JPH0669155A - Contact plug forming method - Google Patents

Abstract

PURPOSE:To form a flat part without any recess at the center of a contact plug by depositing tungsten on the entire surface of a ground substrate with a contact hole, and oxidizing the surface of tungsten, eliminating the oxidation layer of tungsten by heat treatment in vacuum and then etching the entire surface of tungsten. CONSTITUTION:An oxide film 12 is deposited on a silicon substrate 11 and a contact hole 13 is formed. Then, an adhesion barrier layer 14 is deposited and further tungsten 15 is deposited on the adhesion barrier layer 14. The surface convex part of the tungsten 15 is oxidized by heat treatment in oxygen atmosphere, thus eliminating only the surface oxidized part. Then, the tungsten 15 is entirely etched so that the tungsten 15 inside the contact remains, thus preventing a step from being generated due to reduction in the thickness of the tungsten 15 at the contact plug part and forming a contact plug with an improved flatness without any recess at the center of the plug.

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.

[0002]

2. Description of the Related Art In recent years, with the progress of integration of LSI devices, its wiring technology has received a great deal of attention. The contact diameter is becoming finer, the depth thereof is becoming deeper, and the contact aspect ratio (depth / diameter) is becoming larger.
Wiring must be formed in such small and deep contacts.

When a conventional sputtered film is used for wiring, its coverage is poor, and therefore a single layer of aluminum wiring cannot conduct electricity. Therefore, a contact embedding technique is essential. At present, as an embedding technique which has been put into practical use, there is one using polysilicon, but a method using tungsten is considered more promising because of its high contact resistance and complicated process. Tungsten embedding techniques include a tungsten entire surface embedding method, an entire surface etching (etchback) method, and a selective deposition method. A conventional tungsten filling technique will be described below with reference to FIGS.

As shown in FIG. 6A, silicon (Si)
The contact hole 3 is formed by dry etching the oxide film 2 on the substrate 1. Next, as shown in FIG. 6B, the adhesion with the side wall of the oxide film is improved, and alloy spike of tungsten (W) diffusing into silicon is prevented at the connecting portion between tungsten and silicon, and the adhesion barrier layer. 4 is formed. Generally, titanium (Ti), titanium nitride, titanium / tungsten compound film, etc. are used. afterwards,
As shown in FIG. 6C, CVD (Chemical Vapor Deposi)
Tungsten) deposits the tungsten 5 over the entire surface until the contact hole 3 is completely filled. Then, etch back is performed to leave tungsten only in the contact portion. However, as shown in FIG. 6D, the tungsten residue 6 is generated in the just etch-back in which the tungsten in the contact portion appears. Therefore, the etch-back time is lengthened to remove the tungsten residue 6 to form the contact plug of FIG.

In the selective tungsten technique, the contact hole 3 is formed by dry etching the oxide film 2 on the silicon (Si) substrate 1 as shown in FIG. Next, as shown in FIG. 7B, the tungsten 5 is selectively grown only on silicon or metal. It is considered that the adsorption probability of the reactive gas greatly differs between silicon or metal and the oxide film, and the difference in the reactivity on the surface causes the selective growth. Therefore, the selectivity may be broken depending on the surface state, and the tungsten nuclei 7 may be formed on the oxide film 2 as shown in FIG. 7C.

[0006]

As described above, in the method of forming the contact plug by depositing tungsten 5 on the entire surface,
Etch back and only tungsten 5 in contact hole 3
Leave. However, in the above configuration,
As shown in (d), a tungsten residue 6 is generated in the just etch-back where the tungsten 5 in the contact hole 3 appears. This depends on the surface morphology of the tungsten 5 (surface irregularity state). Further, if the etching time is lengthened in order to remove the tungsten residue 6, the height of the entire contact plug is lowered as shown in FIG. In addition, since the film density is small in the central part of the plug, the etching rate is increased and a dent is formed. In the worst case, even the silicon of the substrate is etched.

Since selective tungsten deposition utilizes the reaction difference on the surface, the selectivity is broken depending on the surface state of the oxide film, and the tungsten nucleus 7 is also formed on the oxide film 2. Therefore, there is a problem that surface treatment before deposition is difficult and process control is very difficult. If the tungsten nuclei 7 thus formed are to be removed by etching, the same problems as in the case of depositing the entire surface tungsten 5 described above occur.

