JPH09232257A - Polishing and working method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a polishing and working method whose working efficiency is increased without generating working damage and in which the operating expenses of a polishing treatment are reduced by a method wherein a whetstone which is composed of abrasive grains and of a substance used to bond and hold the abrasive grains is used and a working operation is performed while a polishing liquid containing abrasive grains whose kind is different from that of the abrasive grains constituting the whetstone is being supplied. SOLUTION: A whetstone 35 is fixed onto a surface plate 12 so as to be rotated. A wafer 1 is installed on the whetstone 35 in such a way that it is pressed to a face, to be worked, on which a recessed and protrusing pattern is formed, and it is held by a wafer holder 14. When an oxide film on the silicon wafer on which a circuit pattern is formed is polished, e.g. a soft porous whetstone in which cerium oxide particles in an average particle size of about 1μm are bonded by an organic resin material such as a phenolic resin or the like and whose Young's modulus is at about 100kg/mm<2> is used as the whetstone 35. At this time, even with the whetstone only, the oxide film on the wafer can be polished so as to be flattened, but colloidal silica is used as s slurry in order to obtain its higher working efficiency.

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 or the like, and more particularly to a polishing method for highly efficient and inexpensive flattening without causing processing damage.

[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. 1A shows a cross-sectional view of a wafer on which a first-layer wiring is formed. An insulating film 2 is formed on the surface of the wafer substrate 1 on which the transistor portion is formed, and a wiring layer 3 made of aluminum or the like is provided thereon. Since a hole is opened in the insulating film 2 to form a junction with the transistor, that portion 3'of the wiring layer is somewhat depressed. In the second layer wiring step shown in FIG. 2B, an insulating film 4 and a metal aluminum layer 5 are formed on the first layer, and an exposure photoresist layer 6 is attached to form a wiring pattern on the aluminum layer. To do. Next, as shown in FIG. 3C, a circuit pattern is exposed and transferred onto the photoresist 6 by using a stepper 7. In this case, the concave portions and the convex portions 8 on the surface of the photoresist layer 6 are not focused at the same time, which is a serious obstacle to resolution blurring.

In order to solve the above-mentioned problems, the following flattening process of the substrate surface is performed. After the processing step of FIG. 1A, as shown in FIG. 1D, after the insulating layer 4 is formed, it is polished by the method described below so as to be flat to a level 9 in the figure, Obtain the state of e). After that, a metal aluminum layer 5 and a photoresist layer 6 are formed,
Exposure is performed by the stepper 7 as shown in FIG. In this state, since the resist surface is flat, the problem of resolution blur does not occur.

FIG. 2 shows a chemical mechanical polishing method which has been generally used in the past for flattening the insulating film pattern. The polishing pad 11 is attached to the surface plate 12 and rotated. The polishing pad is, for example, formed by slicing a urethane foam resin into a thin sheet, and various materials and fine surface structures can be selected according to the type of work piece and the degree of surface roughness to be finished. Use properly. On the other hand, the wafer 1 to be processed is fixed to the wafer holder 14 via the elastic pressing pad 13. By rotating the wafer holder 14 and applying a load to the surface of the polishing pad 11, and further supplying the polishing slurry 15 onto the polishing pad 11, the convex portions of the insulating film 4 on the wafer surface are polished and removed to be flattened.

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 with mechanical polishing using only abrasive grains, it has a feature that a dramatically higher processing efficiency and a smooth surface with less processing damage can be obtained.
As described above, the method of processing while supplying the polishing slurry between the polishing pad and the work piece is well known as the free abrasive grain polishing technique.

The conventional wafer flattening technique by free abrasive polishing has two problems which are difficult to solve.
One is the problem of pattern dimension dependency that it cannot be sufficiently flattened depending on the type of pattern and the state of the step, and the other is the problem of excessive consumable cost required in the polishing process. . Hereinafter, these problems will be described in detail.

Generally, a pattern on a semiconductor wafer is formed of a pattern having various dimensions and steps. For example, in the case of a semiconductor memory device, one chip is roughly divided into four blocks as shown in FIG. 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 cells is formed at the boundary between the four memory mat portions 16. 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 section is about 1 mm.

Taking the cross section AA 'of the above chip, FIG.
As shown in (b), the average height of the memory mat portion 16 is higher than the average height of the peripheral circuit portion 17 by about 0.5 to 1 μm.
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 thereof substantially reflects the step shape of the underlying pattern.

