US20010036754A1

Movatterモバイル変換

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Publication number: US20010036754A1
Application number: US09/804,142
Authority: US
Inventors: Kazuo Maeda; Noboru Tokumasu; Yuki Ishii; Toshiro Nishiyama
Original assignee: Canon Marketing Japan Inc
Current assignee: Semiconductor Process Laboratory Co Ltd; Canon Marketing Japan Inc
Priority date: 2000-03-31
Filing date: 2001-03-13
Publication date: 2001-11-01
Anticipated expiration: 2021-03-13
Also published as: JP2001284347A; KR20010100812A; TW579546B; US6432839B2

Abstract

The present invention discloses a method for forming a flattened interlayer insulating film to cover the wiring layer or the like of a semiconductor IC device, and a manufacturing method of a semiconductor device. The film-forming method of the present invention comprises the steps of preparing deposition gas containing an inert gas, and a silicon and phosphorus-containing compound having III valance phosphorus in which oxygen is bonded to at least one of bonding hands of phosphorous, and forming a silicon containing insulating film21containing P₂O₃on a substrate101by using said deposition gas.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention[0001]

The present invention relates to a method for forming a flattened interlayer insulating film to cover the wiring layer or the like of a semiconductor integrated circuit device, and a method for manufacturing a semiconductor device.[0002]

2. Description of the Prior Art[0003]

In recent years, with regard to a semiconductor integrated circuit device (hereinafter, referred to as a semiconductor IC device), a progress has been made to achieve a much higher density, and an increasing number of the structures having a multilayer wiring extended over several layers has been used. In such a case, because of the frequent use of, especially an aluminum material for a wiring layer, a strong request has been made to develop a method for forming a flattened interlayer insulating film, which can be formed at a low temperature equal to 500° C. or lower.[0004]

Conventionally available flattening methods include: one like that shown in FIG. 1, which performs flattening by forming a film by a thermal chemical vapor deposition method (hereinafter, referred to as a TH-CVD method), a plasma enhanced chemical vapor deposition method (hereinafter, referred to as a PE-CVD method) or the like, heating the formed film, and then fluidizing the film; and one like an etch back method shown in FIG. 2 or a chemical mechanical polishing method (hereinafter, referred to as a CMP method) shown in FIG. 3, which performs flattening by removing unevenness on the surface of the insulating film by etching or polishing.[0005]

In the case of the former method, as shown in FIG. 1A, a boro-phospho silicate glass film (hereinafter, referred to as a BPSG film) 4 is formed by a TH-CVD method, which uses any one of the following deposition gases:[0006]

(1) SiH[0007]₄+PH₃+B₂H₆+O₂(PH₃: phosphine)

(2) TEOS+TMOP+TMB or TEB+O[0008]₂or O₃(TEOS: tetraethylorthosilicate (Si(OC₂H₅)₄), TMOP: trimethylphosphate (PO(OCH₃)₃)).

Alternatively, as shown in FIG. 1A, a[0009]

BPSG film

4 is formed by a PE-CVD method, which uses any one of the following deposition gases:

(1) SiH[0010]₄+PH₃+B₂H₆+O₂

(2) TEOS+TMOP+TMB or TEB+O[0011]₂.

For reference, see documents: J. Electrochem. Soc., 134.3,: 657, 1987, by Williams, D. S. and Dein, E. A; J. Vac. Sci. Technol., B1, 1:54, 1983, by Levin, R. M. and Evans-Lutterodt, K; Extended Abstract of Electrochem. Soc. Spring Meeting: 31, 1971, by Sato, J. and Maeda, K.[0012]

Then, as shown in FIG. 1B, the formed BPSG[0013]

film

4 is heated at a temperature of about 850° C., and fluidized to be flattened. In the case of a phospho-silicate glass film (hereinafter, referred to as a PSG film), a film is formed by a TH-CVD method, a PE-CVD method or the like, which uses deposition gas generated by eliminating boron containing gas (B₂H₆, TMB or TEB) from the foregoing gas, then heated at a temperature equal to 1000° C. or lower, and fluidized to be flattened.

