 104 to
It is movable in the axial direction. Further, this Z moving table 103
Is restricted in the X-axis direction on the X-movement table 105 moved in the X-axis direction by the X drive system 106.
Due to the movement of the moving table, the small-diameter cup-type grindstone 101 linearly moves in the grindstone radial direction while maintaining the cutting amount. By this movement, the upper surface of the grindstone 20 is ground to an accurate plane.
On the other hand, the cut amount of the small-diameter cup-shaped grindstone 101 is determined by the positioning coordinates of the Z movable table 103 and given by an instruction of the control system 107.

The dressing system having the above configuration operates as follows. First, prior to wafer polishing, when an instruction to start a dressing operation is given, the polishing grindstone 20 starts rotating, and at the same time, the control device 107 sets the small-diameter cup-shaped grindstone 1
Until 01 comes in contact with the grindstone surface, the Z drive system is instructed to move in the cutting direction. The element (not shown) for detecting the contact state may be any element such as a contact-type sensor or a non-contact sensor such as an optical type, and it is desirable that the spindle motor 102 is rotating.

When the contact between the two is confirmed, the control unit 107 gives a cutting instruction of 1 μm, and at the same time gives an instruction to the X-axis driving system 106 to continuously move at a speed of about 10 mm / s. The X moving table 105 reciprocates a distance corresponding to the radius of the grindstone 20, and the small-diameter cup-shaped grindstone 101 grinds and removes the entire grindstone by 1 μm.

Thus, the surface of the grinding wheel is dressed. The number of reciprocations and the moving speed of the X moving table, the cutting depth, and the rotation speed of the grinding wheel 20 are set to optimal conditions in accordance with the type of the grinding wheel. During this dressing operation, it is desirable to supply pure water as a working fluid for grinding, and it is desirable to remove the waste fluid and chips remaining on the surface of the grinding wheel by vacuum suction.

As another operation method, there is a method of performing dressing simultaneously with flattening and polishing of a wafer. The operation method further includes a method in which the above operation is performed only once during the processing of one wafer and a mode in which the dressing is constantly performed while continuously increasing the cutting amount during the processing.
The latter mode is desirable for those requiring low-speed dressing depending on the type of grinding stone.

However, in the above-mentioned fixed-size dressing system, when using a conventional dressing tool in which a large number of diamond grains having a grain size of about # 50 to # 200 are fixed to a base by electrodeposition, a serious problem has occurred. That is, in the conventional fixed-size dressing tool described above, the diamond grains are liable to fall off due to forced cutting into the hard polishing tool, and the dropped diamond damages the surface of the material to be polished and reduces the yield. is there. Further, when diamond grains having the highest cutting edge attached fall during sharpening, the cutting depth changes.

[0036]

SUMMARY OF THE INVENTION An object of the present invention is to provide a flattening method capable of maintaining the above-mentioned fixed size dress stably for a long period of time and a processing apparatus therefor.

[0037]

The above object can be attained by changing the cutting edge of the dressing tool and adjusting the height of the cutting edge.

[0038]

Embodiments of the present invention will be described below in detail with reference to FIG. A small throw-away tip 201 is screwed into the dressing
Attach with 2. For this reason, the replacement work of the cutting edge can be easily performed. Become. Further, it is desirable to provide a plurality of such small throw-away chips in order to improve the dynamic balance at the time of rotation, and it is preferable to provide 20 or less.

Further, since the height of the small throw-away tip can be adjusted by the screw 202, a change in the cutting position in a fixed size dress can be prevented, and a stable dress can be performed for a long period of time.

Industrial applicability: The present invention can be applied to the production of optical elements having a fine surface structure such as semiconductor elements, liquid crystal display elements, micromachines, magnetic disk substrates, optical disk substrates, and Fresnel lenses. it can.

[0041]

According to the present invention, the dressing tool can be easily replaced during maintenance by making the sharpening portion of the dressing tool a small throw-away tip. Further, since the lower outer tip is large, it is easy to fix it to the dressing tool. For this reason, the fall-away tip can be prevented from falling off, and the clutch is less likely to occur. Polishing can be performed without damaging the surface of a material to be polished such as a semiconductor wafer, and the yield of products can be improved.

[Brief description of the drawings]

FIG. 1 is a side cross-sectional view illustrating each flattening step of a wafer surface.

FIG. 2 illustrates a chemical mechanical polishing method.

3A and 3B are a plan view and a cross-sectional view of a semiconductor memory device.

FIG. 4 is a cross-sectional view illustrating a problem when processing is performed using a soft polishing pad.

FIG. 5 is an enlarged plan view illustrating a configuration of a grindstone used in a fixed abrasive processing method.

FIG. 6 is a view for explaining a conventional dressing method in a fixed abrasive processing method.

FIG. 7 is a view for explaining a fixed-size dressing method suitable for carrying out the present invention.

FIG. 8 is a diagram showing the structure of an embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Wafer board, 2 ... Insulating film, 3 ... Wiring layer, 4 ... Insulating layer, 5 ... Metal aluminum layer, 6 ... Photoresist layer, 7 ... Stepper, 8 ... Irregularities on photoresist, 9 ... Level to flatten, 11: polishing pad, 12: platen, 13: holding pad, 14: wafer holder, 15: polishing slurry, 16:
Memory mat part, 17 ... peripheral circuit part, 20 ... whetstone, 21
... Abrasive grains, 22 ... Resin, 41 ... Diamond grains, 42 ... Conditioning ring, 43 ... Crack, 44 ... Gimbal fulcrum, 51 ... First grindstone platen, 52 ... Second grindstone platen, 53 ... Loader cassette , 54: Handling robot, 55: Wafer to be processed, 56: Linear carrier, 57:
Load ring, 58: Polishing arm A, 59: Wafer polishing holder, 60: Rotating brush, 61: Unload cassette, 62: Polishing arm B, 101: Small diameter diamond grindstone, 102: Spindle motor, 103: Z moving table, 1
05: X movable table, 107: control device.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Yukio Suzuki 882-mo, Oji-shi, Hitachinaka-shi, Ibaraki Co., Ltd.Measurement Division, Hitachi, Ltd. Hitachi, Ltd.Measurement Instruments Division (72) Inventor Kenji Inayoshi, Ibaraki Prefecture, Hitachinaka City, Oji-city 882 Co., Ltd. Hitachi, Ltd.Measuring Instruments Division (72) Inventor Shigeo Otsuki 882, Oji-shi, Oaza, Hitachinaka-shi, Ibaraki Co., Ltd. 3C058 AA04 AA07 AA09 AA15 AA19 CB10 DA17

Claims (6)

[Claims] A step of forming a thin film on a surface of a semiconductor substrate on which an uneven pattern is formed; and a step of pressing a surface of the semiconductor substrate on which the thin film is formed on a polishing tool surface to cause relative movement. Flattening the uneven pattern;
A semiconductor manufacturing method including a step of dressing a polished surface of the polishing tool, wherein a blade portion of a dress tool used in the dressing step of the polishing tool is replaceable. 2. The dressing tool according to claim 1, wherein the number of blades is at most 20.
2. The method for manufacturing a semiconductor according to claim 1, wherein the number is not more than the number. 3. The method according to claim 2, wherein each of the blades of the dressing tool is a single stone diamond. 4. Each of the blade portions of the dressing tool is made of ceramic;
3. The method for manufacturing a semiconductor according to claim 2, wherein the method is a throw-away tool piece. 5. The method according to claim 2, wherein the dressing tool has a function of adjusting a cutting edge height of each blade portion. 6. The method according to claim 5, wherein the polishing tool is a fixed abrasive wheel.