JPH0982665A - Formation of contact plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of forming a contact plug, which can fill a connection hole opened in an interlayer insulating film in the insulating film with a good flatness by etching back a tungsten layer formed by a blanket CVD method. SOLUTION: A high-melting point metal layer 5, such as a W layer, is formed on the whole surface of an interlayer insulating film 3 comprising a connection hole 6 by a blanket CVD method and is etched back using a gas, which contains H and O as its constituent elements, and a gas, which can generate fluorine chemical species. A gas, which can produce sulfur liberating in plasma, may be used under the condition of a two-stage etching and a discharge dissociation. Thereby, a loading effect based on an excessive F radical can be prevented from being generated and and an etch-back, which does not abnormally erode, becomes possible. By performing the two-stage etching, the throughput of the layer 5 is increased. Moreover, the high-smoothness etched-back surface of the layer 5 is obtained utilizing a competitive reaction of deposition of the sulfur with the etching. By these effects, the formation of a highly reliable contact plug becomes possible.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a contact plug forming method applied in the field of manufacturing semiconductor devices,
More specifically, the present invention relates to a method of forming a contact plug by etching back a refractory metal layer formed over the entire surface of an interlayer insulating film including a contact hole.

[0002]

2. Description of the Related Art With the progress of higher integration and higher performance of semiconductor devices such as LSI, the ratio of the area occupied by wiring portions on a semiconductor chip tends to increase. In order to avoid an increase in semiconductor chip area due to this, interlayer connection by multilayer wiring and contact electrodes is an essential process. Conventionally, the electrode / wiring formation method is A
It has been widely practiced to form Al and Al alloys by sputtering. However, in the situation where the multilayer wiring has progressed as described above, and as a result, the surface step of the semiconductor substrate and the aspect ratio of the connection hole are increasing significantly, the deposition method by sputtering may be insufficient in step coverage. Poor connection and disconnection have become serious problems.

Therefore, in recent years, various selective CVD methods have been proposed in which a refractory metal layer of W, Mo, Ta or the like or a metal of Al, Al alloy, Cu or the like is selectively grown and embedded in the connection hole. In this selective CVD, a source gas such as a metal halide, a metal carbonyl, or an organometallic compound is reduced by the lower layer wiring material exposed at the bottom of the contact hole to selectively deposit a constituent metal in the contact hole. However, in the selective CVD, the selectivity gradually deteriorates as the continuous processing is repeated by the same CVD apparatus, and the metal tends to be deposited on an undesired portion such as on the interlayer insulating film. In addition, there is an unsolved problem such as poor controllability when etching back and removing an overgrowth portion called a nail head on a contact hole, and at present it has not reached a practical level.

In view of the above situation, the blanket CVD electrode / electrode is being reviewed in place of the selective CVD.
This is a wiring forming method. Blanket CVD is named because it deposits on the entire surface of the underlayer without selectivity regardless of the chemical properties of the growth underlayer. As an example, a typical example is a process of covering the entire surface of an interlayer insulating film in which a connection hole is opened and forming a refractory metal layer such as W so as to fill the connection hole. An explanatory article on filling a contact hole of W by blanket CVD is available, for example, in the monthly Semiconductor World magazine 19
It is published on page 220 of the November 1990 issue.

[0005]

By the way, in order to embed a refractory metal layer in a contact hole by a blanket CVD to planarize it and use it as a so-called contact plug, an unnecessary refractory metal deposited on the interlayer insulating film is also used. A post-treatment of etching back and removing the metal layer is naturally required. In this etch back process, plasma etching mainly using a radical mode is generally performed using a gas capable of generating a fluorine-based chemical species such as SF _6, but in consideration of non-uniformity of processing within the wafer surface or between wafers. For example, the number 10
% Over-etching is usually performed. However, the underlying interlayer insulating film is exposed at a relatively early stage during the etchback process due to variations in the thickness of the blanket CVD film, uneven plasma density of the etching apparatus, temperature distribution of the substrate stage, and the like. There is an area. In this region, as a result of the reduction of the exposed surface area of the refractory metal layer (F ^* ), which is an etching species, that is, the exposed surface area of the refractory metal layer, the concentration of etching species is relatively increased as compared with other portions. Therefore, in this region, the etching rate is locally increased, and the refractory metal layer and the barrier layer, which are flatly buried in the contact holes, are often eroded. The phenomenon in which the pattern density of the layer to be etched becomes uneven on the same substrate to be etched and the etching rate varies as described above is generally called a loading effect.

