JPH02114534A - Silicon wafer and manufacture thereof - Google Patents

Abstract

PURPOSE:To enhance a mechanical strength in a peripheral part of a silicon wafer and to reduce an occurrence of a dislocation by a method wherein nitrogen is added to the peripheral part of the water including a chamfered part. CONSTITUTION:Nitrogen whose fixing power of a dislocation is large is diffused to and is contained in a peripheral part of a wafer where a working strain remains and whose thermal stress is large, i.e., only a peripheral part of a silicon water including at least a chamfered part. For example, nitrogen is contained in a peripheral part 11 1mm in width including a chamfered part of a silicon wafer 10; a concentration of N2 at a side end of the wafer is about 10a/cm<3>; the concentration of N2 at the inside 1mm in width from the side end is about 10a/cm<3>. A dislocation can be fixed sufficiently at this concentration of N2. Thereby, a mechanical strength of the silicon wafer is enhanced; the dislocation is caused little; reliability and quality of a semiconductor device such as an LSI, a VSLI or the like can be enhanced effectively.

Description

[Detailed Description of the Invention] [Summary] Regarding the structure of a silicon wafer, the purpose of this invention is to increase the mechanical strength of the wafer periphery and reduce the occurrence of dislocations. It has a structure in which nitrogen is added, and its manufacturing method involves grinding a silicon ingot into a cylindrical shape, then heat-treating it to diffuse nitrogen onto the surface of the silicon ingot, and then
It is characterized by being formed into silicon wafers by slicing.

[Industrial application field]

The present invention relates to the construction of silicon wafers.

Semiconductor devices such as LSI are made of silicon wafers (Silicon wafers).
Con wafers are made by forming a large number of fine elements on the surface of the wafer, but as such wafers have become larger in diameter, the occurrence of crystal dislocations due to a decrease in their mechanical strength has become a problem, and countermeasures are needed. has been done.

[Prior art and problems to be solved by the invention] When forming semiconductor devices on silicon wafers, one of the basic manufacturing techniques is wafer heat treatment.
It is said that the quality of the 5i02 film affects the device characteristics of the MO3FET element that constitutes the I device.
Heat treatment at about 1000° C. for 2 hours is required to form an S+02 film of 0 people. Furthermore, impurity diffusion into the wafer is an important factor that determines device characteristics, and it also
Processing is carried out at a high temperature of 00°C.

However, when the above-described high-temperature heat treatment is performed, crystal dislocations (for example, appearing as slip lines) are introduced into the wafer, and FIG. 4 is a diagram showing the dislocations of the conventional wafer. The figure shows a conventional wafer heated to 1150°C.
This is an X-ray topographic image of the occurrence of dislocations after heat treatment for 910 minutes and rapid cooling.
It is known that dislocations cause deterioration of the withstand voltage of OS FETs, etc., and as shown in FIG. 4, dislocations mainly occur around the wafer, and devices in the peripheral area tend to be defective.

Conventionally, methods have been considered to prevent the occurrence of such dislocations, one of which is to reduce the thermal stress within the wafer surface that occurs when the temperature is raised and lowered during wafer heat treatment, and the other is to reduce the thermal stress within the wafer surface. Increasing this mechanical strength by increasing the mechanical strength has the effect of suppressing the generation and proliferation of dislocations. Currently, the former method is exclusively used to reduce thermal stress within the wafer surface, but in order to reduce thermal stress, it is sufficient to equalize the temperature within the wafer. A method is used to slow down the rate of temperature rise and fall by slowly loading and unloading. but,
When it comes to large-diameter wafers with a diameter of 125 mm or more, it has become difficult to handle them alone (“MO3LS
I Manufacturing Technology” Nikkei McGraw-Hill, pp. 55-56).

Therefore, a ramping method has been adopted in which the wafer is inserted into a furnace at a low temperature (800 to 900°C) and then the temperature of the furnace is raised. It has the disadvantage that oxygen atoms tend to precipitate, and this oxygen precipitate is the main cause of crystal defects.

Therefore, the inventor investigated the latter method of preventing dislocations by increasing the mechanical strength of the wafer.

First, the following three methods are known as methods for increasing the mechanical strength of this silicon crystal wafer.

fa) Oxygen present between crystal lattices has the effect of fixing dislocations, so a method of growing a crystal containing a high concentration of interstitial oxygen (e.g. 30 ppma or more) fbl Doping Ge (germanium) into a silicon crystal. Proceedings of the Japan Society of Applied Physics” 1983 (Spring) pp. 662) Method (C) Doping N2 (nitrogen) into silicon crystal (
Applied Physics 51 (11), 1982. pp125
2) method, but among these methods, method (a) has the disadvantage that oxygen tends to precipitate when oxygen is contained in a high concentration, so currently, an appropriate oxygen concentration is selected empirically and the appropriate amount Therefore, a very strong effect cannot be expected, and therefore dislocations around the wafer cannot be removed. (In the bJ method, doped Ge segregates during crystal growth and the Ge concentration is unevenly distributed in the silicon crystal.
Required Ge? M degree cannot be obtained uniformly (Jour, El
electrochem, Soc, 134.3 (198
(see 7)), there is a drawback that dislocations are still likely to occur. (Method C1 is a method of growing a crystal while doping N2 during crystal growth. The dislocation fixing force due to N2 is about 100 times stronger than the dislocation fixing force due to oxygen at the same concentration. , this doping method results in uniform doping. However, the method of doping N2 while growing silicon crystals using the CZ method (pulling method) tends to cause polycrystallization.
In this respect, it is difficult to put it into practical use.

On the other hand, it is clear from FIG. 4 that the dislocations generated in the wafer are concentrated around the wafer, and this is thought to be due to the thermal stress distribution acting on the wafer during heat treatment and the processing strain remaining around the wafer. Among them, a distribution diagram of the thermal stress distribution obtained by calculation is shown in FIG. The negative sign in the figure indicates compressive stress, and the positive sign indicates tensile stress. As shown in the attached figure on the right, R is the radius, σ is the stress in the rotational direction, and σ
is the radial stress. From Figure 5, the area around the wafer (r
/ R = 1) is the largest, and this is due to the rapid change in the wafer shape.

By the way, silicon shape diagrams obtained by processing a silicon ingot into a wafer are shown in Figures 6 fa to el, where (a) shows an ingot crystal-grown by the CZ method, and (b) shows a cylindrical shape of the ingot. An ingot ground into a shape,
Figure (C) shows a rough wafer that has been sliced, Figure +d) shows a rough wafer whose periphery has been chamfered, and Figure (e) shows a mirror-polished wafer. In this way, the wafer surface is mirror polished after chamfering the wafer periphery to prevent damage to the wafer surface.
Processing distortion remains in the chamfered portion around this area, and it is extremely difficult to remove all of this processing distortion. Therefore, it is difficult to eliminate stress concentration around the wafer, and it is almost impossible to eliminate dislocations around the wafer.

Based on such consideration, the present invention proposes a structure of a silicon wafer for the purpose of increasing the mechanical strength of the periphery of the wafer and reducing the occurrence of dislocations.

[Means to solve the problem]

This problem can be solved by using a silicon wafer in which nitrogen is added to the periphery of the silicon wafer, including at least the chamfered portion, and the method for manufacturing it involves grinding a silicon ingot into a cylindrical shape and then heat-treating it to form a silicon ingot. It is characterized by diffusing nitrogen onto the surface and then slicing it into silicon wafers.

[For production]

That is, the present invention diffuses and contains nitrogen, which has a strong dislocation fixing force, only in the peripheral area of the wafer where processing strain remains and the thermal stress is large, that is, in the peripheral area of the silicon wafer including at least the chamfered part, This increases the mechanical strength of this part.

〔Example〕

Examples will be described below with reference to the drawings.

FIG. 1 shows a cross-sectional view of a silicon wafer according to the present invention. Nitrogen is contained in the peripheral portion 11 of the silicon wafer 10 having a width 11 including the chamfered portion, and the N2 concentration at the side edge of the wafer is approximately 10 a/cffl.

