JPH04207036A - Intrinsic gettering method - Google Patents

Abstract

PURPOSE:To more efficiently getter a heavy-metal impurity (especially Fe) which is hard to getter by a method wherein, after at least a final heat treatment out of high-temperature heat treatments at 900 deg.C or higher in a device process, the impurity is heat-treated at a temperature of 800 deg.C or higher and less than 100 deg.C while a wafer is being cooled. CONSTITUTION:It is evident that Fe produces a precipitate at a temperature of 800 deg.C or lower. Consequently, a gettering heat treatment is executed at the temperature of 800 deg.C or lower, Fe is is precipitated. At 100 deg.C or lower, an influence is small when the precipitate of Fe is decomposed. It is proper that the temperature for the heat treatment is at 800 deg.C or higher and less than 1000 deg.C. When the time for the heat treatment is short, the Fe is not diffused to an internal defect layer and the effect of a gettering operation is not obtained. As a result, the time for the heat treatment for 10 minutes or higher is required.

Description

[Detailed Description of the Invention] [Summary] The purpose of this invention is to provide a method for more efficiently gettering heavy metal impurities that are difficult to getter with respect to the intrinsic gettering method, and to provide a method for more efficiently gettering heavy metal impurities that are difficult to getter. Less than 1000℃ (800℃ or higher after the final high temperature heat treatment)
The structure is such that the heat treatment is performed at a temperature below .degree. C. for 10 minutes or more.

[Industrial application field]

The present invention relates to a method for gettering heavy metal impurities in semiconductor wafers.

The present invention particularly relates to the method of intrinsic gettering using oxygen precipitates, and is a method for enhancing the effectiveness thereof.

[Conventional technology]

In the intrinsic gettering method, before the Ukoha is sent to the device process, a defective layer due to oxygen precipitates is formed inside the Ukoha by heat treatment, and heavy metal impurities mixed in during the device process are removed from this layer. This is a method of incorporating (gettering) into an internal defect layer. In this method, only the heat treatment to form a defective layer due to oxygen precipitates inside the wafer is intentionally performed, and then the heat treatment is performed in accordance with the device process. Then, the heavy metal diffuses into the internal defect layer and is captured, so that it no longer functions as an impurity level.

[Problem to be solved by the invention]

However, some heavy metals are difficult to be gettered. Among typical heavy metal impurities, (u, N
Among heavy metals other than i, it is known that Fe is less likely to be gettered than Cu and Ni.

Therefore, an object of the present invention is to provide a method for more efficiently gettering heavy metal impurities (particularly Fe) that are difficult to getter.

[Means for Solving the Problem] The present invention provides heat treatment at a temperature lower than 800°C or higher and lower than 1000°C during cooling of the wafer after the final heat treatment during the high-temperature heat treatment of 900°C or higher in the device process. This is a method in which the process is carried out for 10 minutes or more.

In the present invention, ordinary intrinsic gettering is performed to form an internal defect layer due to oxygen precipitates in the semiconductor wafer, and after high-temperature heat treatment at 900°C or higher in the device process, heat treatment at 800°C or higher and lower than 1000°C is performed on Fe.
Do this for at least 10 minutes to getter the heavy metals.

In normal intrinsic gettering, 1100
℃, after heat treatment for 30 minutes, cooled to 650℃, and heated at 650℃ for 6
A three-stage heat treatment is usually carried out in which nuclei are formed by holding for a certain period of time, followed by heat treatment at 1100° C. for 30 minutes to grow the nuclei.

In the present invention, Fe etc. are dissolved in solid solution at a temperature of 900°C or higher, and if solid solution Fe remains in the wafer, dee
Since p 1 level is produced, heat treatment for gettering of Fe, etc. is performed after the final high temperature heat treatment. This heat treatment may be performed only once, or may be performed each time after the high temperature heat treatment.

Heat treatment for gettering Fe, etc. may be performed during cooling after high-temperature heat treatment, with cooling time from 1000"C to 800°C for 10 minutes or more, but Fe precipitation may occur due to change in solid solubility of Fe. Therefore, it is preferable to carry out the isothermal heat treatment by keeping the temperature constant.
- It may be carried out by a method in which the temperature is raised to a predetermined temperature and maintained after cooling the evaporator to the chamber, or by a method in which the temperature is maintained in the middle of cooling after high-temperature heat treatment.

[Effect]

The phenomenon of gettering is caused by an internal defect layer acting as a preferential precipitation nucleus for heavy metal impurities, resulting in a defect-free layer (DZ).
zone) layer: 10 to 20 μm from the surface as standard
It removes heavy metal impurities from

In this case, it is known that Fe itself forms precipitates (FeSi2) even in the DZ layer, even if it is not in the internal defect layer.

Therefore, in order to getter Fe, it is necessary to set a gettering temperature that does not cause Fe to precipitate within the DZ layer, but allows Fe to precipitate in the internal defect layer.