Problems caused by the loading effect will be described with reference to FIG. The figure is a schematic cross-sectional view for explaining a conventional high-melting-point metal layer etchback process by blanket CVD. Figure 3 shows the substrate to be etched.
As shown in (a), on the semiconductor substrate 1 made of Si or the like having the impurity diffusion layer 2 formed therein, the interlayer insulating film 3 made of SiO ₂ or the like having the connection hole 6 facing the impurity diffusion layer 2 is formed. A barrier layer 4 is formed by sequentially sputtering Ti and TiN so as to cover the entire surface of the substrate, and a refractory metal layer 5 made of W is formed thereon by blanket CVD. The surface of the high melting point metal layer 5 is generally formed as a fine uneven surface. The reason for this is the blanket CV
D is because the growth generally proceeds as an aggregate of fine columnar crystals. Next, the etching back process is performed. At this time, if the etching back is performed using a gas such as SF ₆ which can generate a fluorine-based chemical species, the refractory metal layer 5
The barrier layer 4 is exposed at an early stage in a thin portion of or in a region where the etching rate is high, and F ^* becomes excessive near the exposed surface in a microscopic view. This excess F ^*
Are concentrated on the flat surface of the refractory metal layer 5 embedded in the connection holes 6, and generate large erosion portions 7 of the refractory metal layer during overetching as shown in FIG. 3B. .

Further changing the etching conditions, the barrier layer 4
When Cl 2 is etched back with Cl-based gas, chlorine radicals (Cl ^* ) lose their reaction partners at the portion where the interlayer insulating film 3 is exposed early, so that Cl ^* becomes excessive at this portion.
Excess Cl ^* concentrates on a slight exposed surface of the barrier layer 4 formed on the side wall of the connection hole and attacks it. As a result, as shown in FIG. 3C, the eroded portion 8 of the deep barrier layer is formed. Further, the surface morphology of the refractory metal layer formed by the blanket CVD is the same as that of the interlayer insulating film 3.
There is also a problem in that unevenness is formed on the surface of the interlayer insulating film 3 by being transferred to the surface of the.

The non-uniformity of the etch-back shape and the deterioration of the contact plug shape due to the loading effect described above are one of the factors that prevent the practical use of the multilayer wiring process using the refractory metal layer by blanket CVD. That is, if the contact plug has an abnormally eroded portion, the electrical connection with the upper layer wiring becomes incomplete, which causes problems such as an increase in resistance value, a decrease in ohmic property, and occurrence of electromigration. Further, since the flatness and smoothness of the upper layer wiring formed on the contact plug is deteriorated, D during patterning lithography of the resist layer on the upper layer wiring is reduced.
There are also problems such as a decrease in OF (Depth of Forcus) margin and deterioration of the shape due to irregular reflection of exposure light. It is considered that the single-wafer type etching apparatus will become the mainstream in the future as the diameter of the substrate to be etched increases. Therefore, high-speed etching using high-density plasma is required so as not to reduce throughput, but considering the situation where there is room for improvement in the uniformity of the plasma density of the single-wafer etching apparatus, There is an urgent need to develop an etchback method for refractory metal layers that is not affected by the loading effect.

Therefore, an object of the present invention is to provide a highly reliable and stable method of forming a contact plug by an etching back method of a refractory metal layer without abnormal erosion or shape deterioration due to a loading effect.

Another object of the present invention is to smooth the surface of the refractory metal layer or the barrier layer or the interlayer insulating film buried in the connection hole by etching back, and to further smooth the surface of the upper wiring formed on the upper layer. Another object of the present invention is to provide a semiconductor device which is formed smoothly and has a reliable and stable multilayer wiring structure.

[0011]

A method for forming a contact plug according to the present invention is proposed to solve the above-mentioned problems. In the first invention (claim 1), an interlayer having a connection hole is provided. In the method of forming a contact plug in which a refractory metal layer formed on the entire surface of an insulating film is etched back to form a contact plug in the connection hole, the etching back step includes at least H and O as constituent elements. It is characterized in that it is a step of plasma etching using an etching gas containing a gas and a gas capable of generating a fluorine-based chemical species.

According to a second aspect of the method for forming a contact plug of the present invention (claim 2), the refractory metal layer formed over the entire surface of the interlayer insulating film having a connection hole is etched back to perform the connection. In the method for forming a contact plug in which a contact plug is formed in the hole, the etch-back step is performed by just etching the refractory metal layer using an etching gas mainly containing a gas capable of generating a fluorine-based chemical species. A second etch back process for over-etching the refractory metal layer by using the etch back process of 1 and an etching gas containing a gas containing at least H and O as constituent elements and a gas capable of generating a fluorine-based chemical species. It is characterized in that the steps are performed in this order. The just etching process is
This means an etch-back step immediately before the surface of the underlying interlayer insulating film or barrier layer is exposed or until a very small portion of these underlying layers is exposed.

Further, in the third invention (claim 3) in the method for forming a contact plug of the present invention, the refractory metal layer formed on the entire surface of the interlayer insulating film having the connection hole is etched back to be connected. In the method of forming a contact plug in which a contact plug is formed in a hole, this etch-back step includes a gas containing at least H and O as constituent elements and a halogenation that can generate free sulfur in plasma under discharge dissociation conditions. It is characterized in that it is a step of performing plasma etching while controlling the temperature of the substrate to be etched to room temperature or less while using an etching gas containing a sulfur-based compound gas.

The sulfur-based compound gas capable of producing free sulfur in plasma under the discharge dissociation conditions used in the third invention has an X / S ratio of 6 when X is a halogen element.
Sulfur halide gas of less than S ₂ F ₂ , S
F ₂ , SF ₄ , S ₂ F ₁₀ , S ₂ Cl ₂ , S ₂ Cl ₃ , S
Examples include Cl ₂ , S ₂ Br ₂ , S ₃ Br ₂ and SBr ₂ . Further, H ₂ S may be used although it is not a halogenated sulfur. These can be used alone or in combination. SF _6, which is widely used as a sulfur fluoride-based gas, has an F / S ratio of 6, and it is difficult to generate free sulfur in plasma under discharge dissociation conditions, so this is excluded. The term "room temperature or lower" as used herein means a temperature equal to or lower than the temperature of a clean room used for manufacturing a normal semiconductor device, and is usually about 25 ° C or lower. The lower limit of the temperature is not particularly limited, but as the temperature at which the substrate stage can be cooled by circulating the refrigerant by the chiller or supplying the liquid nitrogen temperature, −several tens of degrees Celsius
From -100 to several tens of degrees is a standard.

In any of the inventions, H ₂ O (steam) and H ₂ are used as the gas containing H and O as constituent elements.
It is preferably at least one of O ₂ . Further, commercially available hydrogen peroxide solution (30% or 2.5 to 3.0%) may be used as the mixture. Since all of them are liquid sources, they are introduced into the etchback chamber by a technique such as bubbling with a carrier gas such as He, heating vaporization or ultrasonic vaporization. The gas that can generate the fluorine-based chemical species is not particularly limited, but SF ₆ , NF ₆ , CF ₄ , ClF ₃ , XeF ₂ and F _2, etc. generate F ^* and F ⁺ in the plasma. It refers to a general gas that can be used.

