JPS6276714A - Silicon wafer - Google Patents

Abstract

PURPOSE:To obtain high impurity absorbing effect by forming an internal defect due to oxygen precipitation in the position deeper than the active region of the front surface of a wafer and forming a transfer assembly on the back surface of the wafer. CONSTITUTION:An internal defect is formed in a region by reducing the density of oxygen precipitation from 10<6> pieces/cm<3> in a region of a wafer surface layer 1mum and increasing the density of the precipitation in the region deeper than the wafer surface 1mum to become 10<6> pieces/cm<3> or more. Further, a transfer assembly having 10<6> pieces/cm<3> of more of density and 0.5mum or larger of size is introduced to the back surface of the wafer. Thus, the internal defect disposed in the region deeper than the position 1mum below the wafer surface, i.e., an electric active region and the impurity absorbing effect by the transfer assembly of the wafer back surface are added to obtain remarkably high impurity absorbing effect.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to silicon wafers, and more particularly to silicon wafers that can significantly reduce contamination on the wafer surface.

``Prior Art'' One of the problems in the silicon semiconductor manufacturing process is a decrease in yield due to impurity contamination. In this case, the electrically active region in many semiconductor devices is approximately 1 μm from the wafer surface.
If the contaminants on the wafer surface are diffused into the inside of the wafer or to the back surface of the wafer and retained there, the electrically active region on the wafer surface can be rescued.

Therefore, in order to rescue the active region on the wafer surface, various gettering techniques have been developed in which defects are introduced inside the silicon wafer or on the backside of the silicon wafer, thereby purifying the active region on the wafer surface (a layer approximately 1 um thick on the surface). has been done.

"Problems to be Solved by the Invention" However, in the conventional gettering technology, there are two separate technologies: one for introducing defects inside the wafer and the other for introducing defects on the backside of the wafer. Although there are gettering technologies, the reality is that no consideration has been given to the synergistic effects of the two gettering technologies.

This invention has been made in view of the above-mentioned facts, and provides a silicon wafer that can synergistically utilize the effects of both gettering techniques and thereby significantly reduce impurity contamination of the silicon wafer surface active layer. The purpose is to

"Means for Solving the Problems" In order to solve the above-mentioned problems, the present invention aims to solve the above-mentioned problems by reducing the density of oxygen precipitates to 1 μm in the wafer surface layer.
am', and the density of oxygen precipitates is 108/cff13 or more in a region deeper than 1 μm below the wafer surface, and 108/cff13 or more on the back surface of the wafer.
Dislocation aggregates with a density of 12 or more and a size of 0.5 μm or more are introduced.

"Operation" Internal defects located deeper than 1 μm below the wafer surface,
This is combined with the impurity absorption effect due to the dislocation aggregates on the back surface of the wafer, resulting in an extremely high impurity absorption effect.

"Example" Examples of the present invention will be described below.

First, we conducted experiments using various combinations of conditions to determine what kind of impurity-absorbing active sites should be introduced on the backside of the wafer to match the internal impurity-absorbing active sites and take advantage of the impurity-absorbing effects of both.

As a result of this experiment, it was found that introducing dislocation aggregates into the back surface of the wafer provides the most stable active points.

Therefore, defects caused by oxides are introduced inside the wafer through a combination heat treatment, and then micro-cracks are generated by spraying fine particle powder onto the backside of the wafer at room temperature, and then microcracks are generated on the backside of the wafer by heating to over 650°C. A wafer with a high density of dislocation aggregates introduced was prepared, and the following experiments were conducted to examine the effect of impurity gettering while changing various conditions on this wafer.

(1) First, we investigated the difference in gettering effect between when there is a dislocation aggregate on the back surface and when there is no dislocation aggregate.

First, in order to introduce defects caused by oxides into the silicon wafer, it was heat treated at 1100°C for 2.5 hours, then heated at 900°C for 2 hours, and then heated at 1050°C.
The mixture was heated for 10 hours. Then, in order to investigate the state of defect introduction in the silicon wafer that had undergone the above heat treatment, a part of the silicon wafer was cleaved, selective etching was performed on the cross section of this cleavage, and the state of the cross section after etching was examined using an optical microscope. . As a result, no defects were observed up to a depth of 21 μm from the surface, but 2.4×10” defects/am’ were observed at positions deeper than 21 μm. When observed using an electron microscope, no defects were observed at a depth of 1 μm from the wafer surface.In this case, the density of defects that could be observed using a transmission electron microscope was approximately 108 defects/ca+'. Since this is the limit, it can be seen that the density of defects at a position up to 1 μm from the surface of the silicon wafer is less than io@1llW/am'.

Next, fine silica particles were struck at high speed to create dents on the back surface of the wafer, thereby creating microcracks. Then, by heating this wafer to 950° C., high-density dislocation aggregates were generated from the microcracks. The size of the dislocation aggregates generated in this case is 0.5 μm or more.The measurement results of the gettering effect of the wafer prepared as described above and the wafer having no dislocation aggregates on the back surface will be described below.

In this case, measurements were taken to measure the oxide film breakdown voltage and minority carrier lifetime, which sensitively reflect the gettering effect.

