JP3480479B2 - Method for manufacturing SOI substrate - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an SOI (Silicon-On-Insulator) substrate having a Si layer formed on an insulating layer. See SIMOX (Separation by
(Implanted Oxygen) technology. 2. Description of the Related Art An SOI substrate is receiving attention as a future ULSI substrate. The SOI substrate manufacturing method includes a bonding method in which silicon substrates are bonded to each other via an insulating film, a method in which a silicon thin film is deposited on an insulating substrate or a substrate having an insulating thin film on its surface, and a SIMOX method. is there. The SIMOX method is one of the methods of embedding an insulating layer inside a silicon substrate. Specifically, after implanting high-concentration oxygen ions into the silicon substrate, the silicon substrate is annealed at a high temperature to perform annealing. In this method, a buried silicon oxide layer is formed in a region at a predetermined depth from the surface, and the Si layer on the surface side is used as an active region. The SIMOX method is a powerful method in which an active Si layer having a uniform thickness can be obtained without grinding and polishing the surface Si layer as in the above bonding method. In recent years, the amount of oxygen ions implanted has been reduced,
A low-dose technology for shortening the processing time of the ion implantation apparatus and reducing the manufacturing cost of the SOI substrate has begun to be put into practical use. In this low dose technology, for example, the acceleration energy 180
After oxygen ions are implanted at a keV of 4 × 10 ¹⁷ / cm ² , a heat treatment is performed at 1350 ° C. This low dose SI
In order to make the buried silicon oxide layer in the SOI substrate continuous by the MOX method and not to form an unoxidized island-like Si region (Si island) in this oxide layer, strict control of the oxygen ion implantation amount is required. Is extremely important. However, even if oxygen ions are implanted under conditions sufficiently controlled by the conventional low-dose SIMOX method, the pinhole density of the buried silicon oxide layer becomes 30%.
/ Cm ² or more (M. Imai et
al., "The Status and Future of Low-Dose SIMOX Tech
nology ", Extended Abstracts of the 1995 International
al Conference on Solid State Devices and Material
s, Osaka, 1995, pp.557-559). If the pinhole density is large, the separation between devices cannot be performed sufficiently. In order to reduce the pinhole density, Japanese Patent Application Laid-Open No. 7-26
No. 3538 discloses an ITOX (Internal Thermal
Oxidation) technology has been proposed. This technology is SIM
Immediately after annealing in the OX method, annealing is further performed in a high-temperature oxygen atmosphere. This is a technique for increasing the thickness of the buried silicon oxide layer and filling any pinholes if any. However, it has been reported that even with this ITOX technique, a pinhole density of about 5 / cm ² exists (M. Imai et al., Supra). An object of the present invention is to provide a method of manufacturing an SOI substrate in which a high-quality buried silicon oxide layer having a very low pinhole density is formed in a region at a predetermined depth from the substrate surface. Another object of the present invention is to provide a method of manufacturing an SOI substrate that improves the flatness of the interface between a Si layer and a buried silicon oxide layer. [0006] According to an aspect of the invention according to claim 1,
As shown in FIGS. 1 and 2, after implanting oxygen ions in the silicon substrate 11, to a final predetermined temperature T ₀ was heated by performing the annealing treatment for holding the final predetermined temperature T ₀ predetermined time t In a method for manufacturing an SOI substrate in which a buried silicon oxide layer 12 is formed in a region at a predetermined depth from the surface of a silicon substrate 11 and an active Si layer 11a is formed on the surface of the substrate 11, at least a temperature increase rate during an annealing process is In the two stages v ₁ and v ₂ , the final predetermined temperature T ₀
Until the temperature rises , the initial heating rate (v
₁ ) is 10 to 3 ° C./min, and the heating rate (v ₁ ) is 12
First predetermined temperature (T ₁ ) within the range of 50 ° C. or more and less than 1350 ° C.
And the final heating rate (v ₂ ) is 7-0.1 ° C / min.
At this heating rate (v ₂ ), silicon
A method for manufacturing an SOI substrate, comprising raising a temperature to a final predetermined temperature (T ₀ ) lower than a point temperature . The buried silicon oxide layer has an Ostwald growth in which small silicon oxide precipitates dissolve as temperature increases and are absorbed by larger precipitates.
d ripening). According to the low-dose SIMOX method, the deposition of silicon oxide on a silicon substrate
In the early stage of the annealing process, silicon and oxygen react with each other in accordance with the oxygen concentration distribution to form a precipitate of silicon oxide, and when Ostwald groWth proceeds to some extent, damage caused by oxygen implantation in the depth direction of the substrate as shoWn in FIG. It occurs mainly at two points, a peak position A and an oxygen injection peak position B. Then, as the temperature rises, the precipitate at the damage peak position A is taken into the precipitate at the oxygen injection peak position B, and finally becomes one silicon oxide layer. A damage distribution diagram and an oxygen concentration distribution diagram are shown on the right side of the substrate 11 in FIG.
In the conventional annealing process, the temperature is increased at a single heating rate, and when the temperature reaches a predetermined temperature, the temperature is maintained for a predetermined time. When the temperature rise rate is relatively high, for example, at 5 ° C./min or more, when the temperature reaches a predetermined temperature, for example, 1300 ° C. or more, Ostwald growth cannot keep up with this temperature rise rate, and deposition occurs in addition to the buried silicon oxide layer. The object remains, and pinholes are present as much as the silicon oxide is not completely taken in. The precipitate is incorporated into the buried silicon oxide layer by a subsequent long-time annealing treatment. The precipitates merge with the buried silicon oxide layer through defects caused by interstitial silicon released with the oxidation of silicon. Therefore, unless a sufficient defect is formed on the pinhole, the pinhole will not be filled. On the other hand, when the heating rate is relatively slow, for example, 1 ° C./min or less, the formed precipitate becomes stable during Ostwald ripening,
Even if the annealing treatment is performed for a long period of time, it cannot be dissolved, resulting in a problem that a precipitate finally exists other than the buried silicon oxide layer. According to the present invention, the initial heating rate v _{1 is set} to 10
３3 ° C./min, and the decelerated final heating rate v ₂ is 7〜
0.1 ° C / min. 1250 ° C at the _first heating rate v1
The temperature is raised to a first predetermined temperature T ₁ within the range of less than 1350 ° C., and the temperature is raised to a final predetermined temperature T ₀ of 1350 ° C. or more and lower than the silicon melting point at a final temperature raising rate v ₂ . afterwards,
The precipitates are sufficiently taken into the buried silicon oxide layer by keeping at the final predetermined temperature T ₀ for a long time, and the interface between silicon and the buried silicon oxide layer is flattened. Final predetermined temperature is 135
If the temperature is lower than 0 ° C., sufficient incorporation of the precipitate is not performed. If the initial heating rate v ₁ is less than 3 ° C./min, the precipitate tends to be stable, and if it exceeds 10 ° C./min, crystal defects called slip tend to occur in the silicon substrate itself. When the first predetermined temperature T ₁ is outside the above range,
Oxygen precipitates are likely to remain even after subsequent annealing. If the final heating rate v ₂ is less than 0.1 ° C./min, the annealing treatment time becomes too long. If the final heating rate v ₂ exceeds 7 ° C./min, precipitates to be taken in are completely dissolved, and the This is because the pinholes are less likely to be filled by the annealing treatment for holding. DETAILED DESCRIPTION OF THE INVENTION The oxygen ion implantation (dos
e) has a low dose. The oxygen ion implantation amount in this case is 3.0 to 5.0 × 10 ¹⁷ / cm ² . In addition, there are at least two stages of the temperature increasing speed at which the temperature is decelerated, and three or four stages may be used. In the present invention, the holding time t at the final predetermined temperature T ₀ is preferably at least one hour.
This is because the minimum one hour is necessary for incorporating the precipitate into the buried silicon oxide layer. The holding time t depends on the final predetermined temperature T ₀ , and the higher the temperature, the shorter the time. Preferably, it is 1 to 6 hours. Next, embodiments of the present invention will be described in detail with reference to the drawings together with comparative examples. <Example 1> Oxygen ions (O ⁺ ) were implanted into a predetermined region (for example, a region approximately 0.4 μm from the substrate surface) of a silicon substrate having a thickness of 625 μm under the following conditions. Acceleration voltage: 180 KeV Beam current: 40-50 mA Dose amount: 4 × 10 ¹⁷ / cm ² Substrate heating temperature: 600 ° C. After ion implantation, the silicon substrate was kept at 800 ° C. in a mixed gas atmosphere of argon and oxygen. Put in the heat treatment furnace,
First, the temperature was raised to 1300 ° C. at a rate of 5 ° C./min. FIG. 3 shows an electron micrograph of the cross section of the substrate at 1300 ° C. Then, the heating rate was changed to 1 ° C./min and 139
The temperature was raised to 0 ° C. FIGS. 4 and 5 show electron micrographs of the cross section of the substrate during the heating process. FIG. 6 shows a photograph at 1390 ° C. Further, the substrate was annealed while being held at 1390 ° C. for 2 hours. FIG. 7 shows a photograph after the annealing. FIG. 1 shows a temperature profile of the annealing process of the first embodiment. <Example 2> After the same silicon substrate as in Example 1 was implanted with oxygen ions under the same conditions, the substrate was replaced with Example 1.
And placed in a heat treatment furnace maintained at 800 ° C. in an Ar gas atmosphere containing the same oxygen as above, and first heated at a rate of 5 ° C./min.
The temperature was raised to 0 ° C. Next, the temperature was raised to 1390 ° C. at a rate of 0.5 ° C./min, and the sample was annealed at 1390 ° C. for 2 hours. FIG. 8 shows a photograph after the annealing. FIG. 1 shows a temperature profile of the annealing process in the second embodiment. Comparative Example 1 After the same silicon substrate as in Example 1 was implanted with oxygen ions under the same conditions, the substrate was replaced with Example 1.
Then, it was placed in a heat treatment furnace maintained at 800 ° C. in an Ar gas atmosphere containing the same oxygen and heated to 1390 ° C. at a rate of 5 ° C./min. FIG. 9 shows an electron micrograph of the cross section of the substrate at 1390 ° C. Next, annealing was carried out at 1390 ° C. for 4 hours. FIG. 10 shows a photograph after the annealing. FIG. 1 shows a temperature profile of the annealing process of Comparative Example 1. Comparative Example 2 The same silicon substrate as in Example 1 was implanted with oxygen ions under the same conditions.
Then, the sample was placed in a heat treatment furnace maintained at 800 ° C. in an Ar gas atmosphere containing the same oxygen as above, and the temperature was raised to 1100 ° C. at a rate of 5 ° C./min. Then, the heating rate was changed to 1 ° C./min and 1390
The temperature was raised to ° C. FIG. 11 shows a photograph when the temperature reached 1390 ° C. FIG. 1 shows the temperature profile of the annealing process of Comparative Example 2. <Comparison Observation> (a) Measurement of Pinhole Density Meanwhile, the pinhole density in the buried silicon oxide layer of each of the SOI substrates of Examples 1 and 2 and Comparative Examples 1 and 2 was measured.
The pinhole density was determined by immersing the SOI substrate between the electrodes on both sides of the electrode in a copper sulfate solution and depositing copper sulfate when energized. Table 1 shows the results. [Table 1] The following points became clear from the pinhole density measurement result (a) and the photograph observation. As shown in FIG. 9 of Comparative Example 1, at 1390 ° C., many precipitates exist on the buried silicon oxide layer, and pinholes are also observed. This is because Ostwald growth (dissolution of small precipitates) could not keep up with the heating rate because the heating rate was high. Pinholes also exist to the extent that the precipitate is not completely taken in. As shown in FIG. 10, the small precipitates seen in the photograph are taken in after the high temperature holding, but the pinholes are not completely filled at first due to the large number of pinholes. In Comparative Example 2, as shown in FIG. 11, a precipitate exists in the SOI substrate other than the buried silicon oxide layer. This is because the heating rate is too slow,
This is because the precipitate at 0 ° C. was present as stable. The pinhole density is large because the precipitate is not completely taken in. On the other hand, FIGS.
FIGS. 5, 6 and 7 show a process of forming a buried silicon oxide layer at 1300 ° C. to 1390 ° C. The temperature rise from 1300 ° C. to 1 ° C./min corresponds to 13 in FIG.
Since the conditions at which the precipitates observed at the time of 00 ° C. allow the Ostwald crystallization to grow sufficiently while taking in are sufficient, even when the starting point is the same as that in Comparative Example 1, when the final predetermined temperature is reached, other than the buried silicon oxide layer, Has no precipitate. The pinhole density is low because the precipitate is completely incorporated into the buried silicon oxide layer. Example 2
As shown in FIG. 8, as in Example 1, since the temperature was raised so that the precipitate at 1300 ° C. could be sufficiently taken in, no precipitate was observed except for the buried silicon oxide layer in the substrate. The pinhole density is also low for the same reason as in the first embodiment. (B) Measurement of the flatness of the interface between the Si layer and the buried silicon oxide layer The interface between the active Si layer on the surface of each SOI substrate and the buried silicon oxide layer in Examples 1 and 2 and Comparative Examples 1 and 2 Atomic force microscope (AFM)
It measured using. This measurement was performed by exposing the interface with the buried silicon oxide layer by selectively etching the SOI substrate with a KOH solution to remove the single crystal silicon layer (Si layer). Table 2 shows the results. In Table 2, Ra
Is the average roughness, Rms is the root-mean-square roughness, and Rmax is the maximum height. [Table 2] As apparent from Table 2, Examples 1 and 2 in which the precipitates were kept at a high temperature for 2 hours corresponded to Comparative Examples 1 and 4 in which the precipitates were completely taken in and kept at a high temperature for 4 hours.
It was found that the interface became flat in a short time as compared with. On the other hand, in Comparative Example 1, since the precipitates were taken in during the high-temperature holding, it took time for the interface to become flat, and in Comparative Example 2, the interface was extremely rough because the high-temperature holding was not performed. found. As described above, according to the SOI substrate manufacturing method of the present invention, the heating rate is set to at least two steps, and the heating rate is sequentially reduced until reaching the final predetermined temperature .
The initial heating rate (v ₁ ) is 10 to 3 ° C./min.
At a temperature rate (v ₁ ) of 1250 ° C or more and less than 1350 ° C
The temperature is raised to the first predetermined temperature (T ₁ ), and the final heating rate (v ₂ ) is 7
０．１0.1 ° C./min , and 1350 at this heating rate (v ₂ ).
The temperature rises to the final specified temperature (T ₀ ) that is higher than or equal to
By heating, a high-quality buried silicon oxide layer having an extremely low pinhole density can be formed, and the flatness of the interface between the Si layer and the buried silicon oxide layer can be improved in a short time.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing a temperature profile of an annealing process of an example and a comparative example after oxygen ion implantation. FIG. 2 is a schematic view showing a partial cross section of a silicon substrate immediately after oxygen ion implantation according to the present invention. FIG. 3 is an electron micrograph of a cross section of the silicon substrate of Example 1 when the temperature is increased to 1300 ° C. at a rate of 5 ° C./min. FIG. 4 is an electron micrograph of a cross section of the silicon substrate of Example 1 in the process of heating from 1300 ° C. at a heating rate of 1 ° C./min. FIG. 5 is an electron micrograph of the cross section of the silicon substrate of Example 1 when the temperature was further increased at a rate of 1 ° C./min. FIG. 6 is an electron micrograph of the cross section of the silicon substrate of Example 1 when the temperature was increased to 1390 ° C. at a rate of 1 ° C./min. FIG. 7 is an electron micrograph of a cross section of the silicon substrate of Example 1 after annealing. FIG. 8 is an electron micrograph of a cross section of the silicon substrate of Example 2 after annealing. FIG. 9 is an electron micrograph of a cross section of the silicon substrate of Comparative Example 1 when the temperature was raised to 1390 ° C. at a rate of 5 ° C./min. FIG. 10 is an electron micrograph of a cross section of the silicon substrate of Comparative Example 1 after annealing. FIG. 11 is a diagram showing a temperature rise to 1100 ° C. at a rate of 5 ° C./min.
The electron microscope photograph figure of the cross section of the silicon substrate of the comparative example 2 at the time of changing the temperature rising rate to 1 ° C./min and increasing the temperature to 1390 ° C. [Description of Signs] 11 Silicon substrate 11a Si layer on substrate surface 12 Embedded silicon oxide layer

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-5-144761 (JP, A) JP-A-62-188239 (JP, A) Stoemenos, et. a l. , "Dislocation Formatted Related with High Oxygen Dose Implantation on Silicon", J. Am. Appl. Phys. Vol. 69, No. 15, January 15, 1991. 2, pp. 793-802H. Yang, et. al. , "Effect of Implantation on Current Density and Annual Time of the Microstructure of SIMOX", Nuclear Instruments and Methods of Medicine, 1991, Nuclear Resources and Methods of Medicine. 56/57, p. 668−671 (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 27/12 H01L 21/26-21/268 H01L 21/322-21/326

Claims (1)

(57) After the Claims to 1. A silicon substrate (11) inside the oxygen ion was implanted, a predetermined temperature increase to the final predetermined temperature (T ₀₎ to a final predetermined temperature (T ₀₎ A buried silicon oxide layer (12) is formed in a region at a predetermined depth from the surface of the silicon substrate (11) by performing an annealing process for holding time (t), and the substrate (11)
In the method for manufacturing an SOI substrate in which an active Si layer (11a) is formed on the surface, the rate of temperature increase during the annealing treatment is at least two steps (v ₁ ,
v ₂₎ is a, said final predetermined temperature (T ₀₎ sequentially decelerated heating rate to reach, a first heating rate (v ₁₎ is ten to three ° C. / min, the temperature
At a temperature rate (v ₁ ) of 1250 ° C or more and less than 1350 ° C
The temperature is raised to the first predetermined temperature (T ₁ ), and the final heating rate (v ₂ ) is 7
０．１0.1 ° C./min , and 1350 at this heating rate (v ₂ ).
The temperature rises to the final specified temperature (T ₀ ) that is higher than or equal to ° C and lower than the silicon melting point temperature.
Heating the SOI substrate.