METHOD FOR MANUFACTURING SEMICONDUCTOR DEVICE

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2012-146030, filed on Jun. 28, 2012; the entire contents of which are incorporated herein by reference.

FIELD

Embodiments are generally related to a method for manufacturing a semiconductor device.

BACKGROUND

A Chemical Mechanical Polishing (CMP) method is used for planarization of a wafer surface in processes such as multilayer interconnection and device isolation in a procedure for manufacturing a semiconductor device. For example, a silicon oxide film and tungsten (W), copper (Cu), and aluminum (Al) films formed on the wafer surface are polished to form interconnects and contact plugs. Along with progress of miniaturization of a semiconductor device, there is a demand for improvement in planarity, reduction in surface defects, and improvement in productivity. Especially, since surface defects such as corrosion and a metal residue have a large influence on manufacturing yield, there is a strong demand for reduction in the surface defects.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view schematically illustrating a polishing apparatus according to an embodiment;

FIGS. 2A to 2D are schematic cross-sectional views illustrating a manufacturing procedure of interconnects according to the embodiment;

FIGS. 3A and 3B are cross-sectional views schematically illustrating a polishing procedure of interconnects according to the embodiment;

FIGS. 4A and 4B are cross-sectional views schematically illustrating another polishing procedure of interconnects according to the embodiment;

FIGS. 5A to 5C are photos showing surfaces of interconnect layers after polishing;

FIG. 6 is a graph showing a polishing characteristic; and

FIG. 7 is a graph showing another polishing characteristic.

DETAILED DESCRIPTION

According to an embodiment, a method for manufacturing a semiconductor device includes polishing a metal layer provided on a surface of a wafer, while supplying slurry to a polishing pad and spraying gas to the polishing pad. The slurry includes an inorganic particle, a resin particle, an oxidant for oxidizing the metal layer, a complexing agent for forming an organic complex on a surface of the metal layer, and a surfactant for forming a hydrophilic film on a surface of the organic complex. The resin particle includes a functional group on a surface, the functional group having a same kind of polarity as that of the inorganic particle. The resin particle contains polystyrene incorporated at a concentration of 0.001% by weight or more and 0.1% by weight or less, and has an average particle diameter of 200 nm or more and 1 μm or less.

Hereinafter, embodiments will be described with reference to the drawings. It is to be noted that identical components in the drawings are shown with the same reference numerals, description of the duplicate components is omitted, and different components are described.

The embodiments relate to a method for manufacturing a semiconductor device and more specifically relate to a method for polishing a silicon insulating film or a metal interconnect layer in an interconnection process for a memory, a system LSI (Large Scale Integrated Circuit), a high-speed logic LSI, a merged memory/logic LSI, or the like.

FIG. 1 is a perspective view schematically showing a polishing apparatus 10 according to an embodiment. The polishing apparatus 10 includes a polishing stage 3, a wafer holder 15, a slurry nozzle 23, and a gas nozzle 27. To an upper surface of the polishing stage 3 is attached a polishing pad 7. On a face of the wafer holder 15 facing the polishing pad 7 is fixed a wafer. The polishing stage 3 is rotated in parallel with a polishing face 7a, and the wafer holder 15 abuts on a surface of the polishing pad 7, to polish a metal layer formed on a surface of a wafer 20.

The surface of the polishing pad 7 is supplied with slurry 25 via the slurry nozzle 23. A polishing procedure according to the embodiment is performed using CMP, and the slurry 25 includes an inorganic particle, a resin particle, an oxidant, a complexing agent, and a surfactant.

Examples of the inorganic particle to be used contain at least one selected from the group consisting of colloidal silica, fumed silica, colloidal alumina, fumed alumina, colloidal titania, and fumed titania. The inorganic particle favorably has a primary particle diameter ranging from 10 to 50 nm and a secondary particle diameter ranging from 10 to 100 nm. In a case where the particle diameters are out of these ranges, surface defects such as corrosion and a scratch may be generated. The corrosion in this context refers to a surface defect caused by progress of a local chemical reaction on a surface of the metal layer, for example, and is revealed as corrosion or a dent such as dishing.

The particle diameter of the inorganic particle can be measured directly by a TEM (Transmission Electron Microscope) or an SEM (Scanning Electron Microscope), for example.

The resin particle is made of a resin containing polystyrene and has on a surface a functional group of a same kind of polarity as that of the inorganic particle. By adding polystyrene, the resin particle is formed to have appropriate hardness. The resin particle also has on the surface at least either a carboxylic group or a sulfonyl group, for example. This prevents aggregation of the inorganic particle and the resin particle.

