JPS6146974B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for forming insulating layers and conductive layers of semiconductor devices such as ICs and LSIs.

When manufacturing semiconductor devices such as ICs and LSIs, it is necessary to form insulating layers and conductive layers for wiring. In this case, the insulating layer has a window to enable electrical connection between the layer above and the layer below. FIG. 1 shows and explains this.

In the figure, a lower conductive layer A is a semiconductor region or a lower wiring region, and an insulating layer B is formed thereon. A window (contact hole) is formed in the insulating layer B by removing a region a-a' by a method such as photoetching. Furthermore, a metal wiring layer C is formed on this by vapor deposition.
In the area of window a-a' of insulating layer B, wiring layer C
is in direct contact with the lower conductive layer A. In this case, if vapor deposition is performed only from the direction indicated by the arrow d in the figure, the portion of the conductive layer C that is in contact with the side surface of the window of the insulating layer B will be deposited because the side surface of the window is approximately parallel to this direction. The metal layer thickness is thinner than other parts. Therefore, disconnections in the wiring layer, so-called "step breaks", are likely to occur at these portions b and b'.
To prevent this, there is a method of increasing the thickness of the evaporated film in portions b and b' by simultaneously using evaporation from the directions of arrows c and e, but this method not only increases the number of steps but also causes the wafer surface of the semiconductor to move in the direction of evaporation. This makes it difficult to perform uniform vapor deposition over the entire wafer surface.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art, and to provide a method for forming insulation and wiring layers of a semiconductor element, which is less likely to cause disconnection of the wiring layer on the side surface of the window of the insulating film, and which is highly productive. .

One feature of the present invention is that in forming an insulating layer of a semiconductor element, a polyimide resin (photosensitive polyimide) containing a photosensitive group therein is used as a material for the insulating layer.

Photosensitive polyimide resin contains photosensitive groups, and like photoresists, the exposed areas are hardened or removed by development processing, and can be developed by exposing the required pattern using a mask etc. Through the treatment, an insulating film of polyimide resin formed in the pattern can be obtained.

Furthermore, in the present invention, as a light source when exposing the photosensitive polyimide, a laser beam focused to a fine spot diameter by a lens or the like is used, and this laser beam is scanned over the entire surface of the wafer to be exposed, Another feature is that a method is used to control the laser beam on and off depending on the pattern to be exposed.

Furthermore, in the present invention, during exposure by scanning irradiation of the laser spot, the intensity distribution in the cross section of the spot is not rectangular but has an intensity distribution that is high at the center and continuously decreases as it moves toward the periphery, like a Gaussian distribution. The exposure amount at the edge of the exposure pattern decreases continuously by a method of slowing down the rise and fall when controlling the laser irradiation power on and off. A feature is that the polyimide film is formed so as to have a gentle slope on the side surface of the window formed as described above.

By using the above method to obtain a polyimide insulating film with a gently sloped edge of the pattern, the wiring material on which a metal material is vapor-deposited has the same thickness on the side of the window as on other parts. Therefore, there is an effect that no breakage occurs in this part.

Hereinafter, the present invention will be explained in detail based on specific examples. FIG. 2 is a block diagram of an apparatus for exposing photosensitive polyimide on a semiconductor wafer by scanning a laser spot. In the figure, 1 is a laser oscillator, and 2 is a laser beam output from the laser oscillator 1. , 3 is a light modulation element, 4 is a drive circuit for the light modulation element 3, 5 is a polygonal rotating mirror that reflects the laser beam 6 outputted via the light modulation element 3, and 8 is a mirror for transmitting the reflected laser beam 6. and a half mirror for reflection, 7 is a detection laser beam reflected by the half mirror 8, 9 is a condensing lens for the laser beam 6 transmitted through the half mirror 8, and 10 is a condensing spot obtained by the lens 9. , 11 is a wafer placed on the sample stage 12, and 16 is a linear encoder attached to the sample stage 12. Further, 13 is a condensing lens that condenses the detection laser beam 7, 14 is a diode array disposed at the condensing spot of the condensing lens 13, and 18 is a lens disposed on the opposite side of the diode array 14. The output laser beam is input to a photodetector 19.
The output of the photodetector 19 and the output of the linear encoder 16 are input to a control device 15, and the output thereof is input to a light modulation element drive circuit 4 to drive and control the light modulation element 3. A reference numeral 20 stores information on whether to perform laser irradiation (pattern to be exposed on the wafer) and sends a signal to that effect to the light modulation element drive circuit 4 via the control device 15. It is.

It is assumed that the laser beam 2 emitted from the laser oscillator 1 shown in FIG. 2 has a wavelength within the photosensitive wavelength range of photosensitive polyimide. The laser beam 2 emitted from the laser oscillator 1 is modulated on and off by an optical modulator 3 driven by a drive circuit 4, then reflected by a multifaceted rotating mirror 5, and after passing through a half mirror 8. A condensing spot 10 is connected by a condensing lens 9 onto a wafer 11 coated with photosensitive polyimide. When the multifaceted rotating mirror 5 rotates in the direction of arrow a, the condensing spot 10 moves on the wafer 11 in the direction of arrow b. On the other hand, the sample stage 12 on which the wafer 11 is placed is moved by a motor (not shown) in a direction perpendicular to the light focusing spot that moves over the wafer 11. A linear encoder 16 is installed on the sample stage 12 and converts the position of the sample stage 12 into an electrical signal and sends it to the control device 15.
Therefore, the condensing spot 10 scans the wafer surface as shown in FIG.

That is, in FIG. 3, the wafer surface is perpendicular to the condensing spot, but arrow a is the direction in which the condensing spot is moved by the multifaceted rotating mirror 5, and arrow b is the direction in which the condensing spot is moved by table movement. It is. By performing both at the same time, the condensing spot moves along the scanning line on the wafer.
The wafer surface is scanned planarly by moving in the order of b and c. In this case, by changing the ratio of the speed of movement in the six directions due to the rotation of the multifaceted rotating mirror 5 and the speed of movement in the direction perpendicular to the direction of movement of the condensing spot due to table feeding, the way in which adjacent scanning lines overlap can be changed. .

Returning to FIG. 2, a portion of the laser beam reflected by the multifaceted rotating mirror 5 is reflected by the half mirror 8.
It is reflected by the laser beam 7 for detection, and is reflected by the condensing lens 13 into the diode array 14.
A light condensing spot 17 is connected to the top. Multi-sided rotating mirror 5
As the lens rotates in the direction of arrow a, the condensing spot 17 moves in the direction of arrow c. The diode array 14 is a flat plate made of a transparent material with many grooves cut into it, and the light that passes through this is bent by a lens 18 and enters a photodetector 19. When the condensing spot 14 moves in the direction of arrow c with the rotation of the multi-faceted rotating mirror 5, the photodetector 19 detects the change in the amount of incident light due to the grooves of the diode array 14, converts this into an electric signal, and controls it. It is sent to device 15.

Based on the electrical signal from the photodetector 19 and the signal from the linear encoder 16, the control device 15 rotates the surface of the wafer 11 in a polygonal manner so that the condensing spot 10 scans the surface of the wafer 11 at a predetermined speed. The rotation speed of the mirror 5 and the moving speed of the sample stage are controlled (therefore, the control device 1
5 to the drive device for the multifaceted rotating mirror 5 and the drive device for the sample stage, but this is not shown in the figure because it would be complicated). In addition, storage device 2
0, a pattern desired to be exposed on the wafer 11 is input in advance. That is, the coordinates on the wafer 11 and an instruction as to whether or not to perform laser irradiation at that location are input into the storage device 20. The control device 15 learns the position of the condensing spot 10 on the wafer 11 based on the signals from the photodetector 19 and the linear encoder 16, and inputs into the storage device 20 whether or not to perform laser irradiation at the coordinates of this position. A signal is sent to the light modulation element drive circuit 4 to determine whether or not to perform laser irradiation.

Based on this signal, the light modulation element drive circuit 4
The power for driving the light modulation element 3 is changed. The light modulation element 3 is a light modulation element using an acousto-optic effect or an electro-optic effect, and modulates the laser beam 2 on and off based on driving power.

With the configuration and functions described above, the photosensitive polyide coated on the wafer 11 is exposed by the laser spot 10 according to a pattern inputted into the storage device 20 in advance.

The laser oscillator 1 has an oscillation wavelength within the photosensitive wavelength range of photosensitive polyimide, and its output mode is high repetition pulse output or continuous output. In the case of pulse output, this is achieved in the present invention as follows.

