JPH10335276A - Surface flattening method and apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable all the surface of a wafer to be flattened by very accurate polishing independent of the size of a pattern, by a method wherein a wafer and a grinding stone are arranged confronting each other and pressed against each other with a prescribed pressure, and at least either of the wafer and the grinding stone is moved in the direction of plane to polish the pattern. SOLUTION: A pressure W is applied onto a wafer holder 14 which holds a wafer 1 from above the holder 14 to press the wafer 1 against a polishing tool 16, the wafer holder 14 and a polishing platen 12 are rotated at the same time of polish the wafer 1. At this point, processing liquid 15 is fed from a liquid supply unit 20 onto the polishing tool 16 at a flow rate of 100 to 1000 ml. The pressure W with which the wafer holder 14 is pressed against the polishing tool 16 is 30 to 500 g/cm<2> , and a friction rate (amount of abrasion/ minute) is nearly proportional to the pressure W. It is preferable that the wafer holder 14 and the polishing platen 12 are rotated in the same direction and set nearly equal to each other in rotational speed to carry out uniform polishing, where the rotational speed is set at 20 to 50 rpm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for planarizing a surface, and more particularly to a method for producing various semiconductor devices, which is particularly suitable for planarizing a semiconductor wafer having various patterns formed on its surface. The present invention relates to a surface flattening method and a surface flattening apparatus used for the method.

[0002]

2. Description of the Related Art A semiconductor manufacturing process includes many process steps. In order to form a fine semiconductor device having a very high integration density, planarization of the surface has become particularly important. As one example, a wiring forming process will be described with reference to FIG.

FIG. 2A shows a state in which a first layer wiring is formed, and an insulating film 2 and a wiring made of aluminum or the like are formed on a surface of a substrate 1 on which a transistor (not shown) is formed. Layer 3 is provided. Since the wiring layer 3 is connected to the transistor via the opening formed in the insulating film 2, the surface 3 'of the wiring layer 3 at the connection portion is slightly dented.

Therefore, as shown in FIG. 2B, when a second insulating film 4, an aluminum film 5 and a photoresist film 6 are sequentially laminated to form a second layer wiring, the photoresist is formed. The surface of the film 6 is not flat, and irregularities occur.

Next, as shown in FIG. 2C, when a predetermined circuit pattern is exposed on the photoresist film 6 by using a stepper 7 and the circuit pattern is transferred, the surface of the photoresist film 6 becomes flat. As is well known, since the depth of focus of the stepper is not deep, it is impossible to focus on the concave and convex portions 8 of the photoresist film 6 at the same time, and a serious obstacle such as resolution blur occurs.

To prevent such a failure, FIG.
After the step shown in FIG. 2A, as shown in FIG. 2D, an insulating film 4 is formed on the entire surface, and then the insulating film 4 is polished to level 9 to flatten the surface. The shape shown in FIG.

Next, an aluminum film 5 and a photoresist film 6 are formed and are exposed using a stepper 7 as shown in FIG. In this case, since the surface of the resist film 6 is flat, there is no possibility that the above-mentioned problem of resolution blur due to unevenness of the surface will occur.

A method of flattening the surface by such polishing is described in, for example, US Pat. No. 4,944,836 and Japanese Patent Publication No. 5-30052.

As a polishing method for flattening the surface,
A method called a chemical mechanical polishing method (hereinafter, referred to as a CMP method) is generally performed. In this method, as shown in FIG. 3, a polishing pad 11 is attached to a surface plate 12, a wafer 1 to be processed is fixed to a wafer holder 14 through an elastic backing pad 13, and the surface plate 12 is fixed. This is a method in which the polishing slurry 15 is supplied onto the polishing pad 11 by rotating, and a load is applied to the surface of the polishing pad 11 while rotating the wafer holder 14.

As a result, the projections of the insulating film 4 on the surface of the wafer 1 are polished and removed, and the surface is flattened. As the polishing pad 11, for example, one obtained by slicing a urethane foam resin into a thin sheet is used. As the polishing slurry 15, for example, when polishing an insulating film such as silicon dioxide, a fine and high-purity slurry is used. Fumed silica in which fine silica particles are suspended in an aqueous alkali solution such as potassium hydroxide or ammonia is generally used.

