JP3601937B2 - Surface flattening method and surface flattening device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a surface flattening method and a surface flattening apparatus, and in particular, in the manufacture of various semiconductor devices, particularly suitable for flattening the surface of a semiconductor wafer having various patterns formed on its surface, The present invention relates to a surface flattening device used for the same.
[0002]
[Prior art]
A semiconductor manufacturing process includes many process steps. In order to form a fine semiconductor device with extremely high integration density, planarization of a surface has become particularly important. As an example, a wiring forming process will be described with reference to FIG.
[0003]
FIG. 2A shows a state in which a first-layer wiring is formed. An insulating film 2 and a wiring layer 3 made of aluminum or the like are formed on a surface of a substrate 1 on which a transistor (not shown) is formed. Is provided. Since the wiring layer 3 is connected to the transistor through the opening formed in the insulating film 2, the surface 3 'of the wiring layer 3 at the connection portion is slightly dented.
[0004]
Therefore, as shown in FIG. 2B, when the second insulating film 4, the aluminum film 5, and the photoresist film 6 are sequentially laminated to form the second layer wiring, the photoresist film 6 The surface is not flat and irregularities occur.
[0005]
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 is not flat but has irregularities. As is well known, since the depth of focus of the stepper is not deep, it is impossible to simultaneously focus on the concave portion and the convex portion 8 of the photoresist film 6, and a serious obstacle such as resolution blur occurs.
[0006]
In order to prevent such a failure, after the process shown in FIG. 2A, the insulating film 4 is formed on the entire surface as shown in FIG. The surface is flattened by polishing until the shape shown in FIG.
[0007]
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.
[0008]
Methods for flattening the surface by such polishing are described in, for example, U.S. Pat. No. 4,944,836 and Japanese Patent Publication No. 5-30052.
[0009]
As a polishing method for planarizing 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 adhered on a surface plate 12, a wafer 1 to be processed is fixed to a wafer holder 14 via 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 while being rotated, and a load is applied to the surface of the polishing pad 11 while rotating the wafer holder 14.
[0010]
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, fine and high-purity is used. Fumed silica in which a suitable silica particle is suspended in an aqueous alkali solution such as potassium hydroxide or ammonia is generally used.
[0011]
[Problems to be solved by the invention]
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 completion of planarization is about ± 0.1 μm or less, Extremely low is required. 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 a significant local polishing, resulting in a significantly uneven thickness of the wafer 1.
[0012]
To avoid this, a somewhat soft polishing pad 11 is used. In this case, 4 As shown in (b), the polishing pad 11 follows the unevenness and undulation of the wafer 1 and the polishing pad 11 comes into contact with both the convex portion and the concave portion on the surface of the wafer 1. Is prevented. However, since the polishing pad 11 uniformly contacts both the convex portion and the concave portion of the wafer 1 and the convex portion and the concave portion are uniformly polished, only the convex portion originally intended is selectively used. The ability to remove and planarize is reduced.
[0013]
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, and several mm square. It has been difficult to completely flatten the steps due to the above large pattern. 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 about 10 mm square, and it is necessary to flatten a large-sized pattern.
[0014]
As a method for improving the trade-off between the step flattening ability and the polishing amount uniformity, Japanese Patent Laid-Open No. 5-212669 proposes a method in which a polishing pad is divided into segments and an elastic support layer is provided as a lower layer. The polishing pad divided into segments follows irregularities on the processed surface of the wafer by deformation of an elastic support layer as a lower layer, so that a high leveling capability of the step and a high uniformity of the polishing amount are compatible.
[0015]
In this method, a hard polishing pad is used, so that the step flattening ability is improved. However, since free abrasive grains (polishing slurry) are used, even the concave portions of the pattern are cut by the rolling free abrasive grains. Would. In addition, each step causes damage to the wafer due to a step formed 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 short, 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. If a porous material with an appropriate elastic modulus is used as a support layer that deteriorates the adhesive strength between the upper polishing pad and the lower support layer, a dried slurry remains in the pores, deteriorating the properties and preventing particle contamination. There have been many problems such as the cause, interference between the slurry and the elastic support layer has a bad effect.
