JPH04111317A - Manufacture of al wiring structure - Google Patents

Abstract

PURPOSE:To sufficiently increase a strength and to improve resistance against a stress migration, etc., by forming an Al wiring layer at a high temperature to form a solid solution state of Al alloy, and then altering the solid solution state to a strength state by treating at a low temperature. CONSTITUTION:After an element such as a transistor, etc., is formed on an Si substrate, a contact hole is opened at an interlayer insulating film. Here, an AlCu alloy film is formed by a sputtering method while heating the substrate at 450 deg.C. Since the film is formed at the high temperature of 450 deg.C, its coverage is advantageous. After the film formation is finished in a sputtering device, it is cooled in a vacuum chamber, and removed in a solid solution state as it is. Then, a strength state forming step is conducted by annealing using a lamp heating in a short time, heating it at 450 deg.C for 30sec, then cooling it, and then heat treating it at 350 deg.C in a normal annealing furnace for 30 min. Thus, half or more of Cu can be altered to precipitate of alloy phase known as theta phase (Al2Cu). Since this precipitate exhibits an action of curing the Al material, an Al wiring strong against a stress migration can be formed.

Description

[Detailed description of the invention] The present invention will be explained in the following order.

Industrial applications Summary of the invention Conventional technology The problem that the invention aims to solve Purpose of invention Means to solve problems action Example Example-1 Example-2 Example-3 Example-4 Example-5 Example-6 Effect of the invention [Industrial application field] The present invention relates to a method for manufacturing an Af wiring structure.

The present invention can be utilized, for example, in forming Al wiring structures in various electronic components (semiconductor devices, etc.).

[Summary of the invention]

A of the present invention! The method for forming the wiring structure is to form an Al wiring layer with A
1. Al is formed by alloying with other metals at a high temperature that forms a solid solution phase, for example, over 400°C, and then treated at a low temperature that forms a strength phase, for example, below 400°C. This suppresses the occurrence of defects in the wiring layer and makes it possible to obtain an Af wiring structure with high reliability.

[Conventional technology]

BACKGROUND ART Conventionally, Al wiring, particularly Al multilayer wiring, has been used in electronic components, for example, semiconductor devices such as semiconductor integrated circuits. /l is advantageous because it has a low resistivity, is easy to form and process, and can be bonded with an Au wire when taking it out.

However, the AI that makes up the A1 wiring! Since these materials have low melting points and are easily deformed, they have the problem of being susceptible to defects such as electromigration and stress migration. This is becoming an increasingly serious problem with the miniaturization of semiconductor devices and the like.

In particular, stress migration is a phenomenon in which wedge-shaped or slit-shaped chips occur in Affi wiring due to the intrinsic stress of the insulating film surrounding the Al wiring and the difference in thermal expansion coefficient between the Al wiring and the surrounding insulating film. Since migration deteriorates the reliability of Al wiring, it is desirable to prevent its occurrence as much as possible.

The cause of stress migration is that tensile stress is generated in the Al wiring due to the deformation of the insulating film formed on the upper layer of AE and contraction due to the difference in thermal expansion coefficient between the upper layer film and Affi, and the movement of AA occurs in an attempt to alleviate this stress. This is thought to be due to the occurrence of

That is, according to the inventor's study, the cause of stress migration is the difference in volume between the Al wiring and the surrounding film, and due to this difference in volume, as schematically shown in FIG. There are wedge-shaped voids a in the Al wiring layer 4,
A slit-like void b is generated. These voids (hollows caused by the disappearance of Al) deteriorate the reliability of the /l wiring.

This volume difference can be considered to occur in three modes shown in FIG. A case where a P-3iN (plasma silicon nitride) film having compressive stress is formed as the insulating film 5 on the A/2 wiring layer 4 will be described. 11th
The case shown in FIG. 3(a) is caused by upward stretching deformation of the insulating film 5 (P-3iN) on the side wall portion of the AI2 wiring layer 4. In this case, the upper part of the insulating film 5 that is in close contact with the side wall extends upward in the figure, causing stress relaxation, and A
The hatched portion of the upper surface of the l wiring layer 4 receives a force in the stretching direction due to the difference in volume, causing deformation. 1st
1(b) shows the insulating film 5 on the Aj2 wiring layer 4.
This is a case caused by the bulging deformation of (P-3iN).

