JPH01239852A - Formation of thin film - Google Patents

Abstract

PURPOSE:To form a film having less plasma damage and less internal stress and a hydrogen content, by introducing first gas not solely deposited on the base even if it is excited by a plasma to excite it, and then introducing second gas to be solely deposited on the base by excitation to deposit a reactive product on the base. CONSTITUTION:A thin film forming apparatus having means for holding a base 3 therein, a reaction vessel 2 having two gas inlets 4a, 4b, electrodes 1 having 1/10 or less of the area of the inner wall of the vessel 2 and mounted near one inlet 4a, and means 5 for applying 1 voltage between the vessel 2 and the electrode 2 to generate a plasma in the gas in the vessel 2 is provided. First gas 10a not solely deposited on the base even if it is excited by the plasma is introduced from the inlet 4a into the vessel 2, and a voltage is applied between the vessel 2 and the electrode 1 to excite the gas 10a. Then, second gas 10b solely deposited on the base by exciting is introduced from the inlet 4b into the vessel 2, reacted with the excited first gas to deposit reactive product on the base 3.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application] The present invention relates to a method for forming a thin film used for forming an insulating film of a semiconductor element, for example.

[Prior Art] Currently, the CVD method occupies an important position as a thin film forming means used for forming insulating films of semiconductor devices, particularly LSIs.

A thermal CVD method is commonly used as a CVD method.

Formation of Si3N4 film by using thermal CVD method is as follows:
For example, it is done as follows. placed in the reaction vessel, 7
A mixed gas of monosilane and ammonia is fed onto the substrate heated to 50 to 950° C. and maintained at a pressure of several Torr. Then, a chemical reaction due to thermal decomposition occurs on the substrate, and a Si and N4 film is deposited and formed on the substrate. In addition, Si3
The N4 film is used as a mask for selective oxidation and a capacitor insulating film.

Further, the formation of a PSG-based film using a thermal CVD method is performed, for example, as follows. placed in a reaction vessel;
A mixed gas of monosilane, oxygen or nitrous oxide, and a doping gas such as phosphine is fed onto the substrate heated to 350 to 450°C, and heated to 1 to 760 Torr.
maintain pressure. Then, a chemical reaction due to thermal decomposition occurs on the substrate, and a PSG-based film is deposited and formed on the substrate. Note that this PSG-based film is used as an insulating film between the eyebrows.

However, for applications such as forming a passivation film after AIL wiring, lowering the temperature is required, and the thermal CVD method is not sufficient. Therefore, the plasma CVD method is used for such applications.

The plasma CVD method usually uses parallel plate plasma CVD.
law is used.

Formation of a P-3iN film using this apparatus is performed, for example, as follows. A mixed gas of monosilane, ammonia, and nitrogen was heated to 0. Under the pressure of an ITorr table, the gas is introduced between the symmetrical parallel plate τ electrodes of a capacitor type, and a high frequency voltage is applied to this electrode to generate plasma, which excites and decomposes these gases into excited active species. Excited active species, 250 ~
P-S by depositing on a substrate heated to 300°C
Form an iN film. P-3iN films are used as passivation films for semiconductor devices.

[Problems to be Solved by the Invention] However, the above-described parallel plate plasma CVD method has the following problems.

■Due to damage caused by ions in the plasma, the electrical properties (e.g. dielectric strength and interface state density) of films and elements formed on the substrate may deteriorate compared to those formed using thermal CVD. It ends up.

(2) Due to the insertion reaction peculiar to the plasma CVD method, internal stress is generated in the film, which deteriorates the anti-migration characteristics of the underlying AJZ wiring. Particularly, as the wiring width becomes finer due to higher integration of elements, migration may cause disconnection of the wiring.

■In order to obtain a uniform film thickness, it is necessary to maintain a uniform plasma density, which becomes extremely difficult as the diameter of the wafer becomes larger.

■Hydrogen easily mixes into the film, and the threshold voltage fluctuates due to hydrogen diffusion into the gate.

[Means for Solving the Problems] The first gist of the present invention is to provide means for holding one or more substrates inside and two gas inlets for introducing gas into the inside. a reaction vessel having; an electrode having an area of 1/10 or less of the inner wall area of the reaction vessel and installed near one of the inlets; applying a voltage between the reaction vessel and the electrode; A thin film forming method using a thin film forming apparatus having: a means for turning gas introduced into a reaction vessel into plasma; a step of introducing a first gas into the reaction container from a gas inlet in which an electrode is installed; after introducing the first gas into the reaction container, applying a voltage between the reaction container and the electrode; a step of exciting the first gas by the excitation;
A step of introducing the gas into the reaction vessel through the 14 uninstalled gas inlets, reacting with the excited first gas, and depositing a reaction product produced by the reaction on the substrate. It exists in the thin film forming method.

[Effect] The constituent elements of the present invention will be explained below along with their effects.

One of the features of the present invention is that a CVD method is used in which the area of the electrode is 1/10 or less of the area of the inner wall of the reaction vessel.

The inventor investigated the cause of the deterioration of the electrical characteristics of a film formed using the conventional plasma CVD method, and found that the cause was damage caused by ions (IS).

Further research was conducted to find out why such damage caused by ion bombardment occurs. As a result, we found that in the conventional plasma CVD method, the plasma intensity does not differ much between the vicinity of the electrode and the vicinity of the substrate, and therefore the plasma intensity near the substrate is also quite strong, which may cause damage to the film. Ta.

Therefore, we worked hard to find a way to avoid this damage, and found that if we made the area of the electrode smaller than the inner wall area of the reaction vessel and applied a voltage between the electrode and the reaction vessel, we could generate a plasma. The strength of the electrode is strong near the electrode and becomes weaker near the substrate, and as a result, the above damage can be avoided, and the present invention has been completed.

Based on the above knowledge, we investigated specifically what area ratio would avoid the above damage.

As a result, it was found that the above-mentioned damage could be avoided if the value of electrode area/inner wall area of reaction vessel (hereinafter referred to as area ratio) was 1/10 or less, so the ratio was limited to 1/10 or less.

In addition, this area ratio is preferably 0.02 to 0.06, more preferably 0.04 to 0.05.

Further, when the area ratio is set to 1/10 or less, internal stress within the film due to insertion reaction is reduced, and therefore migration resistance is improved.

Furthermore, it is possible to accommodate larger diameter substrates simply by increasing the size of the reaction vessel without changing the use of electrodes.

Another feature of the present invention is that the second gas, which is deposited on the substrate even when excited, is introduced into the reaction vessel from the gas inlet where no electrode is installed, and the excited first gas The reaction product produced by the reaction is deposited on the substrate. With such a configuration, the composition of the formed film is less likely to deviate from the stoichiometric composition, and it is possible to prevent the film from adhering to the electrode.

In the present invention, an apparatus having means for irradiating a substrate held in a reaction vessel with ultraviolet light, visible light, or infrared light that is not absorbed by the introduced gas may be used. By this means, when the substrate is irradiated with ultraviolet light, visible light or infrared light,
Desorption of hydrogen is promoted, hydrogen contamination that causes fluctuations in the threshold electrode is suppressed, and a dense film can be formed.

Examples of such a light source include a H8 lamp, a Xe lamp, a Xe-Hg lamp, a W lamp, a halogen lamp, or an N lamp.
Examples include excimer lasers such as 2 laser, Ar laser, YAG laser, and CO2 laser. Of course, any laser other than these may be used as long as it is not absorbed by the source gas.

In the present invention, examples of the substrate on which a thin film can be formed include a silicon substrate, a compound semiconductor substrate such as GaAs, an 8-electrode substrate such as Al1zOs, and Aj! Examples include metal substrates such as.

Examples of the first gas include hydrogen gas, rare gas, gas containing nitrogen atoms, gas containing oxygen atoms, and the like.

In particular, in the present invention, when a gas containing nitrogen atoms is used, it is possible to reduce the hydrogen content in the film formed on the shoulder compared to when the film is formed using the parallel plate plasma CVD method. .

Examples of the second gas include Si and An.

Examples include gases containing atoms such as W, Mo, Ti, and others.

Further, as the thin film to be formed, an appropriate film can be formed by combining the above-described first gas and second gas. - For example, 02 or N20 and SiH4,5f2H6
, SiH2Cj12 or SiH4 etc.
O film, H2 or rare gas and SiH4, Si, H6,5iH
a-St (amorphous silicon) film using 2Cjl□ or S i H4, p-5i (polycrystalline silicon)
Examples include a C-3i (single crystal silicon) film, a metal nitride film using a gas containing hydrogen or a rare gas, and a metal atom, and an oxide film.

The plasma generating means may be a high frequency, a microwave, a magnet, or a combination thereof.

Note that the internal pressure (operating pressure) of the reaction vessel is 1 to 100 m
It is preferable to set it as Torr.

However, below 1 mTorr, as shown in Figure 2 (a), the step coverage (the value is indicated by b / a in Figure 2 (a), the closer this value is to 1, the better the step coverage. ) becomes less noticeable. On the other hand, 100mTo
When rr is exceeded, the improvement in film uniformity becomes less noticeable as shown in FIG. 2(b).

[Example] An embodiment of the present invention will be described below with reference to FIG.

In Figure 1, 1 is an electrode whose area is 200c
rr? Closed. 2 is a reaction container, and this reaction container is grounded. The area of the reaction vessel was 5000 crn'. Therefore, the area ratio is 0.04. 3 is a substrate, and in this example, a 6-inch silicon substrate was used. 4a,
4b is a gas introduction port, and the gas introduction port 4a is provided near the electrode 1 at the upper part of the reaction vessel 2. 5 is a means for applying a voltage between the reaction vessel 2 and the electrode 1 to generate plasma. 6 is a light source, and an xe clamp was used. Hereinafter, an example in which a thin film was formed using this apparatus will be described, and examples of the present invention will be explained in more detail.

Using nitrogen as the first gas 10a at 240 seconds,
A monosilane gas of 40 seconds was used as the second gas 10b. The operating pressure was kept at 10-2 Torr.

First, the first gas 10a was flowed into the reaction vessel 2 from the gas inlet 4a, and the first gas was excited by plasma. The second gas 10b was introduced into the reaction vessel 2 through the gas introduction port 4b.

Plasma was generated by applying 1 kW of a 13.56 MHz high frequency voltage between the capacitively coupled electrode 1 and the reaction vessel 2. At this time, the electron density in the dense plasma (
(which existed near the electrode) was 1X10''/crn', and on the substrate 3 it was 5X10'/C111''.

On the other hand, the light source 6 irradiated the substrate 1 with o, aw/crn' light. Note that this irradiation increases the substrate surface temperature by 300°C.
It was kept at ℃.

After 5 minutes of deposition under the above conditions, 5500±
A 150-layer thick SiN film was formed.

That is, the variation in film thickness was as small as about ±2.5%.

The film formed as described above was evaluated.

■Electrical properties Dielectric strength voltage: 10 MV/cm Interface state density: 1 x 10"1crd ■Internal stress Internal stress was 4 x 10-'dyn/crn" [tensile stress].

■Others The density of the film was as high as 3.1 g/cm'', so the etching rate with buffered hydrofluoric acid was as good as 10 people/min. b of
/a) was 0.7, which was extremely good. Note that the hydrogen content was 5 mo1%.

[Comparative Example] Film formation was performed using the conventional parallel plate plasma CVD method under the conditions shown below.

Film formation conditions SiH4: 6sec Operating pressure: 0.5 Torr RF power: 100W ■Electrical characteristics Dielectric strength voltage: 6MV/cm Interface state density: 5X10”/crr? ■Evaluate internal stress using the same method as the internal stress example As a result, the internal stress was found to be 1 to 8 x 109 dyn/Crrl' [compression stress].

■Other density is 2.6g/cm', etching speed with buffered hydrofluoric acid is 300 people/min, hydrogen content is 30moJZ%
Met. Further, the step coverage of the film was 0.4.

Compared to the thin film of the present invention, the film quality of the comparative example was clearly poor.

[Effects of the Invention] As described above, according to the present invention, the following effects can be obtained.

(2) Since the substrate is separated from the strongest part of the plasma, there is less plasma damage to the substrate and a film with excellent electrical properties can be formed.

(2) It is possible to form a film with low internal stress, and therefore, it is possible to manufacture a semiconductor element with less disconnection of An wiring when increasing the degree of integration.

■It is possible to accommodate larger diameter wafers simply by increasing the size of the reaction vessel.

■ Film adhesion near the electrode can be reduced.

■It is possible to form a film with a similar stoichiometry composition.

■It is possible to form a film with low hydrogen content, and it is possible to suppress fluctuations in threshold voltage.

■

[Brief explanation of the drawing]

FIG. 1 is a conceptual configuration diagram showing an apparatus according to an embodiment of the present invention, FIG. 2(a) is a graph showing step coverage, and FIG. 2(b) is a graph showing film uniformity. . DESCRIPTION OF SYMBOLS 1... Electrode, 2... Reaction container, 3... Substrate, 4a
. 4b... Gas introduction port, 5... Plasma generation means, 6
...Light source, 10a...First gas, tab...Second gas. Figure 2 (a') Operating pressure (Torr)

Claims (4)

[Claims] (1) A reaction vessel having means for holding one or more substrates therein and two gas introduction ports for introducing gas into the interior; 1/10 or less of the inner wall area of the reaction vessel. an electrode having an area of A method for forming a thin film using a thin film forming apparatus having the following method, the first gas being excited, ionized or decomposed (hereinafter referred to as excitation) by plasma but not deposited on the substrate by itself, is reacted through a gas inlet in which an electrode is installed. a step of introducing the first gas into the interior of the reaction container; a step of applying a voltage between the reaction container and the electrode to excite the first gas; A second gas that can be deposited on the substrate is introduced into the reaction vessel from the gas inlet where the electrode is not installed, and reacts with the excited first gas, and the reaction product generated by the reaction is transferred to the substrate. A method for forming a thin film, comprising the steps of: depositing it on the top; (2) The thin film forming method according to claim 1, further comprising the step of irradiating the substrate with ultraviolet light, visible light, or infrared light that is not absorbed by the introduced gas during film formation. (3) The method for forming a thin film according to claim 1 or 2, wherein the pressure inside the reaction container is set to 1 to 100 mTorr. (4) The thin film forming method according to any one of claims 1 to 3, wherein the first gas is a gas containing nitrogen atoms.