In the case of the latter method, as shown in FIG. 2A and FIG. 3A, firstly, a non-doped silicate glass (hereinafter, referred to as an NSG film)[0014]5 is formed by a TH-CVD method, a PE-CVD method or the like, which uses one of the following deposition gases, and then flattened:

(1) SiH[0015]₄+O₂(TH-CVD method or PE-CVD method)

(2) TEOS+O[0016]₂or O₃(TH-CVD method)

(3) TEOS+O[0017]₂(PE-CVD method)

In the etch back method, as shown in FIG. 2B, a resist film[0018]6 is formed on theNSG film5 by coating method, and its surface is flattened. Then, as shown in FIG. 2C, the film6 is subjected to etching from above to form a flattened NSG film5a. In the CMP method, as shown in FIG. 3B, the NSGfilm5 is formed, and then polished to flatten the surface of anNSG film5b.

In FIGS.[0019]1 to3, areference numeral1 denotes a semiconductor substrate;2 a base insulating film; and3aand3bwiring layers formed on the baseinsulating film2.

Incidentally, the above-described flattening methods based on the etch back method or the CMP method are effective especially when a low temperature is required, because these methods can be executed without heating unlike the case of the flattening method based on fluidizing by heating. However, as shown in FIGS. 2 and 3, if any voids are formed between the[0020]

wiring layers

3aand3bor in other recessed parts immediately after theinsulating film5, the voids are left unchanged even after flattening. Currently available methods for forming insulating films having good gap-filling capabilities include a high-density PE-CVD method, a PE-CVD method, an atmospheric pressure TH-CVD method, an spin-on-glass (hereinafter, referred to as SOG) coating method, and the like. However, since the described flattening methods use no thermal fluidity, particularly when a high densification is attained to narrow a space between the wiring layers, recessed parts cannot be completely filled.

On the other hand, in the flattening method based on fluidizing by heating, since thermal fluidity is utilized, as shown in FIG. 1, complete filling can be expected. At present, especially the BPSG[0021]

film

4 is frequently used for such a purpose. However, heating of at least a temperature of 850° C. must be carried out for fluidization. Thus, such a film cannot be applied to thebase film2 of the

wiring layers

3aand3bor theinterlayer insulating film4, where a low temperature is needed for formation. In particular, the film cannot be applied to an insulating film to cover the aluminum wiring layer. In this case, the temperature of fluidization can be somewhat lowered by increasing the concentration of boron or phosphorus. Even so, the temperature is not yet sufficiently low. Rather, new problems may occur, such as a reduction in the stability or humidity resistance of the

insulating films

As an insulating film having a low fluidization temperature, a GeBPSG film formed by adding GeO[0022]₂to the BPSG film has been developed. However, the temperature can be lowered to about 750° C. at least. Thus, it is difficult to apply this film to the base film or the interlayer insulating film, in which a much lower temperature is required.

SUMMARY OF THE INVENTION

A fluidization temperature should preferably be set as low as possible not only when aluminum, copper or the like is used for wiring in a semiconductor large scale integrated circuit (hereinafter, referred to as LSI) or the like, but also to prevent the re-distribution of impurities in an impurity introduction region generally caused by heat.[0023]

An object of the present invention is to provide a method for forming an insulating film, capable of greatly reducing a fluidization temperature for flattening a surface, and a manufacturing method of a semiconductor device.[0024]

The inventors focused on the following points:[0025]

(1) the BPSG film or the phospho-silicate glass film (hereinafter, referred to as PSG film) of the conventional example is a mixture of SiO[0026]₂+P₂O₅+B₂O₃, or of SiO₂+P₂O₅(PH₃of deposition gas SiH₄+PH₃+B₂H₆+O₂is III valance phosphorus, and bonded with externally supplied oxygen to generate not P₂O₃but P₂O₅. This may be attributed to the fact that since PH₃itself contains no oxygen, when it is bonded with externally supplied oxygen, stable P₂O₅is easily generated.);

(2) in the BPSG film having the P[0027]₂O₅-SiO₂, a eutectic point for the composition of 20 to 80 % of P₂O₅is 850° C. theoretically, and its fluidization temperature is dependent on the melting point of P₂O₅itself; and

(3) P[0028]₂O₃has a melting point much lower than that of P₂O₅as described on Table 1.

	TABLE 1


	Melting point	Boiling point

P₂O_{3 (III valance)}	23.8° C.	175.4° C.
P₂O_{5 (V valance)}	580 to 585° C.	300° C. (sublimation)

Accordingly, the inventors considered that a fluidization temperature would be lowered by mainly containing P[0029]₂O₃, instead of P₂O₅, in the BPSG film or the PSG film.

