JPS60107841A - Formation of silicon nitride film - Google Patents

Abstract

PURPOSE:To obtain an Si3N4 surface protective film, the content of H2 therein is little and which has excellent damp-proofness and mechanical strength, by using SiH4, SiF4 and N2 as main reaction gases when an Si3N4 film is formed on the surface of an Si substrate through a plasma CVD method. CONSTITUTION:An upper electrode 2 and a lower electrode 3, the back thereof has a heater 10, are arranged oppositely in a vacuum vessel 1, and the electrodes 2 and 3 are connected to a RF power supply 6 mounted outside the vessel 1. The inside of the vessel 1 is brought to a vacuum state by using a booster pump 4 and a rotary pump 5 cascade-connected, and a mixed gas of SiF4, SiH4 and N2 from bombs 8 is fed into the vessel 1 through a mass flowmeter 7 while glow discharge is generated among a plurality of substrates 9 placed on the electrode 3 and the electrode 2. The gas flow-rate ratio of SiH4 to SiF4 is regulated to 0.05-0.80 at that time, and N2 is not regulated particularly. Or a mixed gas of SiF4 and NH3 may be used as main gases.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a vapor phase growth method using plasma (plasma CVD).
The present invention relates to a method of forming a silicon nitride film using a method (method), and particularly relates to a method of forming a silicon nitride film having a low hydrogen content in the film.

[Background of the invention]

Semiconductor integrated circuits are damaged by moisture corrosion, Na and C
In order to protect the element from contamination by impurities such as 1, a protective film is formed on the surface. Semiconductor integrated circuits encapsulated in plastic require a protective film that is resistant to mechanical stress in order to withstand thermal strain during encapsulation. Further, since this protective film is formed on the At wiring, it is necessary to form it at a temperature of 400 C or less in order to avoid changing purchases of the At wiring. Therefore, a silicon nitride film formed by a plasma CVD method has generally been used as a protective film.

Conventionally, in forming a silicon nitride film by plasma CVD, a mixed gas of monosilica 7 gas (8 iL) and ammonia gas (NH3) or the above gases and nitrogen gas (N2) or argon gas (IAr) has been used. Therefore, in the formed silicon nitride film, the atomic ratio is approximately 2.
Contains 0% hydrogen (Paduschek et al., Quantitative Dete-rmina
t+on of hydrogen in 5ilic
on-nitride filnus using pr
oton-proton 5catter+ngJAp
Plied Physics Letter, Vol. 36, pp. 62-63, published in 198θ]. However, in recent years it has become clear that hydrogen in these silicon nitride/films deteriorates the underlying device characteristics (Fair et al.
+reshold Voltage In5tabil
ity 1nAIIUSFE'l", Due to
Channel Hot-HoleEmission
J IEEE 'll' transactions on
Ele-ctron Dev+ces Magazine Volume 28 83
Negative ~ 94 pages Published in 1981. This is MUS type tiger 7
When the sister is operating, its threshold voltage VTR fluctuates over time, causing the mutual conductor female gm to deteriorate (
g). The mechanism is that hydrogen atoms present in the plasma CVD nitride film diffuse into the gate oxide film, combine with hot carriers (electrons or holes) injected into the gate oxide film, and create a trap level. It is possible to create one.

In order to prevent the above phenomenon, it is effective to form a surface film that does not contain hydrogen. As protective films that do not contain hydrogen, there are beam/glass films and silicon oxide films produced by plasma CVD, but these films are inferior in moisture resistance and mechanical strength compared to plasma CVD silicon nitride films. Therefore, a semiconductor device formed using these films as a surface retention film and sealed in plastic has low moisture resistance and heat resistance.

[Purpose of the invention]

Therefore, it is an object of the present invention to provide a method for forming a surface protective film with less hydrogen content and excellent moisture resistance and mechanical strength.

[Summary of the invention]

In the present invention, in order to achieve the above object, a silicon nitride film is formed by a plasma CVD method using a gas containing monosilane gas (SiH4), silicon tetrafluoride gas (SiF4), and nitrogen gas (N2) t' as a reaction gas. The first feature is that

Hydrogen contained in the silicon nitride/film formed by the plasma CVD method is SjH, which is the reaction gas.

