JPH0316129A - Generation of silicon nitride film - Google Patents

Abstract

PURPOSE:To generate a silicon nitride film close to a stoichiometric composition by a method wherein polycrystalline silicon is used as a target, an electric discharge is generated in a mixed gas of nitrogen and argon by setting a partial pressure ratio of nitrogen at 40% or higher and a magnetron sputtering operation is executed. CONSTITUTION:Polycrystalline silicon is used as a target; an electric discharge is generated in a mixed gas of nitrogen and argon by setting a partial pressure ratio of nitrogen gas or nitrogen at 40% or higher. That is to say, when the polycrystalline silicon is used as the target and a magnetron sputtering operation is executed by using N2 gas or a mixed gas of N2 and Ar, a composition of a generated film is approached to Si2N4 when a film formation temperature is 200 deg.C or lower and the partial pressure ratio of N2 is set at 40% or higher. Thereby, a silicon nitride film which is not coupled with hydrogen atoms deteriorating a characteristic of a semiconductor device can be generated at a low temperature close to room temperature without using a dangerous gas such as SiH4, NH3 or the like.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a mask for selective oxidation,
This article concerns the production method of silicon nitride film used as the final protective film or glabellar insulating film. [Conventional technology] Silicon nitride film has a strong blocking ability against alkali ions, so it is used as the final protective film (bansibasin!). It also has the effect of blocking thermal diffusion of oxygen and water vapor, so it is used as a mask during selective oxidation. Furthermore, it is used in non-dischargeable memory as an MNOS structure, or as a gate insulating film that utilizes a high dielectric constant.

Other insulation properties. It is used as an interlayer insulating film due to its corrosion resistance. First, we will discuss the silicon nitride film used as a mask during selective oxidation. Selective oxidation, called LOGOS technology, is performed for the purpose of electrically insulating semiconductor elements formed on a silicon-based temporary surface. Figure 2(a)~
[0] shows a general selective oxidation technology for silicon substrates.
First, a silicon substrate 1 is thermally oxidized to form silicon oxide lll2 on the surface of the substrate to a thickness of about 0.05 mm. This silicon oxide film 2 is shaped to relieve strain between the silicon substrate 1 and the next formed silicon nitride film 3 (Figure a). The silicon nitride film 3 is made of SiN4-NH3 type or Si}l. c! It is carried out by the chemical vapor deposition method (CVD method) using x-NH3 mixed gas at normal pressure or reduced pressure. The formation wj4 temperature was 700 to 1000°C and the film thickness was O. It is about I 5 ttra. Next, the silicon nitride film in the area to be oxidized is removed, and thermal oxidation is performed at a temperature of around 1000°C (Figure b). Subsequently, the silicon nitride film 3 and the oxide film are removed (Figure C), and the remaining oxide film 2 is used as a separation layer to form an element on the exposed silicon substrate surface. The conditions required for the silicon nitride film used in selective oxidation technology are the temperature (10
It is dense enough to prevent the permeation of oxygen and water vapor without cracking at temperatures around 00°C), and it is chemically resistant to the etching solution used to remove the oxide film. In order to form a silicon nitride film that satisfies this condition, a high temperature of 700 to 1000°C is required.
I! Temperature is required. Final protection of semiconductor devices [
The silicon nitride film used in this process must be kept away from high film temperatures, so it is produced by plasma CVD. In the plasma CVD method, SIH&-
NHS system Sit {Oh-N, system or SiH*-NHi
- Introducing any of the Nm-based mixed gases as a raw material,
By activating the raw material gas, the substrate temperature can be lowered to 200-400℃.
Heat the silicon nitride film at 00°C. [il the invention tries to solve! ! ) As mentioned above, the low pressure CVD method requires a high temperature of 700 to 1000°C, and SiH. ．． , Dangerous moths such as NHs? must be used. On the other hand, plasma CVD
In the SIH method, the temperature is as low as 200 to 400°C, but in the SIH
■It is the same as NHs in that it uses dangerous gas,
There is also the problem of equipment corrosion when using NH. Furthermore, silicon nitride films produced by plasma CVD have problems with their properties. As an example, SiH*
Plasma C using a mixed gas of N83Nt as a raw material
The characteristics of the silicon nitride film prepared by the VD method will be explained. N.H. 1
730sec, Nz was introduced into the reaction chamber of the plasma CVD apparatus at a flow rate of 1000sccs, and 13.56MH
A silicon nitride film that reacts with a plasma generated with a high frequency power of 500 W at a rate of 178 nm/win exhibits the following characteristics. That is, the refractive index is 2. The etching rate of Q35,5G9A in a fluorocarbon solution is 375n-/-1n, and the composition ratio N/St of nitrogen atoms N and silicon atoms SI in the silicon nitride film is 1.0. However, the silicon nitride film is SIsN
The structure of a is the most stable, and the theoretical composition ratio N/
St is 1.33. Among the methods for producing silicon nitride films, the one that has the composition closest to the stoichiometric composition and exhibits excellent properties is the silicon nitride film formed by thermal CVD. Since it requires a film temperature of ~900°C, it is not suitable for the final protective film of semiconductor device I. Figure 3 shows the infrared transmission spectrum of a silicon nitride film produced by plasma CVD. The horizontal axis shows the wave number, and the vertical axis shows the transmittance. Absorption peak A is an absorption based on Si-N bonds, and absorption peak B is an absorption based on N-H bonds.
C is absorption based on Si-H bonds. In this way, SiH. Or the hydrogen atoms supplied from NHs are N-
It exists in the form of H, 31-H bonds. The presence of hydrogen atoms causes problems such as deterioration of the characteristics of semiconductor devices and a decrease in the ability to prevent the diffusion of alkali ions such as N1. In particular, MOSFETs have large fluctuations in threshold voltage. The objects of the present invention are as follows. By solving the problems described above, SIH+. NHz
It is an object of the present invention to provide a method for preserving a silicon nitride film at a low temperature near room temperature, without using dangerous gases such as nitride, etc., without bonding hydrogen atoms that degrade the characteristics of semiconductor devices.