Then, the inventors came up with the idea of oxidizing a phosphorus containing compound in a state of oxygen shortage to form a BPSG or PSG film having a high-concentration of P[0030]₂O₃. As methods for such a purpose, the followings may be possible. That is, (1) a silicon and phosphorus-containing compound, containing phosphorus atom (P atom) in the form of III valance is used as deposition gas; and (2) by using a silicon containing compound or a silicon and phosphorus-containing compound containing oxygen, a film is formed without adding any oxygen or ozone.

Regarding a silicon and phosphorus-containing compound, containing III valance P atom, which can be applied to the method of (1), one may be selected from silicon and phosphorus-containing compounds having the following structural formulas:[0031]
A PSG film or the like was formed by using deposition gas containing the silicon and phosphorus-containing compound, and by a TH-CVD method or a PE-CVD method, and examination was made as to components in the formed film by X-ray fluorescence analysis (XRF) or Fourier transform infrared spectroscopy (FTIR). Then, the presence of high-concentration P[0032]₂O₃in the formed film was verified. Then, a fluidization temperature of 700° C. or lower was obtained.
In addition, the inventors found that it is possible to adjust a fluidization temperature by controlling a concentration of P[0033]₂O₃.
The inventors also found that it is possible to easily adjust a concentration of P[0034]₂O₃by controlling a deposition temperature and the gas flow rate of the silicon and phosphorus-containing compound (flow rate of inert gas carrier), or by controlling a concentration of oxidizing gas when the oxidizing gas is added.
It is now assumed that nitrogen (N[0035]₂) is used as carrier gas of the silicon and phosphorus-containing compound. Since N₂is a diatomic molecule, when a film is formed by reaction of plasma enhanced deposition gas, N₂is prone to be dissociated, and bonded with hydrogen in the film, leaving ammonia (NH3) in the film. According to the present invention, inert gas, e.g., argon or helium is used as carrier gas. Because of little reactivity of argon or helium itself, the amount of ammonia in the film can be reduced substantially to zero.
Further, the use of inert gas, e.g., argon or helium, as carrier gas, resulted in the great reduction in the concentration of phosphorus during heat treatment after deposition, enhancing controllability of the concentration of Phosphorus.[0036]
In addition, by forming a film using only the silicon and phosphorus-containing compound, containing III valance phosphorus, the amount of carbon left in the formed film can be greatly reduced. In this case, the adjustment of a phosphorus concentration can be made by controlling the ratio of flow rates between the silicon and phosphorus-containing compound and the foregoing inert gas in the deposition gas. Accordingly, though a silicon containing compound containing no phosphorus is added in the deposition gas in the conventional method in order to adjust a phosphorus concentration, the silicon containing compound containing no phosphorus can be eliminated from the deposition gas. The silicon containing compound containing no phosphorus has Si—C bonding, causing carbon to be left during deposition. Thus, preferably, the addition of such a compound should be prevented as much as possible. However, the compound can be added as occasion demands.[0037]
Furthermore, the film that has been formed is subjected to nitrogen annealing and oxygen annealing, and then heated in atmosphere containing moisture. This process is called steam annealing. Since the steam annealing has an oxidizing force stronger than that for normal oxygen annealing, residual III valance phosphorus is oxidized, and the moisture absorption resistance of the formed film is enhanced, making it possible to improve film quality.[0038]
The foregoing can be established similarly for the BPSG film.[0039]

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are sectional views showing a method for forming an interlayer insulating film, which includes flattening carried out by fluidization due to heating, according to a conventional example.[0040]

FIGS. 2A to[0041]2C are sectional views showing a method for forming an interlayer insulating film, which includes flattening carried out by etch back, according to a conventional example.

FIGS. 3A and 3B are sectional views showing a method for forming an interlayer insulating film, which includes flattening carried out by CMP, according to a conventional example.[0042]

FIGS. 4A to[0043]4D are sectional views showing a method for forming a PSG film, which comprises a series of steps including a film-forming step, according to a first embodiment of the present invention.

