JP2699468B2 - Method for manufacturing semiconductor device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to a method for manufacturing a semiconductor device such as an IC or an LSI, and more particularly to a method for processing the back surface of a semiconductor wafer after ion implantation.

[Conventional technology]

In recent years, in order to form the source and drain regions of MOS transistors that make up high-density MOS LSIs, it has been necessary to use an ion implantation method that can more precisely control both the semiconductor surface and the depth direction of impurity diffusion. More. To form such a high concentration impurity region with high productivity,
Naturally, the current value at the time of ion implantation is as large as about several to 10 mA. If the current density at the time of ion implantation becomes large as described above, the wafer generates heat, causing a problem of deterioration of a photoresist film used as a mask for ion implantation and deterioration of device characteristics. In general, a wafer cooling mechanism is provided for the purpose of preventing a wafer temperature from rising during ion implantation. For example, in a high-current ion implantation apparatus manufactured by Varian, the silicon rubber is pressed against the back surface of the wafer during ion implantation to cool the wafer. That is, even if a normal metal plate for cooling is pressed against the back surface of the wafer, the metal plate does not uniformly adhere to the back surface of the wafer, so that among the organic materials, silicon rubber having excellent elasticity, heat resistance and thermal conductivity is used. It is used as a wafer cooling material.

[Problems to be solved by the invention]

The above-described conventional wafer cooling method of the large current ion implanter has the following problems. That is, since the back surface of the wafer is in close contact with the silicon rubber at the time of ion implantation, a large amount of organic substances adhere to the back surface of the wafer. For example, in a high-current ion implantation apparatus Extrin 80-80 manufactured by Varian, arsenic was selected as an impurity, and implantation was performed until the impurity concentration reached 10 ¹⁶ / cm ² at an acceleration voltage of 80 KV and a beam current of 8.0 mA as ion implantation conditions. When observing the back surface of the silicon wafer with an optical microscope in the dark field, particles of 0.3 μm or more are 100 to 200
It was confirmed that the particles had adhered to about 10 cm / cm ² . The particles attached to the back of the wafer are analyzed by secondary ion mass spectrometry (Second
Analysis of elemental components using an ary ion mass spectrometer) revealed that the MO of carbon, sodium, potassium, aluminum, etc.
Contaminants have been detected that degrade the characteristics of the S device. Then, the inventor of the present application tried cleaning the wafer on which the contaminant particles adhered to the back surface by a current usual method. That is, the wafer was immersed in the following two kinds of cleaning liquids for a predetermined time, rinsed with pure water, and dried with a centrifugal dryer.

Mixed solution of ammonia water and hydrogen peroxide solution (solution temperature 90 ° C) Mixed solution of sulfuric acid and hydrogen peroxide solution (solution temperature 120 ° C) The back surface of the wafer cleaned by the above two methods was observed with an optical microscope. However, the particle size on the back of the wafer is 0.3 μm
It was confirmed that the above particles were almost 100 to 200 / cm ^2, which was almost the same as before cleaning.

From the above, it has been found that in the current high-current ion implantation method, a large amount of particles adhere to the back surface of the silicon wafer in contact with the silicon rubber for cooling and cannot be removed by subsequent washing.

The silicon wafer into which the impurities have been introduced by ion implantation must then be subjected to heat treatment to form electrically active high-concentration diffusion regions. At this time, organic substances attached to the back surface of the wafer during ion implantation become a source of contamination,
MOS LS also contaminates the wafer and heat treatment furnace
It has been clarified by the study of the present inventor that it has a significant effect on the characteristics and yield of I.

[Means for solving the problem]

The method of manufacturing a semiconductor device according to the present invention includes: a step of selectively introducing an impurity into a main surface of the semiconductor substrate in a state in which a cooling member of the semiconductor substrate is in close contact with a back surface of the semiconductor substrate; And then grinding the back surface of the semiconductor substrate that has been in contact with the cooling member.

[Action]

After the ion implantation, the silicon on the back surface of the wafer is ground by about 2 μm to completely remove dust adhering to the back surface of the wafer at the time of ion implantation, which cannot be removed by a normal cleaning method. Can be reduced.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

1 (a) to 1 (e) are process cross-sectional views of one embodiment of a method for manufacturing a semiconductor device according to the present invention.

