JPH03247767A - Formation of insulating film - Google Patents

Abstract

PURPOSE:To efficiently form an insulating film on the surface of a substrate having steep level-difference parts, in an ECR plasma CVD apparatus, by introducing a plasma raw material gas, a reactive gas and an inert gas into a vacuum vessel and specifying the frequency and power of an RF bias. CONSTITUTION:An SiO film having about 2000Angstrom thickness is formed on an Si substrate, on which a pattern with an Al step structure is formed. Next, an N2 gas and silane are fed to the inside of a vacuum vessel of an ECR plasma CVD apparatus, and by using a microwave and RF power of about <=200W with about 13.56MHz frequency, an SiN film having about 1000Angstrom thickness is formed (b). Then, N2, silane and an Ar gas are fed thereto, and by using a microwave and RF (of about 50W and about 40.68MHz), an Si film having about 1mu thickness is formed and the space is filled up (c). After that, only an Ar gas is fed thereto, and by using a low power micro wave and high power RF of about 500W, projected parts are cut to flatten (d). Furthermore, N2 and silane are fed thereto, and by using microwave and RF (of about 13.56MHz and about <=200W), an SiN film having a desired thickness is formed (e).

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention is particularly applicable to semiconductor manufacturing equipment such as LSI (Large Scale Integrated Circuit) manufacturing equipment, especially for ultra-LSI semiconductor devices that require low-temperature film formation. 1. This invention relates to a method for efficiently forming an insulating film, particularly a silicon nitride film, on the surface of a semiconductor substrate having a steep step, such as a side surface of a wiring, using an ECR plasma cD device used, for example, in the manufacture of DRAM.

[Conventional technology]

First, an outline of the configuration of an ECR plasma CVD apparatus used for manufacturing VLSI semiconductor devices will be explained.

Figure 8 shows the conventionally used ECR plasma CVD
An example of the configuration of the device is shown. Microwaves with two frequencies of 2.45 GHz generated by a microwave generation means (not shown) pass through the inside of a waveguide 11 which is a microwave transmission means, and enter a vacuum through a microwave window 12 made of a dielectric plate. The microwave is introduced into the maintained plasma chamber 13a, and is sent through the gas supply means 17 due to the electron cyclotron resonance effect between the introduced microwave and the magnetic field lines generated by the main solenoid 14 coaxially surrounding the plasma chamber 13a. The plasma source gases such as Ar, O□, and N2 introduced into the plasma chamber 1 are converted into plasma with high efficiency.
A high-density plasma is generated within the chamber 3a at a low degree of vacuum. This plasma passes through the opening 13c along the magnetic lines of force in the direction of low magnetic flux density of the lines of magnetic force generated by the main solenoid, and heads towards the substrate 20 on which the thin film is to be formed. On the other hand, a plurality of gas discharge ports were formed at intervals in the circumferential direction in the processing chamber 13b in which the substrate 20 was placed. An annular gas ring 22a made of a hollow member with a circular cross section is disposed, and Si is introduced into the gas ring 22a from the outside of the processing chamber 13b via an introduction pipe 22b.
A reactive gas such as H, etc. is introduced. The supplied reactive gas is discharged from the gas discharge port of the gas ring 22a to the plasma transfer path and is activated by the plasma, forming a high-quality thin film on the substrate surface at high speed without requiring heating of the substrate. be done. However, the uniformity of the film thickness distribution of this thin film deteriorates as the diameter of the substrate increases. Therefore, an auxiliary solenoid 18 is disposed coaxially with the substrate near the bottom of the processing chamber 13b, and the lines of magnetic force generated by this auxiliary solenoid 18 are Main solenoid 1
4, and the plasma is transported along the combined lines of magnetic force to make the plasma density on the substrate surface uniform. In addition, the substrate 20 has a frequency of 50 MHz to improve the quality of the thin film formed on the surface.
RF bias is applied from a high frequency power source (so-called RF power source) 23 of kHz to several tens of MHz, usually 13.56 MHz, via a matching box 24 containing a matching circuit that performs impedance matching between the plasma and the RF power source side of the substrate. be done.