[0011]

In the manufacture of semiconductor devices, not only is the precision required for planarization significantly higher than in other fields, but also the error in the thickness of the film remaining after planarization is complete. , ± 0.1 μm or less. However, as shown in FIG. 4A, the wafer 1 to be processed held on the wafer holder has undulations on the scale of several mm or more in the horizontal direction in addition to the surface irregularities. When the surface of the wafer 1 having such undulations is polished using the polishing pad 11 having no flexibility and the surface is completely flattened, as shown in FIG. The undulation causes the wafer to be significantly polished locally, resulting in a significantly uneven thickness of the wafer 1.

In order to avoid this, a somewhat soft polishing pad 11 is used. In this case, as shown in FIG. 3B, the polishing pad 11 follows irregularities and undulations of the wafer 1, and the polishing pad 11 comes into contact with both the projections and depressions on the surface of the wafer 1. Local polishing unevenness is prevented. However, wafer 1
The polishing pad 11 uniformly contacts both the projections and the recesses, and the projections and the recesses are uniformly polished. The ability to transform is reduced.

On the other hand, when a wafer on which patterns having different sizes are formed is polished by a conventional standard CMP method using a soft polishing pad, a small-sized pattern is polished faster than a large-sized pattern. Several mm
It has been difficult to completely flatten a step due to a pattern having a size larger than a corner. However, for example, in a memory mat portion of a DRAM, there is a step due to a pattern having a size of several mm square to sometimes about 10 mm square, and it is necessary to flatten a large-sized pattern.

As a method for improving the trade-off between the step flattening ability and the uniformity of the polishing amount, Japanese Patent Laid-Open Publication No. Hei 5-21266 is used.
No. 9 proposes a method of dividing a polishing pad into segments and providing an elastic support layer as a lower layer. The polishing pad divided into segments follows irregularities on the wafer processing surface by deformation of an elastic support layer as a lower layer, so that a high leveling capability for level differences and a uniform polishing amount are both compatible.

According to this method, although a hard polishing pad is used, the step flattening ability is improved. However, since the free abrasive grains (polishing slurry) are used, the recessed portions of the pattern are formed by the rolling free abrasive grains. It will be cut down. In addition, each step causes damage to the wafer due to a step created between a loaded segment and an unloaded segment, the wafer is detached during polishing, and the amount of polishing at the periphery of the wafer is larger than other portions. Are of the same size, the supply of liquid in the center of the wafer is relatively insufficient, and the uniformity of the polishing amount is reduced. The use of an alkaline or acidic slurry limits the materials that can be used as the lower elastic support layer. When a porous material having an appropriate elastic modulus is used as the support layer in which the adhesive strength between the upper polishing pad and the lower support layer is deteriorated,
There are many problems such as the dried slurry remaining in the pores, resulting in deterioration of characteristics and particle contamination, and interference between the slurry and the elastic support layer adversely affecting.

[0016] Furthermore, the method of using a slurry is expensive because the utilization efficiency of the abrasive grains is low, and the abrasive grains in the slurry may be aggregated or settled during storage to change their properties. Need to be careful,
As it causes scattering of particles in the atmosphere,
There are many problems, such as not being originally suitable for use in a clean room for semiconductor manufacturing.

Therefore, the conventional planarization method is applied to, for example, the formation of a semiconductor integrated circuit including a large-sized pattern such as a DRAM or the like, or the shallow trench element isolation step which requires extremely high planarization ability and uniformity. It was difficult to do.

An object of the present invention is to solve the above-described conventional problems, and to uniformly polish and flatten the entire surface of a wafer regardless of the size of a pattern formed on the surface of the wafer. An object of the present invention is to provide a low-cost surface flattening method and a surface flattening apparatus used for the method.

[0019]

According to a first aspect of the present invention, there is provided a method for flattening a surface, comprising: holding a wafer having a desired pattern formed on a surface thereof in a wafer holder; The ratio is held on a low whetstone holding layer, the wafer and the whetstone are opposed to each other and brought into contact with each other at a predetermined pressure, and at least one of the wafer and the whetstone is moved in a plane direction to polish the pattern. It is characterized by the following.

That is, in the present invention, polishing is performed by a grindstone supported on a grindstone support layer having a lower elastic modulus than a grindstone, and free abrasive grains (polishing slurry) are not used. By using a grindstone and a grindstone support layer having a different elastic modulus from that of the grindstone in combination, polishing with a high leveling ability with a fixed abrasive (grindstone) and a uniform polishing amount can be performed. In addition, since the polishing slurry is not used, the cost is low, and the above-mentioned various obstacles caused by the use of the polishing slurry do not occur.

