JP2580939B2 - Method of forming embedded metal wiring - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polishing method and a method for forming a buried metal wiring using the polishing method.

[0002]

2. Description of the Related Art In recent years, due to the miniaturization of semiconductor elements constituting a semiconductor integrated circuit, the width of a metal wiring connecting them has been reduced to 0.1 mm.
It is becoming smaller than 5 μm. In the conventional formation of metal wiring, first, a sputtering method or C
A metal thin film layer is formed on the insulating film surface by the VD method, and the metal thin film is dry-etched using a resist pattern formed by photolithography as a mask. After that, the resist mask is removed.

[0003] However, the problem of the conventional metal wiring forming process has become apparent with the miniaturization of the wiring width. First, there is a problem of metal corrosion (corrosion) after dry etching. For example, when an Al film wiring is formed, dry etching is performed using a chlorine-based gas. After dry etching, chlorine adsorbed on the side wall of the Al wiring reacts with moisture in the air to generate Al. Dissolution and reprecipitation occurs. Short-circuiting occurs between the Al wirings arranged at a fine pitch via the precipitates. There is also a problem in a method for removing a resist mask. On the side surface of the resist remaining on the wiring after the etching of Al, there is a sidewall deposition film made of silicon oxide and carbon or the like in the resist, which is a part of the surface of the silicon oxide film which is a base insulating film and is sputtered off. When the resist remaining on the wiring is entirely composed of only a hydrocarbon compound, it can be removed by oxygen plasma without damaging the Al wiring. However, in order to remove the sidewall deposition film containing silicon, it is necessary to perform treatment with a plasma gas obtained by adding a chlorine-based gas (for example, CF ₄ ) to oxygen. Naturally, the plasma gas containing chlorine also etches the Al and the silicon oxide film, so that the Al wiring is disconnected and the underlying silicon oxide film thickness is reduced. These problems have been particularly apparent as the wiring width has become submicron.

Therefore, a wiring forming method that does not use dry etching of a metal film, that is, uses a polishing technique has been proposed. For example, Bayer et al.
D. Beyer, et. al. ), U.S. Pat.
No. 836, an insulating film 2 having a groove pattern 3 formed thereon.
An Al film 5 thicker than at least the groove pattern is formed by vapor deposition or sputtering (FIG. 7 (a)), the Al film formed outside the groove region is removed by polishing, and the groove 3 is filled with Al. (FIG. 7B). Here, since the Al film is formed by ordinary vapor deposition or sputtering, the surface shape of the Al film before polishing reflects the shape of the underlying insulating film, so that the groove region is depressed. Nevertheless, it is stated that Al can be left only in the groove region by polishing using an acidic aqueous solution (aqueous solution of H ₂ SO ₄ , HNO ₃ or CH ₃ COOH) to which alumina particles are added as a processing liquid. According to the patent, when a slurry in which colloidal silica particles are dispersed in an alkaline aqueous solution of KOH is used as a processing liquid, the processing speed of the insulating film is higher than that of aluminum, and the insulating film is selectively formed on the aluminum wiring. It is stated that it can be removed. That is, in order to selectively remove the Al film using the insulating film as a processing stopper, it is necessary to use an acidic aqueous solution containing solid particles.

[0005] Loerre et al., S. R. Ehl, e.
t. al. , 1992 VMIC Conf. , Pro
c. In p22), aluminum 5 is embedded by a collimator sputtering method capable of embedding a fine groove pattern,
Further, after the aluminum film surface is covered with tungsten 15 by blanket CVD (FIG. 8A), polishing is performed (FIG. 8B). The collimator sputtering method is not suitable for forming a thick Al film because the sputtering rate is extremely low (about 1/10), but the sputtered Al particles have good straightness. Therefore, Al is hardly deposited on the side wall of the groove pattern,
Fine groove filling of 0.5 μm or less has been achieved.
In this case, the aluminum film thickness inside the groove is almost equal to the aluminum film thickness outside the groove. If polishing is performed in this state, scratches and corrosion will occur on the aluminum surface inside the groove, so a tungsten protective film was formed on the aluminum. And

[0006] As described above, the known wiring forming method using polishing is characterized in that a processing liquid containing a solid component such as colloidal silica particles or alumina particles as an abrasive is used.