[0008]

In order to solve the above problems, the method of forming a contact plug according to the present invention comprises a step of depositing tungsten entirely on a base substrate having a contact hole, and then a step of depositing the surface of the tungsten. After oxidation,
The method includes a step of removing the tungsten oxide layer by heat treatment in a vacuum, and then a step of etching the entire surface of the tungsten.

In addition, a step of entirely depositing tungsten on a base substrate having a contact hole, a step of etching the entire surface of the tungsten, then an etching residue of the tungsten is oxidized, and a heat treatment is performed in a vacuum to perform the etching. A step of removing the residue is provided.

Further, a step of selectively depositing tungsten only on the contact holes on a base substrate having contact holes, a step of oxidizing the tungsten deposited except the contact holes, and then removing it by heat treatment in a vacuum. Is equipped with.

[0011]

By using the present invention, the tungsten etching residue can be reduced when etching back is performed after the entire surface of the contact portion is deposited with tungsten. Further, the generated tungsten residue can be removed without performing additional etching. Therefore, a step due to the reduction of the tungsten thickness of the contact plug portion does not occur, and it is possible to form a contact plug having no flatness in the center portion of the plug and excellent in flatness. Alternatively, the selectivity is broken when the selective tungsten is formed on the contact portion, and even if the tungsten nucleus is formed on the portion other than the contact portion, it can be removed without etching. Therefore, the pretreatment before forming the selective tungsten is simplified.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to the drawings. 1A to 1D are cross-sectional views in order of the processes, showing a contact plug forming method of the present invention. First, as shown in FIG. 1A, an oxide film 12 having a thickness of 1000 nm is deposited on a silicon substrate 11 and a contact hole 13 having a bottom diameter of 0.5 μm is formed by dry etching. Next, as shown in FIG. 1B, TiN / Ti was used as an adhesion barrier layer.
The films 14 are each sputter deposited to a thickness of 100/20 nm. At this time, the Ti film forming condition is that the argon (Ar) gas pressure is 6 mTorr and the DC power is 1 kW, and the TiN film forming condition is Ar / N ₂ gas mixture ratio 30/70.
%, Gas pressure 6 mTorr, DC power 6 KW, respectively.

Next, as shown in FIG. 1 (c), tungsten 15 was deposited to a thickness of 500 nm by CVD. The film forming conditions at this time are intended to form tungsten nuclei on the base as the first step. In this case, WF ₆ having a low deposition rate was reduced by SiH ₄ to form a tungsten nucleus. The condition at this time is the gas flow rate ratio WF ₆
/ SiH ₄ = 5 / 3SCCM, gas pressure 1.9 Torr
Deposition was carried out at a substrate temperature of 450 ° C. for 90 seconds. The second step follows the first step and has a high deposition rate, WF ₆
Was reduced with H ₂ to deposit tungsten 15. The conditions at this time are as follows: Gas flow rate ratio WF ₆ / H ₂ = 75
/ 450SCCM, gas pressure 73Torr, substrate temperature 4
It was deposited at 50 ° C. for 100 seconds.

The surface reflectance of tungsten 15 at this time was examined by using a reflectance measuring instrument. The measurement wavelength is 400 nm,
As a reference, the reflectance of the silicon substrate surface is 100
Calculated as a percentage. The reflectance of the surface of tungsten 15 is 45
%Met. Next, the surface roughness was examined by a stylus type surface roughness meter and cross-sectional observation with a scanning electron microscope (SEM).
As a result, the surface of the tungsten 15 had irregularities with an average of 50 nm.

Next, as shown in FIG. 1D, the tungsten (15) is fed into a quartz tube at an oxygen (O ₂ ) flow rate of 50.
500 by halogen lamp in 0SCCM atmosphere
Heat at 10 ° C for 10 seconds. This makes tungsten 1
5. A tungsten oxide film 16 is formed on the surface. The results of analyzing the surface of this film by X-ray diffraction and Auger electron spectroscopy are shown in FIGS.

FIG. 2 shows the result of structural analysis by X-ray diffraction. In order to obtain information from the surface, X-rays were made incident on the sample at an angle of 2 degrees, integrated and analyzed. X
A copper (Cu) Kα ray (wavelength 0.143 nm) was used as a radiation source. The vertical axis represents the diffraction peak intensity (arbitrary unit), and the horizontal axis represents the diffraction angle (2θ). FIG. 2A shows the diffraction peak after the tungsten film is deposited, and FIG. 2B shows the diffraction peak after heating at 500 ° C. for 30 seconds. In FIG. 2A, a peak corresponding to only tungsten appears. In FIG. 2B, the peaks not observed in FIG.
It is recognized around 24 degrees. These peaks are WO ₃ (0
It corresponds to 01) and (200), and it can be said that WO ₃ is formed on the surface. A tungsten peak appears here as in FIG. 2A, but this is a peak from tungsten under the surface oxide film.

