JPH069198B2 - Semiconductor device - Google Patents

Description

The present invention relates to the use of aluminum nitride, for example, as an insulating film for semiconductor electronics by a vapor phase reaction method (hereinafter referred to as a CVD method) using heat and photochemical reaction.

The present invention has a large optical energy band width (about 5.0 eV for silicon nitride) as compared with the conventionally known silicon nitride produced by SiH ₄ and NH ₃ by performing a photochemical reaction between organoaluminum and a nitride gas. ) A highly reliable semiconductor device is provided by using aluminum nitride having about 7 eV, particularly aluminum nitride mixed with oxygen, as a final coating film, a passivation film or an insulator film for capacitors of a semiconductor integrated circuit. Regarding what to do.

The present invention organic compounds such as trimethyl aluminum aluminum _{((CH 3) 3 Al)} , or triethyl aluminum _{((C 2 H 5) 3} Al) with added ammonia (NH _3), hydrazine (N ₂ H ₄₎ , Aluminum nitride (NF ₃ , N ₂ F ₄ ) is added to form aluminum nitride (hereinafter abbreviated as AlN) at a temperature of 800 ° C. or lower, preferably 100 to 500 ° C., for example 300 ° C.

Conventionally, to produce an aluminum nitride film, aluminum chloride (AlCl ₃ ) is reacted with ammonia (NH ₃ ) by a plasma gas phase reaction method using a glow discharge method, and
The coating was prepared at a substrate temperature of 0 to 400 ° C.

However, in such an aluminum nitride film, the dangling bonds of metallic aluminum and the clusters of silicon remain in the film, so that there is variation in the electrical insulating property, and the breakdown voltage is reduced.

Furthermore, residual chlorine became a cause of corrosion when used as the final coating of MOS.IC. In addition, the translucency of ultraviolet light was not sufficient due to the cluster of metallic aluminum. Therefore, there has been a demand for aluminum nitride having an Eg of about 7 eV and excellent ultraviolet light transmissivity.

To this end, Eg
Was only about 5 eV and was not sufficient due to the remaining silicon clusters. Due to these causes, final coating in the process of manufacturing a semiconductor was insufficient as a material.

For the purpose of the present invention, by using organoaluminum, particularly preferably Al (CH ₃ ) ₃ (referred to as trimethylaluminum) and ammonia (NH ₃ ), a photogas phase reaction in which ultraviolet light having a wavelength of 300 nm or less is irradiated By using the method, aluminum nitride is produced and applied as a protective film of a semiconductor device.

The main reaction formula is Al (CH ₃ ) ₃ + NH ₃ AlN + 4CH ₄ .

Its basic physical properties are as follows.

Molecular weight 27.09 Purity 99.9998% (as Al) Density 0.725 g / ml (20 ° C) Melting point 15.3 ° C Vapor pressure Temperature (° C) Vapor pressure (mmHg) 20 9.2 80 157 127 760 The present invention will be described below with reference to the drawings.

FIG. 1 shows an outline of an optical CVD or thermal CVD apparatus used in the present invention.

In the drawing, the reaction vessel or vacuum vessel (1) is made of quartz. The substrate (2) is placed on a holder (22) heated from below by a halogen heater (3) and heated to room temperature to 900 ° C, preferably 200 to 500 ° C, for example 350 ° C. The doping system consists of flowmeters (6), (26) and valve (7), and ammonia and nitrogen are supplied from (9) and (10) respectively. Furthermore, since this nitride gas is a gas even if it undergoes a decomposition reaction, it is blown from the nozzle inside the window of the reaction chamber, and the gas photoexcited by UV irradiation is applied to the lower substrate surface (16).
I wiped it down as shown in. In addition, it also has an effect of preventing trimethylaluminum, which becomes a solid when the decomposition reaction occurs, or its reaction product from reaching the surface of the quartz window.

Trimethyl aluminum (Al (CH ₃ ) ₃ (MP 15.3 ℃))
Since it is a liquid at room temperature, it is filled in the bubbler (20). Nitrogen was bubbled through this trimethylaluminum from (11). The bubbler 20) was heated to 100 ° C. including the flow meter (26) up to the reaction chamber (1) to prevent adsorption of trimethylaluminum on the inner wall of the pipe. Further, this trimethylaluminum was sprayed from the nozzle toward the substrate side as shown in (17).

Thus, trimethylaluminum and ammonia were mixed for the first time in the reaction chamber, and photoexcited to react. In addition, the reactive gas was prevented from adhering to the quartz window.

Further, the pressure adjusting valve (12) and the stop valve (13) were connected from the exhaust port (8) to exhaust from the vacuum pump (14). A lamp with a wavelength of 300nm or less (low pressure mercury lamp, manufactured by Ushio Inc., UL1-45EL2-N-1) for photochemical reaction
10 (4) and the power supply system (5) with it were used. Further, the lamp chamber (28) was connected to an exhaust system and evacuated. In order to prevent the reactive gas from flowing back into this lamp chamber, a small amount of nitrogen gas was introduced from (24) and heated to 600 ° C. by the heater (25) for decomposition. Furthermore, the lamp chamber (28) was adjusted with the bulb (27) under the same pressure as the reaction chamber (1) so as not to damage the quartz glass (26) of the window. Furthermore, in this way, it was possible to prevent the absorption loss of the short wavelength light of 184 nm by the water vapor in the atmosphere before reaching the reaction chamber from the generation source. In addition, the board (2) and the holder (2
A halogen heater (3) for heating 2) is provided below the reaction space (1).

The example is shown below.

Example 1 In this example, aluminum nitride was not formed on a semiconductor substrate by a photochemical reaction between trimethylaluminum and ammonia.

In FIG. 1, a silicon substrate (2) for final coating, on which a semiconductor IC for forming an aluminum nitride film is formed by heating the substrate to 500 ° C. or less by a heater (3), is attached to a holder (22) above the heater. ) Is arranged above. Further valve
(7) was opened and ammonia was introduced. Furthermore, trimethylaluminum was introduced as trimethylaluminum / NH ₃ ≈1 / 5. Further, the pressure in the reaction vessel mixed with oxygen as necessary was set in the range of 0.1 to 100 torr, for example, 10 torr. Then, it was possible to obtain aluminum nitride in the reaction tube at a growth rate of 2.1 Å / sec without using mercury sensitization in the photo-CVD method by irradiation with 184 nm and 254 nm ultraviolet light. The film growth rate decreased to 1.4Å / sec at 3 torr.

When this reaction product was examined by IR (infrared absorption spectrum) with a thickness of 0.2 μm, a broad absorption was observed at 900 cm ^−1, and it was found to be an aluminum nitride film. Further important in the method of the present invention is that both trimethylaluminum and ammonia are excited by light of 300 nm or less for the production of such an aluminum nitride film,
No need to use mercury. Furthermore, since this aluminum nitride film has a thermal conductivity about 5 times better than that of silicon nitride,
In the IC, local heating in the IC chip can be prevented.
Furthermore, since its optical energy band width is about 7 eV (177 nm), it can transmit ultraviolet light (184 nm and 254 nm). Therefore, even if aluminum nitride adheres to the window, it has a feature that ultraviolet light does not reach the reactive gas, that is, it does not act as a so-called barrier. Further, since aluminum nitride is a nitride, a barrier effect against alkali ions such as sodium can be expected at the same time, and it was ideal as a final coating material for semiconductor devices such as ICs.

Example 2 In this example, an aluminum nitride coating was produced on a single crystal silicon substrate by the thermal reaction of trimethylaluminum and ammonia. The method used was the same apparatus as in Example 1. Substrate temperature is 600-900 ℃, 800 ℃, pressure 2torr,
Trimethylaluminum / NH ₃ ≈1 / 8.

A counter electrode was formed on this aluminum nitride (thickness 1000Å), and a CV characteristic was measured as a diode structure. As a result, the interface state density was 4 × 10 ¹¹ cm ^-2 . The breakdown voltage when a DC electric field was applied to the aluminum nitride film was 3 × 10 ⁶ V / cm or more.

That is, the aluminum nitride film formed at a temperature of 500 ° C. or lower is effective as a passivation film for semiconductors. For this purpose, it is effective to utilize the physical property of the organoaluminum of the method of the present invention, which is sensitive to ultraviolet light.
Further, since it is formed at a high temperature of 500 to 900 ° C. to form a dense film, it is effective to use as a gate electrode insulator aluminum nitride mixed with oxygen or a two-layer film of aluminum nitride and SiO ₂ . Furthermore, it is also effective as an insulating film (dielectric film) for RAM capacitors.

As described above, in the present invention shown in Examples 1 and 2, when organic aluminum is used, it is necessary to mix carbon into the coating film. However, the SIMS (Secondary Ion Mass Spectroscopy) result shows that the amount is less than 1%, and it is considered that there is no physical property deterioration due to it. Further, aluminum oxide (alumina) can be simultaneously formed in the film by mixing oxygen.
However, in the case of aluminum nitride containing less than 10% by weight of oxygen, residual stress with the base material can be reduced, and its thermal conductivity can be as high as that of aluminum nitride with a purity of 99% or more. it can.

Further, by mixing oxygen, it was possible to obtain aluminum nitride which is difficult to be cleaved.

In the present invention, triethylaluminum and N are formed by the thermal CVD method.
It is effective to use the reaction of H ₃ , trimethylaluminum and N ₂ H ₄ . In addition, excimer (wavelength 500 to 100 nm) as a photo-CVD method by irradiating light energy of 300 nm or less
It goes without saying that a laser may be used.

In the present invention, it is also possible to simultaneously mix mercury for the excitation of the photochemical reaction and use the mercury excitation method.

However, the method using a mercury bubbler tends to leave mercury in the exhaust gas and cause pollution problems.

As the nitride gas in the present invention, non-oxygenated nitrogen fluoride (NF ₃ , N ₃ F ₄ ) or other non-oxide hydrazine salt may be used.

[Brief description of drawings]

FIG. 1 shows an outline of a CVD apparatus for carrying out the method of the present invention.

Claims (2)

[Claims] 1. A semiconductor device comprising an aluminum nitride film mixed with oxygen or a two-layer film of silicon oxide and aluminum nitride as an insulator of a capacitor of the semiconductor device. 2. A semiconductor device comprising an aluminum nitride film mixed with oxygen as a final coating film on a silicon substrate on which a semiconductor IC is formed.