In the intended flattening step, it is desired to flatten the insulating film 4 on the surface of the wafer as shown by the alternate long and short dash line 32. Generally, the soft polyurethane foam pad 11L which is widely used for this purpose is used. In the case of using, the polishing rate does not depend on the pattern because of the pattern dependence of the polishing rate. That is, as shown in FIG. 4, when a soft polishing pad 18 is used, the polishing pad surface shape is deformed as indicated by the solid line 30 in the figure due to the polishing load. The load concentrates on a fine pattern having a size of micron order, so that the pattern is polished in a short time. However, since a distributed load is applied to a pattern having a large size of millimeter order, the polishing rate becomes slow. As a result, the cross-sectional shape after polishing becomes a broken line 34 in the figure, and the height difference is still:
The d remains.

In order to improve the flattening function, the polishing pad may be made harder, but in this case, there is a problem of processing damage, which will be described later, and a new problem of increased processing unevenness in the wafer surface. The cause of the increase in processing unevenness that occurs when using this hard pad has not yet been elucidated academically, but the abrasive grains supplied on the polishing pad surface are trapped in the fine structure part of the polishing pad surface and the substrate to be processed. It is considered that the probability of entering the space will change.

For the purpose of use in the wiring process of semiconductors, unevenness of ± 5% or less is required, and at present, the upper limit of the hardness of the polishing pad is about 10 kg / mm ² of elastic modulus. Therefore, in a semiconductor element such as a memory element in which patterns of various sizes from millimeter order to micron order are mixed, a sufficient flattening effect cannot be expected, and a pattern with a too large dimension is applicable. It is limited to semiconductor products not included, such as logic LSIs.

The second problem in the conventional flattening technique for semiconductor wafers by the free abrasive polishing method is to reduce expensive running costs. 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 polishing slurry such as colloidal silica at a rate of several hundred cc / min or more for ultra-smooth polishing that does not cause polishing scratches, but most of them are excluded without contributing to actual processing. I will end up. The price of high-purity slurry for semiconductors is extremely high, and most of the cost of the flattening polishing process is determined by this polishing slurry, so that improvement is strongly required.

As a conventional technique other than the above, a fixed abrasive processing method using a grindstone made by mixing fine abrasive particles with metal powder or resin resin as a polishing surface plate is the first international ABC conference (1st Inte
rnational ABTEC Conference (Seoul, November 1993
, Pp. 80-85),
A known defect is that minute scratches often occur on the processed surface.

In order to solve the problem of scratches, it is important to reduce the size of the abrasive grains, and there is a flattening technique using a fine abrasive grain grindstone having an extremely small grain size produced by an electrophoretic method. However, since the grindstone itself becomes hard, the problem of scratches caused by the polishing liquid, dust contained in the processing atmosphere, etc. still remains.

In order to solve these scratch problems, the elastic modulus of the grindstone is emphasized rather than the refinement of the abrasive grains, and the elastic modulus is controlled to 5 to 500 kg / mm ² to give a soft characteristic. (See PCT / JP95 / 01814). The use of this soft whetstone gives an ultra-smooth machined surface without scratches. However, the method using this soft grindstone has a drawback that the machining efficiency is extremely lowered in exchange for the good finished surface.

As described above, in the conventional semiconductor wafer flattening technique by free-abrasive polishing, there are conditions under which a minimum size micron-order fine pattern and a millimeter-order large-size pattern can be processed flat at the same time. Since it does not exist, it cannot be applied to the manufacture of a semiconductor integrated circuit in which patterns of various sizes are mixed, such as a memory LSI. Also, the high running cost required for the polishing treatment has been a major drawback in mass production applications. On the other hand, the wafer flattening technology by fixed abrasive polishing has a low running cost, but if the grindstone is hard, scratches are likely to occur on the processed surface, and if a soft grindstone is used, scratches do not occur but the processing speed is slow. there were. Therefore, it is difficult to satisfy both the condition that scratches do not occur and the condition that the machining efficiency is high.

[0018]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned drawbacks of the prior art and to provide a processing method which has a high processing efficiency and a low running cost of polishing without causing processing damage. It is in.

