HERMETIC CAP LAYERS FORMED ON
LOW-K FILMS BY PLASMA ENHANCED
CHEMICAL VAPOR DEPOSITION
BACKGROUND OF THE INVENTION 5
Semiconductor device geometries have dramatically decreased in size since these devices were first introduced several decades ago. Paralleling this development, semiconductor device clock speeds, often measured in terms of 10 frequency, have gone from kilohertz (kHz) to megahertz (MHz) to gigahertz (GHz), requiring electronic signals to travel across device interconnects with increasing speed. As device geometries shrink, and device speeds increase, the need to reduce increased power consumption and signal 15 slowdown due to the RC time delay of the interconnects becomes increasingly important.
Two significant components of the RC time delay in interconnects are the resistance (R) of the conductive material (e.g., a metal such as Al or Cu) used in the interconnect, 20 and the capacitance (C) of the dielectric materials that insulate the interconnect from other conductive regions. Progress has been made on reducing the resistance of the interconnect by, for example, switching from less conductive aluminum to more conductive copper. Progress has also 25 been made on the development of dielectric materials having a lower dielectric capacity (i.e., low-K materials) to reduce the capacitance side of the RC time delay.
A number of low-K dielectric materials, and techniques for integrating them into semiconductor devices, have been 30 developed. These include, for example, incorporating fluorine or other halogens (e.g., chlorine, bromine) into a silicon oxide layer. Other low-K materials include spin-on-dielectrics such as hydrogen silsesquioxane (HSQ), and carbonsilicon containing dielectrics that are deposited by chemical 35 vapor deposition (e.g., plasma CVD), to form silicon-oxygen-carbon (Si—O—C) dielectric films. These materials are often deposited at low temperature (e.g., about 100° C. to about 200° C.) and low density, and often have substantially high porosity. 40
The high porosity of many of these low-K dielectric films makes them susceptible to being infiltrated by contaminants in an ambient atmosphere. For example, water vapor (i.e., moisture) can quickly permeate a porous dielectric material and increase the dielectric constant of the layer. In some 45 instances, the increase in K-value caused by the moisture can make the dielectric layer higher K than conventional, undoped oxide layers. Thus, there is a need for methods of protecting low-K dielectric layers from moisture infiltration that increases the dielectric constant of the layers. 50
BRIEF SUMMARY OF THE INVENTION
One embodiment of the invention includes a method of forming a cap layer over a dielectric layer on a substrate. The 55 method includes forming a plasma from a process gas that includes oxygen and a silicon containing precursor. The method also includes depositing the cap layer on the dielectric layer, where the cap layer has a thickness of about 600 A or less, and a compressive stress of about 200 MPa or 60 more.
Another embodiment of the invention includes a method of forming a cap layer over a dielectric layer on a substrate. This method includes forming a process gas by flowing together about 200 mgm to about 8000 mgm of a silicon 65 containing precursor, about 2000 to about 20000 seem of oxygen (02), and about 2000 seem to about 20000 seem of
carrier gas. The method also includes generating a plasma from the process gas, where one or more RF generators supply about 50 watts to about 100 watts of low frequency RF power to the plasma, and about 100 watts to about 600 watts of high frequency RF power to the plasma. The method further includes depositing the cap layer on the dielectric layer, where the cap layer has a compressive stress of 200 MPa or more.
Another embodiment of the invention includes a system for forming a cap layer over a dielectric layer on a substrate. The system includes a housing configured to form a processing chamber. The system also includes a gas distribution system to flow about 200 mgm to about 8000 mgm of a silicon containing precursor, about 2000 to about 20000 seem of oxygen (02), and about 2000 seem to about 20000 seem of carrier gas through a gas distribution faceplate and into the processing chamber. The system further includes a plasma generation system configured to form a plasma within the processing chamber, where the plasma generation system comprises one or more RF generators that supply about 50 watts to about 100 watts of low frequency RF power to the plasma, and about 100 watts to about 600 watts of high frequency RF power to the plasma. In addition, the system includes a substrate holder configured to hold the substrate about 350 to about 450 mils from the gas distribution faceplate within the processing chamber, where the cap layer formed has a thickness of about 600 A or less.
Additional features are set forth in part in the description that follows, and in part will become apparent to those skilled in the art upon examination of the following specification or may be learned by the practice of the invention. The features and advantages of the invention may be realized and attained by means of the instrumentalities, combinations, and methods particularly pointed out in the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross-sectional view of device layers including a cap layer formed according to embodiments of the invention;
FIGS. 2A-C are cross sectional views of device layers including a trench for a dual-damascene interconnect and a cap layer formed according to embodiments of the invention;
FIG. 3 is a flowchart illustrating methods of forming a cap layer according to embodiments of the invention;
FIGS. 4A and 4B are cross-sectional views of an embodiment of a chemical vapor deposition apparatus that may be used in conjunction with embodiments of the invention;
FIG. 5 is a plot of humidity induced stress versus cap layer thickness for cap layers formed with varying compressive stresses on a 200 mm wafer; and
FIG. 6 is a plot of humidity induced stress versus cap layer thickness for cap layers formed with varying compressive stresses on a 300 mm wafer.
DETAILED DESCRIPTION OF THE
The present invention includes methods of forming a cap layer on an underlying dielectric layer to prevent moisture from infiltrating the underlying layer and increasing its K-value (among other adverse effects). The cap layer may also act as a barrier for gaseous contaminants (e.g., NHX) diffusing through a porous dielectric layer and poisoning photoresist layers. These and other diffusion problems are