[0007]

By the way, in an integrated circuit, the number of wiring layers has been increased and the second or third wiring layer must be formed after the formation of the first wiring layer. For example, it is necessary to perform at least an interlayer insulating film forming step, a photolithography step, a dry etching step, and the like after burying polishing for forming an Al wiring. For this reason, solid particles and the like must not be present on the surface after the metal embedding polishing. For example, colloidal silica particles and the like can be removed by washing using a mixed solution of ammonia water and hydrogen peroxide solution, but aluminum cannot be used for washing after metal embedding polishing because aluminum is dissolved in this mixed solution. In particular, solid particles having a particle size of 0.1 μm or less added to a processing liquid for conventional polishing have a strong adsorption power and are not easy to remove.

The method of forming a tungsten cover film by the CVD method in order to avoid damage such as scratches on the surface of the buried metal wiring at the time of polishing cannot avoid an increase in manufacturing cost due to an increase in the number of metal film forming steps.

It is an object of the present invention to provide a method for forming a metal wiring using a buried polishing method, and to provide a method for facilitating cleaning after polishing and avoiding a reduction in the thickness of the obtained buried metal wiring layer.

[0010]

SUMMARY OF THE INVENTION According to the present invention, there is provided a semiconductor device having a groove.
A flat surface formed to fill the trench on the insulating film
Among the flat metal thin films, the metal thin film other than the groove region is solid
Free of particles and free of alkali metal ions
Polishing solution consisting of an alkaline aqueous solution and an oxidizing aqueous solution
Selective polishing using a semiconductor integrated circuit
This is a method for forming an embedded metal wiring .

[0011]

【Example】

Embodiment 1 First, the polishing characteristics of an aluminum film using an oxidizing agent aqueous solution and an alkaline aqueous solution, in which the present invention is implemented, will be described.

Here, an embodiment in which a hydrogen peroxide solution is used as an oxidizing agent aqueous solution and a piperazine aqueous solution which is an amine is used as an alkaline aqueous solution will be described. FIG. 9 shows a schematic diagram of the experimental apparatus. 1 μm A on silicon oxide film
The silicon substrate 16 on which the l film is formed is held on a rotating vacuum chuck 17 made of high-purity fused silica, and is pressed against a polishing cloth (polishing pad) 19 stretched on a rotary polishing platen 18 to form a first substrate. Amine solution 2 from the dropping tube 20
20 ml / m of 0.5 wt% aqueous solution of piperazine as 1
The solution was polished for 10 minutes while dropping 0 to 1.2 wt% hydrogen peroxide solution as an oxidizing agent aqueous solution 23 from the second dropping tube 22 at a rate of 10 ml / min. The processing pressure was 0.28 kg / cm ² . When the amount of processing was determined from the change in the sheet resistance of aluminum, the processing speed of aluminum was as low as about 50 angstroms (hereinafter referred to as A) / min when no hydrogen peroxide solution was used. It was confirmed that it increased with the addition. For example, when 0.6 wt% of a hydrogen peroxide solution was added, the processing speed of aluminum increased to 250 A / min.
In addition, aluminum was not processed only by the hydrogen peroxide solution.

[0013] The effects of the dropping concentration of piperazine and the polishing pressure on the processing speed of aluminum were investigated with the amount of hydrogen peroxide added constant (Fig. 1). Here, a piperazine aqueous solution of 0 to 2.0 wt% is dropped at 20 ml / min from the first drop tube 20, and the concentration of the hydrogen peroxide solution is 0.6 wt% from the second drop tube 22.
It was kept constant and dropped at 10 ml / min. FIG. 1 also shows the wet etching rate of aluminum for comparison. It can be seen that the processing speed of aluminum increases with the concentration of piperazine and the processing pressure. It was confirmed that the processing speed of aluminum was higher than the wet etching speed under any of the processing conditions.
FIG. 2 shows the effect of the processing pressure on the ratio (Vp / Ve) of the polishing rate (Vp) to the etching rate (Ve) of aluminum. As the processing pressure increases, (V
It can be seen that p / Ve) has increased.

