JP2000040696A - Dry etching method and device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new method and a device which enable the performance of dry etching without roughening the surface of a polysilicon layer to a silicon wafer having a polysilicon layer and a W metal layer. SOLUTION: A dry etching method is as follows. A silicon wafer 1 which has a polysilicon layer 3 and a W metal layer 4 is placed on a susceptor within a reactive container, and the interior of the reactive container is depressurized, and the susceptor is put to negative potential. Next, the interior of the reactive container is supplied with reactive gas to form plasma and etch the metallic layer. After finish of this etching, the gas within the reactive container is switched to reactive gas consisting of Cl2 and Ar so as to etch the polysilicon layer. At this time, Ar ions equalizes the surface of the polysilicon layer, and also the hemming bottom of the remaining metallic layer can be taken off by sputtering action. Hereby, the later etching of the polysilicon layer can be performed effectively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a dry etching method and apparatus for forming a gate electrode and the like in a semiconductor integrated circuit.

[0002]

2. Description of the Related Art In a semiconductor integrated circuit, it is common to use polysilicon as a gate electrode. In addition, due to recent demands for higher integration and higher performance of semiconductor integrated circuits, a reduction in the wiring resistance of the gate electrode and a demand for a thinner film, a structure in which tungsten (W) is stacked on polysilicon has been developed. . Conventionally, such a gate electrode is generally formed by the following steps.

First, a polysilicon layer, a barrier metal layer made of WN or TiN, and a W layer are sequentially formed on a silicon oxide film (SiO ₂ film) as a gate oxide film by a PVD method or the like, and then formed thereon. A desired mask pattern is formed. In the case of using the CVD method, a W nucleation layer is formed between the barrier metal layer and the W layer in order to improve the adhesion between the two layers.

Then, a reactive gas containing SF ₆ as a main component is applied to the barrier metal layer and the W layer or a layer composed of the barrier metal layer, the W nucleation layer and the W layer, that is, the metal layer. Dry-etch. When this etching progresses and a part of the surface of the polysilicon layer is exposed, the etching on the metal layer is temporarily stopped at that time as an end point.

At the end point, the lower part of the barrier metal layer is not completely removed. For this reason, in the related art, overetching is performed for a predetermined time using the same reactive gas even after the end point to remove the foot of the metal layer beside the wiring. When the over-etching of the metal layer is completed, the etching is switched to the reactive gas containing Cl ₂ as a main component, and the polysilicon layer is dry-etched. Thus, a gate electrode having a desired pattern is formed.

[0006]

However, the above-mentioned conventional dry etching method has the following problems.

First, the reactive gas containing SF ₆ has a selectivity of W to polysilicon (a ratio of an etching rate of W to an etching rate of polysilicon) of 0.2 to 0.1.
Since it is as small as about 3, there is a problem that when the metal layer is over-etched, the surface of the already exposed polysilicon layer becomes rough. This is noticeable in the open space where the space between the masks is wide, as is apparent from the portion A in FIGS. 4A and 4B. If the etching of the polysilicon layer is started in a state where the surface of the polysilicon layer is rough, etching of the concave portion proceeds first, and there is a possibility that pitching (piercing) may occur in the silicon oxide film.

On the other hand, if the over-etching time for the metal layer is shortened to avoid such a problem, the W
There was a tendency for intense residues starting from the layer or barrier metal layer.

An object of the present invention is to provide a novel dry etching method and apparatus which can solve the above problems.

[0010]

Therefore, a dry etching method according to the present invention according to the first aspect of the present invention is to dry a substrate having a polysilicon layer and a metal layer formed thereon on a susceptor in a reaction vessel. A second step of reducing the pressure inside the reaction vessel to a predetermined pressure; a third step of applying a negative bias power to the susceptor; A fourth step of supplying gas and forming a plasma in the reaction vessel to etch the metal layer, and after completion of the fourth step, exhausting the gas in the reaction vessel and removing the gas into the reaction vessel. The fifth reactive gas is supplied to form a plasma in the reaction vessel and etch the polysilicon layer.
Wherein the _second reactive gas includes a Cl ₂ gas and an Ar gas.

