JP3291889B2 - Dry etching method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a dry etching method applied in the field of manufacturing a semiconductor device, in particular for example an etch-back process of the refractory metal layer, relates to a dry etching process for forming electrodes and wiring, etc. .

[0002]

2. Description of the Related Art As the degree of integration and performance of semiconductor devices such as LSIs increase, the proportion of the area occupied by wiring portions on a semiconductor chip tends to increase. In order to avoid an increase in the semiconductor chip area due to this, an interlayer connection using a multilayer wiring and a contact electrode is an essential process. Conventionally, as an electrode / wiring forming method, A
It has been widely practiced to form 1 and Al alloys by sputtering. However, as described above, in a situation where the wiring is multi-layered, and as a result, the surface step of the semiconductor substrate and the aspect ratio of the connection hole are becoming remarkable, the conventional method using sputtering has a step coverage. Insufficient connection or disconnection due to lack has become a serious problem.

In recent years, various selective CVD methods have been proposed in which a high-melting point metal layer such as W, Mo, Ta, or the like, or a metal such as Al, an Al alloy, or Cu is selectively grown and embedded in a connection hole. In the selective CVD, a source gas such as a metal halide, a metal carbonyl, an organometallic compound, or the like is reduced by a lower wiring material exposed at the bottom of the connection hole to selectively deposit a constituent metal in the connection hole. . However, in the case of the selective CVD, the selectivity gradually deteriorates as the number of batches increases, and tends to deposit on an undesired portion such as on an interlayer insulating film. In addition, there is an unsolved problem such as poor controllability of etch-back removal of an overgrown portion on a connection hole called a nail head, and at present it has not yet reached a practical level.

[0004] In view of the above situation, an electrode / electrode by blanket CVD is being reviewed instead of selective CVD.
This is a wiring forming method. Blanket CVD is so named because it deposits without selectivity over the entire surface of the underlying substrate, regardless of the chemical nature of the underlying substrate. As an example, by covering the entire surface of the interlayer insulating film in which the connection hole is opened,
A typical example is a process of forming a high-melting-point metal layer such as W so as to fill this connection hole. In addition, blanket CV
General commentary articles on buried contact hole of W by D have been published, for example, monthly published by Semiconductor World magazine (press journal published by) in the November 1990 issue 220 pages.

[0005]

By the way, in order to bury a high melting point metal layer in a connection hole by blanket CVD and flatten it, and use it as a so-called contact plug, an unnecessary high melting point metal deposited not only in the connection hole is used. Of course, etchback of the metal layer is required. In this etch-back process, over-etching of, for example, about several tens of percent is usually performed from the viewpoint of processing uniformity within the wafer surface. However, due to variations in the thickness of the blanket CVD film and unevenness in the plasma density of the etching apparatus, there are portions where the underlying interlayer insulating film and barrier metal are exposed relatively early in the etch-back process. In the exposed portion, the concentration of the etching species is relatively increased as compared with other portions as a result of the decrease of the reaction partner, that is, the exposed surface of the high melting point metal layer. For this reason, the etching rate locally increases in the exposed portion, and the phenomenon that the surface of the refractory metal layer or the barrier metal, which is once embedded in the continuous hole and flattened, is greatly eroded is often observed. The phenomenon in which the pattern density of the object to be etched varies on the same substrate to be etched, resulting in variations in the etching rate, is generally called a microloading effect.

[0006] This problem is solved by referring to FIGS. 5 (a) to 5 (c).
The explanation is added with reference to. The figure shows a conventional blanket C
It is a figure explaining a problem in an etch back process of a refractory metal layer by VD. First, as shown in FIG. 5A, a Si substrate having a connection hole 6 facing the impurity diffusion layer 2 is formed on a semiconductor substrate 1 such as Si having the impurity diffusion layer 2 formed thereon.
An interlayer insulating film 3 made of O ₂ or the like is formed. Ti and TiN are sequentially sputtered to cover the entire surface of the substrate to form an adhesion layer / barrier metal layer 4, and a high melting point metal layer 5 made of W is formed thereon by blanket CVD. The surface of the refractory metal layer 5 is generally formed as a fine uneven surface. This is because a high melting point metal layer such as W formed by blanket CVD grows as an aggregate of fine columnar crystals. Next, the process proceeds to an etch-back process. In a thin portion of the high melting point metal layer 5 or a region where the etching rate is high, the underlying adhesion layer / barrier metal layer 4 is exposed early. At this time, if etch-back is performed using a fluorine-based gas such as SF ₆ , a large amount of microscopic fluorine radicals (F ^* ) becomes excessive near the exposed surface. This excess F ^* is concentrated on the flat surface of the refractory metal layer 5 buried in the connection hole 6 and generates a large eroded portion 7 during over-etching as shown in FIG. .

