JPH0832066A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To provide a manufacturing method of semiconductor device capable of avoiding abnormal oxidation of a tungsten silicide (WSi) without previously forming an SiO2 film on the surface of a WSi layer as well as improving the flatness of a semiconductor device and the throughput of the semiconductor device manufacture. CONSTITUTION:A polycide layer 23 comprising a polycrystalline silicon layer 2 and a tungsten silicide layer 3 is formed on a semiconductor substrate 1 and after etching away the polycide layer 23 in a specific pattern using a resist pattern 5, the first thermal oxidation process is performed on the semiconductor substrate 1 in the step (d). Next, after the formation of a side wall 7, the second thermal oxidation process is performed in the step (g) and the nitrogen diluted oxygen atmosphere (O2 concentration 10%).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor device using a polycide gate.

[0002]

2. Description of the Related Art When manufacturing a semiconductor device, a process of removing an insulating film such as a silicon oxide film and a thermal oxidation process are performed a plurality of times. Speaking of thermal oxidation treatment, for example, in the case of forming a MOS transistor having a polycide structure, heat treatment for crystallizing a metal silicide layer, polycide gate
Heat treatment for forming a protective oxide film on the oxide layer, heat treatment for forming a buffer oxide film for ion implantation into the diffusion layer, heat treatment for activating implanted impurities, and recovery of implantation damage. The semiconductor device is subjected to a plurality of heat treatments such as the above heat treatment. At that time, film peeling or step breakage may occur in the metal silicide layer, or the metal silicide layer may be abnormally oxidized. The film peeling occurs due to the change in the film stress during the heat treatment, and the step breakage similarly occurs due to the generation of cracks at the step portion due to the change in the film stress. Also, abnormal oxidation occurs as follows.

For example, when the metal silicide layer is a tungsten silicide layer (WSix: x> 2), WSi
When x is once thermally oxidized, WSix + (x-2) O ₂ → WSi ₂ + (x-2) Si
By the reaction represented by the reaction formula of O ₂ , WSix is crystallized and has the stoichiometry of WSi ₂ , forming grains. On the other hand, excess silicon in WSix is oxidized to silicon oxide (SiO ₂ ), which is WSi ₂
Cover the surface of the grain layer. Next, the LD of the transistor
After the first ion implantation for forming a D (Lightly Doped Drain) structure is performed, an insulating film (SiO ₂ film) is formed and then anisotropic etching is performed to form a spacer structure (sidewall). However, at this time, the SiO ₂ film covering the surface of the tungsten silicide layer becomes considerably thin due to anisotropic etching, and the next thermal oxidation treatment step (in the second thermal oxidation treatment step,
In the step of forming an insulating film on the diffusion layer of the transistor), it is difficult to suppress the diffusion supply of oxygen to the tungsten silicide layer. In this state, when the second thermal oxidation treatment is performed, oxygen 32 diffusing in the SiO ₂ film 31 on the surface of the tungsten silicide layer and the lower portion of the tungsten silicide layer as shown in FIG. When the supply balance from the polycrystalline silicon layer on the side with the silicon 35 diffusing the grain boundary of the WSi ₂ grain 34 is maintained, the interface between the tungsten silicide layer and the SiO ₂ film 31 thereabove. In the vicinity, only the reaction represented by the reaction formula of (normal oxidation) Si + O ₂ → SiO ₂ proceeds. On the other hand, when the supply balance is lost and the supply of oxygen 32 becomes excessive, as shown in FIG.
The substance itself is oxidized, and an abnormal oxidation reaction shown by the following formula occurs. (Abnormal oxidation) WSi ₂ + (7/2) O ₂ → WO ₃ + 2S
iO _{2 If an} abnormal oxidation reaction occurs as shown in the above formula, WO ₃
(Tungsten oxide) 36 is generated. Once the abnormal oxidation occurs, the resistance increases due to the destruction of the WSi ₂ grains 34, the volume expansion due to the generation of WO ₃ (tungsten oxide) 36, and the film peeling and the wire breakage occur. In FIG. 3, reference numeral 33 indicates SiO ₂ molecules.

