JPH07135206A - Oxide film forming method - Google Patents

Abstract

PURPOSE:To improve the characteristics of the device formed on an oxide film by obtaining an oxide film of good quality. CONSTITUTION:This film forming method is the method in which an oxide film is formed on the surface of a substrate by heat treating a substrate 7. The substrate 7 is put in a treatment chamber 1 which is in a wet oxidizing state from the first, and the treatment chamber is heated up to an effective temperature. To be more precise, by having the treatment chamber 1 in a wet oxidizing state from the first, an oxide film, which is formed until the treatment chamber 1 reaches the effective temperature, can be obtained in good quality.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a good quality oxide film on a silicon substrate, for example.

[0002]

2. Description of the Related Art Conventionally, in a semiconductor device manufacturing process, a heat treatment apparatus for performing a thermal oxidation process has been used. This will be described with reference to FIG. Reference numeral 1 denotes a vertical cylindrical processing chamber, on the lower surface of which a semiconductor substrate entrance / exit 2
have. Reference numeral 3 denotes an introduction part provided at the top of the processing chamber 1, from which a processing gas (O ₂ ) is introduced through an introduction pipe 4. Reference numeral 5 denotes an exhaust portion provided in the lower portion of the processing chamber 1 for exhausting the processing gas inside the room to the outside.

Reference numeral 6 denotes a cylindrical heating device arranged so as to include the processing chamber 1, and a donut-shaped heater 6a.
It is constituted by stacking ~ 6b. Thus, in the thermal oxidation treatment of the semiconductor substrate group 7, after heating the inside of the processing chamber 1 by the heating device 6 to a stable temperature of about 700 ° C., the inside of the processing chamber 1 is brought into a dry oxidation state, and the processing chamber 1
The semiconductor substrate group 7 is inserted therein, and the temperature inside the processing chamber 1 is raised to the processing temperature (about 850 ° C.). At this time, the inside of the processing chamber 1 is brought into a wet oxidation state, and the silicon oxide film is formed on the surface of the semiconductor substrate group 7. To form.

After the processing, the inside of the processing chamber 1 is drawn down to the temperature and the substrate group 7 is drawn out from the processing chamber 1.

[0005]

FIG. 1 shows the results of an experiment conducted by the present inventor to judge the quality of an oxide film. The horizontal axis represents the ratio of the thickness of wet oxide film to the total oxide film thickness, 6 is a graph in which the vertical axis is the yield rate of semiconductor substrates. As a sample, p-type (100) (impurity concentration ~ 1 x
10 ¹⁵ cm ⁻³ ) and n-type (100) (impurity concentration up to 2 × 1
MO of polysilicon gate on Si substrate of 0 ¹⁵ cm ^-3 ).
What formed S diode was used. The gate oxide film had a finished film thickness of 1 after the wafer was inserted into the furnace at 700 ° C., the temperature was raised to 850 ° C., and the wafer was kept in a dry oxidizing atmosphere.
The wet oxidation time was adjusted so that the thickness was 5 nm.

The ratio of the film thickness by wet oxidation was adjusted by changing the holding time in a dry oxidation atmosphere from 0 minutes to 270 minutes. The non-defective rate was judged by the electrical characteristics of the MOS diode. From this figure, it was found that the higher the degree of forming the oxide film in the wet oxidation state, the lower the possibility of causing defects in the oxide film (the higher the non-defective rate). Moreover, this tendency is almost the same for p-type and n-type.

Further demonstrating this result is the graph of FIG. In FIG. 2, the horizontal axis represents the ratio of the film thickness by wet oxidation to the total oxide film thickness, and the vertical axis represents the surface of the oxide film (marked with a black square in the figure) when an electric field is applied between the gate electrode and the substrate. 6 is a graph showing the degree of roughness Ra of the interface between the oxide film and the substrate (marked by □ in the figure). From this figure, it can be seen that the higher the degree of forming the oxide film in the wet oxidation state, the smaller the roughness Ra of the oxide film surface. In other words, the roughness Ra of the oxide film surface becomes large due to the fact that the degree of forming the oxide film in the dry oxidation state becomes high. As described above, when the roughness of the oxide film surface becomes large, electric field concentration occurs at a specific portion, and the probability of occurrence of defects increases.

