JP3533238B2 - Semiconductor substrate - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor substrate, and more particularly to a semiconductor capable of reducing the interstitial oxygen concentration in the vicinity of the surface of a semiconductor substrate to such an extent that precipitation does not occur. Regarding the substrate. 2. Description of the Related Art Conventionally, a silicon semiconductor substrate used for a silicon semiconductor device has been manufactured by cutting out a silicon single crystal ingot manufactured by the Czochralski method (CZ method). When a silicon single crystal ingot is pulled up from a quartz crucible, oxygen is supersaturated at room temperature when the silicon substrate produced by cutting out the ingot manufactured by the CZ method. Then, this excess oxygen is deposited in the form of, for example, SiO ₂ by heat treatment during the semiconductor manufacturing process. However, near the device fabrication surface of the silicon semiconductor substrate,
The occurrence of such oxygen precipitation adversely affects the device. Therefore, a silicon semiconductor substrate is made of H ₂ , Ar
By performing heat treatment in such a gas atmosphere, supersaturated oxygen is removed from the vicinity of the surface of the silicon semiconductor substrate.
As a result, oxygen precipitates and OSF (Oxidation-induced Stacking Failure) near the surface of the silicon semiconductor substrate
Crystal defects such as t) are greatly reduced, and defects in an oxide film to be subsequently laminated are reduced, for example, in an electric field of 8 MV / cm or less. For this reason, a heat treatment technique in a gas atmosphere of H ₂ , Ar, or the like has attracted attention as a high quality technique for a silicon semiconductor substrate surface. The heat treatment in a gas atmosphere of H ₂ , Ar, or the like is performed at a temperature of 1100 ° C. or higher in order to sufficiently perform the external diffusion of interstitial oxygen near the surface of the silicon semiconductor substrate and sufficiently enhance the effect of improving the quality of the substrate surface. It is done in. [0004] However, 110
When heat treatment with a gas such as H ₂ or Ar is performed at a temperature of 0 ° C. or higher, the resistivity may increase near the surface of the silicon semiconductor substrate. This is H ₂ , A
It is thought that interstitial oxygen near the surface diffuses outward during heat treatment in a gas atmosphere such as r, but at the same time, dopants (impurities) near the surface also diffuse outward as shown in FIG. Have been. For this reason, a silicon semiconductor substrate that has been heat-treated in a gas atmosphere of H ₂ , Ar, or the like can be used, in particular, for highly integrated devices (DRAM, EPROM).
) Causes the following problems. [0005] (1) When the isolation between elements is performed by using the resistivity of the semiconductor substrate, the depletion layers of the drain and the source of the transistor are easily spread by the increase of the resistivity. It is easy to occur. (2) As the resistivity increases, the drain,
An element such as a source, a resistance difference from a well part such as a well part becomes large, and latch-up is easily caused accordingly. (3) When a device is designed to eliminate the problems (1) and (2) in consideration of the increase in resistivity near the surface of the semiconductor substrate, the individual semiconductor substrate and the surface of the semiconductor substrate are designed. Is expected to be much greater after heat treatment than before heat treatment, making device design more difficult. The present invention has been made in view of the above points, and by performing heat treatment in a gas atmosphere of H ₂ , Ar, etc., it is possible to improve the quality near the surface,
It is another object of the present invention to provide a semiconductor substrate capable of preventing high resistivity near the surface. According to the present invention, in a silicon semiconductor, the average interstitial oxygen concentration inside a substrate having a depth of 50 μm or more is five times the average interstitial oxygen concentration on the surface of a substrate having a depth of 3 μm or less. As described above, the average interstitial oxygen concentration on the substrate surface is 2 × 10 ¹⁷ atoms / cm ³ or less, and the difference between the average dopant impurity concentration inside the substrate and the average dopant impurity concentration on the substrate surface is the average dopant impurity inside the substrate. A silicon semiconductor substrate characterized in that the concentration is 5% or less with respect to the concentration. According to the present invention, the average interstitial oxygen concentration on the surface of the semiconductor substrate is 2 × 10 ¹⁷ atms / cm ³ or less, and the average interstitial oxygen concentration in the substrate is lower than the average interstitial oxygen concentration on the substrate surface. Since the oxygen concentration is five times or more, the oxide does not precipitate during the heat treatment during the semiconductor manufacturing process and does not affect the device. Further, since the difference between the dopant impurity concentration in the substrate and the dopant impurity concentration in the substrate surface is 5% or less with respect to the average dopant impurity concentration in the substrate, an increase in resistivity on the surface can be prevented. Embodiments of the present invention will be described below with reference to the drawings. First, the dopant grown by the Czochralski method (CZ method) is an N-type of P (phosphorus) 20 to 30Ω.