For this purpose, it is necessary to accurately know the temperature at which Fe forms a precipitate.・The inventors conducted an experiment and found that 800
It has become clear that Fe forms precipitates at temperatures below .degree. Therefore, if gettering heat treatment is performed at a temperature of 800"C or lower, Fe will precipitate, whereas if heat treatment is performed at a temperature of 800"C or higher, gettering will occur in the internal defect layer without causing Fe precipitation in the DZ layer. can do.

On the other hand, it is known that Fe precipitates decompose at temperatures above 900°C (Reference: Etienne G.

Colas, E, R, Wwber and S, Ha.
hn: Mat, Res, Soc.

Symp, Proc, Vol, 71. p, 13
．． 1986). Therefore, if gettering is performed at a temperature of 900° C. or lower, there is a risk that decomposed Fe will precipitate in the DZ layer in a subsequent process. The inventors have experimentally determined that 100
It was confirmed that the influence of Fe precipitate decomposition is small if the temperature is 0° C. or lower. Therefore, the heat treatment temperature is suitably 800°C or more and less than 1000°C. Furthermore, if the heat treatment time is short, Fe will not diffuse into the internal defect layer and there will be no gettering effect, so a heat treatment time of 10 minutes or more is required.

In the method of the second aspect, since the Fe gettering process is performed only once, there is an advantage that the wafer processing step can be shortened.

Once the wafer is cooled, Fe precipitates are generated, so it is necessary to carry out gettering treatment for Fe or the like during cooling after the high-temperature heat treatment.

Hereinafter, the present invention will be explained in detail with reference to Examples.

〔Example〕

(a) B-doped p-type CZ silicon substrate (b) With or without intrinsic gettering DZ layer thickness 10 μm Internal defect density 5 x 10'cm-'' (c) Fe contamination treatment 60% HNO, solution ([Fel = (d) Fe diffusion treatment 11. Fe is uniformly diffused into the silicon substrate under N2 gas atmosphere at 50° C. for 30 minutes.

(e) Isothermal heat treatment 1000°C, 10 minutes: 900°C, 10 minutes 2850°C, 1
0 minute: 800° C., 10 minutes Near 00° C., 10 minutes The heat treatment patterns of (d) and (e) are shown in FIG.

FIG. 1 shows the Fe concentration measured with the deep 1 level concentration Cm-'' produced by Fe using the CDLTS method with respect to the heat treatment temperature of a sample without intrinsic gettering heat treatment.

When the heat treatment temperature is 900℃ or higher, the Fe concentration is approximately 1.5x.
1O "cm-", and it can be seen that at this concentration, Fe is dissolved in Si to form a total amount of deep 1 level. On the other hand, heat treatment at 800° C. or lower reduces the Fe concentration by one order of magnitude. This is due to Fe precipitation, deep 1e
This shows that the amount of Fe that forms vel is decreasing.

-・- in Fig. 2 is the case where the treatment shown in the chart shown in Fig. 3 is applied to a sample that has been previously subjected to intrinsic gettering heat treatment, that is, at 1150°C.
, shows the Fe concentration when FeO gettering heat treatment (T''C 110 minutes) is performed after heat treatment for 30 minutes.

Moreover, -0- in the same figure shows the Fe concentration when the heat treatment shown in the chart of FIG. 3 is performed without the usual IG heat treatment. It can be seen that gettering of Fe occurs in the temperature range of 800-1000°C.

Moreover, it can be seen that the gettering effect is greater in the case of the present invention in which Fe is gettered to the oxygen precipitates, since there is a difference in Fe concentration depending on whether or not the usual IG heat treatment is performed.

〔Effect of the invention〕

As explained above, according to the present invention, precipitation of heavy metals in the DZ1 can be prevented and heavy metals can be efficiently gettered, so that junction leakage current of sources/drains of DRAMs, photodiodes of CCDs, etc. can be reduced. , yield increases.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between heat treatment temperature and Fe concentration without normal IG heat treatment, FIG. 2 is a graph similar to FIG. 1, and a graph showing changes in Fe concentration with and without normal IG heat treatment, FIG. 3 is a graph showing the heat treatment charts of FIGS. 1 and 2. Temperature temperature Fe f)
Power/Rimoku□5; shiyIWl-,,J:3Fe(ngeichi, tarinfu. 2nd prisoner Fe dirt oh) - @Mepiri pattern figure 3

Claims (1)

[Claims] 1. In the intrinsic gettering method of forming an internal defect layer due to oxygen precipitates in a semiconductor wafer, at least during the cooling of the wafer after the final heat treatment of the high-temperature heat treatment of 900° C. or higher in the device process. So, 800
An intrinsic gettering method characterized by performing heat treatment at a temperature of 1000°C or higher for 10 minutes or more. 2. In the intrinsic gettering method that forms an internal defect layer due to oxygen precipitates in a semiconductor wafer, heat treatment at a temperature of 800°C or more and less than 1000°C is performed only after the final high-temperature heat treatment of 900°C or more in the device process. Intrinsic, which is characterized by being performed for 10 minutes or more
Gettering method. 3. The intrinsic gettering method according to claim 1 or 2, wherein the heat treatment at 800° C. or more and less than 1000° C. is performed as isothermal heat treatment.