In order to avoid these phenomena, a silicon oxide film, a silicon nitride film, or PSG is previously formed on the surface of the metal silicide layer constituting the upper side of the polycide layer.
(Phospho Silicate Glass) film or other insulating cap layer is formed on the semiconductor device.
No. 71) has been proposed. In this case, if the insulating cap layer is formed in advance before the thermal oxidation treatment, the insulating cap layer controls and suppresses the diffusion and supply of oxygen, so that the normal oxidation can be performed without disturbing the supply balance of silicon and oxygen. Can be performed.

Next, as an example of manufacturing a semiconductor device based on the method of manufacturing a semiconductor device disclosed in the above publication based on FIG. 4, in the case of forming a gate electrode of a MOS transistor with a polycide structure Each step will be briefly described. FIG. 4 is a schematic cross-sectional view showing the above steps in order.

Step (a): A 2000 Å polycrystalline silicon layer 2 is formed on the gate oxide film 8 formed on the semiconductor substrate 1 by a low pressure CVD apparatus using SiH ₄ gas (for example, SiH ₄ : 250 sccm, N ₂ : 500 s
It is formed under the conditions of a temperature of 620 ° C. and a pressure of 0.3 Torr by supplying a mixed gas of ccm ratio). Next, using a cold wall type low pressure CVD apparatus, a tungsten silicide layer 3 of 2000 Å is formed by using a mixed gas of WF ₆ and SiH _4.
(For example, WF ₆ : 1.6 sccm, SiH
Supplying mixed gas of ₄ : 300sccm, temperature 3
(Formed under the conditions of 80 ° C. and a pressure of 200 mTorr), the polycide layer 23 is formed. After that, the SiO ₂ cap film 4 serving as an insulating cap layer is SiH
After forming a SiO ₂ cap film 4 as an insulating cap layer using a mixed gas of N ₄ and N ₂ O (for example, plasma C
With VD _{apparatus, SiH 4: 6sccm, N 2} O: 4s
After supplying a mixed gas of ccm ratio and forming it at a temperature of 400 ° C. and a pressure of 2.2 Torr), a resist pattern 5 for forming a gate electrode is formed on the SiO ₂ cap film 4 by a photolithography technique. Form.

Step (b): The SiO ₂ cap film 4 is RI
Etching is performed using CF ₄ gas by E (Reactive Ion Etching), and then the tungsten silicide layer 3 and the polycrystalline silicon layer 2 are etched by RIE using a mixed gas of Cl ₂ and O ₂ .

Step (c): Resist pattern no longer needed
The ash 5 is ashed with O ₂ plasma.

Step (d): 900 ° C. in oxygen atmosphere, 6
The tungsten silicide layer 3 was subjected to a thermal oxidation process for 0 minutes.
Is crystallized and the buffer oxide film 12 for ion implantation is formed in the diffusion layer 14, and then ion implantation for forming the LDD structure is performed. At this time, the SiO ₂ cap film 4 is formed on the tungsten silicide layer 3 as the SiO ₂ film 11 grown by the thermal oxidation process.

Step (e): To form a sidewall, a 2500 Å SiO ₂ film 6 is formed on the silicon substrate 1 using a mixed gas of SiH ₄ and N ₂ O (for example, SiH ₄ : 65 sccm). , N ₂ O: 3250 scc
m mixed gas is supplied, the temperature is 850 ° C., and the pressure is 0.1.
It is formed by the low pressure CVD method under the condition of 35 mTorr).

Step (f): The SiO ₂ film 6 is etched by anisotropic dry etching using a mixed gas of CF ₄ and CHF ₃ , etc. to form side walls 7. At this time, the SiO ₂ film left on the tungsten silicide layer 3 is denoted by reference numeral 13.

Step (g): Oxygen atmosphere (O ₂ concentration 100
%), Subjected to thermal oxidation treatment at 1050 ° C. for 30 minutes,
The O ₂ film 9 is formed.

[0013]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
In the case of manufacturing a semiconductor device based on the method of manufacturing a semiconductor device disclosed in the publication No. 1, there are the following problems. First, as shown in step (a), a step of forming the SiO ₂ cap film 4 as an insulating cap layer in advance is required. In addition, as shown in step (b), S
Since it is necessary to use a fluorine-based gas for etching the iO ₂ cap film 4 and a chlorine-based gas for etching the polycide layer 23, the SiO ₂ cap film 4 and the polycide layer 23 are etched into a predetermined pattern. In order to do so, first, the upper SiO ₂ cap film 4 must be etched, and then the polycide layer 23 must be etched by switching the supply gas species, and a two-step etching process is indispensable. This method has a problem that the semiconductor manufacturing speed becomes slow (throughput becomes low) because both the process time and the number of processes increase.

Furthermore, the insulating film (SiO ₂ film) formed on the tungsten silicide layer 3 is thinned in the insulating film removing process in the semiconductor manufacturing process, and when it becomes thin to a certain extent, it is abnormally oxidized in the thermal oxidation process. For example, when the thickness of the SiO ₂ film 13 in the step (f) is smaller than a predetermined value, an abnormal oxidation reaction occurs in the tungsten silicide layer 3 by the thermal oxidation process in the step (g). Since there is a possibility, the SiO ₂ cap film 4 must first be formed to be quite thick. Therefore, the height of the gate electrode becomes high, and the flatness of the semiconductor device is impaired.

The present invention has been made in view of the above problems, and it is possible to prevent abnormal oxidation of the metal silicide layer without forming an insulating cap layer such as a SiO ₂ film on the metal silicide layer. It is an object of the present invention to provide a semiconductor device manufacturing method capable of improving the flatness of the semiconductor device and the throughput of manufacturing the semiconductor device, as compared with the semiconductor device manufacturing method described above.

[0016]

In order to achieve the above-mentioned object, a method of manufacturing a semiconductor device according to the present invention is a method of manufacturing a semiconductor device using a polycide gate, wherein the polycide gate that has been heat treated once is used. On the other hand, it is characterized in that the second and subsequent heat treatments are performed in an O ₂ atmosphere containing 10% or more of N ₂ .

[0017]

The operation will be described with reference to FIGS. 2 and 3. FIG.
FIG. 3A is a schematic diagram showing the state of the interface between the metal silicide layer and the SiO ₂ film when the oxidation reaction is proceeding normally, and FIG. 3B is the abnormal oxidation reaction proceeding. FIG. 6 is a schematic diagram showing a state of an interface between a metal silicide layer and a SiO ₂ film in a case. Hereinafter, a case where the metal silicide layer is a tungsten silicide (WSi) layer will be described.

The WSi layer formed as a metal silicide layer on the semiconductor substrate is usually in an amorphous state immediately after formation, but once heat-treated, it has a tetragonal structure WSi ₂
Become a crystal. When the thermal oxidation process is performed in the subsequent process, the oxidation reaction proceeds at the WSi ₂ —SiO ₂ film 31 interface in the WSi surface layer portion, but the silicon 35 diffused from the polycrystalline silicon layer (not shown) is used. And the supply of oxygen 32 diffused in the surface SiO ₂ film 31 from the atmosphere maintain the reaction. However, when the SiO ₂ film 31 on the surface of the WSi layer is not present or is very thin, the silicon 35 from the polycrystalline silicon layer (not shown) is formed.
The supply of oxygen 32 is relatively excessive compared to the supply of
The oxygen 32 that has lost the reaction partner is bonded to W of WSi ₂ to generate WO ₃ (tungsten oxide 36), and WSi is abnormally oxidized.

In the actual LSI process, after the tungsten polycide gate is formed, an oxidization process is performed, a process such as ion implantation and an etching of the SiO ₂ film on WSi are performed, and the heat treatment is performed again. At this point, the abnormal oxidation often occurs.

In the prior art, a SiO ₂ cap film having a certain thickness is formed in advance as an insulating cap layer on the WSi layer, and the oxide film controls the supply of oxygen 32 to suppress abnormal oxidation. . The present invention realizes the rate control of the supply of oxygen 32 by not devising the SiO ₂ cap film but by devising the heat treatment atmosphere for the second and subsequent heat treatments for the tungsten polycide gate. That is, the heat treatment atmosphere for the second and subsequent times is 10
By using an oxygen atmosphere diluted with N ₂ instead of using 0% oxygen, the supply of the oxygen 32 is rate-controlled and the supply of the oxygen 32 and the silicon 35 is balanced to suppress the occurrence of abnormal oxidation reaction. There is.

FIG. 2 is a graph showing the SiO ₂ film thickness formed on the WSi layer and the ratio of abnormal oxidation caused by the subsequent thermal oxidation treatment (thermal oxidation treatment at 1050 ° C. for 30 minutes). The SiO ₂ film thickness is plotted along the abscissa and the abnormal oxidation rate is plotted along the ordinate. The graphs marked with ○ indicate the case where the atmosphere was 100% oxygen, and the graph marked with ● represents the nitrogen diluted oxygen concentration 10
% Shows the case of performing in an atmosphere.