As described above, when the reactive gas is switched to a gas containing Cl ₂ gas and Ar gas after the etching of the metal layer, the Ar gas is ionized by the plasma, and the Ar ions are converted to the negative potential susceptor. The metal layer proceeds toward the upper substrate to be processed, and if a part of the metal layer remains as a footing, the part is removed by a sputtering action. In addition, the surface roughened by the etching of the metal layer is struck by Ar ions, and at the same time, the etching action by the Cl plasma is applied, so that the surface to be etched is flattened. Therefore, if the etching of the polysilicon layer is continued in this state, the etching proceeds uniformly as a whole.

In order to obtain such an effect, it is preferable that the second reactive gas comprises only Cl ₂ gas and Ar gas, and the Cl ₂ gas contains 3% to 20% and the Ar gas contains 97%.
% To 80%.

After the surface of the polysilicon layer is smoothed by the action of the plasma of Cl and Ar, the Ar plasma substantially ceases its role, and thus the third reaction more suitable for etching the polysilicon layer. The reactive gas may be supplied into the reaction vessel.

In order to accurately determine the end point of the etching of the metal layer, the emission of the plasma in the reaction vessel may be observed to detect a wavelength band specific to silicon contained in the polysilicon layer. preferable. If it is detected that silicon is present in the plasma, it means that a portion of the polysilicon layer has been exposed, and that the metal layer has been etched beyond a certain level. Therefore, the reactive gas may be switched to the second reactive gas from the time of this detection, or the reactive gas may be switched after further over-etching for a certain period of time.

The invention according to claims 5 to 8 is a dry etching apparatus for effectively performing the dry etching method according to the present invention.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the drawings.

FIGS. 1A to 1E are cross-sectional views schematically showing a structure of a silicon wafer (substrate to be processed) for explaining a dry etching method according to the present invention. FIGS. FIG. 3 is a diagram sequentially showing the states of layers up to FIG. Poly silicon wafer 1 is for cutting the gate electrode, and SiO ₂ film 2 is formed a gate oxide film on the surface, further on the SiO ₂ film 2, the gate electrode layer A silicon layer 3 and a metal layer 4 are formed. The metal layer 4 is formed by a PVD process and includes a barrier metal layer 4a made of TiN or WN and a W layer 4b thereon.
On the W layer 4b, a mask 5 made of an organic material or SiN is formed in a desired pattern.

FIG. 2 is a schematic view showing one embodiment of a plasma type dry etching apparatus 10 according to the present invention. In FIG. 2, the dry etching apparatus 10 includes a reaction vessel 12 whose inside is depressurized. Reaction vessel 1
Reference numeral 2 denotes a cylindrical container main body 14 made of a material obtained by subjecting anodized aluminum to a material, and a lid 16 serving as a discharge component attached to an upper portion of the cylindrical main body 14.

A susceptor 18 on which the silicon wafer 1 is placed is arranged inside the reaction vessel 12. On the upper surface of the susceptor 18, an electrostatic chuck 20 for fixing the silicon wafer 1 is provided. The susceptor 18 also functions as an electrode, and is grounded via the matching unit 22 and the high frequency bias power supply 24. Therefore, when a high frequency bias voltage is applied to the grounded container body 14, the susceptor 18 functions as a cathode and the container body 14
Will function as an anode.

Further, the container body 14 is provided with an exhaust port 26 connected to a vacuum pump (not shown) for exhausting the inside of the reaction container 12, and further introduces a reactive gas into the inside. Gas supply port 28 is provided.

A gas mixing chamber 30 is connected to the gas supply port 28 via a pipe. The gas mixing chamber 30 is a device for mixing various gases uniformly. Various gas supply sources 32 to 42 are connected to the gas mixing chamber 30 via flow control valves 44 to 54, respectively. There are various gases that can be used for etching the metal layer 4 and the polysilicon layer 3. In this embodiment, SF ₆ , HBr, Cl ₂ , N ₂ , A
r and O ₂ are used, and the respective gas supply sources 32 to 42
Is provided.

Opening and closing of each of the flow rate adjusting valves 44 to 54 is controlled by a control device 56 including a microcomputer or the like, and the flow rate of each gas is adjusted. Therefore, it is possible to set the mixing ratio of the reactive gas and the like to a predetermined value.

