JP2824972B2 - Oxide thin film forming method - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a method for forming a single crystal thin film of an oxide, and particularly to an insulator such as an alkaline earth metal oxide, spinel, and sapphire and an oxide high-temperature superconductor. The present invention relates to a method for forming an oxide thin film suitable for forming a solid single crystal thin film on a semiconductor substrate such as silicon (Si).

[Conventional technology]

Conventionally, a single-crystal oxide thin film is formed at a low temperature on a Si substrate due to the necessity of forming a stacked LSI, a high-temperature superconducting wiring, and a high-temperature superconducting transistor. Vacuum evaporation has been widely reported as a method of forming oxides at relatively body temperature, using electron beam impact heating, resistance heating, ionized vacuum evaporation, cluster ion beam evaporation, sputtering, etc. Examples have been reported.

First, in the electron beam shock heating method, an oxide source having the same stoichiometric composition as the film to be formed in an oxygen atmosphere is continuously heated and vapor-deposited to form Al ₂ O ₃ , and first, the constituent metal elements are formed. After vapor deposition, there is an example in which an oxide superconductor YBa ₂ Cu ₃ O _7-X is formed by annealing in an oxygen atmosphere (D. Hof
fman and D. Leibowitz: J.Vac.Sci.Technol.8 (1971) 10
7.and BY.Tsaur, MSDilorio, and AJStrauss: Appl.P
hys. Lett. 51 (1987) 858.).

In the resistance heating method, as a solid oxide source, As ₂ O ₃ and Sb ₂ O ₃ are used as co-evaporation with other metal elements to form Al ₂ O ₃ , SiO _2
2 , MgO and Al ₂ MgO ₄ are formed (K. Pioog, A. Fis
cher, R. Trommer, and M. Hirose: J. Vac. Sci. Technol. 16
(1979) 290. and RAStall: J.Vac.Sci.Technol.B1 (19
83) 135.).

In the ionized vacuum deposition method, there is an example in which molecules evaporated by electron beam impact heating are ionized by accelerated thermoelectrons to grow Al ₂ O ₃ . (Kunihiko Takahama, Hiroshi Hanabusa: IEICE Technical Report, CPM83-11 (1983) 1.).

In addition, regarding the cluster ion beam evaporation method, Zn
Examples of formation of O and BeO have been reported (T. Takagi, I. Yam
ada, K. Matusbara, and H. Takaoka: J. Cryst. Growth 45 (19
78) 318 and T. Takagi, K. Matusbara, and H. Takaoka: J. Ap
pl.Phys. 51 (1980) 5419).

Finally, in the sputtering method, an example in which a single-crystal thin film of an Y-Ba-Cu-O-based oxide conductor is formed and an example in which an Al ₂ O ₃ thin film is formed by RF sputtering a target has been reported ( Y.Enomoto, T.Murakami, M.Suzuki, and K.Mori
waki: Jan. J. Appl. Phys. 26 (1987). And RSNowicki:
J. Vac. Sci. Technol. 14 (1977) 127.) has been reported.

[Problems to be solved by the invention]

However, any of the above techniques has a disadvantage that the Si substrate is oxidized in the initial stage of oxide growth. At present, only the resistance heating method and sputtering have a track record of growing a single crystal film of an oxide on a Si substrate.

That is, in the resistance heating method, an oxide fixed source is used as an oxygen source.
It has been reported that Al ₂ MgO ₄ was grown using Sb ₂ O ₃ and YSZ (stabilized zirconia) was grown by sputtering (Proceedings of the 2nd International Worry).
kshop on Futrure Electron Devices-SOI Technology a
nd 3D Integration (FED SOI / 3D WORKSHOP), 1985, shu
zenji, pp.75-79 and Kakihara Ryowa, Enomoto Shuji, Atsushi Fumihiro, Doi Tsukasa, Shinozaki Toshiyuki, Kiba Masayoshi: IEICE Technical Report, ED86-63 (1986) 7.).

However, even in these techniques, in the former, the optimum partial pressure range of the oxide source for obtaining a single crystal is extremely narrow, and only an unclear spot pattern is confirmed by electron beam diffraction. In the latter, the composition is controlled by the number of Y pellets placed on the Zr target, which has a problem in the reproducibility of the film, and has high energy ions of Ar and oxygen. There is a drawback that point defects tend to occur in the film because of collision with the film.

Therefore, there has been a demand for the development of a growth method that does not oxidize the Si substrate, does not cause ion bombardment on the grown film, performs sufficient surface migration of adsorbed molecules, and has no oxygen deficiency.

