JP2011151228A - Oxide film forming method - Google Patents

Abstract

A Ge oxide film is formed on the surface of a Ge substrate without causing defects in the film.
In an oxidation furnace 13 of a process system 1 for forming a Ge oxide film on a surface of a Ge substrate 2, ozone gas is supplied from an ozone supply device 11 to the Ge substrate 2 under a pressure of 1000 Pa or less and a substrate temperature of 300 ° C. or less. To form a Ge oxide film on the surface of the substrate. The ozone gas is supplied to the substrate at a substrate temperature lower than room temperature to form an ozone molecular layer on the Ge substrate 2. Next, after the supply of the ozone gas is shut off, the surface of the substrate is oxidized by the ozone molecular layer by heating the Ge substrate 2 to room temperature to form a Ge oxide film. After the Ge substrate 2 reaches room temperature, the heating may be interrupted to lower the temperature of the substrate below the room temperature. An infrared light source may be used as a heating source for heating the Ge substrate 2. The ozone gas may have an ozone concentration of 100%.
[Selection] Figure 1

Description

  The present invention relates to a technique for forming an oxide film of a semiconductor element substrate.

Electron mobility and hole mobility in Ge constituting the Ge substrate are both higher than those of Si, and Ge hole mobility is the highest among the semiconductor materials currently studied. It has also been clarified that the interface between GeO ₂ and Ge obtained by oxidizing Ge has superior characteristics to the interface between SiO ₂ and Si obtained by oxidizing Si. For these reasons, Ge-MOS using GeO ₂ as a gate oxide film has attracted attention as a high hole mobility semiconductor element that can replace conventional Si-MOS (Non-patent Document 1).

  Since the Ge single crystal has a much lower melting point than the Si single crystal, it inevitably has a lower temperature than the Ge-MOS fabrication process. The gate oxide film manufacturing temperature that requires the highest process temperature in Si-MOS is 1000 to 1100 ° C. in Si-MOS, but the upper limit is about 550 ° C. in Ge-MOS. Moreover, when Ge forms an interface with a metal material, the Fermi level on the Ge surface is hardly affected by the work function of the metal material, but is depinned by inserting a thin insulating film between Ge and the metal. A metal source drain transistor utilizing this fact has been proposed (Non-patent Document 2).

  FIG. 9 is a schematic configuration diagram showing the configuration of a metal source drain transistor. In this transistor, a thin GeOx insulating film 22 is formed on the entire surface of a sample on a Ge substrate 21, a source metal electrode 23 and a drain metal electrode 26 are formed on the insulating film 22, and a gate insulating film 24 covering the electrode 26. The gate electrode 25 is formed on the substrate. A feature of this transistor is that local doping is unnecessary. The thickness of the insulating film 22 that plays an important role in determining the mobility is 2 nm or less. Therefore, a technique for producing a high-quality insulating film 22 is required.

  On the other hand, due to the remarkable progress made in recent years in the technology for increasing the concentration of ozone gas, the manufacturing process of semiconductor elements using the high concentration ozone gas has gradually permeated. Since ozone has a stronger oxidizing power than oxygen, it is expected that the process temperature using oxygen gas can be lowered. It can also be expected that ozone can be effectively used by increasing the ozone concentration. Recently, a technology that can supply almost 100% ozone gas has been established. As a result of using ozone gas with a concentration of nearly 100 ° C. in the process of manufacturing semiconductor devices, it has been reported that, for example, in the case of thermal oxidation of Si, the process temperature required over 1000 ° C. can be reduced to 400 ° C. when oxygen is used. (Patent Document 1). By introducing the high-concentration ozone process technology into the Ge-MOS fabrication technology in this way, it is expected that an effective fabrication process will be realized at a low temperature.