When forming a silicon nitride film (hereinafter referred to as a SiN film) as an insulating film on the surface of a substrate having a steep stepped portion such as the side surface of a wiring using an ECR plasma CVD apparatus configured as described above. An example of a conventional film forming method will be described below.

Note that EC is used to form insulating films in VLSI semiconductor devices.
The reason for using a device capable of low-temperature film formation with a substrate temperature of 200°C or less, such as an R plasma CVD device, is to use a plasma raw material gas and a reactive gas, each of which has the compositional components of an insulating film, to form a film on the substrate surface. When forming a film, if there is a step-like difference in the surface of the substrate such as the side surface of the wiring, the film cannot be formed sufficiently on the side surface. If a method such as heating the substrate to a temperature of This is because there is a risk of wire breakage.

However, when an insulating film is formed at a low temperature using an ECR plasma CVD apparatus, an RF bias is applied to the substrate, so as shown in FIG.
The insulating film on the top surface of the SiN film protrudes laterally, and the N2 gas or N gas used as the plasma source gas to form the SiN film
The sputter removal effect of the nitrogen ions N'' generated by the plasma formation of the gas into plasma is the effect of the sputtering removal effect on the overhanging portion, which causes oxygen ions O to be removed from the silicon oxide film (SiO If the film continues to be formed as it is, the insulating film will grow as shown in Figure 5, which is one of the most important phenomena to avoid in the manufacturing of VLSIs. become.

Therefore, the inventor proposed the following method (
(See Japanese Patent Application No. 1-188194) This method is
By normal operation of the R plasma CVD apparatus, film formation is performed using a plasma raw material gas and a reactive gas each having compositional components of an insulating film, and the insulating film on the upper end surface 1 of the stepped portion, for example, the top surface of the wiring, is formed into a predetermined film. When the thickness is reached, the film deposition operation is stopped, the gas in the vacuum container is replaced with an inert gas such as a metering gas, and the inert gas is turned into plasma and sputtered with positive ions, resulting in a thin film of insulation. The film is removed to such an extent that the upper surface of the stepped portion is not exposed, and this sputtering step is repeated each time the insulating film reaches a predetermined thickness, thereby removing the stepped portion,
In particular, by forming the film with grooves of submicron order width sufficiently open, an insulating film of good quality can be formed in the step portion. This film forming process is shown in FIG. In the figure, +8+ indicates a cross section of a wiring with a height and width of 1 interval as an example of the shape of the stepped portion, and (b) shows a SiN film formed on the wiring surface up to the point where it is sputtered with cations.
Shows the adhesion state of the film. In addition, in the same figure (C), the lateral overhang of the top surface of the wiring is removed by sputtering with positive ions, and the insulating film 3b deposited on the top surface of the substrate 1 is also sputtered and flattened, and the insulation film 3b by this sputtering is This shows a state in which the film material is attached to the side surface of the wiring.

[Problem to be solved by the invention]

In this way, when forming an insulating film on the surface of the stepped portion, the insulating film is formed over the entire surface of the stepped portion by alternately repeating the film formation process and the step of removing the insulating film on the top surface of the stepped portion by sputtering cations. In this case, it is necessary to replace the gas in the vacuum container each time the two steps are switched, which increases the process time and reduces the throughput of the film forming process.

Therefore, an inert gas for cation generation is supplied into the vacuum container together with a film forming raw material gas consisting of a plasma raw material gas and a reactive gas. When attempting to use a film formation method that forms a film while removing the surface insulating film, it is necessary to input an RF power of 200 to 500 W, which causes a noticeable sputtering effect, if the metering gas is normally used as an inert gas. Ta. On the other hand, in the SiN film formation process with RF bias applied, the stress (compressive stress) in the formed SiN film increases with the RF power, and this stress increases to 1010 dyn.
/cJ, the film may peel off or the aluminum wiring may break due to this stress. The RF power that generates such a large force is 100 to 200 W or more. For this reason, it has been impossible to form a flat insulating film covering the stepped portion while performing the film formation process and the sputtering using Ar gas ions Ar'' in parallel.