FIG. 4 shows the laser power density distribution at the laser spot, with the horizontal axis representing the distance from the center of the laser spot and the vertical axis representing the laser power density. FIG. 4 1 is an example of multimode oscillation, in which the total power is large and the power density distribution shape is nearly rectangular.
Therefore, it is characterized in that the power density decreases rapidly at the ends of the distribution. FIG. 42 shows the case of single mode oscillation, where the total power is lower than in the case of FIG. 41 and forms a Gaussian distribution with the apex at the center of the spot. Therefore, the power density gradually decreases as it moves away from the center of the spot. Single mode oscillation can be obtained by inserting a narrow diameter pinhole on the optical axis within the laser oscillator.

Furthermore, although FIG. 4 3 has a beam cross section similar to that in FIG. 4 2, the power density decreases more gradually as the spot diameter increases and the distance from the center of the spot increases. is a feature. This distribution can be obtained by changing the diameter of a pinhole inserted into the laser oscillator or by changing the focal length of a lens that focuses the laser beam.

FIG. 5 shows the relationship between the exposure amount of photosensitive polyimide and the residual rate after development. Here, the photosensitive polyimide is assumed to be negative type. That is, the exposed portions remain after development, and the unexposed portions are removed after development.

Further, FIG. 61 shows the position of a laser spot irradiated on a wafer surface in the case of a pulsed laser, and the figure shows the wafer viewed from above. That is, the laser beam is scanned in the direction of the arrow and the laser pulses are irradiated at a fixed number of repetitions, so that the laser spots are irradiated at locations A, B, C, and D. The spacing between spots is determined by the relationship between the pulse repetition frequency and the scanning speed, and this is assumed to be set so that adjacent irradiation spots maintain appropriate overlap as shown in the figure.

FIG. 62 shows the irradiation power density distribution on the center lines a and a' of laser scanning in FIG. 61. In this case, the power density distribution of one laser spot has the shape shown in FIG. 4 2 or 3.

FIG. 6 3 shows the cumulative total of the laser energy irradiated in this manner on the vertical axis. That is, it shows the total density of irradiation energy from each spot that is repeatedly irradiated. FIG. 64 shows the remaining amount of photosensitive polyimide determined from the irradiation energy density, ie, the exposure amount, shown in FIGS. 3 and 9 and the graph shown in FIG. 5. Since the intensity is gradually decreasing around the irradiation spot, the thickness of the remaining portion of the photosensitive polyimide in FIG. 6 is gradually decreasing around the irradiation spot. In FIG. 6, a wiring layer is formed by metal vapor deposition from above. In this manner, the thickness changes gently around the photosensitive polyimide and the side surfaces thereof are sloped, so that a wiring layer having a sufficient thickness can be formed on the side surfaces as well as for vapor deposition from above. For this reason, Fig. 6
In this case, so-called step breaks are less likely to occur.

As described above, by repeatedly irradiating a laser spot with a gentle power density distribution to form a pattern, it is possible to form a pattern that is less likely to break. In this case, the objective is to avoid step breakage, and for this purpose, the necessary slope of the side surface of the polyimide film is determined, and the necessary laser power density distribution is determined based on the photosensitive characteristics of polyimide shown in Figure 5, etc., and the laser oscillation is performed. A laser spot with this power density distribution is realized by inserting a pinhole inside the laser beam, changing the focal length of the objective lens, etc.

Next, when the oscillation output of the laser is a continuous output, the object of the present invention can be achieved as follows.

FIG. 71 is a diagram showing signals for turning on and off a laser to form a pattern. That is, it is a signal sent from the control device 15 to the light modulation element drive circuit 4 in FIG. The horizontal direction is the time axis, and the vertical direction shows the magnitude of voltage. It is assumed that the light modulation element performs light modulation so that the laser is irradiated in areas where the voltage is high, and the laser is not irradiated in areas where the voltage is low.

Also in this case, the power density distribution of the laser spot is assumed to have a shape as shown in FIGS. 2 and 3.

FIG. 72 shows the irradiation range of the laser spot that is turned on and off using the waveform of FIG. 71. In FIGS. 3 to 5, the horizontal axis indicates the distance in the moving direction of the laser spot, as in FIG. 6. That is, FIG. 7 3 is a of FIG. 7 2,
The irradiation energy density on the a′ line is shown. FIG. 7 is a cross-sectional view showing the remaining film thickness of the exposed photosensitive polyimide after development.
FIG. 7 is a cross-sectional view of the result of depositing a metal film wiring layer thereon. As shown in these figures, even in the case of continuous output, the power density gradually decreases around the laser spot, so the remaining polyimide film thickness gradually decreases around the periphery, and the slope of the side surface becomes gentle. Therefore, the thickness of the wiring layer is not reduced even on the side surfaces, and step breaks are less likely to occur.