On the other hand, for these technologies, the present applicant proposes an intermittent electron beam impact heating method in an ultra-high vacuum, and a single crystal thin film of SrO having a relatively high dissociation energy is formed on a Si substrate. (Japanese Patent Application Laid-Open No. 61-75578, Y.
Kado and Y. Arita: Extended Abstracts of the 18th Co
nfference on Solid State Devices and Materials, Tok
yo, 1986, pp. 45-48). This method has the disadvantages of a method of continuously heating and depositing an oxide source by an electron beam impact heating method, that is, (1) the oxygen partial pressure in the growth chamber is increased, and the Si substrate is oxidized.

(2) Surface migration of vapor deposition molecules required for single crystal growth is not sufficiently performed.

(3) Since floating electrons generated from the electron gun negatively charge the substrate, incident oxygen ions ionized by electron impact heating are repelled, and oxygen deficiency occurs in the grown film.

And other disadvantages were solved.

However, when an oxide source having a low dissociation energy with oxygen, such as BaO, is subjected to electron beam impact heating, a large amount of oxygen is generated from the source. Was.

Therefore, in order to achieve versatile oxide growth, it is necessary to take measures to positively control the number of oxygen molecules flying from the oxide source and entering the substrate.

[Means for solving the problem]

The present invention has been made to solve the above problems, by controlling the ramp rate of the electron beam,
The oxide thin film is formed on the substrate only when the ratio of the intensity of the oxide molecular flux and the intensity of the oxygen molecular flux flying from the oxide source toward the substrate reaches a predetermined value.

[Action]

The oxide thin film is formed on the substrate only when the ratio between the oxide molecular flux intensity and the oxygen molecular flux intensity reaches a predetermined value.

〔Example〕

 Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a configuration diagram of an ultra-high vacuum vapor deposition apparatus for carrying out the oxide thin film forming method of the present invention.

In the figure, 1 is an electron gun for heating an oxide source, 2
Is a pellet corresponding to the oxide source filled in the hearth of the electron gun, 3 is a control system for controlling the electron beam current of the electron gun and opening and closing of the jatter while monitoring the degree of vacuum in the vacuum chamber, 4 is a Si substrate, and 5 is a vapor deposition A quartz oscillator for monitoring the film thickness, 6 is a quadrupole mass analyzer for analyzing gas species generated from the source when various oxides are subjected to electron beam impact heating, and 7 is a vacuum chamber in the growth chamber. A nude ion gauge for measurement, 8 is a shutter that operates in conjunction with an electron gun and a vacuum gauge via a control system 3, 9 is a substrate holder, 10 is a lower exhaust system, 11 and 12 are upper exhaust systems, 13 Is an ultra-high vacuum chamber.

FIG. 2 is a characteristic diagram showing an example of controlling the electron beam current in the electron gun 1 shown in FIG. Here, a process is shown in which the electron beam current of the electron gun 1 increases at a constant ramp rate, and then quickly returns to zero. Further, I ₁ represents the case where the ramp is 5 mA / sec, I ₂ is the ramp 2 mA / sec.

Further, FIG. 3 is a characteristic diagram showing the signal intensity of each gas type measured by the quadrupole mass analyzer 7 when the pellet 2 shown in FIG. 1 was heated with an electron beam current of a ramp rate of 2 mA / sec. is there. Here, the case where BaO is heated as an oxide is shown.

In the figure, S1 is O ₂ , S2 is O, S3 is H ₂ , S4 is CO, S5 is
The signal strength of CO ₂ is shown.

Next, detection of a gas type in the ultrahigh vacuum chamber 13 will be described. First, when an oxide is heated with an electron beam using the vacuum deposition apparatus shown in FIG. 1, oxide molecules, oxygen molecules, oxygen atoms,
Metal or non-metal atoms are generated. In the case of BaO, Ba
O, O ₂ , O, and Ba are generated. Each partial pressure ratio depends on the magnitude of the dissociation energy of the oxide molecule. However, it is difficult to detect BaO or Ba having a large adhesion coefficient with the quadrupole mass analyzer 6. Therefore, in order to actually estimate these partial pressures, for the gas species (O ₂ , O) having a small adhesion coefficient, the signal intensity by the quadrupole mass analyzer 6 and the gas species (BaO, Ba) having a large adhesion coefficient As regards the above, the amounts deposited on the crystal unit 5 per unit time may be measured, and at the same time, the pressure in the growth chamber may be measured by a nude ion gauge.

