JPH0680635B2 - Method for forming backside sealing film for preventing autodoping - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor integrated circuit device, and more specifically, to prevent autodoping from a semiconductor substrate during vapor phase single crystal growth. The present invention relates to a method for forming a back surface sealing film.

[Prior Art] When various circuit elements are formed in the semiconductor manufacturing technology, for example, a P-type or N-type semiconductor substrate is used, a high-concentration buried layer is formed on the semiconductor substrate, and P is formed thereon. ^- type or N ^- -type epitaxial layer of, to form various circuit elements has been performed on the epitaxial layer.

FIG. 5 shows the above manufacturing process in detail. The manufacturing process will be described in detail with reference to FIG.

First, a semiconductor substrate (mirror surface wafer) 1 as shown in FIG. 5 (A) is subjected to high temperature treatment in an oxidizing atmosphere containing oxygen or water vapor, and as shown in FIG. A thermal oxide film 2 is formed on the entire surface. Next, as shown in FIG. 5C, a resist 3 is applied on the thermal oxide film 2 on the front surface side of the semiconductor substrate 1. Here, the resist 3
Is used as a negative resist. Therefore, as shown in FIG. 5 (D), if the resist 3 is partially exposed using the mask 4 for forming the N ⁺ buried layer and then development is performed, only the resist 3 in the exposed region remains. , The resist 3 in other regions is removed. That is, only the resist 3 on the portion where the N ⁺ buried layer is to be formed is removed, and the state shown in FIG. 5 (E) is obtained. Then, the remaining resist 3 is hard-baked, and the thermal oxide film 2 thereunder is selectively etched using this as a mask. As a result, as shown in FIG. 5 (F), the thermal oxide film 2 on the N ⁺ buried layer formation planned portion is removed and the substrate surface is exposed. At this time, at the same time, the thermal oxide film 2 on the side surface and the back surface of the semiconductor substrate 1 is also removed. Then, as shown in FIG. 5G, the resist 3 used as the mask is removed. Then, using the thermal oxide film 2 remaining on the surface of the semiconductor substrate 1 as a mask, antimony (Sb) diffusion is performed to form an N ⁺ buried layer 5, as shown in FIG. Next, as shown in FIG. 5 (I), the thermal oxide film 2 used as a mask is removed. Then, as shown in FIG. 5 (J), the P ⁻ type epitaxial layer 6 is formed on the entire upper surface of the semiconductor substrate 1.
To form.

By the way, in the case of manufacturing a semiconductor device as described above, the antimony is highly doped in the side surface portion and the back surface portion of the semiconductor substrate 1 during antimony diffusion. Then, after that, the epitaxial layer 6 is formed on the semiconductor substrate 1.
When forming, the problem of autodoping arises. This autodoping phenomenon depends on the solid phase diffusion due to heat from the semiconductor substrate 1 to the epitaxial layer 6, but the impurities (antimony) on the side surface and the back surface of the semiconductor substrate 1 are once released into the gas phase, and Are generated by being transferred to the surface of the epitaxial layer 6.

When such autodoping occurs, the impurity concentration of the epitaxial layer 6 changes, and the impurity concentration in the epitaxial layer 6 becomes nonuniform. In particular, the impurity concentration in the epitaxial layer 6 near the interface between the semiconductor substrate 1 and the epitaxial layer 6 fluctuates, and a considerable amount of the epitaxial layer 6 is wasted in reaching the desired impurity concentration in the epitaxial layer 6.

Therefore, conventionally, in order to avoid the above-mentioned inconvenience, a back surface sealing film made of the thermal oxide film 2 is formed on the back surface of the semiconductor substrate 1 before the antimony diffusion, and the back surface portion of the semiconductor substrate 1 is formed by the sealing film. It was intended to prevent the impurity doping.

Specifically, after the step shown in FIG. 5E, a resist is applied to the back surface of the semiconductor substrate 1 (FIG. 6A), and the thermal oxide film 2 for forming the N ⁺ buried layer is formed. 6th after selective etching of
As shown in FIG. 1B, the thermal oxide film 2 is formed on the back surface of the semiconductor substrate 1.
The back side sealing film made of was left and the antimony diffusion was performed as shown in FIG. 6 (C) with this sealing film attached. This prevents antimony from diffusing into the back surface of the semiconductor substrate 1 during antimony diffusion. This prevents the transfer of antimony to the epitaxial layer 6 when forming the epitaxial layer 6 as much as possible.

[Problems to be Solved by the Invention] By the way, conventionally, the coating of the resist 7 on the back surface of the semiconductor substrate 1 has been performed manually. This is because, for example, when the resist 7 is applied to the back surface of the semiconductor substrate 1 by using a spinner, particles (dust) are trapped between the chuck of the spinner and the resist 3, and the resist 3 is damaged and the resist is damaged. This is because a pinhole or the like is formed in the.

However, if the resist 7 is applied manually, there is a problem that not only the production line cannot be automated, but also the fleutot in the production line becomes worse.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for forming a backside seal film, which enables automation of a manufacturing line and contributes to improvement of throughput in the manufacturing line.

The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.

[Means for Solving the Problems] The outline of the typical inventions among the inventions disclosed in the present application will be described below.

The present invention, when forming a seal film made of an oxide film on the back surface of a semiconductor substrate, forms an oxide film on the entire front and back surfaces of the semiconductor substrate and forms a photoetching film on the oxide film on the front surface side of the semiconductor substrate. A resist is applied, followed by development by a photo-etching technique and baking, and then a protective film made of a water-soluble resin is formed on the resist film, and then a resist film is formed on the oxide film on the back surface of the semiconductor substrate. And apply
After that, the protective film is removed, and the oxide film on the surface of the semiconductor substrate is etched according to the resist opening pattern by using the remaining resist to form a back surface seal film made of an oxide film on the back surface of the semiconductor substrate. It was done like this.

[Operation] According to the above means, after forming the resist on the front surface side of the semiconductor substrate, the protective film made of the water-soluble resin is formed on the resist, and the resist is applied on the back surface side of the semiconductor substrate. Therefore, the resist on the front surface side of the semiconductor substrate is protected by the protective film during chucking. Therefore, the effect of eliminating the need to manually apply the resist enables automation of the semiconductor device manufacturing line and improvement of throughput.

[Embodiment] An embodiment of a method for forming a backside sealing film for preventing autodoping according to the present invention will be described below with reference to the drawings.

FIG. 2 shows the above manufacturing process in detail. The manufacturing process will be described in detail with reference to FIG.

First, a semiconductor substrate (mirror wafer) 11 as shown in FIG. 2 (A) is subjected to high temperature treatment in an oxidizing atmosphere containing oxygen or water vapor, and as shown in FIG.
A thermal oxide film 12 is formed on the entire front and back surfaces of 11. Then, as shown in FIG. 2C, a thermal oxide film on the front surface side of the semiconductor substrate 11 is formed.
A resist 13 is applied onto 12 by a spinner. Here, a negative resist is used as the resist 13. Therefore, as shown in FIG. 2D, the resist 13 is partially exposed by using the mask 14a for forming the N ⁺ buried layer,
After that, if development is performed, only the resist 13 in the photosensitive area remains, and the resist 13 in the other areas is removed. That is,
Only the resist 13 on the portion where the N ⁺ buried layer is to be formed is removed, and the state shown in FIG. After that, the remaining resist 13 was baked.

In this state, a protective film 18 made of a water-soluble resin such as polyvinyl alcohol resin is applied by a spinner on the entire surface of the semiconductor substrate 11 as shown in FIG. 2 (F), and then as shown in FIG. 2 (G). Also on the semiconductor substrate by spinner
A resist 17 is applied on the thermal oxide film 12 on the back surface side of 11.
Specifically, as shown in FIG. 1 (A), the back surface side of the semiconductor substrate 11 is adsorbed to the chuck 19, and the solid content 15
% Polyvinyl alcohol solution about 5cc Semiconductor substrate 11
Then, the semiconductor substrate 11 is spun at 800 rpm for 1.0 second at high speed to shake off excess polyvinyl alcohol solution.
Next, the semiconductor substrate 11 is rotated at 3000 rpm for 9.0 seconds to form a film and dry it. After that, baking is performed twice at 110 ° C. for 25 seconds. As a result, the protective film 18 having a film thickness of 10,000 Å or more is formed. Thereafter, as shown in FIG. 1 (B), the semiconductor substrate 11 is turned upside down, and the surface of the semiconductor substrate 11 is attracted to the chuck 19 and the resist 17 is applied.

After the resist 17 is applied to the back surface side of the semiconductor substrate 1 as described above, the semiconductor substrate 11 is rinsed with pure water to remove the protective film 18, as shown in FIG. After that, the thermal oxide film 12 thereunder is selectively etched by using the residual resists 13 and 17 of the semiconductor substrate 11 as a mask. As a result, as shown in FIG. 2 (I), the thermal oxide film 12 on the portion where the N ⁺ buried layer is to be formed on the surface of the semiconductor substrate is removed. Then, after removing both resists 13 and 17 as shown in FIG. 2 (J), antimony (S
b) Diffusion is performed to form an N ⁺ buried layer 15 as shown in FIG. 2 (K).
To form. By doing so, it is possible to prevent the back surface portion of the semiconductor substrate 11 from being doped with antimony. Then
As shown in FIG. 2L, the thermal oxide film 12 used as a mask is removed. After that, as shown in FIG.
The semiconductor substrate 11 is subjected to high temperature treatment in an oxidizing atmosphere containing oxygen or water vapor, and a thermal oxide film 12 is formed on the entire front and back surfaces of the semiconductor substrate 11.
To form. Next, as shown in FIG. 2N, a resist 13 is applied on the thermal oxide film 12 on the front surface side of the semiconductor substrate 11. Here, a negative resist is used as the resist 13. Therefore, as shown in FIG. 2 (O), if the resist 13 is partially exposed by using the mask 14b for forming the P ⁺ buried layer, and then development is performed, the resist in the exposed area is formed.
Only 13 remains, and the other region resist 13 is removed.
That is, only the resist 13 on the P ⁺ buried layer formation planned portion is removed and the state shown in FIG. 2 (P) is obtained. afterwards,
Bake the remaining resist 13.

In this state, as shown in FIG. 2 (Q), the semiconductor substrate 11
A protective film 18 made of a water-soluble resin is formed on the front surface side of, and a resist 17 is applied on the thermal oxide film 12 on the back surface side of the semiconductor substrate 11, as shown in FIG. The application of the resist 17 is carried out by the same method as shown in FIGS.

Next, as shown in FIG. 2 (S), the semiconductor substrate 11 is rinsed with pure water to remove the protective film 18. Then, the thermal oxide film 12 is selectively etched using the remaining resist 13 as a mask. As a result, as shown in FIG. 2 (T), the thermal oxide film 12 in the P ⁺ buried layer formation planned portion is removed. Then the second
As shown in FIG. (U), the resists 13 and 17 used as masks
To remove. Next, as shown in FIG. 2 (V), boron (B) diffusion is performed using the remaining thermal oxide film 12 as a mask to form a P ⁺ buried layer 20. By doing so, it is possible to prevent the back surface portion of the semiconductor substrate 11 from being doped with boron. Next, as shown in FIG. 2 (W), the thermal oxide film 12 used as a mask is removed. Then, as shown in FIG. 2 (X), a P ⁻ type epitaxial layer 16 is formed on the entire upper surface of the semiconductor substrate 11.

If the sealing film made of the thermal oxide film 12 is formed on the back surface of the semiconductor substrate 11 as described above, the following effects can be obtained.

That is, the protective film 18 is formed on the front surface side of the semiconductor substrate 11, and the semiconductor substrate 11 is chucked through the protective film 18 so that the resist 17 is applied to the back surface side of the semiconductor substrate 11. At this time, the front surface side resist 13 of the semiconductor substrate 11 is not damaged. Therefore, the effect of eliminating the need to manually apply the resist 17 enables automation of the semiconductor device manufacturing line and improvement of throughput.

The following experiments were conducted to support the above effects.

In this experiment, as shown in the table below, a semiconductor substrate that was not subjected to any treatment (Sample 1), a semiconductor substrate that was coated with a front surface resist and was not coated with a back surface (Sample 2),
The generation state of particles (including pinholes) was examined by surf scan for the semiconductor substrate (Sample 3) on which the resist coating was performed by the spinner without forming the protective film 18 and the semiconductor substrate (Sample 4) of this example. . In the table below, x indicates that the process has not been performed, and o indicates that the process has been performed. In this photolithography process, the cleanliness of the atmosphere is class 100,
Each step was performed under the following conditions.

(1) Resist coating process Negative resist OMR-85 (30 cp) and semiconductor substrate 11 5000 rp
Application was performed while rotating at high speed at m, and a resist 13 was formed on the surface side of the semiconductor substrate 19 to a thickness of 7,000 Å. Then 110
The baking was performed twice at 25 ° C. for 25 seconds.

(2) Alignment process The contact aligner was used to expose for 3.0 seconds with an illuminance of 3.6 mW / cm ² .

(3) Developing Step Xylene was used as a developing solution and spray development was performed for 10 seconds. Furthermore, after washing with butyl acetate as a rinse liquid, baking was performed twice at 150 ° C. for 25 seconds.

(3) Protective film coating process A polyvinyl alcohol solution having a solid content of 15% is dropped onto the surface of the semiconductor substrate 11 in an amount of about 5 cc, and the semiconductor substrate 11 is rotated at 3000 rpm for 10 minutes.
It was rotated for 2 seconds to form a film and dried. Then 110 ℃, 2
It was baked for 5 seconds twice. As a result, the protective film 18 having a film thickness of 10,000 Å was formed.

(4) Backside coating process Negative resist OMR-85A (30cp) and semiconductor substrate 11 3000r
While rotating at high speed at pm, it was applied on the back surface side of the semiconductor substrate 19 to form a resist 17 with a thickness of 10000Å. No baking was performed in this step.

(5) Etching process 60 using 1: 9 buffered hydrofluoric acid as an etching solution.
Minute etching was performed. In this step, a considerable amount of over-etching was performed to thicken the pinhole.

(6) Cleaning process Cleaning with H ₂ SO ₄ · H ₂ O ₂ (110 ° C), cleaning with dilute hydrofluoric acid, NH ₄
Cleaning with OH · H ₂ O ₂ (80 ° C.), ultrasonic cleaning, and steam cleaning with isopropyl alcohol were performed for 10 minutes each.

FIGS. 3A to 3D show the generation states of particles corresponding to Sample 1, Sample 2, Sample 3 and Sample 4. 3A to 3D, the vertical axis represents the number of particles and the horizontal axis represents the particle size.

Here, in the sample 1 of FIG. 3A, the number of particles on the surface when the semiconductor substrate 11 is left in the atmosphere of the photolithography process is counted. Also,
In Samples 2 to 4 of FIGS. 3B to 3D, particles mean pinholes formed in the thermal oxide film 12. That is, in Samples 1 to 4, the pinhole generated in the thermal oxide film 12 was measured after performing the photolithography process using the photoresist 13 damaged by the particles. The pinhole in this case is over-etched (usually 15 minutes etching but 60 minutes etching)
Going to make the pinhole thicker than it actually is.

From these drawings, it can be seen that in the sample 3 in which the resist coating is performed by the spinner without forming the protective film 18, 2.31 μm ²
The number of the above particles is incomparably large, and the number of particles of 2.31 μm ² or more is remarkably reduced in the semiconductor substrate of the present embodiment, that is, sample 4, and is substantially the same as sample 2 in which the front surface side resist 13 is provided and the back surface coating is not performed. It can be seen that the number of particles is.

Further, FIG. 4 shows the relationship between the thickness of the protective film 18 and the number of particles, and it is confirmed that the thicker the protective film 18, the smaller the number of particles. FIG. 4 shows the average value and fluctuation range of four semiconductor substrates.

Although the invention made by the present inventor has been specifically described based on the embodiments, the present invention is not limited to the above embodiments and various modifications can be made without departing from the scope of the invention. Nor.

For example, in the above embodiment, in forming the back surface protective film of the semiconductor substrate 11, a water-soluble protective film made of polyvinyl alcohol is formed on the front surface side of the semiconductor substrate 11, but cellulose is used as the water-soluble resin. You may make it use a derivative.

[Effects of the Invention] The typical effects of the invention disclosed in the present application will be described below.

That is, according to the present invention, in forming a seal film made of an oxide film on the back surface of the semiconductor substrate in order to prevent autodoping from the semiconductor substrate, the oxide film is formed on the entire surface of the semiconductor substrate and the front surface side of the semiconductor substrate is formed. A resist film for photo-etching is applied on the oxide film, and development baking is performed by the usual photo-etching technique, and a water-soluble resin is applied on the resist film, and then a back surface of the semiconductor substrate is coated. Apply a resist film on the oxide film, then remove the water-soluble resin, etch the oxide film using the resist as a mask, and use the oxide film remaining on the back surface of the semiconductor substrate as a back surface sealing film. Therefore, the front side resist of the semiconductor substrate 1 is not damaged during chucking. Therefore, it is not necessary to apply the resist manually, so that the manufacturing line of the semiconductor device can be automated and the throughput can be improved.

Further, the method of the present invention, even when performing the photoresist coating on the back surface of the thermally-oxidized semiconductor substrate that is manually patterned photoresist, since the instrument or the like does not directly contact the resist film on the substrate surface, the resist film It is effective for protecting the surface of the film and for preventing the back side coating resist from wrapping around the surface and preventing stains.

[Brief description of drawings]

1 (A) and 1 (B) are partial vertical cross-sectional views of a semiconductor substrate and a chuck showing a protective film forming process and a resist coating process of the embodiment, and FIGS. 2 (A) to (X) are of the embodiment. FIG. 3A to FIG. 3D are graphs showing the generation status of particles of various samples, FIG. 4 is a graph showing the relationship between the thickness of the protective film and the number of particles, and FIG. FIGS. 6A to 6J are vertical cross-sectional views of respective steps of a semiconductor substrate showing a conventional semiconductor manufacturing process, and FIGS. 6A to 6C are semiconductor substrate showing a back seal film forming process. It is a longitudinal section in a process. 11 ... Semiconductor substrate, 12 ... Oxide film, 13, 17 ... Resist, 18 ...
Protective film.

Claims (2)

[Claims] 1. When growing a vapor phase single crystal of an integrated circuit device structure,
In forming a seal film made of an oxide film on the back surface of the semiconductor substrate to prevent autodoping from the semiconductor substrate, an oxide film is formed on the entire front and back surfaces of the semiconductor substrate,
A resist for photo-etching is applied on the oxide film on the surface side of the semiconductor substrate, then developed by photo-etching technique and baked, and a protective film made of a water-soluble resin is formed on the resist. Then, a resist is applied on the oxide film on the back surface side of the semiconductor substrate, then the protective film is removed, and the remaining resist is used to open the oxide film on the surface of the semiconductor substrate into the resist opening. A method for forming a backside sealing film for preventing autodoping, which is characterized by etching according to a pattern to form a backside sealing film made of an oxide film on the backside of the semiconductor substrate. 2. The method for forming a backside sealing film for preventing autodoping according to claim 1, wherein a polyvinyl alcohol resin is used as the water-soluble resin.