Process for forming thin dielectric layers in semiconductor...

Details Process for forming thin dielectric layers in semiconductor... Process for forming thin dielectric layers in semiconductor...

1999-02-08

2001-08-28

Pompey, Ron (Department: 2812)

Semiconductor device manufacturing: process

Coating of substrate containing semiconductor region or of...

By reaction with substrate

C438S771000

Reexamination Certificate

active

06281141

ABSTRACT:

FIELD OF THE INVENTION
The present invention is generally directed to a process for forming thin dielectric layers in semiconductor devices. More particularly, the present invention is directed to a process for forming thin dielectric layers on semiconductor wafers in rapid thermal processing chambers, wherein the layers are formed very quickly while the temperature of the wafer is being increased. In particular, the layers are formed during the “ramp up” portion of a heating cycle. Dielectric layers that may be formed according to the present invention include silicon dioxide layers that may be doped with a nitrogen specie.
BACKGROUND OF THE INVENTION
In general, an integrated circuit refers to an electrical circuit contained on a single monolithic chip containing active and passive circuit elements. Integrated circuits are fabricated by diffusing and depositing successive layers of various materials in a preselected pattern on a substrate. The materials can include semiconductive materials such as silicon, conductive materials such as metals, and low dielectric materials such as silicon dioxide. Of particular significance, the semiconductive materials contained in integrated circuit chips are used to form almost all of the ordinary electronic circuit elements, such as resistors, capacitors, diodes, and transistors.
Integrated circuits are used in great quantities in electronic devices, such as digital computers, because of their small size, low power consumption, and high reliability. The complexity of integrated circuits range from simple logic gates and memory units to large arrays capable of complete video, audio and print data processing. Presently, however, there is a demand for integrated circuit chips to accomplish more tasks in a smaller space while having even lower operating voltage requirements.
As stated above, integrated circuit chips are manufactured by successively depositing layers of different materials on a substrate. Typically, the substrate is made from a thin slice or wafer of silicon. The active and passive components of the integrated circuit are then built on top of the substrate. The components of the integrated circuit can include layers of different conductive materials such as metals and semiconductive materials surrounded by low dielectric insulator materials. In attempting to improve integrated circuit chips, attention has been focused upon reducing the thickness of the layers while improving performance.
For instance, one area of circuit chip technology needing improvement is in the deposition of insulator or dielectric materials used in the chips. Such an insulator material should have a very high resistivity, as low as possible dielectric constant, and sustainability of subsequent process steps and materials used in chip manufacturing. The low dielectric insulator materials are incorporated into integrated circuits in order to reduce power dissipation when the circuit is in use.
Thin dielectric layers are being used routinely in the manufacturing of semiconductor devices for applications such as gates, capacitor dielectrics, besides various other uses. The most prevalent dielectric used in semiconductor devices is silicon dioxide, which can be formed through the reaction of oxygen and silicon at high temperature. Alternatively, steam can be reacted with silicon at high temperature to form silicon dioxide. In the past, silicon dioxide layers have been formed in conventional batch furnaces. Recently, as opposed to batch furnaces, such layers have also been formed in rapid thermal processing systems. The use of rapid thermal processing systems offers the advantages of short time high temperature processing which provides process advantages over using conventional furnaces.
In many advanced applications, silicon dioxide layers need to be doped with desired amounts of a dopant, such as a nitrogen specie, in order to improve the performance of the dielectric. The method by which the nitrogen dopant is incorporated into a silicon dioxide dielectric layer is complicated since it is necessary to control not only the concentration of nitrogen incorporated into the silicon dioxide but also its location within the oxide layer.
As described above, in order to produce advanced, fast acting devices, a need currently exists for producing dielectric layers having a minimal thickness. As the thickness of such dielectric layers decreases, however, significant difficulties arise in being able to properly and repeatably create thin nitrogen doped layers. In fact, even conventional 30 second to 120 second heating cycles conducted in rapid thermal processing chambers that are used to produce such layers become too long to provide controls sufficient to meet some of the requirements that are currently being specified.
Thus, a need currently exists for a process for producing thin dielectric layers that are uniform and that have improved electrical properties. A need also exists for a process for doping thin oxide layers. A need further exists for a rapid process for forming thin silicon dioxide layers doped with a nitrogen species.
SUMMARY OF THE INVENTION
The present invention recognizes and addresses the foregoing disadvantages, and others of prior art constructions and methods.
Accordingly, it is an object of the present invention to provide a process for depositing a material on a substrate.
Another object of the present invention is to provide a process for depositing a thin dielectric layer on a semiconductor wafer.
It is another object of the present invention to provide a process for producing very thin silicon dioxide layers on semiconductor wafers that are doped with a nitrogen species.
Still another object of the present invention is to provide a process for producing thin silicon dioxide layers that are doped with a nitrogen species and which are formed in a rapid thermal processing chamber.
Another object of the present invention is to provide a process for producing thin oxide layers in a rapid thermal processing chamber in which the layers are formed during the ramp up portion of the heating cycle within the chamber, meaning that the layers are formed while the temperature is being increased at a particular rate.
These and other objects of the present invention are achieved by providing a process for forming thin oxide coatings on a semiconductor device. The process includes the steps of placing a semiconductor wafer in a thermal processing chamber, such as a chamber heated using light energy. The semiconductor wafer is heated in the chamber such that the wafer is increased in temperature to a target temperature at a preselected rate. A reactive gas capable of forming an oxide coating on the wafer is circulated through the chamber. The gas is reacted with the semiconductor wafer to form an oxide coating on the wafer while the temperature of the wafer is being increased at the preselected rate to the target temperature. Prior to cooling, the wafer is maintained at the target temperature for a short period of time, such as less than about 2 seconds, and particularly for less than about 1 second. The oxide coating formed according to the present invention is very thin and can have a thickness of up to about 60 angstroms, and particularly from about 10 angstroms to about 50 angstroms, and more particularly from about 15 angstroms to about 40 angstroms.
In one embodiment, the gas circulated within the chamber can form a silicon dioxide coating on the wafer. For instance, the gas can contain molecular oxygen, steam, or mixtures thereof. The target temperature at which the wafer is heated can be from about 700° C. to about 1,200° C. and particularly from about 850° C. to about 1,150° C. The rate at which the wafer is heated can be an average rate of from about 10° C. per second to about 500° C. per second and particularly from about 50° C. per second to about 250° C. per second.
As opposed to conventional processes, the oxide layer is primarily formed while the wafer is being heated. In the past, typically most of the coating was formed while the wafer rema

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