Produced by decomposition of NH3. Therefore, the present invention is based on the idea of using all reaction gases that do not contain hydrogen.
, )'4 and N2 were used to form a silicon nitride film. However, it was not possible to form a silicon nitride film. I thought about the cause as follows. S
iF causes a dissociation reaction in plasma and generates octagonal atoms, fluorine (F) atoms, 5iFxlX=1 to 3) molecules, and the like. Among them, 81 atoms combine with nitrogen (N) atoms to form a silicon nitride film, while a large amount of F atoms dissociated during IHJ etch/blow the formed silicon nitride film. Consequently, film formation and etching compete with each other in this reaction system. In such a competitive process, reactions that produce strong combined sounds proceed. By the way, when we compare the bond energy of 5i-F bond and 5i-N bond, the bond energy of 5i-F bond is 1
The binding energy of the 5i-N bond is 105 kcal/mol, which is 30 kcal/mol, which is larger for the 5i-F bond (Kerr et al., “Strength of Ch.
emotional Bonds J West et al. Ha
nd book of Chemistry and P
hysics 47th Edition F-130 Sada ~ F-132 Negative'l
Published by 'he Chemical Rubber Company, 1966). Therefore, when SII+'4 and N2 are used, the reaction to a stable 8 i -F M combination progresses, and F
It was found that the etching of the Si atoms underlying the atoms was dominant. Unfortunately, SiF4 and N2 did not lead to film formation.

Therefore, the Ministry of the Invention and others investigated a method for removing the dissociated F atoms and suppressing the etching phenomenon. For this purpose, from the above considerations, we thought that VC should be used to generate a compound with F that is more stable than S i -k', and when we independently investigated all fluorides, we found that hydrogen fluoride (IJF) and Boron trifluoride (
BF3) was found to be more stable. For example, H
-F bond energy is 153 kcal/mol, B
The binding energy of -F bond is 186 kcal/mo
It is l. In particular, with regard to H'F, it is known that the reaction rate of H0F - + HF... (1) is extremely fast, and it has been found that the presence of H atoms is responsible for the removal of F atoms. . Therefore, using SiH4 as a source of H atoms, SiF4
When film formation was carried out by adding SiH410cm''/WiR to a reaction gas of 80Crn3/m and N2300cm''/-, a stable silicon nitride film could be completely formed.

On the other hand, when BP3i was treated, it was found that although film formation was possible, surface rC-deposited boron (BN) was also deposited.

This is because the HN#i bond is more stable than the SiN bond. Therefore, it has been found that the addition of the above-mentioned 8iH4 silicon hydride has an effect on stable SiN type J.

Amorphous silicon film used in solar cells, etc.
Also in the formation of a Si film), SiF.

Attempts have been made to form a film using the plasma CVD method using 8iFn as a raw material, but film formation does not occur with 100% 8iFn, and H
2 or SiH4 to form a film (
Daiichi Others “Preparation and plasma analysis of a8i:F:H thin film by glow discharge method” Vacuum Vol. 26, 319-325 Tei 1
(published in 1983). It is clear from the above discussion that Eligas was selected for the same reason.

Furthermore, the flow rate ratio of '4 and 8s H4 to 81 of the reaction gas! A silicon nitride film was created using different methods, and its formation rate and hydrogen content were investigated. Figure 1 shows the results.

From the relationship between the formation speed of J exchange and the flow rate ratio, the gas flow rate ratio is S
It was found that a film was formed when 凰H4/[SiH4+5iF4)>0.05. On the other hand, the hydrogen content is Si
As the proportion of H4 increases, we will issue a warning.

S iH4/ (S iHa +S i F4 is 0.
In the case of 8 or more, the hydrogen content is approximately 14at (%f atomic ratio), compared to the case formed with SiH4 and N2.
No clear significant difference was observed. In other words, it was found that if the value of the gas flow rate ratio SiH4/(SiH4+5iF4) was in the range of 0.05 to 0.80, it was possible to form a silicon nitride film with a lower hydrogen content than in the past. .