The purpose of this invention is to provide an ECR plasma C equipped with an RF power source.
When forming an insulating film on steep steps on the surface of a substrate using a VD system, the film formation time can be significantly shortened without damaging the steps and maintaining the required quality of the insulating film. An object of the present invention is to provide a film forming method that allows

[Means to solve the problem]

In order to solve the above problems, in this invention, RF
A method for forming an insulating film using an ECR plasma CVD apparatus equipped with a power source is described in which a plasma raw material gas, a reactive gas, and an inert gas each having compositional components of an insulating film are introduced into a vacuum chamber of the ECR plasma CVD apparatus. Alternatively, the plasma raw material gas and the reactive gas each having the composition of the insulating film may be formed using the ECR method. Plasma C
Introduced into the vacuum chamber of the VD device, the frequency of the RF bias was set to 1 MHz or less, and the power of the RF bias was set to 2 MHz.
The method is to form an insulating film with a power of 00W or less.

[Effect]

The sputtering efficiency using cations is the sputtering rate 5R (S
R: amount of sputtering per unit time). SR is R
The ion current due to positive ions A' incident on the VDCI insulating film is set to 1. Then, when the cation A+ is Ar gas ion Ar+, Vnc"1000
In the region (v), as shown in FIG. 3, there is a relationship of SR"(VDCVth)"XIA. Here, Vth is the sputtering starting voltage, which is approximately 20 (V) in the case of Ar''. Sputtering is not performed at a bias potential below this voltage. It is known that it depends on the output voltage of the power supply (I: RF power supply output current).Therefore, according to the present invention, if the RF frequency is set to 40MHz or more,
Due to the frequency characteristics of cation mobility, the RF bias potential VOC has a significant difference compared to the normal RF frequency of 13.56M1 (z), and the sputtering rate SR increases according to the -F equation. , RF power (with vxB held constant (VDCVth)
Since 2×IA can be increased, cation sputtering can be performed effectively without increasing stress on the film, and as shown in Figure 2fb), the lateral side of the insulating film grown on the top surface of the wiring The removal of the directional overhang and the adhesion of the insulating film deposited on the underlying layer (SiO film) to the side surfaces of the wiring by sputtering proceed simultaneously, until the grooves between the wirings are filled (in the state shown in the figure (al), i.e., the state between the wirings is Film formation progresses with the grooves always open.

On the other hand, according to the present invention, the frequency of the RF bias can be changed to I
When the frequency is lowered to below MHz, the ion current due to N increases due to the frequency characteristics of the mobility of nitrogen ions N1 generated by plasma generation of N2 gas or NH gas used as plasma source gas, and as shown in Fig. 7 ( 1))
As shown in Figure 2, more low-energy N' falls on the substrate surface compared to the conventional method ((a) in the same figure), and the amount of N' incident on the side wall of the first step, which was insufficient in the past, increases. The adhesion of the film to the side walls and the bottom surface of the step increases, and the formation of the insulating film progresses as shown in FIG. Further, the ion bombardment effect is sufficiently exerted on the film attached to the side wall and the lower end surface of the step, and the film becomes dense.

That is, by setting the RF frequency to I MHz or less, the stepped portion can be covered with a dense film without increasing the RF power and therefore without increasing the stress of the film.

〔Example〕

As a first embodiment of the present invention, the RF frequency is set to 40MHz.
An example in which it is set to z or more will be shown below.

(1) As a semiconductor substrate with step-like steps, the first
As shown in Figure fal, a SiO film is deposited on a silicon substrate to a thickness of 2,000 mm, and a test pattern with an aluminum step structure is formed on this film. The scale of this test pattern is approximately 1 IM in width and height.

