Semiconductor device and manufacturing method thereof

A semiconductor device includes at least one wiring layer containing aluminum as the major constituent and provided through an insulating film on a semiconductor substrate on which components or elements are formed, and a heat resistant high molecular organic film having a radical of small water absorbing property provided on side surfaces of the wiring layer. The heat resisting high molecular organic film is preferably formed of polyphenylene sulfide. A method of the semiconductor device includes the steps of forming components on a semiconductor substrate, forming an insulating film on the components to form an aluminum wiring layer by deposition and patterning, depositing a heat resistant high molecular organic film having a radical of small water absorbing property, and heating the heat resistant high molecular organic film at a temperature to fluidify to and flatten the heat resistant high molecular organic film.

BACKGROUND OF THE INVENTION 
This invention relates to a semiconductor device and a manufacturing method 
thereof, and is used particularly in a semiconductor device having high 
density wiring. 
For forming wirings between internal portions of semiconductor elements or 
components and external portions and/or between or components elements and 
external portions in a semiconductor device, various materials are used. 
Especially, for metal wirings, an aluminum alloy, for example, of aluminum 
and silicon, an alloy of aluminum, silicon and copper, etc. are used. 
Typically, an underlying structure of an electrode of polycrystalline 
silicon, etc. is formed on a semiconductor substrate and a wiring film 
made of an aluminum alloy is formed thereon. This wiring film is formed by 
depositing the aluminum alloy over the entire surface of the underlying 
structure using any one of such methods as sputtering, vacuum deposition 
and CVD, etc. to carry out patterning of a resist using photolithographic 
technique, and thereafter effecting etching with the resist as a mask. 
For preventing the aluminum alloy. film from being exposed and corroded by 
moisture in the air, a protective inorganic insulating film is formed 
thereon. As this inorganic insulating film, phosphosilicate glass (PSG) is 
generally used. 
Furthermore, multilevel wiring layer has often been formed in compliance 
with recent high density requirements. In such a multilayer structure, a 
first wiring film is formed on the underlying structure and a second 
wiring film is further formed thereon. In addition, an interlayer 
insulating film is deposited between these wiring films in order to ensure 
electrical insulating property therebetween. As this interlayer insulating 
film, silicon oxide film (SiO.sub.2) or silicon nitride film (Si.sub.3 
N.sub.4) which has moisture-proof property and an excellent insulating 
property is ordinarily used. Such an insulating film may include an 
impurity such as phosphorus, and is used as a single film or a composite 
film. The wiring width or the line width tends to decrease each year in 
accordance with recent tendencies of high integration and high density and 
has been reduced to the order of micron or submicron in recent years. As a 
result, such problems as breakage of aluminum wiring of a product occur 
during test or use of a semiconductor device. 
Such a breakage of aluminum wiring, is caused by thermal migration produced 
by thermal diffusion, electro migration produced by the movement of 
aluminum atoms as a result of a current flow, corrosion, and the like. 
Where an interlayer insulating film is formed, using the chemical vapor 
deposition (CVD) method, as described above, it is required to raise 
temperature to 300.degree. to 450.degree. C. In such an elevated 
temperature condition, the deposited film is in an equilibrium state 
wherein the stress is small. However, when the temperature is lowered to 
room temperature, great stress will be accumulated in the aluminum film 
due to the difference between the coefficient of thermal expansion of 
aluminum and that of the deposited film. Namely, the stress created in the 
aluminum film containing 1% silicon immediately after the wiring is formed 
by etching of the film is 10.times.10.sup.8 dyn/cm.sup.2, whereas the 
stress created in the aluminum film after Si.sub.3 N.sub.4 film has been 
deposited by plasma CVD at a temperature of 300.degree. C. is changed to 
30.times.10.sup.[ dyn/cm.sup.2. Thus it can be understood that the stress 
is considerably increased. Such a stress measurement is carried out by 
measuring the spacing between lattice planes by X-ray diffraction to 
compare the spacing measured with a lattice plane spacing when a known 
stress is created. 