In the second invention, in order to achieve the above object, silicon tetrafluoride gas (SIF4) and ammonia gas + NHs
) and nitrogen gas (N2)', or SiF4
The second feature is that the 7-licon nitride film is formed by the plasma CVD method using either of the gases containing N1-tsk and N1-tsk as a reaction gas.

As mentioned above, when S i p 4 and 5i) 44 and N2 are used, the addition of 11 atoms becomes F j! This suppresses etch nog in the silicon nitride film caused by F atoms, making it possible to form a silicon nitride film. Therefore, as the supply W of H atoms, NH, is used instead of 811H4 (f-
I tried. As a result, a stable silicon nitride film? was able to form.

Furthermore, in the plasma state of NHs, gas dissociation is difficult and N
Since atoms are generated and serve as a supply source for N atoms, we believe that a silicon nitride film can be formed even if N2 is not included as a reaction gas. As a result, it was found that it was possible to form a silicon nitride film.

[Embodiments of the invention]

The present invention will be explained below using examples. 1st invention lol Mf! Explain I.

Example 1 FIG. 2 shows a schematic configuration diagram of the plasma CVD apparatus used in this example. Inside the vacuum vessel 1, opposing 1L poles consisting of an upper electrode 2 and a lower electrode 3 are provided, and an alternating current voltage is applied from a terminal 6 to RP'. The vacuum container l is evacuated by a booster pump 4 and a rotary pump 5. 8. Tuskaska Valley Bo/Be for silicon nitride film formation. J: After adjusting the flow rate with the mass flow controller 7, the mixture is mixed.
is supplied to the vacuum vessel l. Samples for film formation (84 groups &
) 9 is placed on the lower electrode 3, and a heater 10 for heating the sample is provided below the lower electrode &3. The structure is such that the father current voltage to cause claw discharge can be applied to either of the opposing electrodes, and the content of the present invention was confirmed to be effective in either case.
Here, a case will be described in which a father current voltage is applied to the lower 1 kL pole 3.

The silicon nitride film is formed by the following procedure. First, the lower electrode 3 is preheated by the heater 10 to a desired temperature (
For example, set it to 300r). Next, a sample (Sl group+!i) 9 on which a film is to be formed is placed on the lower electrode 3, and the sample 9 is placed on the lower electrode 3. Pull it empty using 5 rotary robots and 4 booster pumps. When the pressure drops below IPa, cylinder 8
, open the mass 70-controller 7 to perform the flow rate side n,
The source gas flows into the trough 1 in a predetermined manner. The reaction gas pressure is controlled by varying the rotational speed of the booster pump 4 and by changing the exhaust gas 4. When the reaction gas pressure is depleted, the lower part' polarization 3Ic 13.5 from the RF source 6
6 Ml-1z (D AC voltage is applied and film formation is performed by claw blood exsanguination. At this time, the upper SR, 2 and vacuum container 1 are electrically grounded. F9r time (film formation time) After that, the firing voltage is stopped to end the discharge, the source gas is stopped and the inside of the vacuum vessel is once evacuated, the pump is stopped, and the sample is taken out.

Gas flow rate SiH410crr? /Familiar + SiF490
m3/IRiR+ N 2600 crn” / - Binding, reaction residue pressure 30Pa, total input power at 11:8 (1
When glow discharge was performed for 60 minutes with the distance between the opposing electrodes set to 0% and the distance between the opposing electrodes to be k 6 cm, a cured silicon film of about 35 g nm was formed. When the refractive index of this film was measured by elliplymetry, it was found to be about 1.8. Also, Lanf
orduno experiment (written by LBnford et al. The byd
rogen container of plasma-
deposited s+Jicon n1tride
JJournal of Applied Phys+
es magazine, Vol. 49, pp. 2473-2477, published in 1978. For complete reference, we measured the entire infrared absorption spectrum of this film.
The hydrogen content in the film was estimated from the 51-H bond absorption band and the N-H bond absorption band to be approximately 3211%. Furthermore, the hardness of this film was measured using Pinkers Hardness 1 and was 1800 kg/lan"6#7, compared to 2000 kg/'trvn2 of the conventional plasma CVD produced silicon film.
Although it was slightly smaller than that of Plasma CV DH Hayabusa Anri/)yA (approx. 12'00 kg/Suzuki 2) spear/glass membrane (approx. 800 kg/mm2), it had more than 1.5 times the hardness.