As can be seen from FIG. 2, the Si on the WSi layer is
The occurrence rate of abnormal oxidation increases as the O ₂ film thickness decreases. This in SiO ₂ film thickness decreases, the oxygen 32 to reach the SiO ₂ film -WSi surface by diffusing SiO ₂ film
This is because the amount of is rapidly increased. It should be noted here that abnormal oxidation occurs even when the SiO ₂ film on the WSi layer is thinned by using an N ₂ diluted oxygen atmosphere of 10% concentration rather than using an oxygen atmosphere of 100% concentration. It is difficult. In the case of the conventional semiconductor device manufacturing method, the graph of FIG.
iO ₂ film thickness is required about 100nm, in advance SiO ₂
It indicates that the cap film must be formed. However, in the case of the method for manufacturing a semiconductor device according to the present invention, an abnormal oxidation reaction hardly occurs even if the SiO ₂ film thickness on the WSi layer is 50 nm, and the semiconductor device can be formed without forming the SiO ₂ cap film in advance. It is shown that the abnormal oxidation reaction can be sufficiently suppressed by the film thickness of the SiO ₂ film formed on the WSi layer in each heat treatment step. That is, if the method for manufacturing a semiconductor device according to the present invention is used, W
It is possible to prevent abnormal oxidation of the WSi layer without forming a SiO ₂ cap film as an insulating cap layer on the Si layer.

[0023]

EXAMPLES AND COMPARATIVE EXAMPLES Examples of a semiconductor device manufacturing method according to the present invention will be described below with reference to the drawings. FIG. 1 is a schematic cross-sectional view sequentially showing each step in the case of forming a gate electrode of a MOS transistor using the method for manufacturing a semiconductor device according to the embodiment.

Step (a): SiH ₄ , N is formed on the gate oxide film 8 formed on the semiconductor substrate 1 by a low pressure CVD apparatus.
2000Å polycrystalline silicon layer 2 using ₂ mixed gas
(For example, SiH ₄ : 250 sccm, N
₂ : The mixed gas of 500 sccm was supplied, and the temperature was 6
It is formed under the conditions of 20 ° C. and a pressure of 0.3 Torr). Next, using a cold wall type low pressure CVD apparatus, WF ₆ ,
A 2000 Å tungsten silicide (WSi) layer 3 is formed using a mixed gas of SiH ₄ (for example, WF
A mixed gas having a ratio of ₆ : 1.6 sccm and SiH ₄ : 300 sccm is supplied, and the temperature is 620 ° C. and the pressure is 0.3 Tor.
formed under the condition of r). After that, a resist pattern 5 for forming a gate electrode is formed by a photolithography technique.

Step (b): The polycide layer 23 composed of the WSi layer 3 and the polycrystalline silicon layer 2 is etched by RIE using a mixed gas of Cl ₂ and O ₂ .

Step (c): Unused resist pattern
The ash 5 is ashed with O ₂ plasma.

Step (d): The WSi layer 3 is crystallized by performing thermal oxidation treatment at 900 ° C. for 60 minutes, and the diffusion layer 14 is formed.
After forming the buffer oxide film 12 for ion implantation on the top, ion implantation for forming an LDD structure is performed. At this time, SiO ₂ is formed on the WSi layer 3 by the thermal oxidation process.
The film 15 is formed.

Step (e): To form a sidewall, a 2500 Å SiO ₂ film 6 is formed on the semiconductor substrate 1 using SiH ₄ gas and N ₂ O gas (for example, Si
A mixed gas of H ₄ : 65 sccm and N ₂ O: 3250 sccm was supplied, and the temperature was 850 ° C. and the pressure was 0.35 mT.
It is formed by the low pressure CVD method under the condition of orr).

Step (f): anisotropic etching such as CF
_The SiO ₂ film 6 is etched by anisotropic dry etching using a mixed gas of ₄ and CHF ₃ to form sidewalls 7. At this time, the SiO ₂ film left on the WSi layer 3 without being removed by the etching is set to 16.