In the present invention, the polishing is performed by (1) rotating the wafer with an axis in a direction perpendicular to the surface of the wafer as a first rotation axis, and rotating the grinding wheel in parallel with the first rotation axis. The rotation is performed by rotating an axis separated by a predetermined distance from the first rotation axis as a second rotation axis. (2) The rotation is performed by circular movement (revolution) of the wafer on the grinding wheel. 3)
This can be performed by moving the grinding wheel in a linear direction.

The above method (1) is the most practical method, and the rotation speeds of the first and second rotating shafts can be adjusted in a wide range. The above-mentioned method (2) is usually performed stationary without rotating the grindstone layer, but the grindstone layer may be rotated slowly (self-rotation), which is effective in preventing uneven polishing. The wafer may rotate only or may rotate. In the case of the above method (3), the wafer may be kept stationary without rotating, but if the wafer is rotated, it is effective to prevent polishing unevenness.

A bonding layer having a smaller thickness and a higher elastic modulus than the grinding wheel holding layer is provided on the grinding wheel holding layer, and the grinding wheel can be held on the bonding layer. In this way, excessive deformation of the grinding wheel support layer is prevented, and a remarkable effect is obtained particularly when the grinding wheel is divided into a plurality of segments or a contact portion with the wafer is divided into a plurality of sections by grooves. can get.

[0024] Preferably the elastic modulus of the grindstone holding layer is about 1/10 of the elastic modulus of the grindstone, for instance, the elastic modulus of the grindstone ^{1kg / mm 2 ~500kg / mm 2} , the whetstone holding layer The elastic modulus is 0.1 kg / mm ^{2 to} 50 kg
/ Mm ² , practically preferable results are obtained.

When the above-mentioned grindstone is divided into a plurality of segments or a plurality of grooves are formed in the above-mentioned grindstone and a portion other than the bottom of the groove is divided into a plurality of sections, the followability to unevenness and undulation on the wafer surface is improved. And the uniformity of the polishing amount is improved. Further, when the size of the segment or section in the radial direction of the whetstone is changed along the radial direction of the whetstone, and the portion where the center of the wafer contacts is minimized, the supply of water to the center of the wafer is reduced. Can be increased, thereby improving the uniformity of the polishing amount and the polishing speed.

The polishing can be performed while supplying water onto the grinding stone. Unlike the conventional CMP method, water can be used instead of the polishing slurry, so that many obstacles due to the use of the polishing slurry are prevented, which is extremely advantageous in practical use.

[0027] when performing the polishing, if a pressure applied between the wafer and the grindstone and ^{30g / cm 2 ~500g / cm 2} , preferable results are obtained.

The surface flattening method of the present invention is particularly useful for flattening the surface of a semiconductor wafer having various patterns such as wiring patterns formed on the surface.

Further, the surface flattening apparatus according to the present invention comprises: a wafer holder for holding a wafer; means for rotating the wafer holder with an axis perpendicular to the surface of the well holder as a first rotation axis; A grindstone support layer formed on the board and having a lower elasticity than the grindstone to be held, and a second axis parallel to the first rotation axis and separated from the first rotation axis by a predetermined distance. At least means for rotating the polishing platen as a rotation axis, and means for bringing the grinding wheel and the wafer supported on the grinding wheel support layer into contact with each other at a predetermined pressure are provided.

[0030] Preferably the elastic modulus of the grindstone holding layer is about 1/10 of the elastic modulus of the grindstone, the elastic modulus of the grindstone ^{1kg / mm 2 ~500kg / mm 2} , the elastic modulus of the grindstone holding layer Is set to 0.1 kg / mm ^{2 to} 50 kg / mm ² , a practically preferable result is obtained. If the grinding wheel support layer is adhered to the polishing platen via an adhesive tape, the replacement operation is easy.

A bonding layer having a smaller thickness and a higher elastic modulus than the grinding wheel holding layer is provided on the grinding wheel holding layer, and the grinding wheel can be held on the bonding layer. This prevents excessive deformation of the grinding wheel support layer due to unevenness and undulation on the wafer surface.

The grinding stone may be divided into a plurality of segments, or a plurality of grooves may be formed in the grinding stone, and a portion other than the bottom of the groove may be divided into a plurality of sections. As a result, the followability of polishing to unevenness and undulation on the wafer surface is improved, and the uniformity of the polishing amount is improved. In this case, the size of the segment or section in the radial direction of the grinding stone is not the same, but is changed along the radial direction of the grinding stone so that the portion in contact with the center of the wafer is minimized. The amount of water supplied to the center is increased, which is useful for reducing the unevenness of the polishing amount and increasing the polishing speed.

