Pads made of different materials with different physical characteristics have been used for the so-called planarization polishing of the surface of electronic devices such as semiconductor substrates and magnetic disk substrates. Foamed urethane pads have been commonly used for the chemical mechanical polishing (CMP) of semiconductor devices because foamed pads with air bubbles inside have certain advantages such as their ability to take in particles scraped off from the polished surface inside such internally formed bubbles. Pads made of a foamed material such as foamed urethane, however, have certain disadvantages such as the difficulty in controlling the thickness and providing a uniform abrading surface and the inability to carry out a very fine polishing work.

Summary of the Invention It is therefore a general object of this invention to provide a polishing pad without such disadvantages which are common to pads made of a foamed material and hence better suited for the fine polishing.

It is another object of this invention to provide a method of using such a polishing pad to perform an improved polishing work.

This invention is based on the discovery by the present invention that polishing pads made of a non-foamed material and having certain physical characteristics can accomplish the above and other objects, In particular, a polishing pad embodying this invention may be characterized as substantially comprising a non-foamed resin material such as non-foamed acrylic resin, urethane and polyesters and having surface roughness Ra in the range of 0. 1-10, u m, or preferably 0. 5-1. 5, u m and variations in thickness less than 30um, or preferably less than 1011m. Such conditions are normally not satisfied by a pad made of a foamed material such as prior art foamed urethane pads. Polishing pads according to a preferred embodiment of this invention may be further characterized as having Shore D hardness greater than 60 degrees, compressibility less than 3% and elasticity greater than 30% as measured by specified methods.

The polishing surface of the pad may be grooved, such grooves being formed over 30%-70%, or preferably 40%-60% of the total area of the polishing surface.

The polishing pad of this invention thus characterized may be used in a conventional way, being pressed against a target surface to be polished and caused to move relative to the target surface, say, by means of a polishing machine of a known kind. A so-called dressing process of a known kind may be carried out to restore the initial condition of the polishing surface. The dressing process carried out in a method embodying this invention is characterized in that the surface roughness Ra of the polishing surface after the dressing process is again in the range of 0. 1-10pm, or preferably 0.5-1. 51lm.

Detailed Description of the Invention Polishing pads according to this invention, which may be used for fine polishing of semiconductor devices such as semiconductor substrates and magnetic disk substrates, are characterized firstly as being made of a non-foamed resin material such as non- foamed acrylic resin, urethane and polyesters and secondly as having a polishing surface with surface roughness Ra in the range of 0. 1-101lm or preferably 0.5-1. 5um and variations in thickness less than 30um or preferably less than 10pu.

Pads with surface roughness in such ranges can be prepared by using a rotary belt for a buffing process, by a facing process or by using a diamond grinder. Pads with such uniformity in thickness can be produced by a grinding process. Such pads are advantageous because their use can be started without initially subjecting them to a so- called dressing process, which is a process for conditioning the polishing surface of a polishing pad, say, by removing particles clogging the polishing surface. This process is usually time-consuming.

With a polishing pad made of a foamed material, the size and positions of air bubbles are not uniform, and some air bubbles are at the polishing surface, opening to the exterior. Thus, the surface roughness is usually much greater, and it is much more difficult to control its uniformity. In other words, polishing pads made of a non-foamed material according to this invention are better suited for fine polishing of device surfaces requiring a higher degree of precision.

Another advantage of using a non-foamed material is that non-foamed materials generally have a better thermal conductivity than foamed materials because foamed materials have air bubbles inside and air is a poor thermal conductor. Heat is generated as a polishing pad is used for polishing a target surface, and although the rate of chemical mechanical polishing may be improved by raising temperature, a strict temperature control is necessary for reducing variations in the rate of polishing. Table 1 shows a result of an experiment for comparing the thermal conductivity of foamed and non- foamed pads of a same material and a same thickness of 1. Ocm. In this experiment, these pads were placed on a plate maintained at 55°C and the changes in the temperatures at their top surfaces were measured at intervals of 5 minutes. Table 1 clearly shows that a pad made of a non-formed material has a much higher heat conductivity and hence is better suited for the temperature control in chemical physical polishing.

Table 1 Heating Surface temperature of a Surface temperature of time non-foamed pad (°C) a formed pad (°C) (minute) 0 23.8 23.8 5 28.9 27.5 10 31.5 29.2 15 31.7 29.5 20 33.7 30.2 25 34.7 30.4 30 37.9 29.2 35 42.5 36.5 40 43.2 37.0 45 43.9 37.3 Polishing pads made of a foamed material have air bubbles opening on the polishing surface and hence abraded particles can be stored in them. This cannot be done with a pad made of a non-foamed material. Thus, the polishing process with a non- foamed pad can proceed quickly if the target surface being polished is uneven, having protrusions and indentations, but the process slows down after the target surface becomes flat. In the chemical mechanical polishing of an oxide layer formed on a circuit wiring, the process is stopped when the oxide layer is planarized but it is a common practice to continue the polishing until the entire surface is planarized. Since the polishing with a non-foamed pad becomes slower at planarized parts, the thickness of the oxide layer is reduced so as to reduce the burden on the chemical mechanical polishing. If the pad is too soft, the processing becomes too dependent on the wiring pattern. In order to overcome this problem, it is preferable that the Shore D hardness of the pad be greater than 60 degrees, and more preferably greater than 68%.

In terms of compressibility and elasticity, a non-foamed pad of this invention may be characterized as having compressibility less than 3%, or preferably less than 1%, and elasticity greater than 30%, or preferably greater than 50%. The compressibility and elasticity are the values obtained from a sample piece of a suitable size by measuring its thickness To while compressing it with an initial load of 80g, further adding an extra load of 800g for 5 minutes and measuring its thickness Tl afterward, removing this total load of 880g and thereafter subjecting it to the initial load of 80g for 30 seconds to measure its thickness To'again. The compressibility is calculated as 100 (To-Tl)/To and the compressive elasticity is calculated as 100 (To-Tz)/(To-Tl) The polishing surface may be provided with grooves not only for collecting polished off particles but also for stabilizing the slurry flow and distribution pressure uniformly. If the ratio of the portion of the polishing surface where grooves are formed is too large, however, the contact area with the target surface to be polished may become insufficient and efficiency of the polishing is adversely affected. This ratio is preferably 30%-70%, and more preferably 40-60%.

A polishing pad as described above may be used in combination with a polishing machine of a known kind such that its polishing surface is compressed against the target surface to be polished and is caused to move relative to the target surface. After the condition of the polishing surface of a polishing pad has been sufficiently deteriorated by use, it has been known to rejuvenate the pad, for example, by removing the particles that are clogging the polishing surface. The process of bringing back the initial condition of the polishing surface, say, by using a diamond conditioner for polishing, is variously called a dressing process, a conditioning process or a seasoning process. Such a process may also be included as a part of a method according to the invention. The dressing process in a method embodying this invention is characterized in that the polishing surface of a pad made of a non-foamed material, after being subjected to such a dressing process, has surface roughness Ra in the range of 0. 1-10m, orpreferably 0.5-1. 5um.