FIG. 5 is a graph associated with the amount of ammonia in the PSG film formed by the film-forming method of the first embodiment of the present invention and showing substrate temperature dependence thereof.[0044]

FIG. 6 is a graph showing a relation between phosphorus concentration in the PSG film formed by the film-forming method of the first embodiment of the present invention, and a temperature of annealing after film formation.[0045]

FIG. 7 is a graph showing the amount of carbon in the PSG film formed by the film-forming method of the first embodiment of the present invention.[0046]

FIG. 8 is a flowchart showing the film-forming method of the embodiment of the present invention.[0047]

FIGS. 9A to[0048]9E are sectional views showing a method for forming a PSG film, which comprises a series of steps including a film-forming step, according to a second embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Next, the preferred embodiments of the present invention will be described with reference to the accompanying drawings.[0049]

(1) First Embodiment

Description will be made of a method for forming a PSG film through a series of steps including a film-forming step according to a first embodiment of the present invention.[0050]

As shown in FIG. 8, a series of steps include, a film-forming step, an N[0051]₂annealing step, an O₂annealing step, and a steam annealing step.

With regard to deposition gas in the film-forming step, gas generated by mixing a silicon and phosphorus-containing compound, inert gas and oxidizing gas was used. Silicon containing compounds containing no phosphorus should not be used.[0052]

For a phosphorus containing compound, one can be selected from silicon and phosphorus-containing compounds having Si—O—P structures, for which the structural formulas is shown below:[0053]

(i) phosphorus acid dimethyl trimethylsilylester (referred to as SOP-11(a), hereinafter);[0054]
(ii) phosphorous acid dimethoxy trimethylsilylester (referred to as SOP-11(b), hereinafter);[0055]
(iii) P (OSi (CH[0056]₃)₃)₃: or
(iv) P (OSi (CH[0057]₃))₂OCH₃.
Other than the above, a silicon and phosphorus-containing compound having III valance phosphorus, and oxygen being bonded to at least one of the bonding hands of the phosphorus, can be used. In the described embodiment, SOP-11(b) was used.[0058]
For inert gas to be added to the silicon and phosphorus-containing compound, inert gas of argon (Ar) or helium (He) can be used. In the embodiment, argon (Ar) was used for the inert gas.[0059]
With regard to oxidizing gas, it is not always necessary to contain oxidizing gas in the deposition gas. However, when contained, ozone (O[0060]₃), oxygen (O₂), NO, N₂O, NO₂, CO, CO₂, H₂O, or the like can be used as oxidizing gas. In the embodiment, oxygen (O₂) is used as oxidizing gas.
As occasion demands, a silicon containing compound containing no phosphorus may be added to the deposition gas. In this case, as such a silicon containing compound, one can be selected from alkylsilane or arylsilane (general formula R[0061]_nSiH_4-n(n=1 to 4)), alkoxysilane (general formula (RO)_nSiH_4-n(n=1 to 4)), chain siloxane (general formula R_nH_3-nSiO (R_kH_2-kSiO)_mSiH_3-nR_n(n=1 to 3; k=0 to 2; m∞0)), a derivative of cyclic siloxane (general formula (RO)_nH_3-nSiOSiH_3-n(OR)_n(n=1 to 3), chain siloxane (general formula (R_kH_2-kSiO)_m(k=1, 2; m∞2)), and the like. In this case, R is an alkyl group, an aryl group or its derivative.
Compounds containing silicon but no phosphorus are mainly as follows:[0062]
(i) hexamethyl disiloxane (HMDSO): (CH[0063]₃)₃SiOSi(CH₃)₃);
(ii) tetramethyl disiloxane (TMDSO): H(CH[0064]₃)₂SiOSi(CH₃)₂H);
(iii) hexaethyl disiloxane (HEDSO): (C[0065]₂H₅)₃SiOSi(C₂H₅)₃);
(iv) tetraethyl orthosilicate (TEOS: Si(OC[0066]₂H₅)₄);
(v) triethoxy silane (TRIES: HSi(OC[0067]₂H₅)₃); and
(vi) trimethoxy silane (TMS: HSi(OCH[0068]₃)₃).
In the steam annealing step, one made by mixing oxygen and hydrogen in a predetermined ratio is reacted to generate water molecules, and heating is carried out in atmosphere containing the water molecules.[0069]
Conditions for a series of steps are described below. Standard processing conditions are shown in tables. Processing parameters having conditions varied to obtain comparison data are described outside the tables.[0070]

(1) Deposition Condition

[0071]

	TABLE 2


	Deposition	Standard setvalue

	Substrate temperature
	250° C.
	RF power	150 W
	Total gas flow rate	1.0 slm
	Amount of addedO₂	2 sccm

The substrate temperature was changed to 100, 200, and 300° C. Since SOP-11(b) is liquid at a normal temperature, it is contained in carrier gas by bubbling. The inventors prepared two kinds of compounds, i.e., one using Ar carrier as carrier gas, and one using N[0072]₂carrier as such. When inert gas (Ar) was used as carrier gas, the content of SOP-11(b) in deposition gas was adjusted by controlling the flow rate of carrier gas.