[0016]
In addition, the method using slurry is expensive because the efficiency of use of the abrasive grains is low.Abrasive grains in the slurry may aggregate or precipitate due to storage and their properties may change, so care must be taken when handling the slurry. There are many problems such as particles that need to be used and are scattered in the atmosphere, and are not originally suitable for use in a semiconductor manufacturing clean room.
[0017]
Therefore, it is difficult to apply the conventional planarization method 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 isolation process requiring extremely high planarization capability and uniformity. It was difficult.
[0018]
SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned conventional problems and to uniformly polish and flatten the entire surface of a wafer with high accuracy, regardless of the size of a pattern formed on the wafer surface, and to reduce the cost. An object of the present invention is to provide a surface flattening method and a surface flattening apparatus used for the same.
[0019]
[Means for Solving the Problems]
In order to achieve the above object, the surface flattening method of the present invention holds a wafer having a desired pattern formed on its surface in a wafer holder, and holds a grindstone on a grindstone holding layer having a lower elastic modulus than the grindstone. The pattern is polished by bringing the wafer and the grindstone into contact with each other at a predetermined pressure and moving at least one of the wafer and the grindstone in a plane direction.
[0020]
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 elasticity from the grindstone in combination, the polishing with a high flattening ability by the fixed abrasive (grindstone) and the uniformity of the 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.
[0021]
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 grindstone in parallel with the first rotation axis and the second rotation axis; The rotation is performed by rotating an axis that is separated from the first rotation axis by a predetermined distance as a second rotation axis, (2) the wafer is caused to perform a circular motion (revolution) on the grinding wheel, and (3) the rotation is performed. This can be done by moving the grindstone in a linear direction.
[0022]
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 method (2) is usually performed stationary without rotating the grindstone layer, but the grindstone layer may be rotated slowly (self-rotation), which is effective for 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.
[0023]
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]
The elastic modulus of the grinding wheel holding layer is preferably about 1/10 of the elastic modulus of the grinding stone. For example, the elastic modulus of the grinding stone is 1 kg / mm. ² ~ 500kg / mm ² The elastic modulus of the grinding wheel holding layer is 0.1 kg / mm. ² ~ 50kg / mm ² Then, a practically preferable result is obtained.
[0025]
Separate the grindstone into a plurality of segments, or form a plurality of grooves in the grindstone, and divide a portion other than the bottom of the groove into a plurality of sections to improve the followability to unevenness and undulation of the wafer surface, 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 comes into contact 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.
[0026]
The polishing can be performed while supplying water onto the grinding wheel. 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]
The pressure applied between the wafer and the grindstone during polishing is 30 g / cm. ² ~ 500g / cm ² Then, favorable results can be obtained.
[0028]
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.
[0029]
Further, the surface flattening apparatus of 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, and a polishing platen. A whetstone support layer having a lower elastic modulus than the whetstone to be held, and an axis parallel to the first rotation axis and separated from the first rotation axis by a predetermined distance as a second rotation axis Means for rotating the polishing platen, the grindstone supported on the grindstone support layer and the wafer To It is characterized by comprising at least means for contacting each other at a predetermined pressure.
[0030]
The elastic modulus of the grinding wheel holding layer is preferably about 1/10 of the elastic modulus of the grinding stone, and the elastic modulus of the grinding stone is 1 kg / mm. ² ~ 500kg / mm ² The elastic modulus of the grinding wheel holding layer is 0.1 kg / mm. ² ~ 50kg / mm ² In this case, 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.
[0031]
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.
[0032]
The grindstone may be divided into a plurality of segments, or a plurality of grooves may be formed in the grindstone, and a portion other than the bottom of the groove may be divided into a plurality of sections. As a result, the ability of polishing to follow irregularities and undulations 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 wheel is not the same, but is changed along the radial direction of the grinding wheel 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.
[0033]
Practically favorable results can be obtained by forming the segment or section into a square having a side of 5 mm to 50 mm or a desired shape having an area equivalent to the square.
[0034]
As the grindstone, those composed of abrasive grains and a fixing material for fixing the abrasive grains can be used. As the abrasive grains and the fixing agent, for example, cerium oxide and phenol resin can be used, respectively. .