(2) For the first film formation, which is the first stage of film formation, nitrogen gas and silane are supplied into the vacuum chamber of the ECR plasma CVD apparatus, and microwaves and two frequencies of 13.5
The frequency was set to 6MHz. Using an RF power of 200 W or less, SiN is deposited to a thickness of approximately 1000 mm as shown in Figure 1 (b).
Forms a film. (If an inert gas is introduced from the beginning, aluminum will be sputtered and the substrate will be damaged.) (3) For the second film formation, nitrogen, silane, and Ar gas are supplied into the vacuum chamber of the device, and the micro Waves and RF (50W
, 40.68MHz) in Figure 1(C) (7
), a SiN film with a thickness of about 1-100 mm is formed to fill the gap.

Note that ■, ■, and ■ in the figure are lines that indicate the growth state of the SiN film and indicate the shape of the insulating film surface at appropriate times.

(4) For the third film formation, only Ar gas is supplied into the vacuum chamber, and low power microwave and 500W high power RF are used.
Sputtering only with Ar'' was performed using
The protruding portion is shaved and flattened as shown in 81.

(5) For the final film formation, nitrogen and silane are supplied into a vacuum container, and the desired film is formed using microwaves and RF with two frequencies of 13.56 MHz and a power of 200 W or less as shown in Figure 1(e). A SiN film is formed to a certain thickness.

As a second embodiment of the present invention, the RF frequency is set to I MH
An example in which it is less than or equal to z is shown below.

(1) As a semiconductor substrate with step-like steps, the first
As shown in Figure 81, an SfO film with a thickness of 2000 mm is deposited on a silicon substrate, and a test pattern with an aluminum step structure is formed on this film. The scale of this test pattern is approximately 1- in both width and height.

(2) Nitrogen moth, 7. (30SCCM, SCCM is standard condition: o'c.

Gas flow rate (cm3/m1n) converted to atmospheric pressure) and Shira 7 (283 CCM) were supplied into the vacuum container of the ECR Plas 7 CVD equipment, and microwaves (800 W, 2.4
5 GHz) and RF (50 W, 200 kHz) to form a SiN film.

〔Effect of the invention〕

As described above, in the present invention, a method for forming an insulating film using an ECR plasma CVD apparatus equipped with an RF power supply is performed using a plasma raw material gas, a reactive gas, and a non-containing gas, each having a compositional component of an insulating film. The active gas and the ECR
Introduced into the vacuum chamber of plasma CVD equipment and R
Either the insulating film is formed using an F bias frequency of 40 MHz or more and an RF bias power of 200 W or less, or a plasma source gas and a reactive gas each having a composition of an insulating film are placed in the vacuum of the ECR plasma CVD apparatus. We decided to form an insulating film by introducing the RF into the container, setting the frequency of the RF bias to 1 to 12 or less, and the power of the RF bias to 200 W or less.
In the case of the former method in which the bias frequency is set to 40 MHz or more, the film formation process and the sputtering process can proceed in parallel, and the time required to form the insulating film is significantly shortened.

In addition, this SiN film planarization process has become practical, and the SiO film or PSG film (phosphorous glass film), which was previously used as an insulating film between the eyebrows of LSI in the DRAM manufacturing process, has been improved with excellent moisture resistance and insulation properties. It is now possible to replace it with a SiN film.

As a result, the reliability of LSI can be improved compared to the past.