In this case, it is necessary to form a spot shape with an appropriate power density distribution in order to achieve the purpose, as in the case of pulse output described above.

Next, in FIG. 8, another implementation method using a continuous output laser is shown. Figure 8 1 is
This is the original form of the signal that turns the laser on and off to form a pattern, and is the same as in FIG. 71. The method shown in FIG. 8 differs from the method shown in FIG. 7 in that the method shown in FIG.
The signal in FIG. 1 is transformed into the signal in FIG. This allows the signal to rise and fall slowly.

Similarly to FIG. 7, FIG. 3 shows the range irradiated by the laser spot. In this case, the intensity distribution of the laser spot does not necessarily have to have a gentle slope at the periphery.

Since the input signal to the light modulation element driving circuit has the shape shown in FIG. 8, the power density of the irradiated laser becomes as shown in FIG. 8, 4. As a result, Fig. 8 5,
6 is obtained as in the case of FIG. 7.

As is clear from the above-mentioned embodiments, according to the present invention, it is possible to form an insulating layer and a wiring layer of a semiconductor element with high productivity, in which wiring pipes are less likely to break on the window side surface of an insulating film. In addition, in order to scan the laser spot and perform drawing exposure,
It can be directly connected to CAD (Computer Aided Design), eliminates the need for mask production, and provides a system that allows easy pattern changes. Furthermore, since the laser has high power and a single wavelength, there is less loss of optical energy than when exposing with a mask using light with a wide wavelength range such as from a mercury lamp, and the exposure time for the same area is It also has the advantage of being short.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a semiconductor for explaining a method of manufacturing a semiconductor according to the prior art, and FIG. 2 shows an embodiment of the present invention. A schematic configuration diagram of an apparatus for exposing polyimide.
Figure 4 shows the scanning lines on the wafer surface when the laser spot is scanned by the device shown in the figure. Figure 4 shows the power density distribution in the cross section of various laser spots. Figure 5 shows the photosensitive laser spot. Figures 6 1-5 and 7 1-5 are diagrams showing the relationship between the exposure amount of polyimide and the residual rate after development, respectively, when the laser output is pulsed output and continuous output, Figure 4 2, A diagram explaining a method of exposing photosensitive polyimide using a laser spot with a power density distribution in the shape of 3 to increase the thickness of the wiring layer on the side surface of the insulating film to make disconnections less likely to occur. 6, when the laser output is a continuous output, the rise time and fall time are increased by electrical signal conversion to perform on/off modulation of the laser output, thereby exposing the polyimide and wiring on the insulating film surface. FIG. 2 is a diagram illustrating a method of increasing the thickness of a layer to make wire breakage less likely to occur. 1... Laser oscillator, 2, 6, 7... Laser beam, 8... Light modulation element, 4... Light modulation element drive circuit, 5... Multi-faceted rotating mirror, 8... Half mirror, 9, 13... Condensing lens, 10, 17... Focusing spot, 11... Wafer, 12... Sample stage, 14... Diode array, 15... Control device, 16... Linear encoder, 18... Lens, 19... Photo detector, 20... storage device.

Claims (1)

[Scope of Claims] 1. A method for manufacturing a semiconductor device in which an insulating layer is formed on a first conductive layer deposited on a wafer, a portion of the insulating layer is removed, and a second conductive layer is formed thereon. An insulating layer is formed of polyimide resin, and a contact hole is formed by scanning and removing the insulating layer according to a predetermined pattern while controlling on and off a laser spot focused by a lens or the like, and A semiconductor device characterized in that the intensity distribution in the cross section of the laser spot is such that the intensity distribution is high at the center and continuously decreases toward the periphery like a Gaussian distribution, and the side surface of the contact hole is formed as an inclined surface. manufacturing method. 2. In a method for manufacturing a semiconductor device in which an insulating layer is formed on a first conductive layer deposited on a wafer, a portion of the insulating layer is removed, and a second conductive layer is formed thereon, the insulating layer is made of polyimide resin. The surface of the contact hole is scanned and removed according to a predetermined pattern while controlling the on and off of a laser spot focused by a lens, etc., to form a contact hole, and A method for manufacturing a semiconductor device, characterized in that the rise and fall during off control are made gradual, the exposure amount at the end of the exposure pattern is continuously reduced, and the side surface of the contact hole is made into an inclined surface. .