[0019]

The above-mentioned object is to replace a conventional free-abrasive grain polishing process using a polishing pad and polishing slurry or a fixed-abrasive polishing method using only a whetstone with a whetstone and its whetstone. This can be achieved by using a slurry containing different types of abrasive grains in combination with the abrasive grains to be used, and using the synergistic effect of the action of the fixed abrasive grains and the action of the free abrasive grains.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to FIG. The apparatus used in the present invention has a structure in which the polishing pad of a general CMP (chemical mechanical polishing) apparatus is replaced with a grindstone. The grindstone 35 is fixed on the surface plate 12 made of aluminum or stainless steel and rotates.
The wafer 1 is placed against the grindstone 35 so as to press the surface to be processed on which the concavo-convex pattern is formed, and is held by the wafer holder 14. The wafer holder 14 rotates in the same direction as the surface plate. If the number of rotations of the platen 12 and the wafer holder 14 is equal, the amount of movement of the wafer to be polished with respect to the grindstone is equal throughout the wafer surface, and uniform processing can be performed on the wafer. The polishing liquid, that is, the slurry 15 is several hundred ml on the grindstone by the slurry supply device 36.
It is supplied at a rate of about / minute.

When the oxide film on the silicon wafer on which the circuit pattern is formed is polished, the grindstone 35 is, for example,
Cerium oxide having an average particle size of about 1 micron is bonded with an organic resin material such as phenol, Young's modulus is 100 kg /
A soft and porous grindstone of about mm ² is used. Although it is possible to polish and flatten the oxide film on the wafer with only this grindstone, in order to obtain higher processing efficiency,
It is a feature of the present invention that colloidal silica is used together as a slurry. As this colloidal silica, for example, SC-1 manufactured by Cabot Co., which is generally used for CMP (chemical mechanical polishing) of a silicon oxide film, is suitable.

As described above, the present inventors have for the first time found that when a grindstone made of cerium oxide abrasive grains and a colloidal silica slurry are used together, a remarkably high polishing rate can be obtained as compared with the case where the grindstone or the slurry is used alone. I found it.

FIG. 6 shows the polishing rate when a cerium oxide grindstone and colloidal silica were used in combination as a function of the colloidal silica concentration in comparison with the case where only the grindstone was used for polishing and the case where only colloidal silica was used for polishing. It is shown.

First, the result of polishing with supplying water as a polishing liquid to a cerium oxide grindstone without using colloidal silica is shown by a dotted line in FIG. At this time, only the cerium oxide fixed abrasive grains on the grindstone control the polishing action, but the polishing rate is very slow at 5 nm / min.

Data in the case of colloidal silica slurry which is polished by only free abrasive grains is shown by square points in FIG. At this time, on the polishing surface plate instead of the grindstone,
In CMP, a polishing pad IC-1000 manufactured by Rodel Co., which is generally used, is attached and used. As a result, a polishing rate of 43 nm / min was obtained when the colloidal silica concentration was 12 wt%.

Finally, the data when the cerium oxide grindstone and colloidal silica are used at the same time are shown by the circles in FIG. At this time, the polishing rate increased at least twice as compared with the case where only colloidal silica was used. Especially, when the colloidal silica concentration was as low as 0.6 wt%, the polishing rate was almost zero when polishing with colloidal silica alone. For some, the polishing rate is 35 nm
The performance can be improved significantly with / min.

The polishing rate obtained here is significantly higher than the polishing rate obtained by adding the polishing rate using only the cerium oxide grindstone under the same conditions and the polishing rate using only colloidal silica. Thus, in the present invention, fixed abrasive polishing with cerium oxide grindstone, not by simple arithmetic sum of free abrasive polishing with colloidal silica, synergistic action of cerium oxide fixed abrasive and colloidal silica free abrasive. It is characterized by being used.

Regarding the synergistic effect of the combined use of the cerium oxide grindstone and colloidal silica, the mechanism is considered to be as follows. Initially, the surface of the cerium oxide abrasive grains 37 is covered with a resin 38 that is a binding material of a grindstone as shown in FIG. 7A. Since the abrasive grains are in this state not only inside the grindstone but also on the polishing surface 39 on the surface of the grindstone, there is almost no polishing ability as it is, but damage such as scratches does not occur. When the fine colloidal silica particles 15 are present here, the silica particles 15 have a function of removing the resin component 38 covering the cerium oxide particles 37, and the cutting edge of the cerium oxide abrasive grains is formed as shown in FIG. 7B. Exposed. The cerium oxide particles 37 'with the exposed cutting edges scrape off the surface of the wafer, which is the workpiece, for high-speed and scratch-free processing.

It is needless to say that the above embodiment is an example, and a higher polishing rate can be realized without deteriorating the quality of the finished surface by increasing the working pressure and the number of rotations of the platen.