When the etching conditions are further switched and the adhesion layer / barrier metal layer 4 is etched back with a Cl-based gas, Cl ^* is exposed at a portion where the interlayer insulating film 3 is exposed earlier ^.
Loses their opponent, so there is excess in this part. Excess Cl ^* concentrates on a slightly exposed surface of the adhesion metal layer / barrier metal layer 4 formed on the side wall of the connection hole and attacks it. As a result, a deep erosion 8 of the adhesion layer and the barrier metal layer is formed as shown in FIG. Also,
There is also a problem that the surface morphology of the refractory metal layer by blanket CVD is transferred to the surface of the interlayer insulating film 3 as it is, and irregularities are formed on the surface of the interlayer insulating film 3.

The non-uniformity of the etch-back shape and the deterioration of the contact plug shape due to the micro-loading effect described above are one factor preventing the practical use of a multilayer wiring process using a high melting point metal layer by blanket CVD. That is, if there is an abnormally eroded portion in the contact plug, the electrical connection with the upper layer wiring becomes imperfect, resulting in a problem such as an increase in resistance value, a decrease in ohmic properties, and the occurrence of electromigration. In addition, since the flatness and smoothness of the upper wiring formed on the contact plug are deteriorated, the deterioration of the shape due to irregular reflection at the time of lithography of the upper wiring is also a problem. In the future, the diameter of the substrate to be etched will increase, and the single-wafer type etching apparatus will be the mainstream. For this reason, high-speed etching using high-density plasma is required so as not to cause a decrease in throughput, but considering the situation where there is still room for improvement in the uniformity of the plasma density of the single-wafer etching apparatus, There is an urgent need to develop a method for etching back a refractory metal layer that is not affected by the microloading effect.

It is an object of the present invention to provide a dry etching method capable of performing uniform processing without abnormal erosion due to a microloading effect over the entire surface of a substrate to be etched in etching back a refractory metal layer. Further, by this, a high-melting-point metal contact plug buried with good flatness is formed over the entire surface of the substrate to be etched, and a highly reliable multilayer wiring structure is realized.

Another object of the present invention is to provide a dry etching method which performs the above dry etching while maintaining a practical etching rate, and which is excellent in throughput.

Other objects of the present invention will become apparent from the description of the present specification and the accompanying drawings.

[0012]

SUMMARY OF THE INVENTION The dry etching method of the present invention has been proposed in order to solve the above-mentioned problem, and the etching back of the refractory metal layer formed on the entire surface of the base material layer is performed by two times. It is divided into stages and immediately before the underlying material layer is exposed by etching conditions mainly based on radical reactions.
In a first etch-back process of etching a refractory metal layer, the etching conditions mainly the sputtering by ions etch the remaining portion of the refractory metal layer
Te is intended to facilities <br/> a second etch-back process to expose the underlying material layer.

In the two-stage etch-back method, a substrate stage on which a substrate to be etched is mounted is disposed in a high plasma density region, and a substrate bias of a first frequency is applied to the substrate stage to perform etching and etching. First
And a second etch-back step of disposing the substrate stage outside the high plasma region and applying a second substrate bias having a frequency lower than the first frequency to the substrate stage to perform etching. .

Further, the dry etching apparatus of the present invention
A dry etching apparatus includes means for relatively changing the distance between a high plasma density region and a substrate stage, and means for switching a substrate bias frequency applied to the substrate stage.

As means for relatively varying the distance between the high plasma density region and the substrate stage, it is sufficient to move either the substrate stage or the high plasma density region. The switching means for switching the substrate bias frequency applied to the substrate stage includes a plurality of high-frequency power supplies capable of generating different frequencies and a switch for selecting one of the plurality of high-frequency power supplies.
Alternatively, even a single high frequency power supply may be configured to generate high frequencies of a plurality of frequencies under the control of an internal circuit.

As is apparent from the above description, the dry etching apparatus of the present invention is preferably an apparatus which can separately control the plasma generating means and the substrate bias applying means. Such an apparatus includes a substrate bias application type ECR (Electron Cyclotron Res).
once) plasma etching equipment, ICP (In
ductile Coupled Plasma)
Etching equipment, TCP (Transformer)
Coupled Plasma etching system, helicon wave plasma (Helicon Wave Plas)
ma) An etching apparatus and the like can be exemplified. These plasma etching apparatuses are 1 × 10 ¹¹ / cm ³ or more and 1 × 10 ¹⁴ / cm ³ or more.
/ Cm ^{3 or} less,
There is an advantage that high-speed etching can be performed. Technical description of each high-density plasma etching apparatus described above, is omitted because it is described in detail in the individual technical reports, etc., are listed in the month published by Semiconductor World magazine October 1992 issue on page 59 for a review .

[0017]

The first point of the present invention is that the entirety of the underlying material layer
The etching conditions are changed between a first etch-back step in which the base of the refractory metal layer formed on the surface is exposed just before the underlayer is exposed and a second etch-back step in which the remaining part of the refractory metal layer is etched. The point is to switch. The first etch-back step is a so-called bulk etching step in which etching is performed at a high etching rate under etching conditions mainly based on a radical reaction.

