JPH0684856A - Semiconductor substrate and manufacturing method thereof - Google Patents

Abstract

(57) [Summary] [Object] To provide a semiconductor substrate and a manufacturing method thereof which do not bring dust contamination from the semiconductor substrate into a semiconductor device manufacturing process requiring ultra-cleanliness and do not adversely affect product characteristics. [Structure] The entire surface of the semiconductor substrate including the side surfaces is mirror-finished. To manufacture this semiconductor substrate, the end surface of the etched semiconductor substrate is rotated and brought into contact with a mirror polishing member provided on a flexible disk having a surface parallel to this surface, thereby forming a mirror surface of the end surface. The step of performing polishing and placing the rotation axis of the flexible disk parallel to and offset from the semiconductor substrate, and applying pressure toward the center of the semiconductor substrate, the flexible disk is bent. The method includes the steps of bending and performing mirror-polishing on the chamfered surface, mirror-polishing the front surface of the semiconductor substrate, and mirror-polishing the back surface of the semiconductor substrate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is used in VLSIs,
The present invention relates to a semiconductor substrate made of silicon, gallium arsenide or the like and a method for manufacturing the same.

[0002]

2. Description of the Related Art In manufacturing highly integrated semiconductor devices such as VLSI, the amount of dust has a great influence on the yield. For this reason, a semiconductor substrate (wafer) used for manufacturing a semiconductor device requires dust-free super cleanliness.
In order to obtain such ultra-cleanliness, the surface finish is usually a mirror surface on one side and an etched surface on the other side. In addition, chamfering (beveling) is added to the edge to prevent cracking and dust on the wafer. Further, it has been proposed that the edge portion be mirror-finished (for example, Japanese Patent Application Nos. 59-58827 and 59-107520).

FIG. 8 shows a normal semiconductor substrate processing step.

As shown in FIG. 8, first, the outer peripheral surface of the silicon ingot 1 is ground using a grindstone 2 (see FIG. 8).
(1)) Next, after confirming the crystal orientation, the rotary grindstone 3 is traversed and ground to obtain an orientation flat 1
a is formed (FIG. 8 (2)). Next, the whole is adhered and fixed to a stand (not shown) with resin 4 (FIG. 8 (3)), and the silicon ingot 1 is thinly sliced using the hollow disk-shaped diamond blade 5 to obtain the wafer 6 (FIG. 8
(4)). At this time, as described above, since the silicon ingot is fixed to the table by adhesion, the sliced wafer 6 does not come apart.

This wafer 6 is fixed to the rotary chuck 12, and the edges of the side end faces are removed by a rotary grindstone to beveled for rounding (FIG. 8 (5)). Subsequently, the wafer 6 is set on the carrier 11 of the lapping apparatus 10, and the surface is polished by the complicated rotation operation by the planetary motion mechanism (FIG. 8 (6)).

Next, etching is performed in the etching solution 13 (FIG. 8 (7)), and the wafer 6 is bonded on the plate 14 with a solder or the like with the surface to be mirror-finished facing up (FIG. 8).
(8)), the plate 14 is inverted and placed so that the mirror-finished surface comes into contact with the upper surface of the turntable 15, and the plate 14 and the turntable 15 are rotated to mirror-finish one surface of the wafer 6 (FIG. 8).
(9)).

By the way, semiconductor elements typified by VLSI devices have been further improved in performance and density, and the manufacturing process of such semiconductor elements is classified into Class 1
Ultra cleanliness such as 0 is required. Therefore, the same ultra-cleaning is required for all chemicals, water, gas, etc. to be used, and the semiconductor substrate itself in which the element is built also needs the same high degree of cleanliness.

Main methods for evaluating the surface cleanliness of the semiconductor substrate include an element identification method by various instrumental analysis and a dust detection method using reflected light when light is projected on the semiconductor substrate surface. However, because of its simplicity and high performance,
The latter is often used on a daily basis.

