JPH05291097A - Silicon substrate and manufacture thereof - Google Patents

Abstract

PURPOSE:To keep a DZ layer high in crystallinity and gettering capacity and a substrate high in mechanical strength. CONSTITUTION:A silicon substrate is provided with regions composed of a first region whose density distribution of inner defects is less than 1X10<5>cm<-3>, a second region whose density distribution of inner defects is more than 1X10<7>cm<-3>, and a third region whose density distribution of inner defects is less than 1X10<7>cm<-3>, where the regions are made to range in this sequence in a thicknesswise direction from the surface to the center of the substrate. The substrate is formed through such a method that oxygen is diffused inwardly into the substrate, and then solution oxygen in a surface layer is diffused outwardly, whereby a surface region where solution oxygen is less than 5X10<7>cm<-3> and a center region where solution oxygen is more than 5X10<7>cm<-3> are formed in the substrate. Thereafter, the silicon substrate is heated at temperatures of 400 to 1050 deg.C and thermally treated for more than 30 minutes, whereby the substrate possessed of regions of the above density distribution of inner defects can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon substrate having a gettering effect and a method for manufacturing the same.

[0002]

2. Description of the Related Art Factors that deteriorate the electrical characteristics of silicon semiconductor devices include process-induced defects and harmful impurities that are induced in the semiconductor device manufacturing process. It is known that these defects and impurities induce or invade the operating region of the semiconductor device, thereby increasing the leak current of the pn junction of the semiconductor device and decreasing the minority carrier lifetime.

There is an intrinsic gettering method (hereinafter referred to as IG method) as a method for preventing the generation of process-induced defects and detoxifying harmful impurities. The IG method is a defect-free region called a denuded zone (hereinafter referred to as a DZ layer) near the surface of a silicon substrate that is involved in the operation of a semiconductor device.
Is formed and a crystal defect (hereinafter referred to as an internal defect) is intentionally generated inside the substrate to getter harmful impurities into the internal defect to render it harmless.
The most well-known IG method at present is a method of performing a three-step heat treatment on a silicon substrate as described below.

The first step is to hold the silicon substrate at a temperature of 1100 ° C. or higher for about 5 to 10 hours,
The purpose is to outwardly diffuse the solid solution oxygen in the vicinity of the surface, and at the same time, to shrink or eliminate the nuclei of the internal defects formed during the growth of the silicon crystal existing in the vicinity of the surface.
The second stage is intended to form nuclei for the generation of internal defects only inside the substrate by keeping the silicon substrate at a temperature of 600 ° C. to 800 ° C. for 20 hours to 60 hours. In the third step, the silicon substrate is heated from 1000 ° C to 1050 ° C.
The purpose is to hold the temperature of C for 1 to 20 hours to grow the nuclei of internal defects formed in the second stage into internal defects having gettering ability.

As shown in FIG. 2, a DZ layer and an internal defect layer are formed on a silicon substrate processed by the IG method. There is a correlation as shown in FIG. 3 between the defect density of the internal defect layer and the gettering ability of harmful impurities.
It is known that the gettering ability is exhibited at a density of ⁷ cm ^-3 or more. On the other hand, the IG method has a problem that the amount of warp increases because the mechanical strength of the silicon substrate decreases as the defect density of the internal defect layer increases, as shown in FIG. It is known that an increase in the amount of warp reduces the manufacturing yield of semiconductor devices. As is clear from a comparison between FIG. 3 and FIG. 4, the gettering ability and the warp amount have a contradictory relationship.

As a method for solving the problems of the IG method, a method for forming a granular precipitate described in JP-A-61-16532 near the surface layer close to the device operating region, and JP-A-61-61.
There is a method described in JP-A-51930, in which oxygen atoms and silicon atoms are ion-implanted and heat-treated to precipitate oxygen atoms. As shown in FIG. 5, both methods have strong gettering ability due to the high density of crystal defects near the surface layer close to the device operating region, and the warp of the substrate due to the low density of precipitates inside the substrate. There is no increase in quantity. However, the former method is a method in which polycrystalline silicon is grown by solid phase shrimp growth, and the latter method is to implant oxygen atoms and silicon atoms directly under the DZ layer. Therefore, the crystallinity of the DZ layer is determined by the IG method. The crystallinity of the DZ layer obtained in 1. is inferior. A decrease in crystallinity of the DZ layer causes a decrease in manufacturing yield of semiconductor devices.

[0007]

As described above, the present invention has a high crystallinity of the DZ layer, a high gettering ability due to the generation of high-density internal defects, and a mechanical property of the substrate, which have not been possible in the prior art. The present invention provides a silicon substrate ensuring strength and a method for manufacturing the same.

[0008]

DISCLOSURE OF THE INVENTION According to the present invention, the distribution of internal defects in a silicon substrate is a region having a density of 1 × 10 ⁵ cm ⁻³ or less in order from the surface to the center in the thickness direction, 1 × 10 ⁷ cm.
^-3 or more, preferably 1 × 10 ⁸ cm ^-3 or more in the density region,
The area has a density of less than 1 × 10 ⁷ cm ⁻³ . Specifically, in order to obtain the internal defect distribution according to claim 1 without impairing the crystallinity of the substrate surface, the following formula (1) is used in an oxygen gas or a mixed gas atmosphere of an oxygen gas and a non-oxidizing gas. The solid solution oxygen contained in the silicon substrate shown is heated to a temperature equal to or higher than the temperature T at which it becomes unsaturated and lower than or equal to the melting point, and heat-treated for 10 minutes or more, preferably 1 hour or more to diffuse oxygen in gas into the silicon substrate inward. Let

T = 1.77 × 10 ⁴ / 1n (9 × 10 ²² / C) -273 (1) T: Temperature at which solid solution oxygen contained in a silicon substrate becomes unsaturated (unit: C), C: concentration of dissolved oxygen contained in the silicon substrate (unit: c
m ⁻³ ) After inwardly diffusing oxygen, the temperature range up to at least 900 ° C. is cooled at a cooling rate of 1 ° C./min or more and 100 ° C./min or less, or after the silicon substrate is once cooled, the silicon substrate is continuously cooled to 1100 ° C. The solid solution oxygen in the surface layer is outwardly diffused by heating to a temperature lower than the temperature T represented by the equation (1) and heat treatment for 10 minutes or more to obtain the concentration distribution of the solid solution oxygen according to claim 2. A silicon substrate having is manufactured.
After that, the silicon substrate is heated to a temperature of 400 ° C. or higher and 1050 ° C. or lower and heat-treated for at least 30 minutes or longer, preferably 1 hour or longer, to obtain a distribution of internal defects.

[0010]

The operation of the present invention will be described in detail with reference to the drawings. According to the present invention, as shown in FIG. 1, the density distribution of internal defects of a silicon substrate is 1 × 10 ⁵ cm ⁻³ or less in the thickness direction from the surface to the center (DZ layer), and 1 ×
Area with a density of 10 ⁷ cm ⁻³ or more (internal defect layer), 1 × 1
The area has a density of less than 0 ⁷ cm ^-3 . DZ semiconductor device
By producing the layer, it is possible to obtain good electric characteristics without generation of process-induced defects. In the internal defect layer, gettering of harmful impurities that enter during the manufacturing process of the semiconductor device is performed. Unlike the conventional IG method, the internal defect layer having the gettering ability is not distributed over the central portion of the silicon substrate, so that the mechanical density of the silicon substrate is significantly reduced due to the increase in the defect density of the internal defect layer. There is no. Therefore, in order to impart a high gettering ability to the silicon substrate, the defect density of the internal defect layer is set to 1 ×.
Even when it is set to 10 ⁹ cm ^-3 or more, the warp amount is not significantly increased, and therefore the manufacturing yield of semiconductor devices is not reduced.

In the present invention, a three-step heat treatment is performed to manufacture the silicon substrate having the density distribution of internal defects according to claim 1. The feature of the present invention is that oxygen is introduced into the silicon substrate in the first heat treatment. It is to diffuse inward. First
In the heat treatment, the silicon substrate is heated in an oxygen gas or a mixed gas atmosphere of an oxygen gas and a non-oxidizing gas (for example, helium, argon, nitrogen, etc.) to a temperature above the temperature at which the concentration of solid solution oxygen contained in the substrate becomes unsaturated. By heating, oxygen in the atmosphere is diffused inward into the silicon substrate, and the concentration distribution of solid solution oxygen is set to the distribution shown in FIG. 6 (a). The temperature dependence of the concentration of dissolved oxygen in silicon is described in J. C. Mikkelsen, J
r. "The DIFFUSIVITY AND
SOLUBILITY OF OXGEN INSI
LICON "(Oxygen, Carbon, Hydr
ogen and Nitrogen in sili
con, 1986, Material Research
ch Society, page 19) (2)
It is shown by the formula.

[0012] ^{_{C ox = 9 × 10 22 exp}} (-1.52eV / kt a) ····· (2) C ox: dissolved oxygen concentration (in cm ^-3), k: Boltzmann constant, T _a: Absolute temperature (unit: K) According to the equation (2), there is an equation (1) between the temperature T at which the solid solution oxygen contained in the silicon substrate becomes unsaturated and the solid solution oxygen concentration C in the silicon substrate. The relationship shown in is established. T = 1.77 × 10 ⁴ / 1n (9 × 10 ²² / C) -273 (1) T: temperature at which solid solution oxygen contained in a silicon substrate becomes unsaturated (unit: ° C), C: Solid solution oxygen concentration contained in the silicon substrate (unit: c
m ^-3 ) The first heat treatment also has a function of decomposing the generation nucleus of the internal defect formed in the crystal growth process contained in the silicon substrate. The decomposition action described above is more remarkable in the central portion of the silicon substrate which is not affected by the inward diffusion of oxygen, and the density of the internal defects generated in the central portion of the silicon substrate is reduced by the subsequent heat treatment. Then, in order to form a DZ layer on the surface of the silicon substrate, the cooling rate after the first heat treatment is controlled or the silicon substrate is once cooled, and then the second heat treatment is performed.
Again, heat treatment is performed at a temperature of 1100 ° C. or higher for 10 minutes or longer. By performing up to the second heat treatment, the distribution of the concentration of solid solution oxygen in the silicon substrate becomes as shown in FIG. 6 (b), and the silicon substrate according to claim 2 is manufactured. Third
In the heat treatment, in order to form an internal defect layer in a region having a high concentration of dissolved oxygen immediately below the DZ layer, heat treatment is performed at a temperature of 400 ° C. or higher and 1050 ° C. or lower for 30 minutes or longer, and the internal defect layer is 1 × 10 ⁷ cm 2. ^-Internal defects with a density of ^-3 or more are formed. On the other hand, in the central portion of the silicon substrate, the density of the internal defects generated by the third heat treatment does not exceed 1 × 10 ⁷ cm ⁻³ because the nuclei of the internal defects generated by the first heat treatment are decomposed, and therefore the internal defects are not generated. 1 has a density distribution as shown in FIG.

[0013]

EXAMPLES Examples of the present invention will be described below.

All the silicon substrates used for carrying out the examples of the present invention and the comparative examples had a plane orientation (100) and a solid solution oxygen concentration of 9.5.
× 10 ¹⁷ cm ^-3, resistivity of p-type CZ silicon substrate of 5 inches in diameter of 10 .OMEGA.cm. The silicon substrate used in the examples is one in which the solid solution oxygen in the silicon substrate becomes unsaturated at a temperature of 1271 ° C. or higher. All the silicon substrates used in the examples were previously immersed in a 1 wt% dilute hydrofluoric acid aqueous solution to remove the natural oxide film on the surface before heat treatment, and then rinsed with ultrapure water and washed. Then, spin drying was performed.

Inventive Examples 1 to 10 and Comparative Examples 11 to 17 are
After the first heat treatment and the second heat treatment were sequentially performed, the concentration distribution of solid solution oxygen was measured.

In Comparative Example 11, the heat treatment temperature of the first heat treatment was 1250 ° C. while the solid solution oxygen was still supersaturated, and the other conditions were the same as in Invention Examples 1 and 2.

In Comparative Example 12, the heat treatment time of the first heat treatment was 5
Minutes and other conditions were the same as those of Examples 1 and 3 of the invention.

In Comparative Example 13, the heat treatment atmosphere of the first heat treatment was Ar, and the other conditions were the same as in Invention Examples 1, 4, and 5.

In Comparative Examples 14 and 15, the cooling rates of the first heat treatment were 0.5 ° C./min and 150 ° C./min, respectively, and the other conditions were the same as those of Examples 1, 6 and 7 of the present invention.

In Comparative Example 16, the heat treatment temperature of the second heat treatment was 1050 ° C., and the other conditions were the same as in Invention Example 8.

In Comparative Example 17, the heat treatment time of the second heat treatment was 5 minutes, and the other conditions were the same as those of Examples 8 and 10 of the present invention.

The concentration distribution of solute oxygen was measured by secondary ion mass spectrometry on the silicon substrate that had been subjected to the second heat treatment. As a result of the measurement, the solid solution oxygen concentration distribution that satisfies the condition of claim 2 was regarded as acceptable.

Table 1 shows the judgment results of the examples of the present invention and the comparative examples. In all the examples of the present invention, the solid solution oxygen of the silicon substrate has the concentration distribution described in claim 2. In Comparative Examples 11 to 17, the heat treatment conditions of the first heat treatment or the second heat treatment are out of the range described in claim 3 or 4, and therefore the concentration distribution of solid solution oxygen is out of the range in claim 2. ing.

Inventive Examples 18 to 22 and Comparative Examples 23 to 27
Was subjected to a third heat treatment on the silicon substrate according to claim 2 to measure the density distribution of internal defects.

In Comparative Examples 23 and 24, the heat treatment temperature of the third heat treatment was 350 ° C. and 1100 ° C., respectively, and the other conditions were the same as those of Examples 18 to 20 of the invention.

In Comparative Examples 25, 26 and 27, the heat treatment time of the third heat treatment was set to 20 minutes, and other conditions were that Comparative Example 25 was Invention Examples 18 and 21, Comparative Example 26 was Invention Example 19 and
Comparative Example 27 was the same as Examples 20 and 22 of the present invention.

The density distribution of the internal defects was measured by visualizing the internal defects by etching the cross-section of the silicon substrate subjected to the third heat treatment by the Secco etching method. As a result of the measurement, it was judged that the density distribution of the internal defects of the silicon substrate satisfies the condition of claim 1 as a pass.

Table 2 shows the judgment results of the examples of the present invention and the comparative examples. In each of the examples of the present invention, the internal defects have the density distribution described in claim 1, and a silicon substrate having no process-induced defects, an excellent gettering ability of harmful impurities, and no reduction in mechanical strength is manufactured. There is.

In Comparative Examples 23 to 27, the heat treatment condition of the third heat treatment is out of the range described in claim 5, and therefore the density distribution of internal defects is out of the range in claim 1.

[0030]

[Table 1]

[0031]

[Table 2]

[0032]

As described above in detail, according to the present invention, it is possible to manufacture a CZ silicon substrate which has no process-induced defects, has an excellent gettering ability for harmful impurities, and has no significant reduction in mechanical strength. Therefore, semiconductor devices can be manufactured with a high yield, which is extremely effective in industry.

[Brief description of drawings]

FIG. 1 is a diagram showing a density distribution of internal defects shown in claim 1 of the present invention.

FIG. 2 is a diagram showing a distribution of a DZ layer and an internal defect layer by a conventional IG heat treatment.

FIG. 3 is a diagram showing a correlation between gettering ability of harmful impurities and density of internal defects.

FIG. 4 is a diagram showing a correlation between a warp amount (mechanical strength) of a silicon substrate and a density of internal defects.

FIG. 5 is a diagram showing the distribution of internal defect layers that solves the problems in the conventional IG method.

FIG. 6 is a diagram showing a distribution of solute oxygen in a silicon substrate according to the present invention. FIG. 6A is a diagram showing a concentration distribution of solid solution oxygen when oxygen is diffused inward in the first heat treatment. FIG. 6B is a diagram showing the concentration distribution of solid solution oxygen after controlling the cooling rate of the first heat treatment or performing the second heat treatment.

Claims (5)

[Claims] 1. A region having a defect density of 1 × 10 ⁵ cm ⁻³ or less from the surface to the center in the thickness direction of a silicon substrate, 1 ×
A region having a defect density of 10 ⁷ cm ⁻³ or more and 1 × 10 ⁷
A silicon substrate having sequentially regions of defect density of less than cm ^-3 . 2. A solid solution oxygen region of 5 × 10 ¹⁷ cm ⁻³ or less in the surface side region from the surface to the center in the thickness direction of the silicon substrate, and an intermediate region is a solid solution oxygen concentration higher than the solid solution oxygen concentration in the wafer center region. A silicon substrate characterized by being a dissolved oxygen region. 3. A temperature T at which the solid solution oxygen contained in the silicon substrate represented by the following formula (1) becomes unsaturated in an oxygen gas or a mixed gas atmosphere of an oxygen gas and a non-oxidizing gas in the silicon substrate. After heating above the melting point to perform heat treatment for 10 minutes or more to diffuse oxygen in the gas in the silicon substrate inward, a temperature range of at least 900 ° C. is 1 ° C./min or more and 100 ° C. The method for manufacturing a silicon substrate according to claim 2, wherein the cooling is performed at a cooling temperature of / min or less. T = 1.77 × 10 ⁴ / ln (9 × 10 ²² / C) -273 (1) T: Temperature at which solid solution oxygen contained in a silicon substrate becomes unsaturated (unit: ° C) , C: concentration of dissolved oxygen contained in the silicon substrate (unit: c
m ^-3 ) 4. Subsequent to the method according to claim 3, 11
It is heated to a temperature of 00 ° C. or higher and lower than the temperature T represented by the formula (1) of claim 3, and heat-treated for at least 10 minutes to diffuse outwardly the solid solution oxygen in the surface layer. The method for manufacturing the silicon substrate according to claim 2. 5. The silicon substrate according to claim 2, wherein the silicon substrate is heated to a temperature of 400 ° C. or more and 1050 ° C. or less and heat treatment is performed for at least 30 minutes or more. Of manufacturing a silicon substrate of.