The above segment or section has a side of 5
If a square of mm to 50 mm or a desired shape having an area equivalent to the square is used, practically preferable results can be obtained.

As the above-mentioned grindstone, one composed of abrasive grains and a fixing material for fixing the abrasive grains can be used. As the above-mentioned abrasive grains and the fixing agent, for example, cerium oxide and phenol resin are used, respectively. be able to.

Further, a retainer ring to which pressure can be applied independently of the wafer can be provided on the outer peripheral portion of the wafer, so that the polishing speed at the outer peripheral portion of the wafer can be appropriately adjusted.

[0036]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, as a grinding stone,
Fine particles (for example, cerium oxide or the like having an average particle diameter of 1 μm or less) and having a low impurity content can be used by bonding the particles with a fixing agent such as a phenol resin. Resin or polyurethane impregnated nonwoven fabric can be used. As described above, the elastic moduli of the grindstone and the grindstone support layer are 1 to 5 respectively.
Preferable results can be obtained with 00 kg / mm ² and 0.1 to 50 kg / mm ² . The thicknesses of the grindstone and the grindstone support layer can be, for example, about 3 mm and 1 mm, respectively.

The supply amount of the working fluid during polishing is 1
The flow rate is about 00 to 1000 ml / min, and pure water can be used as the processing liquid. The wafer holder and the polishing plate are rotated in the same direction, and the rotation speed is 20 to 50 r each.
pm.

Dividing the whetstone into a plurality of segments,
Alternatively, forming a plurality of grooves to divide the contact portion with the wafer into a plurality of sections is practically advantageous in terms of reduction in polishing unevenness and uniformity of the polishing amount. However, if a sufficiently thin and soft whetstone is used, the whetstone will not be divided into segments in this way, or divided by grooves,
Polishing is also possible.

As the shape of a segment or section,
Various shapes are possible. For example, it is possible to use many shapes of segments and sections, such as a lattice shape shown in FIG. 10A, a round shape and a hexagon shown in FIGS. 10B and 10C, respectively. it can.

[0040]

【Example】

<Embodiment 1> A first embodiment of the present invention will be described with reference to FIG. As is apparent from FIG. 5, the surface flattening apparatus of this embodiment includes a polishing platen 12, a polishing tool 16 mounted on the polishing platen 12, a wafer holder 14 for holding the wafer 1 to be polished, and a polishing plate. In this case, a liquid supply unit 20 for supplying the processing liquid 15 such as water at the time is provided.

As shown in FIG. 1, the polishing tool 16 comprises a grindstone 21, a grindstone support layer 22, and an adhesive layer 23, and is adhered to the polishing platen 12 by the adhesive layer 23. The size of the polishing platen 12 depends on the size of the wafer. When the wafer diameter is 6 inches, the diameter of the polishing platen is about 500 mm.

A pressure W is applied to the wafer holder 14 holding the wafer 1 from above, the wafer 1 is pressed against the polishing tool 16, and the wafer holder 14 and the polishing platen 12 are simultaneously rotated, whereby the wafer 1 is polished. . At this time, 100-1000 m / min from the liquid supply unit 20
About 1 of the working fluid 15 is supplied onto the polishing tool 16.
The force W for pressing the wafer holder 14 against the polishing tool is typically 30 to 500 g / cm ² , and the polishing speed (1
(Abrasion amount per minute) is almost proportional to this force W. The wafer holder 14 and the polishing table 12 were rotated in the same direction.
It is preferable to make the both rotational speeds substantially the same in order to perform uniform polishing. The number of revolutions is typically between 20 and 5
0 rpm.

The polishing tool 16 is provided at the top of the polishing tool 16.
As the grindstone 21 that directly touches the wafer 1, a grindstone in which fine cerium oxide abrasive grains are bonded by a resin can be used. This whetstone has a structure including pores 26 as shown in FIGS. 6 (a) and 6 (b). Depending on the type and use of the resin used, the shape of the pores 26 may be continuous as shown in FIG. 6 (a) or independent as shown in FIG. 6 (b). 2
It is desirable that the impurities in 1 be as small as possible. In the present embodiment, a whetstone 21 in which fine cerium oxide abrasive grains having an average particle diameter of 1 μm or less and bonded with a phenol resin were used.