From the principle, dust detection by reflected light (hereinafter referred to as oblique light inspection) requires that the surface be a perfect mirror surface, and from this viewpoint, the substrate is made a mirror surface. Regarding this mirror surface condition, "Appearance inspection of silicon mirror surface wafer" was established in JIS H0614, "In a dark room with a circumference of 10 lux, a parallel light beam of 3000 lux or more was applied to the sample surface, and the light flux at that location was set to 1". It is defined as the inspection standard that "the lumen is adjusted and the sample surface is observed with the naked eye."

The highest standard of dust on the mirror surface determined by this method is that the number of dust particles of 0.3 μm or more is 10 / substrate or less.

In the manufacturing process of a semiconductor device, a substrate that has been rigorously inspected by a substrate manufacturer is enclosed in a high-quality container designed to maintain cleanliness, and delivered. Generally, 25 sheets are distributed to one cassette.

Dust adhering to the surface of the substrate is suspended in the liquid by the cleaning chemical liquid used in the manufacturing process, and discarded by washing with water. However, when the amount of dust on the surface of the substrate is large, reverse contamination occurs in which the suspended dust adheres to the surface of the substrate again. Therefore, in order to prevent the reverse contamination, the dust standard of the substrate input to the semiconductor device manufacturing process is strictly controlled.

[0013]

However, when the dust standard is strictly controlled, the dust inspection by the oblique light method described above requires that the background be a perfect mirror surface, but the back surface of the substrate is The inspection cannot be performed because the surface is an etched surface after lapping and has a roughness far from a mirror surface.

In addition, the inspection of the board must be carried out over ten or more items such as dimension inspection and appearance inspection.
All inspections are supposed to be performed on the front surface while supporting the back surface, and the vacuum chuck, stage, table, etc. will contact the back surface of the substrate each time the inspection is performed.
As the dust pollution increases, the impact causes the bumps on the back surface to collapse, increasing the dust generation.

Since there is no method for determining whether or not these dusts are attached, the dusts move from the substrate manufacturer to the semiconductor device manufacturer without any restrictions, which affects the yield of the semiconductor device manufacturer. There is a problem that it will end up.

On the semiconductor substrate, as shown in FIG.
Although there is a so-called diffusion substrate having a diffusion layer 6b on one surface, a diffusion substrate manufactured by a conventional method has a small crack 7 on its diffusion surface (rear surface) 6b, and thus is enclosed in a sealed case. During the transportation, the powder separates from the substrate and adheres to the mirror surface of the surface. This is usually counted as dust, but it is known that before encapsulation, 100 or less dusts are significantly increased to 500 to 1000 per substrate after transportation.

Further, when such a diffusion substrate is put into a manufacturing process, as shown in FIG. 10, when it passes through the first thermal process, a scraper peeled off from the back surface may adhere to the mirror surface of the front surface. In this case, phosphorus, which is an impurity, is diffused into the non-diffusion layer, especially when it adheres to the base P ⁺ layer or the collector N ⁻ layer, and I as an element characteristic is obtained.
There is a problem that many _CBO (leakage current between collector and base) defects occur.

The present invention has been made in order to solve the problems associated with the conventional semiconductor substrate described above, and does not introduce dust contamination from the semiconductor substrate into the semiconductor device manufacturing process that requires ultra-cleanliness. An object of the present invention is to provide a semiconductor substrate that does not adversely affect and a method for manufacturing the same.

[0019]

According to the semiconductor substrate of the present invention, there is provided a semiconductor substrate in which the entire surface including side surfaces is mirror-finished.