FIG. 3 shows the results of analysis in the depth direction by Auger electron spectroscopy. The vertical axis represents Auger peak intensity (arbitrary unit), and the horizontal axis represents sputtering time. O ₂ was detected from the surface, which coincides with the result of X-ray diffraction in FIG.
It can be inferred that the thickness is about 70 nm from the relationship with the tungsten peak.

Next, in a quartz tube, 1.0 × 10 ^-7 T
Halogen lamp in orr vacuum 600 ° C, 3
Heat treatment was performed for 0 seconds. The film was analyzed in the depth direction by X-ray diffraction and Auger electron spectroscopy. As a result, the peak of WO ₃ observed in FIG. 2 disappeared, and the result of Auger electron spectroscopy also revealed that the peak of O _{2 was} about the detection limit from the surface. Only the peak was observed. Next, a stylus type surface roughness meter and SE
As a result of examining the surface roughness by observing the cross section of M, the surface was smooth. The reflectance of the surface changed from 45% to 75%. Vapor pressure of tungsten is, for example, 1000
Although it is 5.6 × 10 ^-25 Torr at 0 ° C., the vapor pressure of WO ₃ is as high as 2.0 × 10 ^-4 Torr, which is orders of magnitude higher.

From the above results, it can be said that the convex portion of the tungsten surface was oxidized by the heat treatment in the oxygen atmosphere, and the convex portion oxidized by the subsequent heat treatment in the vacuum was removed as shown in FIG. 1 (e).

Next, the tungsten 15 inside the contact
Then, the entire surface of the tungsten 15 is etched back to leave. The etching conditions are gas flow rate ratio SF ₆ / Ar = 110.
/ 90SCCM, gas pressure 310mTorr, RF power 400W, etching end point detection time (60 seconds on average)
By overetching + 10%, a contact plug as shown in FIG. 1F can be formed. The etching rate of tungsten 15 under these conditions is 500 nm /
Minutes. Note that the TiN / Ti film 14 was left as a barrier layer for the wiring to be formed later.

When the film after the deposition of tungsten 15 described in FIG. 1C is entirely etched back under the same conditions, the tungsten residue remains as shown in FIG. 6D of the conventional example, and the surface after the deposition of tungsten is shown. It can be said that the influence of morphology is great. In order to remove this tungsten residue by etching, 50% overetching was necessary. Therefore, as shown in FIG. 6E, the thickness of tungsten in the contact plug portion is also reduced to 1500 nm to 1250 nm, and a step is generated. Further, since the film density of tungsten is low in the central portion of the contact plug,
As a result, the etching rate is increased and pits are generated.

As in the first embodiment described above, tungsten 15 is entirely deposited in the contact hole 13, the surface of the tungsten 15 is then oxidized, and heat treatment is performed in vacuum to remove only the surface oxidized portion. You can In this way, a flat tungsten surface is obtained. Then, by etching back, the tungsten residue 16 caused by the morphology of the surface of the tungsten 15 can be reduced. The amount of tungsten etched in the contact plug portion can be reduced.

In the first embodiment described above, tungsten 15 is used.
Although the method of oxidizing the surface was a heat treatment in an oxygen atmosphere, it can be easily inferred that the same effect can be obtained by a method such as oxygen plasma treatment or oxygen ion implantation.

The second embodiment will be described below with reference to FIG. 4A to 4D are cross-sectional views in order of the steps, showing the method for forming a contact plug of the present invention. First, as shown in FIG. 4A, a 1000 nm-thick oxide film 42 was deposited on a silicon substrate 41, and a contact hole 43 having a diameter of 0.5 μm at the bottom was formed by dry etching. Next, as shown in FIG. 4B, TiN / Ti was used as an adhesion barrier layer.
The film 44 was sputter deposited to a thickness of 100/20 nm. At this time, the Ti film forming condition is Ar gas pressure of 6 mTorr.
r, DC power 1 kW. TiN film formation conditions are Ar /
N ₂ gas mixture ratio 30/70%, gas pressure 6 mTorr,
It was continuously deposited with a DC power of 6 KW.