Bulging is thought to occur even within the range of elastic deformation,
It is thought that both elastic and plastic deformations can occur. This bulge relieves stress, and AI! The wiring layer 4 is subjected to stress. FIG. 11(c) shows the contraction of AE due to the well-known difference in thermal expansion coefficient. Al is an insulating layer 5 such as P-SiN.
Since AE has a larger coefficient of thermal expansion than P-3iN, when it is cooled from a high temperature state, the degree of contraction of AE is greater than that of P-3iN, etc. Therefore, as shown in the figure, the Al wiring layer 4 will contract in the direction of the arrow to reduce its volume. This creates a force that causes deformation.

One method for preventing the stress migration of the Al wiring described above is to improve the method of forming the Affi upper layer insulating film, and another is to increase the strength of Af itself against deformation.

The former method of improving the method for forming the upper layer insulating film is difficult to adopt, such as when it is desired to ensure flexibility by selecting an arbitrary method for forming the upper layer insulating film. In that case, there is a need for a means that can sufficiently increase the strength of the latter Al-based material itself. Conventionally, such a method has been attempted by adding Cu to Al,
This is done by adding metals such as Ti and Pd. (For such techniques, see IEHE ``V-A IC Conf,
(Refer to "June 13-14, 1988, pp. 76-84). These metals are thought to exhibit an effect of suppressing stress migration and electromigration by precipitating at grain boundaries and reducing grain boundary diffusion.

[Problem that the invention seeks to solve]

However, in reality, the above-mentioned techniques do not necessarily exhibit a sufficient suppressive effect on stress migration.

The effects may vary depending on the manufacturing process.

This is caused by the fact that even if the additive element is in an effective precipitation state during a certain heat treatment, when heat treatment is applied again, it becomes solid solution again, changing its precipitation form.

For example, Figure 1 shows the metallographic structure of the A1-Cu alloy based on a microscopic photograph of its cross section.Cu is arranged neatly along the crystal plane in Al, and it is well-organized. It has great strength.

This is called the θ phase of the AN-Cu alloy.

(In Figure 1, the lower part of the diagram of the Affi-Cu layer is A
A TaSi layer and a Si02 layer are stacked in order from the f-Cu layer.

However, this θ phase has a Cu content of 1.5wt, for example.
%, it will be heated to over 400℃! It becomes a solid solution phase (α phase) in which Cu exists in a solid solution state, and θ
It will not return to phase. Figure 2 shows AI! -C
u phase diagram, as shown, Cu is 1.5wt
%, if the temperature is below 400°C, it is in the θ phase, but
When the temperature exceeds 400°C, it becomes α phase. The α phase, which is a solid solution phase, is modeled as AI! Since Cu is randomly dissolved in the phase, the strength is lower than that of the θ phase.
Even if metals such as Cu are added in the conventional technology, the desired effect may not be obtained depending on the subsequent processing conditions. This is a finding obtained through study by the present inventor.

Note that the deformation of Af is thought to be due to dislocation creep. It is thought that dislocation creep causes deformation, which may result in voids (hollows) or wire breakage.

That is, the movement of a dislocation (dis-1 location) in Al is a short-distance A! It is presumed that the thermal activation process is rate-limited by lattice diffusion.

[Purpose of the invention]

The present invention solves the above-mentioned problems and uses AI that has sufficiently high strength and high resistance to stress migration silane, etc.
The present invention aims to provide a method for manufacturing a wiring structure.

[Means for solving problems]

In the method for manufacturing an Al interconnect structure of the present invention, the Al interconnect layer is
It is characterized by forming an alloy of il and other metals at a high temperature to form a solid solution phase, and then processing at a low temperature to form a strength phase.

In the present invention, alloys of Af and other metals are defined as 2.
The bonding state between Al and other metals is arbitrary, and may be an intermetallic compound.

In the present invention, the solid solution phase refers to a phase in which the strength is weakened because other metals exist in Al in a solid solution state, as explained above with reference to FIG. Moreover, the strong phase refers to a phase in a state where the strength is greater than that of the solid solution phase, and Aj! -Cu alloy corresponds to the θ phase explained using FIGS. 1 and 2.

Such solid solution phase and strength phase can be known from the phase diagram of other A1 alloys. For example, the one shown in FIG. 3 is Ajl! - It is a phase diagram of a Tt binary alloy.