(ii) N[0073]₂annealing

	TABLE 3


	Processing	Standard set value

	Temperature rising rate	10° C./min.
	N_{2 gas flow rate}	10 slm
	Holding temperature	650°C.
	Holding time
	15 min.

For comparison, the heat treatment temperature was changed to 250, 500, and 750° C. In addition, similar processing was carried out for a film formed by containing N[0074]₂instead of Ar in the deposition gas.

(iii) O[0075]₂annealing

	TABLE 4


	Processing	Standard set value

	O₂gas flow rate	10 slm
	Holding temperature	650°C.
	Holding time
	15 min.

(iv) Steam annealing[0076]

	TABLE 5


	Processing	Standard set value

	O₂gas flow rate	6 slm
	H₂gas flow rate	5 slm
	Holding temperature	650°C.
	Holding time
	15 min.

Any one of O[0077]₂annealing and steam annealing among above annealing processes can be ommited.

First, a[0078]

substrate

101 to be deposited shown in FIG. 4A is placed in the chamber of a PE-CVD apparatus. Then, substrate heating is carried out to hold a specified substrate temperature.

Subsequently, the foregoing deposition gas is introduced into the chamber, and plasma is generated and held for a predetermined time. In this way, a[0079]

PSG film

21 having a specified thickness containing high-concentration P₂O₃is formed. In this case, depending on the concentration of P₂O₃or the ratio of P₂O₃/P₂O₅, thePSG film21 may be fluidized at a temperature substantially equal to the substrate temperature during film formation. Accordingly, flattening is achieved simultaneously with the film formation.

Then, as shown in FIG. 4B, after the formation of the[0080]

PSG film

21 on thesubstrate101, heating for flattening is carried out in N₂atmosphere. APSG film21ais fluidized to be flattened.

Then, as shown in FIG. 4C, heating is carried out in atmosphere containing oxygen. In this way, P[0081]₂O₃in a PSG film14ais oxidized and converted to P₂O₅. As a result, a P₂O₅concentration in aPSG film21bis increased to thereby stabilize the PSG film14a.

Then, as shown in FIG. 4D, heating is carried out in atmosphere containing moisture. Because of a high oxidizing force of the moisture, the conversion of P[0082]₂O₃to P₂O₅is further promoted. Accordingly, a P₂O₅concentration in thePSG film21bbecomes much higher.

With regard to the[0083]

PSG film

21 formed in the above film-forming method, the amount of ammonia in the film immediately after its formation was examined.

The result of the examination is shown in FIG. 5. Specifically, FIG. 5 shows the dependence of the amount of ammonia in the formed film after film formation on a substrate temperature during film formation, in which an ordinate axis shows the amount of ammonia (wt. %) in the formed film, expressed in linear scale and an abscissa axis shows a substrate temperature (°C.), expressed in linear scale.[0084]

In the examination, a sample is subjected to thermal desorption spectroscopy (TDS) analysis, thermally desorbed ammonia gas is quantitatively measured, and then comparison is made.[0085]

As can be understood from the result of FIG. 5, there are differences in the tendency of dependence and contents between the case of using Ar as carrier gas and the case of using N[0086]₂as the same. When carrier gas is Ar, the substrate temperature is not affected, and little ammonia is contained in the formed film. When carrier gas is N₂, a content of ammonia is equal to 5 wt. % or higher, and the content is increased corresponding to the increase of the substrate temperature.

Detection was also carried out for a concentration of phosphorus in the formed film by means of X-ray fluorescence analysis (XRF). By the XRF, a total concentration of P[0087]₂O₃+P₂O₅in the formed film can be detected.

The result of analysis is shown in FIG. 6. Specifically, FIG. 6 shows the dependence of a phosphorus concentration in the formed[0088]

Film

21aon the heat treatment temperature of N₂annealing after film formation, in which an ordinate axis shows a P concentration (wt. %) in the PSG film, and an abscissa axis shows a heat treatment temperature (°C.), expressed in linear scale. “As depo” denotes a concentration of phosphorus in thePSG film21 immediately after film formation and before N₂annealing.