[0035]
In addition, a retainer ring to which pressure can be applied independently of the wafer can be provided on the outer peripheral portion of the wafer, whereby the polishing rate at the outer peripheral portion of the wafer can be appropriately adjusted.
[0036]
BEST MODE FOR CARRYING OUT THE INVENTION
In the present invention, a grinding stone formed by bonding abrasive grains such as cerium oxide, which is fine (for example, having an average particle diameter of 1 μm or less) and has a low impurity content, with a fixing agent such as a phenol resin can be used as the grinding stone. As the grindstone support layer, a polyurethane resin or a polyurethane impregnated nonwoven fabric can be used. As described above, the elastic moduli of the grindstone and the grindstone support layer are respectively 1 to 500 kg / mm. ² And 0.1 to 50 kg / mm ² Then, a favorable result can be obtained. The thickness of the grindstone and the grindstone support layer can be, for example, about 3 mm and about 1 mm, respectively.
[0037]
The supply amount of the working fluid during polishing is about 100 to 1000 ml / min, and pure water can be used as the working fluid. The wafer holder and the polishing plate are rotated in the same direction, and the rotation speed is about 20 to 50 rpm, respectively.
[0038]
If the whetstone is divided into a plurality of segments or a plurality of grooves are formed to divide the contact portion with the wafer into a plurality of sections, it is practically advantageous in terms of reduction of polishing unevenness and uniformity of polishing amount. is there. However, if a sufficiently thin and soft grindstone is used, it is possible to perform polishing without dividing the grindstone into segments or dividing by a groove.
[0039]
Various shapes are possible for the shape of the segment or section, and for example, many shapes such as a lattice shape shown in FIG. 10A and a round shape and a hexagon shape shown in FIGS. 10B and 10C, respectively. Segments or sections can be used.
[0040]
【Example】
<Example 1>
A first embodiment of the present invention will be described with reference to FIG. As 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 is provided.
[0041]
As shown in FIG. 1, the polishing tool 16 includes 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.
[0042]
The wafer W is polished by applying a pressure W from above to the wafer holder 14 holding the wafer 1, pressing the wafer 1 against the polishing tool 16, and simultaneously rotating the wafer holder 14 and the polishing platen 12. At this time, the processing liquid 15 of about 100 to 1000 ml per minute is supplied onto the polishing tool 16 from the liquid supply unit 20. The force W for pressing the wafer holder 14 against the polishing tool is typically 30 to 500 g / cm. ² The polishing speed (amount of polishing per minute) is substantially proportional to the force W. The wafer holder 14 and the polishing platen 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 value of the rotational speed is typically between 20 and 50 rpm.
[0043]
As the grindstone 21 provided on the uppermost part of the polishing tool 16 and directly touching the wafer 1, a grindstone obtained by bonding fine cerium oxide abrasive grains with a resin can be used. This whetstone has a structure including pores 26 as shown in FIGS. 6A and 6B. 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). It is desirable that impurities in 21 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.
[0044]
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 is desirable, and 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 grinding wheel support layer 22 is about 10 kg / mm. ² And the elastic modulus of the grindstone 21 is about 100 kg / mm. ² Approximately one order of magnitude smaller. The higher the elastic modulus of the grindstone 21 is, the higher the flattening ability is. The elastic modulus is 500kg / mm ² It was found that polishing scratches could be avoided if the following conditions were satisfied. However, the elastic modulus of the grindstone 21 is 1 kg / mm. ² Since the required flattening ability cannot be obtained in the following, the elastic modulus of the grindstone 21 is 1 to 500 kg / mm from the viewpoint of polishing flaws and flattening ability. ² Is preferably within the range.
[0045]
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. However, when the elasticity is too low, problems such as a reduction in the life of the polishing tool 16 and a reduction in flattening ability occur. In order to obtain a practical flattening ability, the elastic modulus of the grinding wheel support layer 22 is set to 0.1 kg / mm. ² In order to make the uniformity of the polishing amount 5% or less in 1σ, 50 kg / mm ² It was necessary to: 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.
