JPH0527272B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method of manufacturing a MOSFET on a silicon substrate.

(Prior Art) MOSFETs on silicon substrates are widely used in integrated circuits, and in order to further increase the integration density, efforts are being made to miniaturize the element dimensions. Along with this, gate oxide films for MOSFETs have started to be thinner, about 20 nm thick. However, the conventional
The MOSFET manufacturing method involves forming a gate oxide film on the element area of a silicon substrate by thermal oxidation, and then going through various processing steps such as forming the gate electrode, source, and drain regions, which poses the following problems. A drawback of miniaturization and thinning of the gate oxide film is that it is difficult to form devices with good yield. In other words, (a) contamination after the gate oxide film is formed and before the gate electrode material is deposited;
The dielectric strength of the gate oxide film deteriorates. (b) After forming the gate oxide film, a process using ion bombardment, such as plasma CVD method or sputtering method, is used to deposit the film.
When patterning by reactive ion etching or impurity ion implantation is used, dielectric breakdown of the gate oxide film occurs due to charging. (c) After the gate oxide film is formed, if high-temperature heat treatment is performed to anneal the gate electrode material or activate impurity ions, diffusion of the gate electrode material occurs, causing erosion and destruction of the gate oxide film.

These are becoming apparent as major problems in device manufacturing, as gate oxide films become thinner and thinner with device miniaturization, and device manufacturing has to rely more and more on ion-utilizing technology.

(Objective of the Invention) The present invention has been proposed to eliminate these drawbacks, and is characterized by forming a gate oxide film by a reaction at the interface between the gate electrode and the silicon substrate after forming the gate electrode. The purpose is to form MOSFETs with high yield without causing dielectric breakdown of the thin gate oxide film during device manufacturing.

(Structure of the Invention) In order to achieve the above object, the present invention includes a step of depositing a metal layer containing oxygen to cover an exposed silicon region that is to become an element region in a step of manufacturing a MOSFET on a silicon substrate. a step of etching the metal layer to form a gate electrode; a step of depositing an interlayer insulating film that transmits reducing gas species and suppresses permeation of oxygen generated from the metal;
By heat treatment in an atmosphere containing the reducing gas species,
The gist of the invention is a method for manufacturing a MOSFET, which includes the steps of sequentially forming a gate oxide film at the interface between the silicon substrate and the gate electrode.

Next, examples of the present invention will be described. It should be noted that the embodiments are merely illustrative, and it goes without saying that various changes and improvements can be made without departing from the spirit of the present invention.

The present invention utilizes a reaction in which a silicon oxide film is formed at the interface between silicon and a metal containing oxygen through heat treatment. By utilizing this reaction, a gate oxide film made of a silicon oxide film can be formed after the gate electrode is formed, so that surface contamination of the gate oxide film and destruction during formation of the gate electrode can be avoided. Furthermore, high-temperature heat treatment for annealing the gate electrode material, which was conventionally performed after forming the gate oxide film, can be performed simultaneously with the formation of the gate oxide film. can be avoided.

The formation reaction of the silicon oxide film used in the present invention is based on the following principle. In general, the affinity between silicon and oxygen is greater than the affinity between metal and oxygen, so if silicon is in contact with a metal containing oxygen, no change will be observed at room temperature, but when exposed to high temperatures, oxidation of the silicon will occur. At high temperatures, the metal itself recrystallizes,
An increase in the diffusion coefficient of oxygen in metal increases the probability that oxygen will bond to silicon, but the following two conditions are required to form a silicon oxide film efficiently. That is, heat treatment is performed in a reducing atmosphere to promote the release of oxygen in the metal, and a film that does not allow oxygen to pass is provided on the metal to suppress the release of oxygen to the outside.

Based on the above principle, the manufacturing method of the present invention needs to satisfy the following requirements. First, regarding the type of metal, the basic requirement for the above reaction to occur is that the change in free energy in the reaction between the metal oxide and silicon is negative at the temperature of the oxide film forming heat treatment (800 to 1100 degrees Celsius). . Furthermore, it is necessary to select a metal that can contain oxygen and is stable at high temperatures. Metals that meet these requirements include molybdenum, tungsten, chromium, vanadium, niobium, and tantalum. Among them, molybdenum and tungsten have low resistivity even when they contain oxygen and have excellent heat resistance, so they are suitable for the manufacturing method of the present invention.