As the grindstone support layer 22 provided as a lower layer of the grindstone 21, a material having a uniform thickness and a desired elastic modulus can be obtained. For example, a polyurethane resin or a polyurethane-impregnated nonwoven fabric can be used. In this embodiment, a polyurethane resin is used. In this case, the elastic modulus of the grindstone support layer 22 is about 10 kg / mm ^2, which is about one digit smaller than the elastic modulus of the grindstone 21 of about 100 kg / mm ² . The higher the elastic modulus of the grindstone 21, the higher the flattening ability,
If it is too high, it may cause polishing scratches and the like, which is not preferable. It was found that when the elastic modulus was 500 kg / mm ² or less, generation of polishing scratches could be avoided. But,
If the elastic modulus of the grindstone 21 is 1 kg / mm ² or less, the required flattening ability cannot be obtained. Therefore, from the viewpoint of polishing flaws and the flattening ability, the elastic modulus of the grindstone 21 is within the range of 1 to 500 kg / mm ^2. Is preferred.

On the other hand, as the elastic modulus of the grinding wheel support layer 22 is lower, the unevenness in the amount of polishing in the surface of the wafer 1 is reduced. Occur. In order to obtain a practical flattening ability, the elastic modulus of the grinding wheel support layer 22 needs to be 0.1 kg / mm ² or more, and the uniformity of the polishing amount is 5 at 1σ.
%, It was necessary to be 50 kg / mm ² or less. When the elastic modulus of the grindstone support layer 22 was set to about 1/10 of the elastic modulus of the grindstone 21, it was found that the polishing amount uniformity and the flattening ability were compatible.

In this embodiment, the thickness of the grindstone 21 is about 3 m.
m, and the thickness of the grinding wheel support layer 22 was 1 mm. The grindstone 21 and the grindstone support layer 22 are adhered to each other with an adhesive, and an adhesive tape 23 is used to bond the grindstone support layer 22 and the polishing platen 12 in order to facilitate the exchange operation.

In this embodiment, the grindstone 21 is divided into segments each having a square shape with a side of 15 mm in order to improve the dischargeability of the working fluid and the uniformity of the polishing amount. The size of each segment is such that the chip size on the wafer to be flattened is one side 5
15m considering that it is about 15mm to 15mm
m.

Using this polishing apparatus, a silicon wafer on which a p-TEOS film (SiO ₂ film) is uniformly formed on the entire surface is polished using only pure water as a processing liquid.
The polishing amount at each wafer diameter position was measured. The polishing amount was measured using an optical interference type film thickness meter. The film thickness before and after polishing was measured at 15 points on the diameter along the orientation flat of the wafer, and the polishing amount was determined from the difference between the two. I asked. For comparison, the same polishing and measurement were performed using a polishing tool consisting only of a single-layer grinding wheel.

FIG. 7 (a) shows the results obtained when a polishing tool comprising only a single-layer grinding stone and having no grinding wheel support layer is used, and FIG. 7 (b) shows the results obtained by this embodiment. It was shown to. As is clear from FIG. 7A and FIG. 7B, in the case of the present embodiment in which the grindstone support layer 22 having a low elastic modulus is provided below the grindstone 21, the distribution of the polishing amount in the wafer surface is as follows. It was confirmed that it was much more uniform than when only a single-layer whetstone was used, and that there was much less variation in the amount of polishing.
In addition, as the above-mentioned wafer, 6 inch diameter silicon
Using wafer, applied pressure in polishing process is 240g
/ Cm ² , the relative speed was 53 cm / s, and the polishing time was 3 minutes.

<Embodiment 2> A second embodiment of the present invention will be described with reference to FIG.

As is clear from FIG. 8, in this embodiment, a bonding layer 24 is provided between the grindstone 21 and the grindstone support layer 22. The role of the bonding layer 24 is to prevent the soft grinding wheel support layer 22 from being deformed more than necessary during polishing. When the grindstones 21 are segmented, each grindstone 21 is displaced in the vertical direction due to the load during polishing, and a step-like step is generated between the segments, so that polishing scratches, wafer detachment and polishing of the wafer outer peripheral portion are caused. May cause excessive amount.

For this reason, in this embodiment, PET (polyethylene / polyethylene) is thin and has a small elongation with respect to the force in the tensile direction.
A bonding layer 24 made of, for example, a terephthalate) film;
The grindstone 21 is interposed between the grindstone 21 and the grindstone support layer 22.
The displacement of vertical change was suppressed. The other points are the same as in the first embodiment. As a result, the boundary between the segment to which the load is applied and the unloaded segment is not discontinuous, but is smoothly connected, and the obstacles such as the polishing scratches are further reduced.