[0046]
In this embodiment, the thickness of the grindstone 21 is about 3 mm, and the thickness of the grindstone support layer 22 is 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.
[0047]
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 was set to 15 mm in consideration of the fact that the chip size on the wafer to be flattened was about 5 mm to 15 mm on one side.
[0048]
Using this polishing apparatus, a p-TEOS film (SiO ₂ The silicon wafer having the film uniformly formed on the entire surface was polished using only pure water as a processing liquid, and the polishing amount at each wafer diameter direction 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.
[0049]
FIG. 7 (a) shows the results obtained when a polishing tool made of only a single-layer whetstone and having no whetstone support layer was used, and FIG. 7 (b) shows the results obtained in this example. . 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 under 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 the variation in the polishing amount was much less. In addition, a silicon wafer having a diameter of 6 inches was used as the wafer, and the applied pressure in the polishing step was 240 g / cm. ² The relative speed was 53 cm / s, and the polishing time was 3 minutes.
[0050]
<Example 2>
A second embodiment of the present invention will be described with reference to FIG.
[0051]
As is clear from FIG. 8, in the present 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. It may cause excessive amount.
[0052]
Therefore, in the present embodiment, a bonding layer 24 made of a PET (polyethylene terephthalate) film or the like that is thin and has a small elongation with respect to the force in the tensile direction is interposed between the grindstone 21 and the grindstone support layer 22, and The displacement of the 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 a load is applied and the unloaded segment is not discontinuous, but is smoothly connected, and obstacles such as polishing scratches are further reduced.
[0053]
In this example, a PET film having a thickness of 100 μm was used as the bonding layer 24. However, the bonding layer 24 does not necessarily need to be a film-like substance, and can suppress displacement in the vertical direction of each of the segment-shaped grindstones 21, for example, a knitted string-like substance, a metal, a resin, or the like. A mesh-like layer composed of lines may be used. Also, instead of being interposed between the grindstones 21 and the grindstone support layer 22, for example, a bonding layer made of a string-like substance is disposed only between the grindstones 21 or a material having appropriate elasticity is interposed between the grindstones 21. The adjacent grindstones 21 may be connected to each other with intervening.
[0054]
<Example 3>
A third embodiment of the present invention will be described with reference to FIG.
[0055]
As is apparent from FIG. 9, in the present embodiment, the segments of the grindstone 21 are not completely separated as in the first and second embodiments, and the joining portion 25 is formed except for the bottom of the groove. With such a structure, the bonding portion 25 between the segments of the grindstone 21 plays the role of the bonding layer 24 provided in the second embodiment, and a special bonding layer is provided below the grinding stone 21. Without this, the same effects as in Example 2 were obtained.
[0056]
<Example 4>
In the present embodiment, as shown in FIG. 11, the size of the segments 21 is distributed, and the size of the segments 21 is reduced as the portion comes into contact with the central portion of the wafer 1. 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 diametric direction was reduced to increase the ratio of the grooves. Also, by increasing the proportion of the grooves, the amount of water supplied to the central portion of the wafer 1 could be increased. As a result, the polishing amount unevenness 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.
[0057]
<Example 5>
When the grindstone is divided into segments, the height of each segment supported by the relatively soft grindstone support layer varies independently. Therefore, a step is inevitably generated between the segment pressed in contact with the wafer during processing and the segment not contacting the wafer and receiving no 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, it is difficult to polish.
[0058]
The present 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. . When the outer peripheral portion of the wafer 1 is polished particularly quickly, the pressure W1 of the retainer ring 27 is increased. Conversely, when the outer peripheral portion of the wafer 1 is polished late, the pressure W1 of the retainer ring 27 can be reduced. Just fine.
<Example 6>
This embodiment is an example in which the present invention is applied to a shallow groove element isolation step in a semiconductor device manufacturing process.
[0059]
As shown in FIG. 13A, after a silicon nitride film 33 for protecting an element formation portion is formed in a region 32 where an element is to be formed, the surface of the silicon substrate 30 is subjected to a well-known photo-etching process. Grooves 31 were formed.
