DE10126130A1 - Producing contact holes in integrated circuit involves using optical lithography with mask with elongated, slit-shaped openings for producing essentially circular and/or elongated holes - Google Patents

Abstract

The method involves using a mask illuminated with short-wave light in an optical lithographic method. The mask has elongated, slit-shaped openings for producing essentially circular and/or elongated contact holes (2,6). The illumination conditions are selected so that an image reduction of at least 200 to 400 nm. occurs in the longitudinal direction of the openings.

Description

The invention relates to a method for producing cones clock holes, in particular by means of optical lithography, ge according to the preamble of claim 1.

Integrated circuits (ICs) are different Wiring levels connected by contact holes, to make electrical contact. When interpreting the contact holes are subject to two boundary conditions in particular take into account: on the one hand, the individual contact solutions be as small as possible to ensure a tight wiring density to reach; on the other hand, the contact resistance, ins especially with spatially extended structures, such as. B. at Source or drain connection of a transistor, if possible be small in order to keep the power loss as low as possible and to avoid undesirable heating of the IC.

To make contact holes as small as possible, up to long masks with uniformly large square openings used due to light diffraction effects on the Edges of the square openings almost round contact holes map on the IC. The uniform size serves the association fold the optical image. To improve the Kon the contact holes were lithographically minimal distance in the form of contact hole chains next to each other arranged, all contact holes of a contact hole chain the same contact surfaces together.

An example of a conventional arrangement of contact holes is shown in Fig. 1a. The figure shows a section from a transistor layout in which a substrate 1 , a plurality of gate connections 4 and a number of contact holes 2 can be seen. The contact holes 2 are lined up in the form of contact hole chains 3 in order to obtain the lowest possible contact resistance.

The ever smaller structures and distances of the con However, tact holes always lead to small spots in lithography process windows, d. H. especially the scope for the depth of field or the required exposure dose are getting smaller. Under the term "process window" should the permissible tolerances of all process parameters, such as in particular the depth of field or the exposure dose, be understood to be successful in producing a Structure must be adhered to. With getting smaller Structures, the process window is also smaller, with esp special process fluctuations lead to faulty structures who can no longer be tolerated.

The process window in contact hole lithography can only by means of complex and expensive lithographic enhancement Methods such as B. by alternating phase masks on one size required for mass production. Another way to improve the resolution ver is a reduction in the exposure wavelength.

It is therefore an object of the present invention to provide a professional and reliable process for the production of Kon to create clock holes. The contact holes created should have a low contact resistance.

This object is achieved by the in claim 1 given characteristics. Further refinements of the invention are Subject of subclaims.

The main inventive idea is that of Lithography the image shortening effect (imageshortening) use and elongated, slit-like in the exposure mask Provide openings with the same length for different lengths to produce te contact holes.  

Exposure conditions are preferred for lithography wisely chosen so that when making contact perforate a strong image shortening (difference between the Length of the mask opening and the length of the contact created holes) in the longitudinal direction of a rectangular mask opening occurs. An almost circular contact hole is at least around a factor 2 and in particular a factor 3 shorter than that associated slit-like mask opening. An elongated, rectangular opening in the mask, the length of which, for example is three times the length of the con created with it clock hole, creates an almost circular contact hole.

The ratio of length / width provided in the mask NEN opening to create an approximately circular contact lochs is between 1.5 and 4, preferably between 2 and 3 and especially around 2.5.

The effect of image shortening occurs especially with small k1 values, with:

k1 = CD.NA/λ

in which
k1 a process parameter,
CD the resolving power, in particular the width of the contact hole to be realized,
NA the numerical aperture, and
λ the wavelength
designated.

Favorable k1 values for the production of the contact holes are preferably less than 0.7 and in particular also less than 0.5.  

According to a preferred embodiment of the invention, this light used to expose the mask one wavelength of more than 100 nm, preferably 193 nm and in particular 24B nm. The wavelength used is preferably greater than the smallest dimension of a contact hole and possibly also larger larger than the smaller dimension of the slot-like openings in the mask. The width of the contact holes is now at less than 200 nm, namely around 140 nm.

According to a preferred embodiment of the invention, only certain discrete contact hole lengths are permitted. This has the advantage of not having to consider too many different process conditions for the different contact hole lengths. The length of the contact hole is preferably calculated using the formula:

Length (N) = [400 nm + N.250 nm]: V

with N ε Z (0, 1, 2, 3...) and V reduction factor of the Belich processing unit.