Further, the abrasive grain components constituting the grindstone and the slurry are not limited to the combination of cerium oxide and colloidal silica listed in the above-mentioned embodiment, but fixed abrasive grains of the grindstone and loose abrasive grains of the slurry. Any of silicon dioxide, cerium oxide, alumina oxide, or a mixture thereof may be used as long as they are different types of abrasive grains.

[0031]

As described above, according to the present invention, in the polishing process of a semiconductor wafer, C using a conventional polishing pad is used.
By using a grindstone having a higher leveling ability than MP (chemical mechanical polishing), it is possible to obtain a flat processed surface and simultaneously use a slurry containing abrasive grains, so that a high polishing rate can be obtained at the same time. This means that in semiconductor manufacturing, high quality processing can be performed with high throughput.

Further, the grindstone has superior durability as compared with the conventional polishing pad, can reduce the downtime of the production apparatus, and even if the grindstone is used together, a slurry having a low concentration of 1/10 or less can be used. Due to the fact that practically sufficient processing efficiency can be obtained, the cost of the slurry, which used to occupy most of the CMP cost, can be significantly reduced.
The problem of high processing cost, which is a drawback of P, can be solved and the process cost can be reduced. Further, the use of the low-concentration slurry also reduces the burden of cleaning the wafer after polishing, which contributes to cost reduction and throughput improvement.

Needless to say, even if a slurry having a normally used concentration is used instead of a low-concentration slurry, there is an advantage that a very high polishing rate can be obtained, and throughput improvement and process cost reduction can be expected. Yes.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a wafer surface flattening step.

FIG. 2 is a diagram illustrating a chemical mechanical polishing method.

FIG. 3 is a diagram illustrating a problem of a chemical mechanical polishing method.

FIG. 4 is a diagram illustrating a problem of a polishing pad in a chemical mechanical polishing method.

FIG. 5 is a diagram illustrating an embodiment of the present invention.

FIG. 6 is a view showing a synergistic effect of a grindstone and a colloidal silica slurry.

FIG. 7 is a diagram for explaining a synergistic action between a grindstone and a colloidal silica slurry.

[Explanation of symbols]

1 ... Wafer substrate, 2, 4 ... Insulating film, 3 ... Wiring layer, 5 ... Metal aluminum layer, 6 ... Photoresist layer, 7 ... Stepper, 8 ... Convex portion of resist layer, 9 ... Target level of planarization,
11 ... Polishing pad, 12 ... Surface plate, 13 ... Press pad,
14 ... Wafer holder, 15 ... Polishing slurry, 16 ... Memory mat part, 17 ... Peripheral circuit part, 18 ... Soft polishing pad,
30 ... Pad surface, 31 ... Cross-sectional shape, 32 ... Polishing end level, 34 ... Wafer surface after polishing, 35 ... Grinding stone, 36 ... Slurry supplying device, 37 ... Cerium oxide abrasive grains, 38 ... Binder resin, 39 ... Grinding stone surface , 40 ... Colloidal silica abrasive grains.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshio Honma 1-280, Higashi Koikekubo, Kokubunji, Tokyo Inside the Central Research Laboratory, Hitachi, Ltd.

Claims (5)

[Claims] 1. A step of forming a thin film on the surface of a substrate on which an uneven pattern is formed, and a step of loading the polishing tool on the surface of the substrate on which the thin film is formed to relatively move the uneven pattern. In a polishing method including a step of flattening, a grinding stone composed of abrasive grains and a substance for binding and holding the abrasive grains is used as the polishing tool.
A polishing method, characterized in that the polishing is performed while supplying a polishing liquid containing abrasive grains of a type different from that of the abrasive grains constituting the grindstone. 2. The polishing process according to claim 1, wherein the abrasive grains constituting the grindstone of the polishing tool or the polishing liquid are any one of silicon dioxide, cerium oxide and alumina oxide, or a mixture thereof. Method. 3. The polishing method according to claim 2, wherein the grinding stone of the polishing tool and the abrasive grains constituting the polishing liquid are fine particles having an average grain size of 1 micron or less. 4. The elastic modulus of the grindstone of the polishing tool is 5 to 5
The polishing processing method according to claim 1, wherein the polishing processing method has a range of 00 kg / mm ² . 5. The polishing method according to claim 1, wherein among the polishing tools, the abrasive grains constituting the grindstone are cerium oxide and the polishing liquid is a combination of colloidal silica.