[0060]
Next, as shown in FIG. 13 (b), SiO 2 is formed using a well-known CVD method. ₂ The film 34 was formed on the entire surface. Further, using the method described in the first embodiment, polishing is performed to a position indicated by a broken line 35, and the SiO 2 is polished. ₂ The film 34 was left only in the groove, and the other portions were removed to form the structure shown in FIG.
[0061]
When the polishing of the insulating film 34 is performed by using the conventional CMP method, a phenomenon called dishing occurs in which the surface of the insulating film 34 in the groove becomes concave and is not flat. If dishing occurs, desired element characteristics cannot be obtained. However, according to the present embodiment, a shallow trench element isolation with a flat surface can be performed without such dishing.
[0062]
<Example 7>
In the present embodiment, the grinding wheel supported on the grinding wheel support layer of the present invention, the rotation axis of the wafer and the grinding wheel is oriented in the horizontal direction with respect to the floor surface, and the wafer and the grinding wheel move in a plane perpendicular to the floor surface. This is an example in which the present invention is applied to a polishing apparatus of a type, and will be described with reference to FIG.
[0063]
As shown in FIG. 14, the two wafers 1 are held on both surfaces of the wafer holder 14, respectively, and are arranged so as to sandwich the wafer holder 14 by a grindstone 21, and the wafer 1 is polished. Although not shown, a grindstone support layer 22 and an adhesive layer 23 are provided between the grindstone 21 and the surface plate 12, as in the first embodiment.
[0064]
The diameter of the grindstone 21 is preferably at least one time the diameter of the wafer 1. When the supply of the processing liquid (pure water) from the liquid supply unit 20 is performed from the groove on the surface of the grindstone 21, The diameter may be less than twice the diameter of the wafer 1. This embodiment has an advantage that the apparatus can be reduced in size because the rotating polishing surface is perpendicular to the floor surface.
<Example 8>
In the present 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), a polishing pad and a slurry are formed. This is an example in which a well-known polishing process is performed with the use of.
[0065]
According to this embodiment, the final surface roughness can be improved, and the amount of remaining foreign substances can be reduced. This is particularly useful for processing a relatively soft film such as a BPSG film. If the processing amount by the polishing pad and the slurry is excessive, the flatness is reduced. Therefore, the processing amount is preferably set to be approximately 0.1 μm or less in thickness.
<Example 9>
The present embodiment is an example in which polishing is performed using the above-described grindstone 21 (formed on the grindstone support layer 22 and the adhesive layer 23 as shown in FIG. 1) together with a slurry containing abrasive grains. Yes, the polishing speed can be further improved.
[0066]
In the case where fumed silica was added as a slurry on the whetstone, the relationship between the concentration of silica and the polishing speed was determined, and a comparison was made between the case using only the whetstone and the case using the fumed silica slurry and the polishing pad. The results are shown in FIG.
[0067]
As is clear from FIG. 15, since the polishing pressure was as low as 100 g / cm, and the polishing speed was low with emphasis on the roughness of the polished surface, the polishing speed when only the polishing stone was used was 5 nm / cm. Min and low.
[0068]
However, when a commonly used fumed silica slurry having a concentration of 12% is used in combination with the grinding wheel 21, the polishing speed reaches 100 nm / min, and even if the slurry is diluted to lower the concentration to 1.2%, the polishing speed is reduced. It was 40 nm / min. On the other hand, when the polishing is performed only with the slurry and the polishing pad without using the grindstone, the polishing speed 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 slurry was useful for improving the polishing speed.
[0069]
【The invention's effect】
As is clear from the above description, according to the present invention, even with a large pattern exceeding several mm, which was difficult with the conventional method using loose abrasives, good flattening and in-plane wafers were achieved. It has become possible to achieve a sufficiently uniform polishing amount. 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 a finer semiconductor integrated circuit at lower cost than before. In addition, 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 for explaining a CMP method.
