JPS6355191A - Production of compound semiconductor crystal - Google Patents

Abstract

PURPOSE:To form a grown layer of molecular array of a desired crystal along a step of a substrate, by alternately arranging constituent elements in the same plane of a substrate having a step and successively supplying a gas containing the constituent elements under a proper pressure. CONSTITUTION:A step 11 of a compound semiconductor having alternately arranged atoms A and B is formed on a surface of a substrate crystal 13. The step 11 is composed of the atom B. A gas containing the chloride, etc., of the element A is supplied to the substrate crystal 13. In the above process, the temperature of the substrate 13 and the pressure, etc., of the supplied gas are adjusted to an optimum condition to effect the adsorption of the gas of the element A molecule of the supplied gas diffuses on the surface of the substrate 13 and is adsorbed to a part of the step 11. Thereafter, the atmosphere is changed to the element B or its gaseous compound and the element is taken in the position adjacent to the A-Cl adsorbed by the former operation. A row of the compound AB is grown along then step 11 by this process.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for forming compound semiconductor crystals in which growth is controlled with precision in units of molecular rows or -molecules.

(Prior art and its problems) Conventional techniques for forming thin films of compound semiconductors such as GaAs include the vapor phase epitaxial method (VPE method), which uses gaseous raw materials such as constituent elements such as chlorides, hydrides, and organometallic compounds.
In addition, the molecular beam epitaxial method (MB), in which the constituent elements are made into a beam in a high vacuum and irradiated onto the substrate crystal, is used for growth.
E method) is widely used. By the way, these growth methods require precise control of the growth rate in order to form a thin film. However, this requires precise control of factors such as flow rate, pressure, and time, and control is extremely difficult when the thickness reaches the level of a monomolecular layer (about a few people).

Therefore, with such a technique, it is nearly impossible to control the problems that the present invention aims to solve, namely, the growth of atomic/molecular arrays, and furthermore, the growth of individual atoms/molecules.

As another growth method, constituent elements of compound semiconductors,
Alternatively, there is the atomic layer epitaxial method (ALE method), which attempts to grow a desired compound semiconductor as a whole by alternately supplying a gas containing the element and adsorbing it one atomic or molecular layer at a time [Tuomo Suntra (T.

5untola), 16th National Elements and Materials Conference (Extended Abstnact of t
he 16th Conference on 5ol
idState Device and Mat
Kobe, 1984. pp, 647-
6501゜According to this method, in order to control the film thickness,
Unlike traditional growth rate control methods, e.g.
In the GaAsALE method using C1 and AsH3, it has been found that control in molecular layer units is possible by controlling only the number of GaC1 adsorptions over a wide temperature and flow range;
Journal of Ablide Physics (Japan)
eseJournal of Applied Phys.
sics), Vol, 25. No, 3. Marc
h.

1986, pp. L212-L214] Film thickness control technology has been significantly improved.

However, as mentioned above, the conventional ALE method is a method of simply adsorbing and growing a layer of single atoms/molecules uniformly on the substrate surface, and growth is performed in units of atomic rows, molecular rows, or even single atoms/molecules. I couldn't control it.

Of course, conventional methods such as the VPE method and the MBE method for simultaneously supplying the constituent elements are also extremely difficult.

An object of the present invention is to eliminate the drawbacks of the above-mentioned conventional techniques and to provide a method for forming compound semiconductor crystals that can control growth in units of 0 atomic and molecule rows, and furthermore, in units of 1 atom and molecule. It is.

(Means for solving interlocking points) That is, according to the present invention, in a method of performing crystal growth by alternately supplying constituent elements of a compound semiconductor or a gas containing the elements onto a substrate crystal, The substrate is a crystal in which the constituent elements are arranged alternately and has crystallographic steps on the surface, and the optimum substrate is such that during growth, the constituent elements of at least one of the compound semiconductors or the gas containing that element can be adsorbed only to the steps. Formation of compound semiconductor crystals characterized by setting adsorption conditions such as temperature and supply gas pressure to form a line of adsorption layer along the steps, and then supplying other constituent elements to obtain a layer of molecular line growth. You can find a method.

Furthermore, according to the present invention, in a method of growing a crystal by alternately supplying constituent elements of a compound semiconductor or a gas containing the elements onto a substrate crystal, the constituent elements are arranged alternately within the same plane of the crystal, and The optimum substrate temperature is such that when growing, at least one constituent element of the compound semiconductor or a gas containing the element can be adsorbed only at the intersection of the steps;
A method for forming a compound semiconductor crystal is obtained, which is characterized in that a desired crystal is grown by setting adsorption conditions such as supply gas pressure and adsorbing the element at the intersection point and then supplying other constituent elements.

(Function) The present invention grows crystals by alternately supplying constituent elements of a compound semiconductor or gases containing the elements onto a substrate crystal. Select as the substrate. Further, steps are formed on the surface of the substrate by cutting out the substrate crystal slightly inclined from the low index plane. FIG. 1(a) shows a schematic perspective view of a substrate crystal 13 having one step 11 of a compound semiconductor composed of atoms A and B. In FIG. In this diagram, step 1
1 is made up of B atoms. This substrate crystal 13
For example, when a chloride of A is supplied onto the surface, it is adsorbed onto the surface (FIG. 1(b)). The heat of adsorption at this time is shown in Figure 2.

In FIG. 2, 91 is the heat of adsorption when adsorbing on a flat surface.

If the temperature of the substrate crystal 13 is high to a certain extent, the adsorbed molecules will diffuse on the surface and will be adsorbed at a more stable point, which corresponds to step 11 in FIG. If the heat of adsorption at that point is q2, then the relationship q2>ql holds true. Also, some of it leaves the surface.

On the other hand, the total number of adsorption equilibria is generally expressed as K = aexp(q/
RT). Here, α is a constant, q is the heat of adsorption, R is a gas constant, and T is the temperature of the thread.

Therefore, in FIG. 2, RT is greater than 91 and q2 is R.
has a sufficiently large value compared to T (ql<RT<q2)
, and by appropriately selecting the partial pressure of A-C1, it is possible to make the amount of adsorption on a flat surface almost 0, and to make it adsorb only on the surface along the steps. After that, the atmosphere was changed to A-
Converts C1 to element B or its gaseous compound.

As a result, B is taken into the position next to the adsorbed A-CI, and the compound AB grows in a single line as a step (FIG. 1(C)).

FIG. 3(a) shows a schematic diagram of a substrate crystal, which is a compound semiconductor composed of elements A and B, and has steps that intersect perpendicularly on the surface. In this figure, the intersection of the steps is surrounded by B atoms. When a chloride of A, for example, is supplied onto this substrate crystal, it is adsorbed onto the surface (FIG. 3(b)). The heat of adsorption at this time is shown in Figure 4. 93 in Grab is the heat of adsorption when adsorbing on a flat surface. Further, q4 is the heat of adsorption when adsorbing at a step similar to that shown in FIG. 1, and q5 is the heat of adsorption at the intersection of the steps. As with the column adsorption, RT is greater than q3+q4 and q5 is RT
has a sufficiently large value compared to q3. q4<RT<
q5) Furthermore, by appropriately selecting the partial pressure of A-C1, it is possible to make the amount of adsorption on a plane or in a step approximately O, and to cause adsorption only at the intersection of the steps. Thereafter, the atmosphere is changed from A-CI to element B or its gaseous compound. As a result, B is taken into the position next to the adsorbed A-CI, and compound AB grows at the intersection of the steps as shown in FIG. 3(c). Next, the present invention will be specifically explained based on examples.

(Examples) Example 1 In this example, a case will be described in which the method according to the present invention is applied to the molecular side growth of InAs on a GaAs (110) substrate having steps. A schematic diagram of the growth apparatus is shown in FIG. In this growth apparatus, an In source port 2 is placed upstream of the upper growth chamber 1, and HCI gas is supplied together with H2 carrier gas from the upstream side. As a result, In and C1 are generated and transported downstream. On the other hand, AsH3, which is a hydride of As, is supplied to the lower growth chamber 3 together with H2 carrier gas. This gas decomposes in the reaction tube, and in the substrate region it is mainly A.
It is s4. The substrate crystal 4 is GaAs (11
A surface cut out at an angle of several to several tens of degrees from the 0) surface in the (100) direction was used. The temperature of the reaction tube is set to 800°C for the In source part and 300 to 750°C for the substrate crystal part using a resistance heating furnace.
And so. The gas flow conditions are as follows.

Gas type Flow rate MCI (In) 5cc/m1nAsH
35cc/m1n H2 (each growth chamber) When growing at 5000cc/min, first place the substrate crystal 4 in the lower growth chamber 3, and
The temperature was raised to the growth temperature in a s atmosphere. When the growth temperature is reached, HCI is supplied to the upper growth chamber 1, and after a certain period of time, when the flow of HCI reaches a steady state, the substrate crystal 4 is transferred to the upper growth chamber 1.
Moved to. Then, InC1 was sufficiently adsorbed for a certain period of time, and then the substrate crystal 4 was moved to the lower stage growth chamber 3 again. 1 In
A layer is formed by repeating the adsorption of C1 and As as one cycle. Note that when the substrate crystal 4 was moved, the supply of AsH3 was stopped to prevent growth during the movement, and the movement was performed in an InCl atmosphere.

FIG. 6 schematically shows the change in the thickness (1) of the grown layer per cycle with respect to the growth temperature. When the growth temperature is low, t is constant and GaAs(110)
Approximately corresponds to the thickness of one monolayer on the surface. However, as the growth temperature increases, t becomes smaller, and T1 to T2 (
T1: 550°C, T2: 600°C) takes a constant value again, and thereafter t tends to decrease. Figure 6 shows (
110) Cases where the inclination θ from the plane is 5° and 10° are shown, and it is shown that t when the inclination θ from the plane is 10′ is about twice the value when it is 5°. Furthermore, when θ=5°, as shown in Figure 1(a), a step with a height of 1 atom occurs every 10 atoms in the plane direction, and approximately 0.1 steps per cycle occur.
It can be seen that the growth pattern is that of a molecular layer, and growth occurs only along steps.

Example 2 GaAS with vertically intersecting steps on the surface of this example
A case will be described in which the method of the present invention is applied to the growth of InAs on a (110) substrate. Ga as the substrate crystal
Using the As (110) plane as a reference, a wafer was used that was cut by tilting several degrees in the (111) direction so that two mutually perpendicular steps were generated. The growth apparatus and other growth conditions are exactly the same as in Example 1.

FIG. 7 schematically shows the change in the thickness (1) of the grown layer per cycle with respect to the growth temperature.

When the growth temperature is considerably low, t takes a constant value, and its value approximately corresponds to the thickness of a single molecular layer relative to the (110) plane. However, as the growth temperature increases, t decreases,
Next, there is a region where the value is constant again. As described in Example 1, this is a region where the growth film thickness is mainly determined by the number of steps. When the temperature is further increased, a region where the grown film thickness becomes constant again appears in the region T3 to T4 (T3: 620°C, T4: 650°C). When the growth temperature is increased above T4, t also decreases. This region T3 to T4 does not appear in Example 1 and corresponds to growth at the intersection of steps.

(Effects of the Invention) As described above, by using the method for forming a compound semiconductor crystal according to the present invention, it is possible not only to control the one-dimensional crystal growth along the steps on the crystal surface, which has been difficult in the past, but also to control the growth of the crystal along the steps. One-dimensional growth at the intersection of can also be controlled.

Furthermore, by selecting various growth crystals, it is possible to grow heterojunctions in the ridge direction, which is a growth method that will lead to the realization of new devices in the future.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a crystal surface to explain crystal growth according to the present invention, FIG. 2 is a diagram to explain the heat of adsorption on the surface of FIG. 1, and FIG. 3 is a schematic diagram of another crystal surface according to the present invention. Figure 4 is a schematic diagram of the crystal surface to explain the growth of two crystals.
Figure 5 is a schematic diagram of the crystal growth apparatus used in the example, and Figure 6 shows the relationship between the growth temperature and the growth layer thickness per cycle in Example 1c. The figure shown in FIG. 7 is a diagram showing the relationship between the growth temperature and the growth layer thickness per cycle in Example 2. The numbers in the figure are: 1... Upper growth chamber 2... Source port 3... Lower growth chamber 4... Substrate crystal 5... Substrate holder 6... Movement of substrate crystal 11... Step 13...Substrate crystal Fig. 1 (a) Substrate crystal 13 Fig. 2 Fig. 3 Fig. 4 upper q

Claims (2)

[Claims] (1) In a method of crystal growth by alternately supplying the constituent elements of a compound semiconductor or a gas containing the elements onto a substrate crystal, the constituent elements are arranged alternately within the same plane of the crystal, and the surface has crystallographic characteristics. A crystal having a specific step is used as a substrate, and during growth, adsorption conditions such as optimal substrate temperature and supply gas pressure are set so that at least one constituent element of the compound semiconductor or a gas containing the element can be adsorbed only to the step. After forming a line of adsorption layer along the
A method for forming a compound semiconductor crystal, which comprises supplying other constituent elements to obtain a molecular column growth layer. (2) In a method of crystal growth in which the constituent elements of a compound semiconductor or a gas containing the elements are alternately supplied onto the substrate crystal, the constituent elements are arranged alternately within the same plane of the crystal and are arranged vertically on the surface. A crystal with intersecting steps is used as a substrate, and during growth, adsorption conditions such as optimum substrate temperature and supply gas pressure are set such that at least one constituent element of the compound semiconductor or a gas containing that element is adsorbed only at the intersection of the steps. A method for forming a compound semiconductor crystal, characterized in that a desired crystal is grown by supplying other constituent elements after setting and adsorbing them to the intersection points.