Further, according to the method of manufacturing a semiconductor substrate of the present invention, a step of slicing the semiconductor ingot with a blade, a step of performing a chamfering process for removing a corner of an end face of the sliced semiconductor substrate, A step of lapping the semiconductor substrate, a step of etching the whole,
A step of performing mirror-polishing of the end surface by rotating the mirror-polishing member, which is provided on a flexible disk having a surface parallel to this surface, to the end surface of the semiconductor substrate after etching; The rotation axis of the flexible disk is placed at a position parallel to and offset from the semiconductor substrate, and pressure is applied toward the center of the semiconductor substrate to bend the flexible disk to perform the chamfering process. It is characterized by including a step of performing mirror-polishing of the surface, a step of performing mirror-polishing of the surface of the semiconductor substrate, and a step of performing mirror-polishing of the back surface of the semiconductor substrate.

[0021]

In such a semiconductor substrate, in addition to the element-fabricated surface (front surface) of the semiconductor substrate being a perfect mirror surface, the side end surface and the back surface connected to this surface are also mirror surfaces equivalent to the surface. .

In the substrate in which all the surfaces are mirror-finished in this manner, it is possible to visually inspect the dust on the entire surface by the oblique light inspection method, so that the dust is not introduced into the element forming process. In addition, the amount of dust generated during handling in the inspection process and the semiconductor device manufacturing process is very small, and the yield is improved.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Some embodiments of the present invention will be described in detail below with reference to the drawings. (Embodiment 1) FIG. 1 is a sectional view showing a surface state of a semiconductor substrate 20 according to the present invention, and a vertical scale is enlarged for convenience of explanation.

As shown in the figure, the surface 2 of the substrate 20 is
1, the back surface 22, the side end surface 23, and the chamfer (bevel) surface 24 are all mirror surfaces.

FIG. 2 is a flow chart showing the main part of the semiconductor substrate manufacturing process according to the present invention. As shown in FIG. 2, the semiconductor substrate of the present invention has outer diameter grinding (step S101), orientation flat grinding (step S102), slicing (step S103),
Up to the beveling (step S104), the lapping (step S105), and the etching (step S106), the same process as the conventional process shown in FIG. 8 is performed. ) Is performed, and further front surface polishing (step S109) and back surface polishing (step S110) are performed.

FIG. 3 is a cross-sectional view showing a part of the characteristic part of the method for manufacturing a semiconductor substrate according to the present invention, showing the side surface mirror polishing at step S107 and the beveling mirror polishing at step S108 in FIG. ing.

The semiconductor substrate 6 used here has a crystal orientation of (100) ± 1 °, a diameter of 125 ± 0.5 mm, a thickness of 700 ± 20 μm, a parallelism of 5 μm, and a warp of 5 μm. . Also, it is an N type doped with phosphorus,
Resistance 8.0-12.0 Ωμm, dislocation free, oxygen concentration 1.6
It is × 10 ¹⁸ / cm ³ . Further, an orientation flat 6f having a length of 30-35 mm and an orientation of <110> ± 1 ° is formed on this semiconductor substrate.

FIG. 4 is a perspective view of an apparatus for performing the processing shown in FIG.

The semiconductor substrate 6 is mounted on the upper surface of a chuck 25 for supporting and rotating the semiconductor substrate, and the rotating shafts 28a, 28 are provided on the sides of the chuck.
A pair of flexible discs 26a and 26b are provided so that b is parallel to the semiconductor substrate surface and passes directly above the center of rotation of the chuck 25, and the flexible discs 26a and 26b are provided.
Mirror polishing pads 27a, 2 which are polishing cloths are provided on 26b.
7b is attached. Flexible discs 26a, 26b
Is, for example, a thin spring steel disk. Further, the rotary shafts 28a and 28b of the pair of flexible discs 26a and 26b have one (2
4b) is located above the semiconductor substrate 6, and the other (28a) is located below the semiconductor substrate. Further, the flexible discs 26a and 26b can be moved forward and backward along the rotation shafts 28a and 28b.

Mirror polishing using this apparatus will be described with reference to FIG. 3. The semiconductor substrate 6 held by the chuck 25 is rotated at a predetermined number of revolutions, and a mirror surface polishing agent, for example, from above the semiconductor substrate 6. Alumina, silicon carbide, silicon oxide, etc. are supplied (not shown) (FIG. 3A). In this state, the flexible discs 26a and 26b are rotated and brought into contact with the semiconductor substrate 6 to bring them into contact with each other, and light pressure is applied to polish the end faces for 2 minutes (FIG. 3B). Thereby, the side end surface of the semiconductor substrate is polished. In addition, due to the flexibility of the flexible disk, the end face of the orientation flat 6f portion can be followed and excellent polishing can be performed.

Subsequently, when the flexible discs 26a and 26b are further strongly pushed inward of the semiconductor substrate, the flexible discs 26a and 26b are largely deflected as shown in FIG. 2 (c) for mirror polishing. The pads 27a and 27b come into contact with the semiconductor substrate 6 at an angle, and the beveled portion is mirror-polished. The beveled portion is mirror-polished for 3 minutes, and the flexible discs 26a and 26b are separated from the semiconductor substrate to complete the end-face polishing.

Subsequently, polishing (mirror polishing) of the front surface and the back surface of the wafer is performed according to the steps S109 and S110 of FIG. 2 to obtain a wafer whose entire surface is mirror-polished. After that, chemical cleaning is performed to remove the dirt and dust remaining on the surface of the semiconductor substrate, so that both sides are free from dust.

Finally, the semiconductor substrate is supported by an end face using a holder, and the front surface and the back surface are inspected by the oblique light inspection method to confirm the amount of dust. If the amount of dust is 10 pieces / substrate or less, it is passed.

FIG. 5 is a graph comparing the number of dust particles in a liquid when 25 conventional semiconductor substrates and 25 semiconductor substrates according to the present invention are placed in a carrier and washed with a dust cleaning liquid.

According to the figure, it is proved that the in-liquid dust of the semiconductor substrate according to the present invention is remarkably reduced as compared with the conventional one, and the dust adhering to the substrate surface is reduced. .

Further, in the step of cleaning the dust adhering to the substrate with the cleaning liquid, the chemical liquid may be used plural times. At this time, if a large amount of dust floats in the liquid, the cleaning ends with the dust adhering to the surface of the substrate again, causing reverse contamination. FIG. 6 is a graph comparing the state of reverse contamination between the semiconductor substrate according to the present invention and the conventional semiconductor substrate. Obviously, the reverse contamination of the semiconductor substrate according to the present invention is small.

Furthermore, when the semiconductor substrate obtained in Example 1 was put into a VLSI manufacturing process and the effect of dust reduction was confirmed, pattern defects due to dust on the surface were reduced and FCN (function) yield was reduced. It was confirmed that the effect was improved. (Embodiment 2) FIG. 7 is a sectional view showing the second embodiment of the method for manufacturing a semiconductor substrate according to the present invention, which is applied to a so-called diffusion wafer.

The semiconductor substrate 30 used in this embodiment has a lapping finish with a diameter of 125 ± 0.5 mm, a thickness of 500 mm, a parallelism of 1 μm and a warp of 5 μm. Also,
N-type doped with phosphorus, resistance 50-55Ωμ
It has become m. Furthermore, this semiconductor substrate has an orientation <1.
11> ± 1 ° and an orientation flat with a length of 30-35 mm is formed.

First, this substrate was thoroughly washed, and PSG was used as a diffusion source, and 1200 g of phosphorus was used as a diffusion impurity.
Diffusion at a high temperature of ℃
The diffusion layer 31 is formed (FIG. 7B). The surface concentration of this diffusion layer is about 10 ²⁰ cm ^-3 . When boron is used as the diffusion impurity, BSG is used as the diffusion source.

Next, the diffusion layer 31 on one surface is ground by grinding with a grindstone so that the finished thickness becomes 280 μ (FIG. 7).
(C)).

Subsequently, a beveling process using a grindstone as shown in FIG. 8 (6) is carried out, and then the side end faces shown in FIG. 3 are mirror-polished.