From this result, the number of each gas species incident on the Si substrate 4 per unit time during the formation of the oxide thin film can be found. However, it is necessary to analyze the composition of the film adhering to the crystal unit 5 by a backward diffusion method or the like to clarify the deposition amounts of BaO and Ba.
In practice, the composition of the deposited film satisfies the stoichiometric composition, and the amount of Ba deposited can be ignored.

Here, as shown in FIG. 3, when BaO is heated, the partial pressure ratio of oxygen molecules is large, which causes oxidation of the Si substrate 4. Therefore, in order to grow a single crystal of Bao satisfying the stoichiometric composition without oxidizing the Si substrate 4, attention should be paid to the molecular number ratio of BaO and O ₂ incident on the Si substrate 4 per unit time. It turns out that it is good.

Next, FIG. 4 shows O ₂ and Ba incident on the Si substrate 4 per unit time.
FIG. 4 is a characteristic diagram showing the ratio of the number of molecules to O. Here, H ₁ if ramp is 5 mA / sec, H ₂ represents the case where ramp rate of 2 mA / sec. The time on the horizontal axis indicates the time elapsed from the start of heating.

As is clear from this figure, the larger the ramp rate, the smaller the incident number ratio of oxygen molecules, and changes with time.
Therefore, in the initial stage of the growth of BaO on the Si substrate 4, the step of increasing the ramp rate (for example, 5 mA / sec), opening the substrate-side shutter 8 immediately after starting the heating, and repeating the deposition is performed. An oxide single crystal can be grown without oxidizing the Si substrate 4. That is, opening the shutter at time t ₁ as shown in FIG. 4, to close the shutters at time t _2. However, regardless of the molecular number ratio, the partial pressure of oxygen in the growth chamber is maintained at a pressure at which the Si substrate 4 is not oxidized in consideration of the temperature of the Si substrate 4. here,
When the temperature of the Si substrate is 800 ° C., the oxygen partial pressure is 10 ⁻⁵ Torr
The following is assumed. This relationship is described in detail in the technical report (Oxidati by C. Gelain, A. Cassuto, P. Le Goff et al.
on of Metals.Vol.3.No.2,1971).

After that, after the Si substrate 4 is covered with the oxide growth film,
Si Problems substrate oxidation disappears, because rather deficient of oxygen in the grown film becomes a problem, the ramp plates were small (e.g., 2 mA / sec), the shutter 8 at time t ₃ when shown in FIG. 4
Close the shutter 8 at the time t ₄ to open and to repeat the deposition. As a result, the incident oxygen molecular ratio is increased, so that oxygen deficiency can be suppressed and an oxide satisfying the stoichiometric composition can be grown.

As described above, BaO has been described as an example. However, when other oxides (for example, Al ₂ O ₃ , ZrO _2, etc.) are grown by electron beam impact heating, similarly, the ramp rate of electron beam current and The timing at which the shutter 8 is opened can be controlled.

Next, FIGS. 5 (a) to 5 (c) show that the oxide source (pellet 2) is intermittently heated by the electron beam current shown in FIG. 2 and a desired oxide single crystal thin film is formed. 6 is a time chart showing a state in which the shutter 8 is opened only at the optimal timing and vapor deposition is repeated. Here, (a) shows the waveform of the electron beam current (the ramp rate is constant), (b) shows the opening / closing timing of the shutter 8,
FIG. 3C shows the change in the degree of growth vacuum. Note that T ₁
The deposition process time, T ₂ represents an exhaust process time.

As is apparent from this figure, the vapor deposition process in which the electron beam current increases and the subsequent evacuation process are alternately repeated. That is, after the heating of the oxide source (pellet 2) is started with an electron beam increasing at a fixed ramp rate, the pressure in the ultra-vacuum chamber 13 is increased from 10 ^-7 to 10 ^-10 depending on the gas species generated from the oxide source. Upon reaching ^-6 Torr, the size of the electron beam is quickly reduced to zero or to a level where there is no source evaporation. Then, the pressure in the ultrahigh vacuum chamber 13 is increased from 10 ^-7 to 10
^{The process} of recovering the pressure to ^-9 Torr or less, the molecules adsorbed on the Si substrate 4 sufficiently migrate on the substrate surface, and then again starting heating of a certain ramp rate by the electron beam is repeated. Further, it is necessary to make the exhaust stroke time T2 sufficiently long so that surface migration of the oxide molecules attached to the Si substrate 4 is sufficiently promoted. The opening and closing timing of the shutter 8 in FIG. 3B is such that the shutter 8 is opened for a predetermined time after the start of the heating of the electron beam as shown in FIG. Things can grow.