In this embodiment, a PET film having a thickness of 100 μm is used as the bonding layer 24. But,
The bonding layer 24 does not necessarily need to be a film-like substance, but can be used to suppress the displacement in the longitudinal direction of each of the segment-shaped grindstones 21, for example, a knitted string-like substance, or a wire made of metal, resin, or the like. A mesh-like layer may be used. Also, instead of being interposed between the grindstone 21 and the grindstone support layer 22, a bonding layer made of, for example, a string-like substance
1 or a material having appropriate elasticity is interposed between the grinding wheels 21 so that the adjacent grinding wheels 21
May be combined with each other.

<Embodiment 3> A third embodiment of the present invention is shown in FIG.
This will be described with reference to FIG.

As is clear from FIG. 9, in this embodiment, the segments of the grindstone 21 are not completely separated as in the first and second embodiments, and the joining portions 25 are left except for the bottom of the groove. And By adopting such a structure,
The role of the bonding layer 24 provided in the second embodiment is
The bonding part 25 between the respective segments of the grindstone 21 is performed, and without providing a special bonding layer under the grindstone 21, the second embodiment is performed.
The same effect as described above was obtained.

<Embodiment 4> In this embodiment, as shown in FIG. 11, the size of the segments 21 has a distribution, and the size of the segments 21 becomes smaller at the portion in contact with the central portion of the wafer 1. This is an example. Since a water film is likely to be formed in the central portion of the wafer 1 during polishing, the size of the segments 21 in the diameter direction is reduced to increase the ratio of the grooves. Further, by increasing the proportion of the grooves, the amount of water supplied to the central portion of the wafer 1 could be increased.
Thereby, the unevenness in the amount of polishing caused by the formation of the water film and the insufficient water supply was reduced. In addition, since the rotation speed of the platen during polishing can be increased, the polishing speed can be increased.

<Embodiment 5> When the grindstone is divided into segments, the height of each segment supported by the relatively soft grindstone support layer changes independently.
Therefore, a step is inevitably generated between the segment pressed in contact with the wafer during processing and the segment that does not come into contact with the wafer and does not receive a force from the wafer. Due to the step between the segments, an abnormal amount of polishing may occur such that only the periphery of the wafer edge is polished particularly quickly, or conversely, the polishing becomes difficult.

This embodiment is an example in which such an obstacle is prevented. As shown in FIG. 12, the pressure W1 of the retainer ring 27 on the outer periphery of the wafer holder 14 can be applied independently of the pressure W2 of the wafer 1. I did it. When the outer peripheral portion of the wafer 1 is polished particularly quickly, the retainer ring 2
7, if the outer peripheral portion of the wafer 1 is polished slowly, the pressure W1 of the retainer ring 27 may be reduced. <Embodiment 6> This embodiment is an example in which the present invention is applied to a shallow trench element isolation step in a semiconductor device manufacturing process.

As shown in FIG. 13A, after a silicon nitride film 33 for protecting an element forming portion is formed in a region 32 where an element is to be formed, the surface of the silicon substrate 30 is formed by well-known photo-etching. A groove 31 for element isolation was formed.

Next, as shown in FIG. 13B, a SiO ₂ film 34 was formed on the entire surface by using a well-known CVD method.
Further, using the method shown in the first embodiment, the broken line 35
Then, the SiO ₂ film 34 was left only in the groove, and the other portions were removed to form the structure shown in FIG. 13C.

When the above-mentioned insulating film 34 is polished by a conventional CMP method, a phenomenon called dishing occurs in which the surface of the insulating film 34 in the groove is not flat and becomes concave. If dishing occurs, desired device characteristics cannot be obtained. However, according to the present embodiment, shallow trench device isolation with a flat surface can be performed without such dishing.

<Embodiment 7> In this embodiment, a grinding wheel supported on a grinding wheel support layer of the present invention is prepared by rotating a wafer and a grinding wheel in a horizontal direction with respect to a floor surface, This is an example in which the present invention is applied to a polishing apparatus of a type that moves in a plane perpendicular to the plane, and will be described with reference to FIG.

As shown in FIG. 14, the two wafers 1 are held on both sides of the wafer holder 14,
1, the wafer holder 14 is sandwiched therebetween, and the wafer 1 is polished. Although not shown, the first embodiment is provided between the grindstone 21 and the surface plate 12.
As in the case of (1), a grindstone support layer 22 and an adhesive layer 23 are provided.