In addition, in the case of the latter method in which the frequency of the RF bias is set to I MHz or less, when a SiN film is conventionally used as the final protective film of an LSI, the formation of this SiN film is performed by high-temperature treatment or by a combination of multiple processes. This can now be done easily and in a short time using a single process at low temperatures. Therefore, by forming a SiN film using this method, it has become possible to easily protect the device from moisture intrusion and impurities, improve the reliability of the device, extend its lifespan, and stabilize its electrical characteristics.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing each step of the film forming process according to an embodiment of the first insulating film forming method of the present invention, and FIG. 2 is a diagram explaining the principle of the first insulating film forming method of the present invention. In the same figure (bl is an explanatory diagram showing the sputtering effect of Ar gas ions, Figure (a) is an explanatory diagram showing the spuck effect of Ar gas ions, and Figure 3 is an explanatory diagram showing the sputtering effect of Ar gas ions. Figure 3 shows the relationship between RF bias potential (Vnc) and per atom 4th diagram showing the relationship between sputtering rate (SR) and sputtering rate (SR)
The figure is an explanatory diagram showing an example of a conventional insulating film forming method, showing each step of the film forming process. Figure 5 explains the reason why voids occur when a silicon nitride film is formed using the same method as a silicon oxide film. 6 is a cross-sectional view showing the state of an insulating film formed by the second insulating film forming method of the present invention, and FIG. 7 is a sectional view showing the principle of the second insulating film forming method of the present invention compared to the conventional method. FIG. 8 is an explanatory diagram showing the principle of the conventional insulating film forming method and the present invention, respectively, and FIG. 8 is an explanatory diagram showing the principle of the insulating film forming method of the present invention, respectively. ECR plasma C used for insulating film formation by
FIG. 2 is a cross-sectional view showing a configuration example of a VD device. 1: Substrate (semiconductor substrate) 2: Wiring, 3.103: Silicon nitride film, 11: Waveguide (microwave transmission means), 1
3: Vacuum vessel, 14: Main solenoid, 17: Gas supply means, 1st: Auxiliary solenoid, 20: Board, 22: Gas supply means, 23: RF power supply. 9 Yaotsu (0) (b) Figure 2

Claims (1)

[Claims] 1) A microwave generating means, a means for transmitting the microwave, and a plasma raw material coupled to the microwave transmitting means to which the microwave is introduced and fed via the gas supply means. The main solenoid is coaxially surrounded by a main solenoid that generates magnetic lines of force that turn gas into plasma due to the resonance effect with the microwave, and the plasma is transferred along the lines of magnetic force in the direction of low magnetic flux density of the lines of magnetic force generated by the main solenoid. The reactive gas introduced into the passageway is activated and acts on the magnetic lines of force of a vacuum vessel in which a substrate is placed, on which a thin film is formed, and a main solenoid that is arranged coaxially with the vacuum vessel and constitutes the transfer passageway. an auxiliary solenoid that generates magnetic lines of force to control the transfer path so that the plasma density is uniform at the substrate position, and an R for applying an RF bias to the substrate.
In a method of forming an insulating film such as a silicon nitride film on the surface of a semiconductor substrate having a steep step using an ECR plasma CVD apparatus equipped with an F power source and A reactive gas and an inert gas are introduced into the vacuum chamber of the ECR plasma CVD apparatus, and an insulating film is formed by setting the frequency of the RF bias to 40 MHz or more and the power of the RF bias to 200 W or less. Insulating film formation method. 2) A microwave generating means, a means for transmitting the microwave, and a plasma source gas coupled to the microwave transmitting means to which the microwave is introduced and fed through the gas supply means with the microwave. The reaction introduced into the transfer path by the plasma coaxially surrounded by the main solenoid that generates magnetic lines of force that turn into plasma due to the resonance effect of Plasma is generated at the substrate position by acting on the magnetic field lines of the main solenoid, which is arranged coaxially with the vacuum container and which constitutes the transfer path. an auxiliary solenoid that generates magnetic lines of force to control the transfer path so that the density is uniform, and an R for applying an RF bias to the substrate.
In a method of forming an insulating film such as a silicon nitride film on the surface of a semiconductor substrate having a steep step using an ECR plasma CVD apparatus equipped with an F power source and A reactive gas is introduced into the vacuum chamber of the ECR plasma CVD apparatus, and the frequency of the RF bias is set to 1 MHz or less.
A method for forming an insulating film, characterized in that the insulating film is formed with a bias power of 200 W or less.