From the experimental results described above, it can be seen that the polishing of aluminum using piperazine and an aqueous solution of hydrogen peroxide proceeds by a combined action of the etching action (chemical action) by the aqueous solution and the mechanical action by the polishing pad. It is suggested. That is, first, a hydroxide or oxide is formed on the aluminum surface by the action of the oxidizing agent aqueous solution,
It is presumed that the polishing of the aluminum proceeds because the surface film is mechanically removed by contact with the pad.

As shown in FIG. 3, when an oxidizing agent aqueous solution and an amine aqueous solution are used, the polishing speed of the silicon oxide film is extremely slow, and the processing speed ratio of the aluminum: silicon oxide film is 100: 1 or more. FIG. 4 shows a process of forming an aluminum film having a thickness of 1 μm on a silicon oxide film having a contact hole (0.7 μm in diameter) by reflow sputtering while embedding the contact hole, and forming an aqueous solution of an oxidizing agent and an aqueous solution of an amine. And cross-section SE of aluminum plug obtained by polishing with liquid
An M photograph is shown. The reflow sputtering method is a method of forming a film while filling a contact hole with semi-molten aluminum at a substrate temperature of 400 to 450 ° C.
It can be seen that aluminum plugs having no scratches on the surface were obtained by the polishing of aluminum according to the present invention.
No solid particles are found on the surface of the oxide film. The method of forming the aluminum plug shown here is based on the first base.
It is also used for connecting vertical wiring plugs between the Cu wiring of the upper layer and the Cu wiring of the upper second layer.

In this embodiment, the aqueous solution of piperazine belonging to the amines is used as the alkaline aqueous solution.
If H is 10 or more, amines other than piperazine may be used. Also, an aqueous ammonia solution can be used. However, hydroxides of alkali metals such as KO
For H and NaOH, the oxide film after polishing is an alkali metal
It is not preferable because it is contaminated with ions. It was used hydrogen peroxide solution in the present embodiment as an oxidizing agent solution, K ₃ Fe
Cyanides such as (CN) ₆ can also be used.

In the metal polishing method according to the present invention, if the metal surface is oxidized or hydroxylated by the oxidizing agent in the alkaline aqueous solution, the metal processing proceeds.
Therefore, it is obvious that wiring materials such as Al, Al-Cu alloy, copper, titanium and tungsten can be processed. Also, TiN polishing that dissolves in an alkaline aqueous solution is possible. Further, in this embodiment, the oxidizing agent aqueous solution and the alkaline aqueous solution are added by separate dropping tubes, but it is obvious that the same result can be obtained by dropping a working liquid in which both are mixed in advance.

As described above, in the polishing using the oxidizing agent aqueous solution and the alkaline aqueous solution containing the solid component according to the present invention, the metal can be embedded in the silicon oxide film layer without causing any mechanical damage to the surface. It has been demonstrated that substrate surface contamination by solid components is avoided.

The process of the Example 2 invention, particularly aluminum is a low-resistance metal ^- is applied (2.6 x 10 ⁶ [Omega] cm) wiring formed. Here, first, a silicon oxide film 2 is formed on a silicon substrate 1 on which a transistor (not shown) and the like are formed. A groove 3 is formed in the silicon oxide film 2 by photolithography and dry etching, and Ti / Ti is formed as a barrier metal layer 4 by a collimator sputtering method.
TiN or Ti / TiN / Ti is formed on the entire surface of the silicon oxide film 2 including the groove region 3. Further, if necessary, a silicon layer (not shown) of 0.005 to 0.05 μm is formed by a CVD method, and then the substrate temperature is set to 400 to 45 μm.
A semi-molten aluminum 5 is formed to fill the groove 3 by a reflow sputtering method at 0 ° C.

The silicon substrate 1 on which the aluminum film 5 is formed is polished while dropping a processing liquid composed of a hydrogen peroxide solution and an aqueous amine solution. When this processing liquid is used, the aluminum 5 and the barrier metal 4 can be removed using the silicon oxide film 2 as a polishing stopper. That is, when the polishing is completed when the aluminum and the barrier metal 4 on the surface 7 of the silicon oxide film are completely removed, an embedded wiring 6 of aluminum whose side and bottom surfaces are covered with the barrier metal 4 is obtained. Since the processing liquid used here does not contain particles such as colloidal silica and alumina, there is no contamination due to adsorption of solid particles on the processed surface after polishing. In addition, no scratches are generated due to the contact between the aluminum surface and the solid particles.

(Embodiment 3) FIG. 6 shows an embodiment in which filling of a contact hole and filling of a trench wiring according to the present invention are performed simultaneously. First, a silicon oxide film (not shown) is formed on the p ⁻ substrate 1 where the n ⁺ region separated by the element isolation oxide film 8 exists, and then a BPSG film 9 is formed. After forming the silicon oxide film 2 again, the mask aluminum layer 10 is grown (FIG. 6A). A trench 3 for embedding a wiring layer is formed in the silicon oxide film 2 by photolithography and dry etching (FIG. 6B). Here, at the time of dry etching of the silicon oxide film 2, the phosphorus component in the etching gas may be monitored to terminate the etching when the base BPSG layer 9 appears. Thereafter, a contact hole pattern 12 having a diameter larger than the width of the groove 3 is formed in the resist 11.
It is important that the base BPSG film 9 is formed using a fluorine-based gas.
Is to etch. Since the aluminum is not etched by the fluorine-based gas, a contact hole 13 having the same diameter as the groove wiring is formed even though the resist pattern is larger than the groove 3 (FIG. 6C). Ti / TiN
After the / Ti barrier metal 4 is formed by the sputtering method, aluminum 5 is buried in the groove wiring forming region and the contact hole forming region at the same time by the reflow sputtering method (FIG. 6D). Thereafter, the reflow sputtered aluminum 5, barrier metal 4 and mask aluminum 10 on the silicon oxide film 2 are removed by polishing using an oxidizing agent aqueous solution and an alkaline aqueous solution (FIG. 6E). Through this series of steps, embedded wiring 14 having a contact portion with the n ⁺ silicon region is formed.

[0022] Here, shown for embedded wirings formed including connections with n ⁺ -type silicon region, it is obvious that Ru used for buried wiring forming including the connection with the p ⁺ -type silicon region. Also the above-mentioned n ⁺ -type silicon region considered first aluminum wiring formation region, it is replaced by contact holes and via holes, readily be Ru used for the second layer buried aluminum wiring formed including the connection between the first aluminum wiring layer It is obvious.

In this embodiment, aluminum is used as a mask for forming a groove in oxide film 2 (FIG. 6).
(B), it is only necessary to have selectivity with the silicon oxide film, and for example, a polysilicon film may be used. Further, here, a multilayer film composed of the interlayer insulating film BPSG film 9 and the silicon oxide film 2 is used. However, when the end point detection is not required for dry etching when forming the groove 3, the silicon oxide film 2 is a single layer. It is obvious that you can do it.

[0024]

As described above, in the method of manufacturing a semiconductor device according to the present invention, a metal thin film formed on an oxide film having a groove is formed by using an oxidizing agent aqueous solution and an alkaline aqueous solution without containing a solid component. To obtain wiring with a structure in which metal is buried in the trench. Since no solid particles are contained in the working fluid, damage such as scratches does not occur on the metal surface during polishing. Therefore, a step of forming a high-hardness cap film such as tungsten on the surface of the buried metal wiring layer is not required. Further, the substrate is not contaminated with the solid particles after the polishing. Therefore, the substrate cleaning step after the polishing can be simplified.

As described above, by using the manufacturing method according to the present invention, it is possible to easily obtain a buried metal wiring structure by polishing which is advantageous for forming an extremely fine metal wiring at low cost.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between piperazine concentration and processing pressure on the processing speed of aluminum in polishing according to the present invention.