FIG. 4 is a diagram for explaining occurrence of polishing unevenness;
FIG. 5 is a diagram for explaining the configuration of the present invention;
FIG. 6 is a diagram 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 is a diagram showing a ninth embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Wafer, 2 ... 4 Insulating film, 3 ... Wiring layer, 5 ... Aluminum layer, 6 ... Photoresist layer, 7 ... Stepper, 8 ... Concave, 9 ... Target level of flattening, 11 ... Polishing pad, 12 ... Constant Board, 13: Backing pad, 14: Wafer holder, 15: Working liquid, 16: Polishing tool, 20: Liquid supply unit, 21: Grindstone, 22: Grindstone support layer, 23: Adhesive layer, 24: Bonding layer, 25 ... Coupling part, 26 ... pore, 27 ... retainer ring, 30 ... silicon substrate, 31 ... groove for element isolation, 32 ... element formation region, 33 ... silicon nitride film, 34 ... SiO ₂ Film, 35 ... Dashed line indicating the position to be removed.

Claims (11)

A wafer having a desired pattern formed on its surface is held by a wafer holder, and a grindstone is provided on a polishing platen with a grindstone holding layer having a lower elastic modulus than the grindstone and the grindstone provided on the grindstone holding layer. The wafer is held through a bonding layer having a smaller elasticity and a larger elasticity than the holding layer , and the wafer and the grindstone are opposed to each other at a predetermined pressure to move at least one of the wafer and the grindstone in a plane direction. A surface flattening method, wherein the pattern is polished. In the polishing, the wafer is rotated around an axis in a direction perpendicular to the surface of the wafer as a first rotation axis. 2. The method according to claim 1, wherein the rotation is performed by rotating an axis separated by a distance as a second rotation axis, and the first rotation axis of the wafer is circularly moved on the grinding wheel. Surface flattening method. Elastic modulus of the grindstone is ^{1kg / mm 2 ~500kg / mm 2} , the elastic modulus of the grindstone holding layer according to claim 1 to 2, characterized in that a 0.1kg / mm ² ~50kg / mm ² The surface flattening method according to any one of the above. Or the grindstone is separated into a plurality of segments, or from claim 1, characterized in that a plurality of grooves formed on the grinding wheel portion other than the bottom of the groove is divided into a plurality of compartments 3 The surface flattening method according to any one of the above. The size of the segment or section in the radial direction of the grinding wheel varies along the radial direction of the grinding wheel, according to claim, wherein the segment of the grinding wheel at the central portion in the radial direction of the grinding wheel is the smallest 4 Surface flattening method according to 1. Said pressure surface planarization method as claimed in any one of 5, which is a ^{30g / cm 2 ~500g / cm 2} . A wafer holder for holding a wafer, means for rotating the wafer holder with an axis in a direction perpendicular to the surface of the well holder as a first rotation axis, and an elasticity greater than a grindstone to be held formed on the polishing platen A grinding wheel supporting layer having a low modulus, a bonding layer having a higher elastic modulus and a smaller thickness than the grinding wheel holding layer on the grinding wheel holding layer, and the grinding wheel held on the grinding wheel holding layer; Means for rotating the polishing platen with an axis parallel to the first rotation axis and separated from the first rotation axis by a predetermined distance as the second rotation axis; and the grinding wheel supported on the grinding wheel support layer. And a means for bringing the wafer held by the wafer holder into contact with each other at a predetermined pressure. Elastic modulus of the grindstone is ^{1kg / mm 2 ~500kg / mm 2} , the elastic modulus of the grindstone retaining layer according to claim 7, characterized in that the 0.1kg / mm ² ~50kg / mm ² Surface flattening device. Or the grindstone is separated into a plurality of segments, or a plurality of grooves formed on the grinding wheel according to claim 7 or 8, characterized in that the portion other than the bottom of the groove is divided into a plurality of compartments The surface flattening device according to any one of the above. The size of the segment or section in the radial direction of the grinding wheel varies along the radial direction of the grinding wheel, in claim 9, wherein the segment of the grinding wheel is the smallest at the central portion in the radial direction of the grinding wheel The surface flattening apparatus as described in the above. The flat surface according to any one of claims 7 to 11, wherein a retainer ring capable of applying pressure to the grinding wheel is provided on an outer peripheral portion of the wafer independently of the wafer holder. Device.

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