Step (g): Oxygen atmosphere diluted with nitrogen (O ₂
At a concentration of 10%), thermal oxidation treatment is performed at 1050 ° C. for 30 minutes to form the SiO ₂ film 9 on the diffusion layer 14.

As described above, in the method of manufacturing the semiconductor device according to the embodiment, the SiO ₂ cap film 4 is formed in the step (a) as compared with the conventional method of manufacturing the semiconductor device shown in FIG. The step can be omitted, and the step of etching the SiO ₂ cap film 4 in the step (b) can also be omitted. In the step (d) of FIG. 1, a SiO ₂ film 1 of about 1000 Å is formed on the surface of the WSi layer 3.
5 is formed, the SiO ₂ film 15 is a SiO ₂ film 16 having a thickness of about 400 Å in the step (f). In this state, in step (g), the thermal oxidation treatment was performed under the above-mentioned conditions, and then the cross section was observed by SEM, but no abnormal oxidation of the WSi layer 3 was observed.

<Comparative Example> With respect to two kinds of samples of which the film thickness of the SiO ₂ cap film 4 is about 500 Å (sample a) and about 1000 Å (sample b), polycide film is formed according to the process shown in FIG. MOS having a gate electrode
A transistor was manufactured. In the process of FIG. 4D, W
The film thickness of the SiO ₂ film 11 on the upper surface of the Si layer 3 was about 1080 Å in the sample a and about 1330 Å in the sample b, but in the step of FIG.
The thickness of the SiO ₂ film 13 on the upper surface is 490Å in the sample a.
And about 740 Å in sample b. The thermal oxidation treatment in the step of FIG. 4 (g) in this state O _2: 100
%, No abnormal oxidation occurred in sample b, but abnormal oxidation occurred in sample a.

In the case of the conventional semiconductor manufacturing method as described above, as shown in the comparative example and the graph of FIG.
In order to prevent the occurrence of abnormal oxidation reaction, it is necessary to form a SiO ₂ cap film 4 of about 1000 Å (100 nm) as an insulating cap layer on the upper surface of the WSi layer 3, while manufacturing the semiconductor device according to the embodiment. In the case of the method, SiO
₂ It is possible to prevent the abnormal oxidation reaction from occurring without forming an insulating cap layer such as the cap film 4. Further, since it is not necessary to form the insulating cap layer, the height of the gate electrode can be suppressed accordingly, and the flatness of the semiconductor device can be improved (FIGS. 1G and 4G). )reference).

[0034]

As described above in detail, in the method of manufacturing a semiconductor device according to the present invention, SiO ₂ for preventing abnormal oxidation is used.
CVD of insulating cap layer such as cap film before thermal oxidation
Abnormal oxidation can be prevented without forming it on the upper surface of the metal silicide layer by the method. Further, since it is not necessary to form the insulating cap layer, the forming step can be omitted. Therefore, the etching step of the insulating cap layer when forming the electrode pattern can also be omitted. Compared with the method of manufacturing a semiconductor device, the throughput of manufacturing a semiconductor device can be improved. Further, since it is not necessary to form the insulating cap layer, the height of the element can be suppressed and the flatness of the semiconductor device can be improved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view schematically showing each step in the order of manufacturing a semiconductor device using a method for manufacturing a semiconductor device according to an embodiment of the present invention.

FIG. 2 is a graph showing a thickness of a SiO ₂ film formed on a tungsten silicide (WSi) layer and a ratio of occurrence of abnormal oxidation.

FIG. 3A is a cross-sectional view schematically showing a state near an interface between a tungsten silicide (WSi) layer and a SiO ₂ film when a normal oxidation reaction is in progress. (B)
Is the WSi layer and SiO when the abnormal oxidation reaction is in progress.
FIG. 3 is a cross-sectional view schematically showing a state near the interface with the _two films.

FIG. 4 is a cross-sectional view schematically showing steps in the case of manufacturing a semiconductor device by a conventional method of manufacturing a semiconductor device, in order.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semiconductor substrate 2 Polycrystalline silicon layer 3 Tungsten silicide (WSi) layer 23 Polycide layer

Claims (1)

[Claims] 1. A method of manufacturing a semiconductor device using a polycide gate, wherein the _second and subsequent heat treatments are performed in an O ₂ atmosphere containing 10% or more of N ₂ with respect to the polycide gate that has been heat-treated once. A method of manufacturing a semiconductor device, which comprises: