JP3522555B2 - Surface treatment method for semiconductor substrate - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor substrate surface treatment method for reducing the surface roughness (irregularities) of a semiconductor substrate.

[0002]

2. Description of the Related Art The microscopic roughness of the surface of a semiconductor substrate is generally called microroughness. It has been pointed out that this surface roughness adversely affects the device characteristics such as the oxide film breakdown voltage of the device.
This microroughness is a surface roughness on the order of 1 μm or less and several nm. In recent years, a method of reducing or mitigating the microroughness of a silicon substrate by immersing the silicon substrate in a mixed solution of a buffered hydrofluoric acid cleaning solution (hereinafter referred to as buffer HF) and H ₂ O ₂ has been proposed ( Mura
matsu et al., Proc 4th Int SympClean Technol Semico
nd Devices Manuf, p436 (1996)). The mechanism for reducing or mitigating the microroughness in this method is as follows. That is, in the above mixed solution, the oxidation of the surface of the silicon substrate by H ₂ O ₂ and the etching of the surface oxide film by the buffer HF occur simultaneously. When the substrate surface is oxidized by this H ₂ O _{2, the} oxidizing substance is easily supplied from the surroundings to the convex portions on the surface, but it is difficult to supply the oxidizing substance to the concave portions on the surface. Therefore, the convex portion is more likely to be oxidized than the concave portion.
Therefore, the oxidized portion is sequentially etched, but since the more oxidized convex portion is etched more than the non-oxidized concave portion, the unevenness of the surface of the silicon substrate, that is, microroughness is reduced or alleviated. It

[0003]

However, when the surface of the silicon substrate used for manufacturing the device is the (100) plane, when the substrate surface is etched by BHF, the OH ions in the etching solution are (111) plane. It is difficult to further reduce the surface roughness of the (100) plane by the above-mentioned conventional method that relies only on this etching because it has anisotropy that causes An object of the present invention is to provide a surface treatment method for a semiconductor substrate, which can further reduce the surface roughness of the semiconductor substrate.

[0004]

The invention according to claim 1 is
As shown in FIG. 1 and FIG.
3 to the semiconductor substrate 13 or 0.1 nm to 10 nm
The electrode plates 14 having an average surface roughness of less than 1 μm, which are arranged at uniform intervals in the range of μm, are immersed respectively, and a potential difference is applied between the semiconductor substrate 13 and the electrode plates 14 so that the semiconductor substrate 13 This is a surface treatment method for a semiconductor substrate in which an oxide film 18 is formed on the surface and the oxide film 18 formed on the surface of the semiconductor substrate 13 is immersed in an etching solution 21 to be removed. The invention according to claim 2 is the invention according to claim 1, which is the surface treatment method, wherein the electrode plate 14 is a cleavable layered graphite, a silicon substrate that has been subjected to finish polishing, or a silicon substrate having an epitaxial growth film.

The invention according to claim 3 is the invention according to claim 1 or 2, wherein the voltage for providing a potential difference between the semiconductor substrate 13 and the electrode plate 14 is a DC voltage or a biased pulse voltage. Is the way. The invention according to claim 4 is the invention according to any one of claims 1 to 3, wherein the electrolytic solution 11 is an aqueous solution of KCl, HF, NaCl or K ₂ SO ₄ .

The invention according to claim 5 relates to claims 1 to 4.
In the invention according to any one, the etching solution 21 is NH
₄ OH, KOH, NaOH, NH ₄ OH / H ₂ O ₂ , HF,
The surface treatment method is an aqueous solution of HF / H ₂ O ₂ , buffered HF or HF / HCl. The invention according to claim 6 is the invention according to any one of claims 1 to 3, wherein the electrolytic solution 11 and the etching solution 21 are HF aqueous solutions, and the oxide film 18 is formed on the surface of the semiconductor substrate in the same bath. After that, the oxide film 18 is removed.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION In the invention according to claim 1, an electrode plate having an average surface roughness of less than 1 μm is used. As this electrode plate, it is preferable to use an electrode plate having a roughness smaller than the surface roughness of the semiconductor substrate to be surface-treated. When the average surface roughness is 1 μm or more, it becomes difficult to accurately concentrate the electric field on the convex portions on the surface of the semiconductor substrate to be processed, and it becomes difficult to reduce the surface roughness of the semiconductor substrate. The preferred average surface roughness of the electrode plate is less than 10 nm. The surface-treated semiconductor substrate is preferably a silicon substrate (silicon wafer), but may be another semiconductor substrate such as germanium or gallium arsenide.

As shown in FIG. 1, the surface-treated semiconductor substrate 13 is immersed in the electrolytic bath 12 in which the electrolytic solution 11 is stored together with the electrode plate 14. The semiconductor substrate 13 is in close contact with the electrode plate 14 or is arranged with a uniform interval in the range of 0.1 nm to 10 μm. That is, both plates are arranged such that the plate surfaces are parallel to each other. When the distance between the electrode plate 14 and the semiconductor substrate 13 exceeds 10 μm, the substrate 13
The electric field concentration is unlikely to occur on the convex portions, and selective oxidation on the convex portions is unlikely to occur, which is not preferable. When the semiconductor substrate 13 is connected to the anode 16 and the electrode plate 14 is connected to the cathode 17 and a potential difference is applied between the anode 16 and the cathode 17, electric field concentration occurs on the convex portion on the surface of the semiconductor substrate 13,
As a result of promotion of the reaction accompanied by the movement of charges in the protrusion on the anode side, the silicon oxide film 18 is formed on the protrusion on the substrate surface. In FIG. 1, the oxide film 18 is shown in black. On the other hand, the concave portion on the surface of the substrate is different from the convex portion in the electrode plate 1.
4, the electric field concentration is unlikely to occur, and the oxide film in the concave portion is not formed, or even if it is formed, it is formed thinner than the convex portion. As shown in FIG. 2, the semiconductor substrate 13 on the surface of which the oxide film 18 is formed is taken out of the electrolytic bath 12 and immersed in the etching solution 21 stored in the etching bath 19 for a predetermined time. As a result, the oxide film 18 formed on the convex portion of the semiconductor substrate 13 is removed by etching, thereby reducing the unevenness on the surface of the semiconductor substrate 13. A step of forming an oxide film on the convex portion shown in FIG.
By repeating the etching process of the oxide film shown in FIG. 2 once or more, the convex portions are further eliminated, and the surface roughness of the semiconductor substrate is further reduced.

In the invention according to claim 2, when a cleavable layered graphite, a silicon substrate having a finish polishing or a silicon substrate having an epitaxial growth film is used as the electrode plate, the surface of the graphite, the silicon substrate or the epitaxial growth film is smooth. Since it has the average surface roughness according to claim 1, it can be applied to the present invention without any special processing. Also, when it is required that the semiconductor substrate to be processed is free of metal impurities,
These graphite or silicon substrates are preferable because they do not elute metal ions in the electrolytic solution during electrolysis. In the invention according to claim 3, a DC voltage or a biased pulse voltage is applied between the anode 16 and the cathode 17. In the first case where a DC voltage is applied, the cathode 17 is grounded and a DC voltage of + V ₁ is applied to the anode 16, as shown in FIG. This DC voltage is preferably in the range of 0.5 to 50V. If it is less than 0.5 V, oxidation is unlikely to occur even in the convex portion.
If it exceeds 0 V, the concave portion may be oxidized, which is a problem.
In the second case, in which a DC voltage is applied, FIG.
As shown in, a bias voltage of + V ₁ is applied to the anode 16 and a DC voltage of −V ₂ is applied to the cathode 17.
When a further biased pulse voltage is applied, as shown in FIG. 3C, a bias voltage of 0 to + V ₁ is applied to the anode 16 and a bias voltage of 0 to −V ₂ is applied to the cathode 17. Is applied, and the repetition frequency of these voltages is preferably set to 0.1 to 100 Hz.

In the invention according to claim 4, an example of the electrolytic solution 11 is an aqueous solution of KCl, HF, NaCl or K ₂ SO ₄ . If the semiconductor substrate to be treated is required to be free of metal impurities, the electrolyte is preferably HF containing no metal ions. In the invention according to claim 5, NH ₄ OH, KOH, NaOH, N is used as the etching liquid 21.
Examples thereof include aqueous solutions of H ₄ OH / H ₂ O ₂ , HF, HF / H ₂ O ₂ , buffered HF and HF / HCl. Of these, HF and buffer HF are preferable because they etch only the oxide film. In the invention according to claim 6, the electrolytic solution 11 and the etching solution 2
When 1 is an HF aqueous solution, as shown in FIG. 1, the semiconductor substrate 13 and the electrode plate 14 are immersed in the HF aqueous solution in the electrolytic cell 12, and a voltage is applied to the semiconductor substrate 13 to apply the substrate 1 to the substrate 1.
An oxide film 18 is formed on the surface. Subsequently, the semiconductor substrate 1 is applied to the same HF aqueous solution in the electrolytic bath 12 without applying a voltage.
The oxide film 18 is removed by immersing 3 for a predetermined time. Thus, in the invention according to claim 6, when the electrolytic solution and the etching solution are composed of the same solution such as an HF aqueous solution, the tanks for storing this solution can be the same tank, so that the semiconductor substrate The surface treatment process can be simplified, and both electrolysis and etching treatments are performed in the electrolytic bath 12 shown in FIG.

[0011]

EXAMPLES Next, examples of the present invention will be described together with comparative examples in order to show specific embodiments of the present invention. <Example 1> Using the electrolytic cell 12 shown in FIG. 1, a silicon substrate 13 having a crystal orientation of (100) was surface-treated under the following conditions. Average surface roughness (Ra) of this silicon substrate 13
Is 0.90 nm, which is the atomic force microscope (AF
M) was measured in an area range of 10 μm square. The electrode plate 14 used was a silicon substrate having an average surface roughness (Ra) of 0.14 nm and a crystal orientation of (100). Electrolyzer 1
A 5% by weight HF aqueous solution was stored as an electrolytic solution 11 in 2 and the silicon substrate 13 and the electrode plate 14 of the object to be treated were immersed in the solution with their surfaces in contact with each other to give +5 to the silicon substrate 13 side.
A voltage of V was applied for 5 minutes to form a silicon oxide film on the surface of the silicon substrate 13. Subsequently, the silicon substrate 13 was immersed in the 5 wt% HF aqueous solution for 5 minutes to remove the oxide film, and finally the silicon substrate 13 was washed with water and dried. The average surface roughness (Ra) of the silicon substrate 13 thus surface-treated was measured. As a result, Ra is 0.6
It was 7 nm.

<Comparative Example 1> As in Example 1, the electrolytic cell 12 shown in FIG. 1 was used and the silicon substrate 13 was surface-treated. However, in Comparative Example 1, the average surface roughness (Ra) of the silicon substrate 13 was obtained by immersing the silicon substrate 13 in the 5 wt% HF aqueous solution for 5 minutes without applying a voltage to the silicon substrate 13 side, and then washing and drying it. Was measured in the same manner as in Example 1. As a result, Ra was 0.88 nm.

<Comparison Evaluation> As is clear from the results of Example 1 and Comparative Example 1, the silicon substrate 13 of Example 1 is obtained.
Average surface roughness (Ra) of 0.90 nm to 0.67 n
It has been significantly reduced to m. On the other hand, the average surface roughness (Ra) of the silicon substrate 13 of Comparative Example 1 is 0.90n.
Although it is reduced from m to 0.88 nm, the reduction rate is smaller than that in Example 1, and it is understood that the reducing ability of Example 1 is superior to that of Comparative Example 1.

[0014]

As described above, according to the method for surface-treating a semiconductor substrate of the present invention, the semiconductor substrate and the semiconductor substrate are brought into close contact with each other in the electrolytic solution, or a uniform interval is set in the range of 0.1 nm to 10 μm. An electrode plate having an average surface roughness of less than 1 μm, which is placed apart from each other, is immersed in each of them, a voltage is applied to the semiconductor substrate to form an oxide film on the substrate surface, and the semiconductor substrate is immersed in an etching solution to perform the above oxidation. Since the film is adapted to be removed, the oxide film is concentratedly formed on the convex portion of the substrate, and the oxide film formed on the convex portion is removed by etching. As a result, the surface roughness of the semiconductor substrate can be further reduced by the method of the present invention as compared with the conventional method in which the unevenness is reduced only by etching.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing a situation in which an oxide film is formed on the surface of a substrate using the electrolytic solution of the present invention.

FIG. 2 is a diagram schematically showing a situation in which an oxide film is removed using the etching liquid of the present invention.

FIG. 3 is a diagram showing a voltage applied between the anode and the cathode.

[Explanation of symbols]

11 Electrolyte 13 Semiconductor substrate 14 electrode plate 16 Anode 17 cathode 18 Oxide film 21 Etching liquid

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-8-181094 (JP, A) JP-A-10-293294 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01L 21/304-21/3063 H01L 21/308

Claims (6)

(57) [Claims] 1. An average surface roughness which is in close contact with the semiconductor substrate (13) and the semiconductor substrate (13) in the electrolytic solution (11) or which is arranged with a uniform interval in the range of 0.1 nm to 10 μm. Is 1
An electrode film (14) having a thickness of less than μm is immersed in each of the electrodes, and a potential difference is applied between the semiconductor substrate (13) and the electrode plate (14) to form an oxide film (1) on the surface of the semiconductor substrate (13).
A method for surface treatment of a semiconductor substrate, which comprises forming 8) and removing the oxide film (18) formed on the surface of the semiconductor substrate (13) by immersing it in an etching solution (21). 2. The electrode plate (14) is a cleavable layered graphite,
The surface treatment method according to claim 1, wherein the surface-polished silicon substrate or the silicon substrate has an epitaxially grown film. 3. The surface treatment method according to claim 1, wherein the voltage that gives a potential difference between the semiconductor substrate (13) and the electrode plate (14) is a DC voltage or a biased pulse voltage. 4. The surface treatment method according to claim 1, wherein the electrolytic solution (11) is an aqueous solution of KCl, HF, NaCl or K ₂ SO ₄ . 5. The etching solution (21) is NH ₄ OH, KO.
H, NaOH, NH ₄ OH / H ₂ O ₂ , HF, HF / H ₂ O
_2. An aqueous solution of buffered HF or HF / HCl.
5. The surface treatment method according to any one of 4 to 4. 6. The electrolytic solution (11) and the etching solution (21) are each an HF aqueous solution, and after the oxide film (18) is formed on the surface of the semiconductor substrate (13) in the same tank, the oxide film (18) is formed. ) Is removed, the surface treatment method according to any one of claims 1 to 3.