Method of manufacturing a light-emitting device

On a support which supports a light-emitting semiconductor device there is arranged a cap which is hermetically sealed to the support. In the cap there is provided a transparent plate, an inner layer of which facing the semiconductor device consists of a material having a high refractive index (>1.7). On the outer side of the plate there is provided a layer of photosensitive lacquer which is exposed to the light emitted by the semiconductor device. After development of the layer of lacquer, only the exposed part which is situated opposite the semiconductor device remains. This part is heated to the melting point, thus forming a droplet of lacquer, after which the outer layer of the plate and the droplet of lacquer are removed by way of a non-selective etching method, so that a lens which is situated opposite the semiconductor device and a flat window which surrounds the lens are automatically formed at the same time.

BACKGROUND OF THE INVENTION 
The invention relates to a method of manufacturing a light-emitting device 
in which a cap comprising a flat, transparent widow is arranged on a 
support which supports a light-emitting semiconductor device, said cap 
being hermetically sealed to the support and said window being provided 
with a lens. The invention also relates to a light-emitting device 
manufactured by means of the method in accordance with the invention and 
comprising a support on which there is arranged a light-emitting 
semiconductor device and a cap which is arranged on the support and which 
is hermetically sealed thereto, said cap comprising a window with a lens. 
U.S. Pat. No. 3,816,847 discloses a method where a hemispherical lens is 
secured on a window formed by a flat glass plate by means of a suitable 
bonding material. The known method has drawbacks in that the correct 
alignment of the lens with respect to the semiconductor device situated 
within the envelope is difficult and time-consuming and in that very 
severe requirements must be imposed on the bonding material in order to 
prevent discoloration or deterioration of the bonding strength in the 
course of time. 
SUMMARY OF THE INVENTION 
It is the object of the invention to provide a method which ensures that 
the lens automatically occupies the correct position with respect to the 
semiconductor device, without it being necessary to provide a bonding 
material between the lens and the window. 
To this end, the method in accordance with the invention is characterized 
in that the window and the lens are formed by arranging a transparent 
plate in the cap, at least an inner layer of said plate which faces the 
semiconductor device being made of a material having a high refractive 
index, a layer of photosensitive lacquer being provided on the outer side 
of the plate after the connection of the cap to the support, after which a 
part of the layer of lacquer is exposed to light emitted by the 
semiconductor device, followed by development, so that only the exposed 
part which is situated opposite the semiconductor device remains, said 
exposed part subsequently being heated to the melting point, thus forming 
a droplet of lacquer, after which an outer layer of the plate and the 
droplet of lacquer are removed by a non-selective etching method so that 
the lens situated opposite the semiconductor device and a flat window 
surrounding the lens are formed at the same time. A high refractive index 
is to be understood to mean herein a refractive index which amounts to at 
least 1.7 for the light emitted by the semiconductor device. Because the 
photosensitive lacquer is exposed by the semiconductor device itself, the 
lens will be automatically formed in the position where the light of the 
device emerges from the window. Due to the heating, the lacquer melts, 
which means in this context that the lacquer becomes liquid or is softened 
to such an extent that it contracts so as to form a substantially 
dome-shaped droplet due to surface tension. Because the lens and the 
window are made of the same material, no separate bonding material is 
required for the bond between the window and the lens. 
A preferred version of the method in accordance with the invention is 
characterized in that on its side which faces the outer side of the cap, 
the plate which is used to form the window and the lens comprises a layer 
of a material having a refractive index which is lower than that of the 
material of the layer on its inner side, the etching operation being 
continued at least until the outer layer has been completely removed at 
the area of the lens. By a suitable choice of the refractive index and the 
thickness of the layer having a low refractive index, the dimensions of 
the lens can be influenced. This version of the method is related to a 
previous method of applying a lens on the surface of a non-exposed 
semiconductor laser previously proposed by Applicant (in unpublished NL 
Patent Application No. 8204273). 
The device in accordance with the invention is characterized in that the 
lens and the window are formed as one integral unit from a layer of 
material having a high refractive index. The semiconductor device is 
preferably a semiconductor laser.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The device shown in FIG. 1 comprises a metal support 1 with a raised 
portion 3 on which there is provided a light-emitting semiconductor device 
5, in this case a semiconductor laser. An electrode of the laser 5 is 
connected to a first connection pin 9 via the raised portion 3 and a 
connection wire 7. The second electrode is connected to a second 
connection pin 13 via a connection wire 11. The connection pin 13 extends 
to the outer side of the support 1 via a glass passage 17. On the support 
1 there is arranged a metal cap 19 which is hermetically sealed to the 
support by means of a welded joint 21. A hermetically sealed envelope of 
this kind is known, for example, from U.S. Pat. No. 4,295,152. 
