JP3129251B2 - Contact plug formation method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a method of forming a contact plug, and more particularly, to a method of forming a chemical vapor deposition (CV).
D; Chemical Vapor Depositi
The present invention relates to a contact plug forming method for forming a contact plug in a semiconductor device such as an LSI by using the (on) method.

[0002]

2. Description of the Related Art In recent years, high integration of semiconductor devices such as LSIs has been advanced, and along with this, elements have been miniaturized, and the size (contact size) of contact plugs has also been reduced. I have. On the other hand, the thickness of the interlayer insulating film depends on the complexity of the structure of the capacitor formed on the silicon (Si) substrate and the CMP (Chemical and Mechanical Polishing).
On the other hand, the interlayer insulating film tends to be thicker by flattening the interlayer insulating film by the method g) or the like. For this reason, the aspect ratio representing the ratio of the contact size (horizontal dimension) to the contact hole depth (vertical dimension) is, for example, a memory capacity of 4 Mbit.
DRAM has only about two, but the memory capacity is 2
In the case of a 56 Mbit DRAM, the number is 4 or more. When the aspect ratio increases in this manner, a technique for forming a contact plug by filling a contact hole with good step coverage (step coverage) is required.

As a method for meeting this demand, a method of forming a contact plug by forming a tungsten (W) film on the entire surface of a silicon substrate by a CVD method having excellent step coverage is widely used. As an alternative to this method, a method of forming a contact plug by forming an aluminum (Al) film or a copper (Cu) film having a lower specific resistance than the W film by a CVD method has been studied in recent years. As described above, when a W film, an Al film or a Cu film is formed on the entire surface of a silicon substrate by a CVD method and a contact plug is formed, usually, a silicon oxide (Si
In order to improve the adhesion to the O ₂ ) film and to prevent junction breakdown due to mutual diffusion caused by a reaction between a silicon substrate and a source gas used in a CVD method for forming a contact plug, a barrier metal is used as a base. (Barrier metal)
It is necessary to form a film.

Hereinafter, a conventional method for forming a contact plug will be described with reference to FIG. First, after an interlayer insulating film 2 is formed on a silicon substrate 1, a contact hole 3 is formed through steps of resist coating, exposure, dry etching, and resist peeling. Next, in order to reduce the contact resistance, a titanium (Ti) silicide film 4 is formed.
Is formed in the contact hole 3 by the CVD method,
Tungsten hexafluoride (WF) which is a raw material gas for W film formation
₆ ) As a barrier metal film, titanium nitride (Ti)
N) The film 5 is formed. Conventionally, a sputtering method has been widely used as a method for forming the TiN film 5. However, as the aspect ratio has increased, the sputtering method with poor step coverage cannot be used.
The use of the VD method has been studied. Next, a W film is formed on the entire surface of the silicon substrate 1 by the CVD method, the contact hole 3 is buried to form a contact plug 7, and then the W film other than the contact plug 7 is removed by etching (etch back). Then, the Ti film 8, the TiN film 9, the AlCu film 10, and the TiN
After the films 11 are sequentially formed, a wiring pattern is formed by photolithography and etching.

By the way, even if the contact size is reduced, the thickness of the TiN film 5 required as a barrier metal film does not change, so that the ratio of the W film 6 to the volume of the contact plug 7 is reduced as shown in FIG. It tends to decrease as the contact size decreases. In FIG. 4, the thickness of the interlayer insulating film 2 is 2.0 μm, and the curves a to
d is the case where the thickness of the TiN film 5 as the barrier metal film is 50 nm, 100 nm, 300 nm and 500 nm, respectively. For example, the thickness of the TiN film 5 is 100 nm (curve b).
In the case of the contact plug 7 having a contact size of 0.2 μm or less, the contact hole 3 is formed by the TiN film 5.
Is completely embedded. When the thickness of the TiN film 5 is 50 nm (curve a), the contact size is 0.2
In the contact plug 7 of μm, 70% or more of the contact plug 7 is occupied by the TiN film, and the contact size is 0.1%.
In the μm contact plug 7, the contact hole 3 is completely buried by the TiN film 5. Such a problem occurs irrespective of the film material such as W, Al, or Cu, except for the technique of forming the contact plug 7 using the selective CVD method.

