Hot plate unit

Abstract

A hot plate unit for heating semiconductor wafers. The hot plate unit includes a case, a hot plate, a seal element, and a holding ring. The seal element is made of a heat insulative material and is arranged between the case and the hot plate. The hot plate is clamped between the holding ring and the seal element. Screws for fastening the holding ring do not contact the hot plate.

What is claimed is:  
     
         1 . A hot plate unit comprising: 
 a case having a lip;    a hot plate having a heat generator, wherein the hot plate is made of sintered ceramic; and    a seal element, wherein the hot plate is secured to the case via the seal element, wherein the seal element is heat insulative.    
     
     
         2 . The hot plate unit according to  claim 1  further comprising a holder for securing the hot plate to the case, wherein the holder contacts a peripheral part of the upper surface of the hot plate when the holder is fixed to the case.  
     
     
         3 . The hot plate unit according to  claim 2 , wherein the hot plate is disk-shaped, wherein the holder includes an annular plate made of spring steel, the annular plate has a diameter substantially equal to that of the lip, the holder includes a plurality of projections extending inwardly from the annular plate, and the projections contact separate points on the periphery of the upper surface of the hot plate for securing the hot plate to the case.  
     
     
         4 . The hot plate unit according to  claim 2 , wherein the holder includes a plurality of holding plates made of spring steel, each holding plate having a length that is a fraction of the length of the lip.  
     
     
         5 . The hot plate unit according to  claim 1 , wherein the seal element is made of fluororesin.  
     
     
         6 . The hot plate unit according to  claim 1 , wherein the holder is plate-like and has at least one inwardly extending projection, wherein the holder has a hole for receiving a fastener.  
     
     
         7 . The hot plate unit according to  claim 1 , wherein a step is formed at an inner edge of the seal element for supporting the hot plate.  
     
     
         8 . The hot plate unit according to  claim 1 , wherein the holder includes an inwardly projecting portion that is bent toward a lower side of the holder.  
     
     
         9 . The hot plate unit according to  claim 3 , wherein the seal element is annular.  
     
     
         10 . The hot plate unit according to  claim 1 , wherein the seal element is elastic.