JPS6298625A - Semiconductor device - Google Patents

Abstract

PURPOSE:To effectively avoid any abnormal fluctuation with time in gate threshold value voltage by a method wherein a passivation film extremely stabilized for heat-treatment is provided. CONSTITUTION:Within a passivation film of two layer composition, a lower layer 11 near a semiconductor element is formed of a plasma CVD processed film not containing hydrogen H2 deposited with disilicon hexafluoride Si2F6 and nitrogen N2 as mixed gas while an upper layer 12 is formed of another plasma CVD processed film containing H2 deposited with said Si2F6, N2 and H2 as mixed gas with Si and N2 firmly coupled with each other forming stabilized composition subject to high deposition speed. Through these procedures, this passivation film can be prevented from discharging H2 into the semiconductor element in the depositing process of both lower and upper layers doing damage to the same.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a semiconductor device, and particularly to a structure of a semiconductor device including a highly reliable passivation film.

(Prior Art) A passivation film or an interlayer insulating film of a semiconductor device usually contains silicon dioxide (Sift) or silicon nitride (Sift).
Si3N4) or phosphosilicate glass (PSG) is used, but a silicon nitride film is often used when reliability is important. This silicon nitride film has conventionally been made using monosilane (si) i4) and ammonia (NHs) or nitrogen (N
, ) is formed by plasma chemical vapor deposition using a mixed gas. That is, these gases are heated at low temperatures (200~
3 so'c), deposited films reacted under low pressure (10 to 1 torr or less) are commonly used.

(Problems to be Solved by the Invention) This film has advantages such as being thicker than those grown at high temperatures of 800"C or higher, and having fewer cracks. In addition to silicon (Sj) and nitrogen (N, ), it contains (Si-H) and (N-)i, which are bonded with hydrogen (H2), forming an unstable composition. High temperature processing (450-500°C) during deposition and subsequent alloying, assembly or annealing steps
), which also has the disadvantage of releasing hydrogen and deteriorating the characteristics of semiconductor devices. This is greatly affected when the semiconductor element is a MOS type field effect transistor, and for example, an academic journal published in January 1981, ``Trans
Electron Devices (VOL,E
D-28゜Thretsu V, Ludo Portage Inn m
1) Paper published by Jacj rThreshold Volt
age in - stability in moss
EFT Day Two Channel 5tabil
ity in MOS-FET due to
The channel sonopassivation film causes abnormal fluctuations in the gate threshold voltage during operation.

[Purpose of the invention]

In view of the above circumstances, an object of the present invention is to provide a semiconductor device equipped with a passivation film made of a silicon nitride film grown by plasma chemical vapor deposition, which does not release hydrogen during deposition and subsequent high-temperature treatment steps and damage semiconductor elements. It is to be.

[Structure of the invention]

The semiconductor device of the present invention includes a semiconductor substrate, a semiconductor element formed on the semiconductor substrate, and silicon hexafluoride (S).
i2 Fs), nitrogen (N2) and silicon hexafluoride (
The silicon nitride film includes two layers of silicon nitride films deposited as a lower layer and an upper layer, respectively, with plasma chemical vapor deposition films using mixed gases of Si2Fg), nitrogen (N, ), and hydrogen (H8), respectively.

(Means for Solving the Problem) That is, according to the present invention, the padgage blind film has a two-layer structure, and the lower layer near the semiconductor element contains disilicon hexafluoride (Six Fs) and nitrogen (Nz). Due to the plasma chemical vapor deposition film that does not contain hydrogen (H2) deposited as a mixed gas, the upper layer is made of disilicon hexafluoride (Si, Fa).
, containing hydrogen (H8) deposited as a mixed gas of nitrogen (N-rich) and hydrogen (H-rich), which combines strongly with silicon (8i) and nitrogen (N2) to form a stable composition and has a high deposition rate. Each is composed of a plasma-enhanced chemical vapor deposition film.