Shinichi Takagi, “IEDM follow-up, semiconductor manufacturing, Ge channel MOS FET, measures to improve carrier mobility,” [online], December 14, 2007, Nikkei Business Publications, Tech-on, [November 2009] Search on the 24th], Internet <http://techon.nikkeibp.co.jp/article/NEWS/20071214/144282/> Tomonori Nishimura, Koji Kita and Akira Toriumi, “A Significant Shift of Schottky Barrier Heights at Strongly Pinned Metal / Germanium Interface by Inserting an Ultra-Thin Insulating Film”, Appl. Phys. Express 1, 2008, 051406 Choong Hyun Lee, Toshiyuki Tabata, Tomonori Nishimura, Kosuke Nagashio, Koji Kita and Akira Toriumi, “Ge / GeO2 Interface Control with High-Pressure Oxidation for Improving Electrical Characteristics”, Appl. Phys. Express 2, 2009, 071404

JP 2003-209108 A

Since the interface between GeO ₂ and Ge has particularly good interface properties, GeO ₂ is expected to be useful as a gate oxide film for Ge devices. However, it is known that the film quality of GeO ₂ varies greatly depending on the oxidation conditions of Ge, and the establishment of GeO ₂ fabrication technology has become one of the technical issues for practical application of Ge-MOS devices (non-patented). Reference 3). Here, since the melting point of Ge single crystal is lower than that of Si single crystal, the Ge-MOS fabrication process temperature must be lower than that of Si. On the other hand, oxygen deficiency defects in GeO ₂ degrades film properties GeO _2. Specifically, Ge generates GeO particles from an oxygen defect portion in GeO ₂ during an oxidation process at 400 ° C. or higher and scatters in the gas phase. Since Ge scattering further induces generation of defects in the film, it is desirable that the Ge oxidation process temperature be lower than 400 ° C. From the above, low-temperature oxidation is required for the production of a GeO ₂ film with few oxygen defects.

  Therefore, an oxide film forming method according to the present invention for solving the above problems is an oxide film forming method for forming a Ge oxide film on the surface of a Ge substrate, wherein the pressure is 1000 Pa or less and the substrate temperature is 300 ° C. or less. Originally, ozone gas is supplied to the Ge substrate to form a Ge oxide film on the surface of the substrate.

  In the oxide film forming method, when the ozone gas is supplied to the substrate at a substrate temperature lower than room temperature, an ozone molecular layer can be formed on the substrate. Further, ozone oxidation on the surface of the Ge substrate can be suppressed. Furthermore, the desorption of GeO can be further suppressed. In addition, the adsorption rate of ozone molecules on the surface of the Ge substrate can be increased.

  In the oxide film forming method, after the ozone molecular layer is formed, the supply of the ozone gas is interrupted, and then the substrate is heated to room temperature to oxidize the surface of the substrate by the ozone molecular layer. Then, a Ge oxide film may be formed. Further, after the temperature of the substrate reaches room temperature, the heating may be interrupted to lower the temperature of the substrate to a temperature lower than the room temperature. Then, the ozone gas layer is formed on the substrate on which the Ge oxide film is formed by supplying ozone gas again to the substrate after the temperature of the substrate is lowered to a temperature lower than room temperature, and then supplying the ozone gas. The Ge oxide film can be stacked on the substrate by repeating the process of forming a Ge oxide film on the substrate by blocking and then heating the substrate to room temperature.

  An infrared light source may be used as a heating source for heating the Ge substrate. In addition to reducing damage to the substrate by instantaneous heating of the Ge substrate, only ozone molecules adsorbed on the surface of the substrate can contribute to the surface oxidation.

  Further, when ozone gas having an ozone concentration of 100% is used as the ozone gas, the influence of oxidation by oxygen on the Ge substrate can be suppressed.

  According to the above invention, the Ge oxide film can be formed on the surface of the Ge substrate without causing defects in the film.

The block diagram which showed the process system which concerns on 1st embodiment of invention. The block diagram which showed the specific structure of the oxidation furnace which concerns on 1st embodiment of invention. The flowchart figure explaining the procedure of the oxidation process which concerns on 1st embodiment of invention. Ge3d characteristic diagram of the spectrum detected by XPS measurement of GeO ₂ film an under Ge substrate conditions 1-3 was formed by oxidation treatment. The block diagram which showed the specific structure of the oxidation furnace which concerns on 2nd embodiment of invention. The perspective view which showed the one aspect | mode of the ozone gas supply to an oxidation sample. The time chart figure of the oxidation process which concerns on 2nd embodiment of invention. Explanatory drawing explaining the process in which the oxide film layer which consists of GeOx is formed in Ge substrate. 1 is a schematic configuration diagram of a metal source / drain transistor.

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

(Embodiment 1)
The process system 1 according to the first embodiment of the present invention shown in FIG. 1 forms a GeO ₂ film with good thermal stability and interface characteristics on the Ge substrate 2 by using ozone gas. The process system 1 includes an ozone supply device 11, a leak gas supply device 12, and an oxidation furnace 13.

The ozone supply device 11 supplies ozone gas to the oxidation furnace 13 in which the Ge substrate 2 is stored. Examples of the ozone supply device 11 include an ozone gas cylinder or an ozone generator. The ozone concentration of ozone gas is better as it is closer to 100%. Since ozone gas having a low ozone concentration becomes a mixed gas with oxygen gas, the influence of oxygen gas on Ge oxidation cannot be ignored. That is, since ozone has a stronger oxidizing power than oxygen, it is oxidized at a low temperature. However, when oxygen is present at a low temperature, an oxidation process in which defects are easily formed in the formed GeO ₂ film occurs. Thus, the quality of the oxide film obtained tends to deteriorate as the ozone concentration decreases. Then, the influence of oxidation by oxygen can be suppressed by using ozone gas whose ozone concentration is close to 100%. As an ozone generator for supplying ozone gas having an ozone concentration of 100%, for example, a pure ozone generator (MPOG-SM1C1) manufactured by Meidensha may be mentioned.

In addition, since ozone molecules are thermally decomposed into oxygen molecules, when oxidizing at a high temperature, the ozone gas flow rate is sufficient by setting the atmosphere in the oxidation furnace 13 to a reduced pressure atmosphere of 1000 Pa or less (for example, 10 ⁻² Pa to 1000 Pa). Since it becomes quick, the generation amount of oxygen molecules due to thermal decomposition in the oxidation furnace 13 can be suppressed. Further, even in a temperature range where the thermal decomposition of ozone molecules hardly occurs, oxygen generated by the surface reaction on the sample surface is excluded from the oxidation furnace 13 by the gas flow caused by the vacuum atmosphere, so that the Ge substrate 2 in the oxidation furnace 13 is removed. Can always supply fresh ozone gas.

  The leak gas supply device 12 is an exhaust means for discharging the ozone gas remaining in the oxidation furnace 13 that has undergone the oxidation process of the Ge substrate 2 to the outside of the furnace 13 by the leak gas. Examples of the leakage gas include inert gases exemplified by nitrogen gas, argon gas and the like. Examples of the leak gas supply device 12 include a gas cylinder filled with the leak gas and a known generator that generates the leak gas.

  The gases supplied from the supply devices 11 and 12 are supplied to the oxidation furnace 13 via the pipes 15 and 16 corresponding to vacuum (<0.1 Pa), respectively. The pipes 15 and 16 are provided with valves V01 and V02 for adjusting the gas flow rate. In addition, in order to suppress ozone decomposition | disassembly when ozone passes through the piping 15, the process which prevents ozone decomposition | disassembly by inner surface grinding | polishing etc. is given suitably.

  The oxidation furnace 13 stores the Ge substrate 2 to be subjected to oxidation treatment. The treated ozone gas and leakage gas in the oxidation furnace 13 are sucked and exhausted from the pipe 17 by the exhaust pump 18. The pipe 17 is also provided with a valve V03 exemplified as a variable flow rate valve or an open / close valve. The gas containing the ozone gas and the leak gas discharged from the oxidation furnace 13 is detoxified by the ozonolysis apparatus 14 and then released into the atmosphere. The ozone decomposition device 14 decomposes the ozone gas discharged from the oxidation furnace 13 into oxygen. The ozonolysis apparatus 14 may be a known ozonolysis apparatus employed in semiconductor manufacturing technology.

  A specific embodiment of the oxidation furnace 13 will be described with reference to FIG.

  The oxidation furnace 13 has pipes 15 and 16 connected to the ceiling. If the ozone gas and the leaking gas are joined upstream of the oxidation furnace 13, only one pipe for introducing a mixed gas of ozone gas and raw material gas is connected. Further, one or more loading / unloading ports 130 for loading / unloading the Ge substrate 2 as a processing substrate are provided at the end of the oxidation furnace 13. The carry-in / out port 130 can be sealed by the door 131 while the Ge substrate 2 is stored in the oxidation furnace 13.

  The oxidation furnace 13 is formed to be a vacuum-compatible furnace. The ultimate pressure of the oxidation furnace 13 is about 0.01 Pa. The oxidation furnace 13 is desirably provided with a pressure gauge 132. The specification of the pressure gauge 132 may adopt a measurement range pressure corresponding to 0.01 Pa to 10000 Pa. As a material constituting the furnace wall of the oxidation furnace 13, a material that can be used in a vacuum state up to 0.1 Pa exemplified by aluminum, SUS, and quartz glass and is not easily oxidized is employed.

  In the oxidation furnace 13, the Ge substrate 2 is held on the susceptor 133. The susceptor 133 is provided so as to be movable in the oxidation furnace 13 by a rotation mechanism or a transport mechanism. The susceptor 133 can be heated to a predetermined temperature as required by a heating means. For this purpose, the susceptor 133 is provided with a thermocouple for detecting the temperature.

Examples of the heating means include an infrared light source 134 for irradiating the susceptor 133 with infrared light. The infrared light source 134 is arranged below the oxidation furnace 13. An irradiation window 135 is provided at the bottom of the oxidation furnace 13 so that the infrared light from the infrared light source 134 is provided to the Ge substrate 2. As the material of the irradiation window 135, a material that transmits infrared light and visible light exemplified by quartz glass and MgF ₂ is applied. The infrared light source 134 can control the amount of irradiation light based on the temperature detected by the thermocouple of the susceptor 133. The heating temperature of the Ge substrate 2 is controlled so as not to exceed 400 ° C. or 300 ° C. at most. For example, it is controlled in the range of 300 ° C. to room temperature. As the infrared light source 134, a known light source that emits light including at least infrared light and visible light may be applied.

In the oxidation furnace 13, the GeO ₂ film forming process conditions (the ozone supply amount, the process pressure, the light irradiation amount of the infrared light source 134, the process temperature (temperature of the susceptor 133), the exhaust rate (exhaust pump 18) on the Ge substrate 2. The exhaust speed) is controlled as appropriate.

Steps S1 to S8 will be described with reference to FIG. 3 in the process of forming the GeO ₂ film in the process system 1.

  S1: A susceptor 133 on which a Ge substrate 2 is placed as a sample to be processed is carried into the oxidation furnace 13 through a carry-in / out port 131.

S2: The inside of the oxidation furnace 13 is evacuated by the exhaust pump 18. The degree of vacuum is controlled to 10 ⁻² Pa or less, for example. This is because the influence of oxygen in the air can be suppressed.

  S3: The susceptor 133 is heated by the infrared light source 134 to control the temperature of the Ge substrate 2 to a predetermined oxidation process temperature (300 ° C. or lower). Before the heat treatment in S3, the surface of the Ge substrate 2 may be cleaned (S101). As the cleaning gas, the leak gas supplied from the leak gas supply device 12 is used.

  S4: When the temperature of the Ge substrate 2 is stabilized at a predetermined process temperature (300 ° C. or lower to room temperature), ozone gas is supplied from the ozone supply device 11 to the oxidation furnace 13 to start the oxidation process. The pressure in the oxidation furnace 13 is controlled by valves V1 and V3.

  S5: The supply of ozone gas from the ozone supply device 11 is stopped when a predetermined process time has elapsed.

  S6: Cool the Ge substrate 2 until its temperature approaches room temperature.

  S7: When the temperature of the Ge substrate 2 is lowered to room temperature, the leakage gas is supplied from the leakage gas supply device 12 to the oxidation furnace 13, whereby the ozone gas remaining in the furnace 13 is discharged and the internal pressure of the furnace 13 is set to atmospheric pressure. Return to.

  S8: After the internal pressure of the oxidation furnace 13 becomes equal to the atmospheric pressure, the Ge substrate 2 is carried out of the oxidation furnace 13 from the carry-in / out entrance 131.

  In addition, when performing a post process (electrode deposition etc.) in the oxidation furnace 13, you may perform the process of the said post process, before performing the leak step of S7 (S102). However, ozone gas must be exhausted sufficiently. This is because the ozone gas has a strong oxidizing power and the residual ozone gas causes an oxidation reaction with the electrode material.

  An example of this embodiment is shown below.

FIG. 4 shows a specific diagram of a Ge3d spectrum obtained by XPS measurement on a GeO ₂ film obtained by oxidizing non-doped Ge (100) under the conditions shown in Table 1.

According to the characteristic diagram showing the comparison between Condition 1 and Condition 2 in FIG. 4A, the peak near 30 eV is due to Ge0 +, which is a contribution from Ge in the Ge (100) substrate, around 33.5 eV. The peak is due to Ge4 +. Ge0 + peaks and Ge2 + peak intensity ratio of is greatly affected by the film thickness of the GeO _2. The characteristic diagram of FIG. 4 (a), shows that the GeO ₂ film thickness conditions than GeO ₂ film thickness condition 2 1 is large. That is, ozone gas has a much faster oxidation rate than oxygen gas.

Further, according to the characteristic diagram of FIG. 4 (b), because they show that the film thickness of the GeO ₂ conditions 3 than GeO ₂ film thickness condition 1 is large, the ozone gas is GeO ₂ film produced by Ge oxidized at room temperature This means that a large film forming rate can be obtained by oxidizing at 400 ° C. at room temperature. Further, even when the pressure of ozone gas is 1/100 that of oxygen gas, it can be seen that ozone gas has a much stronger Ge oxidizing power than oxygen gas because the oxidizing power of ozone gas is high.

  As described above, according to the process system of the first embodiment, Ge oxidation can be performed at a low temperature of 300 ° C. or lower. In particular, it has been experimentally confirmed that a film can be formed in a temperature range (300 ° C. to room temperature) in which the evaporation of GeO does not become active. Further, in the conventional oxygen gas oxidation, 100 atmospheric pressure (10 MPa) may be required, but a Ge oxide film can be produced at a low pressure of 1000 Pa or less. Since the film can be formed in this pressure range, the oxidation time can be controlled with second accuracy. Moreover, the influence of oxidation by oxygen gas can be eliminated by using high-purity ozone gas having an ozone concentration of 100%.

(Embodiment 2)
In the second embodiment, the thickness of the GeO ₂ film formed on the Ge substrate is controlled with an accuracy of 1 nm or less.

Ge oxidation with ozone gas proceeds at a high film formation rate even at room temperature (Embodiment 1). In particular, since the ozone molecules can reach the interface without diffusing in the GeO ₂ film at the initial stage of the oxidation process, the film growth is extremely fast. Therefore, it becomes difficult to form a film having a thickness of 1 nm or less with high film thickness accuracy. Therefore, the process system according to the present embodiment controls film growth by limiting the number of ozone molecules that reach the interface of the Ge substrate and grow the GeO ₂ film.

The apparatus configuration of the oxidation furnace 13 according to the second embodiment will be described with reference to FIG. 5. The oxidation furnace 13 includes a cold head 51 that holds the susceptor 133 so that it can be cooled to a temperature lower than room temperature. The infrared light source 134 according to the present embodiment is disposed above the outside of the oxidation furnace 13. An irradiation window 52 for introducing irradiation light of the infrared light source 134 into the furnace 13 is provided on the ceiling portion of the oxidation furnace 13. A material having the same specifications as the irradiation window 135 may be applied to the material constituting the irradiation window 52. The oxidation furnace 13 is configured such that the range of vacuum-compatible pressure is up to 10 ⁻⁶ Pa. The oxidation furnace 13 includes a vacuum gauge 54 capable of measuring up to the high vacuum pressure value instead of the pressure gauge 132 according to the first embodiment.

  The Ge substrate 2 is heated on a time scale of several seconds. Moreover, the lower the temperature reached at room temperature or lower, the better. When the temperature of the Ge substrate 2 is set to a low temperature of room temperature or lower, the oxidation reaction that occurs during the adsorption of ozone molecules can be suppressed. Moreover, the adsorption rate of the surface of the Ge substrate 2 with respect to ozone molecules is increased so that the surface can be further covered with ozone. That is, the ozone oxidation reactivity can be suppressed and the adsorption area on the surface of the Ge substrate 2 can be increased by setting the temperature of the Ge substrate 2 to a low temperature of room temperature or lower.