Next, as shown in FIG. 4C, tungsten 45 was deposited to a thickness of 500 nm by CVD. The film forming conditions at this time are WF ₆ having a low deposition rate and Si for the purpose of forming tungsten nuclei on the base as the first step.
Tungsten nuclei were formed by reducing action using H ₄ . The conditions at this time are as follows: Gas flow rate ratio WF ₆ / SiH ₄ = 5 /
3 SCCM, gas pressure 1.9 Torr, substrate temperature 450
It was deposited at 90 ° C. for 90 seconds. As a second step, after the completion of the first step, a tungsten film was continuously deposited by the H ₂ reduction action of WF _{6 having} a high deposition rate. The conditions at this time were as follows: gas flow rate ratio WF ₆ / H ₂ = 75/450 SCCM, gas pressure 73 Torr, substrate temperature 450 ° C. for 100 seconds.

Next, the tungsten 45 inside the contact
The entire surface of the tungsten 45 is etched back so as to leave. The etching conditions are gas flow rate ratio SF ₆ / Ar = 110.
/ 90SCCM, gas pressure 310mTorr, RF power 400W, etching end point detection time (60 seconds) +1
0% over etching was performed. With this,
As shown in (d), a tungsten residue 46 is generated.
This is due to the surface morphology after the deposition of tungsten 45, as described in detail in the first embodiment. When the tungsten residue 46 was examined by a surface inspection machine, it was detected as about 1000 particles.
When these particles were observed with an SEM, most of them had a diameter of 100 to 150 nm and a height of about 50 nm.

Next, an O ₂ flow rate of 500 S was set in the quartz tube.
Halogen lamp in CCM atmosphere, 500 ℃, 1
Heat for 0 seconds. When this tungsten residue was analyzed by an energy dispersive XMA (X-ray Micro Analyzer),
Tungsten and oxygen were detected. From this,
As shown in (e), the tungsten residue 46 is oxidized by heat treatment in an oxygen atmosphere.

Next, in a quartz tube, 1.0 × 10 ^-7 T
Halogen lamp in orr vacuum 600 ° C, 3
The heat treatment for 0 seconds removes the tungsten oxide 47, that is, the tungsten residue 46, and the contact plug of FIG. 4F can be formed. Regarding this phenomenon, as described in detail in the first embodiment, tungsten oxide 4
The vapor pressure of 7 is orders of magnitude higher than that of tungsten 45.
6 can be removed.

When examined by a surface inspection machine, about 50 particles were detected. This particle is S
When observed and analyzed by EM and XMA, it was not due to the tungsten residue 46 but due to other factors. From the cross-sectional observation of the SEM, the decrease in the thickness of tungsten 45 in the contact plug portion was as small as about 70 nm, and no depression in the center portion of the contact plug was observed.

As described above, as in the second embodiment, the tungsten 45 is entirely deposited on the contact portion, and then just etch back is performed. It is possible to remove only the tungsten residue 46 by oxidizing the tungsten residue 46 and performing heat treatment in vacuum without performing overetching.
Therefore, it is possible to form the contact plug with a small reduction amount of the thickness of the tungsten 45 in the contact plug portion.

The third embodiment will be described below with reference to FIG. 5A to 5D are cross-sectional views in order of the processes, showing the method for forming a contact plug of the present invention. First, as shown in FIG. 5A, an oxide film 52 having a thickness of 1000 nm is deposited on a silicon substrate 51, and a contact hole 53 having a bottom diameter of 0.5 μm is formed by dry etching. Next, as shown in FIG. 5B, tungsten 54 is selectively deposited by CVD.

The reason why the selective growth occurs is that the adsorption probability of the reactive gas is greatly different between the silicon or metal and the oxide film. It is considered that the difference in reactivity on these surfaces enables selective growth. Therefore,
Since the surface condition is greatly influenced, the pretreatment technique for removing the natural oxide film on silicon and controlling the oxide film surface condition (particularly the adhered condition of polymer, heavy metal element, etc.) is important.

In this embodiment, in order to remove the natural oxide film on the silicon, the gas flow rate S before the deposition of the tungsten 54 is performed.
F ₆ = 50 SCCM, gas pressure 200 mTorr, RF
It was lightly etched with a power of 150 W for 10 seconds. Continuously, SiH ₄ / WF ₆ = 5/10 SCCM, substrate temperature 3
Deposited at 50 ° C. for 3 minutes.