[Means for Solving the Problems] In order to achieve the above object, the method for preparing a silicon nitride film of the present invention targets polycrystalline silicon and uses nitrogen gas or a nitrogen partial pressure ratio of 40% or more. We will use the magnetron spasota method, which generates a discharge in a mixed gas of nitrogen and argon. [Operation] Polycrystalline silicon is targeted, N2 gas or N
! When performing magnetron sputtering using a mixed gas of
Approach sNa. Accordingly, a silicon nitride film with high density and low etching rate can be obtained. If the partial pressure ratio is small, Si gas increases, dangling bonds increase, and the characteristics of the silicon nitride film, such as low etching rate, deteriorate. Note that no hazardous gas containing hydrogen atoms is used, so there are no hydrogen atomic bonds in the produced film. [Example] In Fig. 1, a polycrystalline silicon target is installed in a magnetron sputtering tank, and N2 gas or NO gas and A
Introducing a mixed gas with r and increasing the gas pressure to 2 mTorr + 1
'li film temperature 200℃. DC power during sputtering 2.5k
Under the conditions of H, N. The refractive index (black circles) and composition (open circles) of silicon nitride films produced by varying the gas flow rate ratio are shown. The refractive index is N! As the gas partial pressure ratio increases, the refractive index goes from a value close to 3.68 of silicon to a value close to that of SiJ4. &I Wei confirms this, and it can be seen that the stoichiometry of S+sNa approaches due to excess silicon. Figure 4 shows that when the flow rate ratio of Nx gas is changed, the membrane temperature 2
The graph shows the density of silicon nitride films exposed to temperatures of 00°C and 30°C. The triangle shows the case at 200°C, and the circle shows the case at 30°C. Other conditions are the same as in Figure 1. The density is high when the partial pressure ratio of Nt is 40% and 60%, and no difference is observed depending on the film temperature. Figure 5 shows N! The etching rate of a cured film with a mixture of 50% hydrofluoric acid and water at a ratio of 1:10 is shown when the gas flow rate ratio is changed. The triangle shows the film temperature at 200°C, the black circle shows the film temperature at 30°C, and the white circle shows the film filmed at 30°C and then heat-treated at 100°C. Other film conditions were the same as in Figure 1. Broken stripe 10 is low pressure CV
The etching rate of the silicon nitride film produced in D is shown, and in the case of a certain film temperature of 200°C, the N8 partial pressure ratio is 35 to 9.
0% indicates a lower value. Under the condition that the membrane remains intact, a partial pressure ratio of 60% shows the best corrosion resistance. FIG. 6 shows the etching rate for a 50% hydrofluoric acid solution.