It is also beneficial for a stable manufacturing process Lich, if all the openings in the mask have the same width, the width in the mask mul multiplied by the reduction factor for the exposure corresponds approximately to the width of the contact hole to be produced.

The exposure mask preferably has none in particular square openings.

Instead of the usual contact hole chains are invented elongated, rectangular contact holes according to the invention. The The distance between two contact holes is at least that half the width and in particular more than the full width of a Contact hole. This also increases the lithographic pro zessfenster, because the occurring structures isolated and  do not occur in groups, for which purpose other process conditions would apply.

The invention is described below with reference to the accompanying drawing Examples explained in more detail. Show it:

Figure 1a, b a section of a transistor with contact holes, and a surface view of a contact arrangement according to the prior art.

FIG. 2a, b a section of a transistor surface with slot-like contact holes and an array of contact holes according to an embodiment of the invention.

FIG. 1a shows an enlarged section of a MOS transistor, on the surface of which several gate contacts 4 can be seen. Furthermore, a plurality of contact holes 2 are arranged on the active region 5 of the transistor.

These are each lined up in three groups to form contact hole chains 3 , in particular in order to keep the contact resistance as low as possible.

The plan view shown in Fig. 1b on the contact hole level of the transistor shows several, each of two to five con contact holes 2 existing contact hole chains 3 , in which the individual contact holes 2 are arranged at a very close distance from each other. This leads to the problems mentioned at the beginning. In particular, such contact hole chains 3 can no longer be resolved with structure dimensions that are smaller than the wavelength itself, because of the image shortening effect.

Fig. 2 shows a section of a MOS transistor with several gate contacts 4 and slot-like contact holes 6 instead of the previous contact hole chains. The contact holes are arranged approximately parallel to the gate contacts 4 .

A plan view of the contact hole plane shown in FIG. 2b makes it clear that the distance between two adjacent contact holes 2 , 6 and 6 , 6 is substantially larger than in the case of contact hole chains 3 and in particular is larger than the width of the contact holes 2 , 6 .

With regard to the square contact holes 2 it should be noted that these, too, were produced with elongated, rectangular mask openings using the image shortening effect. Elongated contact holes are created by correspondingly longer mask openings.

Furthermore, it can be seen in Fig. 2b that only certain contact hole lengths, in the present example four lengths, are present, the contact length being N times (N integer) the basic square length. Contacts with other lengths are not created for reasons of process reliability.

LIST OF REFERENCE NUMBERS

1

integrated circuit

2

square contact hole

3

Contact hole chain

4

Gate contact

5

active area

6

elongated contact hole

Claims (11)

1. A process for the production of contact holes ( 2 , 6 ) in an integrated circuit (IC) using a mask which is exposed in an optical lithography process with short-wave light, characterized in that the mask has elongated, slot-like openings for generating supply has substantially circular and / or elongated contact holes ( 2 , 6 ). 2. The method according to claim 1, characterized, that the exposure conditions are chosen such that ei ne image shortening in the longitudinal direction of the openings by a little at least 200 to 400 nm occurs. 3. The method according to claim 1 or 2, characterized, that the slit-like openings in the mask are approximately rectangular. 4. The method according to claim 3, characterized in that the length of the slot-like openings 1 , 5 to 4 times as large as their width. 5. The method according to any one of the preceding claims, characterized, that to expose the mask a wavelength of more than 100 nm, preferably about 193 nm or 248 nm is used. 6. The method according to any one of the preceding claims, characterized, that lithography is preferred for k1 values less than 0.7 wise less than 0.5 and in particular less than 0.4 leads.   7. The method according to any one of the preceding claims, characterized in that the wavelength used in lithography is greater than the smallest dimension of a contact hole ( 2 , 6 ) to be resolved, in particular also greater than the width of the slot-like openings. 8. The method according to any one of the preceding claims, characterized, that the mask creates slit-like openings both has circular as well as elongated contact holes. 9. The method according to any one of the preceding claims, characterized in that the length of the contact hole is calculated using the formula:
Length (N) = [400 nm + N.250 nm]: V
with N ε Z (0, 1, 2, 3...) and V reduction factor of the exposure device. 10. The method according to any one of the preceding claims, characterized, that all slit-like openings in the mask the same width. 11. The method according to any one of the preceding claims, characterized in that the minimum distance between two adjacent contact holes ( 2 , 6 ) on the integrated circuit (IC) is at least half as large and in particular at least as large as the width of the contact hole ( 2 , 6 ).