Generally, in a plasma etching apparatus of a substrate bias application type, when a high frequency bias is applied to a substrate stage, when the frequency is low, both ions and electrons in the plasma move following the reversal of the electric field. Can be. However, as the frequency increases, it becomes impossible to sequentially follow ions having a large mass-to-charge ratio. When the frequency is further increased, even small-mass electrons cannot follow, and both ions and electrons only oscillate in the plasma. This vibration start point is usually in the HF band (3 to 30).
MHz).

Therefore, when the substrate bias frequency applied to the substrate stage is high, the electrons oscillate in the plasma and generate many radicals and ions due to frequent collisions with etching gas molecules. However, since ions cannot follow the reversal of the electric field, etching in ion mode hardly occurs. For this reason, a condition in which the etching in the radical mode relatively easily proceeds is achieved. As is well known, radical-based etching is highly isotropic and has a high etching rate. In the first etch-back step, a high-speed etching is performed by disposing a substrate stage in the high plasma density region.

On the other hand, in the second etch-back step, the bias frequency applied to the substrate stage is set low, so that the ions can sufficiently follow the reversal of the electric field, so that the ion-mode etching can easily proceed. At the same time, the substrate stage is moved away from the high plasma density region to avoid the influence of radicals, and ions are accelerated by an electric field to collide with the substrate to be etched. Since the ion mode etching does not cause a phenomenon such as local excess of radicals, the microloading effect is effectively prevented.
In the ion mode etching, the anisotropy is strong and the etching rate is generally small. However, in the second etch-back step, the remaining portion of the refractory metal layer has a small thickness, so that the risk of reducing the throughput of the entire process is minimized.

A second point of the present invention is a structure of a dry etching apparatus suitable for performing the above-mentioned two-stage etchback. That is, it is possible to arbitrarily switch between the plasma mode and the ion mode etching by switching the substrate bias frequency and changing the distance between the plasma region and the substrate stage. 1 × 10 ¹¹
/ Cm ³ or more 1 × 10 ¹⁴ / cm can generate a high density plasma of about less than ^3, moreover by using an etching apparatus capable of controlling the substrate bias independently to achieve faster etching, achieve improved throughput You do it.

By the way, a parallel plate plasma etching apparatus that is generally used than conventionally, 1 × 10 ⁹ / cm ³ units as plasma density, a magnetron RIE apparatus 1 even in the × 10 ¹⁰ to use a magnetic field / It has a plasma density on the order of cm ³ , and has some difficulties in terms of plasma density and etching rate. However, if a substrate bias is separately applied, or a means for switching an applied RF frequency, a means for switching between an anode couple and a cathode couple, a means for switching a distance between electrodes, and the like are added, it can be used in accordance with the spirit of the present invention. .

On the other hand, the upper limit of the plasma density is closely related to the etching gas pressure, and is 1 which is the main operating pressure of the high-density plasma etching apparatus used in the present invention.
At a gas pressure of the order of 0 ^-1 Pa, 1 × 10 ¹⁴ / cm ³
Is almost a value close to complete dissociation.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of the present invention will be described.

Embodiment 1 In this embodiment, an etch-back of a W layer formed by blanket CVD is performed by an ECR plasma etching apparatus of a substrate bias application type.

First, a schematic configuration example of a substrate bias application type ECR plasma etching apparatus used in this embodiment will be described with reference to FIGS. 2 (a) and 2 (b).
In the same device, it is generated by the magnetron 10.
A microwave of 45 GHz was introduced into the plasma generation chamber 13 via the microwave waveguide 11 and the microwave introduction window 12 made of quartz or the like, and was excited by a solenoid 14 disposed around the plasma generation chamber. An ECR plasma of an etching gas is generated in the plasma generation chamber 13 by interaction with a magnetic field of 0875T. The substrate to be etched 15 is placed on a substrate stage 16. 17 is a plasma processing chamber. The details of the etching gas introduction hole, the vacuum exhaust system and other details are omitted.

In addition to the basic structure described above, in the present etching apparatus, the support member 20 of the substrate stage 16 can be moved in the direction A by driving means (not shown). That is, in FIG. 2A, the substrate stage is raised to make the substrate to be etched face a high plasma density region in the plasma generation chamber 13. In FIG. 2B, the substrate stage 16 is lowered to be disposed in the plasma processing chamber 17 and is separated from the high plasma density region in the plasma generation chamber 13. At the same time,
The plasma extraction window 21 provided at the boundary between the plasma generation chamber 13 and the plasma processing chamber 17 is moved in the direction B to narrow the aperture and control the profile of the plasma flow 22 by the divergent magnetic field. The plasma extraction window 21 also forms a microwave reflection surface, and the plasma generation chamber 13 also functions as a microwave resonator. Such a plasma extraction window 21 can achieve a smooth operation by applying, for example, an aperture blade system of an optical lens system.
Note that the plasma opening window 21 with variable opening degree may be omitted if it is not necessary to control the profile of the plasma flow 22.

Further, the present etching apparatus has a first RF power supply 24 of 13.56 MHz as a power supply for applying a substrate bias, and a second RF power supply 25 of 800 kHz having a lower frequency than the power supply. An arbitrary frequency can be selected. Substrate stage 16 described above
Up / down operation, control of the opening degree of the plasma extraction window 21,
The switching means 23 and the substrate bias switching means 23 operate in conjunction with each other to select and use an arbitrary combination.

Next, the description will proceed to the dry etching method of the present invention. As described above, this embodiment is an example in which the etch back of the W layer formed by blanket CVD is performed by two-step etching. This process is illustrated in FIG.
This will be described with reference to FIG. In the figure, the same parts as those described in FIG. 5 are denoted by the same reference numerals, and the duplicate description thereof will be omitted.

First, as shown in FIG. 1A, for example, an interlayer insulating film 3 such as SiO ₂ is formed on a semiconductor substrate 1 such as Si on which an impurity diffusion layer 2 is formed in advance, and the impurity diffusion layer 3 is formed. 2 are opened. The thickness of the interlayer insulating film 3 is, for example, 0.7 μm, and the opening diameter of the connection hole 6 is 0.35 μm. Next, Ti and TiN are sputtered on the entire surface in this order, and an adhesion layer / barrier metal layer 4 is conformally deposited. The thickness of the adhesion layer / barrier metal layer 4 is, for example, 70 nm in total. Further, connection holes 6
And a high melting point metal layer 5 made of W is formed by blanket CVD so as to form a substantially flat surface by embedding the adhesive layer and also covering the adhesion layer / barrier metal layer 4 on the interlayer insulating film 3. This blanket CVD was performed under the following conditions as an example. _{First, WF 6 25 sccm SiH 4 10} sccm Gas pressure 1.1 × 10 ⁴ Pa 20 seconds at a substrate temperature of 475 ° C., after nucleation of _{W, WF 6 60 sccm H 2} 360 sccm gas pressure 1. The deposition is performed under the condition of 1 × 10 ⁴ Pa substrate temperature of 475 ° C. The thickness of the refractory metal layer 5 on the adhesion layer / barrier metal layer 4 is, for example, 0.3 μm.
m. Immediately above the connection hole, a seam that is a joint of the growth surfaces is formed. The sample formed so far is
The substrate to be etched is used.

Next, an etch-back step, which is a part of the present invention, is started. The substrate to be etched 15 is set on the substrate stage 16 of the substrate bias applying type ECR plasma etching apparatus described above, and is raised to a position where the opening of the plasma extraction window 21 is closed as shown in FIG. I do. The plasma extraction window 21 is retracted in the direction B and has a large aperture. A 13.56 MHz first RF power supply 24 is connected to the substrate stage 16 by the switching means 23.

In this state, as an example, the first etching back of the high melting point metal layer 5 is performed under the following conditions, and the operation is stopped immediately before the adhesion layer / barrier metal layer 4 on the interlayer insulating film 3 is exposed. The end point of the first etch-back was determined based on the elapsed etching time by previously etching the same sample under the same etching conditions and measuring the etching rate. SF ₆ 40 sccm O ₂ 10 sccm Gas pressure 1.3 Pa Microwave power 850 W (2.45 GHz) RF bias power 150 W (13.56 MH)
z) Temperature of substrate to be etched Room temperature In this etching process, a radical reaction by F ^* generated in a large amount in the plasma by dissociation of SF ₆ is accelerated by assisting ions such as O ⁺ , SF _x ^{+ and the} like. Etching proceeds. As a result, as shown in FIG. 1B, most of the high melting point metal layer 5 is etched back, and a thin remaining portion of the high melting point metal layer is formed on the adhesion layer / barrier metal layer 4 on the interlayer insulating film 3. 5a remains.

Next, the substrate stage 16 is lowered in the direction A as shown in FIG. 2 (b), and is disposed in the sample chamber 17, the plasma extracting window 21 is squeezed to reduce the opening diameter, and the switching means 23 is Switch to the 800 kHz second RF power supply. In this state, as an example, the second
Is applied to remove the remaining portion 5a of the refractory metal layer. SF ₆ 30 sccm O ₂ 20 sccm Gas pressure 1.3 Pa Microwave power 850 W (2.45 GHz) RF bias power 200 W ( 800 kHz ) Substrate temperature to be etched Room temperature In this etching process, it is applied to the substrate stage 16. Since the substrate bias frequency is reduced, ions such as O ⁺ and SF _x ^{+ having} a large mass can sufficiently follow the reversal of the electric field. The substrate RF bias power and O ₂
By setting the flow rate to be larger than that in the first etch-back process, the radicality of the reaction system is suppressed, and instead, ion mode etching is mainly performed. Therefore, Ti /
Immediately after the surface of the adhesion layer / barrier metal layer 4 made of TiN was exposed, F ^* did not become excessive in the exposed portion, and abnormal erosion based on the microloading effect was prevented. As a result, as shown in FIG. 1C, the inside of the connection hole 6 was buried flat with the high melting point metal layer 5.

Next, the adhesion layer / barrier metal layer 4 on the interlayer insulating film 3 is etched back under the following conditions as needed. Cl ₂ 40 sccm O ₂ 10 sccm Gas pressure 1.3 Pa Microwave power 850 W (2.45 GHz) RF bias power 200 W (13.56 MH)
z) Temperature of substrate to be etched Room temperature Etching of adhesion layer / barrier metal layer 4 proceeds while maintaining selectivity with refractory metal layer 5 and interlayer insulating film 3, and as a result, connection as shown in FIG. The inside of the hole 6 was buried flat by the high melting point metal layer 5 and the adhesion layer / barrier metal layer 4, and no erosion was observed.

In this embodiment, most of the refractory metal layer 5 is etched by the first etch-back with a high etching rate using a high-density plasma of the order of 10 ¹¹ / cm ³ . Since the second etch-back is performed under the condition where there is no abnormal erosion due to the microloading effect, a high-quality contact plug having a high throughput and a flat buried surface can be formed. The fact that two-stage etching can be performed only by switching the etching conditions in the same etching apparatus also contributes to an improvement in throughput.

Embodiment 2 In this embodiment, the etch back of a W layer also formed by blanket CVD is performed by ICP with a variable substrate bias frequency.
This is an example in which etching is performed by an etching apparatus.

The schematic structure of the etching apparatus used in this embodiment will be described with reference to FIG. In FIG. 3, parts performing the same functions as those in FIG. 2 are denoted by the same reference numerals, and a description thereof will be partially omitted. The power of an ICP power supply 33 is supplied into the plasma generation chamber 13 by an inductive coupling coil 32 wrapped around a side wall 31 of the plasma generation chamber made of a dielectric material such as quartz, and high-density plasma is generated there. 17 is a plasma processing chamber, and 34 is an upper ground electrode. Illustration of details such as an etching gas introduction hole and a vacuum exhaust system is omitted. The feature of this apparatus is that the large-sized multi-turn inductive coupling coil 32 enables high-power plasma excitation and enables etching with high-density plasma of the order of 10 ¹² / cm ³ .

In addition to the basic structure described above, the etching apparatus of the present invention can be moved in the direction B by a driving mechanism (not shown) and can be moved in the direction A by a driving mechanism (not shown). Substrate stages 16, 13.56 directly connected to a certain substrate stage support member 20
MHz first substrate bias power supply 24 and 800 kHz
And a switching unit 23 for selectively switching the second substrate bias power supply 25 to supply the second substrate bias power supply 25 to the substrate stage 16.
The operation of each member and the like are substantially the same as those described in the ECR plasma etching apparatus of the first embodiment.

Next, the description will proceed to the dry etching method of this embodiment. The substrate to be etched used in the present embodiment is the same as that in Embodiment 1, and will be described with reference to FIG.
A duplicate description will be omitted. The substrate to be etched 15 shown in FIG. 1A is placed on a substrate stage 16 of a substrate bias applying type ICP etching apparatus, and the substrate stage support member 20 is raised to close the opening of the plasma extraction window 21 with the substrate stage 16. Then, the substrate to be etched 15 is disposed so as to face the high plasma density region of the plasma generation chamber 13. In addition, the first RF power supply 24 of 13.56 MHz is applied to the substrate stage 16 by operating the switching unit 23.

In this state, as an example, the first etching back of the high melting point metal layer 5 is performed under the following conditions, and the operation is stopped immediately before the adhesion layer / barrier metal layer 4 on the interlayer insulating film 3 is exposed. The end point of the first etch-back was determined based on the elapsed etching time by previously etching the same sample under the same etching conditions and measuring the etching rate. SF ₆ 40 sccm Cl ₂ 10 sccm Gas pressure 1.3 Pa ICP power 900 W (2 MHz) RF bias power 150 W (13.56 MH)
z) Temperature of substrate to be etched Room temperature In this etching process, radical reaction by F ^* generated in a large amount in plasma by dissociation of SF ₆
High-speed etching proceeds in a form assisted by ions such as Cl ⁺ and SF _x ⁺ . As a result, as shown in FIG. 1B, most of the high melting point metal layer 5 is etched back, and a thin remaining portion of the high melting point metal layer is formed on the adhesion layer / barrier metal layer 4 on the interlayer insulating film 3. 5a remains.

Next, the substrate stage 16 is lowered along the direction A shown in FIG. 3, is disposed in the sample chamber 17, narrows the plasma extracting window 21 to narrow the opening diameter, and further, the switching means 23 is operated at 800 kHz. 2 is switched to the RF power supply 25. In this state, for example, a second etch-back is performed under the following conditions to remove the remaining portion 5a of the refractory metal layer. SF ₆ 25 sccm Cl ₂ 25 sccm Gas pressure 1.3 Pa ICP power 900 W (2 MHz) RF bias power 200 W (800 kHz) Substrate temperature to be etched Room temperature In this etching process, the substrate bias frequency applied to the substrate stage 16 is Since the frequency is lowered, ions such as Cl ⁺ and SF _x ^{+ having} a large mass can sufficiently follow the reversal of the electric field. The substrate RF bias power and C
By setting the l ₂ flow rate to be larger than that in the first etch-back process, the radicality of the reaction system is suppressed, and instead, ion mode etching is mainly performed. Therefore, T
Immediately after the surface of the adhesion layer / barrier metal layer 4 made of i / TiN was exposed, F ^* did not become excessive in the exposed portion, and abnormal etching caused by the microloading effect was prevented. As a result, as shown in FIG. 1C, the inside of the connection hole 6 was buried flat with the refractory metal layer 5.

Thereafter, the adhesion layer / barrier metal layer 4 on the interlayer insulating film 3 is removed by etching back as necessary under the following conditions. Cl ₂ 40 sccm O ₂ 10 sccm Gas pressure 1.3 Pa ICP power 900 W (2 MHz) RF bias power 200 W (13.56 MH)
z) Temperature of substrate to be etched Room temperature Etching of adhesion layer / barrier metal layer 4 proceeds while maintaining selectivity with refractory metal layer 5 and interlayer insulating film 3, and as a result, connection as shown in FIG. The inside of the hole 6 was buried flat by the high melting point metal layer 5 and the adhesion layer / barrier metal layer 4, and no erosion was observed.

In this embodiment, a large multi-turn inductive coupling coil 3
2 enables high-speed etching with high-density plasma on the order of 10 ¹² / cm ³ , and achieves a high-throughput etch-back process.

Embodiment 3 In this embodiment, W is similarly formed by blanket CVD.
TCP with variable substrate bias frequency for etch back of layer
This is an example in which a plasma etching apparatus is used.

A schematic configuration of a TCP plasma etching apparatus used in this embodiment will be described with reference to FIG. The TCP plasma etching apparatus shown in FIG. 4 is also the EC shown in FIG.
Portions having the same functions as those of the R plasma etching apparatus are denoted by the same reference numerals, and the description thereof will be partially omitted. The spiral coil 36 arranged on the top plate 35 of the plasma generation chamber made of a dielectric material such as quartz makes the TC
The power of the P power supply 37 is introduced into the plasma processing chamber 13,
Here, high-density plasma is generated. In FIG. 4, details such as an etching gas introduction system and a vacuum exhaust system are not shown. The feature of this device is that the inductive coupling between the large spiral coil 36 and the etching gas in the plasma processing chamber 13 enables
The point is that high-density plasma on the order of 10 ¹² / cm ³ can be generated. In addition to the above basic configuration, the configuration of the drive mechanism for the substrate stage 16 and the plasma extraction window 21, the configuration of the substrate bias switching means 23, and the like are the same as those of the ICP etching apparatus described with reference to FIG.

Next, the description will proceed to the dry etching method of this embodiment. The substrate to be etched used in the present embodiment is the same as that used in the first embodiment, and will be described again with reference to FIG. 1, and redundant description will be omitted. The substrate to be etched shown in FIG. 1A is set on the substrate stage 16 of the substrate bias applying type TCP etching apparatus, and the substrate stage supporting member 20 is raised to a position where the substrate stage 16 closes the opening of the plasma extraction window 21. The etching substrate 15 is disposed so as to face the high plasma density region of the plasma generation chamber 13. In addition, the first RF power supply 24 of 13.56 MHz is applied to the substrate stage 16 by operating the switching unit 23.

In this state, as an example, the first etch-back of the refractory metal layer 5 is performed under the following conditions, and the process is stopped immediately before the adhesion layer / barrier metal layer 4 on the interlayer insulating film 3 is exposed. The end point of the first etch-back was determined based on the elapsed etching time by previously etching the same sample under the same etching conditions and measuring the etching rate. SF ₆ 30 sccm S ₂ Cl ₂ 20 sccm Gas pressure 1.3 Pa TCP power 900 W (13.56 MH)
z) RF bias power 150 W (13.56 MH)
z) Temperature of substrate to be etched Room temperature In this etching process, radical reaction by F ^* generated in a large amount in plasma by dissociation of SF ₆
High-speed etching proceeds in a form assisted by ions such as Cl ⁺ and SF _x ⁺ . At the same time, S ^* generated by dissociation from S ₂ Cl ₂ becomes free sulfur and is deposited on the high-melting-point metal layer 5 made of W, which causes a competitive reaction between etching and deposition. Sulfur is left in fine concave portions on the surface of the refractory metal layer where the incidence of ions is small, so that the convex portions of the refractory metal layer 5 are preferentially etched, so that a smooth etch-back surface can be obtained. . As a result, as shown in FIG. 1B, most of the refractory metal layer 5 is etched back, and the refractory metal layer having a smooth surface is formed on the adhesion layer / barrier metal layer 4 on the interlayer insulating film 3. A thin residue 5a of the layer remains.

Next, the substrate stage 16 is lowered along the direction A shown in FIG. 4, and is disposed in the sample chamber 17, the plasma extraction window 21 is squeezed to narrow the opening diameter, and the switching means 23 is operated at 800 kHz. 2 is switched to the RF power supply 25. In this state, for example, a second etch-back is performed under the following conditions to remove the remaining portion 5a of the refractory metal layer. SF ₆ 25 sccm S ₂ Cl ₂ 30 sccm Gas pressure 1.3 Pa ICP power 900 W (13.56 MH)
z) RF bias power 200 W (800 kHz) Substrate temperature to be etched Room temperature In this etching process, since the substrate bias frequency applied to the substrate stage 16 is reduced, ions such as Cl ⁺ and SF _x ^{+ having} a large mass are used. Can sufficiently follow the reversal of the electric field. Also, the substrate RF bias power and S
By setting the flow rate of ₂ Cl ₂ to be higher than that in the first etch-back step, the radicality of the reaction system is suppressed, and instead, ion mode etching is mainly performed. Therefore, immediately after the surface of the adhesion layer / barrier metal layer 4 made of Ti / TiN was exposed, F ^* did not become excessive in the exposed portion, and abnormal erosion based on the microloading effect was prevented. As a result, as shown in FIG. 1C, the inside of the connection hole 6 was buried flat with the refractory metal layer 5.

Thereafter, the adhesion layer / barrier metal layer 4 on the interlayer insulating film 3 is removed by etching back, if necessary, under the following conditions. Cl ₂ 40 sccm O ₂ 10 sccm Gas pressure 1.3 Pa TCP power 900 W (13.56 MH)
z) RF bias power 200 W (13.56 MH)
z) Temperature of substrate to be etched Room temperature Etching of adhesion layer / barrier metal layer 4 proceeds while maintaining selectivity with refractory metal layer 5 and interlayer insulating film 3, and as a result, connection as shown in FIG. The inside of the hole 6 was buried flat by the high melting point metal layer 5 and the adhesion layer / barrier metal layer 4, and no erosion was observed.

In the present embodiment, in addition to the prevention of the microloading effect, high-speed etching with high-density plasma on the order of 10 ¹² / cm ³ is possible by plasma excitation with a large spiral coil, and high throughput is achieved. An etchback process can be achieved. In addition, a smooth etch-back surface is obtained by performing the etch-back while simultaneously using the deposition of sulfur, and the surface morphology of the refractory metal layer 5 is transferred to the adhesion / cum-barrier metal layer 4 and the interlayer insulating film 3. Never.

By the way, as shown in this embodiment, the deposition of sulfur
In order to take advantage of the competitive reaction due to
Sulfur-based compound gas capable of releasing free sulfur into zuma
Is effective. Such gases include S_Two
F_Two, SF_Two, SF_Four, S_TwoF_TenSF-based gas such as S_Two
Cl_Two, S_ThreeCl_Two, SCl_TwoSCl-based gas such as S _Two
Br_Two, S_ThreeBr_Two, SBr_TwoSBr-based gas such as
H_TwoS and the like can be exemplified. Sulfur is generally affected
When the etching substrate is below room temperature,
It can be removed by sublimation at about 90 ° C or more.
There is no risk of contamination. In addition, these sulfur-based compound gases
And N_TwoIf N-based gas is added, polythiazyl
(SN)_nEtch back is possible with the deposition of
Becomes The substrate to be etched is polythiazyl below room temperature
Deposits in the case of temperature, can be sublimated and removed at about 150 ° C or more,
Also in this case, there is no substrate contamination.

Although the present invention has been described with reference to the three embodiments, the present invention is not limited to these embodiments.

For example, the process of forming a contact plug by embedding a refractory metal layer in a connection hole has been described in the embodiments, but the embedding process in a via hole formed in an interlayer insulating film on a lower wiring is described. May be applied. Further, the present invention can be applied not only to connection plugs but also to formation of various electrodes and wirings using blanket CVD.

Although W is exemplified as the refractory metal layer 5, M
Other high melting point metals such as o and Ta may be used. Although the adhesion layer / barrier metal layer 4 is exemplified by Ti / TiN,
ON, TiW, TiSi _x, etc., may be appropriately selected various materials depending on the material of the base and the refractory metal layer.

As the etching apparatus, a substrate bias application type ECR plasma etching apparatus, an ICP etching apparatus and a TCP etching apparatus have been exemplified, but a helicon wave plasma etching apparatus can also be used. Since the present apparatus can perform an etching process at a plasma density of the order of 10 ¹³ / cm ³ , a higher etching rate can be obtained. Of course, the two-stage etching of the present invention may be applied to a process using a parallel plate type plasma etching apparatus.

Further, although the frequencies of 13.56 MHz and 800 kHz have been exemplified as the RF power source for applying the substrate bias, the present invention is not limited to these frequencies.

Further, it goes without saying that the etching conditions, the etching gas, the configuration of the substrate to be etched, and the like can be appropriately changed.

[0058]

As is apparent from the above description, the present invention provides a dry etching method for etching back a refractory metal layer by performing a two-stage etching with different etching modes to obtain an excess F at the time of over-etching.
^{* The} microloading effect caused by ^* can be prevented.

In the first etch-back, most of the thickness of the refractory metal layer is removed by radical mode high-speed etching at a high plasma density. As a result, a practical etching rate can be maintained.

Further, in order to perform the two-stage etching, the position of the substrate to be etched can be arbitrarily set inside the high plasma density region and outside the high plasma density region, and at the same time, the substrate bias frequency can be arbitrarily selected. By using a plasma etching apparatus of the type, a two-step etch-back process can be achieved in the same apparatus without lowering the throughput.

As an etching apparatus, 1 × 10 ¹¹ / cm
With the plasma etching apparatus in which the plasma density of less than ³ or more 1 × 10 ¹⁴ / cm ³ is obtained, it can be further subjected to high-speed etching.

Further, S ₂ C is used as an etching gas.
By using a gas containing sulfur halide-based gas l ₂ etc., the surface and the interlayer insulating film of a refractory metal layer is etched back, the surface of the adhesive layer and the barrier metal layer can extremely smoothly formed, and the upper wiring It also contributes to smoothing.

By the above effect, the process of embedding a high melting point metal such as W in the connection hole can be achieved with good uniformity by depositing a blanket CVD film and etching back the same.
The surface of the embedded contact plug has excellent flatness,
Abnormal erosion can be prevented. It is also possible to ensure the smoothness of the surface as viewed microscopically. Therefore, a low-resistance ohmic contact with the upper wiring formed on the contact plug can be realized. Since the surface morphology of the refractory metal layer by blanket CVD is not transferred to the interlayer insulating film, the surface of the interlayer insulating film after the etch back is also flat and smooth. For this reason, there is no irregular reflection of exposure light at the time of patterning lithography of the upper wiring formed on the interlayer insulating film, and accurate processing can be performed.

With the above-described effects, the interlayer connection of the multilayer wiring based on the fine design rules can be performed with high reliability, and the present invention greatly contributes to the manufacturing process of semiconductor devices and the like.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view for explaining Examples 1, 2 and 3 to which the present invention is applied in the order of steps, and FIG. 1 (a) shows an adhesion layer / barrier metal layer and a high melting point over the entire surface of a substrate having connection holes. In the state where the metal layer is formed, (b) is a state where the high melting point metal layer is etched back halfway, (c) is a state where the high melting point metal layer is etched back and embedded in the connection hole, (d)
Is a state where the exposed adhesion layer / barrier metal layer is removed by etching back.

FIGS. 2A and 2B are schematic cross-sectional views of a substrate bias application type ECR plasma etching apparatus used in Example 1 to which the present invention is applied, wherein FIG. 2A shows first etching in a plasma mode, and FIG. This is a state in which the second etching is being performed.

FIG. 3 is a schematic sectional view of a substrate bias application type ICP etching apparatus used in Example 2 to which the present invention is applied.

FIG. 4 is a schematic sectional view of a substrate bias applying type TCP etching apparatus used in Embodiment 3 to which the present invention is applied.

FIG. 5 is a view for explaining a problem of a conventional process in etching back a refractory metal layer by blanket CVD. FIG. 5 (a) shows an adhesion layer / barrier metal layer and a refractory metal over the entire surface of a substrate having connection holes. (B) is a state in which abnormal erosion of the high melting point metal layer has occurred due to the microloading effect, and (c) is a state in which abnormal erosion has occurred during removal of the adhesion layer and the barrier metal layer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semiconductor substrate 2 Diffusion layer 3 Interlayer insulating film 4 Adhesion layer and barrier metal layer 5 High melting point metal layer 6 Connection hole 7 Erosion part of high melting point metal layer 8 Erosion part of adhesion layer and barrier metal layer 13 Plasma generation chamber 15 Etching Substrate 16 Substrate stage 17 Plasma processing chamber 20 Substrate stage support member 21 Plasma extraction window 23 Switching means 24 First RF power supply 25 Second RF power supply

Claims (3)

(57) [Claims] 1. A dry etching method for performing etching back of the refractory metal layer formed on the entire surface of the base material layer, the etching conditions mainly a radical reaction, wherein
A first etch-back step of etching the refractory metal layer until just before the base material layer is exposed , and etching the remaining portion of the refractory metal layer by etching conditions mainly using ion sputtering. Before
A second etch-back step of exposing the underlayer material layer . 2. A high melting point formed on the entire surface of a base material layer.
Dry etching method to etch back metal layer
The substrate stage in the high plasma density region
A first high-frequency bias is applied to the substrate stage to
By the etching conditions mainly based on the dical reaction,
Etch the refractory metal layer until just before the base material layer is exposed.
A first etch-back step of arranging the substrate stage outside the high plasma density region;
A second stage having a frequency lower than the first high frequency
By applying a high frequency bias of
The high melting point metal
Etching the remainder of the layer to expose the underlayer
A second etch-back step.
Etching method. 3. An end point of the first etch back step,
The same sample is used in advance under the same conditions as the first etch-back condition.
Measure the etching rate by etching under the etching conditions.
And set the etching rate based on the etching rate.
2. The method according to claim 1, wherein the determination is made based on a switching time.
Or the dry etching method according to 2.