In the region where the nitrogen gas flow rate ratio is lower than 40%, the etching rate is slow due to excess silicon. When the nitrogen gas partial pressure ratio exceeds 40%, the etching rate becomes stable, and when it exceeds 60%, it increases. The white circle indicates when the membrane temperature is 200℃,
The black circles are for the case of 30°C. In addition, the broken line 11 in the figure indicates silicon nitride released by the thermal CVD method, which has the composition closest to the stoichiometric composition among the silicon nitride film shapes and methods and exhibits excellent characteristics, as described above. It shows the etching rate of the film. Figure 7 shows the dielectric strength distribution of a silicon nitride film with a thickness of 1 when the flow rate ratio of N2 gas is changed. (A) is nitrogen gas partial pressure ratio 100%, (b) is 80%, (C》 is 40%)
% is shown. As the nitrogen gas flow rate ratio decreases, the frequency of dielectric breakdown at low electric field strength increases. When the partial pressure ratio of nitrogen gas is less than 40%, the silicon atoms are excessive and resistivity is exhibited, so that the dielectric strength voltage does not reach 2)'IV/value. FIG. 8 shows a silicon nitride film formed by introducing only nitrogen gas, with film thicknesses of Q, lg+a, and Q. It shows the dielectric strength distribution at 5g, 1-. 11! When the thickness is around 0.5μ, the degree of destruction in the range of 0 to 2) TV/am becomes low, and
The frequency of the region of ~6 MV/csi increases. That is,
In order to obtain a silicon nitride film with excellent insulating properties required for a protective film, the nitrogen gas partial pressure ratio should be 40% or more and the film thickness should be 0.5%.
51 or more is desirable. Next, the n-type MOSFET
The threshold voltage when applying a silicon nitride film shaped by changing the flow rate ratio of N and gas at a gas pressure of 2 mTorr and a film temperature of 200° C. during a spa-soter according to an embodiment of the present invention is shown below. It is shown in Figure 9. In the figure, dashed line 1
2 shows the threshold voltage when the final protective film is not formed,
In addition, the black circle indicates the case where the DC power during the spa soter is 1 kW, the triangle indicates the case of 1.5 kW, and the square indicates the case of 2.5 kW. Nz
When the gas partial pressure ratio is 40% or more, the final maintenance time is t! for any DC power. The value is within ±0.03 V from the threshold voltage when the film is not exposed, so it does not pose a big problem in practice. The reason why a threshold voltage with such little fluctuation is obtained is because there are no hydrogen atoms in the silicon nitride film. Figure 10 shows the data that is the basis for this, and as above, the gas pressure at 2 mTorr and the membrane temperature at 200
The figure shows the infrared transmission spectra of silicon nitride films obtained by changing the flow rate ratio of N8 gas at ℃. The dashed-dotted line in the figure is N,
Gas partial pressure ratio 20%. The broken line is for 60%, and the solid line is for 100%. In both cases, plasma CVD shown in Fig. 3 is used.
Infrared i3iJ of silicon nitride film formed by the method: Absorption peak B. due to N-H, si-Hv3 combination appearing in spectrum C is not observed, and only absorption peak A based on Si-N bonds is observed, indicating that no hydrogen atoms exist within the film. Figure 11 shows gas pressures of 2 mTorr and 8 mTorr+
The film speed of the silicon nitride film is shown under the conditions of Wi film temperature of 30°C and 200°C, DC power of 2.5 kV at the time of spa 7 evening, and varying the flow rate ratio of N- gas. The black circle is *
*I degree 30℃. In the case of gas pressure of 2 mTorr during svanta, the white circle indicates the rfi film temperature of 200℃ and the pressure of 2 mTorr during svanta.
In the case of mTorr, the triangle corresponds to a film temperature of 200°C. This is the Ffi membrane speed when the gas pressure is 9 mTorr. In either case, there is no significant difference in film speed at the same nitrogen gas partial pressure ratio. In the region where the partial pressure ratio of nitrogen gas is 20 to 40%, the spatter rate with respect to Sl is N! Since there is a large amount of larger Ar, the membrane velocity is large. Next, selective oxidation using a silicon nitride film produced according to an embodiment of the present invention will be explained with reference to FIG.