In addition, "under high temperature to form a solid solution phase" and "under low temperature to form a strength phase" refer to each critical temperature for forming the above-mentioned solid solution phase and strength phase, and Aj! -For a Cu alloy, it is 400"C. That is, for a 64!-Cu alloy, an Al wiring layer is formed with the alloy at a high temperature exceeding 400"C, and then it is treated at a temperature of 400°C or less. By doing so, the present invention can be implemented. According to the phase diagram in Figure 2, Cu is approximately 1.5wt% at 400'C.
However, according to the inventor's experiments, Al-Cu
Regarding the alloy, it has been found that the desired effect can be obtained practically by treating the alloy at a temperature of 400° C., regardless of the Cu content. However, it is preferable to carry out the treatment at a high temperature state or a low temperature state with the critical point determined by the phase diagram as a boundary, depending on the Cu content.

[For production]

According to the present invention, since the A1 wiring layer is formed at a high temperature where a solid solution phase is formed by the A1 alloy, in this process, other metals are uniformly dissolved in the Al throughout, and the solid solution phase is solid at that temperature. Since the solubility (the solubility of other metals in , 11) is fixed, the other metals are constantly and uniformly contained in the formed layer.

Then, by treatment at low temperature, the solid solution phase transforms into a strength phase and has sufficient strength to provide sufficient resistance to stress migration and silane. For example, in the case of an Al-Cu alloy, treatment at 400°C or lower forms a θ phase, resulting in a wiring layer with increased strength.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings. However, it goes without saying that the present invention is not limited to the following examples.

Embodiment 1 This embodiment embodies the present invention in the case of forming a multilayer Af wiring structure in manufacturing a semiconductor device such as a miniaturized and integrated SRAM. Particularly, in this embodiment, an Al alloy wiring having high stress migration resistance is obtained by optimizing the final heat treatment process. Here, Affi-Cu alloy was used as the A1 alloy.

In this example, first, AI in a solid solution state is
! Alloy (solid solution phase Af gold alloy forms a film.

That is, after forming elements such as transistors on a Si substrate, contact holes are opened in the glabella insulating film (SiOx film, SiN film, etc.). Here, an Al-Cu alloy film with a Cu content of about 2% by weight is formed by sputtering while heating the substrate to 450"C. In the conventional general method, the temperature during film formation is 150 to 200"C. ℃, but here, in order to form a solid solution phase, the temperature is set to exceed 400℃, specifically 450℃.Since the film is formed at a high temperature of 450℃, Coverage is also advantageous.The solid solubility of Cu in Al at 450°C is approximately 2% by weight, so Cu is almost in a solid solution state during film formation. After the membrane is finished, it is cooled in the next vacuum chamber and taken out in a solid solution state.

The reason for cooling in a vacuum chamber is that slow cooling tends to cause Cu to precipitate at the interface, so it is advantageous to form a uniform solid solution state by cooling.

The above is the solid solution phase forming step in this example.

Next, a strong phase forming step is performed. Specifically, in this example, the sintering step was improved to form this strong phase forming step. That is, in a normal process, a heat treatment process called a sintering process at 400 to 450°C is included in the final process of forming the Af wiring layer. This sintering process
This is done to convert SiO□, which is a natural oxide film, into Si in order to make ohmic contact with the substrate, or to stabilize vth when it has become unstable due to plasma damage during the process. . This sintering process is
Generally, the process is carried out at a high temperature exceeding 400°C, so even if a strong phase is formed before this sintering process, the strong phase (
In this example, Cu in the θ phase) re-dissolves into a solid solution phase and precipitates at the interface with the base during the cooling process, eliminating the expected effect. By improving this sintering process itself, the desired effect was obtained.

That is, in this embodiment, the sintering process itself is optimized. Here, the sinter utilizes a short anneal using lamp heating. After heating at 450°C for 30 seconds, it is cooled, and then heat treated at 350°C for 30 minutes in a normal annealing furnace. As a result, more than half of the Cu is removed from the θ phase (A
1□Cu). This precipitate is deposited almost uniformly in the film. In addition, this precipitate can exhibit the effect of hardening the Affi material by being caught when the dislocations in Af move. Therefore, the θ phase corresponds to the intensity phase. The above is the process of forming a strong phase.

As a result of forming the θ phase, which is a strong phase, in this way, an Al wiring resistant to stress migration can be formed.

Example 2 This example forms an Al wiring structure similar to Example 1, but is applied in a case where the sintering step is not necessary.

In this example, an AlCu alloy film in a solid solution state is first formed on a Si substrate in the same manner as in the solid solution phase forming step of Example-1.

Next, a heat treatment was applied at 350°C for 30 minutes, thereby performing the same process as in the strong phase forming step of Example-1.
Forms θ phase. After that, no heat treatment above 350'C is applied.