It has been known that when such a stress is created, the possibility of 
breaking the aluminum layer is greatly accelerated so that breakage is 
likely to occur. 
Such problem also occurs in an interlayer insulating film of multilayer 
wiring. Particularly, breakage of the aluminum wiring which is the first 
layer presents the same problem. As a solution of this problem, a method 
has been proposed wherein a polyimide layer is formed between inorganic 
insulating films for the purpose of alleviating the stress of an aluminum 
wiring (e.g., Japanese Laid-Open patent specification No. 85724/1977). 
However, to form a polyimide layer, since it is required to dissolve the 
polyimide in a solvent to coat the solution and dry it, long-time heat 
treatments for drying and/or heat treatment for the subsequent 
polymerization are required. For this reason, the reduction of volume is 
large and it is difficult to form a flat polyimide layer on an irregular 
surface. 
A further problem is that a polyimide layer has large water absorbing 
capability, resulting in a tendency to give rise corrosion of aluminum, 
and that polarization is produced as a result of application of a voltage 
for a long time and thus the threshold value of the transistor changes due 
to polarization, so that an erroneous operation is likely to occur. 
SUMMARY OF THE INVENTION 
Therefore, an object of this invention is to provide a semiconductor device 
and a manufacturing method thereof capable of alleviating the stress 
created in an aluminum wiring layer thereby preventing breakage thereof. 
Another object of this invention is to provide a novel method of 
manufacturing a semiconductor device, at a high yield and which can 
operate stably. 
According to one aspect of this invention there is provided a semiconductor 
device comprising: 
a one wiring layer containing aluminum as major constituent part and 
provided on an insulating film on a semiconductor substrate on which 
semiconductor elements are formed; and 
a heat resistant high molecular organic film having a radical of small 
water absorbing property of less than 10 PPM the organic film being 
provided on a side surface of the wiring layer. 
According to another aspect of this invention there is provided a method of 
manufacturing a semiconductor device comprising the steps of: 
forming semiconductor elements on a semiconductor substrate; 
forming an insulating film on the semiconductor elements; 
forming an aluminum wiring layer on the insulating film by deposition and 
patterning thereon; 
depositing a heat resistant high molecular weight organic film containing a 
radical having a small water absorbing property on an entire surface of 
the semiconductor device; and 
heating said heat resistant high molecular organic film at a temperature to 
fluidify and flatten said heat resisting high molecular organic film. 
In a modified method of this invention a semiconductor device is 
manufactured by a method of manufacturing a semiconductor device 
comprising the steps of: 
forming components of said semiconductor device on said element on a 
semiconductor substrate; 
forming an insulating film to form an aluminum wiring layer by deposition 
and patterning; 
depositing an inorganic insulating film on said aluminum wiring layer, said 
inorganic insulating film having a thickness larger than that of said 
aluminum wiring layer; 
back etching said inorganic insulating film to expose surface of said 
aluminum wiring layer; and 
depositing a heat resistant high molecular organic film having a radical of 
small water absorbing property on the entire surface.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIGS. 1A to 1C are cross sectional views of successive process steps 
showing a method of manufacturing a semiconductor device according to this 
invention. 
On a semiconductor substrate 11, is formed an aluminum wiring layer 13 
having a thickness of 0.8 .mu.m and a width of 0.12 .mu.m, for example, 
through a silicon oxide film 12 formed by thermal oxidation, etc. In the 
semiconductor substrate 11 are formed impurity diffused regions (not 
shown) to be utilized as source and drain, electrodes, respectively. After 
that, an organic film 14 is formed thereon (FIG. 1A). As the material for 
this organic film, polyphenylene sulfide (PPS) is used and film deposition 
is carried out by sputtering. Namely, a target consisting of polyphenylene 
sulfide and a substrate subject to deposition are mounted in an atmosphere 
of argon with the target held opposite to the substrate. By applying a 
high frequency power of, e.g., 13.56 MHz to the target, glow discharge is 
produced to deposite scattered molecules of polyphenylene sulfide on the 
substrate subject to deposition. Such a condition is shown in FIG. 1A. The 
deposited organic film has an excellent step coverage characteristic over 
rib shaped aluminum wiring layer 13 and the thickness of the organic film 
is about 0.4 .mu.m substantially uniformly over the entire surface. 
