JPS58110496A - Silicon crystal - Google Patents

Abstract

PURPOSE:To provide a silicon crystal which provides semiconductor devices having excellent electrical characteristics by specifying the concn. of oxygen to be contained therein. CONSTITUTION:The concn. of oxygen contained in a silicon crystal is set at (1.6+ or -0.1)X10<3>cm<-3>. The semiconductor device using the substrate produced by slicing this silicon crystal into a wafer has less crystal defects in element forming areas and improves the electrical characteristics of semiconductor devices, for example, a longer time for holding storage of storage devices.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Technical division of the invention The present invention relates to silicon crystals forming semiconductor elements, and particularly to silicon crystal materials from which semiconductor devices with excellent electrical characteristics can be obtained.

(No Technology Background In recent years, semiconductor devices have become smaller and more integrated, and IC
, LSI, and VLSI, the quality of semiconductor crystals has become increasingly important.

In particular, the CZ (CZ) method, which is the mainstream method for producing silicon (St) crystals, is a
11(0) is an impurity that is mixed with other impurities (C) and iron (
It is also difficult to avoid contamination with heavy metals such as F.).

Moreover, in the case of heavy metals, they often get mixed in during the silicon crystal creation process and also during the wafer processing process for silicon wafers.If these impurities are included, crystal defects! This induces stacking faults, dislocations, etc., resulting in a decrease in the electrical characteristics of the semiconductor device, such as an increase in junction leakage current and a decrease in memory retention time.

(3) Prior art and problems Therefore, studies have been made to reduce crystal defects as much as possible, such as by forming a layer of highly concentrated impurities (e.g., phosphorus) on the back side of a silicon wafer, or by applying a layer of silicon nitride to the surface. A defect layer is created on the back surface by laser irradiation, and gettering (g@t t ring), which intentionally absorbs impurities on the back surface, is used to create a gettering effect on the surface of the silicon wafer on which semiconductor devices are formed. A method for reducing crystal defects has also been proposed, as well as a heat treatment method in the wafer state for creating a defect-free layer (denuded zone) on the surface of a silicon wafer. The formation of a nude zone is rather the formation of crystal defects based on the precipitation of acid holes on the inner surface, which getter heavy metals (intrinsic g@tte).
ring) effect. This is thought to be related to the amount of oxygen contained in the silicon crystal.

(Purpose of the Invention The present invention focuses on the amount of oxygen contained, and in order to improve the electrical characteristics of a semiconductor element, the optimum oxygen concentration in a silicon crystal has been investigated.

(5) Structure of the invention As a result, the oxygen concentration is (1,6±0.1) x 10”
It has been found that a silicon crystal having a concentration of I11! is the most suitable for semiconductor devices. Therefore, it is proposed that a silicon crystal having such a concentration of I11! be used as a substrate for a semiconductor device. It is something.

(6) Examples of the invention To explain in detail below, the cabinet is made of silicon! The horizontal axis is the oxygen concentration COi contained in the crystal, and the lifetime [ffJ
A data chart with the vertical axis shown. As is well known, Generation Life@Time is
The iIP life time until electrons and holes generated in the crystal recombine and disappear is related to impurities and defects, and the longer they survive, the better the crystal purity.

Therefore, in general, the lifetime should decrease as the impurity concentration increases, but according to the results of the study, the highest lifetime value is obtained when the nest concentration is l-6X 10%l-'' as shown in the figure. All samples were heated at 1,000 °C in an inert gas, taking into consideration the heat treatment conditions for semiconductor devices.
It was heated for several tens of minutes at ~1100°C, and this is considered to have a large influence. However, the surface of semiconductor devices may become ridged at the above temperatures, and impurity diffusion may occur.
Since heat treatment is performed at the time of ion implantation, the samples were heat-released and salted under conditions similar to #4.

In the figure, the aI elementary concentration region of 1.5 x lO"ai"" or less A*1.5~L7 Assuming that the concentration region is C, the oxygen concentration in region A is low, so there are few crystal defects due to oxygen precipitation, which reduces the number of heavy metal getters, and it is inferred that the presence of heavy metals shortens the lifetime. In addition, in region C, the oxygen content is high and crystal defects occur near the surface due to oxygen precipitation, shortening the lifetime9, while in region B, an appropriate amount of crystal defects occur due to an appropriate oxygen concentration, which are caused by heavy metals. In addition to the gettering, oxygen is evaporated from the sample surface by the above-mentioned thermal ringing, which seems to result in fewer crystal defects and a longer lifetime.

Therefore, unlike other trace impurities, the amount of supersaturated oxygen contained in silicon crystals is due to diffusion and release due to heat treatment.
Alternatively, since the element formation region on the surface becomes a defect-free layer by precipitation and has the effect of gettering impurities such as heavy metals in the internal defect-free region, it is preferable that the element be included to some extent.

Such limited oxygen content adjustment can be carried out by changing the crystal growth conditions, the shape of the quartz crucible, the rotation speed of the cypress and crucible, etc. when producing a silicon single crystal using the C2 method.

Further, the oxygen content can be measured by infrared absorption spectroscopy, and the above measurement values are based thereon.

Incidentally, carbon-containing lids can be obtained by the same measuring method, but it is better to have as little carbon as possible, and the above sample should be less than the value detected by the same measuring method, that is, less than 1 × 10 mu 1. there was.

(7) Effects of the Invention As is clear from the above explanation, the present invention is a proposal for regulating the oxygen concentration of silicon crystals forming semiconductor elements within a certain range, and that such silicon crystals can be cut into wafers and used. Therefore, a semiconductor device using this as a substrate has fewer crystal defects in the element formation region, which greatly contributes to improving the electrical characteristics of the semiconductor device, for example, by increasing the memory retention time of the storage element.

[Brief explanation of the drawing]

The figure is a chart showing the relationship between oxygen concentration and lifetime. In the figure, area B is (1,6±0.1) x 10”tm-
” indicates the range. 593-

Claims (1)

[Claims] The oxygen concentration is (1,6±Q,l) X IQ"ar
A silicon crystal that is characterized by the following.