FIG. 2 shows the ratio (V) between the polishing rate of aluminum and the wet etching rate in polishing according to the present invention.
It is a figure which shows the influence of the working pressure on p / Ve).

FIG. 3 is a diagram showing a comparison of processing speeds of aluminum and a silicon oxide film in polishing according to the present invention.

FIG. 4 is a surface and cross-sectional electron micrograph showing a fine pattern formed on a substrate after polishing of aluminum according to the present invention.

FIG. 5 is a sectional process view illustrating a buried wiring forming step according to the present invention.

FIG. 6 is a cross-sectional process diagram illustrating a process of simultaneously forming a buried contact and a buried wiring according to the present invention.

FIG. 7 is a sectional process view for explaining the formation of a buried wiring by a conventional polishing method.

FIG. 8 is a sectional process view for explaining the formation of a buried wiring by a conventional polishing method.

FIG. 9 FIG. 2 is a diagram showing a polishing apparatus used in the present invention.
You.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Silicon substrate 2 Silicon oxide film 3 Groove area 4 Barrier metal 5 Aluminum 6 Embedded aluminum wiring 7 Silicon oxide film surface 8 Element isolation oxide film 9 Boron phosphorus glass 10 Mask aluminum 11 Resist 12 Resist contact hole pattern 13 Boron phosphorus glass layer Formed contact hole 14 Embedded aluminum wiring having contact hole 15 Tungsten film by blanket CVD 16 Aluminum film formed 6 inch silicon substrate 17 Quartz vacuum chuck 18 Polishing platen 19 Polishing pad 20 First drip tube 21 Alkaline aqueous solution 22 Second dripping tube 23 Oxidizing agent aqueous solution

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-62-85445 (JP, A) JP-A-3-13125 (JP, A) JP-A-2-275629 (JP, A) JP-A-4- 259221 (JP, A) JP-A-1-87157 (JP, A) JP-A-3-121186 (JP, A) JP-A-4-101418 (JP, A) JP-A-4-45530 (JP, A) JP-A-63-180465 (JP, A) JP-A-63-180467 (JP, A) JP-A-63-267159 (JP, A) JP-A-1-20966 (JP, A) JP-A-63-84872 (JP, A) JP-A-4-179225 (JP, A) JP-A-4-63427 (JP, A) JP-A-4-123432 (JP, A) JP-A-54-157079 (JP, A) JP-A-4-144113 (JP, A) JP-A-5-226203 (JP, A) PROC. VMIC, 1992, p. 22-28 (1992 ISMIC-101 / 92/0022) IEDM, 92-305 to 308

Claims (6)

(57) [Claims] 1. A groove is buried on an insulating film having the groove.
Among flat metal thin film formed surface in the, the metal thin film other than the trench regions free of solid particles and alkali
Alkaline aqueous solution and oxidizing agent that do not contain metal ions
A method for forming a buried metal wiring of a semiconductor integrated circuit, characterized by selectively polishing using a polishing liquid comprising an aqueous solution . (2) Each of the alkaline aqueous solution and the oxidizing agent aqueous solution
Alkaline aqueous solution and oxidizing agent
Claims: A polishing liquid by mixing with an aqueous solution.
2. The method for forming a metal wiring according to 1. (3) The metal thin film is formed by a reflow sputtering method.
That it was grown by filling the groove
3. The formation of the metal wiring according to claim 1 or 2,
Method. (4) Reflow sputtering on insulating film with grooves
Forming a metal film so as to fill the groove by a method
And selectively polishing and removing the metal thin film other than the groove region
Forming a metal wiring. (5) Reflow by setting the substrate temperature to 400 to 450 ° C
Claims characterized by performing a sputtering method
3. The method for forming a metal wiring according to any one of items 3 and 4. 6. As the groove, a groove for wiring and a hole for hole
Grooves are formed, and both grooves are buried at once
And selectively polishing the metal thin film outside both groove portions
Holes at the same time as wiring
The metal distribution according to any one of claims 1 to 5,
The method of forming the line.