Next, as shown in FIG. 8 (8), on the surface without the diffusion layer 31.
Polishing according to (9) is performed to obtain a single-sided mirror-polished surface having a finished thickness of 255 μ ± 5 μm and a parallelism of 5 μm.

Next, the surface of the substrate is reversed, and the surface of the diffusion layer 31 is polished according to FIGS.
A mirror-finished surface having a parallelism of 2 to 5 μm is obtained.

The substrate on which the above steps have been completed is subjected to chemical cleaning to make both the front surface and the back surface dust-free, and it is confirmed by oblique light inspection that the number of dust particles is 10 pieces / substrate or less.

Thus, a semiconductor substrate having a diffusion layer 30 having a thickness of 150 μ on one surface and a non-diffusion layer having a thickness of 100 μm for device fabrication on the surface and having all surfaces mirror-polished can be obtained. (FIG. 7 (d)).

When the substrate obtained in Example 2 was put into a power element manufacturing process and its effect was confirmed, the increase in dust after transportation hardly changed, and leakage due to unnecessary diffusion due to a fragment of the diffusion layer. No occurrence of defects such as current was observed.

[0047]

According to the semiconductor substrate of the present invention, since the entire surface is mirror-finished, the generation of dust is extremely small and the product reliability and the yield can be improved.

Since the semiconductor substrate manufacturing method according to the present invention includes the step of performing mirror finishing on the entire surface, it is possible to reliably obtain a semiconductor substrate having a mirror surface.

Although the silicon wafer has been described in the above embodiments, the present invention is applicable to gallium arsenide, gallium phosphide,
It can be applied to a semiconductor substrate using various semiconductor materials such as indium phosphide.

[Brief description of drawings]

FIG. 1 is a sectional view showing a surface of a semiconductor substrate according to the present invention.

FIG. 2 is a flowchart showing manufacturing steps of a semiconductor substrate according to the present invention.

FIG. 3 is an explanatory view showing a mirror polishing step of an end surface.

FIG. 4 is a perspective view showing the external appearance of an apparatus for performing mirror polishing of an end surface.

FIG. 5 is a graph showing the effect of reducing dust in liquid by applying the present invention.

FIG. 6 is a graph showing the effect of reducing dust adhering to a substrate by applying the present invention.

FIG. 7 is a sectional view for each step showing the manufacturing process according to the second embodiment of the present invention.

FIG. 8 is an explanatory view showing a general manufacturing process of a semiconductor substrate.

FIG. 9 is an enlarged cross-sectional view showing a surface state of a conventional diffusion wafer.

FIG. 10 is an explanatory view showing a problem in a conventional diffusion wafer.

[Explanation of symbols]

 20 semiconductor substrate 21 front surface 22 back surface 23 side end surface 24 chamfered surface 25 chucks 26a, 26b flexible disc

Claims (3)

[Claims] 1. A semiconductor substrate characterized in that the entire surface including side surfaces is mirror-finished. 2. The semiconductor substrate according to claim 1, wherein the front surface is a non-diffusion layer for forming an element and the back surface is a diffusion layer. 3. A step of slicing a semiconductor ingot with a blade, a step of removing a corner of an end face of a sliced semiconductor substrate, a step of lapping the semiconductor substrate, and a step of etching the whole. A step of mirror-polishing the end surface of the semiconductor substrate after etching by contacting the mirror-polishing member provided on a flexible disk having a surface parallel to this surface while rotating, The rotation axis of the flexible disk is placed at a position parallel to and offset from the semiconductor substrate, and pressure is applied toward the center of the semiconductor substrate to bend the flexible disk to perform the chamfering process. A semiconductor substrate comprising: a step of performing mirror-polishing of the surface that has been performed; a step of performing mirror-polishing of the surface of the semiconductor substrate; and a step of performing mirror-polishing of the back surface of the semiconductor substrate. Manufacturing method.