Example 3 In this example, an Al wiring layer was formed by filling a contact hole with an Af gold alloy.

In this embodiment, as shown in FIG. 4(a), a semiconductor substrate 1
A structure in which grooves 2 were formed was formed using a single-wafer type magnetron sputtering device. This device consists of two or more chambers, and a Ti layer 3 and an Affi alloy wiring layer 4 are formed in each chamber. Each chamber can apply an RF bias to the substrate during sputtering. In addition, a heater block close to the substrate is installed on the back side of the substrate, and by introducing a gas such as Ar between the substrate and the heater block, it is possible to heat the substrate with good controllability and uniformity.

The groove 2 forming the connection hole of this embodiment has a diameter of 0.5 μm or slightly smaller, and an aspect ratio of 1. That is, ffi in the figure = 0.5 μm (below), f
, = 0.5 μm (or less).

In this embodiment, first, a Ti layer 3 is formed by depositing about 500 layers of Ti in the first chamber. Next, AI! similar to Example-1 was used. , -About 8,000 people deposit a Cu alloy. At this time, the substrate is heated to about 425 to 450° C., and an RF bias of about OV (non-bias) to about 300 μ is applied. By heating at this time, a solid solution phase similar to that described in Example-1 is formed. Then 350″C13
A heat treatment is applied for about 0 minutes to form an Al wiring layer 4 made of a strong phase. The obtained structure is shown in FIG. 4(b).

A comparative example is shown in Fig. 6. When the groove (connection hole) 2 with the same opening diameter and aspect ratio is conventionally heated at 425°C and the RF bias OV (non-bias) is applied, the Affi alloy is sufficiently applied to the connection hole 2. It can be seen that the voids (spaces) 5 that were not filled in were successfully filled in in this example, as shown in FIG.

As mentioned above, in this example, while heating a contact hole with a diameter of 0.55 μm or less at 425 to 450°C (RF bias may also be applied), A/2
Since an alloy film is formed to achieve Affi filling of holes, the film can be formed at a lower temperature, and as a result, problems such as surface roughness of the /l film and Ai penetration of the barrier metal can be solved.

Further, since it is not necessary to apply a bias, or embedding can be achieved with a low bias, it is possible to avoid deterioration in film quality caused by this.

In this example, the above effects can be achieved even with an Af-3i (for example, Al containing 1% by weight) alloy, without necessarily performing high-temperature treatment and low-temperature treatment using an A i -Cu alloy. By using this, a strong Al wiring layer could be obtained.

Example-4 In this example, a groove (connection hole) having the same shape as in Example-3 was used.
Regarding No. 2, the upper portion of the trench 2 was tapered by approximately 0.1 am and was filled in. Groove (connection hole) 2
The taper portion is indicated by the reference numeral 20.

In this case, sufficient embedding and planarization were achieved by heating at 425° C. and using a bias of 0 or a linon bias. That is, the temperature can be lowered by slightly tapering the upper part.

As mentioned above, in addition to the effects of Example-3, this example has
There is also the advantage that the temperature can be lowered. In addition, Example-3
Similarly, Al-3i (for example, Af containing 1% by weight of Si) alloy can also have the above effect without necessarily performing high-temperature treatment and low-temperature treatment using Af-Cu alloy.
By using the present invention, a strong Affi wiring layer could be obtained.

Example 5 In this example, the formation of wiring layers 1 and 11 at high temperature and subsequent treatment at low temperature were performed using a multi-chamber apparatus.

In this embodiment, as shown in FIG. 7, a substrate 10 (semiconductor wafer) on which an Al wiring structure is to be formed, which is a material to be processed, is transported from a wafer case 10' and placed on a wafer holder 7 in a load lock chamber 60. It is placed and sequentially rotated to pass through the process chambers 6a to 6d. Depending on the manufacturing process, operations are performed at high and low temperatures in two appropriate chambers. That is, first, an Affi wiring layer is formed at high temperature in one of the chambers, and then in a subsequent chamber,
Processing is performed at a low temperature to form an A1 wiring layer consisting of a strength layer.

FIG. 8 shows the wafer holder 7 and the substrate 10 (wafer) placed thereon.

fart! As the conditions for forming the wiring and forming the strength layer, any of the conditions for each side described above can be adopted depending on the structure to be formed.

Example 6 In this example, when forming an Affi wiring layer by sputtering, the multi-chamber described in FIGS. 7 and 8 was used, and the Al wiring structure obtained in this way was
This is to which the present invention is applied.