First, a positive resist pattern 11 serving as a mask for ion implantation is formed on the main surface 10 on the silicon wafer 1. This resist pattern is applied, for example, by coating a positive resist OFPR-800 manufactured by Tokyo Ohka Kogyo Co., Ltd. to a thickness of 1.35 μm, and applying a reduction projection exposure apparatus NSR-1505G manufactured by Nippon Kogaku.
The exposure is performed by selectively exposing only the portions a and 3b, and thereafter performing a developing process using a developing solution mainly containing an aqueous solution of tetramethylammonium hydroxide to remove the resist film in the portions 3a and 3b. Thereafter, the silicon wafer 1 is subjected to a heat treatment at 120 ° C. for 3 minutes on a hot plate to increase the adhesion of the resist film 11 to the main surface 1. (Fig. 1 (a)) Next, an ion implantation apparatus Extrin 80-
Arsenic is implanted on the main surface 10 of the wafer 1 by 10. The implantation conditions were an acceleration voltage of 80 KV and a beam current of 8.0 mA, and the concentration of the implanted arsenic was 10 ¹⁶ atms · cm ^-2 .
Arsenic high concentration impurity regions 2a, 2b are formed in openings 3a, 3b of main surface 2 of
Is formed. On the other hand, on the back surface 20a of the silicon wafer 1, the organic substances 4a and 4
b and 4c are attached. (FIG. 1 (b)) Next, a high-viscosity positive resist FH-PC 120C.P. manufactured by Fuji Hunt Electronics Technology Co., Ltd. is applied on the main surface of the silicon wafer 1 to a thickness of about 5 μm by a spin coating method. After that, heat treatment at 130 ° C for 5 minutes on a hot plate to evaporate the solvent component in the resist,
A thick film resist 12 for backside grinding is formed. (FIG. 1 (c)) Next, the back surface 20a of the silicon wafer 1 is mechanically ground to a thickness of about 2 μm to form a ground back surface 20b (FIG. 1 (d)). The backside grinding method of the silicon wafer will be described in more detail. As shown in FIG. 2, the wafer 1 is placed on a Teflon wafer chuck 30 with the main surface 10 down, and the holes 31 When the degree of vacuum is set to about 750 mmHg, the wafer 1 is fixed on the Teflon chuck 30.
In addition, a disk-shaped CBD grinding wheel (Ceramic bonded diamond) 40 for silicon grinding manufactured by Disco Corporation is connected and fixed to the metallic rotating shaft 41. At this time, the size of the grindstone 40 is almost the same as that of the wafer 1, and the positional relationship between the two is exactly shifted by the radius of the wafer 1, and
40 is located slightly above wafer 1. After that, the wafer chuck 30 is centered on the central axis 31 and the disk grinding wheel 40
Is rotated around the central axis 41 at a rotation speed of 1000 revolutions / minute, and while pouring an appropriate amount of pure water onto the back surface 20 of the wafer 1, the rotating disk grindstone 40 is lowered together with the rotating shaft 41.
The whetstone 40 is placed on the back surface 20 of the wafer 1 with a load of 1.2 kg.
Press. In this grinding method, diamond fine particles contained in the grinding wheel are precipitated, and the silicon surface is reduced by 0.5%.
Grind at a speed of μm / min. Therefore, when about 4 minutes have elapsed after the start of the grinding by this method, the surface 20 of the wafer 1 becomes 2.0
The back surface 20b is newly formed by grinding by about μ, and the organic substances 4a, 4b, and 4c attached to the back surface 20a are completely removed together with the silicon.

Subsequently, the wafer 1 is immersed in a mixed solution of sulfuric acid and hydrogen peroxide heated to 120 ° C. to remove the resist films 11 and 12, and further mixed with ammonia water and hydrogen peroxide heated to 90 ° C. The wafer 1 is washed by being immersed in the liquid. At this stage, when the back surface 20 of the wafer 1 was observed with an optical microscope,
Deposits having a particle size of 0.3 μm or more were reduced to 0.1 particles / cm ² or less, almost 1/1000 or less before back grinding, and it was confirmed that the level was almost no problem. Finally, when the wafer 1 is subjected to a heat treatment at 950 ° C. for 30 minutes in an N ₂ atmosphere, the impurity diffusion regions 2a, 2
For b, an electrically active high-concentration N-type diffusion region is completed (FIG. 1 (e)).