Therefore, as the contact size is reduced, for example, K. Ohto, K. Urabe, T. Taguwa, S.
Chikaki, T. Kikkawa, International Electron Device
s Meeting Technical Digest 1996, IEEE, pp. 361-364
In recent years, a method of forming a contact plug using a TiN film conventionally used as a barrier metal film has been studied. As a typical method of forming a TiN film using a CVD method, a low pressure (LP) CVD (Low Pressure CVD) method using titanium tetrachloride (TiCl ₄ ) and ammonia (NH ₃ ) as a source gas has been widely studied. ing. The TiN film formed using this method is:
Even with a contact plug having an aspect ratio of 5, step coverage close to 100% can be obtained.

[0007]

The above-mentioned T
In a conventional method of forming a contact plug using an iN film, the residual chlorine (C
In order to remove 1) and reduce the specific resistance, the temperature at the time of film formation needs to be 600 ° C. or higher, and the film stress (tensile stress) is as high as about 2 × 10 ¹⁰ dyne / cm ² . Nevertheless, after the formation of the TiN film, the silicon substrate is once cooled and taken out of the CVD apparatus, and post-processing such as etch-back is performed by an etching apparatus or another apparatus.

For this reason, when a thick TiN film is formed in order to form a contact plug having a large contact size, when the silicon substrate is cooled for post-processing such as etch-back, heat shrinkage occurs at that time. , FIG.
As shown in (a), the surface of the TiN film 5 is cracked or the TiN film 5 is peeled off. In particular, T
When a crack is formed on the surface of the iN film 5 and the TiN film 5 is etched back, the pattern of the crack is transferred to the interlayer insulating film 2 as shown in FIG. As a result, there is a possibility that the interlayer insulating film 2 may be cracked. Therefore, there is a disadvantage that a contact plug having a large contact size cannot be formed.

The present invention has been made in view of the above circumstances, and when a contact plug is formed by a TiN film, a contact plug having a large contact size is prevented without cracking or peeling of the film surface. An object of the present invention is to provide a method and apparatus for forming a contact plug that can be formed.

According to a first aspect of the present invention, there is provided a method for forming a contact plug, comprising: a first step of forming an insulating film on a silicon substrate; A second step of forming a hole, a third step of forming a titanium nitride film on the entire surface so as to completely fill the contact hole at a predetermined temperature by using a plasma CVD method, and a step subsequent to the third step. A fourth step of plasma etching the titanium nitride film until the insulating film is exposed while maintaining the predetermined temperature, and a fifth step of annealing the silicon substrate after the fourth step is completed. And the third to fifth steps are performed in the same housing.

According to a second aspect of the present invention, there is provided the contact plug forming method according to the first aspect, wherein a titanium silicide film is formed on a surface of the silicon substrate exposed to the contact hole before the third step. It has a sixth step of forming.

According to a third aspect of the present invention, there is provided the contact plug forming method according to the first or second aspect, wherein in the third step, the titanium nitride film is formed by a CVD method using titanium tetrachloride and ammonia as a source gas. In the fourth step, the titanium nitride film is removed by a plasma etching method using a gas containing chlorine or fluorine as an etching gas.

According to a fourth aspect of the present invention, there is provided the contact plug forming method according to the third aspect, wherein in the third and fourth steps, together with the raw material gas or the etching gas,
It is characterized in that a rare gas is also used.

According to a fifth aspect of the present invention, there is provided the contact plug forming method according to the third or fourth aspect, wherein the etching gas is chlorine, boron trichloride, sulfur hexafluoride, ethane hexafluoride, nitrogen trifluoride. Or methane tetrafluoride, or a mixture of any two or more of these.