The lid 16 which is a part of the reaction vessel 12 is made of a dielectric material. A coil antenna 58 is provided on the outer periphery of the lid 16.
As a result, an electromagnetic field is induced inside the reaction vessel 12 through the lid 16 to generate plasma, and energy is supplied to electrons in the plasma, so that the plasma is maintained at a high density. Note that a high-frequency power supply 62 is connected to the coil antenna 58 via a matching unit 60. Further, the lid 16
A shield 64 is provided on the outside of the device to prevent the generated high frequency from leaking to the outside.

Further, a transparent window 66 is provided at an appropriate position of the container body 14.
Is provided so that the inside can be observed. A monochromator 70 is connected to the transparent window 66 via an optical fiber 68. The monochromator 70 is set so as to be able to detect light in a wavelength band unique to Si, which is generated when Si emits light by plasma. The output of the monochromator 70 is sent to the control device 56.

Next, the dry etching apparatus 1 having the above configuration
The case where the gate electrode is formed by applying the dry etching method of the present invention to the silicon wafer 1 having the layer configuration shown in FIG.

First, the silicon wafer 1 is placed on the susceptor 18 in the reaction vessel 12 and fixed by the electrostatic chuck 20. Next, the pressure inside the reaction vessel 12 is reduced by a vacuum pump to a predetermined degree of vacuum, for example, about 4 mTorr.

Next, the flow control valves 44, 46, 48, and 50 are opened at required opening degrees according to a signal from the controller 56, and SF ₆ gas and HBr gas are supplied from the gas supply sources 32, 34, 36, and 38, respectively. , Cl ₂ gas and N ₂ gas are derived. These gases are mixed in the gas mixing chamber 30 and supplied into the reaction vessel 12 from the gas supply port 28. The mixed gas (first reactive gas) is conventionally known as a gas suitable for etching the metal layer 4 having the W layer 4b as a main layer.

When the supply of the first reactive gas is started, the high frequency bias power supply 24 is turned on, and a high frequency bias power of, for example, 13.56 MHz is applied between the container body 14 and the susceptor 18. Since the container body 14 is grounded, the susceptor 18 has a negative potential and functions as a cathode. A high frequency power supply 62 is connected to the coil antenna 58.
For example, when high frequency power of, for example, 12.56 MHz is applied, plasma is generated in the reaction vessel 12 and the plasma is maintained at a high density. The first reactive gas is dissociated by the plasma, and the F ions present in the plasma mainly contribute to the etching of the metal layer 4, and the etching proceeds. At this time, since the F ions travel toward the susceptor 18 having the negative potential, the anisotropic etching in the vertical direction is performed.

As the etching of the metal layer 4 proceeds,
Eventually, a part of the polysilicon layer 3 will be exposed (see FIG. 1B).
For example, it becomes remarkable in an open space B such as a portion where the interval between the masks 5 is wide or an outermost peripheral portion.

In the state shown in FIG. 1B, the polysilicon layer 3 is also etched, and the removed layer material floats in the reaction vessel 12 and is dissociated by plasma. Therefore,
The plasma contains Si which is a component of the polysilicon layer 3. The presence of Si is detected by the monochromator 70 set to detect the wavelength band specific to Si from the emission of the plasma, and the control device 56 changes from the output signal of the monochromator 70 to the state shown in FIG. At the same time, the time when Si is detected is determined as the end point of the etching of the methane layer 4.

As is clear from FIG. 1B, at this end point, the barrier metal layer 4a in the metal layer 4 still remains in a large amount, so that a certain period of time elapses from the end point. Then, the etching of the metal layer 4 is continued using the first reactive gas. If the over-etching time is excessively long, the surface of the polysilicon layer 3 becomes rough because the reactive gas containing SF ₆ as a main component is used, as described above in the section of “Prior Art”. Becomes significant. Therefore, in this embodiment, FIG.
The over-etching time is set relatively short so that the barrier metal layer 4a slightly remains as shown in FIG.

After the set over-etching time has elapsed and the etching of the metal layer 4 has been completed,
The flow control valves 44, 46, 48, and 50 are closed, and the gas in the reaction vessel 12 is exhausted. Then, after adjusting the pressure in the reaction vessel 12, it is connected to the gas supply sources 36 and 40 so as to supply a mixed gas of Cl ₂ gas and Ar gas as the _second reactive gas into the reaction vessel 12. The flow control valves 48 and 52 are opened. In this case, the composition of the second reactive gas is 3% to 20% of Cl ₂ gas and A
It is preferable that the r gas is 97% to 80%.

When this second reactive gas is supplied into the reaction vessel 12, the Ar gas is dissociated into Ar ions. The Ar ions travel toward the negatively biased susceptor 18 and strike the surface of the silicon wafer 1 fixed on the susceptor 18 (see FIG. 1C). As a result, the remaining barrier metal layer 4a becomes A
It is removed by the sputtering action of r ions. Conventionally, the residual portion of the barrier metal layer has been a cause of a residue generated by etching the polysilicon layer later. However, according to the present invention, the residual portion is removed by sputtering. To be reduced.

Further, this Ar ion is applied to the polysilicon layer 3.
After a certain period of time has passed after the introduction of the second reactive gas, the surface of the polysilicon layer 3 becomes smooth as shown in FIG. It is considered that the smoothing of the polysilicon layer 3 is due to the Ar ions pressing against the polysilicon layer 3 in combination with the etching action by Cl ions.

After the surface of the polysilicon layer 3 is flattened, the etching of the polysilicon layer 3 may be continued by using the second reactive gas as it is. However, when the roughness of the surface of the polysilicon layer 3 is eliminated, problems such as pitching of the SiO ₂ film 2 do not occur. Therefore, another reactive gas suitable for etching the polysilicon layer 3 should be used. Is valid. Therefore, in this embodiment, after etching with the second reactive gas is performed for a certain period of time, the flow control valves 48 and 52 are closed. After the gas in the reaction vessel 12 is exhausted and the pressure is readjusted, the flow control valves 46, 48 and 54 are opened, and the HBr gas and Cl ₂ are supplied from the gas supply sources 34, 36 and 42, respectively.
Gas and O ₂ gas are supplied into the reaction vessel 12 through the gas mixing chamber 30 as a third reactive gas. The composition of this third reactive gas is conventionally known, and the polysilicon layer 3 is etched using this gas, and finally the mask is removed by an ashing process or the like. A gate electrode having a shape as shown in FIG.

Although the preferred embodiments of the present invention have been described in detail, it goes without saying that the present invention is not limited to the above embodiments. For example, the compositions of the first and third reactive gases are not limited to those described above. Further, as the second reactive gas, a gas obtained by adding another gas to the Cl ₂ gas and the Ar gas may be considered.

Further, in the above embodiment, the end point of the etching of the metal layer 4 is determined as an end point (when Si is detected).
After that, the over-etching is further performed to set the end point. However, depending on the thickness of the layer or the like, the etching with the first reactive gas may be ended at the end point and the etching with the second reactive gas may be started. Also, the method of detecting the end point may be a detection means other than the monochromator.

Further, the metal layer 4 of the above embodiment is made of P
Since the barrier metal layer 4 is formed by the VD method,
Although a two-layer structure of a and a W layer 4b is used, in the case of the CVD method, a three-layer structure having a W nucleation layer between the barrier metal layer and the W layer is obtained. The W nucleation layer is formed using SiH ₄ and WF ₆ as a process gas, and is a porous layer. When the metal layer having such a porous W nucleation layer is etched, the surface roughness of the polysilicon layer becomes more remarkable. Therefore, the present invention for avoiding the surface roughness of the polysilicon layer is particularly effective for such a three-layer metal layer.

[0039]

Next, a description will be given of an embodiment in which the effect of etching by a reactive gas comprising Ar gas and Cl ₂ gas is verified.

In this embodiment, a silicon wafer is used as a substrate to be processed, a 5 nm SiO ₂ film is formed on the surface thereof, a 10 nm polysilicon layer is formed thereon, and a 10 nm TiN layer is formed thereon. It is formed as a layer. Moreover, 100 nm is formed on the barrier metal layer.
A tungsten layer having a thickness of 160 n
m, 0.25 μm wide SiN mask reduces gap width to 0.25 μm
μm.