However, the selectivity was broken probably because of poor pretreatment conditions, and tungsten nuclei 55 were also formed on the oxide film 52 as shown in FIG. 5C. This tungsten nucleus 55
Was observed by SEM, the average size was about 50 nm. Next, O ₂ flow rate = 300 SCCM, gas pressure 300 mTorr, RF power 500 W, substrate temperature 250
Plasma treatment is performed at 30 ° C. for 30 minutes to form a tungsten oxide 56 as shown in FIG. When analyzed by XMA, tungsten 54 and oxygen were detected. It can be said that the tungsten nuclei 55 on the oxide film 52 have been oxidized by the above process. Next, the tungsten oxide 56 can be removed by heat treatment in a quartz tube in a vacuum of 1.0 × 10 ⁻⁷ Torr with a halogen lamp at 600 ° C. for 30 seconds. Therefore, the contact plug as shown in FIG. 5E can be formed.

As described above, when tungsten is selectively deposited in the contact hole by selective tungsten growth as in the third embodiment, it is very difficult to control the pretreatment for deposition to maintain the selectivity. However, by using the present invention, even if the selectivity is broken and the tungsten nuclei are formed on the oxide film, the tungsten nuclei can be removed by oxidation and heat treatment in vacuum. Therefore, it is possible to form a contact plug with a small amount of reduction in tungsten thickness of the contact plug portion.

In the third embodiment, the oxygen plasma treatment step is used in the step of oxidizing tungsten, but the heat treatment step in the oxygen atmosphere described in the first and second embodiments may be used.

[0037]

As described above, according to the present invention, a tungsten etching residue can be reduced when performing etch back after depositing tungsten on the entire contact surface. In addition, the generated tungsten residue can be removed without performing additional etching. Therefore, a step due to the decrease in the tungsten thickness of the contact plug portion does not occur, and it is possible to form a contact plug having no depression in the center portion of the plug and having excellent flatness. Alternatively, the selectivity is broken when the selective tungsten is formed on the contact portion,
Even if the tungsten nuclei are formed in areas other than the contact portion, they can be removed without etching. Therefore, the control of the pretreatment conditions prior to the formation of the selective tungsten is simplified, and the selective tungsten technique, which is advantageous for filling finer contacts, can be put into practical use.

[Brief description of drawings]

1A to 1C are cross-sectional views in order of the steps, showing a contact plug forming method according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a result of X-ray diffraction structural analysis in the first embodiment of the present invention.

FIG. 3 is a diagram showing a result of analysis in the depth direction by Auger electron spectroscopy according to the first embodiment of the present invention.

4A to 4C are cross-sectional views in order of the steps, showing a contact plug forming method according to a second embodiment of the present invention.

5A to 5C are cross-sectional views in order of the steps, showing a contact plug forming method according to a third embodiment of the present invention.

FIG. 6 is a sectional view for explaining a conventional contact plug forming method.

FIG. 7 is a sectional view for explaining a conventional contact plug forming method.

[Explanation of symbols]

 1 Silicon Substrate 2 Oxide Film 3 Contact Hole 4 Adhesion Barrier Layer 5 Tungsten 6 Tungsten Residue 7 Tungsten Nucleus 11 Silicon Substrate 12 Oxide Film 13 Contact Hole 14 TiN / Ti Film 15 Tungsten 16 Tungsten Oxide Film 41 Silicon Substrate 42 Oxide Film 43 Contact Hole 44 TiN / Ti film 45 Tungsten 46 Tungsten residue 47 Tungsten oxide film 51 Silicon substrate 52 Oxide film 53 Contact hole 54 Tungsten 55 Tungsten nucleus 56 Tungsten oxide film

Claims (3)

[Claims] 1. A step of entirely depositing tungsten on a base substrate having a contact hole, a step of oxidizing the surface of the tungsten and a heat treatment in a vacuum to remove the oxide layer of tungsten, and thereafter. A method of forming a contact plug, comprising the step of etching the entire surface of the tungsten. 2. A step of entirely depositing tungsten on a base substrate having a contact hole, a step of etching the entire surface of the tungsten, followed by oxidizing an etching residue of the tungsten, and then performing a heat treatment in a vacuum to perform the etching. A method for forming a contact plug, comprising a step of removing a residue. 3. A step of selectively depositing tungsten only on the contact holes on a base substrate having the contact holes,
A method for forming a contact plug, comprising the step of oxidizing the tungsten deposited in a portion other than the contact hole and then removing the tungsten by heat treatment in a vacuum.