In any of the inventions, in its preferred embodiment, Ti, Ti is in contact with the lower surface of the refractory metal layer, that is, in contact with the upper surfaces of the interlayer insulating film and the connection hole.
It is desirable to have a barrier layer such as N, TiON, TiSi ₂ or WN.

The technical idea consistent with the first to third inventions is that at least H ₂ O or H ₂ O ₂ is contained in the etching gas.
Is added, and H atoms and O atoms are supplied to the plasma by the dissociation of these gases. H atoms in the plasma capture F ^* which is an etchant of the refractory metal layer such as W,
It is removed to the outside of the etching chamber in the form of HF or HOF to control the F ^* concentration of the etching reaction system. This alleviates the concentration of F ^{* on} the surface of the contact plug exposed early during overetching, and prevents abnormal erosion and deterioration of shape due to the loading effect. On the other hand, O atoms in the plasma oxidize the surface of the refractory metal layer such as W, and the etchback progresses in such a manner that the oxidation reaction and the etching reaction compete with each other. Therefore, in addition to fluorides such as WF _x , many oxyfluorides such as WOF _x are produced as reaction products of etching. The boiling points of WF ₆ and WOF ₄ , which are typical compounds among these compounds, are calculated according to the CRC Handbook of Chemist.
ry and Physics, 75th. Editi
on (1994-1995), 17.5 ° C and 187.5 ° C. That is, since the oxyfluoride of W has a higher boiling point than the fluoride of W and therefore has a low vapor pressure, ion bombardment having a certain amount of energy is required for desorption of the reaction product from the layer to be etched. is there. For this reason, the form of etch-back, which has mostly depended on the radical reaction in the past, has many elements of the ion-assisted reaction, resulting in abnormal erosion and shape deterioration due to the loading effect caused by the excessive radical reaction during overetching. Is also prevented from this aspect. Further, compared with the conventional etchback mainly using a gas that can generate a fluorine-based chemical species, the presence of O atoms in the plasma improves the etching selection ratio with respect to the underlying interlayer insulating film such as SiO _2. However, it also has an effect of reducing the film loss of the interlayer insulating film.

In the second invention, the etch back is 2 times.
By increasing the etching rate in the just etching process by stepwise etching, it is possible to perform etchback with high throughput. In the overetching step, the microloading effect can be prevented by adding a gas containing H and O as constituent elements, as in the first invention.

In the third aspect of the present invention, the radical reaction is suppressed because the substrate to be etched is controlled at a low temperature below room temperature. In addition, the sulfur deposition on the layer to be etched in competition with the etching significantly reduces the loading effect, though it is a one-step etchback, and almost no contact plug erosion is observed. Further, as for the unevenness of the surface of the refractory metal layer such as W formed by the blanket CVD, the sulfur-based material is deposited on the concave portion, and the sulfur deposited on the convex portion is immediately removed by sputtering, and the exposed convex portion is selectively etched. Etching back progresses while being smoothed. As a result, the surface morphology of the refractory metal layer is not transferred to the barrier layer or the interlayer insulating film to cause surface roughness. Therefore, the surface of the upper layer wiring formed in a later step is also flattened, and the reliability of the wiring is improved. In addition to a sulfur-based compound capable of releasing free sulfur (S) in plasma under discharge ionization conditions,
Further, by adding an N-based gas such as N _2, it is possible to proceed with etching while depositing a sulfur nitride-based compound such as (SN) _n (polythiazyl) on the substrate to be etched. The deposited film of polythiazyl exerts a stronger surface protection effect than sulfur. As N-based gas,
Can be used N ₂ H ₂ and its derivatives and NF ₃ or the like in addition to the N _2. The sulfur-based material deposited here is
It is possible to remove the sublimation by heating the substrate to be etched after the etching back is completed, and no contamination or particle contamination remains on the substrate to be etched. The sublimation temperature is about 90 ° C. for sulfur and about 150 ° C. for polythiazyl in a reduced pressure atmosphere.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments of the present invention will be described below with reference to the accompanying drawings. The same components as those in FIG. 3 referred to in the description of the prior art are designated by the same reference numerals.