For reference, FIGS. 4 and 5 show FIGS.
On the other hand, the horizontal axis is the ratio of the film thickness by dry oxidation to the total oxide film thickness. The Ra is JIS
It was calculated according to the standard of B 0601 "Definition and display of surface roughness". Ra is simply a measurement length L portion extracted from the roughness curve in the direction of the center line, the center line of the extracted portion is taken as the X axis, and the vertical magnification direction is taken as the Y axis, and the roughness curve is expressed as y = When expressed by f (x), it means a value obtained by the following formula.

[0009]

[Equation 1]

In the conventional example, since the inside of the processing chamber is in a dry oxidation state while the temperature inside the processing chamber rises from the stable temperature of 700 ° C. to the processing temperature of 850 ° C., some defective oxide film is formed on the substrate during this period. To be done. After that, although a good-quality oxide film is formed in a wet oxidation state, there is a problem that a defective product rate as a semiconductor substrate is lowered due to a defective oxide film of a base formed by dry oxidation.

The present invention relates to an improved method for forming an oxide film,
This problem is solved.

[0012]

The present invention is a method of forming an oxide film on the surface of a substrate by heat-treating the substrate, wherein the substrate is placed in a processing chamber that has been in a wet oxidation state from the beginning, and an effective temperature is set. To raise the temperature to.

[0013]

6A shows a non-defective product rate with respect to the film thickness formed by dry oxidation in the step (dry oxidation → wet oxidation) when forming an oxide film of 15 nm. It can be seen that the yield rate is higher as the dry oxidation time is shorter (the dry oxidation film thickness is thinner, that is, the wet oxidation time is longer).

FIG. 6B shows that an oxide film having a thickness of 15 nm was formed by dry oxidation for the entire time. As can be seen from comparison with FIG. 6A, if the wet oxidation step is included during the formation of the oxide film, the yield rate increases. Therefore, by keeping the inside of the processing chamber in a wet oxidation state from the beginning, a good quality oxide film can be obtained until the temperature inside the processing chamber reaches the effective temperature.

In the case of oxidizing at the same temperature and for the same time, since the oxide film formed by wet oxidation is thicker than that by dry oxidation, the time for obtaining a desired film thickness is shortened accordingly.

[0016]

Embodiments of the present invention will be described with reference to the drawings.
The embodiment of the present invention is carried out by using the same thermal oxidation device as the conventional example shown in FIG. The semiconductor substrate group 7 is thermally oxidized by heating the inside of the processing chamber 1 by the heating device 6 to a stable temperature of about 700 ° C., and then introducing the introducing pipe 4 into the processing chamber 1.
A gas containing water vapor is introduced from the introduction section 7 to obtain a wet oxidation state.

Next, the semiconductor substrate group 7 is inserted into the processing chamber 1 and the temperature inside the processing chamber 1 is raised to the processing temperature (about 850 ° C.). Even during this temperature rise, a silicon oxide film is formed on the surface of the semiconductor substrate group 7. After the temperature in the processing chamber 1 reaches the processing temperature, a desired film thickness (for example, 15
(nm) silicon oxide film.

After that, the inside of the processing chamber 2 is replaced with an inert gas (N ₂ or Ar, etc.) atmosphere to complete the oxidation. Since this silicon oxide film is formed in a wet oxidation state until the inside of the processing chamber 1 reaches the processing temperature from the stable temperature and after the processing temperature is reached, it is a good quality film.

[0019]

According to the method of forming an oxide film of the present invention, a good quality oxide film can be obtained, so that the characteristics of the device formed on the oxide film are also improved.

[Brief description of drawings]

FIG. 1 is a graph showing a relationship between a wet oxide film ratio and a non-defective product ratio.

FIG. 2 is a graph showing a relationship between a wet oxide film ratio and Ra.

FIG. 3 is an internal mechanism diagram of a heat treatment apparatus in an example of the present invention and a conventional example.

FIG. 4 is a graph showing a relationship between a dry oxide film ratio and a non-defective product ratio.

FIG. 5 is a graph showing the relationship between the dry oxide film ratio and Ra.

FIG. 6 is a characteristic graph showing a comparison of non-defective product ratios including and not including a wet oxidation process in the oxide film forming process.

[Explanation of symbols]

 1 processing chamber 7 substrate group

Claims (1)

[Claims] 1. A method of forming an oxide film on a surface of a substrate by heat-treating the substrate, wherein the substrate is put into a furnace which is in a wet oxidation state from the beginning, and the temperature is raised to an effective temperature. Method for forming an oxidized film.