As can be understood from FIG. 6, there is a difference in the concentration of P[0089]₂O₃or in the ratio of P₂O₃/P₂O₅in the formedPSG film21abetween the case of using Ar as carrier gas and the case of using N₂as the same. The concentration of P₂O₃or the ratio of P₂O₃/P₂O₅can be reduced more when Ar is used as carrier gas than when N₂is used as the same. For both cases, it was discovered that the concentration of phosphorus can be adjusted by a heat treatment temperature.

In addition, a melting temperature or a fluidization temperature of the[0090]

PSG film

21afor each of the above case becomes lower as the concentration of P₂O₃or the ratio of P₂O_3/P₂O₅is higher. In the experiment, a melting temperature or a fluidization temperature equal to 700° C. or lower was obtained.

Further, FIG. 7 shows the result of examining the amount of Si—CH[0091]₃bonding, i.e., a carbon content, in the formedfilm21b.Specifically, an ordinate axis of FIG. 7 shows an absorption intensity (arbitrary unit) by Fourier transform infrared spectroscopy (FTIR), while an abscissa axis shows the number of waves (cm−1).

According to the result shown in FIG. 7, a content of Si—C H[0092]₃bonding in the formedfilm21bvaries between the case of using Ar as carrier gas and the case of using N₂as the same. In other words, a peak height of an absorption intensity is lower in the case of using Ar as carrier gas than that in the case of using N₂as the same, and thus a content of Si—CH₃bonding in the formedfilm21bis smaller.

As apparent from the foregoing, according to the first embodiment of the present invention, since a phosphorus containing compound, which contains III valance phosphorus, is used for deposition gas, it is possible to form a PSG film having a high P[0093]₂O₃content immediately after film formation. Accordingly, the PSG film can be fluidized at a low temperature.

Moreover, inert gas, e.g., argon or helium, is used as carrier gas in the deposition gas. Because of little reactivity of argon or helium itself, the amount of ammonia in the formed film can be set substantially to zero. Thus, the quality of the formed film can be improved.[0094]

(2) Second Embodiment

Next, description will be made of a method for forming a PSG film containing P[0095]₂O₃by means of PE-CVD method according to a second embodiment of the present invention.

FIG. 8 is a flowchart showing a film-forming method according to the second embodiment of the invention. a set of FIGS. 9A to[0096]9F is a sectional view of the film-forming method of the second embodiment of the present invention.

As deposition gas, mixed gas of SOP-11(b)+Ar was used. To set a sufficient state of oxygen shortage, no oxygen (O[0097]₂) was added different from the case of the first embodiment.

As a film-forming method, a PE-CVD method by a film forming apparatus having a well-known parallel plate type electrode was used. Plasma enhanced method by the parallel plate type electrode is a method for applying an RF power between upper and lower electrodes placed oppositely to each other, and then converting deposition gas between these electrodes into plasma. The lower electrode serves also as a substrate holder and, as occasion demands, power for substrate biasing may be applied to the lower electrode.[0098]

A deposition condition is described below.[0099]

	TABLE 6


	Deposition parameter	Deposition condition

	SOP-11(b) (bubbling by Ar)	0.1 to 2 slm
	Ar	0.1 to 1 slm
	Substrate temperature	20 to 400° C.
	Pressure range	66 to 2667Pa
	RF power
	100 to 700 W
	Frequency	13.56 MHz
	Substrate bias power	0 to 300 W
	Frequency	13.56 MHz or 400 kHz

FIG. 9A is a sectional view of a[0100]

substrate

101 to be deposited before film formation. Thesubstrate101 is constructed in a manner that abase insulating film12, e.g., a silicon oxidized film, is formed on a silicon substrate (semiconductor substrate)11, and wiring layers13aand13bcomposed of, e.g., aluminum films, are formed on thebase insulating film12.

In this state, first, the[0101]

substrate

101 is placed on the substrate holder in a deposition chamber. Subsequently, thesubstrate101 is heated or controlled to a temperature of the range of 20 to 400° C.

Then, as shown in FIG. 9B, mixed gas of SOP-11(b)+Ar is introduced into a plasma chamber, and gas pressure is maintained at 0.5 to 20 Torr. Ar is used as carrier gas of SOP-11(b). A flow rate of Ar carrier gas containing SOP-11(b) was set in the range of 0.1 to 2 SLM, and a flow rate of added Ar was set in the range of 0.1 to 1 SLM.[0102]

Then, power 0 to 300 W of a frequency 13.56 MHz is applied to the substrate holder, and a bias voltage is applied to the[0103]

substrate

101. Further, power 50 to 2.3 kW of a frequency 13.56 MHz is applied to the upper electrode, and deposition gas is converted into plasma.