Example 1 In this example, the first invention is applied, and a refractory metal layer of W formed by blanket CVD is formed of SF ₆ and H _2.
This is an example in which a contact plug is formed by etching back with a mixed gas of O, and this will be described with reference to FIGS. First, as an example, as shown in FIG.
An interlayer insulating film 3 such as SiO ₂ is formed on a semiconductor substrate 1 such as Si in which an active region such as an impurity diffusion layer 2 is formed in advance,
The connection hole 6 facing the impurity diffusion layer 2 is opened. In addition,
The thickness of the interlayer insulating film 3 is 0.7 μm, for example, and the opening diameter of the connection hole 6 is 0.35 μm. Next, Ti and TiN are sputtered or reactively sputtered in this order on the entire surface to deposit a conformal barrier layer 4. The total thickness of the adhesion layer / barrier metal layer 4 is, for example, 70 nm. Further, the refractory metal layer 5 made of W is formed by blanket CVD so that the contact holes 6 are buried and the barrier layer 4 on the interlayer insulating film 3 is also covered to form a substantially flat surface. This blanket CVD was formed under the following conditions as an example. First, after WF ₆ 25 sccm SiH ₄ 10 sccm gas pressure 1.1 × 10 ⁴ Pa substrate temperature 475 ° C. for 20 seconds, nucleation of W was performed on the entire surface, and then WF ₆ 60 sccm H ₂ 360 sccm gas pressure The condition is changed to 1.1 × 10 ⁴ Pa and the substrate temperature is 475 ° C., and thick deposition is performed. The thickness of the refractory metal layer 5 on the adhesion layer / barrier metal layer is, for example, 0.3.
μm. Immediately above the connection hole, a seam that is a seam of the growth surface is formed.

Next, the etch back step, which is a feature of the present invention, is entered. Set the substrate to be etched on the substrate stage of the magnetic field microwave plasma etching apparatus,
As an example, the high melting point metal layer 5 is etched back under the following conditions. SF ₆ 40 sccm H ₂ O 10 sccm Gas pressure 1.3 Pa Microwave power 850 W (2.45 GHz) RF bias power 200 W (2.0 MHz) Etching substrate temperature Normal temperature In this etchback step, SF ₆ The radical reaction by F ^* generated in the plasma by dissociation is
Etching proceeds by a mechanism assisted by ions such as _x ⁺ and O ⁺ . Similarly, the trapping of F ^* by H atoms generated in the plasma and the generation of WOF _x having a relatively low vapor pressure as a reaction product make the etching mode conventional radical-mode-based etching by SF _6. In comparison, since the mode is mainly based on the ion assist reaction, the etching rate is slightly small.

Therefore, even in the region where the surface of the barrier layer 4 made of Ti / TiN is exposed first, the etchant mainly composed of radicals is concentrated on the surface of the refractory metal layer 5 remaining in the connection hole 6 and abnormal due to the loading effect. No erosion occurred, and the inside of the connection hole 6 was buried flat.
The state after the end of the etch back is shown in FIG.

When it is necessary to remove the barrier layer, the etching conditions are switched next, and the barrier layer 4 on the interlayer insulating film 3 is changed.
Is etched back under the following conditions. The barrier layer 4 is shown in FIG.
An upper wiring layer (not shown) made of an Al-based metal or the like may be immediately deposited from the state of (b) and patterned together with the upper wiring layer. 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 (2.0 MHz) Substrate temperature to be etched Room temperature Normal temperature Barrier layer 4 is etched in connection hole 6 The process proceeds while maintaining selectivity with the remaining refractory metal layer 5 and the interlayer insulating film 3, and as a result, the refractory metal layer 5 and the adhesion layer / barrier metal are formed in the connection hole 6 as shown in FIG. 1C. The contact plug that was evenly embedded in the layer 4 was completed, and no abnormal erosion was observed.

