JPH0462922A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To inhibit the growth of a natural oxide film and to obtain the high break- down strength characteristics of a semiconductor device by a method wherein an oxide film on the surface of a substrate is removed with an HF solution and thereafter, a surface treatment is performed using a ketone solvent, a carboxylic acid solvent or a phosphoric acid solvent or the mixed solvent of these solvents and an HF solvent and after that, a rinsing and a drying are performed. CONSTITUTION:An n<+> drain layer 12 is formed on the surface on one side of an n- high-resistance silicon semiconductor substrate 11, which has a resistivity of 3.5 to 5.5OMEGAcm and the face (100), and thereafter, a normal oxidation pretreatment is performed and an oxidation by buroing hydrogen is performed for 60 minutes at 1100 deg.C in an HCl atmosphere to form a field oxide film 13. One part of this film 13 is etched to form an opening. Then, a BPG film 14 is deposited, a heat treatment is performed for one hour at 1200 deg.C in a diffusion furnace installed in an atmosphere of N2/O2=100/1 and p-type base layers 15 are formed. The diffusion depth of the layers 15 is 3mum and the surface concentration of the layers 15 is 0.5 is 0.5 to 1X10<19>/cm<3>. After that, the whole surface is washed out with an HF treating liquid and a pretreatment is performed on the exposed substrate surface.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a method of manufacturing a semiconductor device, and in particular, a method of surface treatment of a semiconductor substrate to reduce reverse leakage current of a pn junction. Regarding.

(Prior art) In semiconductor devices having a pn junction on the surface of a semiconductor substrate, especially insulated gate type semiconductor devices that require high breakdown voltage, pn
Reducing the junction's reverse leakage current is important. In many cases, the reverse leakage current characteristics of a pn junction do not match the theoretical value, and include a current component that increases with voltage. This is because the reverse leakage current of the pn junction includes a surface recombination current in addition to a diffusion current and a generation-recombination current, and is strongly dependent on the surface state of the element. Therefore, it has been pointed out that leakage current largely depends on differences in surface treatment, and that it is important to suppress defects that are introduced into the oxide film formed on the surface and defects that are introduced into the Si substrate through heat treatment in order to reduce leakage current. has been done.

Conventional methods for treating exposed p-n junction surfaces include treating with an HF-based treatment solution, washing with water, and drying, mixed hydrochloric acid/hydrogen peroxide treatment (SC-2 treatment), and quaternary ammonium base/peroxide treatment. A method of carrying out an oxidizing agent treatment such as a mixture treatment of hydrogen water (NC-2 treatment) or a mixture treatment of sulfuric acid and hydrogen peroxide solution (SH treatment) followed by washing with water and drying is used.

However, when these treatments are performed, a native oxide film that is not very clean is formed on the substrate surface.

FIGS. 8(a) to 8(d) show channel fluctuations due to changes in the surface state of a Si substrate having a pn junction. FIG. 8(a) shows a state in which an oxide film 2 is formed on an n-type silicon substrate 1, and a p-type layer 3 is formed by doping impurities from the opening of this oxide film 2. At this time, oxide film 2
is contaminated with positive ions, channel 4 as shown in the figure.
is formed.

When this oxide film 2 is removed, the channel 4 becomes smaller as shown in FIG. 8(b). Incidentally, an HF-based treatment solution is normally used to remove the oxide film, but when HF treatment is performed, F- ions are adsorbed to the substrate surface as shown in Figure 8 (C). Thus, a reverse channel 5 is formed. When the adsorbed ions are desorbed using an oxidizing agent-based treatment liquid, the natural oxide film 6 that is subsequently formed becomes contaminated with metal ions, etc., as shown in FIG. 8(d). A channel 7 is formed. When treated with an oxidizing agent-based treatment solution, the metal in the natural oxide film formed has Na+ of 1012atIIl/cm2Fe+ of 5×1
It can reach as much as 011at/cm2.

The formation of the above-described native oxide film with many defects can be expressed as follows from the viewpoint of electrode reaction.

S i +2HF ten(2-n)e" as i F2+2H+ten e--(1)2S i
F-3i (p) +S i F4...
(2) S i (p) +2H20→SiO2+2H2
...(3) A natural oxide film is easily formed by the reaction of 5i(p) produced from the decomposition of SiF2 with water, but since this 5i(p) is porous and has a large actual surface area, Capture and adsorption of various impurities occurs easily.

Such a natural oxide film causes an increase in reverse leakage current of the pn junction on the substrate surface and deterioration of the quality of the gate insulating film when an insulated gate structure is formed.

The surface of the silicon substrate treated with the HF-based treatment liquid is shown in Figure 8 (
As shown in C), there is adsorption of F- ions, and this
It will be about 0.17 atm/cm2. For example, when a treatment liquid such as hydrogen peroxide approaches this adsorption interface, the above (2)
) to (3) reactions occur near the surface, a natural oxide film is formed, and leakage current increases. The situation is shown in FIG. A similar tendency is observed only in the water washing treatment after the HF treatment. The situation is as shown in FIG. It can be seen from these FIGS. 9 and 10 that the increase in the reverse leakage current almost corresponds to the increase in the natural oxide film thickness. In particular, the above-mentioned conventional method is suitable for pretreatment before forming a gate oxide film for devices with gate electrodes with a periphery length of 5 to 10 m, and for pretreatment before forming a passivation film covering a pn junction surface that requires a high breakdown voltage. If this method is used, desired high breakdown voltage characteristics cannot be obtained due to a reduction in the breakdown voltage of the pn junction, a reduction in the gate breakdown voltage, etc.

(Problems to be Solved by the Invention) As described above, in the conventional surface treatment method, a porous and not very clean natural oxide film is generated on the surface of the silicon substrate, which is the cause of increasing the reverse leakage current of the pn junction. It has become.

An object of the present invention is to provide a method for manufacturing a semiconductor device having a pn junction with a small reverse leakage current by suppressing the growth of such a natural oxide film.

[Structure of the Invention] (Means for Solving the Problems) The present invention provides that after removing an oxide film on the surface of a semiconductor substrate with an HF-based solution, a ketone-based solvent, a carboxylic acid-based solvent, a phosphoric acid-based solvent, or a combination thereof is used. It is characterized by using a process of performing surface treatment with a mixed solvent of HF-based solvents, followed by washing with water and drying.

(Function) When the processing method of the present invention is used, the growth of a native oxide film is suppressed, and a semiconductor device having high breakdown voltage characteristics can be obtained.

(Example) The present invention will be explained in detail below.

FIGS. 1(a) to 1(d) show the manufacturing process of a vertical insulated gate MO8FET according to an embodiment of the present invention. After forming an n-type drain layer 12 on one side of a high-resistance n-type silicon semiconductor substrate 11 with a specific resistance of 3.5 to 5.5 Ωcm and a (100) plane, a normal oxidation pretreatment is performed and the substrate is heated in an HCfi atmosphere. 1100℃.

A field oxide film 13 is formed by hydrogen combustion oxidation for 60 minutes. This field oxide film 13 is partially etched to form an opening ((a)). Next, a BSG film 14 was deposited and heat treated at 1200'C for 1 hour in a diffusion furnace set to an atmosphere of N2102 = 100/1.
A p-type base layer 15 is formed ((b)). The p-type base layer 15 has a diffusion depth of 3 μm and a surface concentration of 0.5 to 1×1o1.
9/eII+3.

After that, wash out the entire surface with HF treatment solution,
Pretreatment is performed on the exposed substrate surface ((c)).

Specific preprocessing and its effects will be described later.

Thereafter, a gate oxide film 16 is formed, a gate electrode 17 made of a polycrystalline silicon film is formed, and an n-type source layer 18 is diffused using the gate electrode 17 as a mask, according to a normal process. Then, the entire surface is covered with a CVD oxide film 19, a contact hole is made in this to form a source electrode 20, and a drain electrode 21 is formed on the back surface to form a MOSFET.
is completed ((d)).

Figure 2 shows the measurement of the p-n junction reverse leakage current when CH3CO0H was used as the carboxylic acid treatment liquid for the pretreatment in Figure 1 (C), followed by 10 minutes of water washing. This is the result.

The natural oxide film is as thin as 2 to 5 thick, and the leakage current has not increased at all with this pretreatment.

For comparison, the results of S(-2 treatment using an oxidizing agent-based treatment liquid and NC-2 treatment) are shown in Figures 6 and 7, respectively. It is clear that the growth of a native oxide film is suppressed and the leakage current is significantly reduced by using the carboxylic acid treatment liquid, compared to the results obtained when the pretreatment method is used.

FIG. 3 shows the case where pretreatment was performed using a phosphoric acid treatment liquid instead of a carboxylic acid treatment liquid.

The water washing treatment after the phosphoric acid treatment is 10 minutes. In this case as well, the growth of the native oxide film is small, and the current in the reverse direction is also reduced.

Figure 4 further shows (CH3)2C as a ketone-based treatment liquid.
This is a case where preprocessing using 0 is performed. (CH3)2
Data for 1 minute and 10 minutes of water washing treatment after C0 treatment are shown. Similar effects were obtained in this case as well.

FIG. 5 shows the case where pretreatment was performed using a mixed solution of CH, COOH and dilute HF. Even if HF is mixed in this way, an effect can be obtained. Although data not shown, phosphoric acid treatment,
Similar good results can be obtained by mixing HF in ketone-based treatments.

Vertical MO8FET completed after the above pre-processing
not only has less leakage current, but also has a higher breakdown voltage between the gate and source than when conventional pretreatment is performed.
It was also confirmed that the threshold stability was excellent.

The present invention is not limited to the above embodiments. In the example, vertical MO
Although a 3FET has been described, other elements having an insulated gate structure, such as insulated gate thyristors and IGBTs, as well as elements without an insulated gate structure, are also effective.

[Effects of the Invention] As described above, according to the present invention, by improving the pretreatment process of the pn junction surface, it is possible to obtain a semiconductor device in which the reverse leakage current of the pn junction is reduced.

[Brief explanation of drawings]

FIGS. 1(a) to (d) are vertical MO3Fs according to embodiments of the present invention.
Figure 2 is a diagram showing the manufacturing process of ET. Figure 2 is a diagram showing the reverse leakage current characteristics due to pretreatment using CH and COOH before the formation of the gate oxide film. Figure 3 is a diagram showing the reverse leakage current characteristics due to pretreatment using the same <H3PO4. Figure 4 is a diagram showing the reverse leakage current characteristics. Figure 4 is a diagram showing the reverse leakage current characteristics after pretreatment using the same <(CH3)2 cO. Figure 5 is a diagram showing the reverse leakage current characteristics when the same dilute HF/(CH3)COOH was used. Figure 6 shows the reverse leakage current characteristics when the conventional 5C-2 treatment is performed. Figure 7 shows the reverse leakage current characteristics when the conventional NC-2 treatment is performed. 8(a) to 8(d) are diagrams for explaining the state of channel formation depending on the surface condition. FIG. 9 is a diagram showing the reverse leakage current characteristics due to conventional pretreatment and FIG. 10 is a diagram showing the state of film growth, and FIG. 10 is a diagram showing the state of leakage current and natural oxide film growth by another conventional pretreatment. 11... High resistance n-type silicon substrate (n-type base layer),
]2...n-type drain layer, 13...field oxide film, 14...BSG film, 15...n-type base layer, 1
6... Gate oxide film, 17... Gate electrode, 18.
...N-type source layer, 19...CVD oxide film, 20...
- Source electrode, 21... drain electrode. Applicant's agent Patent attorney Takehiko Suzue [yrl] M; m! , −r+ [4u? [v
rl] Sosen 6-/City 9y F 1st figure (Washing 1/'rf) 5 minutes 01If Fig. 1 (Water washing 1 bamboo) (2 minutes) (5 minutes) Fig. 10 (10 bamboos)

Claims (1)

[Claims] A method for manufacturing a semiconductor device having a pn junction on the surface of a semiconductor substrate, comprising: removing an oxide film on the pn junction surface of the substrate with an HF solution; A method for manufacturing a semiconductor device, comprising the steps of surface treating with a ketone solvent, a carboxylic acid solvent, a phosphoric acid solvent, or a mixed solvent of these and HF, and then washing and drying the substrate.