The N2 concentration inside the width IB from the side edge is about 10a/-. Sufficient fixation of dislocations can be obtained with this level of N2 concentration. Note that the width of the chamfered end is usually approximately 500 mm.
Since the width is μm, nitrogen addition with a width of l*** is sufficient.

Figure 2 is an X-ray topographic image of the occurrence of dislocations after the wafer according to the present invention was heat-treated in oxygen at 1150°C for 10 minutes and then rapidly cooled. A significant reduction in dislocations is evident.

By the way, the diffusion constant of N2 into silicon crystal at high temperatures is extremely large, for example, at a heating temperature of 1200°C, it is approximately 1.
O-6 crl/sec (“Proceedings of the Japan Society of Applied Physics” 19
87 (Autumn)-1, pp. 241). Therefore, 12
When heat treated at 00℃ for 1 hour, nitrogen becomes 2 atoms = 2
f'5I = 1 However, D: Diffusion constant of N2: t: It is possible to diffuse to a depth of diffusion time.

Next, FIG. 3 (al to (dl) shows step-by-step sectional views of the manufacturing method according to the present invention. First, FIG. 3 (al is CZ
FIG. 2 is a cross-sectional view of a cylindrical ingot obtained by grinding a silicon ingot grown by the method.

Next, ultrasonic cleaning is performed sequentially using trichlene, acetone, and alcohol, followed by water washing, etching with an aqueous solution (fluorine + nitric acid), and finally washing with water again.

This is a cleaning process that removes surface impurities and is an important process for maintaining crystal quality.

Next, as shown in Figure 3 (bl), nitrogen is diffused from the surface by heat treatment for 1 hour at 1200°C to form a nitrogen-added layer 12, and then quickly cooled to room temperature. This is to prevent the spread of
Immediately after taking it out of the heating furnace, it is cooled while blowing N2 gas. This cooling is also an important process from the viewpoint of manufacturing.

The wafer is then sliced to form rough wafers with angular edges, as shown in FIG. 3(C). The left side of the figure is a plan view, and the right side is a sectional view.

Thereafter, as shown in FIG. 3Fdl, the end portions are chamfered and rounded, and the surface is mirror polished to finish the silicon wafer according to the present invention.

The silicon wafer according to the present invention can be formed by such a manufacturing method, and thus the silicon wafer according to the present invention is a wafer with few occurrences of dislocations and extremely improved mechanical strength.

Note that the present invention is naturally applicable not only to silicon wafers made from ingots grown by the CZ method, but also to silicon wafers made from ingots grown by the FZ method (zone growth method).

[Brief explanation of drawings]

FIG. 1 is a silicon ribbon wafer according to the present invention. FIG. 2 is a diagram showing dislocations of the wafer according to the present invention. FIG. 3 is a cross-sectional view of the manufacturing method according to the present invention in the order of steps. Fig. 5 is a diagram showing the distribution of thermal stress, and Fig. 6 is a diagram showing the shape of silicon as it is processed from an ingot to a wafer. In the figure, 10 indicates the peripheral portion of the silicon wafer 11, and 12 indicates the nitrogen-added layer. [Effects of the Invention] As is clear from the above explanation, the silicon wafer according to the present invention has increased mechanical strength, so that fewer dislocations occur, and the reliability of semiconductor devices such as LSI and VLSI is improved.
This has a remarkable effect on improving quality. Figure 1 8E4. Moat 2j Unihab Rotation 41, Wood TG 2nd figure - Vermilion wafer / Irz Buzaiba T (f8 4th figure right 1. 3 How to make sE tile if vinegar side ■ Figure 3!'! N〃-Imafu episode 5th figure

Claims (2)

[Claims] (1) A silicon wafer characterized in that nitrogen is added to the peripheral portion of the silicon wafer including at least the chamfered portion. (2) A method for manufacturing a silicon wafer, which comprises: grinding a silicon ingot into a cylindrical shape, heat-treating it to diffuse nitrogen onto the surface of the silicon ingot, and then slicing it to form a silicon wafer.