  Further, as illustrated in FIG. 6, when the ozone gas supply line (pipe 15) is extended to the vicinity of the surface of the Ge substrate 2, the ozone gas 70 discharged from the pipe 15 does not directly hit the wall surface of the oxidation furnace 13. The surface of the substrate 2 can be reached. Thereby, ozone molecules can be reliably adsorbed to the Ge substrate 2.

  The cold head 51 includes a cooling mechanism that can control at least a low temperature of minus 10 ° C. or less. In the example of the first embodiment (FIG. 4), it is known that the Ge oxidation reaction proceeds quickly even when ozone is at room temperature. Therefore, the cold head 51 can be used to control the progress of the oxidation reaction to be “negative”. ing. Examples of the cooling mechanism include a water-cooling system using an antifreeze liquid, a thermal contact system using liquid nitrogen, and a compressor.

  On the other hand, the oxidation furnace 13 of the present embodiment is provided with a mechanism capable of heating the Ge substrate 2 to about room temperature for a relatively short time so that the time during which ozone adsorbed on the surface of the substrate 2 can be oxidized can be controlled. It has become. In the oxidation furnace 13, an infrared light source 134 is applied as a heating mechanism for the surfaces of the substrate 2 and the susceptor 133. Since the susceptor 133 can be instantaneously heated, the progress of the Ge oxidation reaction on the Ge substrate 2 is “ It can be controlled positively.

  In addition, a filter 53 that cuts light having a wavelength of 400 nm or less emitted from the infrared light source 134 is disposed between the irradiation window 52 of the oxidation furnace 13 and the infrared light source 134, so Damage to the Ge substrate 2 due to light can be suppressed.

  As described above, the process system of the present embodiment lowers the temperature of the Ge substrate 2 and instantaneously heats it to a temperature of about room temperature, so that the ozone pressure of the oxidation furnace 13 and the temperature of the Ge substrate 2 are scheduled. Can be changed.

  A time chart for controlling the temperature of the Ge substrate 2 and the ozone gas pressure in the oxidation furnace 13 of the process system according to the second embodiment shown in FIG. 7 will be described with reference to FIG.

  The vertical axis 1001 of the time chart of FIG. 7 means the pressure of the oxidation furnace 13 and the temperature of the Ge substrate 2. The pressure and temperature values on the vertical axis 1001 are defined to increase in the positive direction. The horizontal axis 1007 of the time chart is the process elapsed time, and the value of the time is defined to increase in the positive direction. The temporal changes in the pressure 1008 of the oxidation furnace 13 and the temperature 1006 of the Ge substrate 2 are indicated by a dotted line and a solid line, respectively. Note that reference numerals 1001 to 1008 shown in the figure are symbols indicating terms and not numerical values.

First, with the ozone pressure kept at a pressure of 10 ⁻⁵ Pa or less, the temperature of the Ge substrate 2 shown in FIG. 8A is set to a target temperature 1003 (for example, −10 ° C. or less) from room temperature (T = t1) to room temperature or less. (T = t2). Here, the pressure of 10 ⁻⁵ Pa or less is determined from an empirical formula (Langmuir equilibrium adsorption) in order to make the molecular adsorption amount on the surface of the Ge substrate 2 1 layer or less.

  Next, ozone gas is supplied to gradually increase the pressure (T = t3). When the ultimate pressure 1004 is reached (T = t4), the vacuum is maintained for a certain period of time (T = t5), and the high vacuum is set again. At this time, ozone molecules are adsorbed on the surface of the Ge substrate 2 shown in FIG. Since the temperature of the Ge substrate 2 is a low temperature below room temperature, the oxidation reaction does not proceed.

  Next, instantaneous heating of the Ge substrate 2 by the infrared light source 134 is started (T = t6), the target temperature 1005 is reached in a few seconds, and then the light irradiation from the infrared light source 134 is cut off. Waiting for cooling of the Ge substrate 2. As the temperature of the Ge substrate 2 rises instantaneously, the ozone molecules adsorbed on the surface cause an oxidation reaction with the Ge substrate 2, and the oxide film layer 202 is formed on the surface of the Ge substrate 2 as shown in FIG. It is formed. The oxide film layer 202 has a very small thickness because only ozone molecules adsorbed on the surface contribute to the oxidation. The film thickness of the oxide film layer 202 can be controlled by changing the adsorption amount of ozone molecules, the instantaneous heating time, and the temperature of the Ge substrate 2. Thereafter, the temperature of the Ge substrate 2 starts to be raised (t8), and reaches the room temperature (t9), the oxidation process of the Ge substrate 2 is completed.

  When the above stepwise oxide film formation is performed several times, heating to room temperature is not performed at T = t8, and a loop is performed at T = t3. By looping, it is possible to adsorb ozone molecules to the oxide film layer 202 of the Ge substrate 2 to form the ozone molecule layer 201. By causing an oxidation reaction thereto, as shown in FIG. In addition, the oxide film layer 202 can be further increased. The loop is repeatedly executed arbitrarily in accordance with a desired oxide film thickness. Further, the adsorption amount of ozone molecules, the instantaneous heating time, and the temperature of the Ge substrate 2 may be appropriately adjusted for each cycle. By repeating this cycle number, the distance between the ozone molecule adsorption layer and the surface of the Ge substrate 2 is increased, and the heating temperature and the heating time necessary for the oxidation are different for each cycle.

  Therefore, according to the process system according to the second embodiment, the temperature of the Ge substrate is controlled to be in the range of room temperature or lower. Therefore, in addition to the effect of the process system according to the first embodiment, the surface of the Ge substrate 2 Can suppress ozone oxidation. Further, the desorption of GeO can be further suppressed. Furthermore, the adsorption rate of ozone molecules on the surface of the Ge substrate 2 can be increased. In particular, when the temperature of the Ge substrate is set to −10 ° C. or lower in the time zone in which ozone gas is supplied, negative control of the oxidation reaction of the Ge substrate can be performed more reliably. On the other hand, the instantaneous heating of the Ge substrate 2 by the infrared light source can reduce damage to the substrate and contribute only the ozone molecules adsorbed on the surface of the substrate to the surface oxidation. it can. As a result, the thickness of the Ge oxide film can be controlled at the growth level of the first layer and the second layer. Further, since stepwise film formation can be repeatedly performed, a Ge oxide film can be formed with good film quality.

DESCRIPTION OF SYMBOLS 1 ... Process system 2 ... Ge board | substrate, 201 ... Ozone molecular layer, 202 ... Oxide film layer 11 ... Ozone supply device 12 ... Leak gas supply device 13 ... Oxidation furnace, 133 ... Susceptor, 134 ... Infrared light source 51 ... Cold head

Claims (9)

An oxide film forming method for forming a Ge oxide film on a surface of a Ge substrate,
A method for forming an oxide film, comprising forming a Ge oxide film on a surface of a Ge substrate by applying ozone gas to the Ge substrate under a pressure of 1000 Pa or less and a substrate temperature of 300 ° C. or less.   2. The method of forming an oxide film according to claim 1, wherein the ozone gas layer is formed on the substrate by supplying the ozone gas to the substrate at a substrate temperature lower than room temperature. After the ozone molecular layer is formed, the supply of the ozone gas is interrupted, and then the substrate is heated to room temperature to oxidize the surface of the substrate by the ozone molecular layer to form a Ge oxide film. The method for forming an oxide film according to claim 2.   4. The method for forming an oxide film according to claim 3, wherein the heating is interrupted after the temperature of the substrate reaches room temperature, and the temperature of the substrate is lowered to a temperature lower than room temperature.   After the temperature of the substrate is lowered below room temperature, ozone gas is supplied to the substrate again to form an ozone molecular layer on the substrate on which the Ge oxide film is formed, and then the ozone gas supply is shut off. 5. The oxidation according to claim 4, wherein the Ge oxide film is laminated on the substrate by repeating the step of further forming a Ge oxide film on the substrate by heating the substrate to room temperature. Film forming method.   The method for forming an oxide film according to claim 3, wherein an infrared light source is used as a heating source for heating the Ge substrate. The atmosphere when heating the temperature of the substrate to room temperature after shutting off the supply of the ozone gas is a vacuum atmosphere of 10 ^-5 Pa or less. Oxide film formation method.   The method for forming an oxide film according to claim 2, wherein the substrate temperature is −10 ° C. or lower.   The oxide film forming method according to claim 1, wherein the ozone gas has an ozone concentration of 100%.

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