The resin particle is also incorporated at a concentration of 0.001% by weight or more and 0.1% by weight or less and has an average particle diameter of 200 nm or more and 1 μm or less. The average particle diameter of the resin particle can be derived by measuring a surface area of the particle by a BET method, causing this value to be subjected to spherical reduction to obtain a particle diameter, and calculating an average of the particle diameters, for example. Alternatively, a particle diameter may be measured by the TEM or the SEM to calculate the average particle diameter.

The oxidant oxidizes a surface of the metal layer, and the complexing agent forms an organic complex combined with metal oxide on the surface of the metal layer. The organic complex protects the surface of the metal layer and restricts a chemical reaction of the metal layer. The surfactant forms a hydrophilic film on a surface of the hydrophobic organic complex. Polishing progresses as the inorganic particle and the hydrophilic resin particle scrape away the organic complex formed on the surface of the metal layer. That is, in the procedure of the CMP, polishing progresses as the organic complex is formed to protect the surface of the metal layer while the organic complex is scraped away. This restricts generation of corrosion to enable the metal layer to be polished uniformly.

In a case where the metal layer is copper (Cu), ammonium persulfate or a hydrogen peroxide solution can be used for the oxidant, for example. To accelerate oxidation on the surface of the Cu layer, a concentration of the oxidant is favorably at least 0.1% by weight or more. On the other hand, in a case where the content of the oxidant is excessive, the solubility of the organic complex formed on the surface of the Cu layer increases, and corrosion may be generated excessively. Thus, the upper limit of the concentration is favorably 5% by weight or less.

Examples of the complexing agent to be used can be at least one selected from the group consisting of quinaldinic acid (quinoline carboxylic acid), quinolinic acid (pyridine-2, 3-dicarboxylic acid), benzotriazole (BTA), nicotinic acid (pyridine-3-dicarboxylic acid), picolinic acid, malonic acid, oxalic acid, succinic acid, maleic acid, citric acid, glycine, alanine, and aqueous ammonia.

A concentration of the complexing agent is favorably approximately 0.01 to 1% by weight. In a case where the concentration is less than 0.01% by weight, the organic complex is not formed sufficiently. On the other hand, in a case where the concentration is more than 1% by weight, the organic complex becomes thick, and polishing speed is lowered.

Examples of the surfactant include ammonium dodecylbenzene sulfonate, potassium dodecylbenzene sulfonate, polyvinyl pyrrolidone, polyvinyl alcohol, ammonium polyacrylate, hydroxy cellulose, acetylene diol-based nonion, and polyoxyethylene alkylene ether. To form a hydrophilic film on the surface of the organic complex, a concentration of the surfactant is desirably at least 0.01% by weight or more. Further, to avoid solution of the organic complex, the upper limit of the concentration is favorably 0.5% by weight.

The polishing apparatus 10 also includes the gas nozzle 27, and the metal layer is polished while gas 33 is sprayed to the polishing face 7a of the polishing pad 7. Examples of the gas 33 are compressed air and nitrogen.

A temperature of the polishing face 7a rises by frictional heat or reaction heat generated between the wafer 20 and the polishing face 7a, for example. It may facilitate a chemical reaction on the surface of the metal layer, causing corrosion to be generated easily. Hence, the temperature is lowered in the embodiment by spraying the gas 33 to the polishing pad 7 in order to restrict the generation of corrosion.

Next, a method for manufacturing a semiconductor device according to the embodiment will be described with reference to FIGS. 2A to 2D. FIGS. 2A to 2D are schematic cross-sectional views showing a procedure for forming interconnects on a surface of the wafer 20.

As shown in FIG. 2A, an insulating layer 43 is formed on a silicon substrate 13 which include transistors and the like (not shown) formed thereon, for example. The insulating layer 43 is a silicon oxide film, for example. Interconnect grooves 41 are formed in the insulating layer 43. The interconnect grooves 41 include a contact hole 42 communicating with a contact area 17 formed in the silicon substrate 13.

Subsequently, as shown in FIG. 2B, a barrier metal (BM) layer 45 is formed, which is a first metal layer covering an upper surface of the insulating layer 43 and inner surfaces of the interconnect grooves 41. For the BM layer 45, titanium (Ti), tantalum (Ta), or nitride of one of these is used, for example. The BM layer 45 contacts the contact area 17 on the bottom surface of the contact hole 42.

Subsequently, a second metal layer 47 (hereinafter, a metal layer 47) is formed on the BM layer 45. The metal layer 47 is an electrolytic plating layer of copper (Cu), for example, fills insides of the interconnect grooves 41, and covers a surface of the BM layer 45.