・ Production of cm silicon ingot. Next, the silicon ingot is cut into a predetermined thickness, mirror-polished on one side, washed, and the like, to produce a silicon semiconductor substrate 10 (FIG. 5). Next, for this silicon semiconductor substrate 10,
H containing about 7 ppm PH ₃ in the heat treatment furnace
Heat treatment (annealing) is performed at 1200 ° C. for one hour in a _two- gas atmosphere. FIG. 3 shows an oxygen concentration profile and a dopant impurity profile of the semiconductor substrate 10 after the heat treatment according to the present invention. The heat treatment at 1200 ° C. for 1 hour in a conventional H ₂ gas atmosphere containing no PH ₃ is shown. FIG. 4 shows the oxygen concentration profile and the dopant impurity profile of the semiconductor substrate 10 after the above. In the present invention shown in FIG. 3, the dopant impurity concentration does not decrease near the surface 10a of the semiconductor substrate 10 and is substantially constant, whereas in the conventional example shown in FIG. 4, the dopant impurity concentration decreases near the surface. . As described above, by subjecting the silicon semiconductor substrate to a heat treatment in an H 2 gas atmosphere, oxygen atoms near the surface 10a of the semiconductor substrate 10 can be diffused outward, thereby allowing the silicon semiconductor substrate 10 to be diffused. The oxygen concentration in the vicinity of the surface 10a can be reduced. Further, by mixing PH ₃ in H ₂ gas, P (phosphorus) is introduced into the semiconductor substrate 10 during the heat treatment.
Can be introduced. Therefore, the shortage of P (phosphorus) that diffuses outward from the inside of the semiconductor substrate 10 during the heat treatment can be compensated for, and a decrease in the concentration of P (phosphorus) near the surface 10a of the semiconductor substrate 10 can be prevented. An increase in resistivity near 10a can be prevented. The concentration of PH ₃ contained in the H ₂ gas is set to an appropriate value so that the resistivity of the substrate 10 before the heat treatment is equal to the resistivity of the substrate 10 after the heat treatment. The concentration is also determined so that the resistivity of the substrate 10 before and after the heat treatment becomes the same. As shown in FIG. 3, according to the present embodiment, the average interstitial oxygen concentration in the substrate 10 having a depth of 50 μm or more is 1.6 × 10 ¹⁸ atms / cm ³ , and the substrate having a depth of 3 μm or less is provided. The average interstitial oxygen concentration on the surface 10a of the sample 10 is 1.8 × 1
0 ¹⁷ atms / cm ³ . Therefore, the ratio between the two is 8.8: 1.
It becomes. The average dopant impurity concentration inside the substrate 10 is 7 × 10 ¹⁴ atms / cm ³ ,
The average dopant impurity concentration of a is also 7 × 10 ¹⁴ atms
/ Cm ³ . The average interstitial oxygen concentration on the substrate surface is 2
× is the 10 ¹⁷ atms / cm ³ or less, the average interstitial oxygen concentration in the substrate is equal to or more than 5 times the average interstitial oxygen concentration of the substrate surface, affecting the device in the heat treatment in the semiconductor manufacturing process Never. When the difference between the dopant impurity concentration in the substrate and the dopant impurity concentration in the substrate surface is 5% or less of the average dopant impurity concentration in the substrate, an increase in the surface resistivity can be prevented. As shown in FIG. 3, according to the present embodiment, it is understood that the above-described criteria that do not affect the device are satisfied. In this embodiment, the PH ₃ content is set to 7 ppm and the heat treatment concentration is set to 1200 ° C. However, the present invention is not limited to this, and the PH ₃ content in the H ₂ gas atmosphere is set to ₂ to 10 p.
pm, it is possible to prevent a decrease in the dopant impurity concentration in the vicinity of the surface 10a of the semiconductor substrate 10;
Can be obtained. Also P
The heat treatment temperature in an H ₂ gas atmosphere containing H ₃ is 120.
The temperature is not limited to 0 ° C. and may be 1100 ° C. to 1250 ° C.
Further, Ar gas may be used instead of H ₂ gas. When a P-type silicon substrate having a boron dopant is heat-treated, 1 to 5 ppm, preferably 3.5 ppm, of B ₂ H ₆ is contained in H ₂ gas,
By performing the heat treatment at 00 ° C., a result substantially similar to the result shown in FIG. 3 can be obtained. (Specific Example) Next, in H ₂ gas containing PH ₃ gas according to the present invention, 120
0 ° C., and the silicon semiconductor substrate obtained by the heat treatment method of heating 1 hour, with H ₂ gas containing no PH ₃ 120
Semiconductor devices were fabricated using a conventional silicon semiconductor substrate heat-treated at 0 ° C. for 1 hour and a comparative silicon semiconductor substrate not heat-treated in H ₂ gas. Next, the occurrence rates of punch-through and latch-up were examined for each semiconductor substrate. The result is shown in FIG. As shown in FIG. 1, the occurrence rates of punch-through and latch-up in a semiconductor device are as follows: Thus, in the case of the heat treatment in the H ₂ gas containing PH _{3 according} to the present invention, a remarkable improvement can be seen as compared with the conventional case not containing PH ₃ . Further, a gate oxide film (SiO ₂ film) having a thickness of 20 nm is
It was formed by O ₂ oxidation at 0 ° C. Thereafter, a gate electrode was formed to form a MOS capacitor, and the dielectric breakdown voltage of the gate oxide film was measured using the MOS capacitor. The result is shown in FIG. As shown in FIG. 2, the oxide film dielectric strength failure rate at 8 MV / cm or less is given by: It can be seen that the heat treatment in H ₂ gas at a temperature of 1200 ° C. for one hour greatly improves the oxide withstand voltage. As described above, according to the present embodiment, the heat treatment is performed in a gas atmosphere containing molecules including a dopant, such as H ₂ or Ar, thereby improving the quality of the silicon substrate such as good oxide film characteristics. In addition, it is possible to prevent the problem of increasing the resistance near the surface 10a of the substrate 10 due to the heat treatment. As a result, it is possible to prevent the characteristic degradation of the semiconductor device such as latch-up and punch-through. As described above, according to the present invention, oxides do not precipitate during the heat treatment in the semiconductor manufacturing process and do not affect the device. Further, an increase in resistivity on the substrate surface can be prevented. Therefore, a highly accurate semiconductor substrate can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing the occurrence rates of punch-through and latch-up in a semiconductor device in comparison with the present invention, a conventional example, and a comparative example. FIG. 2 is a diagram showing the oxide film dielectric strength failure rate at 8 MV / cm or less, comparing the present invention, a conventional example, and a comparative example. FIG. 3 is a distribution diagram of a dopant impurity concentration and an interstitial impurity concentration in a depth direction from a substrate surface in the present invention. FIG. 4 is a distribution diagram of a dopant impurity concentration and an interstitial impurity concentration in a depth direction from a substrate surface in a conventional example. FIG. 5 illustrates a semiconductor substrate. [Description of Signs] 10 Semiconductor substrate 10a Substrate surface

──────────────────────────────────────────────────の Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 21/22 H01L 21/322 H01L 21/324

Claims (1)

(57) Claims 1. In a silicon semiconductor, the average interstitial oxygen concentration inside a substrate having a depth of 50 µm or more is at least 5 times the average interstitial oxygen concentration on a substrate surface having a depth of 3 µm or less. Wherein the average interstitial oxygen concentration on the substrate surface is 2 × 10 ¹⁷ atoms / cm ³ or less, and the difference between the average dopant impurity concentration inside the substrate and the average dopant impurity concentration on the substrate surface is the average dopant impurity concentration inside the substrate. 5% or less of the silicon semiconductor substrate.