Regarding the sputtered A1 film, which has conventionally been generally used as a wiring layer for VLSI, etc., recently, for example, TiN
/ A l / T i N multilayer wiring structure is used, and in order to form these films continuously and independently, single-wafer multi-chamber type sputtering equipment is mainly used. .

In this type, wafers (substrates to be processed) set in a wafer cassette are taken out one by one by vacuum chucking by an arm, transported to a load lock chamber by transport in the atmosphere, and then transported to the load lock chamber. There is a single-wafer type load rotor device in which the exposed wafer is held by a wafer holder and is evacuated for the first time. Thereafter, the wafer is conveyed in vacuum while being held in the wafer holder by rotating the entire holder as shown in FIG. 7, and is sequentially processed in each process chamber.

This device has a very simple transport mechanism,
■Highly reliable conveyance, ■Less particle generation (
There are advantages such as (no belt conveyance), (1) rapid conveyance and high throughput.

However, in this mechanism, the wafer holding operation by the wafer holder is performed in the atmosphere. In other words, the wafer holder is always exposed to the atmosphere each time it holds a wafer.
At this time, adsorption of gases in the atmosphere (including adsorption of moisture) on the surface of the wafer holder material is unavoidable, so when this wafer holder is next transported to the process chamber,
Degassing of gases that were previously adsorbed from the wafer holder surface may occur, which may affect the quality of the sputter-deposited film, especially when the film is deposited during wafer heating at a high temperature of about 450"C. The problem of decreased specular reflectance of the film is significant.

In this embodiment, the above problems are solved.

The method for forming the Aj2 wiring film in this example will be described below.

The process chamber configuration is A7! A sputter etch chamber is used before the film sputter chamber. In this example, the process chamber 6a
is used as a sputter etch chamber, and chambers 6b to 6
d was used as a sputtering chamber.

After the wafer, which is the substrate 1 to be processed, is transported from the wafer case 10' to the load rotor chamber 60 by being transported in the atmosphere (A) L in the figure C and rotated (B in the figure), first, before forming the Al film, the wafer is transferred to the etch chamber 6a. Then, sputter etching is performed on the entire surface of the wafer. Here, as the process gas, for example, Ar
A thermal oxide film of 20
Perform the amount equivalent to zero-person etching.

During this sputter etching, the Ar ions that perform etching collide not only within the wafer surface but also on a portion of the wafer holder around the wafer. That is, as shown in FIG.
Ar ions also collide with a portion of the wafer holder 7 that supports the wafer (wafer) corresponding to the periphery of the substrate 1 (particularly indicated by a diagonal line 7'). Thereby, the wafer holder 7 is easily heated. By this heating, the gas adsorbed on the surface of the wafer holder 7 in the load lock chamber is degassed.

When an Al film is subsequently formed in the Af sputtering chambers 6b to 6d, since the wafer holder has been degassed in advance in the etching chamber, the Af film can be grown almost without being affected by this degassing.

The present invention can be embodied by using the chambers 6b to 6d as appropriate in the same manner as in Example-5.

The apparatus and conveyance system in FIG. 7 are T i /T i N/T
Aj2 having an i layer and an Al layer, e.g. Af-1%Si layer
It can also be preferably used for forming wiring structures.

That is, in FIG. 9, after sputter etching, T i /T i
N/T i + A l -1%Si (~6500
This shows the reflectance of a sample in which a film was formed and a sample in which the same film was formed without sputter etching. At this time, A!
The wafer heating temperature during film formation was 450°C, and the case where an RF bias of 300 V or 450 V was applied during Af film formation with and without sputter etching is shown. The symbol IIa is bias 300V with etching, nb is 450V with etching, and m
a is 300v, no etching, mb is 450v,
No etching. On the film forming side, T i/T i N/T
i/AN-3i, and the film was formed at 450°C in 30 seconds.

As is clear from FIG. 9, the film formed after sputter etching has a higher reflectance than the film formed without sputter etching.

〔Effect of the invention〕

As described above, according to the present invention, a strong A1 wiring layer can be obtained and stress migration can be prevented.

4...Af wiring layer, α...solid solution phase (α phase), θ...
・Intensity phase (θ phase).

Claims (1)

[Claims] 1. A method for manufacturing an Al wiring structure, which comprises forming an Al wiring layer at a high temperature to form a solid solution phase with an alloy of Al and another metal, and then treating it at a low temperature to form a strength phase. .