Subsequently, as shown in FIG. 2C, the metal layer 47 formed on the BM layer 45 is removed using a CMP method (main polishing). The metal layer 47 remains in the insides of the interconnect grooves 41. At this time, gas is sprayed to the polishing pad 7 to cool the polishing pad 7.

Subsequently, as shown in FIG. 2D, the BM layer 45 formed on an upper surface of the insulating layer 43 is removed using the CMP method (touch-up polishing). Thus, the BM layer 45 and the metal layer 47 on the upper surface of the insulating layer 43 are removed to form interconnects 49 each containing the metal layer 47 and the BM layer 45 in the inside of the interconnect groove 41.

Next, a polishing method according to the embodiment will be described with reference to FIGS. 3A to 3B and FIGS. 4A to 4B. FIGS. 3A to 3B and FIGS. 4A to 4B are partial cross-sectional views schematically illustrating interconnect layers 40 to 60 provided on a surface of the wafer 20. Meanwhile, in each of FIGS. 3A to 4B, the wafer illustrated in FIGS. 2A to 2D is shown upside down for the purpose of showing a polishing procedure.

FIG. 3A shows a polishing procedure of removing the metal layer 47 formed on an upper surface of the interlayer insulating film 43 and leaving the metal layer 47 in the interconnect grooves 41 formed in the interlayer insulating film 43.

As shown in FIG. 3A, in a final phase of the polishing procedure, there is a case in which an organic complex 51 remaining thinly on a polishing face of the interconnect layer 40 cannot be scraped away completely by an inorganic particle 53 having a small particle diameter and remains as a metal residuum. Since the organic complex 51 remaining on the interconnect layer is conductive, the organic complex 51 short-circuits adjacent interconnects. Thus, a resin particle 57 having a large particle diameter is added to the slurry 25 to scrape away the organic complex 51, which cannot be removed by the inorganic particle 53. Thereby, the amount of metal residues remaining on the surface of the interconnect layer 40 is reduced.

FIG. 3B shows a polishing procedure in the interconnect layer 50. The interlayer insulating film 43 has interconnect grooves 41a and 41b having different widths. As shown in FIG. 3B, in a case where the slurry 25 to which the resin particle 57 having a large particle diameter has been added is used, the wider interconnect groove 41a is polished more deeply than the narrower interconnect groove 41b. Thus, a step d_sof a metal face 63 of the interconnect groove 41a is larger than a step of a metal face 65 of the interconnect groove 41b.

In this manner, adding the resin particle 57 enable polishing to follow a structure of a foundation. For example, the interconnect layer has unevenness reflecting a device structure of a lower layer. When the metal layer 47 formed on the surface of the interconnect layer is to be removed, the metal layer 47 is desirably polished along a shape of the unevenness.

The interconnect layer 60 shown in FIG. 4A has on a surface a recess 71. The metal layer 47 formed on the recess 71 is similar to the metal layer 47 filled in a wide interconnect groove, and the polishing amount is larger than that on a polishing face 75 of a narrow interconnect groove 41c. Thus, for example, polishing on a metal face 73 in the recess 71 progresses more, and the metal layer 47 can be removed along the recess 71 of the interconnect layer 60 as shown in FIG. 4B. As a result, the amount of residues of the metal layer 47 remaining on the surface of the recess 71 can be reduced, and short between interconnects can be prevented.

In this manner, by adding a resin particle having a large particle diameter to the slurry, followability of the polishing amount to a foundation can be improved.

Next, an example will be described with reference to FIGS. 5A to 5C, FIG. 6, and FIG. 7. In the example, a foamable pad manufactured by Nitta Haas (IC1000) was used as a polishing pad.

Components of slurry are as follows:

inorganic particle: colloidal silica (0.4% by weight, average particle diameter: 30 nm),

resin particle: polystyrene particle (0.1% by weight, average particle diameter: 200 nm, the resin particle has on a surface a carboxylic group and a sulfonyl group),

oxidant: ammonium persulfate (1.5% by weight),

complexing agent: quinaldinic acid (0.1% by weight), BTA (0.0001% by weight), alanine (0.4% by weight), ammonium dodecylbenzene sulfonate (0.02% by weight), aqueous ammonia (0.2% by weight),

surfactant: acetylene diol ethylene oxide adduct (HLB value: 18, 0.1% by weight),

pH adjuster: a moderate amount of potassium hydroxide (pH9), and

rest: water.

As Comparative Example 1, an example of using slurry to which the resin particle among the above components is not added is shown. Further, as Comparative Example 2, an example of not spraying gas to the polishing pad is shown.