The dry etching apparatus used in the examples is shown in FIG. 2, and the gas species used are the same as those described in the above embodiment. The high-frequency power applied between the susceptor and the container body was 13.56 Mhz, and the high-frequency power applied to the coil antenna was 12.56 Mhz.

In the etching of the metal layer, the pressure in the reaction vessel was set at 4 mTorr. Also, as a first reactive gas for etching the metal layer, SF ₆ gas is used at a gas flow rate of 50 sccm, HBr gas is used at 10 sccm,
The reaction vessel was supplied with N ₂ gas at 45 sccm and Cl ₂ gas at 10 sccm. Twenty-five seconds after the start of the etching of the metal layer, monochromator detected Si in the plasma. When this Si is detected (end point)
Then, under the same conditions, the metal layer was continuously over-etched for 7 seconds.

Thereafter, the pressure in the reaction vessel was increased to 4 mTorr.
, And a mixed gas of Cl ₂ gas and Ar gas was introduced into the reaction vessel as a second reactive gas. 20 Cl ₂ gas
sccm (10% of total gas flow rate), Ar gas is 1
The flow was performed at 80 sccm (90% of the total gas flow rate), and etching with the second reactive gas was performed for 30 seconds.

FIG. 3 shows an etching pattern of the silicon wafer obtained through the above steps. FIG.
(A) is an SEM showing a cross-sectional shape of the silicon wafer.
FIG. 3B is an SEM micrograph of the surface of the silicon wafer taken in an overhead view. Note that these photographs are obtained by photographing the silicon wafer from which the SiN mask has been removed by the ashing process and the HF cleaning process.

Here, the photograph of FIG. 4 used in the description of the prior art shows that the etching was performed under substantially the same conditions as in the above embodiment, but the etching was not performed by the second reactive gas, but instead. The length is extended to 15 seconds of over-etching. 4 and FIG. 3 of the present invention,
It will be appreciated that the present invention smoothes the surface of the polysilicon layer and provides a distinct improvement over prior art methods.

[0046]

As described above, according to the present invention, by performing dry etching on a polysilicon layer and a metal layer having a W layer as a main layer, the surface of the polysilicon layer roughened by the etching of the metal layer. Can be improved to a smooth state. Further, generation of a residue starting from the metal layer can be prevented. Therefore, it is possible to prevent an adverse effect on the lower layer of the polysilicon layer, for example, pitching and the like, and it is possible to contribute to miniaturization and high performance of a semiconductor integrated circuit in the future.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view showing an embodiment in which a dry etching method of the present invention is applied to a silicon wafer having a polysilicon layer and a W metal layer, and (a) to (b) of FIG.
(E) is a figure which shows the change of the cross-sectional shape from before etching processing to after processing, respectively.

FIG. 2 is a sectional view schematically showing one embodiment of a dry etching apparatus according to the present invention.

3A and 3B are SEM micrographs showing an etching pattern of a silicon wafer obtained according to an example of the present invention, wherein FIG. 3A shows a cross-sectional shape thereof, and FIG. 3B shows a surface of the silicon wafer in a bird's-eye view. It is a microscope picture.

FIG. 4 is an SEM micrograph similar to FIG. 4 showing an etching pattern of a silicon wafer obtained by a conventional dry etching method.

[Explanation of symbols]

1. Silicon wafer (substrate to be processed) 2: SiO ₂ film,
3 ... polysilicon layer, 4 ... metal layer, 4a ... barrier metal layer, 4b ... tungsten layer, 5 ... mask, 10 ... dry etching apparatus, 12 ... reaction vessel, 18 ... susceptor,
24 ... High frequency bias power supply (bias means), 32-4
2: Gas supply source, 44 to 54: Flow control valve, 56:
Control device, 62 high frequency power supply (plasma generating means), 7
0: Monochromator (silicon detection means).