[0015]

[0016]

[0017]

[0018]

According to the structure of the present invention, the formation of the titanium nitride film, the etch-back of the titanium nitride film, and the annealing process are continuously performed in the same housing, so that the film surface may be cracked or the film may be peeled off. Instead, a contact plug having a large contact size can be formed of a titanium nitride film.

[0019]

Embodiments of the present invention will be described below with reference to the drawings. The description will be made specifically using an embodiment. FIG. 1 is a process chart showing a contact plug forming method according to one embodiment of the present invention. Hereinafter, the manufacturing process will be described step by step. First, a 1.0 μm-thick interlayer insulating film 22 is formed on a silicon substrate 21, a resist is applied, and a resist pattern of a contact hole is formed by exposure. Next, after forming a contact hole 23 on the diffusion layer region of the silicon substrate 21 by dry etching, the resist is removed (FIG. 1).
(A)). Next, in order to reduce the contact resistance, a Ti silicide film 24 is formed in the contact hole 23 by a CVD method (see FIG. 1B).

Next, a contact plug is formed using the contact plug forming apparatus shown in FIG. The contact plug forming apparatus shown in FIG. 2 is constituted by a CVD apparatus having a parallel plate type plasma generating source 41. First, a silicon substrate that has undergone the process shown in FIG. 1A is placed as a target 44 on a susceptor 43 installed inside a housing 42 of a contact plug forming apparatus, and then decompression means such as a vacuum pump (not shown). ), The pressure inside the housing 42 is reduced to 20 Torr, and the target 44 is indirectly heated to 650 ° C. by heating the susceptor 43 with the heater 45 provided inside the susceptor 43.

In this state, as a source gas, 40 sccm
(Standard cubic centimeter per minute) TiCl
₄ and 60 sccm NH ₃ as a rare gas, 3000 sccm
Of N _2, respectively mass flow controllers (MFC, MFC; Mass Flow Controller) after the mass flow rate controlled by 46a and MFC46b, by ejecting like a shower in the housing 42 by the shower head 47, the target 44 over the entire surface Then, a 300 nm-thick TiN film 25 is formed, and the contact holes 23 are buried to form contact plugs 26.

Next, a target 44 is set inside the housing 42.
After the pressure inside the housing 42 was reduced to 5 Torr while maintaining the temperature of 650 ° C., 10
0 sccm of Cl ₂ , 100 sccm of He as a noble gas,
The mass flow rate is controlled by the MFC 46c and the MFC 46b, respectively, and the shower head 47 squirts the shower 42 into the housing 42. Then, when the gas pressure is stabilized, the power is turned on to the plasma generation source 41 and the susceptor 43 is turned on.
A high frequency power is applied between the power supply and the shower head 47 to generate plasma in the housing 42 and raise the high frequency (RF) power to 500 W, thereby etching back the TiN film 25 other than the contact plug 26. .

Next, after reducing the pressure inside the housing 42 to 20 Torr, the mass flow rate of 3000 sccm of NH ₃ is controlled by the MFC 46b, and the shower head 47 controls the mass flow rate.
The target 44 is anneal-treated to desorb chlorine (Cl) in the contact plug 26 by squirting it into a shower-like shape and adjusting the temperature of the susceptor 43 by a heater 45 provided inside the susceptor 43. After that, the target 44 is taken out of the housing 42 of the contact plug forming device (see FIG. 1B). Next, FIG.
As shown in (c), the Ti film 27,
After sequentially forming the TiN film 28, the AlCu film 29, and the TiN film 30, a wiring pattern is formed by photolithography and etching.

As described above, according to the configuration of this example, Ti
Excess Ti on the interlayer insulating film 22 at the same temperature in the housing 42 in which the N film 25 is formed and the contact plug 26 is formed.
Since the N film 25 is etched back, T
No cracking or peeling of the iN film 25 occurs. Therefore,
Since the TiN film 25 having a large thickness can be formed, the contact plug 26 having a large contact size can be formed of TiN. Further, since the annealing process is performed in the housing 42 after the above-described etch back, the Cl
Is easily removed, the etching gas residue adsorbed on the surface of the interlayer insulating film 22, the etching gas and by-products remaining in the housing 42 are removed, and a wiring pattern formed of a metal film formed after the annealing process. And the residue can be prevented from reacting. Thus, the specific resistance of the contact plug 26 formed of TiN can be reduced.