The diameter of the grindstone 21 is preferably at least one time the diameter of the wafer 1. When the supply of the working liquid (pure water) from the liquid supply unit 20 is performed from the groove on the surface of the grindstone 21, The diameter of the grindstone 21 may be less than twice the diameter of the wafer 1. This embodiment has a feature that the apparatus can be miniaturized because the rotating polishing surface is perpendicular to the floor surface. <Embodiment 8> In this embodiment, after polishing with high flatness is performed using the grinding wheel 21 (formed on the grinding wheel support layer 22 and the adhesive layer 23 as shown in FIG. 1). ,
This is an example in which a known polishing process using a polishing pad and a slurry is performed.

According to this embodiment, the final surface roughness can be improved and the amount of remaining foreign substances can be reduced, and this is particularly useful for processing a relatively soft film such as a BPSG film. . In addition, if the processing amount by the polishing pad and the slurry is excessive, the flatness deteriorates. Therefore, it is preferable that the processing amount be approximately 0.1 μm or less in thickness. <Embodiment 9> In this embodiment, polishing is performed by using a slurry containing abrasive grains in combination with the grinding wheel 21 (formed on the grinding wheel support layer 22 and the adhesive layer 23 as shown in FIG. 1). The polishing speed can be further improved.

The relationship between the concentration of silica and the polishing rate when fumed silica was added as a slurry to the grindstone was determined. A comparison was made between the case where only the grindstone was used and the case where the fumed silica slurry and the polishing pad were used. The results obtained are shown in FIG.

As is apparent from FIG. 15, the polishing pressure is 10
Since a grinding stone having a low polishing rate of 0 g / cm and a low polishing rate was used with emphasis on the roughness of the polished surface, the polishing rate when only the grinding stone was used was as low as 5 nm / min.

However, when fumed silica slurry having a concentration of 12%, which is generally used, is used in combination with the grinding wheel 21, the polishing speed reaches 100 nm / min, and even if the concentration is reduced to 1.2% by diluting the slurry, The polishing rate was 40 nm / min. On the other hand, the polishing speed in the case where polishing is performed only with the slurry and the polishing pad without using a grindstone is 40 nm / min when the slurry concentration is 12% and almost 0 when the slurry concentration is 1.2%.
It was confirmed that the combined use of the grinding stone and the polishing slurry was useful for improving the polishing speed.

[0069]

As is apparent from the above description, according to the present invention, it is possible to obtain a good flatness even with a large pattern exceeding several mm, which has been difficult with the conventional method using loose abrasive grains. It has become possible to achieve a sufficiently uniform polishing amount within the wafer surface. In addition, since processing can be performed using pure water alone without using an alkaline or acidic slurry, stable processing can be performed for a long period of time without deteriorating equipment and processing tools, as well as cost reduction. It was realized.
Furthermore, the focus margin of lithography has become smaller, and it has become possible to manufacture finer semiconductor integrated circuits at lower cost than in the past. Also, polishing in the element isolation step, which has been difficult in the past, can be performed without causing dishing.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first embodiment,

FIG. 2 is a process chart for explaining a wafer surface flattening process;

FIG. 3 is a diagram illustrating a CMP method.

FIG. 4 is a diagram for explaining occurrence of polishing unevenness;

FIG. 5 is a diagram for explaining a configuration of the present invention;

FIG. 6 is a view showing a pore shape of a grindstone;

FIG. 7 is a diagram showing an example of the effect of the present invention;

FIG. 8 is a diagram showing a second embodiment;

FIG. 9 is a diagram showing a third embodiment;

FIG. 10 is a diagram showing an example of the shape of a segment;

FIG. 11 is a diagram showing a fourth embodiment;

FIG. 12 is a diagram showing a fifth embodiment;

FIG. 13 is a process chart showing a sixth embodiment.

FIG. 14 is a diagram showing a seventh embodiment;

FIG. 15 shows a ninth embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Wafer, 2 and 4 ... Insulating film, 3 ... Wiring layer, 5 ... Aluminum layer, 6 ... Photoresist layer, 7 ... Stepper, 8 ... Depression, 9 ... Target level of planarization, 11 ... Polishing pad, 12
... Surface plate, 13 backing pad, 14 wafer holder, 15 working fluid, 16 polishing tool, 20 liquid supply unit, 21 grinding wheel, 22 grinding wheel support layer, 23 adhesive layer, 24 bonding layer, 25 ... connecting part, 26 ... pore, 27 ...
Retainer ring, 30: silicon substrate, 31: groove for element isolation, 32: element formation region, 33: silicon nitride film, 3
4: SiO ₂ film, 35: broken line indicating the position to be removed.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Katsuhiko Yamaguchi, Inventor 1-280 Higashi Koigakubo, Kokubunji-shi, Tokyo Inside the Central Research Laboratory, Hitachi, Ltd.