When the aluminum film is sintered at a temperature of about 450.degree. 
C., since PPS is a thermoplastic material having a glass transition 
temperature of approximately 280.degree. C., the deposited organic film 
becomes thin on the upper surfaces of the respective aluminum wiring 
layers and becomes thick between aluminum wiring layers because the 
deposited organic film has fluidity at high temperatures, resulting in an 
organic film 14' having uneven less thickness (FIG. 1B). In this instance, 
since PPS has a high heat resistant (decomposition temperature: over 
450.degree. C.) property, it :s slightly softened by heat during sintering 
or CVD process for depositing such as inorganic protective layer but does 
not change its nature, such as decomposition. It is to be noted that PPS 
is a thermoplastic high molecular compound having a chain polymerized 
structure such as 
##STR1## 
In each unit sulfur is coupled with a phenol ring. This compound has 
excellent properties in that the heat resistant property is good and the 
water absorbing property is low (less than 10 PPM) because the molecules 
have no polarity. It is well known that this water absorbing property 
(hydroscopicity) can be easily measured by the mass analysis of water 
content before and after vaporization by heating. 
Subsequently, a silicon nitride film 15 is deposited on the organic film 
14' by plasma CVD method to a thickness of about 0.5 .mu.m (FIG. 1C). 
The stress in the aluminum film 10.times.10.sup.8 dyn/cm.sup.2 after the 
aluminum pattern has been formed, 12.times.10.sup.8 dyn/cm.sup.2 after the 
organic film has been formed and sintered, and 15.times.10.sup.8 
dyn/cm.sup.2 after silicon nitride film has been formed by CVD method. 
Thus, it is seen that the stress is greatly less than that in the prior 
art method. 
FIG. 2 is a graph showing the relationship between the aluminum line width 
and the time elapsed until before breakage, wherein the ordinate shows 
Mean Time to Failure (MTF) required until one half of the aluminum lines 
are broken when a current of 2.times.10.sup.9 A/cm.sup.2 is caused to flow 
at a temperature of 200.degree. C. in the conventional structure and the 
structure according to this invention respectively. This graph, shows that 
in the conventional structure, MFT abruptly lowers as the line width 
becomes narrower, whereas in the structure of the invention, the MFT is 
not affected even if the line width becomes narrower so that high MTF is 
maintained. It is considered that this is because that the stress is 
relieved by the organic film layer. 
FIGS. 3A to 3C are cross sectional views of successive process steps 
showing a second embodiment according to this invention. In this 
embodiment, organic film (PPS) 16 is deposited to be thicker than that of 
the above-mentioned embodiment shown in FIG. 1, i.e., it has a thickness 
of 0.8 .mu.m. The organic film 16 is further flattened by heat treatment 
(FIG. 3A). 
Then, etching using oxygen plasma is carried out to remove the upper 
surface of the organic film 16, thus allowing the upper surfaces aluminum 
film 13 and the organic film 16' to be at substantially the same level 
(FIG. 3B). Thereafter, a silicon nitride film 17 is deposited thereon to a 
thickness of 0.5 .mu.m (FIG. 3C). In this case, the stress created between 
the silicon nitride film and the aluminum film is only shearing stress 
along the surface A in FIG. 3C. Thus, the entire stress will be greatly 
reduced when compared to the case where stress is applied to the side 
surfaces of the aluminum film. 