FIG. 3 is an apparatus sectional view showing another example of the wafer grinding method.

The wafer 1 is fixed on the Teflon chuck 30 when the wafer 1 is placed on the wafer chuck 30 made of Teflon with the main surface 10 down, and the vacant portion is evacuated to a degree of vacuum of about 700 to 750 mmHg. Then, a cylindrical stainless steel nozzle 50 having a hole 51 is placed at a position 10 mm above the back surface of the wafer 1.
The nozzle 50 is installed vertically so that the tip 52 of the wafer 50 is located, and has a mechanism capable of moving the nozzle 50 in a plane by at least the length of the diameter portion of the wafer 1. Then, the wafer chuck 30 is rotated about the central axis 31 at a rotation speed of 4000 revolutions / minute. After that, the alumina (Al
The fine particles 60 of ₂ O ₃ ) are blown out together with air, and the wafer 1
Spray on the back surface 20a of the. At this time, the diameter of the fine particles is
A nozzle having a diameter of about 0.5 to 10 μm is used, and the speed of the air blown from the nozzle 50 is adjusted to about 50 m / sec. In this state, when the alumina fine particles 60 are moved at a predetermined speed in the diameter direction of the wafer 1 so as to uniformly hit the back surface 20a of the wafer 1, the silicon wafer on the back surface 20a of the wafer 1 is ground, and the grinding depth is reduced. Is about 2μ, the back surface 20b
Are formed, and the organic substances 4a, 4b, 4c attached to the back surface 20 are completely removed together with the silicon. After this, 120
The wafer 1 was immersed for 5 minutes in a resist stripping agent containing alkylbenzenesulfonic acid and ortho-dichlorobenzene as main components heated to 130 ° C. to remove the resist films 11 and 12, and further heated to 130 ° C. with sulfuric acid and peroxide. The wafer 1 is immersed in a mixed solution with hydrogen water for about 10 minutes, rinsed with pure water and centrifugally dehydrated to remove water on the wafer 1, thereby completing the cleaning of the wafer 1. After that, when the back surface 20 of the wafer 1 was observed in a dark field with an optical microscope, the number of deposits having a particle size of 0.3 μm or more was 0.1 particles / cm ² or less, almost 1/1000 immediately after ion implantation.
It was confirmed that the level decreased to the following level, which was almost no problem.

〔The invention's effect〕

As described above, the present invention has the effect of completely removing the organic matter adhering to the back surface of the wafer at the time of ion implantation, which was impossible to remove conventionally, by grinding the back surface of the wafer after ion implantation. As a result, contamination of the subsequent heat treatment furnace for forming the diffusion layer is significantly reduced as compared with the conventional case, and the characteristics of MOS devices such as carbon, sodium, potassium, and aluminum which are taken into the semiconductor wafer by the heat treatment are deteriorated. Pollutants are significantly reduced and MO
The characteristics and yield of the S device can be improved.

[Brief description of the drawings]

1 (a) to 1 (e) are process cross-sectional views of an embodiment of a method of manufacturing a semiconductor device according to the present invention, FIG. 2 is a device cross-sectional view showing a method of grinding the back surface of a wafer, and FIG. It is an apparatus sectional view showing other examples of a grinding method. 1 ... silicon wafer, 2a, 2b ... impurity region, 3a, 3b ... exposure region, 10 ... wafer main surface, 11 ... positive resist pattern, 12 ... thick resist layer, 4a, 4b, 4c ... … Organic matter, 20a, 20b… back side of wafer after grinding back side, 30… wafer chuck, 31… wafer chuck hole, 30c… wafer chuck center line, 40… CBD grinding wheel, 41… grinding wheel rotation axis , 40c: Center line of the grindstone rotation axis, 50: Nozzle, 51: Nozzle hole, 60: Fine alumina particles.

Claims (1)

(57) [Claims] A step of selectively introducing an impurity into a main surface of the semiconductor substrate in a state in which the cooling member of the semiconductor substrate is in close contact with the back surface of the semiconductor substrate; and after removing the cooling member, Grinding the back surface of the semiconductor substrate in contact with the cooling member.