Pattern shift measuring method

A method of measuring pattern shift on a diffused semiconductor wafer after an epitaxial process including measuring a ratio between the line width of a linear pattern vertical to an orientation flat and line width of a linear pattern parallel to the orientation flat and estimating the shift between these patterns.

BACKGROUND OF THE INVENTION 
1. Field of the Invention: 
This invention relates to a method of measuring shift of patterns of a 
diffused semiconductor wafer after growth of an epitaxial layer thereon, 
and more particularly to a method of measuring the pattern shift without 
destroying the semiconductor wafer and in a short period of time. 
2. Description of the Related Art: 
It is essential to control the shift of a buried diffusion pattern after 
growth of an epitaxial layer in a bipolar transistor in an IC. For this 
purpose, the growth conditions (such as reaction temperature and reaction 
speed) should be always controlled to assure constant pattern shift. 
However, it is very difficult to strictly control the growth conditions 
since frequent measurement of the pattern shift is inevitable. 
Conventionally, the angular lapping stain method is used for this purpose. 
This method comprises: (1) slicing chips having a buried layer in parallel 
to and perpendicular to the orientation flat by using a dicing saw; (2) 
angular polishing of optional surfaces of the sliced tips 
(.theta.=11.degree. 32'); (3) etching the polished surfaces (Sirtl, 2 to 3 
seconds); and (4) measuring the shift of the patterns of the buried layers 
by using differential, interference micrographs (x 150). 
The pattern shift factor is obtained by the following equation: 
##EQU1## 
However since it takes approximately two hours to measure the pattern shift 
and requires destruction of specimens, this conventional method cannot be 
used so frequently and is rather expensive. 
To solve the problem of the conventional method, some proposals are made to 
perform the pattern shift measurement through non-destructive tests as 
disclosed in such publications as Japanese Patent Laid Open Publications 
64-31413 and 64-31414. Under the present circumstances, there is a great 
demand for a more simplified and reliable method of measuring the pattern 
shift. 
SUMMARY OF THE INVENTION 
It is therefore an object of this invention to provide a method of reliably 
measuring the pattern shift of a semiconductor wafer in a short period of 
time without destroying the semiconductor wafer. 
According to this invention, there is provided a method of measuring a 
shift between a diffusion pattern and a corresponding pattern on an 
epitaxial layer of a semiconductor wafer after the epitaxial process. The 
method comprises measuring a ratio between the line width of a linear 
pattern vertical to the orientation flat and line width of a linear 
pattern parallel to the orientation flat to determine the shift between 
these patterns. 
The pattern shift can be also determined only by measuring the line width 
of a linear pattern vertical to the orientation flat. 
Further, the pattern shift is determined only by measuring the line width 
of a linear pattern parallel to the orientation flat. 
According to this invention, the pattern shift can be reliably and 
inexpensively measured in about five minutes without destroying the 
semiconductor wafers. 
Many other objects, advantages and features of the present invention will 
be better understood from the following description taken in conjunction 
with the accompanying drawings.

DETAILED DESCRIPTION 
One embodiment of this invention will now be described with reference to 
the accompanying drawings. 
Measurement was performed under the following conditions: 
Specimens; CZ p-type semiconductor wafer &lt;111&gt; off-angle 3.degree. 30' in 
&lt;112&gt; 100.phi., 10-20.OMEGA.-cm, OF&lt;110&gt; 
Buried diffusion layer; Sb, 15.OMEGA./.quadrature., depth 8 mm 
Width of the buried diffusion layer; 60 .mu.m 
Epitaxial layer growth; 10 .mu.m, 1.OMEGA.-cm 
Reaction furnaces used; Cylindrical and vertical furnaces 
Reaction temperatures; 1150.degree., 1100.degree. and 1050.degree. C. 
Reaction speeds; 0.30 and 0.60 .mu.m/min 
Reaction pressure; 760 Torr 
Measurement; A Nomarski differential microscopic interferometer 
(magnification factor, .times.200) was used to measure the line width 
(W.sub.V) of a pattern vertical to the OF(orientation flat), and the line 
width (W.sub.H) of a pattern parallel to the OF. The measured values and 
the ratio W.sub.V /W.sub.H are shown in Table 1. 
TABLE 1 
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Reac- Conven- 
tion Reac- tional 
temper- tion pattern 
Furnace 
ature speed shift W.sub.V 
W.sub.H 
type (.degree.C.) 
.mu.m/min 
ratio (.mu.m) 
(.mu.m) 
W.sub.V /W.sub.H 
______________________________________ 
Vertical 
1150 0.30 0.594 61.9 63.2 0.98 
furnace 
" 0.54 0.900 61.9 63.9 0.97 
1100 0.30 0.986 61.3 65.2 0.94 
" 0.53 1.11 60.6 66.5 0.91 
1050 0.30 1.32 58.7 69.1 0.85 
" 0.53 1.32 56.7 68.5 0.83 
Cylin- 1150 0.25 0.98 61.9 63.9 0.97 
drical " 0.56 1.23 60.6 65.9 0.92 
furnace 
1100 0.28 1.35 60.6 67.8 0.89 
" 0.57 1.48 58.7 69.8 0.84 
1050 0.30 2.11 54.8 70.4 0.78 
" 0.58 2.01 56.7 70.4 0.81 
______________________________________ 
W.sub.V /W.sub.H =Line width (W.sub.V) vertical to OF&lt;110&gt;/Line width 
(W.sub.H) parallel to OF&lt;110&gt; . 
FIGS. 1 to 3 are graphs showing the correlation between the pattern shift 
ratios determined by the conventional method (angular lapping stain 
method), and the values W.sub.V /W.sub.H, W.sub.V and W.sub.H determined 
by the method of this invention. 
Any of W.sub.V /W.sub.H, W.sub.V and W.sub.H have correlations to the 
pattern shift ratio of the conventional method (W.sub.V /W.sub.H and 
W.sub.V have negative correlations and W.sub.H has a positive correlation 
to the conventional pattern shift ratio). It was confirmed that the 
pattern shift can be determined by measuring W.sub.V /W.sub.H, and W.sub.V 
or W.sub.H. 
In this embodiment, the buried diffusion layer is antimony (Sb). The method 
of this invention is also applicable to buried diffusion layers of 
impurities such as boron (B), phosphorous (P) and arsenic (As). 
According to this invention, it is possible to measure the pattern shift of 
the epitaxial semiconductor wafer in a short period of time without 
destroying the wafer. Therefore, measurement can be performed very 
frequently so that the growth conditions can be always kept optimum.