FIG. 6 is a configuration diagram showing an ultra-high vacuum deposition apparatus for growing a multi-element oxide according to the present invention.

In the figure, 21 to 23 are electron guns, 24 is a shutter, 25 is a substrate holder, and 26 is an intermittent deposition and exhaust by controlling the electron guns 21 to 23 and the shutter 24 while monitoring the degree of vacuum in the growth chamber. A control system constituting a means for repeating, 27 is a gate valve, 28 is a lower exhaust system, 29 and 30 are gate valves, 31
Numeral 32 is an upper exhaust system, numeral 33 is a Si substrate, numeral 34 is a nail ion gauge for monitoring the degree of vacuum in the growth chamber, and numeral 35 is an ultrahigh vacuum tank. A to C are constituent elements necessary for growing the multi-component oxide and oxide sources of the constituent elements.
Although this embodiment is an apparatus for forming a ternary oxide at the maximum, an electron gun can be further added to grow quaternary or more constituent elements.

Next, an embodiment of a combination of fixed sources when growing multiple oxides with the above-described ultra-high vacuum deposition apparatus will be described. First, Sr _X B
When forming a _1-X O, BaO and SrO are filled into an electron gun as a fixed source. In forming a Ba-La-Cu-O-based oxide superconducting film, (BaO, La ₂ O ₃ , CuO) or (BaO, La ₂ O ₃ , C
u) etc., and the quaternary oxide superconducting oxide Sr-
In the Ba-Bi-Cu-O system, (SrO, BaO, Bi, CuO) and (Sr, Ca, B
i, CuO).

FIG. 7 is a time chart showing a process for growing a ternary oxide using the apparatus shown in FIG. Here, FIG. 2A shows the waveform of the electron beam current (the lamp chart is assumed to be constant), and FIG.
24 shows the opening / closing timing, and FIG. 17C shows the change in the degree of growth vacuum. Incidentally, T ₁ is the deposition step time, T ₂ represents the exhaust stroke time. Note that A to C in FIG. 3A indicate the respective oxide sources.

Now, the above-mentioned ultra-high vacuum vapor deposition apparatus intermittently heats oxide sources A to C of three kinds of constituent elements with an increasing electron beam current at a constant ramp rate, and obtains a desired oxide single crystal thin film. Only at the best time to form
The shutter 24 is opened and the deposition is repeated.

Further, the oxygen partial pressure in the ultra-high vacuum chamber 35 is maintained at a pressure that does not oxidize the Si substrate 33 even during the vapor deposition process. Then, in the evacuation process, the inside of the ultra-high vacuum chamber 35 is quickly evacuated to the ultra-high vacuum region. The exhaust stroke time T2 is Si
It is necessary to make the molecules adsorbed on the substrate 33 long enough for the surface migration of the molecules necessary for high-quality crystal growth.

As described above, in the formation of a multi-element oxide thin film, a plurality of constituent elements necessary for forming a film having a desired stoichiometric composition or an oxide source of the constituent elements are sequentially heated as described above. A layer having a thickness necessary for achieving a desired stoichiometric composition and having a uniform mixed crystal film is sequentially deposited and laminated on the substrate, and the total deposited film thickness becomes a desired film thickness. Until this process is repeated.

Next, FIGS. 8A and 8B are explanatory views showing an oxide thin film formed by using the above-described oxide thin film forming method. Here, (a) shows the Sr _X Ba _{1 -X} O mixed crystal film grown on the Si substrate, and (b) shows the backscattering / changing spectrum of (a). The arrow Ba in FIG.
Indicates the signal start point of Ba, and the arrow Sr indicates the signal start point of Sr.

The grown film shown in FIG. 7A is alternately subjected to the steps of vapor deposition and evacuation by using the ultrahigh vacuum vapor deposition apparatus shown in FIG. 7 with SrO and BaO as oxide sources, and has a desired composition. Is a film formed by controlling the amount of vapor deposition per one time to realize the above. Here, the ratio of the align yield to the random yield near the surface, which is a measure of the crystal quality, is about 3.7% (the ratio at the position indicated by the broken line in FIG. 3B). ,
Extremely good values can be realized.

As described above, according to the method for forming an oxide thin film in this embodiment, the ratio of the intensity of the oxide molecules to the intensity of the oxygen molecules generated from the source is increased by shock-heating the oxide source with an electron beam that changes at a constant ramp rate. Paying attention to the fact that it changes depending on the time from the start of heating, vapor deposition is performed on the substrate only when the intensity ratio is optimal to form a film satisfying the stoichiometric composition.

In addition, the vapor deposition process and the exhaust process are alternately repeated, and in the exhaust process, the gas is evacuated quickly until a hyper-vacuum region is reached, and the surface migration of the vapor deposited molecules is sufficiently promoted.

Furthermore, in multi-element oxide growth, a plurality of necessary oxide sources are sequentially and intermittently evaporated.

Therefore, in the present embodiment, unlike the conventional continuous electron beam bombardment method, the oxidation of the Si substrate is suppressed in the initial stage of the oxide growth by changing the ratio of the intensity of the oxide molecules to the intensity of the oxygen molecules incident on the substrate. After that, it is possible to grow the film by increasing the number of incident oxygen molecules so that oxygen deficiency of the growth film does not occur.

In addition, since an oxide source is used, unlike the method of straightening a metal in an oxygen atmosphere, there is no need to increase the oxygen partial pressure, and the pressure during growth can be maintained at a high vacuum, which promotes surface migration of adsorbed molecules. . Since the intermittent deposition is repeated, unlike the conventional continuous deposition, the substrate is not charged by the floating electrons of the electron gun.

Further, unlike ionized vacuum evaporation, cluster ion beam evaporation, and sputtering, ions with high energy do not collide with the oxide growth film, so that point defects do not occur due to physical impact.

In the above embodiment, as shown in FIG. 8 (a), the example of the Sr _X Ba _1-X O single crystal thin film formed on Si is shown, but the method of forming an oxide thin film according to the present invention is described. Is versatile and can grow single crystal thin films of other multi-element oxides on various substrates.

〔The invention's effect〕

As described above, according to the present invention, by controlling the ramp rate of the electron beam, the ratio between the intensity of the oxide molecular flux and the intensity of the oxygen molecular flux flying from the oxide source toward the substrate reaches a predetermined value. Only when the oxide thin film was formed on the substrate, the stoichiometric composition was satisfied on the substrate without oxidizing the substrate and suppressing the oxygen deficiency in the oxide growth film. A high-quality oxide single crystal thin film can be formed. This makes it possible to form single-crystal thin films of insulators such as alkaline earth metal oxides, spinel and sapphire and oxide high-temperature superconductors on semiconductor substrates such as Si. And the realization of stacked LSI, high-temperature superconductivity and the integration of conventional Si-based microelectronics on the same substrate.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an ultra-high vacuum vapor deposition apparatus for carrying out the oxide thin film forming method of the present invention, and FIG. 2 is a characteristic diagram showing an example of controlling an electron beam current in the electron gun 1 shown in FIG. ,
FIG. 3 is a characteristic diagram showing the signal intensity of each gas species measured by the quadrupole mass spectrometer 7, and FIG. 4 is a diagram showing the number ratio of O ₂ and BaO incident on the Si substrate per unit time. 5 (a) to 5 (c) are time charts showing the electron beam heating, the shutter and the change in the degree of vacuum in FIG. 1, and FIG. 6 grows a multi-element oxide according to the present invention. FIG. 7 is a configuration diagram of an ultra-high vacuum vapor deposition apparatus for this purpose, FIG. 7 is a time chart showing heating of an electron beam, a shutter and changes in the degree of vacuum in FIG. 6, and FIGS. FIG. 4 is an explanatory view showing an oxide thin film formed by using the method for forming an object thin film. 1,21 to 23 ... Electron gun, 2 ... Pellet, 3,26 ... Control system, 4,33 ... Si substrate, 5 ... Quartz resonator, 6 ... Quadrupole mass analyzer, 7 ... … Nude ion gauge, 8,24 …… Shutter, 9 …… Substrate holder, 10,28 …… Lower exhaust system, 1
1,12,31,32 …… Upper exhaust system, 13,35 …… Ultra-high vacuum chamber, 25
…… Substrate holder, 27,29,30 …… Gate valve, 34 ……
Nade ion gauge.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) C23C 14/00-14/58

Claims (1)

(57) [Claims] 1. An oxide thin film forming method for forming an oxide thin film on a substrate by heating and evaporating an oxide source provided in an ultra-high vacuum chamber with an electron beam, comprising the steps of: By controlling the
An oxide thin film is formed on the substrate only when the ratio between the intensity of the oxide molecular flux and the intensity of the oxygen molecular flux that fly from the oxide source toward the substrate reaches a predetermined value. An oxide thin film forming method.