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Daisuke Tajima 14-3 Shinzumi, Narita-shi, Chiba Pref. Nogedaira Industrial Park Applied Materials Japan Co., Ltd. (72) Inventor Takanori Nishizawa 14-3 Shinzumi, Noizumi, Narita-shi, Chiba Applied Materials Japan Co., Ltd. (72) Inventor Hiroki Sasano 14-3 Shinsen, Narita-shi, Chiba Applied Materials Japan Co., Ltd. (72) Inventor Hitoshi Matsuo Niizumi, Narita-shi, Chiba 14-3 Nogedaira Industrial Park Applied Materials Japan Co., Ltd. F-term (reference) 4K057 DA04 DA11 DA14 DB06 DB08 DB11 DB12 DB15 DD01 DD02 DE01 DE06 DE11 DE14 DE20 DG07 DG12 DG13 DG15 DJ03 DN01 5F004 BA06 BC03 BD01 CB02 CB15 DA00 DA04 DA18 DA23 DA25 DA26 DB02 DB12 EA07 EA10

Claims (8)

[Claims] A first step of disposing a substrate to be processed having a polysilicon layer and a metal layer including a barrier metal layer and a tungsten layer formed thereon on a susceptor in a reaction vessel; A second step of reducing the pressure in the vessel to a predetermined pressure, a third step of applying a negative bias power to the susceptor, and supplying a first reactive gas into the reaction vessel,
A fourth step of forming a plasma in the reaction vessel and etching the metal layer; and after the fourth step, evacuating the gas in the reaction vessel to form a second plasma in the reaction vessel. A fifth step of supplying a reactive gas and forming a plasma in the reaction vessel to etch the polysilicon layer, wherein the second reactive gas comprises Cl A dry etching method comprising _two gases and an Ar gas. 2. The method according to claim 1, wherein the second reactive gas comprises Cl ₂ gas and Ar gas, wherein the Cl ₂ gas is 3% to 20% and the Ar gas is 97% to 80%. 3. The dry etching method according to 1. 3. After performing the etching in the fifth step for a predetermined time, the gas in the reaction vessel is exhausted to supply a third reactive gas into the reaction vessel,
3. The dry etching method according to claim 1, further comprising a step of forming a plasma in the reaction vessel to further etch the polysilicon layer. 4. A step of determining the end point of the fourth step by observing the emission of the plasma in the reaction vessel and detecting a wavelength band unique to silicon contained in the polysilicon layer. The dry etching method according to any one of claims 1 to 3, further comprising: 5. A dry etching apparatus for etching a polysilicon layer formed on a substrate to be processed and a metal layer including a barrier metal layer and a tungsten layer formed thereon under a plasma environment. A reaction vessel whose pressure is reduced to a predetermined pressure; a susceptor that supports the substrate to be processed in the reaction vessel; bias means for applying a negative bias power to the susceptor; and a metal layer in the reaction vessel. A first gas supply unit for supplying a first reactive gas for etching a gas, a _second gas containing a Cl ₂ gas and an Ar gas in the reaction vessel.
Second gas supply means for supplying a reactive gas of the type described above, plasma generating means for generating plasma in the reaction vessel, and the first reactive gas for etching the metal layer in the reaction vessel. Controlling the first gas supply means so as to supply the reaction gas into the reaction vessel, and after the etching of the metal layer is completed, the reaction gas supplied into the reaction vessel from the first reaction gas to the second reaction gas. Control means for controlling said first and second gas supply means so as to switch to said reactive gas. 6. The second gas supply means, wherein the second reactive gas comprises Cl ₂ gas and Ar gas, wherein the Cl ₂ gas is 3% to 20% and the Ar gas is 97% to 80%. 6. The dry etching apparatus according to claim 5, wherein the value of the dry etching is adjusted. 7. A silicon detecting means for detecting a wavelength band specific to silicon from light emission of the plasma in the reaction vessel, wherein silicon from the polysilicon layer is contained in the reaction vessel during etching of the metal layer. When the silicon detecting means detects that the silicon is contained in the plasma,
The dry etching apparatus according to claim 5, wherein the control unit determines a termination time point of the etching of the metal layer. 8. The reaction vessel according to claim 5, further comprising a third gas supply unit for supplying a third reactive gas for etching the polysilicon layer.
8. The dry etching apparatus according to any one of items 7 to 7.