was thermally oxidized at 1000° C. to form a silicon oxide film 2 with a thickness of about 0.057llI. Next, the etching pressure was 11 mTorr and the high frequency power was 250 W. High-frequency sputtering of Ar gas was performed at an etching temperature of 200°C to remove a thickness of 0.02u from the surface of the oxide llI2.
A clean surface was obtained. Immediately after etching, a polycrystalline silicon target was sputtered using a magnetron sputtering method using a mixed gas of nitrogen and argon to form a silicon nitride film 4 on the silicon oxide film 2. , gas pressure 2m during spa sota
7orr. The thickness of the nitride film 4 obtained at a mixing ratio of nitrogen and argon of 60:40, a film formation temperature of 200°C, a DC power of 2.5 kW, and a sputtering time of 3 minutes was 0.3 mm. Next, the portion of the silicon nitride film 4 having a width of approximately 5 f)m to be subjected to selective oxidation was removed by dry etching, and oxidation was performed in water vapor at 1100°C (Figure b). At this time, the crank did not enter the silicon nitride film 4. After this, dry etching silicon nitride II! 4 and the thin silicon oxide film 2 below it
As a result, an element region with a width of 50 mm was obtained using the oxide film 2 as a separation layer. The conditions for forming a silicon nitride film by the magnetron vanta method using a polycrystalline target can usually be selected within the following range. The gas pressure during sputtering is 1 to 1QmTorr, the gas mixture ratio of nitrogen and argon is ArO to 60%, the membrane temperature during sputtering is room temperature to 250°C, and the DC power during sputtering is 0.5 to 250°C.
2.5 kll, sputtering time is 30 to 300 seconds.
[Effects of the Invention] According to the present invention, polycrystalline silicon is used as a target and magnetron sputtering is performed by generating discharge in a mixed gas of nitrogen and argon with a nitrogen partial pressure ratio of 40% or more. Highly dense and chemically resistant at film formation temperatures, stoichiometric 'IE' stable up to 1000℃!
We were able to produce a silicon nitride film close to the second precept.
Such a silicon nitride film is not only a mask for selective oxidation, but also a final protective film. It can be used extremely effectively as a glabellar insulating film or a gate insulating film. Furthermore, since the film does not contain hydrogen atoms, it is possible to suppress fluctuations in the threshold voltage of the MOSFET.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the relationship between the nitrogen partial pressure ratio in the nitrogen/argon mixed gas and the #Jl bottom of the Svanta silicon nitride film, and Figure 2 is a cross-sectional diagram showing the conventional selective oxidation process in the order of (11) to (C+). , FIG. 3 is an infrared transmission spectrum diagram of a silicon nitride film formed by the conventional plasma CVD method, FIG. 4 is a relationship diagram between the nitrogen partial pressure ratio and the density of the super-soter silicon nitride film, and FIG. Figure 6 shows gPJ where the nitrogen partial pressure ratio and concentration change.
The relationship between the etching efficiency of a sputtered silicon nitride film using an acid solution.
l. (bl. (Dielectric breakdown electric field strength distribution diagram of a super-soldered silicon nitride film indicated by Cl. Figure 8 shows the dielectric breakdown electric field strength distribution of a super-soldered silicon nitride film indicated by Cl. ta+. Distribution diagram, Figure 9 is MOSF
ET's final guarantee! Relationship diagram between nitrogen partial pressure ratio and threshold voltage when a silicon nitride film is used as the film, 10th
The figure shows an infrared transmission spectrum of a sputtered silicon nitride film formed by changing the nitrogen partial pressure ratio.
The figure is a cross-sectional view showing a selective oxidation process using a sputtered silicon nitride film according to an embodiment of the present invention in the order of (al to (Cl). 1: silicon substrate, 2 silicon dioxide film, 4 NZ/[NZ+Ay) ( o/o) Rod?■■ Mitamaro-1 (C-1) System 3 Mouth 0 20 40 60 80 100 Nz/(Nl'rAr) N2/(Hawk+Ar) Torg Leopard■ Sz/(NZ+Ay) Reibaku Samodan't Kairekidoshi (MVnml (d) (b) CC) Toji Ichihei 7 Zuarabakujokondenkawo■ (MV/C?TI) 8th Zuasakazu (C Nae゛゛1 ) 0th (2) Nz/ (N2 +Ar) (%ノ○ zO 40 ω 80 100 N2 / (NZ -? Ay ) [ 7o) Cumulative 11 ?■■

Claims (1)

[Claims] 1) A method for producing a silicon nitride film characterized by using polycrystalline silicon as a target and using a magnetron sputtering method in which discharge is generated in nitrogen gas or a mixed gas of nitrogen and argon with a nitrogen partial pressure ratio of 40% or more. .