Claims (20)

[Claims] 1. A wafer having a desired pattern formed on a surface thereof is held by a wafer holder, a grindstone is held on a grindstone holding layer having a lower elastic modulus than the grindstone, and the wafer and the grindstone face each other. A surface flattening method, wherein the pattern is polished by bringing at least one of the wafer and the grindstone in a plane direction by bringing them into contact with each other at a predetermined pressure. 2. The polishing includes rotating the wafer with an axis in a direction perpendicular to the surface of the wafer as a first rotation axis, and rotating the grinding wheel in parallel with the first rotation axis and the first rotation axis. The surface flattening method according to claim 1, wherein the method is performed by rotating an axis separated by a predetermined distance from the rotation axis as a second rotation axis. 3. The method according to claim 1, wherein the polishing is performed by circularly moving the wafer on the grindstone. 4. The method according to claim 1, wherein the polishing is performed by moving the grindstone in a linear direction. 5. The grinding wheel is held on a bonding layer having a smaller thickness and a higher elastic modulus than the grinding wheel holding layer provided on the grinding wheel holding layer. The surface flattening method according to any one of the above. 6. The grinding wheel has an elastic modulus of 1 kg / mm ² to 50.
0 kg / mm ² , and the elastic modulus of the grinding wheel holding layer is 0.1 kg / mm ² .
Surface planarization method as claimed in any one of 5, which is a ^{1kg / mm 2 ~50kg / mm 2} . 7. The grinding wheel is divided into a plurality of segments, or a portion other than a bottom portion of the groove is divided into a plurality of sections by a plurality of grooves formed in the grinding wheel. Item 7. The surface flattening method according to any one of Items 1 to 6. 8. The size of the segment or section in the radial direction of the whetstone varies along the radial direction of the whetstone, and is smallest at a portion where the center of the wafer contacts. Surface flattening method according to 4. 9. The surface flattening method according to claim 1, wherein the polishing is performed while supplying water onto the grinding stone. 10. The pressure is from 30 g / cm ^{2 to} 500 g / cm ² .
The method according to any one of claims 1 to 9, wherein the surface flattening is cm ² . 11. The method according to claim 1, wherein the wafer is a semiconductor wafer. 12. A wafer holder for holding a wafer, means for rotating the wafer holder with an axis perpendicular to the surface of the well holder as a first axis of rotation, and a holder formed on a polishing platen. A grindstone supporting layer having a lower elastic modulus than the grindstone to be rotated, and rotating the polishing platen with a second parallel rotation axis that is parallel to the first rotation axis and separated from the first rotation axis by a predetermined distance. A surface flattening apparatus comprising at least means for causing the grinding wheel supported on the grinding wheel support layer and the wafer held by the wafer holder to come into contact with each other at a predetermined pressure. 13. An elastic modulus of the grinding stone is 1 kg / mm ² -5.
Was 00kg / mm ^2, the surface planarization apparatus according to claim 12, wherein the elastic modulus of the grindstone holding layer is ^{0.1kg / mm 2 ~50kg / mm 2} . 14. The surface flattening device according to claim 12, wherein the grinding wheel support layer is adhered on the polishing platen via an adhesive tape. 15. A bonding layer having a smaller thickness and a higher elastic modulus than the grinding wheel holding layer is provided on the grinding wheel holding layer, and the grinding wheel is held on the bonding layer. Item 15. The surface flattening device according to any one of Items 12 to 14. 16. The grinding wheel is divided into a plurality of segments, or a portion other than the bottom of the groove is divided into a plurality of sections by a plurality of grooves formed in the grinding wheel. Item 16. The surface flattening device according to any one of Items 12 to 15. 17. The apparatus according to claim 16, wherein the size of the segment or section in the radial direction of the grinding wheel varies along the radial direction of the grinding wheel, and is smallest at a portion where the center of the wafer contacts. A surface flattening apparatus according to item 1. 18. The segment or section according to claim 16, wherein the segment or section is a square having a side of 5 mm to 50 mm, or has a desired shape and an area substantially equal to the square. Surface flattening device. 19. The surface flattening apparatus according to claim 12, wherein the grinding wheel is made of abrasive grains and a fixing material for fixing the abrasive grains. 20. The flat surface according to claim 12, wherein a retainer ring to which pressure can be applied independently of the wafer is provided on an outer peripheral portion of the wafer. Device.