Opposite the laser 5 (at the upper side in FIG. 1), the cap 19 comprises an 
aperture which is hermetically sealed by a transparent plate 23 through 
which light can emerge from the laser. During the phase of the method 
shown in FIG. 1, the plate 23 is provided on its outer side (the side 
which is remote from the laser 1) with a layer of photosensitive lacquer 
25. When the laser 5 emits a light-beam 27, a part of the layer 25 which 
is situated directly over the laser is exposed. 
FIG. 2 is a view at an enlarged scale of the part of the plate 23 with the 
layer 25 which is situated directly over the laser 5. The active part of 
the laser 5 is denoted by the reference numeral 29 in FIG. 2. The layer of 
lacquer 25 consists of a lacquer which is sensitive to the light which is 
emitted by the laser 5 at a wavelength of, for example 850 nm. These types 
of lacquers are commercially available, for example as Kodak 747 and 
Solvarist 6000. Due to the exposure, the solubility of the lacquer in the 
developer is reduced. 
In the embodiment shown, the plate 23 consists of two layers, that is to 
say a first layer 31 which is situated on the inner side of the envelope 
(facing the laser 5) and which consists of a material having a high 
refractive index, and a second, outer layer 33 which has a lower 
refractive index. The material of the first layer 31 has a refractive 
index of at least 1.7 for the light emitted by the laser 5. Suitable 
materials for this layer are, for example Y.sub.2 O.sub.3, As.sub.2 
S.sub.3, Dy.sub.2 O.sub.3, Gd.sub.2 O.sub.3, Tm.sub.2 O.sub.3, Yb.sub.2 
O.sub.3, Ga.sub.2 O.sub.3, HfO.sub.2, ZnS. Furthermore, various suitable 
types of glass having a high refractive index are also commercially 
available. The second layer consists of a material having a lower 
refractive index, for example SiO.sub.2, MgF.sub.2, or Al.sub.2 O.sub.3. 
The divergence of the light beam 27 emitted by the laser 5 is substantially 
less in the first layer 31 than in the space between the laser and the 
first layer. In the second layer 33, in which the refractive index is 
lower, the divergence is again higher. Consequently, the thickness of the 
outer layer 33 determines the width of the beam 27 at the area of the 
layer of lacquer 25 to a high degree. The choice of this thickness (and 
evidently also of the refractive index), therefore, determines the lateral 
extent of the exposed part 35 of the layer of lacquer 25 to a high degree. 
It will be apparent that the outer layer 33 may be omitted when extension 
of the width of the exposed part 35 of the layer of lacquer is not 
considered necessary. 
After the exposure, the layer of the lacquer 25 is developed, the exposed 
part 35 then remaining behind. The situation then obtained is shown in 
FIG. 3. 
The exposed part 35 of the layer is then heated to such a temperature that 
it melts. This temperature is below 100.degree. C. for most types of 
lacquer. Heating can be performed, for example by arranging the entire 
device in an oven or by exposing the part 35 to infrared light. In 
reaction to melting, the exposed part assumes the shape of a droplet of 
lacquer 37. Surface tension ensures that the surface of the droplet 37 
becomes spherical as appears from FIG. 4. The shape and the dimensions of 
the droplet 37 are depending on the shape and the dimensions of the 
exposed part 35 and, consequently, are co-determined by the thickness of 
the outer layer 33. 
After solidification of the droplet 37, the droplet, the outer layer 33 and 
a part of the inner layer 31 are removed by means of a non-selective 
etching method which produces the ultimate result shown in FIG. 5. A 
non-selective etching method is to be understood to mean herein an etching 
method which is approximately the same etching rate for the three 
materials of the layers 25, 33, 31, so that ultimately a lens 39 whose 
shape corresponds approximately to the shape of the droplet 37 is formed 
in the layer 31. A suitable etching method is, for example reactive ion 
etching. The part of the layer 31 which is situated adjacent the lens 39 
forms a flat window 41. FIG. 5 clearly shows that, thanks to the method 
used, the lens 39 is automatically formed exactly over the active part 29 
of the laser 5. 
FIG. 6 shows the complete light-emitting device after execution of the 
method in a sectional view which corresponds to that of FIG. 1. It appears 
that substantially no material has been removed from the cap 19 during the 
etching operation. This can be achieved by choosing an etching method 
which does not discriminate between the materials of the layer of lacquer 
25 and the plate 23, but which does not substantially affect the metal of 
the cap 19. Alternatively, the cap 19 may be protected by a layer of 
lacquer (not shown) during etching, said layer leaving an opening in the 
cap free at the window.