On the other hand, as mentioned above, oxygen in the metal is used to form a silicon oxide film, so controlling the amount of oxygen in the metal as well as heat treatment conditions is an important requirement to improve the reproducibility of silicon oxide film formation. Become. As a method for incorporating oxygen into the metal, it is possible to use a vapor deposition method in a trace amount of oxygen, a chemical vapor deposition method, or a sputtering method in an oxygen-containing gas atmosphere. Especially when using the spatuta method,
We have found that the amount of oxygen in the metal can be varied over a wide range by adjusting the gas partial pressure, and that the formation of particles can be controlled with good reproducibility. For example, although it depends on the type of metal, the amount of oxygen in the metal can be controlled to 40 at.% by adjusting the oxygen partial pressure during sputtering, making it possible to contain enough oxygen to form a silicon oxide film.

The atmosphere during heat treatment to form a silicon oxide film is as follows:
It is necessary to contain a gas species that is reducing to the metal, and a reducing atmosphere containing hydrogen with excellent permeability in the substance is suitable, but is not limited thereto in principle.

Furthermore, in order to effectively use the oxygen liberated from the metal during heat treatment for the reaction at the silicon interface,
It is important to suppress the release of oxygen from the metal surface to the outside. For this reason, it is necessary to deposit a film on the metal that allows the above-mentioned reducing gas species to permeate but suppresses the release of oxygen. A suitable material for this film is silicon dioxide, which is often used as an interlayer insulating film in semiconductor devices and which is permeable to hydrogen but is less permeable to oxygen.If the above conditions are met, It is not limited to this.

Note that when heat treatment is used in a reducing atmosphere containing hydrogen, the silicon oxide film thickness can be controlled by the amount of oxygen in the metal, heat treatment temperature, hydrogen content in the heat treatment atmosphere, and heat treatment time, and a film thickness of about 6 nm to 50 nm can be achieved. can be easily formed with good reproducibility. Also, the insulation voltage is
It has a good value of about 11 MV/cm, and the surface state at the interface between silicon and silicon oxide film is equivalent to that formed by normal thermal oxidation, and has sufficient characteristics as a gate oxide film for a MOSFET.

Hereinafter, the present invention will be explained with reference to examples.

Embodiment 1 FIGS. 1A to 1G show a method for manufacturing a p-channel MOSFET according to a first embodiment of the present invention in the order of steps.

A field oxide film 2 was formed on the surface of a (100) plane n-type silicon substrate 1 having a resistivity of 3 to 5 Ωcm by a steam oxidation method, and an opening was formed by a photoetching process to form an element region 3. (A) In conventional MOSFET manufacturing methods, a gate oxide film is usually formed next, but in this method, a gate oxide film is not formed and a gate electrode is directly formed on the exposed silicon region of the device region 3. About 300 nm of molybdenum 4 containing oxygen was deposited. Molybdenum containing oxygen is about 10% oxygen in argon,
It was deposited by the reactive sputtering method in a mixed gas with a partial pressure of about 0.13 Pa. Molybdenum contains about
Contains 30at.% oxygen, but the specific resistance is approximately 3×
It was 10 ^-5 Ωcm and could be used as electrode wiring. (B) Next, the gate electrode part is covered with resist 5 by a photo process, and the other part is removed by reactive ion etching using a gas mixed with CCl ₂ F ₂ and oxygen.
The shape of the gate electrode 6 was processed. (C) Next, using this resist 5, gate electrode 6, and field oxide film 2 as a mask, B ⁺ ions were implanted at 5×10 ¹⁵ /cm ² at 40 KeV to form source and drain regions 7 and 8. (D) Next, after the resist 5 is ashed and removed in oxygen plasma, a silicon dioxide film is formed as a film that transmits hydrogen and suppresses the release of oxygen from the gate electrode metal surface during the heat treatment for forming the gate oxide film. 9
was deposited to a thickness of approximately 800 nm using the sputtering method. In addition,
This silicon dioxide film 9 also functioned as an interlayer insulating film. (E) Next, heat treatment was performed at 900° C. for 60 minutes in nitrogen containing 50% hydrogen to form a gate oxide film 10 with a thickness of about 50 nm at the interface between the gate electrode 6 and the silicon substrate 1.
Further, by this heat treatment, the impurities implanted into the source and drain regions 7 and 8 were activated, and the sheet resistance was made approximately 50Ω/□. (F) Next, contact holes 11, 12, 13 are formed by a photo-etching process, and an aluminum alloy (containing 3 at.% silicon) layer is deposited by sputtering, and then aluminum alloy wirings 14, 15, 16 are formed by a photo-etching process. A MOSFET was manufactured by forming the following. (G) p-channel MOSFET manufactured according to this example
exhibited characteristics equivalent to those of MOSFETs manufactured by conventional methods, and the threshold voltage was approximately -1.9V. Furthermore, if we convert the number of devices whose gate oxide film was destroyed in the device manufacturing process prior to measurement into defects in the gate oxide film per unit area, it will be approximately 50 defects/cm ² , making it possible to create MOSFETs with less dielectric breakdown during the process. was possible.