Accordingly, reaction occurs in the plasma of the deposition gas, and the deposition of a reactive product on the[0104]

substrate

101 is started. A PSG film16 under film formation showed a flowability to flow into a recessed part between the wiring layers13aand13beven at the substrate temperature of about 200° C. In this case, phosphorus may be contained in the PSG film16 in the form of III valance P₂O₃. Because of no external supply of oxygen, the state of an oxygen shortage is maintained in a reaction system, and Si and P may be respectively contained in the PSG film16 in the form of Si—O and P—O being bonded with oxygen atoms present in molecules.

Then, after its removal from the film-forming apparatus, the[0105]

substrate

101 is conveyed in vacuum or atmosphere, and set in a heat treatment furnace held at a deposition temperature or lower. Subsequently, as shown in FIG. 9C, N₂is introduced into the heat treatment furnace at a flow rate of 10 SLM, and thesubstrate101 is heated. A temperature rising rate is set about 10° C./min., and after the substrate temperature reaches 650° C, this state is maintained for several minutes. The processing comes to an end with the passage of about 15 minutes after the temperature rising. N₂annealing breaks the glass structure of a formedfilm15a, and re-flowing brings about void filling and formed film flattening. In addition, a gas component contained in the formedfilm15ais eliminated therefrom during heating, and thus aPSG film15ahaving III valance phosphorus is formed.

Then, as shown in FIG. 9D, while the substrate temperature is maintained at 650° C., oxygen is introduced at a flow rate of 10 SLM, and the[0106]

substrate

101 is heated in oxygen atmosphere for about 15 minutes. III valance phosphorus has very high reactivity, and is prone to be oxidized. Thus, the phosphorus can be converted into stable V valance phosphorus by exposing it to oxygen atmosphere at a high temperature. In this way, thePSG film15acontaining the unstable III valance phosphorus becomes aPSG film15bcontaining stable V valance phosphorus.

As described above, by annealing carried out in atmosphere containing oxygen after film formation, P[0107]₂O₃is converted into P₂O₅to stabilize thePSG film15b. Moreover, the final composition of P₂O₅provides a passivation effect to thePSG film15b, and contributes to the stabilization of an interface characteristic. Noted that residual carbon in the formed film is simultaneously oxidized by the annealing.

Then, an oxygen flow rate is adjusted to 6 SLM while the substrate temperature is maintained at 650° C., hydrogen is newly added at a flow rate of 5 SLM, and then these are introduced through a burning heater into the chamber. The burning heater is heated to 850° C. beforehand. Mixed gas is ignited to cause reaction so as to generate water molecules, and as shown in FIG. 9E, heating is carried out in atmosphere containing moisture for about 15 minutes. Since an oxidizing force for the heating carried out in the moisture containing atmosphere, so-called steam annealing is stronger than that for normal oxygen annealing, film quality can be further improved by oxidizing residual III valance phosphorus, and increasing the moisture absorption resistance. By examination, the reduction in the amount of moisture in the film to about {fraction (1/10)} was verified. A reason for such a reduction is not yet definite. However, a likely reason may be that a moisture absorbing site remaining in the network of SiO[0108]₂can be greatly reduced by strong oxidation provided by the steam annealing.

As apparent from the foregoing, according to the second embodiment of the present invention, since insulating[0109]

films

21 and15 having high-concentration of P₂O₃as a phosphorous component are formed, a fluidization temperature can be reduced to 700° C. or much lower. Accordingly, such a film can be used as an interlayer insulating film to cover aluminum wiring. Moreover, even when such a film is used as the base insulating film of a wiring layer in a semiconductor device having a narrower diffused layer with a higher densification of the semiconductor device, impurities in the diffused layer can be prevented from being re-distributed.

Further, the necessity of a flattening processing technology such as a CMP method or the like can be eliminated, and the interlayer insulating film can be flattened by thermally fluidizing the formed film. Thus, a recessed part between the wiring layers can be filled without any gaps.[0110]

Assuming that nitrogen is used as carrier gas, since N[0111]₂is a diatomic molecule, when a film is formed by reaction of the plasma enhanced deposition gas, N₂is prone to be dissociated, leaving ammonia (NH3) in the formed film. According to the second embodiment of the present invention, inert gas, e.g., argon or helium, is used as carrier gas. Because of little reactivity of argon or helium itself, such interference compound can be prevented from forming.

