Cure process for manufacture of low dielectric constant...

Details Cure process for manufacture of low dielectric constant... Cure process for manufacture of low dielectric constant...

1998-11-12

2001-03-13

Nelms, David (Department: 2818)

Semiconductor device manufacturing: process

Radiation or energy treatment modifying properties of...

By differential heating

C438S308000, C438S522000

Reexamination Certificate

active

06200913

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the field of semiconductor manufacturing. Specifically, the invention relates to improved methods for curing semiconductor thin films, and more specifically, the invention relates to methods for regulating the temperature and temperature changes to which semiconductor thin films are exposed during the curing process. The invention also relates to semiconductor products made using the curing processes.
2. Discussion of the Related Art
Interlayer dielectric layers comprise insulating materials whose purpose is to electrically separate conductive elements of integrated circuits. One property of dielectric materials is the dielectric constant. For certain purposes it is desirable to use materials with low dielectric constants. The manufacture of interlayer dielectric semiconductor thin films is typically carried out by first depositing the desired thin film on a semiconductor substrate. One common way of depositing thin films is by spin-on deposition. During spin-on deposition, a solution of precursor for the thin film is applied to a semiconductor wafer, and thereafter, the wafer is rotated at sufficiently high speed (rapid spinning step) to thin and even the layer of precursor solution. After the rapid spinning step, the solvents are permitted to evaporate, leaving a dried film of dielectric material. However, typically, some of the commonly used dielectric materials require subsequent processing, including curing the thin film at high temperature. The high temperature curing step can cross-link the precursor molecules together, making a tighter, stronger film with a low dielectric constant.
Unfortunately, the currently available methods for curing spin-on deposition films are inadequate for producing high-quality thin films. In one example of a prior art method, after a precursor solution is allowed to dry on a semiconductor wafer, the wafer is typically placed in a pre-heated oven or furnace to cure the thin film. SiO
2
—like films are typically cured at a temperature of about 400° C. The wafer is maintained at that high temperature for about one hour, and is then removed from the curing oven. Such treatments have disadvantages. If the wafer is placed into an oven pre-heated to a temperature that is too high, the thin film is subjected to high thermal/mechanical stress, and can crack, becoming weak and having an undesirably low dielectric strength and mechanical strength. Similarly, if the wafer is abruptly removed from the heated oven, the rate of cooling can be too high, causing high thermal/mechanical stresses, which degrade the performance of the film. Moreover, in the manufacture of multilayered films, with several levels of semiconductor features, the repeated heating and cooling of the underlying layers can cause progressively greater defects in the films.
Therefore, methods are needed which result in the rapid, efficient curing of spin-on thin films, while maintaining the desired low dielectric constant, high dielectric efficiency, and high mechanical strength.
SUMMARY OF THE INVENTION
Therefore, one object of this invention is the development of new methods for rapidly curing spin-on thin films for semiconductor manufacture.
Another object of this invention is the manufacture of spin-on dielectric thin films with improved dielectric properties.
A further object of this invention is the manufacture of spin-on dielectric thin films with improved mechanical strength.
Thus, the invention comprises new methods for heating and cooling semiconductor thin films, wherein the semiconductor with a solution of dielectric precursor is placed in a curing oven at a temperature above room temperature and the temperature is raised or “ramped up” at a predetermined rate to a maximum temperature, maintained at that maximum temperature for a period of time, and then cooled at a predetermined rate “ramped down” to a temperature sufficiently low to permit the wafer to be removed from the oven and exposed to ambient temperature conditions without the creation of undue mechanical stress.
One aspect of this invention is apparatus to cure semiconductor wafers, comprising a heating oven, and heating elements controlled by a processor to provide a predetermined temperature and rate of heating, maximum temperature, and the rate of cooling.
Another aspect of this invention is a method for increasing the temperature in a curing oven, whereby the rate of heating is regulated to minimize the thermomechanical stress to which the wafer thin films is subjected to during curing.
Another aspect of the invention is the curing of a semiconductor thin film beginning at a temperature sufficiently high to minimize the total curing time required, while minimizing the thermomechanical stresses to which the wafer is subjected.
Yet another aspect of the invention is the regulation of the rate of wafer cooling, whereby the thermomechanical stresses are minimized, while minimizing the total time taken to cure semiconductor wafers.
An additional aspect of this invention is the minimization of oxidation of the dielectric film by the use of inert gases in the curing oven to obtain desirable electrical properties.


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