(Function) Therefore, this passivation film does not release hydrogen to the semiconductor element and damage it in either the lower layer or upper layer deposition process. That is, the semiconductor device is not exposed to any hydrogen-containing atmosphere during the deposition of the lower layer, and the penetration of the hydrogen-containing atmosphere into the device during the deposition of the upper layer is prevented by this lower layer. Furthermore, even during subsequent high-temperature processing steps exceeding 400°C such as alloying, assembly, and annealing, the lower layer film does not originally contain hydrogen, and the upper layer film has a stable composition and does not easily release hydrogen. , no hydrogen is allowed to enter the inside of the semiconductor device even at any similar stage of the manufacturing process. That is, unlike the conventional passivation film, it is extremely unlikely to cause abnormal fluctuations in the gate threshold voltage of the MO8 field effect transistor during operation. The present invention will be described in detail below with reference to the drawings.

(Example) FIG. 1 is a cross-sectional structural diagram showing an example in which the present invention is applied to an M08% field effect transistor. In this embodiment, a P-type silicon substrate 1, a thick field oxide film 2, n-type regions 3 and 4 forming a source and a drain, respectively, a gate insulating film 5, a polycrystalline silicon gate electrode 6, A P layer 7 forming a channel stopper, an aluminum wiring conductor 9, a silicon oxide insulating film 10, and plasma chemical vapor deposition films 11 and 12 of different silicon nitride film quality forming lower and upper passivation films, respectively. including.

Here, for the deposition of the lower plasma chemical vapor deposition film 11, a mixed gas of disilicon hexafluoride (SixFll) and nitrogen (N) at a pressure of 0.8 torr is used, for example, at a flow rate ratio of 1:12. For the deposition of the upper plasma chemical vapor deposition film 12, a mixed gas of disilicon hexafluoride (5ixFs), nitrogen (N), and hydrogen (H2) at a pressure of 1.4 torr is used, for example, at a flow rate ratio of 1:14:18. are used. At this time, the flow rate of hydrogen may be changed as appropriate. These mixed gases are sequentially introduced into the reaction chamber to deposit each growth film on the silicon oxide insulating film 10 of the wafer. The high-frequency power density for plasma generation is 0.6, respectively.
W/cttF and 0.8 W/cn? , the substrate set temperatures are 350°C and 390°C, respectively.

According to the results of the spectral analysis, the lower layer vapor growth film 11 has an absorption spectrum due to (Si-N) bonds, and the upper layer vapor growth film 12 has absorption spectra due to (Si-N) and (N-H) bonds.
Absorption spectra due to the two combinations of , respectively, appear,
(Si-F) and (N-F) bonds are (Si-F) and (N-F) bonds.
-N) is hidden in the absorption spectrum due to the bond. Therefore, all of these deposited films are made of silicon nitride. Furthermore, according to the results of Auger Electronic Public Party measurement,
In addition to silicon (Sl) and nitrogen (N), fluorine (F
) is included in any conversion, (8i −N) and (N−
Since it acts to strengthen the bonds of H), it is shown that the film has extremely stable film quality without releasing hydrogen during the heat treatment process. Originally, the vapor-phase grown film 11 does not contain hydrogen and has a very thermally stable composition, but it also has a film quality that slightly reacts with water (N20). The film 12 is grown to compensate for the defects 2
A layered passivation film hardly allows hydrogen to enter the semiconductor element during the deposition process or during the subsequent high-temperature treatment process exceeding 450°C. The characteristics of this film quality can also be confirmed from the following experiment.