FIGS. 4A to 4C are cross sectional views of successive process steps 
showing a third embodiment according to this invention, respectively. In 
this embodiment, a silicon oxide film 18 is deposited by the CVD method to 
a thickness thicker than that in the second embodiment, i.e., it has a 
thickness of about 0.9 .mu.m. Then an ordinary resist 19 is coated so that 
the thickest portion thereof has a thickness of about 2.0 .mu.m. Then it 
is flattened (FIG. 4A). 
Then, by using a plasma etching method under a condition wherein the 
etching speeds of the resist and the silicon oxide film 18' are 
substantially equal to each other, etch back is carried out until the 
surface of the aluminum film 13 is exposed (FIG. 4B). 
Thereafter, a PPS film 20 (0.4 .mu.m thick, and a silicon nitride film 21 
are deposited by the sputtering and the CVD method, respectively. At this 
time, since the silicon nitride film 21 is formed on a flattened surface 
in the same manner as in the case shown in FIG. 3C, stress is limited to 
only shearing stress acting along the flattened surface. Thus, total 
stress is reduced to an extremely small value, with the result that the 
possibility of breaking is decreased (FIG. 4C). 
FIG. 5 is a cross sectional view of a device showing an example where this 
invention is applied to a multilayer wiring. Etch back is carried out so 
that the PPS film is present on both the sides of aluminum film 13 in the 
same manner as in FIG. 3B to form a silicon oxide film 22 on the entire 
surface. Contact holes 24 for connecting a first aluminum layer 13 with a 
second aluminum layer 23 are opened at predetermined positions of the 
silicon oxide film 22. Then a second aluminum layer 23 is formed by vacuum 
deposition and etching processes, and a PPS film 25 and a silicon nitride 
film 26 are formed. The PPS film 25 and nitride film 26 are formed in the 
same manner as shown in FIGS. 1A to FIG. 1C. In such a construction, the 
stress applied to the aluminum wiring layer of the first layer will be 
relieved by the organic film 16, and the stress applied to the aluminum 
wiring layer 23 of the second layer will be relieved by the PPS film 25 
and the silicon oxide film 26. 
FIGS. 6 and 7 are explanatory views showing an example of the sedimentation 
method as the deposition method instead of sputtering in forming PPS film. 
As shown in these figures, a liquid 32 such as water which is chemically 
inert to PPS is filled within a vessel 31. On a supporting body 34 
provided at the bottom surface of the vessel 31, is mounted a 
semiconductor substrate 11 having aluminum wiring 13 with its upper 
surface to be deposited positioned upwardly. Fine grains 33 of PPS are 
mixed into the liquid 32. As such fine grains 33, a powder of PPS having a 
mean diameter of 0.1 .mu.m is used. 
A method of depositing PPS using a device will be now described. Fine 
grains 33 of PPS are heavier than water because its specific gravity is 
1.6. Accordingly, when the mixture of such fine grains 33 and water is 
stirred and then left to stand still, the grains gradually sink and 
deposit on semiconductor substrate 11 as shown in FIG. 7, resulting in a 
deposited film 35. This deposited film 35 cannot be used as it is because 
it has many voids and therefore its density is small. However, by carrying 
out heat treatment for twenty minutes in an atmosphere of nitride gas at a 
temperature of 500.degree. C., a film having a density similar to a bulk 
film can be provided. 
While PPS is used as the organic material in the above-mentioned 
embodiments, other materials having a low glass transition temperature and 
soft, high decomposition temperature, excellent heat resistant property, 
no molecular polarity, and low hygroscopicity (less than 10 PPM) may be 
used. Such materials may be used for the heat resistant high molecular 
weight material, 
##STR2## 
having no polarity and having radicals of small water absorbing property 
as S, CO, etc. 
In addition, as a method of forming an organic film, various methods, e.g. 
the electrostatic coating method wherein electric charge is applied to a 
powder of organic material for attracting the particles onto a 
semiconductor substrate by application of an electric field to thereby 
deposit them, and the like may be used.