Further, the excess TiN film existing on the susceptor 43 at the time of the etch back is removed, and
Since the inside is cleaned, periodic cleaning inside the housing 42 is not required, and the atmosphere inside the housing 42 is always kept constant. Thereby, variation in characteristics of the target 44 can be suppressed, and the throughput is improved.

The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and changes in the design and the like may be made without departing from the gist of the present invention. Even if there is, it is included in the present invention. For example, in the above-described embodiment, an example in which Cl ₂ is used as an etching gas is described. However, the present invention is not limited to this. Instead, a Cl-based gas such as boron trichloride (BCl ₃ ), Sulfur (SF ₆ ), ethane hexafluoride (C ₂ F ₆ ) and oxygen (O ₂ ), or fluorine (F) based gas such as nitrogen trifluoride (NF ₃ ) or methane tetrafluoride (CF ₄ ) Alternatively, a mixed gas of these may be used.

[0027]

As described above, according to the structure of the present invention, the formation of the titanium nitride film, the etch-back of the titanium nitride film and the annealing process are successively performed in the same housing, whereby the contact plug is formed. Therefore, a contact plug having a large contact size can be formed without cracking or peeling of the film surface, and the specific resistance of the contact plug can be suppressed low.

[Brief description of the drawings]

FIG. 1 is a process chart showing a contact plug forming method according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing a configuration of a contact plug forming apparatus according to one embodiment of the present invention.

FIG. 3 is a cross-sectional view illustrating a configuration example of a semiconductor device manufactured by a conventional contact plug forming method.

FIG. 4 is a view for explaining disadvantages of a conventional contact plug forming method.

FIG. 5 is a diagram for explaining disadvantages of a conventional contact plug forming method.

[Explanation of symbols]

 1,21 silicon substrate 2,22 interlayer insulating film 3,23 contact hole 4,24 Ti silicide film 5,9,11,25,28,30 TiN film 6 W film 7,26 contact plug 8,27 Ti film 10, 29 AlCu film 41 Plasma source 42 Case 43 Susceptor 44 Target 45 Heater 46a-46c MFC 47 Shower head

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 21/28-21/288 H01L 21/44-21/445 H01L 29/40-29/43 H01L 29 / 47 H01L 29/872 H01L 29/3205 H01L 21/321-21/3213 H01L 21/768

Claims (5)

(57) [Claims] 1. A first method for forming an insulating film on a silicon substrate.
A second step of forming a contact hole at a desired position in the insulating film; and a second step of forming a titanium nitride film on the entire surface so as to completely fill the contact hole at a predetermined temperature using a plasma CVD method. A third step of plasma-etching the titanium nitride film until the insulating film is exposed while maintaining the predetermined temperature following the third step; and the fourth step is completed. And a fifth step of annealing the silicon substrate after performing the third step, wherein the third to fifth steps are performed in the same housing. 2. The contact plug according to claim 1, further comprising a sixth step of forming a titanium silicide film on a surface of the silicon substrate exposed to the contact hole before the third step. Forming method. 3. In the third step, the titanium nitride film is formed by a CVD method using titanium tetrachloride and ammonia as source gases, and in the fourth step, chlorine or fluorine is used as an etching gas. 3. The method according to claim 1, wherein the titanium nitride film is removed by a plasma etching method using a gas to be used. 4. The method according to claim 3, wherein in the third and fourth steps, a rare gas is used together with the source gas or the etching gas. 5. The etching gas comprises chlorine, boron trichloride, sulfur hexafluoride, ethane hexafluoride, nitrogen trifluoride or methane tetrafluoride, or a mixture of any two or more thereof. 5. The method for forming a contact plug according to claim 3, wherein: