JPS62179717A - Thin film forming method - Google Patents

Abstract

PURPOSE:To deposit only an element which constitutes a film dissociating a chemical species except the element which constitutes the film after covering a surface with a gas by providing a process of introducing the gas which is the element of constituting the film, a process wherein the gas is adsorbed in one layer on the surface of a substrate and a process of reacting the gas adsorbed on the surface of the substrate. CONSTITUTION:An AXY gas 20 which contains an element (A) 21 which constitutes a film is introduced on the surface 2 of a substrate. The gas is adsorbed on the surface 2 of the substrate by the interaction of the surface 2 of the substrate and an X group 22 and if the adsorption is continued, an adsorption layer 20a can be formed on the surface 2. In this case, if the attraction by the interaction between Y groups 23 and between the X group 22 and the Y group 23 is weak, the AXY gas 20 is not adsorbed on the adsorption layer 20a. After the not yet adsorbed AXY gas 20 is removed in this state, the X group 22 and the Y group 23 are dissociated by light irradiation or rapid heating and the element (A) 21 is deposited in one atom layer on the surface 2 of the substrate.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method of forming a thin film by controlling the film thickness on the order of one atom.

[Conventional technology]

In the conventional CVD method or VPE method using a reactive gas, a thin film is formed using a gas phase or a decomposition reaction on a substrate surface. For example, as shown in Figure 5, a gas 1 called AX4 (where A is a constituent element of the film to be deposited and
=Cl1. F, H.

CH,,C! When the substrate surface 2 is placed in an atmosphere of H, etc.) and the temperature is raised, the gas decomposes in the gas phase and the constituent elements of the film (
Decomposed into A) 3 and terminal group (X) 4, membrane constituent element (A)
3 is deposited on the substrate surface 2. The terminal group (X) 4 is gasified as it is, in the form of a molecule such as X2, or in the form of a reaction with another gas (A X or a gas flowing simultaneously with A X a gas).

If there is a film-constituting element other than A, a gas containing that element as the central element is used to cause a decomposition reaction as shown in FIG.

Similarly, instead of being decomposed in the gas phase as shown in Fig. 5, gas AX4 is directly transferred to the substrate surface as shown in Fig.
This adsorbed species 1a decomposes into membrane constituent elements (A).
3 is deposited and gasified as shown in FIG. 6 (bl).

[Problem that the invention seeks to solve]

In the method described above, since the decomposition of AX4 gas 1 continues to occur continuously, the A element 3 is deposited one after another on the A element 3, as shown in FIG. 7 (al, fbl). In other words, the A element 3 is deposited at a certain deposition rate. Therefore, by controlling the deposition time, it is possible to deposit the element equivalent to one atomic layer. However,
With this method, there is no guarantee of a complete monoatomic layer; in addition to areas where one atomic layer of A atoms have been deposited, there are also areas where no A atoms are deposited at all, and areas where two or more atomic layers of A atoms have been deposited. Figure 8).

A similar phenomenon occurs also in the method shown in FIG. In the example of FIG. 9, AXZY2 gas (here, the terminal group Y does not have to be a different chemical species from the terminal group X) 5 is used as the gas containing the A element 3, and the B element (A element 3 may be the same element as ) 7 and flows into the substrate surface 2 covered with the X groups 4 . AXZY! End group Y of gas 5
6 side is the substrate surface 2 side, AX2Y, gas 5 is adsorbed onto the substrate surface 2, and becomes adsorbed gas 5a (Fig. 9(a)
).

The Y group 6 and the X group 4 on the substrate surface 2 react to form x-y chemical species 8 and are eliminated, and the A element 3 forms a bond with the B element 7 (FIG. 9(b)). If the reaction stops here, it becomes possible to form a film of one atomic layer at a time, but AX.

Adsorption of Y2 gas 5 continues to occur, and the adsorbed gas 5b in the second layer shown in FIG. 9 (C1) reacts to form a second layer of A atoms. , and complete monolayer deposition cannot be guaranteed.

In addition, the soundtrack etc. is “Nisu I Day 80 Digest (SID80DIGEST), p. 108, 198
In 0J, Nishizawa et al.
Em, Soc, ), vol. 132, p. 1197.

In 1985J, ZnS semiconductor and GaAs semiconductor, respectively.
We have proposed a method for depositing semiconductor thin films with atomic-order thickness control.

An example of ZnS such as soundtrack will be explained with reference to FIG. First, ZnCj! , gas 9 is introduced onto the substrate surface 2 (Fig. 10+a)), Zn is bonded to the surface, and a single atomic layer of ZnCj! , 9a (10th
Figure (b)). Next, after removing unbonded ZnCl2 gas 9, H, S gas 12 is introduced, and HCj! is generated by a reaction between H of Has gas 12 and the terminal group (CI) 11 of Zn(1!z9a) on the substrate surface 2. is dissociated, and the S element 13 is deposited on the Zn element 10 (FIG. 10 (C1, (dl)).

Similarly, Nishizawa et al. formed a GaAs atomic layer film using AsH3 and GaMex (here, Me is a CH3 group). In this case, GaMe forms a triangular male bond with Ga16 as the apex, as shown in FIG. The same applies to Z n Cl z and HzS, and as shown in Fig. 1θ, a CZ group 11 and a H group 14 are bonded to one side of the Zn element 1o and the S element 13, respectively. 10th
The characteristic of the reaction shown in the figure is that it is limited to gases in which the film constituent elements of the gas (Zn and S in the case of Fig. 10) can directly react with the substrate. In addition, since the S element 13 is exposed on the surface side and is not protected as a film is formed, H2s gas 13 is placed on top of it.
The disadvantage is that it has a structure that is susceptible to adsorption of 2 or residual gas. ``Therefore, complete film formation of each atomic layer cannot be guaranteed. If in the previous examples, ZnS was deposited one atomic layer at a time, this may be due to the fact that adsorption of the HtS gas 12 on the S element 13 was difficult to occur (the probability of adhesion was small). Conceivable. This kind of thing is related to group II-Vl (Z n
S, ZnO, etc.) or m-v group (GaAs,
In the case where the film constituent elements are different for each atomic layer (such as InP), the film constituent elements have ionicity, so that the probability of attachment of the same kind of element onto the film may be reduced. However, such an example is special; for example, S
Since this does not occur on a film that does not have ionic properties, such as a film made of T, Ge, etc., the method shown in FIG. 10 cannot be applied.

[Means for solving problems]

In order to solve these problems, the present invention provides a process for forming a thin film, including a step of introducing a gas containing film constituent elements onto the substrate surface, a step of making this gas further adsorbed onto the substrate surface, and a step of introducing a gas containing film constituent elements onto the substrate surface. The method includes a step of reacting the gas adsorbed on the surface.

[Effect]

In the present invention, for example, in order to prevent A atoms from being continuously deposited on A atoms, a gas containing a chemical species that is not used in the film structure is used around the film constituent elements, and the gas is once applied to the surface. After being adsorbed into an atomic layer and covering the surface with this gas, chemical species other than the film constituent elements are dissociated by light irradiation or rapid heating, and only the film constituent elements are deposited.

Therefore, this differs from conventional methods in which gas adsorption and dissociation occur almost simultaneously, or in which the adsorption and reaction steps are not controlled separately.

(Example) FIG. 1 is an explanatory diagram for explaining an example of the method for forming a thin film according to the present invention. AXY gas 20 is introduced onto the substrate surface 2 as a gas containing the constituent element (A) 21 of the film. Here, the X group 22 and the Y group 23 are H, C1, F
, C2H4, CH3, πC3H3 (cyclopentadiene), and the like.

This gas is adsorbed onto the surface 2 by interaction between the substrate surface 2 and the X group 22 (dipole interaction, hydrogen bond, van der Waals force, etc.). If this adsorption is continued, an adsorption layer 20a can be formed on the surface 2, as shown in FIG. 1(b). At this time, Y groups 23 and X group 22 and Y group 23
If the attractive force due to the interaction between the adsorption layer 20a and
There is no adsorption of AXY gas 20 on top. After removing the unadsorbed AXY gas 20 in this state, the X group 22 and the Y group 23 are dissociated by light irradiation or rapid heating, and one atomic layer of the element 21 can be deposited on the substrate surface 2.

Next, a second embodiment of the method for forming a thin film according to the present invention will be described with reference to FIG. Elements constituting the substrate surface 2 (B
) 25 has a terminal group (Z) 24, the Z group 2
4 and the X group 22 so that the interaction between the X group 22.
Select Z base 24. The type of Z group 24 on the surface 2 can be selected by chemical treatment of the surface. Due to the interaction force between the gas 20 and the Z groups 24, a surface adsorption layer 20a is formed as shown in FIG. If the action is weak, the gas 20 is not adsorbed onto the adsorption layer 20a.In this state,
After removing the unadsorbed AXY gas 20 from the atmosphere, it is irradiated with light or rapidly heated to form X group 22, Z group 24 and Y group 2.
By dissociating 3 (the Y group 23 does not necessarily have to be dissociated), one atomic layer of the A element 21 can be deposited on the substrate surface 2 (FIG. 2(C)). At this time, A element 21
has a broken bond 26 on the surface side, and the A element 21 is in a reactive state. Therefore, in order to protect this surface, if a gas 27 containing a surface protective group (U) 28 as a constituent element is introduced, and the U group 28 is bonded to the surface of the A element 21 to stabilize it, it will remain in the atmosphere. AXY gas 2
0 adhesion can also be avoided.

Figure 2 (fl shows the progress during the process).

In order to carry out these treatments at the same time, it is necessary to form one monolayer of the adsorption layer 20a in FIG.
After or before removing the Y gas 20, or simultaneously with the introduction of the AXY gas 20, a gas 27 containing a surface protective group (U) 28 as a constituent element is introduced (Fig. 2 fdl>, l
, and later, as shown in FIG. 2 te+, the X group 22. Z
Group 24. Dissociation of Y group 23 and A element 21 and protecting group (U) 2
It is also possible to perform eight combinations at the same time. In addition, if a gas containing surface protective group (U)28 as a constituent element is selected, AX
There may be no need to exclude Y gas 20.

Next, a third embodiment will be described using FIG. 3. 1st. In the second embodiment, a case has been described in which the A element 21 has two bonding hands, but it goes without saying that there is no limit to the number of bonding hands.

This third embodiment will be explained by taking as an example a case where there are four joining hands. Similarly to the second embodiment, when the element (B) 25 constituting the surface 2 has a terminal group (Z) 24, the X group 22 of the gas species A X t Y z 30
If the respective terminal groups are selected so that the interaction between the two groups 24 is large and the interaction between the Y groups 23 or between the Y groups 23 and the X groups 22 is small, then the gas AXzYz30 An adsorption layer 30a of A can be formed.When this adsorption layer 30a is formed in one atomic layer, unadsorbed A
X 2 Y z gas 30 is removed and X groups 22, Y groups 23. are removed by surface irradiation or rapid heating. The Z group 24 can be dissociated and the A element 21 can be deposited (Fig. 3(C)
).

As a slightly more complicated example, there is also a method in which reactions between gases occur at the same time. This will be explained as a fourth embodiment using FIG. 4. Using a gas 4o called AXYUV as shown in FIG. 4, an adsorption layer 40a of the AXYUV gas 40 is formed by the interaction between the X group 22 and the Z group 24 on the surface 2 at the same time.

At this time, only the interaction force between the X group 22 and the Z group 24 is strong,
If the interaction forces between other groups and between other groups are made weak, adsorption of the AXYUV gas 4o onto the adsorption layer 40a will not occur. When one atomic layer of this adsorption layer 40a is formed, the unadsorbed AXYUV gas 4o is removed, and the Z group 24, the X group 22. Y group 23
．． U group 28. V group 29 is dissociated, A atom 21 and B atom 2
A bond with 5 and a bond between A atoms 21 are formed, and A atoms 21 are deposited.

In the above example, when the nuclear terminal group dissociates and leaves, the diagram shows that the group itself leaves and becomes gas, but this does not necessarily have to be the case. , for example, in the example in Figure 2, the 2 XZ, UV
It is also possible to gasify as a compound of two groups or a compound of two same groups such as Y2.

Furthermore, when making a single atom imitation of the adsorption structure as described above, it is important to keep the substrate at a relatively low temperature, and desorption of the adsorbed gas becomes a problem at high temperatures.

Additionally, in the case of decomposing adsorbed gas molecules, it may be effective to use the interaction between the solid surface and the adsorbed gas molecules. For example, when a solid is a semiconductor or an insulator, electrons and holes are excited between the bands of the solid by light or heat, and by giving one of them to gas molecules, the electronic state in the gas molecules changes. One possible method is to take advantage of the fact that the adsorbed molecules are easily decomposed.If such a method is used, it becomes possible to selectively decompose only the adsorbed molecules, and in this case, there is no need to remove the unadsorbed gas. In some cases,

〔Effect of the invention〕

As explained above, the present invention includes a step of introducing a gas containing film constituent elements onto the substrate surface, a step of making this gas further adsorbed on the substrate surface, and a step of reacting the gas adsorbed on the substrate surface. By having a multi-layered film of various elements, it is possible to control the film thickness on the atomic order, and the controllability of the film thickness is greatly improved. This has the effect of allowing adjustment.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram for explaining one embodiment of the thin film forming method according to the present invention, and FIGS.
FIGS. 5 to 11 are explanatory diagrams illustrating a conventional thin film forming method. 20...AXY gas, 20a, 30a, 40a...
...Adsorption layer, 21...A element, 22...X group,
23...Y group, 24...Z group, 25...B
Element, 26... Bonding hand, 27... UV gas,
28...U group, 29...Y group, 30...A
XtY, gas, 40...AXYUV gas.

Claims (1)

[Claims] a step of introducing a gas containing a film constituent element onto the substrate surface; a step of further adsorbing this gas onto the substrate surface;
A method for forming a thin film, comprising the step of reacting the gas adsorbed on the surface of the substrate.