JPS61163277A - Synthesizing method of aln thin film - Google Patents

Abstract

PURPOSE:To synthesize efficiently a high-density AlN thin film without accompanying the formation of powder by introducing a gaseous halide of Al and gaseous NH3 into a growth chamber respectively through the separated routes and setting properly both the temp. of a mixing part of gaseous raw material and the temp. of a providing part of a substrate. CONSTITUTION:Gaseous halide of Al such as gaseous AlCl3 formed in a raw material chamber 1 and gaseous NH3 are respectively introduced into a growth chamber 2 through the introduction ports 5, 6 which are the separated routes and provided to a counter electrode. The temp. distribution in the growth chamber 2 is set so that the temp. is regulated to 350-400 deg.C in a mixing part 3 of gaseous raw material and it is regulated to >=420 deg.C in a providing part 4 of a substrate. Thereby the formation of the powdery crystal in the gas phase and the decrease of the film growth velocity can be prevented. Furthermore the growth temp. of AlN onto the substrate can be made minimum.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a method for synthesizing All5I thin films.

(Prior art and its problems) Conventional methods for vapor phase synthesis of AIN thin films include the MOCVD method using an organic metal such as trimethylaluminum (TMA) and ammonia NH,=i as raw material gases.

There is a CVD method using an aluminum halide compound iX@ (X is a halogen element) and NH■.

Synthesis using the MOCVD method requires a substrate temperature of about 1200°C, and since organic metals decompose easily at high temperatures, the substrate itself is locally heated by high-frequency induction heating to decompose the organic metal only in the vicinity of the substrate surface. It is not an industrially advantageous method because the temperature must be controlled so that the nitridation reaction between An obtained by decomposition and NH occurs, and it is not suitable for large-area growth. In contrast, the synthesis method using Air Xs and NIP
AlN can be synthesized at a temperature as low as 800°C, and growth over a large area is also possible by using uniform heating using resistance heating.However, AA? X, 10NH Spring → A/N + 31 (The reaction X has a large equilibrium constant, and a uniform reaction occurs in the gas phase to produce powdered crystals. From K, powder is deposited in the process of film growth. A film with low density is formed.

Alternatively, AIN reacts violently with the walls of the growth chamber and adheres to the walls, resulting in problems such as slow film growth and easy damage to the reaction tube.

(Objective of the Invention) The object of the present invention is to eliminate the drawbacks of the conventional vapor phase synthesis method of AIN# film, and to produce a high-density A/N film without powder formation.
The present invention provides a method for industrially synthesizing thin films at low temperatures and high growth rates.

(composition) The present invention relates to a reaction system between hlX* and NH.

AlX, gas, and NH gas were all introduced into the growth chamber through separate routes, and the temperature distribution in the growth chamber was adjusted so that the temperature at the part where the raw material scraps were mixed was below 400°C, and the temperature at the substrate installation part was 42°C.
AlN characterized by being set to be 0°C or higher
This is a thin film C'VD synthesis method.

(Detailed explanation of the structure) In order to grow a film with uniform thickness over a large area with good reproducibility in crystal growth using the CVD method, the following three elemental conditions are necessary. That is, (1) the raw material gases are sufficiently mixed and the concentration is constant.

■This is caused by the gas flow becoming laminar on the substrate surface. ■The temperature of the source gas is uniformly controlled near the substrate. The present invention satisfies these conditions.

The AlN synthesis apparatus of the present invention is shown in FIG. In order to satisfy the above condition (■), A and lma were used, and AI+3)1(J-→kljc1.12■
(, in the reaction, generated fi, l1c1. gas and N
H and gas were introduced into the growth chamber 2 through separate routes through inlets 5 and 6 provided at opposite poles of the growth chamber, respectively. As a result, the raw material gases for klcl and NH are in a turbulent state.
The raw material gases are mixed together to form a mixed raw material gas with a uniform concentration. Here, hlCla was generated by AI and ■I (J.
When lCl a is used as a raw material, it is because AltJa has a strong early decomposition property and mixing with oxygen is avoided. If mixing of oxygen is not to be taken into account, AljClj may be vaporized and used as the raw material gas. Furthermore, since this apparatus is of a horizontal type, the mixed raw material gas enters a laminar flow state while reaching the substrate installation part 4 consisting of the substrate 8 and the support stand 9, and satisfies the condition (2) above. In order to fully satisfy the above conditions (■■), resistance heating was used as the heating method. Direct heating of the substrate by high-frequency heating not only makes the temperature distribution in the growth chamber non-uniform, but also causes thermal convection, which does not satisfy the above condition (2).

When synthesizing AlN using the above apparatus, what is important is the temperature distribution in the gas flow direction in the reaction chamber. As mentioned above (Al
Cl! , +NH,→A! Since the equilibrium constant Kp of the reaction P + 3 HC 1 l is large, the concentration of the mixed raw material gas is high in some parts of the mixing section 3, causing a homogeneous reaction in the gas phase, producing powdery crystals or depositing on the wall. A7N is synthetically attached. For this reason, when powdery crystals are deposited during the film growth process and a dense film cannot be formed, the concentration of the mixed raw material gas near the substrate is sucked down, slowing down the growth rate of the film. Therefore, the temperature distribution was set so that the temperature of the raw material gas mixing part 3 was 400'C or higher, and the temperature 4 of the substrate installation part was 420"C or higher.The temperature of the raw material gas mixing part 3 was set to be 400"C or lower. This prevents the formation of powdery crystals in the gas phase and a reduction in the growth rate, and also minimizes the temperature at which A7N grows on the substrate.

In addition, the temperature of the raw material gas mixing section T. or AIC) 350
If the temperature is as low as 0.degree. C., Icl is likely to condense and adhere to the raw material gas mixing section 3, which will impede the transportation of the raw material, which is undesirable.

(Example 1) A7N was synthesized on a (100) Si single crystal substrate using the above-described reactor it+.

The temperature T1 of the substrate installation part 4 is fixed at 600°C, and the temperature T of the raw material gas mixing part 3 is set at 600°C. The temperature was set within a total range of 350 to 600°C. A mixed gas of N and Hl is used as a transport gas at a total flow rate of 9.
It was run at Ql/rni. H (J flow rate is 80α
Shi'min NHs flow ill O,61/mj n,
! : L7'c. The synthesized film is subjected to FF value by X-ray diffraction and electron beam diffraction.
I confirmed that it was N. Furthermore, when the surface of the film was observed using isEM, it was clear that as the temperature of the source gas mixing section 3 became lower, the irregularities on the surface became smaller.

Powder can be seen with the naked eye in samples with highly uneven surfaces.

The degree of unevenness on the surface and the amount of powder correspond to each other, and the protrusions 11 to 7 on the surface are caused by fine particle crystals deposited on the surface during the process of film growth. Table 1 shows the results of measuring the film thickness by optical interferometry and calculating the total growth rate. As is clear from Table 1, the growth rate is almost constant when the temperature of the raw material mixing section 3 is below 400°C, and the decrease in the concentration of the mixed raw material gas near the substrate due to AlN synthesis in the raw material mixing section 3 is suppressed. ing.

If it is desired to further increase the growth rate, the flow rate of HCI gas may be increased.

Table 1 (Example 2) Under the same gas flow conditions as in Example 1, the temperature To of the raw material gas mixing part was fixed at 400°C, and the temperature T of the substrate installation part M was
was set in the range of 350 to 800°C to form an AlNl gold film. Crystal evaluation was performed on each sample by X-ray diffraction and electron beam diffraction, and the results shown in Table 2 were obtained.

Table 2 However, the synthesized film when T1 was 420°C was amorphous and A7N could not be identified by X-ray diffraction or electron diffraction.
When the film was annealed at 800° C. for 2 hours in an H. gas atmosphere, the above evaluation showed that a diffraction peak of polycrystalline AIIN appeared, and it was confirmed that the synthesized film was IN.

Conventionally, there has been no example of AIN k synthesis using the CVD method at a low temperature of 400°C.

Although the reason for this is not clear, in the present invention.

By setting the IM of the raw material gas mixing part to 35°C to 0°C and giving the growth chamber a characteristic temperature distribution, the state of the raw material gas in the substrate installation part, that is, the mixed state, concentration, and laminar flow state of the raw material gas is extremely ideal. A7 with low energy
It became possible to synthesize N.

Similar results were obtained in Examples 1 and 2 when HBr or a mixed gas of both was used instead of HCI.

(Effects of the Invention) As explained in detail in the Examples, according to the present invention, a dense AIN thin film that does not involve the deposition of powder crystals during the film growth process can be synthesized at a high growth rate, and moreover, it is possible to synthesize a dense AIN thin film at a high growth rate. In comparison, the synthesis temperature of AIN is low, and its industrial value is great.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a CVD apparatus used in Examples.

Claims (1)

[Claims] (1) In the reaction system of aluminum halide compound and ammonia, the aluminum halide gas and ammonia gas are introduced into the growth chamber through separate routes, and the temperature distribution in the growth chamber is adjusted to mix the aluminum halide compound gas and ammonia gas. The temperature of the part is 350-400℃
A method for synthesizing an AlN thin film, characterized in that the temperature of the substrate installation part is set to 420° C. or higher.