JPH02248044A - Formation of oxide film - Google Patents

Abstract

PURPOSE:To eliminate a reduction and a variability in a breakdown strength per unit film thickness even if the film thickness of an oxide film is 100Angstrom thinner by a method wherein before the surface of an Si substrate is oxidized, the substrate is heated in a vacuum exceeding 10<-8>Torr. CONSTITUTION:An Si substrate is subjected to RCA cleaning and pure cleaning and is dried. Then, the substrate is put in a molecular beam epitaxial device and after being heated in a vacuum exceeding 10<-8>Torr, the substrate is cooled and is taken out. Then, while hydrogen and oxygen are flowed in a flow rate ratio of 1:1, the substrate is put in a core tube heated to 1000 deg.C and an oxidation is performed.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for forming an oxide film, and more specifically, the present invention relates to a method for forming an oxide film, and more particularly, to a method for forming an oxide film, and more particularly, to a method for forming an oxide film, it is particularly concerned with the production yield of silicon (S r Structure of metal/insulating film/semiconductor ()letalOxide Se
The present invention relates to an oxide film forming method applied to the formation of an insulating film/semiconductor structure that affects the characteristics of a field effect transistor.

[Prior Art] Oxidation of the 3i surface is frequently performed during the manufacturing stage of 3i integrated circuits, especially in the fabrication of S1-MOS transistors. There are various methods of oxidation, but after 3 times of cleaning, etc., it is oxidized in a furnace containing oxygen or a little moisture.
It was to be carried out at about 00°C.

[Problems to be Solved by the Invention] However, it has recently been found that there is a problem with the interface between 3i and the oxide film thus formed. In other words, as LSI density increases, the required oxide film thickness becomes thinner, which is a requirement from the well-known scale law, but when the oxide film thickness becomes less than 100 Å, the oxide film unit becomes thinner. Problems have arisen, such as a significant variation or decrease in breakdown voltage per film thickness within a wafer.

Although the cause of this is not clear at present, recent observation methods at the atomic level, such as lattice images using an electron microscope, have revealed that there are irregularities at the Si/oxide film interface. This unevenness is usually several atomic layers, but may extend to about 10 atomic layers in some cases. Irregularities on the order of several atomic layers can be recalculated into variations in oxide film thickness on the order of a few to 10 layers, but if the oxide film is on the order of several hundred
The unevenness at this interface, which was not a problem in the case of
It is easy to imagine that this will become more obvious when the number of people falls below 00.

The present invention was made in order to solve the conventional problems as described above, and provides a method for forming an oxide film without a drop in breakdown voltage or variation per unit film thickness even when the film thickness is 100 Å or less. The purpose is to

[Means for Solving the Problems] The present invention provides that, prior to oxidizing the surface of an 8i substrate, a 10-
This is an oxide film forming method characterized by heating a 3i substrate in a vacuum exceeding 8 Torr.

In the method of the present invention, the temperature when heating the 3i substrate in a vacuum exceeding 10-8 Torr is 800 to 1100 Torr.
Approximately ℃ is appropriate.

[Operation] The 3i surface is usually mirror polished by chemical mechanical polishing. Prior to oxidation, the 3i surface is washed with an organic solvent, boiled in nitric acid or sulfuric acid, or subjected to a treatment commonly called RCA washing.

Although the chemical mechanically polished surface can be considered to be a mirror surface by ordinary optical means, severe irregularities exist at the atomic layer level.

However, this unevenness can hardly be expected to be reduced by surface treatment prior to oxidation as described above.

In fact, the existence of such irregularities on the Si surface is due to the oxidation of the 3i surface after such treatment, and the resulting 3i and S
This can be recognized by observing the iO2 interface using a cross-sectional electron microscope.

In the present invention, in order to reduce the unevenness of the Si surface at the atomic layer level prior to this oxidation, heating is performed in a vacuum exceeding 10 −8 Torr. At this heat treatment stage, the mobility of the 3i atoms constituting the vicinity of the 3i surface is high, and it is clear from surface treatment results such as molecular beam epitaxial growth that the unevenness of the 3i surface is organized into steps of about one atomic layer. It has been.

In other words, if the surface oxidation process is started after the 3i surface is made into steps of about one atomic layer, the unevenness of the resulting oxide film/Si interface will be reduced, and the interface with only steps of about one atomic layer will be reduced. can get.

[Example] Examples of the present invention will be described in detail below.

Here, we first performed RCA cleaning and pure cleaning on the 3i board.
Dry. Next, the 81 substrate was placed in a molecular beam epitaxial apparatus, and after creating a vacuum of 10" Torr or less, the temperature was reduced to 9.
00'C and heated for about 20 minutes. After this heating, the surface of the wafer was heated using an RHE attached to a molecular beam epitaxial device.
When observed using an ED device, a 2X1 surface structure appeared when the 3i substrate surface was a (100) plane, and a 7X7 structure appeared when the 3i substrate surface was a (111) plane with good reproducibility. After cooling the wafer after the heat treatment in the molecular beam epitaxial apparatus, it was taken out and heated for 10 minutes while flowing hydrogen and oxygen at a flow rate ratio of 1:1.
It was inserted into a furnace tube heated to 00°C and oxidized.

The thickness of the obtained oxide film is 50.

The oxidized layer on the surface of the Si substrate formed as described above was evaluated by observation using a cross-sectional electron microscope, and its breakdown voltage was measured. First, when a fairly wide cross-section of the substrate was observed with an electron microscope, it was determined that although unevenness of one atomic layer was present, there were no cases of unevenness of three or more atomic layers. In addition, the pressure resistance test was conducted by placing a tungsten needle with a tip diameter of 20 mm on the oxide film at 1 mm intervals, and it showed an extremely high value of 9 x 106 /CIR, and the variation was less than ±2%. The value was shown. The results of the breakdown voltage measurements can be said to suggest that the variation in the SiO2 film thickness of the 50 people was within the range of about one atomic layer of 3i crystal.

The analysis results for the Si substrate surface oxide layer as described above could be obtained with good reproducibility for a plurality of Si substrates.

[Effects of the Invention] As explained above, according to the present invention, an oxide film forming method is provided in which there is no drop in breakdown voltage per unit film thickness even when the oxide film thickness is extremely small, and the variation thereof is suppressed to a small level. .

Claims (1)

[Claims] (1) Prior to oxidizing the Si substrate surface, 10^-^
An oxide film forming method characterized by heating a Si substrate in a vacuum exceeding 8 Torr.