In this embodiment, a contact plug having a flat embedded surface without an abnormal erosion portion due to the loading effect can be formed although the etching rate is slightly small. In addition, the fact that the refractory metal layer can be etched back in one step and with a single etching gas contributes to simplification of the process.

Example 2 In this example, the second invention is applied, and the W layer formed by blanket CVD is etched back until just before the underlying layer is exposed, and overetching is performed by adding H ₂ O _2. This is an example of performing two-step etching of the process. This process will be described with reference to FIG. Note that the substrate to be etched shown in FIG. 2A is the same as the substrate to be etched shown in FIG. 1A used in the first embodiment, and therefore, duplicated description will be omitted.

The substrate to be etched shown in FIG. 2A is subjected to a first etch-back process under the etching conditions using the following first mixed gas as an example, and the barrier layer 4 on the interlayer insulating film 3 as a base is subjected to the first etch-back process. The etching was stopped immediately before the exposure. The end point at this time was determined by obtaining the etching rate of the refractory metal layer 5 in advance under the same etching conditions and determining the elapsed time. SF ₆ 50 sccm Gas pressure 1.3 Pa Microwave power 850 W (2.45 GHz) RF bias power 200 W (2.0 MHz) Etching substrate temperature Room temperature In this just etching process, SF ₆ is dissociated into plasma by dissociation of SF _6. Since the radical reaction by a large amount of F ^* generated causes the etching to proceed by a mechanism assisted by ions such as SF _x ⁺ , the etching rate is large.
As a result, as shown in FIG. 2B, most of the refractory metal layer 5 in the thickness direction is etched, and the refractory metal layer residual portion 5a is slightly left.

Next, as an example, the etching conditions are switched as follows, the residual portion 5a of the refractory metal layer is etched back using a mixed gas containing H ₂ O _2, and the barrier layer 4 on the interlayer insulating film 3 is etched. Stop when is exposed. SF ₆ 35 sccm H ₂ O ₂ 15 sccm Gas pressure 1.3 Pa Microwave power 850 W (2.45 GHz) RF bias power 200 W (2.0 MHz) Etching substrate temperature Room temperature This second etch back step is over This is an etching step, and the addition of H ₂ O ₂ weakens the radical reactivity of the etching reaction system, thereby suppressing the reactivity of radicals and effectively preventing the loading effect. As a result, as shown in FIG. 2C, the refractory metal layer 5 was flatly embedded in the connection hole 6, and no abnormal erosion occurred.

After the etching back of the refractory metal layer 5 is completed, if necessary, the barrier layer 4 exposed on the interlayer insulating film 3 is removed under the same etching conditions as in Example 1 and shown in FIG. As described above, the contact plug formed by the refractory metal layer 5 and the barrier layer 4 was flatly embedded in the connection hole 6, and no eroded portion was observed.

According to the present embodiment, by combining the just etching process by high speed etch back and the over etching process without loading effect,
A contact plug with excellent throughput and flatness can be formed, and an extremely practical process can be realized.

Example 3 In this example, the third invention is applied, and a refractory metal layer of W formed by blanket CVD is formed with H ₂ O and S.
This is an example of etching back with a mixed gas of ₂ F ₂ to form a contact plug, which is again shown in FIG.
This will be described with reference to FIG.

The substrate to be etched shown in FIG. 1 is set on the substrate stage of a magnetic field microwave plasma etching apparatus, and as an example, the refractory metal layer 5 is etched back under the following conditions. S ₂ F ₂ 40 sccm H ₂ O 10 sccm Gas pressure 1.3 Pa Microwave power 850 W (2.45 GHz) RF bias power 200 W (2.0 MHz) Etching substrate temperature 0 ° C. In this etch back step, The etching proceeds by a mechanism in which a radical reaction mainly caused by F ^* generated in plasma due to dissociation of S ₂ F ₂ is assisted by ions such as SF ⁺ and O ⁺ . Since the substrate temperature to be etched is controlled to be low, the reactivity of radicals is suppressed,
The loading effect is extremely effectively prevented because, for example, the process of depositing sulfur on the surface of the refractory metal layer 5 by the dissociation of S ₂ F ₂ by discharge and the process of removing it by sputtering compete with each other. . Further, due to competition between sulfur deposition and removal by sputtering, the surface of the refractory metal layer 5 during the etching back is smoothed, and the morphology of the refractory metal layer 5 is not transferred to the barrier layer 4.

The state after completion of the etch back is shown in FIG. After that, the exposed barrier layer 4 is removed as necessary in the same manner as in Example 1. As a result, a contact plug having a good shape without abnormal erosion was formed as shown in FIG.

According to this embodiment, in addition to the prevention of the microloading effect, the effect of improving the surface morphology of the etched back barrier layer 4 or the interlayer insulating film 3 can be obtained.

Although the present invention has been described with reference to the three examples, the present invention is not limited to these examples. For example, in the embodiment, the process of forming the contact plug by embedding the refractory metal layer in the connection hole has been described as an example. However, embedding in the via hole formed in the interlayer insulating film on the lower layer wiring such as polycrystalline silicon. It may be applied to the process. Further, it can be applied not only to the connection plug but also to formation of various electrodes and wirings using a refractory metal.

Although W is exemplified as the refractory metal layer 5, M
Other refractory metals such as o and Ta may be used. The barrier layer 4 is exemplified by Ti / TiN, but TiW, TiSi _x
For example, various materials may be appropriately selected depending on the material of the base or the refractory metal layer.

H as a gas containing H and O as constituent elements
_{Although 2} O is exemplified, H ₂ O ₂ can be used.

As the gas capable of generating the fluorine-based chemical species, in addition to SF ₆ exemplified in the examples, NF ₃ , ClF ₃ and Xe are used.
Compounds having F atoms such as F ₂ can be used. In addition, when a rare gas such as He or Ar is used as the additive gas, various effects such as sputtering, cooling, dilution, and discharge stability can be obtained.

Further, the ECR plasma etching apparatus of the substrate bias application type was adopted as the etching apparatus to be used. The parallel plate type RIE apparatus, the helicon wave plasma etching apparatus, the ICP (Inductively Coupled Plasm).
a) Etching equipment, TCP (Transformer Coupled Plas)
Of course, it is possible to use various etching devices such as ma) etching devices.

Further, it goes without saying that the etching conditions, the structure of the substrate to be etched, etc. can be changed as appropriate.

[0041]

As is apparent from the above description, the present invention is a method for forming a contact plug by etching back a refractory metal layer, wherein H and O are used as etching gases.
By using a mixed gas of a gas having a constituent element of and a gas capable of generating a fluorine-based chemical species, it is possible to prevent a loading effect due to excess F ^* during overetching.

Similarly, in the method of forming the contact plug by etching back the refractory metal layer, the just etching step mainly uses a gas capable of generating a fluorine-based chemical species, and the overetching step uses H and O.
By adopting the two-step etching by switching to the mixed gas of the gas containing the constituent elements and the gas that can generate the fluorine-based chemical species, the loading effect at the time of overetching can be prevented and the high-speed etching in the just etching process can be prevented. Can be achieved.

Further, in the same method for forming a contact plug by etching back a refractory metal layer, a gas containing H and O as constituent elements and free sulfur in plasma under discharge dissociation conditions such as S ₂ F ₂ are used. By etching while depositing sulfur on the substrate to be etched using a mixed gas with a gas that can be generated, the loading effect during overetching can be more effectively prevented, and the surface of the refractory metal layer that has been etched back Can be formed extremely smooth.