FIGS. 5A to 5C are photos showing surfaces of interconnect layers after polishing. FIG. 5A shows the surface after polishing with the slurry not including the resin particle according to Comparative Example 1. FIG. 5B shows the surface after polishing according to Comparative Example 2, in which air is not sprayed to the polishing pad. FIG. 5C shows the surface after polishing according to the example.

On the surface in Comparative Example 1 shown in FIG. 5A, multiple white metal residues are seen on a surface of the metal layer 47 and on a surface of the interlayer insulating film 43 surrounding the metal layer 47. These are the organic complexes 51, which show polishing is insufficient. That is, the organic complexes are not removed completely since the slurry in Comparative Example 1 does not include a resin particle.

Conversely, as shown in FIGS. 5B and 5C, no organic complexes 51 remain on the surfaces after polishing in the example and Comparative Example 2. Further, since no differences are seen between the surfaces shown in FIGS. 5B and 5C, whether or not gas is sprayed results in no differences in polishing force in a case of using the slurry to which the resin particle is added.

FIG. 6 is a graph showing planarity of the metal layer 47 relative to a line width (width). Graph A shows a characteristic in the example, and Graphs B and C show characteristics in Comparative Examples 1 and 2, respectively. Line density is 50%.

Graph C shows a height of a step increases when a line width exceeds 10 μm. On the other hand, in Graph A, a height of a step increases when a line width exceeds 30 μm. This difference is caused by whether or not air is sprayed to the polishing pad and shows that polishing force is lowered by cooling the surface of the polishing pad. Further, in Graph B, a height of a step increases when a line width exceeds 50 μm.

When Graph C is compared with Graph B, Graph C remarkably shows an increase in the height of the step resulting from addition of the resin particle to the slurry. That is, in Comparative Example 2, followability to a foundation shape is drastically improved by the effect of the resin particle. On the other hand, in the example, it can be said that followability to a foundation shape is greater than that in Comparative Example 1 although it is inferior to that in Comparative Example 2.

In addition, experiments were carried out by changing a kind of the resin particle. Table 1 shows results of Experiments 1 to 4 using PMMA (polymethyl methacrylate resin) and PST (polystyrene resin) as the resin particle. ◯-mark in the table shows “no Cu residue,” “no Cu corrosion,” and “good foundation followability.” Here, “no Cu residue” and “no Cu corrosion” include states in which generation of Cu film residues and Cu corrosion is in a practically problem-free level although Cu film residues and Cu corrosion are generated. ×-mark shows “Cu residue generated,” “Cu corrosion generated,” and “poor foundation followability.”

As shown in Table 1, foundation followability is good in any of the resin particles. However, in a result of Experiment 1 using PMMA, Cu residues and Cu corrosion are generated. In a case of Experiment 2 using PST, good results are obtained in terms of Cu residues, but Cu corrosion is generated. On the other hand, as shown in a result of Experiment 3, even using PST generates Cu residues in a case where the PST has a functional group of a different kind of polarity as that of the inorganic particle. Further, as shown in Experiment 4, generation of Cu residues is improved when PST is added to PMMA.

In this manner, it is found that using a resin particle having a functional group of a same kind of polarity as that of the inorganic particle and containing PST can improve foundation followability and reduce the amount of Cu residues.

TABLE 1

Resin
Functional
Cu
Cu
Foundation

Experiment
particle
group
residue
corrosion
followability

1
PMMA
Same
X
X
◯

polarity

2
PST
Same
◯
X
◯

polarity

3

Different
X
X
◯

polarity

4
PMMA-
Same
◯
X
◯

PST
polarity

Next, experiments were carried out by changing a particle diameter and a mixing concentration of PST. The diameter of the resin particle was set to 150 nm, 200 nm, and 500 nm, and the mixing concentration in respective cases was changed in a range of 0.0001% by weight (wt %) to 0.1% by weight.

Table 2 shows results of the experiments. Here, ∘ and × show equal evaluations to those in Table 1, and Δ show that preferable results of certain degree are seen but are still insufficient.

TABLE 2

Particle

Experi-
diameter
Concentration
Cu
Cu
Foundation

ment
(nm)
(wt %)
residue
corrosion
followability

5
150
0.0001
X
◯
X

6

0.001
X
Δ
X

7

0.01
Δ
X
Δ

8

0.1
Δ
X
Δ

9
200
0.0001
X
Δ
X

10

0.001
◯
Δ
◯

11

0.01
◯
X
◯

12

0.1
◯
X
◯

13
500
0.0001
X
Δ
X

14

0.001
◯
Δ
◯

15

0.01
◯
X
◯

16

0.1
◯
X
◯

As shown in Table 2, in cases of using PST having a particle diameter of 150 nm (Experiments 5 and 6), generation of Cu residues and foundation followability are improved as the concentration of the resin particle is raised but do not reach sufficient levels. On the other hand, Cu corrosion is generated more significantly as the concentration of the resin particle is raised. In cases of using PST having particle diameters of 200 nm and 500 nm (Experiments 9 to 16), results of no Cu residues and good foundation followability are obtained at a concentration of 0.001% by weight or more. On the other hand, there is still a tendency toward more significant generation of Cu corrosion along with rising of the concentration.