Next, an example in which film formation is performed by increasing the gas flow rate ratio will be described. Adjust the gas flow rate to 8iH450cm”/cm.

S IF < 50cm3/sin, N2600cm"
/wn, and other conditions were the same as the above formation conditions. Approximately 1.2 μIT after 30 minutes of glow discharge
A positive silicon nitride film was formed. The refractive index and Vickers hardness of this film are 2.2 and approximately 1800 kg/
rtun”.The hydrogen content was approximately 10 at
, I fell in love with Chi.

Next, we measured the characteristics of confectionery when using these protective membranes with a low hydrogen content, and compared them with the conventional membrane with a high hydrogen content (maximum 25 at, %). . For the measurement, a nitride/licon film τ was formed as a protective film on the surface of the MUδ transistor fabricated by the convenient method, and the NO. 8), > 7
We investigated the variation in threshold 111 tonne pressure due to VC made by DCtXJJ of JISTA.

A schematic cross-sectional view of an element with four phases in the side rectangle is shown in FIG. p
Type S, nPvl of poly Sl gate 15 on the surface of Kyokei 11
(JS) U7 resistor 16 is formed.

The thickness of the gate oxide film 14 is 35 nm, the gate length of the poly-Sl gate 15 is 2 μm, and the gate width is 10 μm.

Diffusion layer 12 is a drain or a source. On the upper part of the transistor, 0.8μ
A 0.8 .mu.m thick At film was formed as a wiring and a 0.8 .mu.m thick At film was formed thereon, and a 0.3 .mu.n glue/glass 19 and a 1.0 .mu.m thick silicone/film 20 were further formed as a peritoneal membrane. As the silicon nitride/film 20, in addition to the uninvented silicon nitride film with a hydrogen content of 3 at, %, 1 Oat, %, there are four specifications: a conventional silicon nitride film with a hydrogen content of 3 at, %, 25 at, 0%. All elements were created. Measurement is 1, MU
S) Measure the threshold voltage of the transistor, then apply a predetermined DC stress, and change the threshold voltage to l1lII
I went back and forth on deciding what to do. An example of the results is shown in FIG.

Here, the threshold voltage measurement conditions are: drain/voltage 5V;
Substrate voltage -3V, drain/current I III A,
DC stress conditions are drain/voltage 8V, gate voltage 2
The results are obtained when DC stress is applied for 10 minutes at a plate voltage of -3V. When measuring the threshold voltage, the drain/source is completely reversed from when stress is applied. From FIG. 4, it can be seen that the silicon nitride/film with reduced hydrogen content M according to the present invention has less fluctuation in threshold voltage and is superior to conventional films as a protective film.

Furthermore, 256I (bit n
M (JSDRAM fL) dynamic Random
I went to the Access Men + Ory I Gekisui Shinsi Exam@, and there were no problems.

Example 2 Next, an actual 1M example of the second invention will be described.

In this embodiment, the same plasma CV as in the first embodiment is used.
A silicon nitride film was formed using the D apparatus. The formation procedure is also the same except that the source gas used is different. Gas a, quantity k S i L 100 crn”/sin.

NHs 100cnr”/=n, N2 500cm”/
When z = n, a glow discharge was performed for 60 minutes at a reaction gas pressure 'j (30 Pa + input capacitance 'i) of 800 W, and a total spacing of 6 squares between opposing electrodes, a capping silicon/film of about 400 nm was formed. This film has a refractive index of 1.9, a Vickers hardness of 1800 kg/w2, a hydrogen content of approximately 10 a
It was L.1.