First, in order to perform measurements, the wafer surface is oxidized and AI
(Aluminum) electrodes were attached to create a MOS capacitor. Then, the applied voltage value at the time when the leakage current value reaches 1G-5A when voltage is applied through the electrode is defined as the oxide film breakdown voltage, and the rate of capacitance increase when the applied voltage is reversed is determined. The lifetime was measured from the transient characteristics).

The measurement results are shown in Table 1.

As can be seen from Table 1, wafers with dislocation aggregates on the back side have a higher oxide film breakdown voltage and longer lifetime than wafers without dislocation aggregates on the back side, and gettering It was confirmed that the effect was good.

The difference in gettering effect when the degree of introduction of dislocation aggregates on the back surface is changed will be explained.

First, heat treatment to create internal defects was performed at 1100℃ for 2 hours.
．． After heating for 5 hours, the temperature was raised from 550°C to 950°C at a rate of 1°C per minute, and after being held at 950°C for 10 minutes, the temperature was lowered. As a result, no defects were observed in the 1 μm region of the wafer surface layer when observed using a transmission electron microscope, but about 106 defects/defects were observed in the region deeper than 1 μm below the surface.
cm3 of oxide was observed.

Next, in order to create samples with different dislocation aggregate densities on the backside of the wafer, two types of wafers were created in which the fine-particle silica was applied for different times. Then, these wafers were
When heated to 0°C to generate dislocation aggregates on the backside, one wafer had a density of 105/am'';
In the other wafer, dislocation aggregates were generated at a density of 107 pieces/cm2. In this case, the size of the dislocation aggregates was 0.5 μm or more in both cases. The results of measuring the oxide film breakdown voltage of these wafers are shown in Table 2, and as can be seen from this table, the density of dislocation aggregates is 10
It was observed that when the density was 7 pieces/am', the gettering effect was remarkable and the oxide film breakdown voltage was high, but when the density was 10 5 pieces/cm 2 , the breakdown voltage was low and the gettering effect was low. In this case, as a result of further experiments, it was found that the gettering effect becomes obsolete when the density of dislocation aggregates on the back surface of the wafer becomes equal to or higher than lO'(Ii!I/c+n').

Here, to summarize the experimental results of (1) and (2) above,
Even if defects are introduced inside the wafer, the gettering effect is better if dislocation aggregates are introduced to the back surface, and the size of the dislocation aggregates introduced to the back surface is 0.
The necessary conditions for obtaining a good gettering effect are that the diameter is 5 μm or more and the density is 10 6 pieces/Cm 2 or more.

(3) Next, the relationship between the distribution of internal defects and the gettering effect will be explained.

First, for a wafer in which there are approximately 10I0/am' or more of oxides that can be observed with a transmission electron microscope in a region of 1 μm from the bottom of the wafer surface, the number of dislocation aggregates on the back surface is 7×105fJJ/
Two types of samples were created, one with a density of cm2 and one with a density of 10"f[!II/cm2 or more, and
There are no defects in the area 20 μm below the wafer surface, and oxides exist in the area below that at a density similar to that of the sample above.
In addition, samples were prepared in which the density of dislocation aggregates on the back surface was 106 pieces/cm" or higher.The oxide film breakdown voltage of these samples was measured, and the results are shown in Table 3.As can be seen from this table, , internal defects are near the surface (1 μm below the surface)
), the oxide film breakdown voltage is lower than that with no defects near the surface, and the gettering effect is inferior. In addition, as a result of repeated experiments, even if there is a defect 1 μm below the surface, the gettering effect is good as long as there is no defect 1 μm below the surface.
It was confirmed that wafers with no defects in the region up to the point where the gettering effect is better for wafers with defects only in the deeper region.

Furthermore, it has been determined that if there are oxygen precipitates with a density of 106 particles/cm3 or more inside the wafer, the gettering effect due to internal defects is sufficient.

To summarize the above measurement results, the density of oxygen precipitates is less than 1 μm/cm3 (unobservable with a transmission electron microscope) in the region 1 μm below the surface of the wafer, and the density of oxygen precipitates is less than 108 cm3 in the region deeper than 1 μm below the surface. The conditions for obtaining a good gettering effect are that the density is 106 pieces/cm3 or more, and that 106 dislocation aggregates with a size of 0.5 μm or more are introduced on the back surface of the wafer at a density of 7 cm2 or more. .

"Effects of the Invention" As explained above, according to the present invention, the density of oxygen precipitates is 106 particles/cm3 in a 1 μm area of the wafer surface layer.
In addition, the density of oxygen precipitates should be 106/cm3 or more in the region deeper than lJ, Lm below the wafer surface, and the density of oxygen precipitates should be 106/cm2 or more on the back surface of the wafer, and the size should be 0. Since dislocation aggregates of 5 μm or more are introduced, the Geckling effects both inside the wafer and on the back surface of the wafer are synergistically utilized, thereby providing the advantage of significantly reducing impurity contamination of the silicon wafer surface active layer.

Claims (1)

[Claims] In the 1 μm area of the wafer surface layer, the density of oxygen precipitates is 10
Less than ^6 pieces/cm^3, and 1μ below the wafer surface
In the region deeper than m, the density of oxygen precipitates is 10^6/c
m^3 or more, and 10^ on the back side of the wafer.
A silicon wafer characterized in that dislocation aggregates having a density of 6 pieces/cm^2 or more and a size of 0.5 μm or more are introduced.