It is apparent from these results that using the resin particle containing PST having a particle diameter of 200 nm or more and having a mixing concentration of 0.001% by weight or more can achieve a state of no Cu residues and good foundation followability. On the other hand, Cu corrosion is generated more significantly as the concentration of the resin particle is raised.

FIG. 7 is a graph for comparison of corrosion count generated on the metal layer 47 after polishing. When a corrosion count in Comparative Example 1 and a corrosion count in Comparative Example 2 shown in FIG. 7 are compared, it is found that corrosion is generated more significantly in the polishing method according to Comparative Example 2, in which the resin particle is added. The reason for this may be that, since polishing force is improved by the slurry including the resin particle, the extent of exposure of a copper surface not covered with the organic complex is great, and a chemical reaction is accelerated.

On the other hand, in the example, regardless of use of the slurry including the resin particle, a corrosion count is less than that of Comparative Example 2 and is in an equal level to that of Comparative Example 1. The reason for this may be that spraying air for cooling the polishing pad restricts a chemical reaction on the surface of the metal layer 47, suppressing the generation of corrosion.

Table 3 shows results in cases of spraying air to the polishing pad (500 L of compressed air/minute) under equal conditions to those in Experiments 10 to 12 and 14 to 16, in which a concentration of the resin particle is 0.001% by weight or more.

TABLE 3

Particle

Experi-
diameter
Concentration
Cu
Cu
Foundation

ment
(nm)
(wt %)
residue
corrosion
followability

10
200
0.001
Δ
◯
Δ

11

0.01
◯
◯
◯

12

0.1
◯
◯
◯

14
500
0.001
Δ
◯
Δ

15

0.01
◯
◯
◯

16

0.1
◯
◯
◯

In the results in which the mixing concentration is 0.001% by weight (Experiments 10 and 14), Cu residues remain, and foundation followability is slightly worse. However, in cases of higher concentrations, good results are obtained in terms of Cu residue and foundation followability. Generation of Cu corrosion is restricted in any of the concentrations of 0.001% by weight or more.

According to the above results, using the slurry to which the resin particle is added can improve polishing force and reduce metal residues (organic complexes) remaining on the surface of the interconnect layer. The above results also show followability to a foundation shape can be improved. However, improvement in polishing force by addition of the resin particle causes a disadvantage of easy generation of corrosion. The cooling method of spraying gas to the polishing pad is effective to alleviate this conflicting relation. In other words, by adding the resin particle to the slurry and performing polishing while spraying gas to the polishing pad, a polishing method in which the amount of metal residues is reduced (clearness of metal residues), foundation followability is improved, and generation of corrosion is restricted can be achieved.

Further, to improve clearness of metal residues and foundation followability, a resin particle having an average particle diameter of 200 nm or more is desirably added to the slurry. Further, the average particle diameter of the resin particle is desirably 1 μm or less. When the average particle diameter exceeds 1 μm, sedimentation occurs, which makes it difficult to disperse the resin particles in the slurry uniformly.

Furthermore, a concentration of the resin particle is desirably 0.001% by weight or more and 0.1% by weight or less. When the concentration of the resin particle is below 0.001% by weight, clearness of metal residues and foundation followability are degraded. On the other hand, when the concentration exceeds 0.1% by weight, polishing force is excessive, and corrosion is generated significantly.

As described above, the embodiment achieves a polishing method in which generation of corrosion on the surface of the metal layer is restricted, and clearness of metal residues and foundation followability are improved. In a procedure of manufacturing a semiconductor device with use of this polishing method, generation of short-circuit between interconnects is suppressed, and manufacturing yield can be improved.

Although the above example has been described taking CMP of a Cu layer using slurry to which a resin particle is added as an example, the embodiment is not limited to this. For example, the embodiment can be applied to a procedure for forming aluminum interconnect. Further, a method for cooling a polishing pad is not limited to spraying gas, but it may be possible to supply cooled slurry, for example.

While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the invention.

METHOD FOR MANUFACTURING SEMICONDUCTOR DEVICE

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