Example 2 In Example 1, a p-type substrate with a specific resistance of 3 to 5 Ω (100) was used instead of the n-type substrate with a specific resistance of 3 to 5 Ω,
By implanting 5×10 ¹⁵ /cm ² of A _S ⁺ ions at 130 KeV instead of B ⁺ ions to form the source and drain regions, an n-channel MOSFET with a threshold voltage of about 0.15 V was formed. The characteristics of this MOSFET were equivalent to those of the MOSFET manufactured by the conventional method, and the number of dielectric breakdowns of the gate oxide film was as small as in Example 1, making it possible to form a MOSFET with a high yield.

Example 3 The gate oxide film thickness was the same as in Example 1 by using tungsten containing oxygen instead of molybdenum containing oxygen in Example 1 and performing heat treatment at 1000°C for 60 minutes in a nitrogen atmosphere containing 10% hydrogen. Approximately 50n
m p-channel MOSFETs were formed, and the threshold voltage was approximately -1.5V. In this case, by using tungsten as the gate electrode, the specific resistance of the electrode was approximately 6×10 ^-5 Ωcm. The number of dielectric breakdowns in the gate oxide film was also small as in Example 1, and it was possible to form a MOSFET with a high yield.

(Effects of the Invention) As explained above, according to the present invention, since the formation of the gate electrode is completed before the formation of the gate oxide film, the surface of the gate oxide film is not exposed to the atmosphere, thereby preventing deterioration of dielectric strength due to contamination. In addition, it does not cause dielectric breakdown of the gate oxide film due to charging during processes such as gate electrode formation, and it also prevents dielectric breakdown of the gate oxide film due to charging during processes such as gate electrode formation. The high-temperature heat treatment that was previously performed after formation can be performed at the same time as gate oxide film formation, and destruction of the gate oxide film due to erosion of the gate electrode material can be avoided, so there is an advantage that MOSFETs with thin gate oxide films can be formed with high yield.

Furthermore, since the formation of the gate oxide film and the activation of the source and drain regions can be performed simultaneously by the same heat treatment, it also has the advantage of increasing the manufacturing efficiency of FETs.

[Brief explanation of drawings]

FIG. 1 shows the method for manufacturing a MOSFET according to the present invention in the order of steps. DESCRIPTION OF SYMBOLS 1...Silicon substrate, 2...Field oxide film, 3...Element region, 4...Molybdenum containing oxygen, 5...Resist, 6...Gate electrode, 7, 8
... Source, drain region, 9 ... Silicon dioxide film, 10 ... Gate oxide film, 11, 12, 13
... Contact hole, 14, 15, 16 ... Aluminum alloy wiring.

Claims (1)

[Claims] 1. In the process of manufacturing a MOSFET on a silicon substrate, a process of depositing a metal layer containing oxygen to cover an exposed silicon region that is to become an element region, and etching the metal layer to form a gate electrode. the silicon substrate by a step of forming an interlayer insulating film that transmits a reducing gas species and suppresses the transmission of oxygen generated from the metal, and a heat treatment in an atmosphere containing the reducing gas species. and forming a gate oxide film at the interface of the gate electrode. 2 As a metal layer, molybdenum, tungsten,
2. The method for manufacturing a MOSFET according to claim 1, wherein any one of chromium, vanadium, niobium, tantalum, or an alloy thereof is used. 3. The method of manufacturing a MOSFET according to claim 1, wherein the metal layer containing oxygen is deposited by sputtering in an oxygen-containing gas atmosphere.