Further, by using inert gas as carrier gas, a concentration of phosphorus was greatly reduced during heat treatment after film formation, enhancing controllability of the concentration of phosphorus.[0112]

In addition, by forming a film using only a phosphorus containing compound, which contains III valance phosphorus, the amount of carbon left in the formed film can be greatly reduced. In this case, the adjustment of concentration of phosphorus can be made by controlling the ratio of flow rates between the silicon and phosphorus-containing compound and the inert gas in the deposition gas. Thus, the addition of a compound containing silicon but no phosphorus, which is conventionally added to the deposition gas was made unnecessary in principle. Also, the compound containing silicon but no phosphorus has Si—C bonding, causing carbon to be left in the formed film. Thus, such a compound should preferably be added as little as possible. However, addition thereof may be permitted as occasion demands.[0113]

In addition, after film formation, so-called steam annealing is carried out, which heats the formed film in atmosphere containing moisture after nitrogen annealing and oxygen annealing. Since the steam annealing has a stronger oxidizing force than that of normal oxygen annealing, film quality can be further improved.[0114]

The invention has been described in detail with reference to the preferred embodiments. However, the scope of the invention is not limited to the specified embodiments. Various changes and modifications can be made without departing from the gists of the invention, and such changes and modifications are within the scope of the invention.[0115]

For example, in the second embodiment, no oxygen is used for deposition gas. Needless to say, however, as in the case of the first embodiment, by adding oxygen, a melting temperature or a fluidization temperature can be adjusted by controlling a concentration of P[0116]₂O₃or the ratio of P₂O₃/P₂O₅. In addition, by controlling other deposition parameters, e.g., a substrate temperature and the flow rate of inert gas, as in the case of the first embodiment, a melting temperature or a fluidization temperature can also be adjusted through the adjustment of a concentration of P₂O₃or the ratio of P₂O₃/P₂O₅.

Further, the PE-CVD method is used. However, a TH-CVD method for activating deposition gas by heat may be used. In this case, for example, deposition conditions described in Table 7 can be used.[0117]

TABLE 7


TH-CVD Method

	Deposition parameter	Depositioncondition

	Substrate temperature
	200 to 400° C.
	Ozone concentration	0.3 to 2.5%
	Gas flow rate of SOP-11(b)	0.1 to 1.5 slm
	Gas flow rate of TMB or TEB	0.1 to 1.0 slm

Also, in the case of the TH-CVD method, ammonia may be generated when N[0118]₂is contained in deposition gas. However, by using a compound containing no N₂in the deposition gas, the amount of ammonia in the formed film can be reduced substantially to zero.

In stead of the foregoing annealing, or together with annealing, a cover insulating film for moisture absorption prevention may be formed on the[0119]

PSG film

15b.

As a CVD apparatus, the TH-CVD apparatus or the PE-CVD apparatus is used, and the furnace for annealing is used to improve the film quality. However, in order to enable the film to be reformed without exposure to atmosphere after film formation, a film forming apparatus entirely having a constitution, where the CVD apparatus and the annealing furnace are connected by a load-lock chamber should preferably be used.[0120]

As apparent from the foregoing detailed description, the present invention is advantageous in the following respects. Since the PSG film or the BPSG film is formed in a state of oxygen shortage, the PSG film or the BPSG film having a high-concentration of P[0121]₂O₃as a phosphorous component can be formed, making it possible to reduce a fluidization temperature to 700° C. or much lower. Thus, such a film can be used as a flattened base film below the wiring layer, or a flattened interlayer insulating film to cover the wiring layer.

Since the interlayer insulating film can be flattened by thermally fluidizing the formed film, a recessed part between the wiring layers can be filled without any gaps.[0122]

Inert gas, e.g., argon or helium, is used as carrier gas,. Because of little reactivity of argon or helium itself, the amount of ammonia in the formed film can be reduced substantially to zero, making it possible to improve film quality.[0123]

Furthermore, by using inert gas as carrier gas, a concentration of phosphorus is greatly reduced during heat treatment after film formation, making it possible to enhance controllability of the concentration of phosphorus.[0124]