Due to the above effects, the formation of the contact plug in which the refractory metal such as W is buried in the contact hole can be reliably achieved by depositing the blanket CVD film and etching back the blanket CVD film, and the surface of the buried contact plug is flat. It is also excellent, and it is possible to achieve microscopic surface smoothness. Therefore, low resistance ohmic contact with the upper layer 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 etching back is also flat and smooth. Therefore, there is no irregular reflection of exposure light during patterning lithography of the upper wiring formed on the interlayer insulating film, and accurate processing can be performed.

Therefore, the interlayer connection of the multilayer wiring based on the fine design rule can be performed with high reliability, and the present invention greatly contributes to the manufacturing process of the highly integrated semiconductor device and the like.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view for explaining Examples 1 and 3 to which the present invention is applied in the order of steps, in which (a) shows a barrier layer and a refractory metal layer formed on the entire surface of an interlayer insulating film having a connection hole. 6B is a state in which the refractory metal layer is etched back and buried in the connection hole, and FIG. 7C is a state in which the exposed barrier layer is etched back and removed to complete the contact plug.

2A and 2B are schematic cross-sectional views illustrating Example 2 to which the present invention is applied in the order of steps, in which FIG. 2A shows a state in which a barrier layer and a refractory metal layer are formed on the entire surface of an interlayer insulating film having a connection hole. (B) is a state in which the refractory metal layer is subjected to the first etch back, (c) is a state in which the refractory metal layer is subjected to the second etch back and embedded in the connection hole, (d) Is a state in which the exposed barrier layer is etched back and removed to complete the contact plug.

FIG. 3 is a diagram illustrating a problem of a conventional process in etching back a refractory metal layer by blanket CVD. FIG. 3A is a diagram showing a barrier layer and a refractory metal layer on the entire surface of an interlayer insulating film having connection holes. The state in which the refractory metal layer is formed is shown in FIG. 7B, and the state in which the refractory metal layer is abnormally eroded due to the loading effect is shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semiconductor substrate 2 Diffusion layer 3 Interlayer insulating film 4 Barrier layer 5 Refractory metal layer 5a Remaining part of refractory metal layer 6 Connection hole 7 Corrosion part of refractory metal layer 8 Corrosion part of barrier layer

Claims (5)

[Claims] 1. A method of forming a contact plug, wherein a refractory metal layer formed on the entire surface of an interlayer insulating film having a connection hole is etched back to form a contact plug in the connection hole, wherein the etch back step is performed. A contact comprising plasma etching the refractory metal layer using an etching gas containing a gas containing at least H and O as constituent elements and a gas capable of generating a fluorine-based chemical species. How to form the plug. 2. A method of forming a contact plug, wherein a refractory metal layer formed on the entire surface of an interlayer insulating film having a connection hole is etched back to form a contact plug in the connection hole, wherein the etch back step is performed. A first etch back step of just etching the refractory metal layer by plasma etching using an etching gas mainly containing a gas capable of generating a fluorine-based chemical species, and at least H and O as constituent elements A contact characterized by performing a second etchback step of overetching the refractory metal layer by plasma etching using an etching gas containing a gas and a gas capable of generating a fluorine-based chemical species in this order. How to form the plug. 3. A method for forming a contact plug, wherein a refractory metal layer formed on the entire surface of an interlayer insulating film having a connection hole is etched back to form a contact plug in the connection hole, wherein the etch back step is performed. , An etching gas containing at least a gas containing H and O as constituent elements and a halogenated sulfur compound gas capable of producing free sulfur in plasma under discharge dissociation conditions is used, and the substrate to be etched is kept at room temperature or below. A method for forming a contact plug, which is a step of controlling plasma etching. 4. The method of forming a contact plug according to claim 1, further comprising a barrier layer in contact with the lower surface of the refractory metal layer. 5. A gas containing H and O as constituent elements is H
_The method for forming a contact plug according to claim 1, wherein the contact plug is at least one selected from ₂ O and H ₂ O ₂ .