Furthermore, this film was formed as the protective film 20 of the MOS transistor 16 shown in FIG. 3, and the fluctuation of the threshold voltage of the M(JS) transistor was investigated. Dry DC stress conditions/
When the voltage is 8V, the gate plate voltage is -3■, and the L)C stress is applied for 10 minutes, the change in threshold voltage is 0. 10 V,
The amount of change was smaller than that of conventional membranes. The threshold voltage measurement conditions were: drain/voltage 5V, substrate type fi3V,
The drain/current was 1 mA, and measurements were taken with the drain and source reversed from when DC stress was applied. This membrane is also used as a pot for holding knives. nMO8DR
I conducted the AM face l wetness test and found no problems.

Furthermore, the gas flow rate ksiF4100cIT+”/mtn
, NHs600cm"/IHn, and the other conditions were the same as before, and a glow of 77 volts was applied for 60 minutes.
Approximately 550 old n (DW silicon 7 film was formed. This film has a refractive index of 1.9 and a Vickers hardness of 17 rJOkg.
/Order 2. Approximately 1 2 at. %Met. In addition, when this film was formed as a protective film for a MOS transistor, all changes in the threshold voltage of the transistor due to DC stress were measured. o. I was disappointed with ISV. Here, the DC stress conditions and the measurement conditions for the threshold voltage are t
The conditions are exactly the same as above. Furthermore, we tested the moisture resistance of a 256 Kbit nMO8 DRAM using this film as a protective layer, but no problems were found.

As described above, regarding the present invention, the nMU8 transistor and 25
Although the example of nMO8DRAM was explained in 6.
The present invention is based on the method of forming a nitride 7-layer film with a low hydrogen content, and the use of this film is not limited to the above-mentioned devices.

[Effects of the Invention] According to the present invention, a plasma CVD silicon nitride film can be formed that contains less water cables in the film compared to conventional plasma CVD silicon nitride film, which has been a problem in the case. Deterioration of device inertia (variation of threshold voltage, deterioration of mutual conductor/s) caused by hydrogen in the silicon nitride reflective film can be reduced. This has made it possible to manufacture semi-bedded elements with higher reliability than before.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between the gas flow rate ratio of 5iI4n and SiF4, the hydrogen content of the silicon nitride film, and the formation rate.
Figure 2 shows an embodiment of the present invention using FC plasma CVD.
A schematic configuration diagram of the apparatus, Figure 3 is a cross-sectional schematic diagram of the element used to examine the effects of the present invention, and Figure 4 shows the hydrogen content and threshold value in the film showing the effects of the silicon nitride/film of the present invention. This is a graph showing the relationship with voltage fluctuation. DESCRIPTION OF SYMBOLS 1...Vacuum container, 2...Upper pole, 3...Lower electrode, 6...RF power supply, 7...Mass flow controller, 8...Gas cylinder/vehicle, 9... Sample, lO...Heater, 11...Silicon/Substrate, 16...MO8 type transistor, 17, 19...S/Crow film, 18.
...Aluminum grass 1 Figure 5LH4°F4 Grass 2 Figure 3 No reservations 4 Figure Hydrogen consumption (^t2%) Continued from page 1 0 Inventor Mukai Ki - Department Kokubunzenfu Central Research Institute p

Claims (1)

[Claims] 1. In the plasma CVD method, in which all reactant gases are introduced into a reaction vessel and a film is grown in a vapor phase by glow discharge, monosilane gas (Si)44) and silicon tetrafluoride gas (44) are used as main reactant gases. 8iFi) and nitrogen gas (N2). 2. The above SiI'4 and Si1. +4 gas flow rate ratio (S
tH4/(SiH4+8iF4)) is 0.05~
The method for forming a silicon nitride film according to claim 1, wherein the silicon nitride film has a thickness of 0.80. 3. Introduce the reaction gas into the reaction vessel and create a glow discharge9.
A method for producing silicon nitride/films using a plasma CVD method for vapor phase growth of films, which uses silicon tetrafluoride gas (15iF+) and nitrogen gas (N)I3JTh as main reaction gases. Formation method. 4. In the plasma CVD method, in which a reactive gas is introduced into a reaction vessel and an EL film is vapor-phase grown in a glow discharge, silicon tetrafluoride gas (iSi) and ammonia gas (NHs) are used as the main reactive gases. A method for forming silicon nitride/film, characterized by using nitrogen gas (1N2).