That is, FIG. 2 is a side view showing how the effective surface charge density of the passivation film of the present invention changes in a high-temperature atmosphere in comparison with a conventional film. MIs type diodes A and B each having a vapor-phase grown film according to the present invention and a conventional vapor-grown film as insulators were prepared as the samples, and a high-temperature nitrogen atmosphere with a temperature of 500°C was prepared as the high-temperature atmosphere. be done. The two samples were placed in this atmosphere for 20
The change in effective surface charge density (ρ/-) after being left for a minute can be calculated from the change in capacitance-voltage characteristics at times tl and t before and after this. As is clear from FIG. 2, the capacitance-voltage characteristics of diode A hardly change before and after being placed in a high temperature atmosphere.

That is, the passivation film of the present invention has extremely stable film quality against high-temperature treatment, and the effective surface charge density hardly changes before and after the treatment. Therefore, when used in MO8 field effect transistors, it is possible to solve the conventional problem of abnormal fluctuations in gate threshold voltage during operation.

FIG. 3 is an actual measurement diagram illustrating how the gate threshold voltage fluctuates during operation when the present invention is applied to an MO8 field effect transistor in comparison with a conventional transistor. As is clear from FIG. 3, when the present invention is implemented, the gate threshold fluctuation characteristic I of the 108z field effect transistor has both a smaller amount of fluctuation and a smaller slope than the conventional fluctuation characteristic ■, and the degree of improvement is extremely remarkable. be.

Since the passivation film of the present invention has a two-layer structure, it has the drawback of complicating the production process a little, but since the deposition rate of the upper layer plasma chemical vapor deposition film 12 is extremely fast, it does not particularly increase the production cost. In other words, disilicon hexafluoride (SizFs) is easily decomposed, so the deposition rate is 4
00A/min speed (conventional silicon tetrafluoride (SiFi)
), the deposition rate is significantly higher than that of a mixed gas of nitrogen (N2) and hydrogen (N2), which is 150 A/m1nK. In addition, silicon difluoride (SiF), which is said to be relatively fast,
), the speed is much higher than the 250 A/min using the 250 A/min, and combined with the excellent film quality, there is no particular problem in the production process.

〔Effect of the invention〕

As explained in detail above, the semiconductor device of the present invention includes a passivation film that is extremely stable against heat treatment,
Since hydrogen is not emitted and the semiconductor elements are not damaged as in the conventional method, the reliability of fine semiconductor devices such as VLSIs can be significantly improved.

In particular, if applied to the MO81jL field effect transistor, it will be possible to very effectively solve the phenomenon of abnormal fluctuations in gate threshold voltage that occur over time.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional structural diagram showing an example of a MO8tO8 field effect transistor according to the present invention, and Fig. 2 shows a change in the effective surface charge density of the passivation film of the present invention in a high-temperature atmosphere by comparing it with a conventional film. FIG. 3 is an actual measurement diagram illustrating fluctuations in gate threshold voltage during operation when the present invention is applied to an MO8 field effect transistor in comparison with a conventional one. 1...P type silicon substrate, 2...Thick field oxide film, 3 and 4...N region forming source and drain, respectively, 5... ...Gate insulating film, 6...Polycrystalline silicon gate electrode, 7
・・・・・・+ P layer forming channel stopper, 8, 9...
. . . Aluminum wiring conductor, 10 . A and B...
... MIS type diode using the vapor-phase grown film according to the present invention and the vapor-grown film by the conventional method as an insulator, ■...
- Gate threshold variation characteristics of the kO8fi field effect transistor according to the present invention, ■... Gate threshold variation characteristics of the conventional MO8 field effect transistor, ■?・・・・・・
...Gate threshold voltage. Agent Patent Attorney Oto Uchihara 87th prisoner

Claims (1)

[Claims] A semiconductor substrate, a semiconductor element formed on the semiconductor substrate, disilicon hexafluoride (Si_2F_6) and nitrogen (N
_2) and a two-layer silicon nitride film in which plasma chemical vapor deposition films using disilicon hexafluoride (Si_2F_6), nitrogen (N_2), and hydrogen (H_2) as mixed gases are deposited as the lower and upper layers, respectively. A semiconductor device characterized by: