JPH06112135A - Thin film forming apparatus and thin film growing method - Google Patents

Abstract

PURPOSE:To control internal stress generated in a formed thin film by additionaly providing a stress measuring device in an epitaxial growing apparatus. CONSTITUTION:A heater is arranged for the outer surface parts of Knudsen cells 14, 15 and 16. The inner parts of the cells are filled with component raw materials of thin-film growing elements 14a, 15a and 16a. Thus, an epitaxial growing device 10 is constituted. A semitransparent mirror 25 is arranged on the vertical axis of the surface of a semiconductor 12 at the angle of 45 deg. with respect to the vertical axis in the vicinity of the outside of a window 17. A filter 24 and a lens 23 are arranged on the axis forming the angle of 45 deg. with respect to the semitransparent mirror 25. A light source 22 is arranged at a position, where the focal point of the lens 23 is focused. Thus, a stress measuring device 20 using a Newton ring interference method is constituted. The stress generated in the Si substrate is measured with the stress measuring device. A thin film is grown by changing the annealing temperature and/or the film thickness during the measurement.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film forming apparatus and a thin film growth method using the apparatus, and more particularly, to a thin film forming apparatus used for manufacturing a compound semiconductor substrate for optical or high speed devices and the like. The present invention relates to a thin film growth method.

[0002]

2. Description of the Related Art Epitaxial growth for forming a thin film of an ordered semiconductor crystal with a crystal axis aligned with the single crystal on a semiconductor single crystal plate as a substrate is
Generally, MBE (Molecular Beam Epitaxy) method and MOCVD (Metal Organic Chemic)
al Vapor Deposition: metal organic chemical vapor deposition) method and the like.

This epitaxial growth includes homoepitaxial growth in which a thin film of the same material as the substrate is grown and heteroepitaxial growth in which a thin film of a material different from the substrate is grown.

Si is used for the heteroepitaxial growth.
A thin film of Ge (germanium) grown on a (silicon) substrate (hereinafter referred to as Ge / Si) (WDNIX: M
et allurgical Transactions, A 20A (1989), p2217),
A GaAs (gallium arsenide) thin film grown on a Si substrate (hereinafter referred to as GaAs / Si) (SFFang et al.
al.:J. Appl. Phys., 68 (1990), pR31), etc., and research aiming at fabrication of devices having new functions and provision of inexpensive substrates has been actively conducted.

FIG. 3 shows GaA used in the conventional MBE method.
It is a schematic sectional drawing which showed the s / Si growth apparatus typically,
In the figure, 11 indicates a chamber. A vacuum pump (not shown) is connected to the chamber 11, and the Si substrate 12 is held above the inside of the chamber 11 to
2 A heater 13 is arranged near the upper surface. In the lower part of the chamber 11, Ga14a and As15a, which are raw materials for thin film growth, are filled in the lower part, and a heater (not shown) is wound around the outer periphery of the chamber to form a bottomed cylindrical Knudsen Cell (Knudsen Cell) 14. 15 are provided, and their central axes are attached so as to face the Si substrate 12, respectively. When epitaxially growing using the apparatus configured as described above, the degree of vacuum in the chamber 11 is set to 10 ^-9 Torr or less, and the Knudsen cells 14 and 15 are heated to predetermined temperatures, respectively, and Ga14a and As1 of the component elements are heated.
5a is vaporized and ejected in a beam shape to adhere to the lower surface of the substrate 12 heated by the heater 13 to a predetermined temperature.

GaAs / Si used for MOCVD
In the growth device, TMG (T
ri Methyl Gallium) nozzle and AsH ₃ nozzle.

[0007]

In the above-mentioned heteroepitaxial growth, the material of the substrate and the epitaxial thin film layer (hereinafter referred to as a thin film) are different, and the respective crystal lattice constants and thermal expansion coefficients are different. Therefore, during growth in these systems, compressive stress is generated in crystals with a large lattice constant and tensile stress is generated in crystals with a small lattice constant. Causes compressive stress, which causes various problems.

First, there is a problem that the substrate warps due to the internal stress. This warpage causes defocusing in the lithography process, deteriorates pattern accuracy, and lowers the mechanical strength of the substrate. There were challenges (Kitsuki et al .: Proceedings of the 38th Joint Lecture on Applied Physics, (1991), p231 28a-ZV-4).

Secondly, there is a problem in that the internal stress causes a modulation in the energy band structure of the thin film, which adversely affects optical characteristics and electrical characteristics.

Third, when the internal stress exceeds the critical stress, dislocations occur in the thin film or the substrate, or dislocation lines remaining at the interface between the thin film and the substrate propagate to the surface of the thin film and crystallize. There was a problem of degrading the property (Osamu Ueda: Applied Physics, 61 (1992), p126). FIG. 4 is a graph showing a growth process of a conventional two-step growth method in GaAs / Si, in which 31 is a step of cleaning the Si substrate surface before growth at a high temperature (T = T ₃ ), and 32 is a first step.
Is a step of forming the GaAs buffer layer at low temperature (T = T ₁ ), 33 is a step of forming the second GaAs layer at high temperature (T = T ₂ ), and 34 is a step of cooling. Immediately after the thin film is formed in this way, HCl-GaCl is formed 33a.
The etch pit density (Etch Pit Density: hereinafter referred to as EPD) of the thin film vapor-phase-etched with gas is about 10
It is about ⁴ cm ^-2 , but when the thin film is cooled to room temperature 34a after it is formed, the EP of the thin film etched by molten KOH
D has increased to about 10 ⁶ cm ^-2 , and remarkable deterioration of crystallinity has occurred (M. Tachikawa, H.Mori: Appl.
Phys. Lett. 56 (1990), p2225).

The present invention has been made in view of the above problems, and suppresses the generation of internal stress of a thin film in heteroepitaxial growth, thereby suppressing the warp of the substrate and suppressing the focus blur in the lithography process, and the pattern. The accuracy of the substrate and the mechanical strength of the substrate, and the modulation of the energy band structure in the thin film to improve the optical and electrical characteristics. It is an object of the present invention to provide a thin film forming apparatus and a thin film growth method capable of suppressing and improving crystallinity.

[0012]

In order to achieve the above object, a thin film forming apparatus according to the present invention is characterized in that a stress measuring apparatus is additionally provided in an epitaxial growth apparatus.

The thin film growth method according to the present invention is characterized in that the thin film forming apparatus is used to control the stress generated in the thin film by changing the annealing temperature and / or the film thickness while measuring the stress.

[0014]

As a result of investigating, analyzing and researching the above-mentioned conventional technique, the present inventors have determined that the internal stress in heteroepitaxial growth is determined by the density of mismatched dislocations formed in the substrate or thin film, and It was found that the density changes depending on the growth temperature, the film thickness, the annealing temperature after growth, and the like. That is, if the epitaxial growth or annealing temperature is sufficiently high and the film thickness is sufficiently thick, a sufficient number of mismatched dislocations are formed to relax the difference in lattice constant, so that the internal stress at this temperature (high temperature) is It becomes almost zero. On the other hand, when the epitaxial growth or annealing temperature is low or the film thickness is thin, dislocations are hard to move and a sufficient number of mismatched dislocations are not formed so as to relax the difference in lattice constant. Internal stress occurs at. Also, in the process of cooling from the epitaxial growth or annealing temperature to room temperature, internal stress is generated due to the difference in thermal expansion coefficient between the substrate and the thin film.
This is due to the difference between the mismatched dislocation density required at the epitaxial growth or annealing temperature and the mismatched dislocation density required at room temperature.

Based on the above findings, the growth temperature is sufficiently high,
Table 1 below shows the effects of the lattice constant difference and the thermal expansion coefficient difference between the substrate and the thin film on the internal stress, divided into the case where the film thickness is sufficiently thick and the case where the growth temperature is low or the film thickness is thin. As shown.

[0016]

[Table 1]

In the table, a _f is the lattice constant of the thin film, a _s is the lattice constant of the substrate, α _f is the thermal expansion coefficient of the thin film, α _s is the thermal expansion coefficient of the substrate, T _G is the epitaxial growth temperature, RT is room temperature,
The stress indicates the internal stress of the thin film.

From Table 1, the internal stress is complicatedly influenced by the epitaxial growth conditions and the subsequent cooling operation. In all cases where the growth temperature is high and the film thickness is thick, the internal stress of the thin film is increased at the growth temperature. Was very small, but it was found that tensile or compressive internal stress was generated in the subsequent cooling process. If the growth temperature is low or the film thickness is thin, the lattice constant of the thin film is larger than that of the substrate and the coefficient of thermal expansion of the thin film is smaller than that of the substrate, or vice versa. Alternatively, it was found that a compressive internal stress was generated and further increased in the subsequent cooling process. Then, in the case shown by * 1 and * 2 in the table (both the lattice constant and the thermal expansion coefficient of the thin film are larger or smaller than those of the substrate), by appropriately selecting the annealing condition and / or the film thickness condition. It was found that a thin film with very low internal stress can be obtained at room temperature.

By the way, as a method of measuring the internal stress, the following cantilever method, diffraction method, disk method, etc. are known (Kanehara, Fujiwara: "Thin film", Sohuabo, p127-p131). . (1) Cantilever method: When one end of a thin substrate formed in a strip shape is fixed and a thin film is vapor-deposited, the other end opposed to the fixed one end is displaced due to the magnitude of internal stress generated. This is a method of obtaining stress by measuring this displacement amount. (2) Diffraction method: a method in which the substrate is irradiated with an X-ray or an electron beam and the change in the lattice constant of the deposited thin film is measured from the position of the obtained diffraction line to determine the internal stress. (3) Disc method: When a thin film is deposited on a disc-shaped substrate, the curvature of the substrate changes depending on the magnitude of the internal stress generated. The stress is obtained by measuring the change in the curvature by an interferometry method using a Newton ring or the displacement amount of the reflected light of the laser. As a result of investigating the above-mentioned measuring methods of various internal stresses, it was found that the disk method of (3) can be applied as a measuring method that allows in-situ observation (in-situ observation) in epitaxial growth.

According to the thin film forming apparatus of the present invention, since the stress measuring device is attached to the epitaxial growth device, the epitaxial growth can be performed while measuring the internal stress.

According to the thin film growth method of the present invention,
Since the stress generated in the thin film is controlled by changing the annealing temperature and / or the film thickness while measuring the stress using the thin film forming apparatus, it is possible to suppress the generation of the internal stress of the thin film in the heteroepitaxial growth. Therefore, the warp of the substrate is suppressed, the defocusing in the lithography process is suppressed, the accuracy of the pattern is improved, and the reduction in the mechanical strength of the substrate is suppressed. Further, the modulation of the energy band structure in the thin film is suppressed, and the optical characteristics and electrical characteristics are improved. Further, generation of dislocations and propagation of dislocation lines are suppressed, and crystallinity is improved.

[0022]

EXAMPLES AND COMPARATIVE EXAMPLES Examples of a thin film forming apparatus and a thin film growth method according to the present invention will be described below with reference to the drawings.
It should be noted that components having the same functions as those of the conventional example are designated by the same reference numerals. FIG. 1 is a schematic sectional view schematically showing an embodiment of a thin film forming apparatus according to the present invention.
Reference numeral 1 indicates a chamber. A vacuum pump (not shown) is connected to the chamber 11,
A lower surface of the substrate 12 is placed on a holder 18 arranged above the inside so that the lower surface of the substrate 12 becomes a thin film growth surface, and a heater 13 is arranged near the upper surface of the substrate 12. Chamber 11
A window 17 is formed in the lower part of the inside so as to face the substrate 12. Further, cylindrical Knudsen cells (14, 15, 16) having a bottomed cylindrical shape are arranged around the window 17 and are attached so that their central axes face the substrate 12, respectively. A heater (not shown) is provided on the outer peripheral portion of 16 and the inside thereof is filled with the component raw materials 14a, 15a, 16a of the thin film growth element to form an epitaxial growth apparatus. Further, on the vertical axis of the surface of the substrate 12, a semi-transparent mirror 25 is formed near the outside of the window 17 at an angle of 45 ° with the vertical axis.
Is provided, the lens 26 is provided next, and the image receiving device is provided at a position where the focal point of the lens 26 is focused. On the axis that makes an angle of 45 ° with the semi-transparent mirror 25, the filter 2
4. The lens 23 is provided, and the light source 22 is provided at the position where the focal point of the lens 23 is connected, whereby a stress measuring device using the Newton ring interferometry is configured.

When epitaxial growth is performed using the apparatus thus constructed, the vacuum degree in the chamber 11 is set to 10 ^-9 Torr or less, and the Knudsen cells 14, 15, 1 are used.
6 is heated to a predetermined temperature by a heater to evaporate the component elements 14a, 15a and 16a, and is ejected in a beam shape and attached to the lower surface of the substrate 12 heated to a predetermined temperature by the heater 13. And the stress measuring device 20
While measuring the stress generated in the Si substrate 12, the annealing temperature and / or the film thickness is changed to grow a thin film.

Below, the substrate 12 is made of Si having a diameter of 4 inches.
And the raw materials 14a, 15a, 16
The results of performing GaAs / Si growth by changing the annealing temperature while measuring the internal stress using Ga, As, and Si for a (case of * 1 in Table 1 above) will be described.

FIG. 2 is a graph showing the growth process of the GaAs / Si growth method according to the embodiment. First, the cleaned Si substrate 12 is put into the epitaxial growth apparatus 10 and the vacuum degree in the chamber 11 is 10 ^-9 Torr or less. And about 50
The attached water is removed by heating to a temperature of 0 ° C (41 in the figure), and further heated to a temperature of about 1000 ° C for about 15 minutes.
After holding for about one minute, the oxide film on the surface of the Si substrate 12 was removed (42 in the figure). Next, the temperature of the Si substrate 12 is lowered to about 3
A buffer layer was grown at a low temperature of 00 ° C. at a growth rate of 0.3 μm / hr to a film thickness of about 0.05 μm (43 in the figure). In addition, As was irradiated when the temperature of the Si substrate 12 reached a temperature of 600 ° C. (43 a in the figure). Next, the temperature of the Si substrate 12 is raised again to about 600 ° C. and the temperature is maintained for about 5 minutes to anneal the buffer layer (4 in the figure).
4), reduce the temperature again, and perform ME at a low temperature of approximately 300 ° C.
Approximately 1.0μ by E (Migration-Enhanced Epitaxy) method
A GaAs layer was grown to a thickness of m and Si was doped to about 6 × 10 ¹⁵ cm ^-3 (45 in the figure). It is confirmed that the compressive stress acts on the thin film from the Newton ring using the stress measuring device 20 (45a in the figure), and then the temperature of the Si substrate 12 is observed until the compressive stress becomes substantially zero while observing the Newton ring. After raising (46 in the figure), S
The temperature of the i substrate 12 was lowered to 300 ° C. Then, a GaAs layer was grown to a film thickness of approximately 2.0 μm by the MEE method (47 in the figure), cooled to room temperature (48 in the figure), and the Si substrate 12 was taken out from the epitaxial growth apparatus 10.

As a comparative example, the same GaAs was prepared by the two-step growth method in a device without the stress measuring device 20.
/ Si growth was performed.

The results shown in Table 2 were obtained by comparing the stress and crystallinity of the thin films grown by the methods of Examples and Comparative Examples.

[0028]

[Table 2]

As is clear from these results, according to the thin film forming apparatus and the thin film growing method of this embodiment, the stress of the GaAs / Si thin film is suppressed and the crystallinity is excellent as compared with the conventional apparatus and method. A thin film has been obtained. Therefore,
When a GaAs / Si thin film having the relationship of a _f > a _s and α _f > α _s is grown at a low temperature of 300 ° C. to a thickness of about 1.0 μm (45a in the growth process), the thin film has compressive stress. The reason for this is that the misfit dislocation density in the thin film is 300.
It can be seen that it is insufficient to alleviate the difference in lattice constants at 0 ° C., and the subsequent annealing (growth process 46) forms sufficient mismatched dislocations in the thin film, resulting in zero internal stress. In addition, in the case indicated by * 1 in Table 1 above, it was confirmed that a thin film having very small internal stress at room temperature can be obtained by appropriately selecting the annealing condition and / or the film thickness condition.

In the thin film forming apparatus according to the present embodiment, an MB having a Newton ring interference type stress measuring apparatus is provided.
Although the E-type epitaxial growth apparatus was used, the same result can be obtained by using a laser reflected light method or the like as the stress measuring apparatus and MOCVD or the like as the epitaxial growth apparatus. Similar results can be obtained for the cases indicated by * 2 in Table 1 above.

[0031]

As described above in detail, in the thin film forming apparatus according to the present invention, since the stress measuring device is attached to the epitaxial growth device, the epitaxial growth can be performed while measuring the internal stress.

In the thin film growth method according to the present invention, the thin film forming apparatus is used to control the stress generated in the thin film by changing the annealing temperature and / or the film thickness while measuring the stress. It is possible to suppress the generation of internal stress in the thin film during epitaxial growth. Therefore, it is possible to suppress the warp of the substrate, suppress the defocus in the lithography process, improve the accuracy of the pattern, and suppress the decrease in the mechanical strength of the substrate. Further, modulation of the energy band structure in the thin film can be suppressed to improve optical characteristics and electrical characteristics. Furthermore, the generation of dislocations and the propagation of dislocation lines can be suppressed to improve the crystallinity.

[Brief description of drawings]

FIG. 1 is a schematic sectional view schematically showing an embodiment of a thin film forming apparatus according to the present invention.

FIG. 2 is a graph showing a growth process of a GaAs / Si growth method according to an example.

FIG. 3 is a schematic sectional view schematically showing a GaAs / Si growth apparatus used in a conventional MBE method.

FIG. 4 is a graph showing a growth process of a conventional two-step growth method on GaAs / Si.

[Explanation of reference numerals] 10 Epitaxial growth apparatus 20 Stress measurement apparatus

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H01L 21/203 M 8422-4M

Claims (2)

[Claims] 1. A thin film forming apparatus, wherein a stress measuring device is attached to an epitaxial growth device. 2. A method for growing a thin film, which comprises using the thin film forming apparatus to control the stress generated in the thin film by changing the annealing temperature and / or the film thickness while measuring the stress.